Electron conductance in curved quantum structures
DEFF Research Database (Denmark)
Willatzen, Morten; Gravesen, Jens
2010-01-01
is computationally fast and provides direct (geometrical) parameter insight as regards the determination of the electron transmission coefficient. We present, as a case study, calculations of the electron conductivity of a helically shaped quantum-wire structure and discuss the influence of the quantum......A differential-geometry analysis is employed to investigate the transmission of electrons through a curved quantum-wire structure. Although the problem is a three-dimensional spatial problem, the Schrodinger equation can be separated into three general coordinates. Hence, the proposed method...
Electron Liquids in Semiconductor Quantum Structures
International Nuclear Information System (INIS)
Pinczuk, Aron
2009-01-01
The groups led by Stormer and Pinczuk have focused this project on goals that seek the elucidation of novel many-particle effects that emerge in two-dimensional electron systems (2DES) as the result from fundamental quantum interactions. This experimental research is conducted under extreme conditions of temperature and magnetic field. From the materials point of view, the ultra-high mobility systems in GaAs/AlGaAs quantum structures continue to be at the forefront of this research. The newcomer materials are based on graphene, a single atomic layer of graphite. The graphene research is attracting enormous attention from many communities involved in condensed matter research. The investigated many-particle phenomena include the integer and fractional quantum Hall effect, composite fermions, and Dirac fermions, and a diverse group of electron solid and liquid crystal phases. The Stormer group performed magneto-transport experiments and far-infrared spectroscopy, while the Pinczuk group explores manifestations of such phases in optical spectra.
Electronic structure of semiconductor quantum films
International Nuclear Information System (INIS)
Zhang, S.B.; Yeh, C.; Zunger, A.
1993-01-01
The electronic structure of thin (≤30 A) free-standing ideal films of Si(001), Si(110), and GaAs(110) is calculated using a plane-wave pseudopotential description. Unlike the expectation based on the simple effective-mass model, we find the following. (i) The band gaps of (001) quantum films exhibit even-odd oscillation as a function of the number N of monolayers. (ii) In addition to sine-type envelope functions which vanish at the film boundaries, some states have cosine envelope functions with extrema at boundaries. (iii) Even-layer Si(001) films exhibit at the valence-band maximum a state whose energy does not vary with the film thickness. Such zero confinement states have constant envelope throughout the film. (iv) Optical transitions in films exhibit boundary-imposed selection rules. Furthermore, oscillator strengths for pseudodirect transitions in the vicinity of forbidden direct transitions can be enhanced by several orders of magnitude. These findings, obtained in direct supercell calculations, can be explained in terms of a truncated crystal (TC) analysis. In this approach the film's wave functions are expanded in terms of pairs of bulk wave functions exhibiting a destructive interference at the boundaries. This maps the eigenvalue spectra of a film onto the bulk band structure evaluated at special k points which satisfy the boundary conditions. We find that the TC representation reproduces accurately the above-mentioned results of direct diagonalization of the film's Hamiltonian. This provides a simple alternative to the effective-mass model and relates the properties of quantum structures to those of the bulk material
Electronic conductance of quantum wire with serial periodic potential structures
International Nuclear Information System (INIS)
Fayad, Hisham M.; Shabat, Mohammed M.; Abdus Salam International Centre for Theoretical Physics, Trieste
2000-08-01
A theory based on the total transfer matrix is presented to investigate the electronic conductance in a quantum wire with serial periodic potentials. We apply the formalism in computation of the electronic conductance in a wire with different physical parameters of the wire structure. The numerical results could be used in designing some future quantum electronic devices. (author)
Indium antimonide quantum well structures for electronic device applications
Edirisooriya, Madhavie
The electron effective mass is smaller in InSb than in any other III-V semiconductor. Since the electron mobility depends inversely on the effective mass, InSb-based devices are attractive for field effect transistors, magnetic field sensors, ballistic transport devices, and other applications where the performance depends on a high mobility or a long mean free path. In addition, electrons in InSb have a large g-factor and strong spin orbit coupling, which makes them well suited for certain spin transport devices. The first n-channel InSb high electron mobility transistor (HEMT) was produced in 2005 with a power-delay product superior to HEMTs with a channel made from any other III-V semiconductor. The high electron mobility in the InSb quantum-well channel increases the switching speed and lowers the required supply voltage. This dissertation focuses on several materials challenges that can further increase the appeal of InSb quantum wells for transistors and other electronic device applications. First, the electron mobility in InSb quantum wells, which is the highest for any semiconductor quantum well, can be further increased by reducing scattering by crystal defects. InSb-based heteroepitaxy is usually performed on semi-insulating GaAs (001) substrates due to the lack of a lattice matched semi-insulating substrate. The 14.6% mismatch between the lattice parameters of GaAs and InSb results in the formation of structural defects such as threading dislocations and microtwins which degrade the electrical and optical properties of InSb-based devices. Chapter 1 reviews the methods and procedures for growing InSb-based heterostructures by molecular beam epitaxy. Chapters 2 and 3 introduce techniques for minimizing the crystalline defects in InSb-based structures grown on GaAs substrates. Chapter 2 discusses a method of reducing threading dislocations by incorporating AlyIn1-ySb interlayers in an AlxIn1-xSb buffer layer and the reduction of microtwin defects by growth
Electronic structure and lattice relaxations in quantum confined Pb films
Mans, A.
2005-01-01
Epitaxial films that are only several atoms layers thick exhibit interesting properties associated with quantum confinement. The electrons form standing waves, just like a violin string, clamped at both ends. In ultrathin lead films, this so-called `quantum size effect' (QSE) alters the physical
Quantum Monte Carlo for electronic structure: Recent developments and applications
International Nuclear Information System (INIS)
Rodriguez, M.M.S.; Lawrence Berkeley Lab., CA
1995-04-01
Quantum Monte Carlo (QMC) methods have been found to give excellent results when applied to chemical systems. The main goal of the present work is to use QMC to perform electronic structure calculations. In QMC, a Monte Carlo simulation is used to solve the Schroedinger equation, taking advantage of its analogy to a classical diffusion process with branching. In the present work the author focuses on how to extend the usefulness of QMC to more meaningful molecular systems. This study is aimed at questions concerning polyatomic and large atomic number systems. The accuracy of the solution obtained is determined by the accuracy of the trial wave function's nodal structure. Efforts in the group have given great emphasis to finding optimized wave functions for the QMC calculations. Little work had been done by systematically looking at a family of systems to see how the best wave functions evolve with system size. In this work the author presents a study of trial wave functions for C, CH, C 2 H and C 2 H 2 . The goal is to study how to build wave functions for larger systems by accumulating knowledge from the wave functions of its fragments as well as gaining some knowledge on the usefulness of multi-reference wave functions. In a MC calculation of a heavy atom, for reasonable time steps most moves for core electrons are rejected. For this reason true equilibration is rarely achieved. A method proposed by Batrouni and Reynolds modifies the way the simulation is performed without altering the final steady-state solution. It introduces an acceleration matrix chosen so that all coordinates (i.e., of core and valence electrons) propagate at comparable speeds. A study of the results obtained using their proposed matrix suggests that it may not be the optimum choice. In this work the author has found that the desired mixing of coordinates between core and valence electrons is not achieved when using this matrix. A bibliography of 175 references is included
Quantum Monte Carlo for electronic structure: Recent developments and applications
Energy Technology Data Exchange (ETDEWEB)
Rodriquez, Maria Milagos Soto [Lawrence Berkeley Lab. and Univ. of California, Berkeley, CA (United States). Dept. of Chemistry
1995-04-01
Quantum Monte Carlo (QMC) methods have been found to give excellent results when applied to chemical systems. The main goal of the present work is to use QMC to perform electronic structure calculations. In QMC, a Monte Carlo simulation is used to solve the Schroedinger equation, taking advantage of its analogy to a classical diffusion process with branching. In the present work the author focuses on how to extend the usefulness of QMC to more meaningful molecular systems. This study is aimed at questions concerning polyatomic and large atomic number systems. The accuracy of the solution obtained is determined by the accuracy of the trial wave function`s nodal structure. Efforts in the group have given great emphasis to finding optimized wave functions for the QMC calculations. Little work had been done by systematically looking at a family of systems to see how the best wave functions evolve with system size. In this work the author presents a study of trial wave functions for C, CH, C_{2}H and C_{2}H_{2}. The goal is to study how to build wave functions for larger systems by accumulating knowledge from the wave functions of its fragments as well as gaining some knowledge on the usefulness of multi-reference wave functions. In a MC calculation of a heavy atom, for reasonable time steps most moves for core electrons are rejected. For this reason true equilibration is rarely achieved. A method proposed by Batrouni and Reynolds modifies the way the simulation is performed without altering the final steady-state solution. It introduces an acceleration matrix chosen so that all coordinates (i.e., of core and valence electrons) propagate at comparable speeds. A study of the results obtained using their proposed matrix suggests that it may not be the optimum choice. In this work the author has found that the desired mixing of coordinates between core and valence electrons is not achieved when using this matrix. A bibliography of 175 references is
Electronic properties in a quantum well structure of Weyl semimetal
International Nuclear Information System (INIS)
You, Wen-Long; Zhou, Jiao-Jiao; Wang, Xue-Feng; Oleś, Andrzej M.
2016-01-01
We investigate the confined states and transport of three-dimensional Weyl electrons around a one-dimensional external rectangular electrostatic potential. The confined states with finite transverse wave vector exist at energies higher than the half well depth or lower than the half barrier height. The rectangular potential appears completely transparent to the normal incident electrons but not otherwise. The tunneling transmission coefficient is sensitive to their incident angle and shows resonant peaks when their energy coincides with the confined spectra. In addition, for the electrons in the conduction (valence) band through a potential barrier (well), the transmission spectrum has a gap of width increasing with the incident angle. Interestingly, the electron linear zero-temperature conductance over the potential can approach zero when the Fermi energy is aligned to the top and bottom energies of the potential, when only electron beams normal to the potential interfaces can pass through. The considered structure can be used to collimate the Weyl electron beams.
Spinor-electron wave guided modes in coupled quantum wells structures by solving the Dirac equation
International Nuclear Information System (INIS)
Linares, Jesus; Nistal, Maria C.
2009-01-01
A quantum analysis based on the Dirac equation of the propagation of spinor-electron waves in coupled quantum wells, or equivalently coupled electron waveguides, is presented. The complete optical wave equations for Spin-Up (SU) and Spin-Down (SD) spinor-electron waves in these electron guides couplers are derived from the Dirac equation. The relativistic amplitudes and dispersion equations of the spinor-electron wave-guided modes in a planar quantum coupler formed by two coupled quantum wells, or equivalently by two coupled slab electron waveguides, are exactly derived. The main outcomes related to the spinor modal structure, such as the breaking of the non-relativistic degenerate spin states, the appearance of phase shifts associated with the spin polarization and so on, are shown.
International Nuclear Information System (INIS)
Sęk, Grzegorz; Andrzejewski, Janusz; Ryczko, Krzysztof; Poloczek, Przemysław; Misiewicz, Jan; Semenova, Elizaveta S; Lemaitre, Aristide; Patriarche, Gilles; Ramdane, Aberrahim
2009-01-01
We report on the electronic properties of GaAs-substrate-based structures designed as a tunnel-injection system composed of self-assembled InAs quantum dots and an In 0.3 Ga 0.7 As quantum well separated by a GaAs barrier. We have performed photoluminescence and photoreflectance measurements which have allowed the determination of the optical transitions in the QW–QD tunnel structure and its respective references with just quantum dots or a quantum well. The effective mass calculations of the band structure dependence on the tunnelling barrier thickness have shown that in spite of an expected significant tunnelling between both parts of the system, its strong asymmetry and the strain distribution cause that the quantum-mechanical-coupling-induced energy shift of the optical transitions is almost negligible for the lowest energy states and weakly sensitive to the width of the barrier, which finds confirmation in the existing experimental data
Simulation of electronic structure Hamiltonians in a superconducting quantum computer architecture
Energy Technology Data Exchange (ETDEWEB)
Kaicher, Michael; Wilhelm, Frank K. [Theoretical Physics, Saarland University, 66123 Saarbruecken (Germany); Love, Peter J. [Department of Physics, Haverford College, Haverford, Pennsylvania 19041 (United States)
2015-07-01
Quantum chemistry has become one of the most promising applications within the field of quantum computation. Simulating the electronic structure Hamiltonian (ESH) in the Bravyi-Kitaev (BK)-Basis to compute the ground state energies of atoms/molecules reduces the number of qubit operations needed to simulate a single fermionic operation to O(log(n)) as compared to O(n) in the Jordan-Wigner-Transformation. In this work we will present the details of the BK-Transformation, show an example of implementation in a superconducting quantum computer architecture and compare it to the most recent quantum chemistry algorithms suggesting a constant overhead.
Modern quantum chemistry introduction to advanced electronic structure theory
Szabo, Attila
1996-01-01
The aim of this graduate-level textbook is to present and explain, at other than a superficial level, modem ab initio approaches to the calculation of the electronic structure and properties of molecules. The first three chapters contain introductory material culminating in a thorough discussion of the Hartree-Fock approximation.The remaining four chapters describe a variety of more sophisticated approaches, which improve upon this approximation.Among the highlights of the seven chapters are (1) a review of the mathematics (mostly matrix algebra) required for the rest of the book, (2) an intr
Electronic structures of GaAs/AlxGa1-xAs quantum double rings
Directory of Open Access Journals (Sweden)
Li Shu-Shen
2006-01-01
Full Text Available AbstractIn the framework of effective mass envelope function theory, the electronic structures of GaAs/AlxGa1-xAs quantum double rings (QDRs are studied. Our model can be used to calculate the electronic structures of quantum wells, wires, dots, and the single ring. In calculations, the effects due to the different effective masses of electrons and holes in GaAs and AlxGa1-xAs and the valence band mixing are considered. The energy levels of electrons and holes are calculated for different shapes of QDRs. The calculated results are useful in designing and fabricating the interrelated photoelectric devices. The single electron states presented here are useful for the study of the electron correlations and the effects of magnetic fields in QDRs.
Hot electron and real space transfer in double-quantum-well structures
International Nuclear Information System (INIS)
Okuno, Eiichi; Sawaki, Nobuhiko; Akasaki, Isamu; Kano, Hiroyuki; Hashimoto, Masafumi.
1991-01-01
The hot electron phenomena and real space transfer (RST) effect are studied in GaAs/AlGaAs double-quantum-well (DQW) structures, in which we have two kind of quantum wells with different widths. The drift velocity and the electron temperature at liquid helium temperature are investigated as a function of the external electric field applied parallel to the heterointerface. By increasing the field, the electron temperature rises and reaches a plateau in the intermediate region, followed by further rise in the high-field region. The appearance of the plateau is attributed to the RST effect between the two quantum wells. The threshold field for the appearance of the plateau is determined by the difference energy between the quantized levels in two wells. The energy loss rate as a function of the electron temperature indicates that the RST is assisted by LO phonon scattering. (author)
Self-consistent electronic structure of spin-polarized dilute magnetic semiconductor quantum wells
International Nuclear Information System (INIS)
Hong, S. P.; Yi, K. S.; Quinn, J. J.
2000-01-01
The electronic properties of spin-symmetry-broken dilute magnetic semiconductor quantum wells are investigated self-consistently at zero temperature. The spin-split subband structure and carrier concentration of modulation-doped quantum wells are examined in the presence of a strong magnetic field. The effects of exchange and correlations of electrons are included in a local-spin-density-functional approximation. We demonstrate that exchange correlation of electrons decreases the spin-split subband energy but enhances the carrier density in a spin-polarized quantum well. We also observe that as the magnetic field increases, the concentration of spin-down (majority) electrons increases but that of spin-up (minority) electrons decreases. The effect of orbital quantization on the in-plane motion of electrons is also examined and shows a sawtoothlike variation in subband electron concentrations as the magnetic-field intensity increases. The latter variation is attributed to the presence of ionized donors acting as the electron reservoir, which is partially responsible for the formation of the integer quantum Hall plateaus. (c) 2000 The American Physical Society
Electronic structure of nitride-based quantum dots
Energy Technology Data Exchange (ETDEWEB)
Winkelnkemper, Momme
2008-11-07
In the present work the electronic and optical properties of In{sub x}Ga{sub 1-x}N/GaN and GaN/AlN QDs are studied by means of eight-band k.p theory. Experimental results are interpreted in detail using the theoretical results. The k.p model for the QD electronicstructure calculations accounts for strain, piezo- and pyroelectric effects, spin-orbit and crystal-field splitting, and is implemented for arbitrarily shaped QDs on a finite differences grid. Few-particle corrections are included using the self-consistent Hartree method. Band parameters for the wurtzite and zinc-blende phases of GaN, AlN, and InN are derived from first-principle G{sub 0}W{sub 0} band-structure calculations. Reliable values are also provided for parameters that have not been determined experimentally yet. The electronic properties of nitride QDs are dominated by the large built-in piezo- and pyroelectric fields, which lead to a pronounced red-shift of excitonic transition energies and extremely long radiative lifetimes in large GaN/AlN QDs. In In{sub x}Ga{sub 1-x}N/GaN QDs these fields induce a pronounced dependence of the radiative excitonic lifetimes on the exact QD shape and composition. It is demonstrated that the resulting variations of the radiative lifetimes in an inhomogeneous QD ensemble are the origin of the multi-exponential luminescence decay frequently observed in time-resolved ensemble measurements on In{sub x}Ga{sub 1-x}N/GaN QDs. A polarization mechanism in nitride QDs based on strain-induced valence-band mixing effects is discovered. Due to the valence-band structure of wurtzite group-III nitrides and the specific strain situation in c-plane QDs, the confined hole states are formed predominantly by the two highest valence bands. In particular, the hole ground state (h{sub 0} {identical_to} h{sub A}) is formed by the A band, and the first excited hole state (h{sub 1} {identical_to} h{sub B}) by the B band. It is shown that the interband transitions involving h{sub A} or h
Electronic structure of charge carriers in a polysilane quantum wire
International Nuclear Information System (INIS)
Kumagai, J.; Yoshida, H.; Ichikawa, T.
1997-01-01
The ESR, ESEEM and spectrophotometric studies on polysilane radical ions revealed that charge carriers, hole and conducting electrons, are not delocalized all over the Si-Si main chain but confined to a part of the chain composed of only six Si atoms, probably near the branch on the main chain. Comparison of the ESR spectra of the radical cations and anions revealed that the hole can migrate from the main chain to an adjacent polymer chain via the side chains, whereas the conducting electron can not migrate since the side chains act as good intermolecular insulators for the electron. (author)
Characterization of quantum well structures using a photocathode electron microscope
Spencer, Michael G.; Scott, Craig J.
1989-01-01
Present day integrated circuits pose a challenge to conventional electronic and mechanical test methods. Feature sizes in the submicron and nanometric regime require radical approaches in order to facilitate electrical contact to circuits and devices being tested. In addition, microwave operating frequencies require careful attention to distributed effects when considering the electrical signal paths within and external to the device under test. An alternative testing approach which combines the best of electrical and optical time domain testing is presented, namely photocathode electron microscope quantitative voltage contrast (PEMQVC).
Seibert, Jakob; Bannwarth, Christoph; Grimme, Stefan
2017-08-30
A fully quantum mechanical (QM) treatment to calculate electronic absorption (UV-vis) and circular dichroism (CD) spectra of typical biomolecules with thousands of atoms is presented. With our highly efficient sTDA-xTB method, spectra averaged along structures from molecular dynamics (MD) simulations can be computed in a reasonable time frame on standard desktop computers. This way, nonequilibrium structure and conformational, as well as purely quantum mechanical effects like charge-transfer or exciton-coupling, are included. Different from other contemporary approaches, the entire system is treated quantum mechanically and neither fragmentation nor system-specific adjustment is necessary. Among the systems considered are a large DNA fragment, oligopeptides, and even entire proteins in an implicit solvent. We propose the method in tandem with experimental spectroscopy or X-ray studies for the elucidation of complex (bio)molecular structures including metallo-proteins like myoglobin.
The Bravyi-Kitaev transformation for quantum computation of electronic structure
Seeley, Jacob T.; Richard, Martin J.; Love, Peter J.
2012-12-01
Quantum simulation is an important application of future quantum computers with applications in quantum chemistry, condensed matter, and beyond. Quantum simulation of fermionic systems presents a specific challenge. The Jordan-Wigner transformation allows for representation of a fermionic operator by O(n) qubit operations. Here, we develop an alternative method of simulating fermions with qubits, first proposed by Bravyi and Kitaev [Ann. Phys. 298, 210 (2002), 10.1006/aphy.2002.6254; e-print arXiv:quant-ph/0003137v2], that reduces the simulation cost to O(log n) qubit operations for one fermionic operation. We apply this new Bravyi-Kitaev transformation to the task of simulating quantum chemical Hamiltonians, and give a detailed example for the simplest possible case of molecular hydrogen in a minimal basis. We show that the quantum circuit for simulating a single Trotter time step of the Bravyi-Kitaev derived Hamiltonian for H2 requires fewer gate applications than the equivalent circuit derived from the Jordan-Wigner transformation. Since the scaling of the Bravyi-Kitaev method is asymptotically better than the Jordan-Wigner method, this result for molecular hydrogen in a minimal basis demonstrates the superior efficiency of the Bravyi-Kitaev method for all quantum computations of electronic structure.
Electron quantum optics as quantum signal processing
Roussel, B.; Cabart, C.; Fève, G.; Thibierge, E.; Degiovanni, P.
2016-01-01
The recent developments of electron quantum optics in quantum Hall edge channels have given us new ways to probe the behavior of electrons in quantum conductors. It has brought new quantities called electronic coherences under the spotlight. In this paper, we explore the relations between electron quantum optics and signal processing through a global review of the various methods for accessing single- and two-electron coherences in electron quantum optics. We interpret electron quantum optics...
Camp, Piet
1985-01-01
The 1984 Advanced Study Institute on "Electronic Structure, Dynamics and Quantum Structural Properties of Condensed Matter" took place at the Corsendonk Conference Center, close to the City of Antwerpen, from July 16 till 27, 1984. This NATO Advanced Study Institute was motivated by the research in my Institute, where, in 1971, a project was started on "ab-initio" phonon calculations in Silicon. I~ is my pleasure to thank several instances and people who made this ASI possible. First of all, the sponsor of the Institute, the NATO Scientific Committee. Next, the co-sponsors: Agfa-Gevaert, Bell Telephone Mfg. Co. N.V., C & A, Esso Belgium·, CDC Belgium, Janssens Pharmaceutica, Kredietbank and the Scientific Office of the U.S. Army. Special thanks are due to Dr. P. Van Camp and Drs. H. Nachtegaele, who, over several months, prepared the practical aspects of the ASI with the secretarial help of Mrs. R.-M. Vandekerkhof. I also like to. thank Mrs. M. Cuyvers who prepared and organized the subject and material ...
Energy Technology Data Exchange (ETDEWEB)
Mousavi-Khoshdel, S. Morteza, E-mail: mmousavi@iust.ac.ir [Department of Chemistry, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Jahanbakhsh-bonab, Parisa [Department of Chemistry, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Targholi, Ehsan [Young Researchers and Elite Club, Abhar Branch, Islamic Azad University, Abhar (Iran, Islamic Republic of)
2016-10-07
Using DFT calculations, we study the structural parameters, electronic properties and quantum capacitance of N, B, and P-doped armchair carbon nanotubes (CNTs). Fermi level shifts towards conduction band and valence band in N- and B-doped CNTs, respectively. While in the case of P atom, despite having an extra valence electron than carbon, there is no shift in Fermi level. The results revealed from a symmetric capacitance enhancement in P-doped CNT and an asymmetric capacitance enhancement in B and N-doped CNTs. The greatest amount of quantum capacitance of N-doped (6, 6) CNT could be achieved at the concentration range of 0.1–0.15. - Highlights: • Exploration of variation in quantum capacitance of CNTs through doping N, B and P atoms. • Quantum capacitance of CNTs is sensitive to impurities entered in carbon nanotubes. • Maximum quantum capacitance of N-doped CNTs is achieved at the concentration range of 0.1–0.15.
Quantum Monte Carlo methods and strongly correlated electrons on honeycomb structures
Energy Technology Data Exchange (ETDEWEB)
Lang, Thomas C.
2010-12-16
In this thesis we apply recently developed, as well as sophisticated quantum Monte Carlo methods to numerically investigate models of strongly correlated electron systems on honeycomb structures. The latter are of particular interest owing to their unique properties when simulating electrons on them, like the relativistic dispersion, strong quantum fluctuations and their resistance against instabilities. This work covers several projects including the advancement of the weak-coupling continuous time quantum Monte Carlo and its application to zero temperature and phonons, quantum phase transitions of valence bond solids in spin-1/2 Heisenberg systems using projector quantum Monte Carlo in the valence bond basis, and the magnetic field induced transition to a canted antiferromagnet of the Hubbard model on the honeycomb lattice. The emphasis lies on two projects investigating the phase diagram of the SU(2) and the SU(N)-symmetric Hubbard model on the hexagonal lattice. At sufficiently low temperatures, condensed-matter systems tend to develop order. An exception are quantum spin-liquids, where fluctuations prevent a transition to an ordered state down to the lowest temperatures. Previously elusive in experimentally relevant microscopic two-dimensional models, we show by means of large-scale quantum Monte Carlo simulations of the SU(2) Hubbard model on the honeycomb lattice, that a quantum spin-liquid emerges between the state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator. This unexpected quantum-disordered state is found to be a short-range resonating valence bond liquid, akin to the one proposed for high temperature superconductors. Inspired by the rich phase diagrams of SU(N) models we study the SU(N)-symmetric Hubbard Heisenberg quantum antiferromagnet on the honeycomb lattice to investigate the reliability of 1/N corrections to large-N results by means of numerically exact QMC simulations. We study the melting of phases
InN/GaN quantum dot superlattices: Charge-carrier states and surface electronic structure
Kanouni, F.; Brezini, A.; Djenane, M.; Zou, Q.
2018-03-01
We have theoretically investigated the electron energy spectra and surface states energy in the three dimensionally ordered quantum dot superlattices (QDSLs) made of InN and GaN semiconductors. The QDSL is assumed in this model to be a matrix of GaN containing cubic dots of InN of the same size and uniformly distributed. For the miniband’s structure calculation, the resolution of the effective mass Schrödinger equation is done by decoupling it in the three directions within the framework of Kronig-Penney model. We found that the electrons minibands in infinite ODSLs are clearly different from those in the conventional quantum-well superlattices. The electrons localization and charge-carrier states are very dependent on the quasicrystallographic directions, the size and the shape of the dots which play a role of the artificial atoms in such QD supracrystal. The energy spectrum of the electron states localized at the surface of InN/GaN QDSL is represented by Kronig-Penney like-model, calculated via direct matching procedure. The calculation results show that the substrate breaks symmetrical shape of QDSL on which some localized electronic surface states can be produced in minigap regions. Furthermore, we have noticed that the surface states degeneracy is achieved in like very thin bands located in the minigaps, identified by different quantum numbers nx, ny, nz. Moreover, the surface energy bands split due to the reduction of the symmetry of the QDSL in z-direction.
Electronic structure and correlated wave functions of a few electron quantum dots
Energy Technology Data Exchange (ETDEWEB)
Sako, Tokuei [Laboratory of Physics, College of Science and Technology, Nihon University, 7-24-1 Narashinodai, Funabashi, Chiba 274-8501 (Japan); Ishida, Hiroshi [College of Humanities and Sciences, Nihon University, Tokyo 156-8550 (Japan); Fujikawa, Kazuo [Institute of Quantum Science, College of Science and Technology, Nihon University, Chiyoda-ku, Tokyo 101-8308 (Japan)
2015-01-22
The energy spectra and wave functions of a few electrons confined by a quasi-one-dimensional harmonic and anharmonic potentials have been studied by using a full configuration interaction method employing a Cartesian anisotropic Gaussian basis set. The energy spectra are classified into three regimes of the strength of confinement, namely, large, medium and small. The polyad quantum number defined by a total number of nodes in the wave functions is shown to be a key ingredient to interpret the energy spectra for the whole range of the confinement strength. The nodal pattern of the wave functions exhibits normal modes for the harmonic confining potential, indicating collective motions of electrons. These normal modes are shown to undergo a transition to local modes for an anharmonic potential with large anharmonicity.
Quantum electronics basic theory
Fain, V M; Sanders, J H
1969-01-01
Quantum Electronics, Volume 1: Basic Theory is a condensed and generalized description of the many research and rapid progress done on the subject. It is translated from the Russian language. The volume describes the basic theory of quantum electronics, and shows how the concepts and equations followed in quantum electronics arise from the basic principles of theoretical physics. The book then briefly discusses the interaction of an electromagnetic field with matter. The text also covers the quantum theory of relaxation process when a quantum system approaches an equilibrium state, and explai
Arjunan, V; Thillai Govindaraja, S; Jose, Sujin P; Mohan, S
2014-07-15
The Fourier transform infrared and FT-Raman spectra of 2-benzothiazole acetonitrile (BTAN) have been recorded in the range 4000-450 and 4000-100 cm(-1) respectively. The conformational analysis of the compound has been carried out to obtain the stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers derived theoretically by B3LYP gradient calculations employing the standard 6-31G(**), high level 6-311++G(**) and cc-pVTZ basis sets. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The (1)H (400 MHz; CDCl3) and (13)C (100 MHz;CDCl3) nuclear magnetic resonance (NMR) spectra are also recorded. The electronic properties, the energies of the highest occupied and lowest unoccupied molecular orbitals are measured by DFT approach. The kinetic stability of the molecule has been determined from the frontier molecular orbital energy gap. The charges of the atoms and the structure-chemical reactivity relations of the compound are determined by its chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods. The non-linear optical properties of the compound have been discussed by measuring the polarisability and hyperpolarisability tensors. Copyright © 2014 Elsevier B.V. All rights reserved.
International Nuclear Information System (INIS)
Gusakov, V.E.; Bel'ko, V.I.; Dorozhkin, N.N.
2015-01-01
We report on adaptation of quantum chemistry software - Quantum Espresso and LASTO - for the electronic structure calculations for the complex solid-state systems on the GeForce series GPUs using the nVIDIA CUDA technology. Specifically, protective covering based on transition metal nitrides are considered. (authors)
First-principles study of the electronic structure of CdS/ZnSe coupled quantum dots
Ganguli, N.; Acharya, S.; Dasgupta, I.
2014-01-01
We have studied the electronic structure of CdS/ZnSe coupled quantum dots, a novel heterostructure at the nanoscale. Our calculations reveal CdS/ZnSe coupled quantum dots are type II in nature where the anion p states play an important role in deciding the band offset for the highest occupied
Quantum Monte Carlo algorithms for electronic structure at the petascale; the endstation project.
Energy Technology Data Exchange (ETDEWEB)
Kim, J; Ceperley, D M; Purwanto, W; Walter, E J; Krakauer, H; Zhang, S W; Kent, P.R. C; Hennig, R G; Umrigar, C; Bajdich, M; Kolorenc, J; Mitas, L
2008-10-01
Over the past two decades, continuum quantum Monte Carlo (QMC) has proved to be an invaluable tool for predicting of the properties of matter from fundamental principles. By solving the Schrodinger equation through a stochastic projection, it achieves the greatest accuracy and reliability of methods available for physical systems containing more than a few quantum particles. QMC enjoys scaling favorable to quantum chemical methods, with a computational effort which grows with the second or third power of system size. This accuracy and scalability has enabled scientific discovery across a broad spectrum of disciplines. The current methods perform very efficiently at the terascale. The quantum Monte Carlo Endstation project is a collaborative effort among researchers in the field to develop a new generation of algorithms, and their efficient implementations, which will take advantage of the upcoming petaflop architectures. Some aspects of these developments are discussed here. These tools will expand the accuracy, efficiency and range of QMC applicability and enable us to tackle challenges which are currently out of reach. The methods will be applied to several important problems including electronic and structural properties of water, transition metal oxides, nanosystems and ultracold atoms.
Transmission electron microscopy investigations of the CdSe based quantum structures
International Nuclear Information System (INIS)
Roventa, E.
2006-01-01
In this work, the structural morphology of the active region of the ZnSe laser diode: quaternary CdZnSSe quantum well or CdSe quantum dots embedded in CdSe/ZnSSe superlattices is investigated using Transmission Electron Microscopy. The conventional as well as high resolution imaging studies indicated that the degradation of the ZnSe laser diodes is connected with the formation of extended defects in the optical active region leading to a local strain relaxation of the quantum well. Furthermore the outdiffusion of Cd from the quantum well occurs predominantly where the defects are located. The chemical composition and ordering phenomena in CdSe/ZnSSe supperlattices were also investigated, employing a series of five-fold structures with different spacer layer thickness and a ten-fold structure. The composition in the CdSe/ZnSSe superlattice was determined to a certain extent using different techniques. Generally, the encountered difficulties regarding the accuracy of the obtained values are correlated with the complexity of the investigated system and with the available experimental methods used. Regarding the alignment of the dots, experimental results support a strain driven ordering process, in which the strain fields from buried dots lead to heterogeneous nucleation conditions for the dots in the subsequently deposited layers. An increased ordering with subsequent stacking of the dot layers is was also found. An anisotropy of the lateral alignment of the CdSe dots was also observed in two different left angle 110 right angle zone axes. The similar plan-view images shows that the preferential alignment of the dots does not follow low-index crystallographic directions. However, it is assumed that this is attributed to the anisotropic elastic strain distribution combined with surface diffusion. (orig.)
Transmission electron microscopy investigations of the CdSe based quantum structures
Energy Technology Data Exchange (ETDEWEB)
Roventa, E.
2006-09-22
In this work, the structural morphology of the active region of the ZnSe laser diode: quaternary CdZnSSe quantum well or CdSe quantum dots embedded in CdSe/ZnSSe superlattices is investigated using Transmission Electron Microscopy. The conventional as well as high resolution imaging studies indicated that the degradation of the ZnSe laser diodes is connected with the formation of extended defects in the optical active region leading to a local strain relaxation of the quantum well. Furthermore the outdiffusion of Cd from the quantum well occurs predominantly where the defects are located. The chemical composition and ordering phenomena in CdSe/ZnSSe supperlattices were also investigated, employing a series of five-fold structures with different spacer layer thickness and a ten-fold structure. The composition in the CdSe/ZnSSe superlattice was determined to a certain extent using different techniques. Generally, the encountered difficulties regarding the accuracy of the obtained values are correlated with the complexity of the investigated system and with the available experimental methods used. Regarding the alignment of the dots, experimental results support a strain driven ordering process, in which the strain fields from buried dots lead to heterogeneous nucleation conditions for the dots in the subsequently deposited layers. An increased ordering with subsequent stacking of the dot layers is was also found. An anisotropy of the lateral alignment of the CdSe dots was also observed in two different left angle 110 right angle zone axes. The similar plan-view images shows that the preferential alignment of the dots does not follow low-index crystallographic directions. However, it is assumed that this is attributed to the anisotropic elastic strain distribution combined with surface diffusion. (orig.)
Electronic fine structure and recombination dynamics in single InAs quantum dots
Energy Technology Data Exchange (ETDEWEB)
Seguin, R.
2008-01-28
In the work at hand single InAs/GaAs quantum dots (QDs) are examined via cathodoluminescence spectroscopy. A thorough analysis of the spectra leads to an unambiguous assignment of the lines to the decay of specific excitonic complexes. A special aspect of the Coulomb interaction, the exchange interaction, gives rise to a fine structure in the initial and final states of an excitonic decay. This leads to a fine structure in the emission spectra that again is unique for every excitonic complex. The exchange interaction is discussed in great detail in this work.QDs of different sizes are investigated and the influence on the electronic properties is monitored. Additionally, the structure is modified ex situ by a thermal annealing process. The changes of the spectra under different annealing temperatures are traced. Finally, recombination dynamics of different excitonic complexes are examined by performing time-resolved cathodoluminescence spectroscopy. (orig.)
Electronic fine structure and recombination dynamics in single InAs quantum dots
International Nuclear Information System (INIS)
Seguin, R.
2008-01-01
In the work at hand single InAs/GaAs quantum dots (QDs) are examined via cathodoluminescence spectroscopy. A thorough analysis of the spectra leads to an unambiguous assignment of the lines to the decay of specific excitonic complexes. A special aspect of the Coulomb interaction, the exchange interaction, gives rise to a fine structure in the initial and final states of an excitonic decay. This leads to a fine structure in the emission spectra that again is unique for every excitonic complex. The exchange interaction is discussed in great detail in this work.QDs of different sizes are investigated and the influence on the electronic properties is monitored. Additionally, the structure is modified ex situ by a thermal annealing process. The changes of the spectra under different annealing temperatures are traced. Finally, recombination dynamics of different excitonic complexes are examined by performing time-resolved cathodoluminescence spectroscopy. (orig.)
Quantum Phase Extraction in Isospectral Electronic Nanostructures
Energy Technology Data Exchange (ETDEWEB)
Moon, Christopher
2010-04-28
Quantum phase is not a direct observable and is usually determined by interferometric methods. We present a method to map complete electron wave functions, including internal quantum phase information, from measured single-state probability densities. We harness the mathematical discovery of drum-like manifolds bearing different shapes but identical resonances, and construct quantum isospectral nanostructures possessing matching electronic structure but divergent physical structure. Quantum measurement (scanning tunneling microscopy) of these 'quantum drums' [degenerate two-dimensional electron states on the Cu(111) surface confined by individually positioned CO molecules] reveals that isospectrality provides an extra topological degree of freedom enabling robust quantum state transplantation and phase extraction.
Electron states in quantum rings with structural distortions under axial or in-plane magnetic fields
International Nuclear Information System (INIS)
Planelles, J; Rajadell, F; Climente, J I
2007-01-01
A comprehensive study of anisotropic quantum rings, QRs, subject to axial and in-plane magnetic field, both aligned and transverse to the anisotropy direction, is carried out. Elliptical QRs for a wide range of eccentricity values and also perfectly circular QRs including one or more barriers disturbing the QR current are considered. These models mimic anisotropic geometry deformations and mass diffusion occurring in the QR fabrication process. Symmetry considerations and simplified analytical models supply physical insight into the obtained numerical results. Our study demonstrates that, except for unusual extremely large eccentricities, QR geometry deformations only appreciably influence a few low-lying states, while the effect of barriers disturbing the QR current is stronger and affects all studied states to a similar extent. We also show that the response of the electron states to in-plane magnetic fields provides accurate information on the structural anisotropy
Kolesnikova, Inna N.; Putkov, Andrei E.; Rykov, Anatolii N.; Shishkov, Igor F.
2018-06-01
The equilibrium (re) molecular structure of thiobenzamide along with rh1 structure has been determined in gas phase using gas electron-diffraction (GED) at about 127 °C and quantum-chemical calculations (QC). Rovibrational distance corrections to the thermal averaged GED structure have been computed with anharmonic force constants obtained at the MP2/cc-pVTZ level of theory. According to the results of GED and QC thiobenzamide exists as mixture of two non-planar enantiomers of C1 symmetry. The selected equilibrium geometrical parameters of thiobenzamide (re, Å and ∠e, deg) are the following: (Cdbnd S) = 1.641(4), (Csbnd N) = 1.352(2), (Csbnd C) = 1.478(9), (Cdbnd C)av = 1.395(2), CCN = 114.7(5), CCS = 123.4(5), C2C1C7S = 31(4), C6C1C7N = 29(4). The structure of thiobenzamide in the gas phase is markedly different to that in the literature for the single crystal. The differences between the gas and the solid structures are ascribed to the presence of intermolecular hydrogen bonding in the solid phase.
International Nuclear Information System (INIS)
Sauerwald, Andres
2008-01-01
Aim of this thesis was to apply the analytical methods of the scanning transmission electron microscopy to the study of self-organized In(Ga)As quantum structures. With the imaging methods Z contrast and bright field (position resolutions in the subnanometer range) and especially with the possibilities of the quantitative chemical EELS analysis of the scanning transmission electron microscope (STEM) fundamental questions concerning morphology and chemical properties of self-organized quantum structures should be answered. By the high position resolution of the STEM among others essentail morphological and structural parameters in the growth behaviour of ''dot in a well'' (DWell) structures and of vertically correlated quantum dots (QDs) could be analyzed. For the optimization of DWell structures samples were studied, the nominal InAs-QD growth position was directedly varied within the embedding InGaAs quantum wells. The STEM offers in connection with the EELS method a large potential for the chemical analysis of quantum structures. Studied was a sample series of self-organized InGaAs/GaAs structures on GaAs substrate, the stress of which was changed by varying the Ga content of the INGaAs material between 2.4 % and 4.3 % [de
Electronic structure and quantum spin fluctuations at the magnetic phase transition in MnSi
Povzner, A. A.; Volkov, A. G.; Nogovitsyna, T. A.
2018-05-01
The effect of spin fluctuations on the heat capacity and homogeneous magnetic susceptibility of the chiral magnetic MnSi in the vicinity of magnetic transition has been investigated by using the free energy functional of the coupled electron and spin subsystems and taking into account the Dzyaloshinsky-Moriya interaction. For helical ferromagnetic ordering, we found that zero-point fluctuations of the spin density are large and comparable with fluctuations of the non-uniform magnetization. The amplitude of zero-point spin fluctuations shows a sharp decrease in the region of the magnetic phase transition. It is shown that sharp decrease of the amplitude of the quantum spin fluctuations results in the lambda-like maxima of the heat capacity and the homogeneous magnetic susceptibility. Above the temperature of the lambda anomaly, the spin correlation radius becomes less than the period of the helical structure and chiral fluctuations of the local magnetization appear. It is shown that formation of a "shoulder" on the temperature dependence of the heat capacity is due to disappearance of the local magnetization. Our finding allows to explain the experimentally observed features of the magnetic phase transition of MnSi as a result of the crossover of quantum and thermodynamic phase transitions.
Energy Technology Data Exchange (ETDEWEB)
Bubanja, Vladimir, E-mail: vladimir.bubanja@callaghaninnovation.govt.nz
2015-06-15
We present schemes for quantum teleportation and entanglement swapping of electronic spin states in hybrid superconductor–normal-metal systems. The proposed schemes employ subgap transport whereby the lowest order processes involve Cooper pair-electron and double Cooper-pair cotunneling in quantum teleportation and entanglement swapping protocols, respectively. The competition between elastic cotunneling and Cooper-pair splitting results in the success probability of 25% in both cases. Described implementations of these protocols are within reach of present-day experimental techniques.
Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.
2014-05-01
The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.
Resonant tunneling of electrons in quantum wires
International Nuclear Information System (INIS)
Krive, I.V.; Shekhter, R.I.; Jonson, M.; Krive, I.V.
2010-01-01
We considered resonant electron tunneling in various nanostructures including single wall carbon nanotubes, molecular transistors and quantum wires formed in two-dimensional electron gas. The review starts with a textbook description of resonant tunneling of noninteracting electrons through a double-barrier structure. The effects of electron-electron interaction in sequential and resonant electron tunneling are studied by using Luttinger liquid model of electron transport in quantum wires. The experimental aspects of the problem (fabrication of quantum wires and transport measurements) are also considered. The influence of vibrational and electromechanical effects on resonant electron tunneling in molecular transistors is discussed.
Advances in quantum electronics
Goodwin, D W
1974-01-01
Advances in Quantum Electronics, Volume 2 deals with the effects of quantum mechanics on the behavior of electrons in matter. This book is divided into three chapters. Chapter 1 reviews the statistical properties of optical fields and spectral processing techniques, including the use of photon correlation techniques to measure scattering effects in a number of different media. The use of optical E.P.R. and excitation spectroscopic techniques and techniques for establishing the location of impurity ions in the chalcogenides are describe in Chapter 2. The last chapter surveys the field of mode l
Kim, Jeongnim; Baczewski, Andrew D.; Beaudet, Todd D.; Benali, Anouar; Chandler Bennett, M.; Berrill, Mark A.; Blunt, Nick S.; Josué Landinez Borda, Edgar; Casula, Michele; Ceperley, David M.; Chiesa, Simone; Clark, Bryan K.; Clay, Raymond C., III; Delaney, Kris T.; Dewing, Mark; Esler, Kenneth P.; Hao, Hongxia; Heinonen, Olle; Kent, Paul R. C.; Krogel, Jaron T.; Kylänpää, Ilkka; Li, Ying Wai; Lopez, M. Graham; Luo, Ye; Malone, Fionn D.; Martin, Richard M.; Mathuriya, Amrita; McMinis, Jeremy; Melton, Cody A.; Mitas, Lubos; Morales, Miguel A.; Neuscamman, Eric; Parker, William D.; Pineda Flores, Sergio D.; Romero, Nichols A.; Rubenstein, Brenda M.; Shea, Jacqueline A. R.; Shin, Hyeondeok; Shulenburger, Luke; Tillack, Andreas F.; Townsend, Joshua P.; Tubman, Norm M.; Van Der Goetz, Brett; Vincent, Jordan E.; ChangMo Yang, D.; Yang, Yubo; Zhang, Shuai; Zhao, Luning
2018-05-01
QMCPACK is an open source quantum Monte Carlo package for ab initio electronic structure calculations. It supports calculations of metallic and insulating solids, molecules, atoms, and some model Hamiltonians. Implemented real space quantum Monte Carlo algorithms include variational, diffusion, and reptation Monte Carlo. QMCPACK uses Slater–Jastrow type trial wavefunctions in conjunction with a sophisticated optimizer capable of optimizing tens of thousands of parameters. The orbital space auxiliary-field quantum Monte Carlo method is also implemented, enabling cross validation between different highly accurate methods. The code is specifically optimized for calculations with large numbers of electrons on the latest high performance computing architectures, including multicore central processing unit and graphical processing unit systems. We detail the program’s capabilities, outline its structure, and give examples of its use in current research calculations. The package is available at http://qmcpack.org.
Electronic structure and quantum transport properties of metallic and semiconducting nanowires
Simbeck, Adam J.
The future of the semiconductor industry hinges upon new developments to combat the scaling issues that currently afflict two main chip components: transistors and interconnects. For transistors this means investigating suitable materials to replace silicon for both the insulating gate and the semiconducting channel in order to maintain device performance with decreasing size. For interconnects this equates to overcoming the challenges associated with copper when the wire dimensions approach the confinement limit, as well as continuing to develop low-k dielectric materials that can assure minimal cross-talk between lines. In addition, such challenges make it increasingly clear that device design must move from a top-down to a bottom-up approach in which the desired electronic characteristics are tailored from first-principles. It is with such fundamental hurdles in mind that ab initio calculations on the electronic and quantum transport properties of nanoscale metallic and semiconducting wires have been performed. More specifically, this study seeks to elaborate on the role played by confinement, contacts, dielectric environment, edge decoration, and defects in altering the electronic and transport characteristics of such systems. As experiments continue to achieve better control over the synthesis and design of nanowires, these results are expected to become increasingly more important for not only the interpretation of electronic and transport trends, but also in engineering the electronic structure of nanowires for the needs of the devices of the future. For the metallic atomic wires, the quantum transport properties are first investigated by considering finite, single-atom chains of aluminum, copper, gold, and silver sandwiched between gold contacts. Non-equilibrium Green's function based transport calculations reveal that even in the presence of the contact the conductivity of atomic-scale aluminum is greater than that of the other metals considered. This is
Electronic structure of self-organized InAs/GaAs quantum dots bounded by {136} facets
International Nuclear Information System (INIS)
Yang, Weidong; Lee, Hao; Johnson, Thomas J.; Sercel, Peter C.; Norman, A. G.
2000-01-01
Recent experiments indicate that the shape of self-organized InAs quantum dots grown on GaAs [001] is an elongated pyramid with bounding facets corresponding to a family of four {136} planes. This structure, which possesses C 2v symmetry, is quite different from square-base pyramidal or lens geometries, which have been assumed in previous electronic structure calculations for this system. In this paper, we consider theoretically the influence of the {136} shape on the electronic structure and optical properties of the quantum dots. We present a valence force-field calculation of the inhomogeneous strain and incorporate the results into an eight band k(vector sign)·p(vector sign) electronic structure calculation. The size dependence of the electronic structure is calculated and compared to experimental photoluminescence spectra. The effects of perturbations on the {136} shape are also considered. Calculations based on the {136} shape give good agreement with the observed level structure and optical polarization properties of self-organized InAs/GaAs quantum dots. (c) 2000 The American Physical Society
2 D electron transport in selectively doped Ga As/Inx Ga1-x As multiple quantum well structures
International Nuclear Information System (INIS)
Kulbachinskii, V.A.; Kytin, V.G.; Babushkina, T.S.; Malkina, I.G.
1996-01-01
Photoluminescence, temperature dependence of conductivity (0.4 x Ga 1-x As multiple quantum well (MQW) structures were investigated. The dependence of electron mobility on the width of the quantum wells and temperature were measured. It was shown that in narrow MQW structures the value of mobility is restricted by interface roughness scattering. In wider MQW structures neither interface roughness scattering nor change impurity scattering can describe the values and temperature dependence of mobility. Negative magnetoresistance was observed. From detailed comparison between theory of weak localization and experiment the relaxation time of the wave function phase τ ψ and temperature dependence of τ ψ were evaluated. Quantum Hall effect was investigated in all samples at T=0.4-4.2 K in magnetic fields up to 40 T. (author). 9 refs., 5 figs., 1 tab
Energy Technology Data Exchange (ETDEWEB)
Prabakaran, K.; Ramesh, R.; Jayasakthi, M.; Surender, S.; Pradeep, S. [Crystal Growth Centre, Anna University, Chennai (India); Balaji, M. [National Centre for Nanoscience and Nanotechnology, University of Madras, Guindy Campus, Chennai (India); Asokan, K. [Inter-University Accelerator Centre, New Delhi (India); Baskar, K., E-mail: drbaskar2009@gmail.com [Crystal Growth Centre, Anna University, Chennai (India); Manonmaniam Sundaranar University, Tirunelveli (India)
2017-03-01
Highlights: • Effects on InGaN/GaN QW structures by Au{sup 7+} (100 MeV) ion have been investigated. • Structural defects of the irradiated InGaN/GaN QW structures are determined. • The intermixing effect in irradiated InGaN/GaN QW structures were understood. • Modified luminescence was observed in the PL spectra due to heavy ion irradiation. • Surface modification was observed due to the heavy ion irradiation. - Abstract: The present study focuses on the electronic excitation induced structural and optical properties of InGaN/GaN quantum well (QW) structures grown by metal organic chemical vapor deposition technique. These excitations were produced using Au{sup 7+} ion irradiation with 100 MeV energy. The X-ray rocking curves intensity and full width at half-maximum values corresponding to the planes of (0 0 0 2) and (1 0 −1 5) of the irradiated QW structures show the modifications in the screw and edge-type dislocation densities vary with the ion fluences. The structural characteristics using the reciprocal space mapping indicate the intermixing effects in InGaN/GaN QW structures. Atomic force microscopy images confirmed the presence of nanostructures and the surface modification due to heavy ion irradiation. The irradiated QW structures exhibited degraded photoluminescence intensity and a subsequent decrease in the yellow luminescence band intensity with the fluences of 1 × 10{sup 11} and 5 × 10{sup 12} ions/cm{sup 2} compared to the pristine QW structures.
Statistical Exploration of Electronic Structure of Molecules from Quantum Monte-Carlo Simulations
Energy Technology Data Exchange (ETDEWEB)
Prabhat, Mr; Zubarev, Dmitry; Lester, Jr., William A.
2010-12-22
In this report, we present results from analysis of Quantum Monte Carlo (QMC) simulation data with the goal of determining internal structure of a 3N-dimensional phase space of an N-electron molecule. We are interested in mining the simulation data for patterns that might be indicative of the bond rearrangement as molecules change electronic states. We examined simulation output that tracks the positions of two coupled electrons in the singlet and triplet states of an H2 molecule. The electrons trace out a trajectory, which was analyzed with a number of statistical techniques. This project was intended to address the following scientific questions: (1) Do high-dimensional phase spaces characterizing electronic structure of molecules tend to cluster in any natural way? Do we see a change in clustering patterns as we explore different electronic states of the same molecule? (2) Since it is hard to understand the high-dimensional space of trajectories, can we project these trajectories to a lower dimensional subspace to gain a better understanding of patterns? (3) Do trajectories inherently lie in a lower-dimensional manifold? Can we recover that manifold? After extensive statistical analysis, we are now in a better position to respond to these questions. (1) We definitely see clustering patterns, and differences between the H2 and H2tri datasets. These are revealed by the pamk method in a fairly reliable manner and can potentially be used to distinguish bonded and non-bonded systems and get insight into the nature of bonding. (2) Projecting to a lower dimensional subspace ({approx}4-5) using PCA or Kernel PCA reveals interesting patterns in the distribution of scalar values, which can be related to the existing descriptors of electronic structure of molecules. Also, these results can be immediately used to develop robust tools for analysis of noisy data obtained during QMC simulations (3) All dimensionality reduction and estimation techniques that we tried seem to
Electron correlations in quantum dots
International Nuclear Information System (INIS)
Tipton, Denver Leonard John
2001-01-01
Quantum dot structures confine electrons in a small region of space. Some properties of semiconductor quantum dots, such as the discrete energy levels and shell filling effects visible in addition spectra, have analogies to those of atoms and indeed dots are sometimes referred to as 'artificial atoms'. However, atoms and dots show some fundamental differences due to electron correlations. For real atoms, the kinetic energy of electrons dominates over their mutual Coulomb repulsion energy and for this reason the independent electron approximation works well. For quantum dots the confining potential may be shallower than that of real atoms leading to lower electron densities and a dominance of mutual Coulomb repulsion over kinetic energy. In this strongly correlated regime the independent electron picture leads to qualitatively incorrect results. This thesis concentrates on few-electron quantum dots in the strongly correlated regime both for quasi-one-dimensional and two-dimensional dots in a square confining potential. In this so-called 'Wigner' regime the ground-state electronic charge density is localised near positions of classical electrostatic minima and the interacting electronic spectrum consists of well separated spin multiplets. In the strongly correlated regime the structure of low-energy multiplets is explained by mapping onto lattice models with extended-Hubbard and Heisenberg effective Hamiltonians. The parameters for these effective models are calculated within a Hartree approximation and are shown to reproduce well the exact results obtained by numerical diagonalisation of the full interacting Hamiltonian. Comparison is made between square dots and quantum rings with full rotational symmetry. In the very low-density regime, direct diagonalisation becomes impractical due to excessive computer time for convergence. In this regime a numerical renormalisation group method is applied to one-dimensional dots, enabling effective spin-interactions to be
Mondal, Abhisek; Datta, Saumen
2017-06-01
Hydrogen bond plays a unique role in governing macromolecular interactions with exquisite specificity. These interactions govern the fundamental biological processes like protein folding, enzymatic catalysis, molecular recognition. Despite extensive research work, till date there is no proper report available about the hydrogen bond's energy surface with respect to its geometric parameters, directly derived from proteins. Herein, we have deciphered the potential energy landscape of hydrogen bond directly from the macromolecular coordinates obtained from Protein Data Bank using quantum mechanical electronic structure calculations. The findings unravel the hydrogen bonding energies of proteins in parametric space. These data can be used to understand the energies of such directional interactions involved in biological molecules. Quantitative characterization has also been performed using Shannon entropic calculations for atoms participating in hydrogen bond. Collectively, our results constitute an improved way of understanding hydrogen bond energies in case of proteins and complement the knowledge-based potential. Proteins 2017; 85:1046-1055. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
Quantum chemical studies on electronic structure and photodynamics of ruthenium complexes
International Nuclear Information System (INIS)
Freitag, L.
2015-01-01
Ruthenium complexes have found their way into many applications in the last decades. Among those, ruthenium polypyridyl compounds have been employed as light harvesting devices and photosensitisers in artificial photosynthesis and molecular photocatalysis. Ruthenium nitrosyl complexes are rapidly emerging as NO delivery agents to biological tissues with promising applications in anticancer photodynamic therapy, thanks to their ability to photorelease nitric oxide (NO). This thesis encompasses computational studies on reactivity, electronic structure, excited states and photodynamics of several ruthenium nitrosyl and polypyridyl complexes. The first part of the thesis deals with ruthenium nitrosyls. The cis-trans isomerisation mechanism of RuHIndNO, a ruthenium nitrosyl derivate of the prominent anti-cancer drug candidate KP1019, is investigated with density functional theory calculations. Next, the electronic structure of the ground and the first excited triplet state of RuHIndNO is studied with multiconfigurational methods including the density-matrix renormalisation group (DMRG). The obtained multiconfigurational wavefunctions and DMRG-based orbital entanglement analysis provides theoretical insight into the non-innocence of the NO ligand in nitrosyl complexes by describing the electron correlation in the Ru--NO bond and assigning oxidation states to the metal and the NO ligand. Another study is performed on excited states of ruthenium nitrosyl complexes with quantum chemical calculations and surface-hopping dynamics to obtain insights into the photodissociation mechanism of NO. The second part of this thesis is devoted to the excited states and photophysics of ruthenium polypyridyl complexes. Accurate excitation energies of tris(2,2-bipyridine)ruthenium (II), the prototype ruthenium polypyridyl are obtained with multiconfigurational calculations assisted by an orbital entanglement analysis. Subsequently, the effect of the ligand substitution on the photophysics
Theory of the electronic structure and carrier dynamics of strain-induced (Ga, In)As quantum dots
International Nuclear Information System (INIS)
Boxberg, Fredrik; Tulkki, Jukka
2007-01-01
Strain-induced quantum dots (SIQD) confine electrons and holes to a lateral potential minimum within a near-surface quantum well (QW). The potential minimum is located in the QW below a nanometre-sized stressor crystal grown on top of the QW. SIQD exhibit well-resolved and prominently atomic-like optical spectra, making them ideal for experimental and theoretical studies of mesoscopic phenomena in semiconductor nanocrystals. In this report we review the theory of strain-induced confinement, electronic structure, photonics and carrier relaxation dynamics in SIQD. The theoretical results are compared with available experimental data. Electronic structure calculations are mainly performed using the multiband envelope function approach. Many-body effects are discussed using a direct diagonalization method, albeit, for the sake of computational feasibility, within a two-band model. The QD carrier dynamics are discussed in terms of a master equation model, which accounts for the details of the electronic structure as well as the leading photon, phonon and Coulomb interaction processes. We also discuss the quantum confined Stark effect, the Zeeman splitting and the formation of Landau levels in external fields. Finally, we review a recent theory of the cooling of radiative QD excitons by THz radiation. In particular we discuss the resonance charge transfer of holes between piezoelectric trap states and the deformation potential minima. The agreement between the theory and experiment is fair throughout, but calls for further investigations
Directory of Open Access Journals (Sweden)
R. K. Nayak
2015-11-01
Full Text Available We show that sharp nonmonotic variation of low temperature electron mobility μ can be achieved in GaAs/AlxGa1-xAs barrier delta-doped double quantum well structure due to quantum mechanical transfer of subband electron wave functions within the wells. We vary the potential profile of the coupled structure as a function of the doping concentration in order to bring the subbands into resonance such that the subband energy levels anticross and the eigen states of the coupled structure equally share both the wells thereby giving rise to a dip in mobility. When the wells are of equal widths, the dip in mobility occurs under symmetric doping of the side barriers. In case of unequal well widths, the resonance can be obtained by suitable asymmetric variation of the doping concentrations. The dip in mobility becomes sharp and also the wavy nature of mobility takes a rectangular shape by increasing the barrier width. We show that the dip in mobility at resonance is governed by the interface roughness scattering through step like changes in the subband mobilities. It is also gratifying to show that the drop in mobility at the onset of occupation of second subband is substantially supressed through the quantum mechanical transfer of subband wave functions between the wells. Our results can be utilized for performance enhancement of coupled quantum well devices.
International Nuclear Information System (INIS)
Peng Juan; Li Shu-Shen
2012-01-01
We study the electronic spectrum of coupled quantum dots (QDs) arranged as a graphene hexagonal lattice in the presence of an external perpendicular magnetic field. In our tight-binding model, the effect of the magnetic field is included in both the Peierls phase of the Hamiltonian and the tight-binding basis Wannier function. The energy of the system is analyzed when the magnetic flux through the lattice unit cell is a rational fraction of the quantum flux. The calculated spectrum has recursive properties, similar to those of the classical Hofstadter butterfly. However, unlike the ideal Hofstadter butterfly structure, our result is asymmetric since the impacts of the specific material and the magnetic field on the wavefunctions are included, making the results more realistic. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Superconducting quantum electronics
International Nuclear Information System (INIS)
Kose, V.
1989-01-01
This book reviews recent accomplishments, presents new results and discusses possible future developments of superconducting quantum electronics and high T c superconductivity. The three main parts of the book deal with fundamentals, sensitive detectors, and precision metrology. New results reported include: correct equivalent circuits modelling superconducting electronic devices; exact solution of the Mattis-Bardeen equations describing various experiments for thin films; complete theoretical description and experimental results for a new broad band spectrum analyzer; a new Josephson junction potentiometer allowing tracing of unknown voltage ratios back to well-known frequency ratios; and fast superconducting SQUID shift registers enabling the production of calculable noise power spectra in the microwave region
Energy Technology Data Exchange (ETDEWEB)
Hassani Nia, Iman; Fathipour, Vala; Mohseni, Hooman, E-mail: hmohseni@ece.northwestern.edu [Bio-Inspired Sensors and Optoelectronics Laboratory (BISOL), Department of Electrical Engineering, Northwestern University, Evanston, Illinois 60208 (United States)
2015-08-15
We report the first observation of non-threshold Auger mechanism for a quantum well structure with Type-I band alignment. Excitation-dependent photoluminescence measurements were used to extract the Auger recombination coefficients from 77 K up to room temperature. The results verify the role of interface mediated momentum exchange as well as suppression of Auger recombination for delocalized electron-hole wavefunctions.
Directory of Open Access Journals (Sweden)
Tatiya Chokbunpiam
2010-01-01
Full Text Available This study aimed to design a new series of compounds consisting of a porphyrin macrocycle linked to a perylene unit via a thiophenic bridge. The structural and electronic properties of the molecules, and the effects of mono- and di-substituents R on C3 and R′ on C4 of the thiophene ring were investigated using a quantum calculation approach. The results from the method validation revealed that using the density functional theory approach at B3LYP/6–31G(d data set was the optimal one, considering the accuracy attained and maintaining the computer time required within tractable limits. The results from the B3LYP/6–31G(d approach indicated that significant changes of the torsion angle between the molecular planes of the porphyrin and perylene rings, compared to that of the unsubstituted derivatives, were found in the di-substituted systems bearing R = R′ = −OCH3 and −NH2, and in a mono-substituted system having R = −H and R′=−NH2. The symmetric di-substitution does not provide a significantly lower HOMO-LUMO energy gap (ΔEg. Noticeable decreases in ΔEg were found only with the substitution patterns of: R, R′ = −OCH3, −H; −OH, −H; −N(CH32, −H; −H, −NH2. UV-visible spectra of all derivatives exhibited characteristic absorption maxima of the free bases of porphyrin and perylene.
Quantum Hall Electron Nematics
MacDonald, Allan
In 2D electron systems hosted by crystals with hexagonal symmetry, electron nematic phases with spontaneously broken C3 symmetry are expected to occur in the quantum Hall regime when triplets of Landau levels associated with three different Fermi surface pockets are partially filled. The broken symmetry state is driven by intravalley Coulombic exchange interactions that favor spontaneously polarized valley occupations. I will discuss three different examples of 2D electron systems in which this type of broken symmetry state is expected to occur: i) the SnTe (111) surface, ii) the Bi (111) surface. and iii) unbalanced bilayer graphene. This type of quantum Hall electron nematic state has so far been confirmed only in the Bi (111) case, in which the anisotropic quasiparticle wavefunctions of the broken symmetry state were directly imaged. In the SnTe case the nematic state phase boundary is controlled by a competition between intravalley Coulomb interactions and intervalley scattering processes that increase in relative strength with magnetic field. An in-plane Zeeman field alters the phase diagram by lifting the three-fold Landau level degeneracy, yielding a ground state energy with 2 π/3 periodicity as a function of Zeeman-field orientation angle. I will comment on the possibility of observing similar states in the absence of a magnetic field. Supported by DOE Division of Materials Sciences and Engineering Grant DE-FG03-02ER45958.
International Nuclear Information System (INIS)
Khleskov, V.I.; Kolpakov, E.V.; Smirnov, A.B.
1992-01-01
The work contains results of quantum-chemical calculations of electronic structure and Moessbauer spectra parameters for low spin S=1/2 hexa-coordinated ferri-porphyrin complexes with cyanide (CN) and pyridine (Py) as axial ligands. Theoretical results made it possible to explain experimentally observed regularity of anomalous quadrupole splitting decrease after substitution of Py-ligands by CN. Comparison of theoretical and experimental data indicated that 2 E g must be the ground state of investigated hemichromes. In this state unpaired electron symmetrically occupies d π -orbitals of Fe-ion. (orig.)
Browne, David A.; Mazumder, Baishakhi; Wu, Yuh-Renn; Speck, James S.
2015-01-01
on electron transport through quantum well active regions. These unipolar structures served as a test vehicle to test our 2D model of the effect of compositional fluctuations on polarization-induced barriers. Variables that were systematically studied included
Formation, atomic structure, and electronic properties of GaSb quantum dots in GaAs
Energy Technology Data Exchange (ETDEWEB)
Timm, R.
2007-12-14
In this work, cross-sectional scanning tunneling microscopy and spectroscopy are used for the first time to study the shape, size, strain, chemical composition, and electronic properties of capped GaSb/GaAs QDs at the atomic scale. By evaluating such structural results on a variety of nanostructures built using different epitaxy methods and growth conditions, details on the underlying QD formation processes can be revealed. A cross-over from flat quantum wells (QWs) to optically active QDs can be observed in samples grown by metalorganic chemical vapor deposition (MOCVD) with increasing amount of GaSb, including self-assembled Sb accumulations within a still two-dimensional layer and tiny three-dimensional GaSb islands probably acting as precursor structures. The QWs consist of significantly intermixed material with stoichiometries of maximally 50% GaSb, additionally exhibiting small gaps filled with GaAs. A higher GaSb content up to nearly pure material is found in the QDs, being characterized by small sizes of up to 8 nm baselength and about 2 nm height. In spite of the intermixing, all nanostructures have rather abrupt interfaces, and no significant Sb segregation in growth direction is observed. This changes completely when molecular beam epitaxy (MBE) is used as growth method, in which case individual Sb atoms are found to be distributed over several nm above the nanostructures. Massive group-V atomic exchange processes are causing this strong inter-mixing and Sb segregation during GaAs overgrowth. In combination with the large strain inherent to GaSb/GaAs QDs, this segregation upon overgrowth is assumed to be the reason for a unique structural phenomenon: All MBE-grown QDs, independent of the amount of deposited GaSb, exhibit a ring structure, consisting of a ring body of high GaSb content and a more or less extended central gap filled with GaAs. These rings have formed in a self-assembled way even when the initial GaSb layer was overgrown considerably fast
Stark shifting two-electron quantum dot
International Nuclear Information System (INIS)
Dineykhan, M.; Zhaugasheva, S.A.; Duysebaeva, K.S.
2003-01-01
Advances in modern technology make it possible to create semiconducting nano-structures (quantum dot) in which a finite number of electrons are 'captured' in a bounded volume. A quantum dot is associated with a quantum well formed at the interface, between two finite-size semiconductors owing to different positions of the forbidden gaps on the energy scale in these semiconductors. The possibility of monitoring and controlling the properties of quantum dots attracts considerable attention to these objects, as a new elemental basis for future generations of computers. The quantum-mechanical effects and image potential play a significant role in the description of the formation mechanism quantum dot, and determined the confinement potential in a two-electron quantum dot only for the spherical symmetric case. In the present talk, we considered the formation dynamics of two-electron quantum dot with violation of spherical symmetry. So, we have standard Stark potential. The energy spectrum two-electron quantum dot were calculated. Usually Stark interactions determined the tunneling phenomena between quantum dots
The Quasi-Electron Shell Structure of the Fractional Quantum Hall Effect
Haxton, Wick; Haxton, Daniel
2015-04-01
The fractional quantum Hall effect (FQHE) formulated on a sphere resembles the nuclear shell model, with the desired translationally invariant states having total angular momentum zero. This property was exploited by Ginocchio and Haxton (GH) to derive a new set of scalar operators and a first-Landau-level representation of the full set of hierarchy states (fillings 1/3, 2/5, 3/7, etc.), with overlaps identical to those of Jain, who used unphysical higher Landau levels excitations followed by numerical projection. We demonstrate that the GH operators produce an appealing description of the FQHE as shells filled by non-interacting quasi-electrons, or composite fermions. These are explicitly constructed, and their planar forms are also found. The evolution of the shells and their quasi-electrons is quite unusual. The connections with electron correlations and Laughlin's variational arguments are described. We discuss how ``new states'' found experimentally at fillings such as 4/11 and 5/13 fit into this scheme. Work support in part by the US DOE Offices of Nuclear Physics and Basic Energy Sciences.
Quantum chemistry the development of ab initio methods in molecular electronic structure theory
Schaefer III, Henry F
2004-01-01
This guide is guaranteed to prove of keen interest to the broad spectrum of experimental chemists who use electronic structure theory to assist in the interpretation of their laboratory findings. A list of 150 landmark papers in ab initio molecular electronic structure methods, it features the first page of each paper (which usually encompasses the abstract and introduction). Its primary focus is methodology, rather than the examination of particular chemical problems, and the selected papers either present new and important methods or illustrate the effectiveness of existing methods in predi
International Nuclear Information System (INIS)
Selli, Daniele; Baburin, Igor; Leoni, Stefano; Seifert, Gotthard; Zhu, Zhen; Tománek, David
2013-01-01
We investigate the interaction of a graphene monolayer with the C(111) diamond surface using ab initio density functional theory. To accommodate the lattice mismatch between graphene and diamond, the overlayer deforms into a wavy structure that binds strongly to the diamond substrate. The detached ridges of the wavy graphene overlayer behave electronically as free-standing polyacetylene chains with delocalized π electrons, separated by regions containing only sp 3 carbon atoms covalently bonded to the (111) diamond surface. We performed quantum transport calculations for different geometries of the system to study how the buckling of the graphene layer and the associated bonding to the diamond substrate affect the transport properties. The system displays high carrier mobility along the ridges and a wide transport gap in the direction normal to the ridges. These intriguing, strongly anisotropic transport properties qualify the hybrid graphene–diamond system as a viable candidate for electronic nanodevices. (paper)
International Nuclear Information System (INIS)
Guan, Chun; Xing, Yunhui; Zhang, Chao; Ma, Zhongshui
2014-01-01
Due to quantum interference, light can transmit through dense atomic media, a phenomenon known as electromagnetically induced transparency (EIT). We propose that EIT is not limited to light transmission and there is an electronic analog where resonant transparency in charge transport in an opaque structure can be induced by electromagnetic radiation. A triple-quantum-dots system with Λ-type level structure is generally opaque due to the level in the center dot being significantly higher and therefore hopping from the left dot to the center dot is almost forbidden. We demonstrate that an electromagnetically induced electron transparency (EIET) in charge of transport can indeed occur in the Λ-type system. The direct evidence of EIET is that an electron can travel from the left dot to the right dot, while the center dot apparently becomes invisible. We analyze EIET and the related shot noise in both the zero and strong Coulomb blockade regimes. It is found that the EIET (position, height, and symmetry) can be tuned by several controllable parameters of the radiation fields, such as the Rabi frequencies and detuning frequencies. The result offers a transparency/opaque tuning technique in charge transport using interfering radiation fields
Energy Technology Data Exchange (ETDEWEB)
Tiutiunnyk, A. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Department of Physics, Donbass State Engineering Academy, Shkadinova 72, 84313 Kramatorsk (Ukraine); Akimov, V. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Department of Physics, Donbass State Engineering Academy, Shkadinova 72, 84313 Kramatorsk (Ukraine); Universidad de Medellín, Carrera 87 No 30-65 Medellín (Colombia); Tulupenko, V. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Department of Physics, Donbass State Engineering Academy, Shkadinova 72, 84313 Kramatorsk (Ukraine); Mora-Ramos, M.E. [Centro de Investigación en Ciencias, Instituto de Investigación en Ciencias Básicas y Aplicadas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Kasapoglu, E. [Cumhuriyet University, Physics Department, 58140 Sivas (Turkey); Ungan, F. [Cumhuriyet University, Faculty of Technology, Deparment of Optical Engineering, 58140 Sivas (Turkey); Sökmen, I. [Department of Physics, Dokuz Eylül University, 35160 Buca, İzmir (Turkey); and others
2016-03-01
Electronic structure and optical properties in equilateral triangular GaAs/Al{sub 0.3}Ga{sub 0.7}As quantum dots are studied extensively. The effects of donor and acceptor impurity atoms positioned in the orthocenter of the triangle, as well as of the external DC electric field are taken into account. Binding energies of the impurity, exciton energies, interband photoluminescence peak positions as well as linear and non-linear optical properties in THz range caused by transitions between excitonic states are calculated and discussed.
International Nuclear Information System (INIS)
Tiutiunnyk, A.; Akimov, V.; Tulupenko, V.; Mora-Ramos, M.E.; Kasapoglu, E.; Ungan, F.; Sökmen, I.
2016-01-01
Electronic structure and optical properties in equilateral triangular GaAs/Al_0_._3Ga_0_._7As quantum dots are studied extensively. The effects of donor and acceptor impurity atoms positioned in the orthocenter of the triangle, as well as of the external DC electric field are taken into account. Binding energies of the impurity, exciton energies, interband photoluminescence peak positions as well as linear and non-linear optical properties in THz range caused by transitions between excitonic states are calculated and discussed.
International Nuclear Information System (INIS)
Vilk, Y.M.
1992-01-01
This thesis is concerned with theoretical studies of various manybody correlation effects in two-dimensional electron systems, with application to electrons in quantum well structures (QW) and electrons on the surface of liquid helium. The author investigates the influence of correlation effects on escape rates of electrons from the 2D electron liquid and crystal on the helium surface. Within the framework of a harmonic lattice model the effective potential for the escaping electron as a function of the electron density and the external pressing or pulling electric field is found. This approach takes into account the deformation effects in the electron system. It is shown that under realistic experimental conditions the correlation correction can completely dominate the physics of the escaping electrons. The calculated concentration dependence of the escape rate of surface electrons is in excellent agreement with experiments in both thermal-activated and tunneling regimes. The thesis describes studies of the optical luminescence spectra of two types of magnetoplasma realized in QW: a charged electron plasma and a neutral electron-hole plasma, in the context of a mean field approximation. It is shown that strong enhancements in oscillator strengths are associated with excitons between different Landau levels. The strongest effect is found near the chemical potential and is analogous to the x-ray singularities well known in metals. The theory also predicts the existence of plateaus in the concentration dependence of transition energies in the sufficiently strong magnetic field. These plateaus are associated with the change in the filling factor: at the strongest field, while the filling of the level is varied, the transition energy between Landau levels i e - i h (i e = i h = i) remains constant. With decreasing magnetic fields, the plateau disappears and the transition energy increases with the filling of the Landau level
Electronic structure of transition metal-isocorrole complexes: A first quantum chemical study
van Oort, B; Tangen, E; Ghosh, A.
2004-01-01
DFT calculations indicate that the broad electronic-structural features of metalloisocorroles are rather similar to those of analogous metallocorroles. Thus, like their corrole analogues, many metalloisocorroles feature substantially non-innocent ligands. Another key point is that both corroles and
Baranov, P.G.; Romanov, N.G.; Bundakova, A.P.; de Mello-Donega, Celso; Schmidt, J.
2016-01-01
High-frequency electron paramagnetic resonance (EPR), electron spin echo (ESE), electron-nuclear double resonance (ENDOR) and optically detected magnetic resonance (ODMR) were applied for the investigation of the electronic properties of ZnO colloidal quantum dots (QDs) which consist of a ZnO
Arjunan, V.; Raj, Arushma; Santhanam, R.; Marchewka, M. K.; Mohan, S.
2013-02-01
Extensive vibrational investigations of 2-amino-4-methoxybenzothiazole have been carried out with FTIR and FT-Raman spectral techniques. The electronic structure of the molecule has been analysed by UV-Visible and NMR spectroscopies. The DFT studies were carried out with B3LYP and HF methods utilising 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets to determine the structural, thermodynamical, vibrational, electronic characteristics of the compound and also to understand the electronic and steric influence of the methoxy amino groups on the skeletal frequencies. The mixing of the fundamental modes was determined with the help of total energy distribution (TED). The energies of the frontier molecular orbitals have also been determined. The kinetic and thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. 1H and 13C NMR chemical shifts and the electronic transitions of the molecule are also discussed.
Arjunan, V; Raj, Arushma; Santhanam, R; Marchewka, M K; Mohan, S
2013-02-01
Extensive vibrational investigations of 2-amino-4-methoxybenzothiazole have been carried out with FTIR and FT-Raman spectral techniques. The electronic structure of the molecule has been analysed by UV-Visible and NMR spectroscopies. The DFT studies were carried out with B3LYP and HF methods utilising 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets to determine the structural, thermodynamical, vibrational, electronic characteristics of the compound and also to understand the electronic and steric influence of the methoxy amino groups on the skeletal frequencies. The mixing of the fundamental modes was determined with the help of total energy distribution (TED). The energies of the frontier molecular orbitals have also been determined. The kinetic and thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. (1)H and (13)C NMR chemical shifts and the electronic transitions of the molecule are also discussed. Copyright © 2012 Elsevier B.V. All rights reserved.
Zwanenburg, Floris Arnoud; Dzurak, Andrew S.; Morello, Andrea; Simmons, Michelle Y.; Hollenberg, Lloyd C.L.; Klimeck, Gerhard; Rogge, Sven; Coppersmith, Susan N.; Eriksson, Mark A.
2013-01-01
This review describes recent groundbreaking results in Si, Si=SiGe, and dopant-based quantum dots, and it highlights the remarkable advances in Si-based quantum physics that have occurred in the past few years. This progress has been possible thanks to materials development of Si quantum devices,
Electronic structure effects on stability and quantum conductance in 2D gold nanowires
International Nuclear Information System (INIS)
Kashid, Vikas; Shah, Vaishali; Salunke, H. G.
2011-01-01
In this study, we have investigated the stability and conductivity of unsupported, two-dimensional infinite gold nanowires using ab initio density functional theory (DFT). Two-dimensional ribbon-like nanowires with 1–5 rows of gold atoms in the non-periodic direction and with different possible structures have been considered. The nanowires with >2 rows of atoms exhibit dimerization, similar to finite wires, along the non-periodic direction. Our results show that in these zero thickness nanowires, the parallelogram motif is the most stable. A comparison between parallelogram- and rectangular-shaped nanowires of increasing width indicates that zero thickness (111) oriented wires have a higher stability over (100). A detailed analysis of the electronic structure, reveals that the (111) oriented structures show increased delocalization of s and p electrons in addition to a stronger delocalization of the d electrons and hence are the most stable. The density of states show that the nanowires are metallic and conducting except for the double zigzag structure, which is semiconducting. Conductance calculations show transmission for a wide range of energies in all the stable nanowires with more than two rows of atoms. The conductance channels are not purely s and have strong contributions from the d levels, and weak contributions from the p levels.
Belova, Natalya V.; Girichev, Georgiy V.; Kotova, Vitaliya E.; Korolkova, Kseniya A.; Trang, Nguyen Hoang
2018-03-01
The molecular structure of 4-methylpiridine-N-oxide, 4-MePyO, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both, quantum chemistry and GED analyses resulted in CS molecular symmetry with the planar pyridine ring. Obtained molecular parameters confirm the hyperconjugation in the pyridine ring and the sp2 hybridization concept of the nitrogen and carbon atoms in the ring. The experimental geometric parameters are in a good agreement with the parameters for non-substituted N-oxide and reproduced very closely by DFT calculations. The presence of the electron-donating CH3 substituent in 4-MePyO leads to a decrease of the ipso-angle and to an increase of r(N→O) in comparison with the non-substituted PyO. Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme. The nature of the semipolar N→O bond is discussed.
Energy Technology Data Exchange (ETDEWEB)
Maryński, A.; Sĕk, G.; Musiał, A.; Andrzejewski, J.; Misiewicz, J. [Institute of Physics, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław (Poland); Gilfert, C.; Reithmaier, J. P. [Technische Physik, Institute of Nanostructure Technology and Analytics, CINSaT, University of Kassel, Heinrich Plett-Str. 40, D-34132 Kassel (Germany); Capua, A.; Karni, O.; Gready, D.; Eisenstein, G. [Department of Electrical Engineering, Technion, Haifa 32000 (Israel); Atiya, G.; Kaplan, W. D. [Department of Materials Science and Engineering, Technion, Haifa 32000 (Israel); Kölling, S. [Fraunhofer Institute for Photonic Microsystems, Center for Nanoelectronic Technologies, Königsbrücker Straße 180, D-01099 Dresden (Germany)
2013-09-07
The optical and structural properties of a new kind of InAs/InGaAlAs/InP quantum dot (QD)-like objects grown by molecular beam epitaxy have been investigated. These nanostructures were found to have significantly more symmetrical shapes compared to the commonly obtained dash-like geometries typical of this material system. The enhanced symmetry has been achieved due to the use of an As{sub 2} source and the consequent shorter migration length of the indium atoms. Structural studies based on a combination of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) provided detailed information on both the structure and composition distribution within an individual nanostructure. However, it was not possible to determine the lateral aspect ratio from STEM or APT. To verify the in-plane geometry, electronic structure calculations, including the energy levels and transition oscillator strength for the QDs have been performed using an eight-band k·p model and realistic system parameters. The results of calculations were compared to measured polarization-resolved photoluminescence data. On the basis of measured degree of linear polarization of the surface emission, the in-plane shape of the QDs has been assessed proving a substantial increase in lateral symmetry. This results in quantum-dot rather than quantum-dash like properties, consistent with expectations based on the growth conditions and the structural data.
Energy Technology Data Exchange (ETDEWEB)
Genderen, E. van; Clabbers, M. T. B. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University of Basel, CH-4058 Basel (Switzerland); Das, P. P. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Stewart, A. [Department of Physics and Energy, Materials and Surface Science Institute (MSSI), University of Limerick, Limerick (Ireland); Nederlof, I. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Amsterdam Scientific Instruments, Postbus 41882, 1009 DB Amsterdam (Netherlands); Barentsen, K. C. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Portillo, Q. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Centres Científics i Tecnològics de la Universitat de Barcelona, University of Barcelona, Carrer de Lluís Solé i Sabaris, 1-3, Barcelona (Spain); Pannu, N. S. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Nicolopoulos, S. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Gruene, T., E-mail: tim.gruene@psi.ch [Biology and Chemistry, Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen (Switzerland); Abrahams, J. P., E-mail: tim.gruene@psi.ch [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University of Basel, CH-4058 Basel (Switzerland); Biology and Chemistry, Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen (Switzerland)
2016-02-05
A specialized quantum area detector for electron diffraction studies makes it possible to solve the structure of small organic compound nanocrystals in non-cryo conditions by direct methods. Until recently, structure determination by transmission electron microscopy of beam-sensitive three-dimensional nanocrystals required electron diffraction tomography data collection at liquid-nitrogen temperature, in order to reduce radiation damage. Here it is shown that the novel Timepix detector combines a high dynamic range with a very high signal-to-noise ratio and single-electron sensitivity, enabling ab initio phasing of beam-sensitive organic compounds. Low-dose electron diffraction data (∼0.013 e{sup −} Å{sup −2} s{sup −1}) were collected at room temperature with the rotation method. It was ascertained that the data were of sufficient quality for structure solution using direct methods using software developed for X-ray crystallography (XDS, SHELX) and for electron crystallography (ADT3D/PETS, SIR2014)
International Nuclear Information System (INIS)
Sahoo, N.; Sahu, T.
2014-01-01
We study the multisubband electron mobility in a barrier delta doped Al x Ga 1−x As parabolic quantum well structure under the influence of an applied electric field perpendicular to the interface plane. We consider the alloy fraction x = 0.3 for barriers and vary x from 0.0 to 0.1 for the parabolic well. Electrons diffuse into the well and confine within the triangular like potentials near the interfaces due to Coulomb interaction with ionized donors. The parabolic structure potential, being opposite in nature, partly compensates the Coulomb potential. The external electric field further amends the potential structure leading to an asymmetric potential profile. Accordingly the energy levels, wave functions and occupation of subbands change. We calculate low temperature electron mobility as a function of the electric field and show that when two subbands are occupied, the mobility is mostly dominated by ionised impurity scattering mediated by intersubband effects. As the field increases transition from double subband to single subband occupancy occurs. A sudden enhancement in mobility is obtained due to curtailment of intersubband effects. Thereafter the mobility is governed by both impurity and alloy disorder scatterings. Our analysis of mobility as a function of the electric field for different structural parameters shows interesting results. (semiconductor physics)
Quantum Electronics for Atomic Physics
Nagourney, Warren
2010-01-01
Quantum Electronics for Atomic Physics provides a course in quantum electronics for researchers in atomic physics. The book covers the usual topics, such as Gaussian beams, cavities, lasers, nonlinear optics and modulation techniques, but also includes a number of areas not usually found in a textbook on quantum electronics. It includes such practical matters as the enhancement of nonlinear processes in a build-up cavity, impedance matching into a cavity, laser frequencystabilization (including servomechanism theory), astigmatism in ring cavities, and atomic/molecular spectroscopic techniques
Quantum interference effects for the electronic fluctuations in quantum dots
Energy Technology Data Exchange (ETDEWEB)
Ramos, J.G.G.S. [Universidade Federal da Paraiba (UFPB), Rio Tinto, PB (Brazil). Departamento de Ciencias Exatas; Hussein, M.S. [Universidade de Sao Paulo (USP), SP (Brazil). Instituto de Fisica; Barbosa, A.L.R. [Universidade Federal Rural de Pernambuco (UAEADTec/UFRPE), Recife, PE (Brazil). Unidade Academica de Ensino a Distancia. Pos-Graduacao em Fisica Aplicada
2014-07-01
For the main quantum interference term of coherent electronic transport, we study the effect of temperature, perpendicular and/or parallel magnetic fields, spin-orbit coupling and tunneling rates in both metallic grains and mesoscopic heterostructures. We show that the Zeeman effects determines a crucial way to characterize the quantum interference phenomena of the noise for anisotropic systems (mesoscopic heterostructures), qualitatively distinct from those observed in isotropic structures (metallic grains). (author)
Quantum interference effects for the electronic fluctuations in quantum dots
International Nuclear Information System (INIS)
Ramos, J.G.G.S.; Hussein, M.S.; Barbosa, A.L.R.
2014-01-01
For the main quantum interference term of coherent electronic transport, we study the effect of temperature, perpendicular and/or parallel magnetic fields, spin-orbit coupling and tunneling rates in both metallic grains and mesoscopic heterostructures. We show that the Zeeman effects determines a crucial way to characterize the quantum interference phenomena of the noise for anisotropic systems (mesoscopic heterostructures), qualitatively distinct from those observed in isotropic structures (metallic grains). (author)
Quantum dots: Rethinking the electronics
Energy Technology Data Exchange (ETDEWEB)
Bishnoi, Dimple [Department of Physics, S. S. Jain Subodh PG College, Jaipur, Rajasthan Pin-302004 (India)
2016-05-06
In this paper, we demonstrate theoretically that the Quantum dots are quite interesting for the electronics industry. Semiconductor quantum dots (QDs) are nanometer-scale crystals, which have unique photo physical, quantum electrical properties, size-dependent optical properties, There small size means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Cheaper than modern commercial solar cells while making use of a wider variety of photon energies, including “waste heat” from the sun’s energy. Quantum dots can be used in tandem cells, which are multi junction photovoltaic cells or in the intermediate band setup. PbSe (lead selenide) is commonly used in quantum dot solar cells.
Theoretical study of the electronic structure of f-element complexes by quantum chemical methods
International Nuclear Information System (INIS)
Vetere, V.
2002-09-01
This thesis is related to comparative studies of the chemical properties of molecular complexes containing lanthanide or actinide trivalent cations, in the context of the nuclear waste disposal. More precisely, our aim was a quantum chemical analysis of the metal-ligand bonding in such species. Various theoretical approaches were compared, for the inclusion of correlation (density functional theory, multiconfigurational methods) and of relativistic effects (relativistic scalar and 2-component Hamiltonians, relativistic pseudopotentials). The performance of these methods were checked by comparing computed structural properties to published experimental data, on small model systems: lanthanide and actinide tri-halides and on X 3 M-L species (X=F, Cl; M=La, Nd, U; L = NH 3 , acetonitrile, CO). We have thus shown the good performance of density functionals combined with a quasi-relativistic method, as well as of gradient-corrected functionals associated with relativistic pseudopotentials. In contrast, functionals including some part of exact exchange are less reliable to reproduce experimental trends, and we have given a possible explanation for this result . Then, a detailed analysis of the bonding has allowed us to interpret the discrepancies observed in the structural properties of uranium and lanthanides complexes, based on a covalent contribution to the bonding, in the case of uranium(III), which does not exist in the lanthanide(III) homologues. Finally, we have examined more sizeable systems, closer to experimental species, to analyse the influence of the coordination number, of the counter-ions and of the oxidation state of uranium, on the metal-ligand bonding. (author)
Energy Technology Data Exchange (ETDEWEB)
Vexler, M. I., E-mail: vexler@mail.ioffe.ru; Illarionov, Yu. Yu.; Grekhov, I. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation)
2017-04-15
The prerequisites for electron storage in the quantum well of a metal–oxide–p{sup +}-Si resonant-tunneling structure and the effect of the stored charge on the voltage distribution are theoretically investigated. Systems with SiO{sub 2}, HfO{sub 2}, and TiO{sub 2} insulators are studied. It is demonstrated that the occurrence of a charge in the well in the case of resonant transport can be expected in structures on substrates with an acceptor concentration from (5–6) × 10{sup 18} to (2–3) × 10{sup 19} cm{sup –3} in the range of oxide thicknesses dependent on this concentration. In particular, the oxide layer thickness in the structures with SiO{sub 2}/p{sup +}-Si(10{sup 19} cm{sup –3}) should exceed ~3 nm. The electron density in the well can reach ~10{sup 12} cm{sup –2} and higher. However, the effect of this charge on the electrostatics of the structure becomes noticeable only at relatively high voltages far above the activation of resonant transport through the first subband.
International Nuclear Information System (INIS)
Nevedomskiy, V. N.; Bert, N. A.; Chaldyshev, V. V.; Preobrazhenskiy, V. V.; Putyato, M. A.; Semyagin, B. R.
2013-01-01
Electron microscopy studies of GaAs-based structures grown by molecular beam epitaxy and containing arrays of semiconductor InAs quantum dots and metal As quantum dots are performed. The array of InAs quantum dots is formed by the Stranski-Krastanov mechanism and consists of vertically coupled pairs of quantum dots separated by a GaAs spacer 10 nm thick. To separate the arrays of semiconductor and metal quantum dots and to prevent diffusion-induced mixing, the array of InAs quantum dots is overgrown with an AlAs barrier layer 5 or 10 nm thick, after which a GaAs layer is grown at a comparatively low temperature (180°C). The array of As quantum dots is formed in an As-enriched layer of the low-temperature GaAs by means of post-growth annealing at 400–760°C for 15 min. It is established that the AlAs barrier layer has a surface profile corresponding to that of a subbarrier layer with InAs quantum dots. The presence of such a profile causes the formation of V-shaped structural defects upon subsequent overgrowth with the GaAs layer. Besides, it was obtained that AlAs layer is thinned over the InAs quantum dots tops. It is shown that the AlAs barrier layer in the regions between the InAs quantum dots effectively prevents the starting diffusion of excess As at annealing temperatures up to 600°C. However, the concentration of mechanical stresses and the reduced thickness of the AlAs barrier layer near the tops of the InAs quantum dots lead to local barrier breakthroughs and the diffusion of As quantum dots into the region of coupled pairs of InAs quantum dots at higher annealing temperatures
Quantum-mechanical calculations of the electronic structure of calcium and cadmium vanadate apatites
International Nuclear Information System (INIS)
Karbovskij, V.L.; Soroka, A.P.; Kasiyanenko, V.Kh.; Shpak, A.P.
2011-01-01
Electronic structures of compounds Me 10 (VO 4 ) 6 X 2 , where Me = Ca or Cd and X = F, Cl, OH are investigated using the full potential APW + lo method. The degrees of distortions of VO 4- tetrahedra with respect to the Td point group are analyzed using a relaxation of atomic positions. Apatites in the form of Ca 10 (VO 4 ) 6 X 2 , where X = F, Cl, OH, are established to decrease the band gap by 0.5-1.0 eV under the isomorphic substitution of calcium for cadmium. Apatites Ca 10 (VO 4 ) 6 X 2 , where X = F, Cl, OH are proven to decrease the degree of covalency of the oxygen-halogen bond under the isomorphic substitution of calcium for cadmium.
International Nuclear Information System (INIS)
Anon.
1976-01-01
Efficiency measurements in the rare gas excimers show that up to 50 percent of the energy deposited in a high-pressure rare gas by an electron beam can be converted to excimer fluorescence. The production kinetics and radiative properties of rare gas oxide excimers have been explored and show that short pulse lasers near 1 percent efficiency with energy storage of 10 J/liter can be constructed. The rare gas-halogen and dihalogen systems have been explored as a class of efficient radiators to complement the rare gas excimers. A Br 2 laser at 292 nm has been demonstrated, and XeBr fluorescence efficiency of 11 percent has been measured. An XeBr excimer-pumped atomic iodine laser has been demonstrated, and the systems considerations involved in scaling atomic iodine lasers to large sizes have been identified and are discussed. Oxygen, sulfur, and selenium have been analyzed as candidates for an optically pumped, visible energy storage laser. The physical and radiative properties of gaseous rare earth compounds, which may be suitable for energy storage lasers, have been measured and are discussed. Scaling considerations have been identified for drivers for large, electron-beam-pumped lasers. Theoretical studies bearing on an understanding of the basic atomic and molecular physics which must be understood for laser development and isotope separation projects have been carried out. These include efforts to develop a theoretical understanding rare-gas halogen structure and kinetics, copper vapor laser kinetics, electron interactions such as dissociative attachment, and other areas
International Nuclear Information System (INIS)
Reilly, Neil J.; Kokkin, Damian L.; McCarthy, Michael C.; Changala, P. Bryan; Baraban, Joshua H.; Stanton, John F.
2015-01-01
We report the gas-phase optical detection of Si 2 C near 390 nm and the first experimental investigation of the rovibrational structure of its 1 A 1 ground electronic state using mass-resolved and fluorescence spectroscopy and variational calculations performed on a high-level ab initio potential. From this joint study, it is possible to assign all observed K a = 1 vibrational levels up to 3800 cm −1 with confidence, as well as a number of levels in the K a = 0, 2, and 3 manifolds. Dixon-dip plots for the bending coordinate (ν 2 ) allow an experimental determination of a barrier to linearity of 783(48) cm −1 (2σ), in good agreement with theory (802(9) cm −1 ). The calculated (K a , ν 2 ) eigenvalue lattice shows an archetypal example of quantum monodromy (absence of a globally valid set of quantum numbers) that is reflected by the experimentally observed rovibrational levels. The present study provides a solid foundation for infrared and optical surveys of Si 2 C in astronomical objects, particularly in the photosphere of N- and J-type carbon stars where the isovalent SiC 2 molecule is known to be abundant
Aly, Shawkat Mohammede
2015-03-05
Charge transfer (CT) at donor (D)/acceptor (A) interfaces is central to the functioning of photovoltaic and light-emitting devices. Understanding and controlling this process on the molecular level has been proven to be crucial for optimizing the performance of many energy-challenge relevant devices. Here, we report the experimental observations of controlled on/off ultrafast electron transfer (ET) at cationic porphyrin-CdTe quantum dot (QD) interfaces using femto- and nanosecond broad-band transient absorption (TA) spectroscopy. The time-resolved data demonstrate how one can turn on/off the electron injection from porphyrin to the CdTe QDs. With careful control of the molecular structure, we are able to tune the electron injection at the porphyrin-CdTe QD interface from zero to very efficient and ultrafast. In addition, our data demonstrate that the ET process occurs within our temporal resolution of 120 fs, which is one of the fastest times recorded for organic photovoltaics. © 2015 American Chemical Society.
Zhang, Ya-Jing; Zhang, Lian-Lian; Jiang, Cui; Gong, Wei-Jiang
2018-02-01
We theoretically investigate the electronic transport through a parallel-coupled multi-quantum-dot system, in which the terminal dots of a one-dimensional quantum-dot chain are embodied in the two arms of an Aharonov-Bohm interferometer. It is found that in the structures of odd(even) dots, all their even(odd) molecular states have opportunities to decouple from the leads, and in this process antiresonance occurs which are accordant with the odd(even)-numbered eigenenergies of the sub-molecule without terminal dots. Next when Majorana zero modes are introduced to couple laterally to the terminal dots, the antiresonance and decoupling phenomena still co-exist in the quantum transport process. Such a result can be helpful in understanding the special influence of Majorana zero mode on the electronic transport through quantum-dot systems.
Quantum ratchets reroute electrons
International Nuclear Information System (INIS)
Haenggi, P.; Reimann, P.
1999-01-01
Is it possible to extract energy from random fluctuations and put it to use? This challenging question has provoked discussion ever since the early days of Brownian-motion theory. For large-scale or macroscopic fluctuations, the answer is ''yes'' - the principle is demonstrated, for example, in the self-winding wristwatch. Much subtler is the issue of whether microscopic random fluctuations, such as thermal Brownian motion or even the haphazard motion of quantum particles, acting as a random energy source can cause the particles to flow in one direction only. In recent years this field has been the scene of remarkable activity, motivated by the prospect of potentially high-profile technological and biological applications, such as molecular motors. In particular the directed transport of particles in an asymmetric potential known as a ratchet has received a lot of attention. This research, however, has focused on ''thermal ratchets'' in which the particles undergo thermal Brownian motion: the next challenge is to move from the classical world and account for quantum mechanical effects. Recently a collaboration between physicists at Lund University in Sweden and the Niels Bohr Institute in Copenhagen has taken a significant step forward and built a quantum ratchet (H Linke et al. 1998 Europhys. Lett. 44 341 and 45 406). The device is based on an aluminium-doped gallium arsenide (GaAs/AlGaAs) quantum dot with a ratchet-like, triangular-shaped cavity. In this article the authors discuss the implications of this work. (UK)
Bravyi-Kitaev Superfast simulation of electronic structure on a quantum computer.
Setia, Kanav; Whitfield, James D
2018-04-28
Present quantum computers often work with distinguishable qubits as their computational units. In order to simulate indistinguishable fermionic particles, it is first required to map the fermionic state to the state of the qubits. The Bravyi-Kitaev Superfast (BKSF) algorithm can be used to accomplish this mapping. The BKSF mapping has connections to quantum error correction and opens the door to new ways of understanding fermionic simulation in a topological context. Here, we present the first detailed exposition of the BKSF algorithm for molecular simulation. We provide the BKSF transformed qubit operators and report on our implementation of the BKSF fermion-to-qubits transform in OpenFermion. In this initial study of a hydrogen molecule we have compared BKSF, Jordan-Wigner, and Bravyi-Kitaev transforms under the Trotter approximation. The gate count to implement BKSF is lower than Jordan-Wigner but higher than Bravyi-Kitaev. We considered different orderings of the exponentiated terms and found lower Trotter errors than the previously reported for Jordan-Wigner and Bravyi-Kitaev algorithms. These results open the door to the further study of the BKSF algorithm for quantum simulation.
Magnee, P.H.C.; den Hartog, S.G.; Wees, B.J.van; Klapwijk, T.M; van de Graaf, W.; Borghs, G.
1995-01-01
The influence of low energy (80-500 eV) Ar-ion milling cleaning techniques on InAs based quantum well structures is investigated. It is found that both etching with a Kaufmann source and sputter-etching with a rf-plasma enhances the electron density and reduces the mobility. An anneal at 180 degrees
Vishnevskiy, Yuri V.; Abaev, Maxim A.; Ivanov, Arkadii A.; Vilkov, Lev V.; Dakkouri, Marwan
2008-10-01
The molecular structure and conformation of tris(cyclopropylsilyl)amine (TCPSA) has been studied by means of gas-phase electron diffraction at 338 K and quantum-chemical calculations. A total of 12 relatively stable conformations of TCPSA molecule were considered. According to the experimental results and the DFT calculations the most stable conformer corresponds to a configuration (according to the Prelog-Klyne notation) of the type (-ac)(-ac)(+ac)-(-ac)(-ac)(+ac), where the first three parentheses describe the three different Si-N-Si-C torsional angles and the latter ones depict the rotation of the three cyclopropyl groups about the C ring-Si axes, respectively. The quantum-mechanical calculations were performed using various density functional (B3LYP, X3LYP and O3LYP) and perturbation MP2 methods in combination with double- and triple- ζ basis sets plus polarization and diffuse functions. The most important experimental geometrical parameters of TCPSA ( ra Å, ∠ h1 degrees) are: (Si-N) av = 1.741(3), (Si-C) av = 1.866(4), (C-C) av = 1.510(3), (C-C(Si)) av = 1.535(3), (N-Si-C) av = 115.1(18)°. For the purpose of comparison and searching for reasons leading to the planarity of the Si 3N moiety in trisilylated amines we carried out NBO analysis and optimized the geometries of numerous silylamines. Among these compounds was tris(allylsilyl)amine (TASA), which is isovalent and isoelectronic to TCPSA. Utilizing the structural results we obtained we could show that Si +⋯Si + electrostatic repulsive interaction is predominantly responsible for the planarity of the Si 3N skeleton in TCPSA and in all other trisilylamines we considered. We also found that regardless the size and partial charges of the substituents the Si-N-Si bond angle in various disilylamines amounts to 130 ± 2°.
Designs for a quantum electron microscope.
Kruit, P; Hobbs, R G; Kim, C-S; Yang, Y; Manfrinato, V R; Hammer, J; Thomas, S; Weber, P; Klopfer, B; Kohstall, C; Juffmann, T; Kasevich, M A; Hommelhoff, P; Berggren, K K
2016-05-01
One of the astounding consequences of quantum mechanics is that it allows the detection of a target using an incident probe, with only a low probability of interaction of the probe and the target. This 'quantum weirdness' could be applied in the field of electron microscopy to generate images of beam-sensitive specimens with substantially reduced damage to the specimen. A reduction of beam-induced damage to specimens is especially of great importance if it can enable imaging of biological specimens with atomic resolution. Following a recent suggestion that interaction-free measurements are possible with electrons, we now analyze the difficulties of actually building an atomic resolution interaction-free electron microscope, or "quantum electron microscope". A quantum electron microscope would require a number of unique components not found in conventional transmission electron microscopes. These components include a coherent electron beam-splitter or two-state-coupler, and a resonator structure to allow each electron to interrogate the specimen multiple times, thus supporting high success probabilities for interaction-free detection of the specimen. Different system designs are presented here, which are based on four different choices of two-state-couplers: a thin crystal, a grating mirror, a standing light wave and an electro-dynamical pseudopotential. Challenges for the detailed electron optical design are identified as future directions for development. While it is concluded that it should be possible to build an atomic resolution quantum electron microscope, we have also identified a number of hurdles to the development of such a microscope and further theoretical investigations that will be required to enable a complete interpretation of the images produced by such a microscope. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.
Electronic Conduction through Atomic Chains, Quantum Well and Quantum Wire
International Nuclear Information System (INIS)
Sharma, A. C.
2011-01-01
Charge transport is dynamically and strongly linked with atomic structure, in nanostructures. We report our ab-initio calculations on electronic transport through atomic chains and the model calculations on electron-electron and electron-phonon scattering rates in presence of random impurity potential in a quantum well and in a quantum wire. We computed synthesis and ballistic transport through; (a) C and Si based atomic chains attached to metallic electrodes, (b) armchair (AC), zigzag (ZZ), mixed, rotated-AC and rotated-ZZ geometries of small molecules made of 2S, 6C and 4H atoms attaching to metallic electrodes, and (c) carbon atomic chain attached to graphene electrodes. Computed results show that synthesis of various atomic chains are practically possible and their transmission coefficients are nonzero for a wide energy range. The ab-initio calculations on electronic transport have been performed with the use of Landauer-type scattering formalism formulated in terms of Grben's functions in combination with ground-state DFT. The electron-electron and electron-phonon scattering rates have been calculated as function of excitation energy both at zero and finite temperatures for disordered 2D and 1D systems. Our model calculations suggest that electron scattering rates in a disordered system are mainly governed by effective dimensionality of a system, carrier concentration and dynamical screening effects.
Electron states in semiconductor quantum dots
International Nuclear Information System (INIS)
Dhayal, Suman S.; Ramaniah, Lavanya M.; Ruda, Harry E.; Nair, Selvakumar V.
2014-01-01
In this work, the electronic structures of quantum dots (QDs) of nine direct band gap semiconductor materials belonging to the group II-VI and III-V families are investigated, within the empirical tight-binding framework, in the effective bond orbital model. This methodology is shown to accurately describe these systems, yielding, at the same time, qualitative insights into their electronic properties. Various features of the bulk band structure such as band-gaps, band curvature, and band widths around symmetry points affect the quantum confinement of electrons and holes. These effects are identified and quantified. A comparison with experimental data yields good agreement with the calculations. These theoretical results would help quantify the optical response of QDs of these materials and provide useful input for applications
Single-electron quantum tomography in quantum Hall edge channels
International Nuclear Information System (INIS)
Grenier, Ch; Degiovanni, P; Herve, R; Bocquillon, E; Parmentier, F D; Placais, B; Berroir, J M; Feve, G
2011-01-01
We propose a quantum tomography protocol to measure single-electron coherence in quantum Hall edge channels, and therefore access for the first time the wavefunction of single-electron excitations propagating in ballistic quantum conductors. Its implementation would open the way to quantitative studies of single-electron decoherence and would provide a quantitative tool for analyzing single- to few-electron sources. We show how this protocol could be implemented using ultrahigh-sensitivity noise measurement schemes.
Designs for a quantum electron microscope
International Nuclear Information System (INIS)
Kruit, P.; Hobbs, R.G.; Kim, C-S.; Yang, Y.; Manfrinato, V.R.; Hammer, J.; Thomas, S.; Weber, P.; Klopfer, B.; Kohstall, C.; Juffmann, T.; Kasevich, M.A.; Hommelhoff, P.; Berggren, K.K.
2016-01-01
One of the astounding consequences of quantum mechanics is that it allows the detection of a target using an incident probe, with only a low probability of interaction of the probe and the target. This ‘quantum weirdness’ could be applied in the field of electron microscopy to generate images of beam-sensitive specimens with substantially reduced damage to the specimen. A reduction of beam-induced damage to specimens is especially of great importance if it can enable imaging of biological specimens with atomic resolution. Following a recent suggestion that interaction-free measurements are possible with electrons, we now analyze the difficulties of actually building an atomic resolution interaction-free electron microscope, or “quantum electron microscope”. A quantum electron microscope would require a number of unique components not found in conventional transmission electron microscopes. These components include a coherent electron beam-splitter or two-state-coupler, and a resonator structure to allow each electron to interrogate the specimen multiple times, thus supporting high success probabilities for interaction-free detection of the specimen. Different system designs are presented here, which are based on four different choices of two-state-couplers: a thin crystal, a grating mirror, a standing light wave and an electro-dynamical pseudopotential. Challenges for the detailed electron optical design are identified as future directions for development. While it is concluded that it should be possible to build an atomic resolution quantum electron microscope, we have also identified a number of hurdles to the development of such a microscope and further theoretical investigations that will be required to enable a complete interpretation of the images produced by such a microscope. - Highlights: • Quantum electron microscopy has the potential of reducing radiation damage. • QEM requires a fraction of the electron wave to pass through the sample
Designs for a quantum electron microscope
Energy Technology Data Exchange (ETDEWEB)
Kruit, P., E-mail: p.kruit@tudelft.nl [Department of Imaging Physics, Delft University of Technology, Lorentzweg 1, 2628CJ Delft (Netherlands); Hobbs, R.G.; Kim, C-S.; Yang, Y.; Manfrinato, V.R. [Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Hammer, J.; Thomas, S.; Weber, P. [Department of Physics, Friedrich Alexander University Erlangen-Nürnberg (FAU), Staudtstrasse 1, d-91058 Erlangen (Germany); Klopfer, B.; Kohstall, C.; Juffmann, T.; Kasevich, M.A. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Hommelhoff, P. [Department of Physics, Friedrich Alexander University Erlangen-Nürnberg (FAU), Staudtstrasse 1, d-91058 Erlangen (Germany); Berggren, K.K. [Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
2016-05-15
One of the astounding consequences of quantum mechanics is that it allows the detection of a target using an incident probe, with only a low probability of interaction of the probe and the target. This ‘quantum weirdness’ could be applied in the field of electron microscopy to generate images of beam-sensitive specimens with substantially reduced damage to the specimen. A reduction of beam-induced damage to specimens is especially of great importance if it can enable imaging of biological specimens with atomic resolution. Following a recent suggestion that interaction-free measurements are possible with electrons, we now analyze the difficulties of actually building an atomic resolution interaction-free electron microscope, or “quantum electron microscope”. A quantum electron microscope would require a number of unique components not found in conventional transmission electron microscopes. These components include a coherent electron beam-splitter or two-state-coupler, and a resonator structure to allow each electron to interrogate the specimen multiple times, thus supporting high success probabilities for interaction-free detection of the specimen. Different system designs are presented here, which are based on four different choices of two-state-couplers: a thin crystal, a grating mirror, a standing light wave and an electro-dynamical pseudopotential. Challenges for the detailed electron optical design are identified as future directions for development. While it is concluded that it should be possible to build an atomic resolution quantum electron microscope, we have also identified a number of hurdles to the development of such a microscope and further theoretical investigations that will be required to enable a complete interpretation of the images produced by such a microscope. - Highlights: • Quantum electron microscopy has the potential of reducing radiation damage. • QEM requires a fraction of the electron wave to pass through the sample
International Nuclear Information System (INIS)
Hübner, Olaf; Hornung, Julius; Himmel, Hans-Jörg
2015-01-01
The electronic ground and excited states of the vanadium monoxide (VO) molecule were studied in detail. Electronic absorption spectra for the molecule isolated in Ne matrices complement the previous gas-phase spectra. A thorough quantum chemical (multi-reference configuration interaction) study essentially confirms the assignment and characterization of the electronic excitations observed for VO in the gas-phase and in Ne matrices and allows the clarification of open issues. It provides a complete overview over the electronically excited states up to about 3 eV of this archetypical compound
Electron-electron interaction in Multiple Quantum Wells
Zybert, M.; Marchewka, M.; Tomaka, G.; Sheregii, E. M.
2012-07-01
The complex investigation of the magneto-transport effects in structures containing multiple quantum well (MQWs) based on the GaAs/AlGaAs-heterostructures has been performed. The MQWs investigated have different electron densities in QWs. The parameters of 2DEG in MQWs were determined from the data of the Integer Quantum Hall Effect (IQHE) and Shubnikov-de Haas oscillations (SdH) observed at low temperatures (0.6-4.2 K). The method of calculation of the electron states energies in MQWs has been developed which is based on the splitting of these states due to the exchange interaction (SAS-splitting, see D. Płoch et al., Phys. Rev. B 79 (2009) 195434) including the screening of this interaction. The IQHE and SdH observed in these multilayer structures with the third degree of freedom for electrons are interpreted from this.
Electron Raman scattering in quantum well wires
International Nuclear Information System (INIS)
Zhao Xiangfu; Liu Cuihong
2007-01-01
Electron Raman scattering (ERS) is investigated in a semiconductor quantum well wire (QWW) of cylindrical geometry for T=0K and neglecting phonon-assisted transitions. The differential cross-section (DCS) involved in this process is calculated as a function of a scattering frequency and the cylindrical radius. Electron states are confined within a QWW. Single parabolic conduction and valence bands are assumed. The selection rules are studied. Singularities in the spectra are interpreted for various cylindrical radii. ERS discussed here can provide direct information about the electron band structure of the system
Arjunan, V.; Anitha, R.; Marchewka, M. K.; Mohan, S.; Yang, Haifeng
2015-01-01
The Fourier transform infrared (FTIR) and FT-Raman spectra of cis-2-methoxycinnamic acid have been measured in the range 4000-400 and 4000-100 cm-1, respectively. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The geometry was optimised without any symmetry constrains using the DFT/B3LYP method utilising 6-311++G∗∗ and cc-pVTZ basis sets. The thermodynamic stability and chemical reactivity descriptors of the molecule have been determined. The exact environment of C and H of the molecule has been analysed by NMR spectroscopies through 1H and 13C NMR chemical shifts of the molecule. The energies of the frontier molecular orbitals have also been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. The vibrational frequencies which were determined experimentally are compared with those obtained theoretically from density functional theory (DFT) gradient calculations employing the B3LYP/6-311++G∗∗ and cc-pVTZ methods.
The electronic properties of semiconductor quantum dots
International Nuclear Information System (INIS)
Barker, J.A.
2000-10-01
This work is an investigation into the electronic behaviour of semiconductor quantum dots, particularly self-assembled quantum dot arrays. Processor-efficient models are developed to describe the electronic structure of dots, deriving analytic formulae for the strain tensor, piezoelectric distribution and diffusion- induced evolution of the confinement potential, for dots of arbitrary initial shape and composition profile. These models are then applied to experimental data. Transitions due to individual quantum dots have a narrow linewidth as a result of their discrete density of states. By contrast, quantum dot arrays exhibit inhomogeneous broadening which is generally attributed to size variations between the individual dots in the ensemble. Interpreting the results of double resonance spectroscopy, it is seen that variation in the indium composition of the nominally InAs dots is also present. This result also explains the otherwise confusing relationship between the spread in the ground-state and excited-state transition energies. Careful analysis shows that, in addition to the variations in size and composition, some other as yet unidentified broadening mechanism must also be present. The influence of rapid thermal annealing on dot electronic structure is also considered, finding that the experimentally observed blue-shift and narrowing of the photoluminescence linewidth may both be explained in terms of normal In/Ga interdiffusion. InAs/GaAs self-assembled quantum dots are commonly assumed to have a pyramidal geometry, so that we would expect the energy separation of the ground-state electron and hole levels in the dot to be largest at a positive applied field. This should also be the case for any dot of uniform composition whose shape tapers inwards from base to top, counter to the results of experimental Stark-shift spectroscopy which show a peak transition energy at a negative applied field. It is demonstrated that this inversion of the ground state
International Nuclear Information System (INIS)
Ovchinnikov, S. G.; Makarov, I. A.; Shneyder, E. I.
2011-01-01
We present a theoretical study of the electronic structure of bilayer HTSC cuprates and its evolution under doping and in a high magnetic field. Analysis is based on the t-t′-t″-J* model in the generalized Hartree-Fock approximation. Possibility of tunneling between CuO2 layers is taken into account in the form of a nonzero integral of hopping between the orbitals of adjacent planes and is included in the scheme of the cluster form of perturbation theory. The main effect of the coupling between two CuO 2 layers in a unit cell is the bilayer splitting manifested in the presence of antibonding and bonding bands formed by a combination of identical bands of the layers themselves. A change in the doping level induces reconstruction of the band structure and the Fermi surface, which gives rise to a number of quantum phase transitions. A high external magnetic field leads to a fundamentally different form of electronic structure. Quantum phase transitions in the field are observed not only under doping, but also upon a variation of the field magnitude. Because of tunneling between the layers, quantum transitions are also split; as a result, a more complex sequence of the Lifshitz transitions than in single-layer structures is observed.
Electronic structure and microscopic model of V2GeO4F2-a quantum spin system with S = 1
International Nuclear Information System (INIS)
Rahaman, Badiur; Saha-Dasgupta, T
2007-01-01
We present first-principles density functional calculations and downfolding studies of the electronic and magnetic properties of the oxide-fluoride quantum spin system V 2 GeO 4 F 2 . We discuss explicitly the nature of the exchange paths and provide quantitative estimates of magnetic exchange couplings. A microscopic modelling based on analysis of the electronic structure of this systems puts it in the interesting class of weakly coupled alternating chain S = 1 systems. Based on the microscopic model, we make inferrences about its spin excitation spectra, which needs to be tested by rigorous experimental study
Ksenafontov, Denis N.; Moiseeva, Natalia F.; Khristenko, Lyudmila V.; Karasev, Nikolai M.; Shishkov, Igor F.; Vilkov, Lev V.
2010-12-01
The geometric structure of piracetam was studied by quantum chemical calculations (DFT and ab initio), gas electron diffraction (GED), and FTIR spectroscopy. Two stable mirror symmetric isomers of piracetam were found. The conformation of pyrrolidine ring is an envelope in which the C4 atom deviates from the ring plane, the angle between the planes (C3 sbnd C4 sbnd C5) and (C2 sbnd C3 sbnd C5) is 154.1°. The direction of the deviation is the same as that of the side acetamide group. The piracetam molecule is stabilized in the gas phase by an intramolecular hydrogen bond between the N9H 2 group and the oxygen O6, bonded to C2. The principal structural parameters ( re, Å and ∠e, degrees; uncertainties are 3 σLS values) were found to be: r(С3 sbnd С4) = 1.533(1), r(C4 sbnd C5) = 1.540(1), r(N1 sbnd C5) = 1.456(1), r(C2 sbnd C3) = 1.520(1), r(N1 sbnd C7) = 1.452(1), r(C7 sbnd C8) = 1.537(1), r(N1 sbnd C2) = 1.365(2), r(C8 sbnd N9) = 1.360(2), r(C2 dbnd O6) = 1.229(1), r(C8 dbnd O10) = 1.221(1), ∠C2 sbnd N1 sbnd C5 = 113.4(6), ∠N1 sbnd C2 sbnd C3 = 106.9(6), ∠N1 sbnd C7 sbnd C8 = 111.9(6), ∠C7 sbnd C8 sbnd N9 = 112.5(6), ∠N1 sbnd C2 sbnd O6 = 123.0(4), ∠C3 sbnd N1 sbnd C7 = 120.4(4), ∠C7 sbnd C8 sbnd O10 = 120.2(4), ∠C5 sbnd N1 sbnd C2 sbnd O6 = 170(6), ∠C3 sbnd C2 sbnd N1 sbnd C7 = 178(6), ∠C2 sbnd N1 sbnd C7 sbnd C8 = 84.2, ∠N1 sbnd C7 sbnd C8 sbnd O10 = 111.9.
Advances in quantum electronics 3
Goodwin, D W
2013-01-01
Advances in Quantum Electronics, Volume 3 covers articles on the theoretical and experimental work undertaken in the field of optical pumping and on gaseous ion lasers. The book presents an overview of the optical-pumping field and a review of the use and properties of the density matrix as applied to the statistical behavior of assemblages of atoms or ions. The text discusses the application of the density matrix approach to the theory of optical-pumping r.f. spectroscopy and spin-exchange optical pumping. Optical-pumping experiments are also considered. The book further provides a comprehens
Correlated electrons in quantum matter
Fulde, Peter
2012-01-01
An understanding of the effects of electronic correlations in quantum systems is one of the most challenging problems in physics, partly due to the relevance in modern high technology. Yet there exist hardly any books on the subject which try to give a comprehensive overview on the field covering insulators, semiconductors, as well as metals. The present book tries to fill that gap. It intends to provide graduate students and researchers a comprehensive survey of electron correlations, weak and strong, in insulators, semiconductors and metals. This topic is a central one in condensed matter and beyond that in theoretical physics. The reader will have a better understanding of the great progress which has been made in the field over the past few decades.
Electron transport in quantum dots
2003-01-01
When I was contacted by Kluwer Academic Publishers in the Fall of 200 I, inviting me to edit a volume of papers on the issue of electron transport in quantum dots, I was excited by what I saw as an ideal opportunity to provide an overview of a field of research that has made significant contributions in recent years, both to our understanding of fundamental physics, and to the development of novel nanoelectronic technologies. The need for such a volume seemed to be made more pressing by the fact that few comprehensive reviews of this topic have appeared in the literature, in spite of the vast activity in this area over the course of the last decade or so. With this motivation, I set out to try to compile a volume that would fairly reflect the wide range of opinions that has emerged in the study of electron transport in quantum dots. Indeed, there has been no effort on my part to ensure any consistency between the different chapters, since I would prefer that this volume instead serve as a useful forum for the...
International Nuclear Information System (INIS)
Sahu, Trinath; Shore, K Alan
2009-01-01
We analyse the effect of interface roughness scattering on low temperature electron mobility μ n mediated by intersubband interactions in a multisubband coupled Ga 0.5 In 0.5 P/GaAs quantum well structure. We consider a barrier δ-doped double quantum well system in which the subband electron mobility is limited by the interface roughness scattering μ IR n and ionized impurity scattering μ imp n . We analyse the effect of the intersubband interaction and coupling of subband wavefunctions through the barrier on the intrasubband and intersubband transport scattering rates. We show that the intersubband interaction controls the roughness potential of different interfaces through the dielectric screening matrix. In the case of lowest subband occupancy, the mobility is mainly governed by the interface roughness of the central barrier. Whereas when two subbands are occupied, the interface roughness of the outer barrier predominates due to intersubband effects. The influence of the intersubband interaction also exhibits interesting results on the well width up to which the interface roughness dominates in a double quantum well structure
Coldea, Amalia
FeSe is a unique and intriguing superconductor which can be tuned into a high temperature superconducting state using applied pressure, chemical intercalation and surface doping. In the absence of magnetism, the structural transition in FeSe is believed to be electronically driven, with the orbital degrees of freedom playing an important part. This scenario supports the stabilization of a nematic state in FeSe, which manifests as a Fermi surface deformation in the presence of strong interactions, as detected by ARPES. Another manifestation of the nematicity is the enhanced nematic susceptibility determined from elastoresistance measurements under applied strain. Isovalent Sulphur substitution onto the Selenium site constitutes a chemical pressure, which subtly modifies the electronic structure of FeSe, suppressing the structural transition without inducing high temperature superconductivity. I will present the evolution of the electronic structure with chemical pressure in FeSe, as determined from quantum oscillations and ARPES studies and I will discuss the suppression of the nematic electronic state and the role of electronic correlations. Experiments were performed at high magnetic field facilities in Tallahassee, Nijmegen and Toulouse and Diamond Light Source, UK. This work is mainly supported by EPSRC, UK (EP/I004475/1, EP/I017836/1) and I acknowledge my collaborators from Refs. .
Quantum electronics maser amplifiers and oscillators
Fain, V M; Sanders, J H
2013-01-01
Quantum Electronics, Volume 2: Maser Amplifiers and Oscillators deals with the experimental and theoretical aspects of maser amplifiers and oscillators which are based on the principles of quantum electronics. It shows how the concepts and equations used in quantum electronics follow from the basic principles of theoretical physics.Comprised of three chapters, this volume begins with a discussion on the elements of the theory of quantum oscillators and amplifiers working in the microwave region, along with the practical achievements in this field. Attention is paid to two-level paramagnetic ma
Electron Spins in Semiconductor Quantum Dots
Hanson, R.
2005-01-01
This thesis describes a series of experiments aimed at understanding and controlling the behavior of the spin degree of freedom of single electrons, confined in semiconductor quantum dots. This research work is motivated by the prospects of using the electron spin as a quantum bit (qubit), the basic
Browne, David A.
2015-05-14
© 2015 AIP Publishing LLC. Unipolar-light emitting diode like structures were grown by NH3 molecular beam epitaxy on c plane (0001) GaN on sapphire templates. Studies were performed to experimentally examine the effect of random alloy fluctuations on electron transport through quantum well active regions. These unipolar structures served as a test vehicle to test our 2D model of the effect of compositional fluctuations on polarization-induced barriers. Variables that were systematically studied included varying quantum well number from 0 to 5, well thickness of 1.5 nm, 3 nm, and 4.5 nm, and well compositions of In0.14Ga0.86N and In0.19Ga0.81N. Diode-like current voltage behavior was clearly observed due to the polarization-induced conduction band barrier in the quantum well region. Increasing quantum well width and number were shown to have a significant impact on increasing the turn-on voltage of each device. Temperature dependent IV measurements clearly revealed the dominant effect of thermionic behavior for temperatures from room temperature and above. Atom probe tomography was used to directly analyze parameters of the alloy fluctuations in the quantum wells including amplitude and length scale of compositional variation. A drift diffusion Schrödinger Poisson method accounting for two dimensional indium fluctuations (both in the growth direction and within the wells) was used to correctly model the turn-on voltages of the devices as compared to traditional 1D simulation models.
Shimada, Toru; Hasegawa, Takeshi
2017-10-05
The pH dependent chemical structures of bromothymol blue (BTB), which have long been under controversy, are determined by employing a combined technique of multivariate analysis of electronic absorption spectra and quantum chemistry. Principle component analysis (PCA) of the pH dependent spectra apparently reveals that only two chemical species are adequate to fully account for the color changes, with which the spectral decomposition is readily performed by using augmented alternative least-squares (ALS) regression analysis. The quantity variation by the ALS analysis also reveals the practical acid dissociation constant, pK a '. The determination of pK a ' is performed for various ionic strengths, which reveals the thermodynamic acid constant (pK a =7.5) and the number of charge on each chemical species; the yellow form is negatively charged species of -1 and the blue form that of -2. On this chemical information, the quantum chemical calculation is carried out to find that BTB molecules take the pure quinoid form in an acid solution and the quinoid-phenolate form in an alkaline solution. The time-dependent density functional theory (TD-DFT) calculations for the theoretically determined chemical structures account for the peak shift of the electronic spectra. In this manner, the structures of all the chemical species appeared in equilibrium have finally been confirmed. Copyright © 2017 Elsevier B.V. All rights reserved.
Shimada, Toru; Hasegawa, Takeshi
2017-10-01
The pH dependent chemical structures of bromothymol blue (BTB), which have long been under controversy, are determined by employing a combined technique of multivariate analysis of electronic absorption spectra and quantum chemistry. Principle component analysis (PCA) of the pH dependent spectra apparently reveals that only two chemical species are adequate to fully account for the color changes, with which the spectral decomposition is readily performed by using augmented alternative least-squares (ALS) regression analysis. The quantity variation by the ALS analysis also reveals the practical acid dissociation constant, pKa‧. The determination of pKa‧ is performed for various ionic strengths, which reveals the thermodynamic acid constant (pKa = 7.5) and the number of charge on each chemical species; the yellow form is negatively charged species of - 1 and the blue form that of - 2. On this chemical information, the quantum chemical calculation is carried out to find that BTB molecules take the pure quinoid form in an acid solution and the quinoid-phenolate form in an alkaline solution. The time-dependent density functional theory (TD-DFT) calculations for the theoretically determined chemical structures account for the peak shift of the electronic spectra. In this manner, the structures of all the chemical species appeared in equilibrium have finally been confirmed.
Spin polarization of electrons in quantum wires
Vasilchenko, A. A.
2013-01-01
The total energy of a quasi-one-dimensional electron system is calculated using density functional theory. It is shown that spontaneous ferromagnetic state in quantum wire occurs at low one-dimensional electron density. The critical electron density below which electrons are in spin-polarized state is estimated analytically.
Indication for quantum Darwinism in electron billiards
Brunner, R.; Akis, R.; Meisels, R.; Kuchar, F.; Ferry, D. K.
2010-02-01
In this paper, we investigate the dynamics in electron billiards by using classical and quantum mechanical calculations. We report on the existence of pointer states in single-dot and double-dot electron billiards. Additionally, we show that the two types of pointer states have the propensity to create offspring, i.e. they can be observed in the individual modes propagating between the external reservoirs. This can be understood as an indication that quantum Darwinism is present in the electron billiards.
Electron Raman scattering in a HgS/CdS spherical quantum dot quantum well
International Nuclear Information System (INIS)
Zhong Qinghu; Lai Liping
2013-01-01
Electron Raman scattering (ERS) is investigated in a spherical HgS/CdS quantum dot quantum well (QDQW). The differential cross section (DCS) is calculated as a function of the scattering frequency and the sizes of QDQW. Single parabolic conduction and valence bands are assumed. The selection rules for the processes are studied. Singularities in the spectra are found and interpreted. The ERS studied here can be used to provide direct information about the electron band structure of these systems. (semiconductor physics)
Roy-Gobeil, Antoine; Miyahara, Yoichi; Grutter, Peter
2015-04-08
We present theoretical and experimental studies of the effect of the density of states of a quantum dot (QD) on the rate of single-electron tunneling that can be directly measured by electrostatic force microscopy (e-EFM) experiments. In e-EFM, the motion of a biased atomic force microscope cantilever tip modulates the charge state of a QD in the Coulomb blockade regime. The charge dynamics of the dot, which is detected through its back-action on the capacitavely coupled cantilever, depends on the tunneling rate of the QD to a back-electrode. The density of states of the QD can therefore be measured through its effect on the energy dependence of tunneling rate. We present experimental data on individual 5 nm colloidal gold nanoparticles that exhibit a near continuous density of state at 77 K. In contrast, our analysis of already published data on self-assembled InAs QDs at 4 K clearly reveals discrete degenerate energy levels.
Energy Technology Data Exchange (ETDEWEB)
Landesman, Jean-Pierre, E-mail: jean-pierre.landesman@univ-rennes1.fr [Institut de Physique de Rennes, CNRS-UMR 6251, Université Rennes 1, F-35042 Rennes (France); Jiménez, Juan; Torres, Alfredo [GdS Optronlab, Dpto. Fisica de la Materia Condensada, Universidad de Valladolid, 47011 Valladolid (Spain); Levallois, Christophe; Léger, Yoan; Beck, Alexandre [UMR FOTON, CNRS, INSA-Rennes, 20 avenue des buttes de Coësmes, F-35708 Rennes (France); Pommereau, Frédéric [III-V Lab, 1 Avenue Augustin Fresnel, RD128, F-91767 Palaiseau (France); Frigeri, Cesare [CNR-IMEM Istituto, Parco area delle Scienze 37/A, 43010 Parma (Italy); Rhallabi, Ahmed [Institut des Matériaux Jean-Rouxel, CNRS-UMR 6502, Université Nantes 1, F-44322 Nantes (France)
2016-07-15
The general objective is the investigation of the defects formed by dry etching tools such as those involved in the fabrication of photonic devices with III–V semiconductors. Emphasis is put on plasma exposures with chlorine-based chemistries. In addition to identifying these defects and describing their effects on the electro-optic and structural properties, the long-term target would be to predict the impact on the parameters of importance for photonic devices, and possibly include these predictions in their design. The work is first centered on explaining the experimental methodology. This methodology starts with the design and growth of a quantum well structure on indium phosphide, including ternary indium arsenide/phosphide quantum wells with graded arsenic/phosphor composition. These samples have then been characterized by luminescence methods (photo- and cathodoluminescence), high-resolution transmission electron microscopy, and secondary ion mass spectrometry. As one of the parameters of importance in this study, the authors have also included the doping level. The samples have been exposed to the etching plasmas for “short” durations that do not remove completely the quantum wells, but change their optical signature. No masking layer with lithographic features was involved as this work is purely oriented to study the interaction between the plasma and the samples. A significant difference in the luminescence spectra of the as-grown undoped and doped samples is observed. A mechanism describing the effect of the built-in electric field appearing as a consequence of the doping profile is proposed. This mechanism involves quantum confined Stark effect and electric-field induced carrier escape from the quantum wells. In the following part, the effects of exposure to various chlorine-based plasmas were explored. Differences are again observed between the undoped and doped samples, especially for chemistries containing silicon tetrachloride. Secondary ion
Instructional Approach to Molecular Electronic Structure Theory
Dykstra, Clifford E.; Schaefer, Henry F.
1977-01-01
Describes a graduate quantum mechanics projects in which students write a computer program that performs ab initio calculations on the electronic structure of a simple molecule. Theoretical potential energy curves are produced. (MLH)
Electron-electron interaction in p-SiGe/Ge quantum wells
International Nuclear Information System (INIS)
Roessner, Benjamin; Kaenel, Hans von; Chrastina, Daniel; Isella, Giovanni; Batlogg, Bertram
2005-01-01
The temperature dependent magnetoresistance of high mobility p-SiGe/Ge quantum wells is studied with hole densities ranging from 1.7 to 5.9 x 10 11 cm -2 . At magnetic fields below the onset of quantum oscillations that reflect the high mobility values (up to 75000 cm 2 /Vs), we observe the clear signatures of electron-electron interaction. We compare our experiment with the theory of electron-electron interaction including the Zeeman band splitting. The observed magnetoresistance is well explained as a superposition of band structure induced positive magnetoresistance and the negative magntoresistance due to the electron-electron interaction effect
Physical foundations of quantum electronics
Klyshko, David; Kulik, Sergey
2011-01-01
This concise textbook introduces a graduate student to the various fields of physics related to the interaction between radiation and matter. The scope of the book is very broad, ranging from nonlinear to quantum optics and from quantum transitions in atoms to the dispersion of polaritons in continuous media. The author, Professor David Klyshko (1929-2000), is one of the founders of modern quantum optics, renowned for his theory of Spontaneous Parametric Down-Conversion (SPDC) and its applications in quantum metrology and the optics of nonclassical light. Most parts of the book contain the lec
Electron quantum interferences and universal conductance fluctuations
International Nuclear Information System (INIS)
Benoit, A.; Pichard, J.L.
1988-05-01
Quantum interferences yield corrections to the classical ohmic behaviour predicted by Boltzmann theory in electronic transport: for instance the well-known ''weak localization'' effects. Furthermore, very recently, quantum interference effects have been proved to be responsible for statistically different phenomena, associated with Universal Conductance Fluctuations and observed on very small devices [fr
Quantum aspects of the free electron laser
Energy Technology Data Exchange (ETDEWEB)
Gaiba, R.
2007-03-15
We study the role of Quantum Mechanics in the physics of Free Electron Lasers. While the Free Electron Laser (FEL) is usually treated as a classical device, we review the advantages of a quantum formulation of the FEL. We then show the existence of a regime of operation of the FEL that can only be described using Quantum Mechanics: if the dimensionless quantum parameter anti {rho} is smaller than 1, then in the 1-dimensional approximation the Hamiltonian that describes the FEL becomes equivalent to the Hamiltonian of a two-level system coupled to a radiation field. We give analytical and numerical solutions for the photon statistics of a Free Electron Laser operating in the quantum regime under various approximations. Since in the quantum regime the momentum of the electrons is discrete, we give a description of the electrons in phase space by introducing the Discrete Wigner Function. We then drop the assumption of a mono-energetic electron beam and describe the general case of a initial electron energy spread G({gamma}). Numerical analysis shows that the FEL quantum regime is observed only when the width of the initial momentum distribution is smaller than the momentum of the emitted photons. Both the analytical results in the linear approximation and the numerical simulations show that only the electrons close to a certain resonant energy start to emit photons. This generates the so-called Hole-burning effect in the electrons energy distribution, as it can be seen in the simulations we provide. Finally, we present a brief discussion about a fundamental uncertainty relation that ties the electron energy spread and the electron bunching. (orig.)
Electron billiards: einselection and quantum Darwinism
International Nuclear Information System (INIS)
Brunner, R.; Meisels, R.; Kuchar, F.; Akis, R.; Ferry, D.K.
2008-01-01
Full text: The measurement of open quantum systems has been a main topic since the advent of quantum theory. It is a basic ingredient in quantum information processing. Here, the border where the two worlds of classical and quantum mechanics meet is of significant importance due to the problem of measurement. It has been shown by Zurek that in an open system the environment imposes so-called superselection rules leading to environment-induced superselection (einselection). This means that a set of preferred states (pointer states) survive the coupling with the environment. These pointer states are characterized by their robustness and their ability to create offspring. This ability to advertise information about themselves makes it possible for different observers to measure the same information. The natural promotion of certain information in a quantum system is known as quantum Darwinism. The 'fitness' in the Darwinian sense of the selected states is essentially a measure of their classicality. That is in order to measure a quantum system objectively a system has to be designed where the transition between the classical and quantum world is observable. In this respect we show by a combination of experiment and calculation that an array of electron billiards (open quantum dots) is very well suited. We demonstrate that einselection takes place in electron billiards and a set of pointer states arises. We illustrate that beside the 'regular' (single dot) pointer states a new type of einselected states arise when two or more quantum dots are coupled together and to the environment. This new type of states can not be represented by a linear combination of pointer states of the individual dots. Finally, we discuss the propensity of the new type of einselected states to make offspring in order to see if quantum Darwinism is in action in the array of electron billiards.(author)
Zamani, A.; Setareh, F.; Azargoshasb, T.; Niknam, E.
2017-10-01
A wide variety of semiconductor nanostructures have been fabricated experimentally and both theoretical and experimental investigations of their features imply the great role they have in new generation technological devices. However, mathematical modeling provide a powerful means due to definitive goal of predicting the features and understanding of such structures behavior under different circumstances. Therefore, effective Hamiltonian for an electron in a quantum ring with axial symmetry in the presence of both Rashba and Dresselhaus spin-orbit interactions (SOI) is derived. Here we report our study of the electronic structure and electron g-factor in the presence of spin-orbit (SO) couplings under the influence of external magnetic field at finite temperature. This investigation shows that, when Rashba and Dresselhaus couplings are simultaneously present, the degeneracy is removed and energy levels split into two branches. Furthermore, with enhancing the applied magnetic field, separation of former degenerate levels increases and also avoided crossings (anti-crossing) in the energy spectra is detected. It is also discussed how the energy levels of the system can be adjusted with variation of temperature as well as the magnetic field and geometrical sizes.
Electronic properties of superlattices on quantum rings.
da Costa, D R; Chaves, A; Ferreira, W P; Farias, G A; Ferreira, R
2017-04-26
We present a theoretical study of the one-electron states of a semiconductor-made quantum ring (QR) containing a series of piecewise-constant wells and barriers distributed along the ring circumference. The single quantum well and the superlattice cases are considered in detail. We also investigate how such confining potentials affect the Aharonov-Bohm like oscillations of the energy spectrum and current in the presence of a magnetic field. The model is simple enough so as to allow obtaining various analytical or quasi-analytical results. We show that the well-in-a-ring structure presents enhanced localization features, as well as specific geometrical resonances in its above-barrier spectrum. We stress that the superlattice-in-a-ring structure allows giving a physical meaning to the often used but usually artificial Born-von-Karman periodic conditions, and discuss in detail the formation of energy minibands and minigaps for the circumferential motion, as well as several properties of the superlattice eigenstates in the presence of the magnetic field. We obtain that the Aharonov-Bohm oscillations of below-barrier miniband states are reinforced, owing to the important tunnel coupling between neighbour wells of the superlattice, which permits the electron to move in the ring. Additionally, we analysis a superlattice-like structure made of a regular distribution of ionized impurities placed around the QR, a system that may implement the superlattice in a ring idea. Finally, we consider several random disorder models, in order to study roughness disorder and to tackle the robustness of some results against deviations from the ideally nanostructured ring system.
Katsiev, Khabiboulakh
2013-11-15
The direct observation of the complete electronic band structure of a family of PbS CQD solids via photoelectron spectroscopy is reported. We investigate how materials processing strategies, such as the latest passivation methods that produce record-performance photovoltaics, achieve their performance advances. Halide passivated films show a drastic reduction in states in the midgap, contributing to a marked improvement in the device performance. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Katsiev, Khabiboulakh; Ip, Alex; Fischer, Armin H.; Tanabe, Iori; Zhang, Xin; Kirmani, Ahmad R.; Voznyy, Oleksandr; Rollny, Lisa R.; Chou, Kang Wei; Thon, Susanna; Carey, Graham H.; Cui, Xiaoyu; Amassian, Aram; Dowben, Peter A.; Sargent, E. H.; Bakr, Osman
2013-01-01
The direct observation of the complete electronic band structure of a family of PbS CQD solids via photoelectron spectroscopy is reported. We investigate how materials processing strategies, such as the latest passivation methods that produce record-performance photovoltaics, achieve their performance advances. Halide passivated films show a drastic reduction in states in the midgap, contributing to a marked improvement in the device performance. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Quantum cluster algebra structures on quantum nilpotent algebras
Goodearl, K R
2017-01-01
All algebras in a very large, axiomatically defined class of quantum nilpotent algebras are proved to possess quantum cluster algebra structures under mild conditions. Furthermore, it is shown that these quantum cluster algebras always equal the corresponding upper quantum cluster algebras. Previous approaches to these problems for the construction of (quantum) cluster algebra structures on (quantized) coordinate rings arising in Lie theory were done on a case by case basis relying on the combinatorics of each concrete family. The results of the paper have a broad range of applications to these problems, including the construction of quantum cluster algebra structures on quantum unipotent groups and quantum double Bruhat cells (the Berenstein-Zelevinsky conjecture), and treat these problems from a unified perspective. All such applications also establish equality between the constructed quantum cluster algebras and their upper counterparts.
Energy Technology Data Exchange (ETDEWEB)
Voit, Kay-Michael
2008-06-16
In the first part we considered the quantum phase space in terms of noncommutative differential geometry. Following relevant literature, a short introduction to vector fields and differential forms on the differential vector space M{sub N}(C) was given. Special emphasis has been laid on the construction of a canonical symplectic form analogous to the one known from classical mechanics. The canonical choice of this form has been shown to be just the (scaled) commutator of two matrices. Using the Schwinger basis, the symplectic form derived in the first sections has been further examined by calculating concrete expressions for products of general matrices and their commutators which are, as we remember, just the symplectic form. Subsequently, a discrete analog to the continuous theory has been developed, in which the lattice of the quantum phase space forms the base space, and the Heisenberg group including the Schwinger elements is identified with the fiber space. In the continuum limit it could be shown that the discrete theory seamlessly passed into the commonly known continuous theory of connection forms on fiber bundles. The connection form and its exterior covariant derivation, the curvature form, have been calculated. It has been found that the curvature form can even be pulled back to the symplectic form by the section defined by the Schwinger elements. (orig.)
Electron Transport in Coupled Quantum Dots
National Research Council Canada - National Science Library
Antoniadis, D
1998-01-01
In the course of the investigation funded by this proposal we fabricated, modeled, and measured a variety of quantum dot structures in order to better understand how such nanostructures might be used for computation...
Quantum frustrated and correlated electron systems
Directory of Open Access Journals (Sweden)
P Thalmeier
2008-06-01
Full Text Available Quantum phases and fluctuations in correlated electron systems with frustration and competing interactions are reviewed. In the localized moment case the S=1/2 J1 - J2 - model on a square lattice exhibits a rich phase diagram with magnetic as well as exotic hidden order phases due to the interplay of frustration and quantum fluctuations. Their signature in magnetocaloric quantities and the high field magnetization are surveyed. The possible quantum phase transitions are discussed and applied to layered vanadium oxides. In itinerant electron systems frustration is an emergent property caused by electron correlations. It leads to enhanced spin fluctuations in a very large region of momentum space and therefore may cause heavy fermion type low temperature anomalies as in the 3d spinel compound LiV2O4 . Competing on-site and inter-site electronic interactions in Kondo compounds are responsible for the quantum phase transition between nonmagnetic Kondo singlet phase and magnetic phase such as observed in many 4f compounds. They may be described by Kondo lattice and simplified Kondo necklace type models. Their quantum phase transitions are investigated by numerical exact diagonalization and analytical bond operator methods respectively.
The Quantum World Unveiled by Electron Waves
International Nuclear Information System (INIS)
Akira Tonomura
1998-08-01
This book emphasizes the experimental aspects of the author's own laboratory. Instead of merely presenting a dry collection of knowledge, the author unfolds to the readers his vivid experiences of enthusiasm, sheer pleasure, and yet frustrations in the course of his own research. In this way, the book aims to arouse the reader's curiosity in the strange behaviors of electrons in the microscopic world, which differ significantly from our common sense and daily experiences of the macroscopic world. The fields of physics explored in the book are quantum mechanics, superconductivity, electron microscopy, holography, magnetism, and unified theory - areas of the author's study using electron waves. A world-renowned expert in electron holography, the author promises the interested reader a fascinating ride through the quantum world of electron waves, accompanied by many colorful illustrations that delight the senses and captivate the imagination
Quantum electronics for atomic physics and telecommunication
Nagourney, Warren G
2014-01-01
Nagourney provides a course in quantum electronics for researchers in atomic physics and other related areas (including telecommunications). The book covers the usual topics, such as Gaussian beams, optical cavities, lasers, non-linear optics, modulation techniques and fibre optics, but also includes a number of areas not usually found in a textbook on quantum electronics, such as the enhancement of non-linear processes in a build-up cavity or periodically poled waveguide, impedance matching into a cavity and astigmatism in ring cavities.
Analysis of quantum semiconductor heterostructures by ballistic electron emission spectroscopy
Guthrie, Daniel K.
1998-09-01
The microelectronics industry is diligently working to achieve the goal of gigascale integration (GSI) by early in the 21st century. For the past twenty-five years, progress toward this goal has been made by continually scaling down device technology. Unfortunately, this trend cannot continue to the point of producing arbitrarily small device sizes. One possible solution to this problem that is currently under intensive study is the relatively new area of quantum devices. Quantum devices represent a new class of microelectronic devices that operate by utilizing the wave-like nature (reflection, refraction, and confinement) of electrons together with the laws of quantum mechanics to construct useful devices. One difficulty associated with these structures is the absence of measurement techniques that can fully characterize carrier transport in such devices. This thesis addresses this need by focusing on the study of carrier transport in quantum semiconductor heterostructures using a relatively new and versatile measurement technique known as ballistic electron emission spectroscopy (BEES). To achieve this goal, a systematic approach that encompasses a set of progressively more complex structures is utilized. First, the simplest BEES structure possible, the metal/semiconductor interface, is thoroughly investigated in order to provide a foundation for measurements on more the complex structures. By modifying the semiclassical model commonly used to describe the experimental BEES spectrum, a very complete and accurate description of the basic structure has been achieved. Next, a very simple semiconductor heterostructure, a Ga1-xAlxAs single-barrier structure, was measured and analyzed. Low-temperature measurements on this structure were used to investigate the band structure and electron-wave interference effects in the Ga1-xAlxAs single barrier structure. These measurements are extended to a simple quantum device by designing, measuring, and analyzing a set of
Si quantum dot structures and their applications
Shcherbyna, L.; Torchynska, T.
2013-06-01
This paper presents briefly the history of emission study in Si quantum dots (QDs) in the last two decades. Stable light emission of Si QDs and NCs was observed in the spectral ranges: blue, green, orange, red and infrared. These PL bands were attributed to the exciton recombination in Si QDs, to the carrier recombination through defects inside of Si NCs or via oxide related defects at the Si/SiOx interface. The analysis of recombination transitions and the different ways of the emission stimulation in Si QD structures, related to the element variation for the passivation of surface dangling bonds, as well as the plasmon induced emission and rare earth impurity activation, have been presented. The different applications of Si QD structures in quantum electronics, such as: Si QD light emitting diodes, Si QD single union and tandem solar cells, Si QD memory structures, Si QD based one electron devices and double QD structures for spintronics, have been discussed as well. Note the significant worldwide interest directed toward the silicon-based light emission for integrated optoelectronics is related to the complementary metal-oxide semiconductor compatibility and the possibility to be monolithically integrated with very large scale integrated (VLSI) circuits. The different features of poly-, micro- and nanocrystalline silicon for solar cells, that is a mixture of both amorphous and crystalline phases, such as the silicon NCs or QDs embedded in a α-Si:H matrix, as well as the thin film 2-cell or 3-cell tandem solar cells based on Si QD structures have been discussed as well. Silicon NC based structures for non-volatile memory purposes, the recent studies of Si QD base single electron devices and the single electron occupation of QDs as an important component to the measurement and manipulation of spins in quantum information processing have been analyzed as well.
International Nuclear Information System (INIS)
Yu-Min, Liu; Zhong-Yuan, Yu; Xiao-Min, Ren
2009-01-01
Calculations of electronic structures about the semiconductor quantum dot and the semiconductor quantum ring are presented in this paper. To reduce the calculation costs, for the quantum dot and the quantum ring, their simplified axially symmetric shapes are utilized in our analysis. The energy dependent effective mass is taken into account in solving the Schrödinger equations in the single band effective mass approximation. The calculated results show that the energy dependent effective mass should be considered only for relatively small volume quantum dots or small quantum rings. For large size quantum materials, both the energy dependent effective mass and the parabolic effective mass can give the same results. The energy states and the effective masses of the quantum dot and the quantum ring as a function of geometric parameters are also discussed in detail. (general)
Quantum lifetime in electron storage rings
International Nuclear Information System (INIS)
Chao, A.W.
1977-02-01
One of the mechanisms which contribute to beam lifetime in electron storage rings is the quantum emission of energetic photons causing particles to be lost from the rf bucket. This quantum lifetime is among other things important in defining the required aperture in a storage ring. An approximate expression of quantum lifetime, predicted by a one-dimensional model which takes into account only the betatron motion, has been used in most storage ring designs. If the beam is aperture-limited at a position with nonzero dispersion, both the betatron and synchrotron motions have to be included and a two-dimensional model must be used. An exact expression of quantum lifetime for the one-dimensional case and an approximate expression for the two-dimensional case are given
Quantum lifetime in electron storage rings
International Nuclear Information System (INIS)
Chao, A.W.
1977-01-01
One of the mechanisms which contributes to beam lifetime in electron storage rings is the quantum emission of energetic photons causing particles to be lost from the rf bucket. This quantum lifetime is among other things important in defining the required aperture in a storage ring. An approximate expression of quantum lifetime, predicted by a one-dimensional model which takes into account only the betatron motion, has been used in most storage ring designs. If the beam is aperture-limited at a position with nonzero dispersion, both the betatron and synchrotron motions have to be included, and a two-dimensional model must be used. An exact expression of quantum lifetime for the one-dimensional case and an approximate expression for the two-dimensional case are given
International Nuclear Information System (INIS)
Giricheva, N.I.; Shlykov, S.A.; Girichev, G.V.; Galanin, I.E.
2006-01-01
The saturated vapor over LaI 3 has been studied using the electron diffraction method with mass-spectral monitoring. It was determined that at a temperature 1142(10) K, along with monomer molecules, dimers are present in the vapor in the quantity of 0.7 mol.%. Effective configuration parameters of LaI 3 molecule were obtained: r g (La-I)=2.961(6) A, g (I-La-I)=116.5(9) deg, l(La-I)=0.106(1) A and l(I...I)=0.412(7) A. A small deviation of the valence angle g (I-La-I) from 120 deg can be totally caused by a contraction effect of the distance r g (I...I) of LaI 3 molecule with planar equilibrium configuration. The electronic structure of LaI 3 molecule was examined by the B3LYP/SDD method. In terms of the NBO-analysis, the participation of lanthanum 4f-AO in bonding orbitals La-I is noted. It is shown that the NBO-analysis describes the bond La-I in LaI 3 molecule as predominantly ionic one with a noticeable covalence component. The energy of the heterolytic bond breakage E(La-I) het =1216 kJ/mole was calculated [ru
Energy Technology Data Exchange (ETDEWEB)
Chan, Garnet Kin-Lic [Princeton Univ., NJ (United States)
2017-04-30
This is the final technical report. We briefly describe some selected results below. Developments in density matrix embedding. DMET is a quantum embedding theory that we introduced at the beginning of the last funding period, around 2012-2013. Since the first DMET papers, which demonstrated proof-of- principle calculations on the Hubbard model and hydrogen rings, we have carried out a number of different developments, including: Extending the DMET technology to compute broken symmetry phases, including magnetic phases and super- conductivity (Pub. 13); Calibrating the accuracy of DMET and its cluster size convergence against other methods, and formulation of a dynamical cluster analog (Pubs. 4, 10) (see Fig. 1); Implementing DMET for ab-initio molecular calculations, and exploring different self-consistency criteria (Pubs. 9, 14); Using embedding to defi ne quantum classical interfaces Pub. 2; Formulating DMET for spectral functions (Pub. 7) (see Fig. 1); Extending DMET to coupled fermion-boson problems (Pub. 12). Together with these embedding developments, we have also implemented a wide variety of impurity solvers within our DMET framework, including DMRG (Pub. 3), AFQMC (Pub. 10), and coupled cluster theory (CC) (Pub. 9).
Dynamics of Quantum Causal Structures
Castro-Ruiz, Esteban; Giacomini, Flaminia; Brukner, Časlav
2018-01-01
It was recently suggested that causal structures are both dynamical, because of general relativity, and indefinite, because of quantum theory. The process matrix formalism furnishes a framework for quantum mechanics on indefinite causal structures, where the order between operations of local laboratories is not definite (e.g., one cannot say whether operation in laboratory A occurs before or after operation in laboratory B ). Here, we develop a framework for "dynamics of causal structures," i.e., for transformations of process matrices into process matrices. We show that, under continuous and reversible transformations, the causal order between operations is always preserved. However, the causal order between a subset of operations can be changed under continuous yet nonreversible transformations. An explicit example is that of the quantum switch, where a party in the past affects the causal order of operations of future parties, leading to a transition from a channel from A to B , via superposition of causal orders, to a channel from B to A . We generalize our framework to construct a hierarchy of quantum maps based on transformations of process matrices and transformations thereof.
Dynamics of Quantum Causal Structures
Directory of Open Access Journals (Sweden)
Esteban Castro-Ruiz
2018-03-01
Full Text Available It was recently suggested that causal structures are both dynamical, because of general relativity, and indefinite, because of quantum theory. The process matrix formalism furnishes a framework for quantum mechanics on indefinite causal structures, where the order between operations of local laboratories is not definite (e.g., one cannot say whether operation in laboratory A occurs before or after operation in laboratory B. Here, we develop a framework for “dynamics of causal structures,” i.e., for transformations of process matrices into process matrices. We show that, under continuous and reversible transformations, the causal order between operations is always preserved. However, the causal order between a subset of operations can be changed under continuous yet nonreversible transformations. An explicit example is that of the quantum switch, where a party in the past affects the causal order of operations of future parties, leading to a transition from a channel from A to B, via superposition of causal orders, to a channel from B to A. We generalize our framework to construct a hierarchy of quantum maps based on transformations of process matrices and transformations thereof.
Orientation-dependent imaging of electronically excited quantum dots
Nguyen, Duc; Goings, Joshua J.; Nguyen, Huy A.; Lyding, Joseph; Li, Xiaosong; Gruebele, Martin
2018-02-01
We previously demonstrated that we can image electronic excitations of quantum dots by single-molecule absorption scanning tunneling microscopy (SMA-STM). With this technique, a modulated laser beam periodically saturates an electronic transition of a single nanoparticle, and the resulting tunneling current modulation ΔI(x0, y0) maps out the SMA-STM image. In this paper, we first derive the basic theory to calculate ΔI(x0, y0) in the one-electron approximation. For near-resonant tunneling through an empty orbital "i" of the nanostructure, the SMA-STM signal is approximately proportional to the electron density |φi) (x0,y0)|nudge quantum dots on the surface and roll them, thus imaging excited state electronic structure of a single quantum dot at different orientations. We use density functional theory to model ODMs at various orientations, for qualitative comparison with the SMA-STM experiment. The model demonstrates that our experimentally observed signal monitors excited states, localized by defects near the surface of an individual quantum dot. The sub-nanometer super-resolution imaging technique demonstrated here could become useful for mapping out the three-dimensional structure of excited states localized by defects within nanomaterials.
Correlated electron phenomena in ultra-low disorder quantum wires
International Nuclear Information System (INIS)
Reilly, D.J.; Facer, G.R.; Dzurak, A.S.; Kane, B.E.; Clark, R.G.; Lumpkin, N.E.
1999-01-01
Full text: Quantum point contacts in the lowest disorder HEMTs display structure at 0.7 x 2e 2 /h, which cannot be interpreted within a single particle Landauer model. This structure has been attributed to a spontaneous spin polarisation at zero B field. We have developed novel GaAs/AlGaAs enhancement mode FETs, which avoid the random impurity potential present in conventional MODFET devices by using epitaxially grown gates to produce ultra-low-disorder QPCs and quantum wires using electron beam lithography. The ballistic mean free path within these devices exceeds 160 μm 2 . Quantum wires of 5 μm in length show up to 15 conductance plateaux, indicating that these may be the lowest-disorder quantum wires fabricated using conventional surface patterning techniques. These structures are ideal for the study of correlation effects in QPCs and quantum wires as a function of electron density. Our data provides strong evidence that correlation effects are enhanced as the length of the 1D region is increased and also that additional structure moves close to 0.5 x 2e 2 /h, the value expected for an ideal spin-split 1D level
Electron Raman scattering in a cylindrical quantum dot
International Nuclear Information System (INIS)
Zhong Qinghu; Yi Xuehua
2012-01-01
Electron Raman scattering (ERS) is investigated in a CdS cylindrical quantum dot (QD). The differential cross section is calculated as a function of the scattering frequency and the size of the QD. Single parabolic conduction and valence bands are assumed, and singularities in the spectrum are found and interpreted. The selection rules for the processes are also studied. The ERS studied here can be used to provide direct information about the electron band structure of these systems. (semiconductor physics)
Exact wave functions of two-electron quantum rings.
Loos, Pierre-François; Gill, Peter M W
2012-02-24
We demonstrate that the Schrödinger equation for two electrons on a ring, which is the usual paradigm to model quantum rings, is solvable in closed form for particular values of the radius. We show that both polynomial and irrational solutions can be found for any value of the angular momentum and that the singlet and triplet manifolds, which are degenerate, have distinct geometric phases. We also study the nodal structure associated with these two-electron states.
Turi, László
2016-04-01
We evaluate the applicability of a hierarchy of quantum models in characterizing the binding energy of excess electrons to water clusters. In particular, we calculate the vertical detachment energy of an excess electron from water cluster anions with methods that include one-electron pseudopotential calculations, density functional theory (DFT) based calculations, and ab initio quantum chemistry using MP2 and eom-EA-CCSD levels of theory. The examined clusters range from the smallest cluster size (n = 2) up to nearly nanosize clusters with n = 1000 molecules. The examined cluster configurations are extracted from mixed quantum-classical molecular dynamics trajectories of cluster anions with n = 1000 water molecules using two different one-electron pseudopotenial models. We find that while MP2 calculations with large diffuse basis set provide a reasonable description for the hydrated electron system, DFT methods should be used with precaution and only after careful benchmarking. Strictly tested one-electron psudopotentials can still be considered as reasonable alternatives to DFT methods, especially in large systems. The results of quantum chemistry calculations performed on configurations, that represent possible excess electron binding motifs in the clusters, appear to be consistent with the results using a cavity structure preferring one-electron pseudopotential for the hydrated electron, while they are in sharp disagreement with the structural predictions of a non-cavity model.
Energy Technology Data Exchange (ETDEWEB)
Turi, László, E-mail: turi@chem.elte.hu [Department of Physical Chemistry, Eötvös Loránd University, P.O. Box 32, H-1518 Budapest 112 (Hungary)
2016-04-21
We evaluate the applicability of a hierarchy of quantum models in characterizing the binding energy of excess electrons to water clusters. In particular, we calculate the vertical detachment energy of an excess electron from water cluster anions with methods that include one-electron pseudopotential calculations, density functional theory (DFT) based calculations, and ab initio quantum chemistry using MP2 and eom-EA-CCSD levels of theory. The examined clusters range from the smallest cluster size (n = 2) up to nearly nanosize clusters with n = 1000 molecules. The examined cluster configurations are extracted from mixed quantum-classical molecular dynamics trajectories of cluster anions with n = 1000 water molecules using two different one-electron pseudopotenial models. We find that while MP2 calculations with large diffuse basis set provide a reasonable description for the hydrated electron system, DFT methods should be used with precaution and only after careful benchmarking. Strictly tested one-electron psudopotentials can still be considered as reasonable alternatives to DFT methods, especially in large systems. The results of quantum chemistry calculations performed on configurations, that represent possible excess electron binding motifs in the clusters, appear to be consistent with the results using a cavity structure preferring one-electron pseudopotential for the hydrated electron, while they are in sharp disagreement with the structural predictions of a non-cavity model.
Azadegan, B.
2013-03-01
The presented Mathematica code is an efficient tool for simulation of planar channeling radiation spectra of relativistic electrons channeled along major crystallographic planes of a diamond-structure single crystal. The program is based on the quantum theory of channeling radiation which has been successfully applied to study planar channeling at electron energies between 10 and 100 MeV. Continuum potentials for different planes of diamond, silicon and germanium single crystals are calculated using the Doyle-Turner approximation to the atomic scattering factor and taking thermal vibrations of the crystal atoms into account. Numerical methods are applied to solve the one-dimensional Schrödinger equation. The code is designed to calculate the electron wave functions, transverse electron states in the planar continuum potential, transition energies, line widths of channeling radiation and depth dependencies of the population of quantum states. Finally the spectral distribution of spontaneously emitted channeling radiation is obtained. The simulation of radiation spectra considerably facilitates the interpretation of experimental data. Catalog identifier: AEOH_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOH_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 446 No. of bytes in distributed program, including test data, etc.: 209805 Distribution format: tar.gz Programming language: Mathematica. Computer: Platforms on which Mathematica is available. Operating system: Operating systems on which Mathematica is available. RAM: 1 MB Classification: 7.10. Nature of problem: Planar channeling radiation is emitted by relativistic charged particles during traversing a single crystal in direction parallel to a crystallographic plane. Channeling is modeled as the motion
Quantum Computing with an Electron Spin Ensemble
DEFF Research Database (Denmark)
Wesenberg, Janus; Ardavan, A.; Briggs, G.A.D.
2009-01-01
We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized...
Priebe, Katharina E.; Rathje, Christopher; Yalunin, Sergey V.; Hohage, Thorsten; Feist, Armin; Schäfer, Sascha; Ropers, Claus
2017-12-01
Ultrafast electron and X-ray imaging and spectroscopy are the basis for an ongoing revolution in the understanding of dynamical atomic-scale processes in matter. The underlying technology relies heavily on laser science for the generation and characterization of ever shorter pulses. Recent findings suggest that ultrafast electron microscopy with attosecond-structured wavefunctions may be feasible. However, such future technologies call for means to both prepare and fully analyse the corresponding free-electron quantum states. Here, we introduce a framework for the preparation, coherent manipulation and characterization of free-electron quantum states, experimentally demonstrating attosecond electron pulse trains. Phase-locked optical fields coherently control the electron wavefunction along the beam direction. We establish a new variant of quantum state tomography—`SQUIRRELS'—for free-electron ensembles. The ability to tailor and quantitatively map electron quantum states will promote the nanoscale study of electron-matter entanglement and new forms of ultrafast electron microscopy down to the attosecond regime.
Quantum coherent optical phase modulation in an ultrafast transmission electron microscope.
Feist, Armin; Echternkamp, Katharina E; Schauss, Jakob; Yalunin, Sergey V; Schäfer, Sascha; Ropers, Claus
2015-05-14
Coherent manipulation of quantum systems with light is expected to be a cornerstone of future information and communication technology, including quantum computation and cryptography. The transfer of an optical phase onto a quantum wavefunction is a defining aspect of coherent interactions and forms the basis of quantum state preparation, synchronization and metrology. Light-phase-modulated electron states near atoms and molecules are essential for the techniques of attosecond science, including the generation of extreme-ultraviolet pulses and orbital tomography. In contrast, the quantum-coherent phase-modulation of energetic free-electron beams has not been demonstrated, although it promises direct access to ultrafast imaging and spectroscopy with tailored electron pulses on the attosecond scale. Here we demonstrate the coherent quantum state manipulation of free-electron populations in an electron microscope beam. We employ the interaction of ultrashort electron pulses with optical near-fields to induce Rabi oscillations in the populations of electron momentum states, observed as a function of the optical driving field. Excellent agreement with the scaling of an equal-Rabi multilevel quantum ladder is obtained, representing the observation of a light-driven 'quantum walk' coherently reshaping electron density in momentum space. We note that, after the interaction, the optically generated superposition of momentum states evolves into a train of attosecond electron pulses. Our results reveal the potential of quantum control for the precision structuring of electron densities, with possible applications ranging from ultrafast electron spectroscopy and microscopy to accelerator science and free-electron lasers.
Electronic states in a quantum lens
International Nuclear Information System (INIS)
Rodriguez, Arezky H.; Trallero-Giner, C.; Ulloa, S. E.; Marin-Antuna, J.
2001-01-01
We present a model to find analytically the electronic states in self-assembled quantum dots with a truncated spherical cap (''lens'') geometry. A conformal analytical image is designed to map the quantum dot boundary into a dot with semispherical shape. The Hamiltonian for a carrier confined in the quantum lens is correspondingly mapped into an equivalent operator and its eigenvalues and eigenfunctions for the corresponding Dirichlet problem are analyzed. A modified Rayleigh-Schro''dinger perturbation theory is presented to obtain analytical expressions for the energy levels and wave functions as a function of the spherical cap height b and radius a of the circular cross section. Calculations for a hard wall confinement potential are presented, and the effect of decreasing symmetry on the energy values and eigenfunctions of the lens-shape quantum dot is studied. As the degeneracies of a semicircular geometry are broken for b≠a, our perturbation approach allows tracking of the split states. Energy states and electronic wave functions with m=0 present the most pronounced influence on the reduction of the lens height. The method and expressions presented here can be straightforwardly extended to deal with more general Hamiltonians, including strains and valence-band coupling effects in Group III--V and Group II--VI self-assembled quantum dots
Electron quantum optics in ballistic chiral conductors
Energy Technology Data Exchange (ETDEWEB)
Bocquillon, Erwann; Freulon, Vincent; Parmentier, Francois D.; Berroir, Jean-Marc; Placais, Bernard; Feve, Gwendal [Laboratoire Pierre Aigrain, Ecole Normale Superieure, CNRS (UMR 8551), Universite Pierre et Marie Curie, Universite Paris Diderot, Paris (France); Wahl, Claire; Rech, Jerome; Jonckheere, Thibaut; Martin, Thierry [Aix Marseille Universite, CNRS, CPT, UMR 7332, Marseille (France); Universite de Toulon, CNRS, CPT, UMR 7332, La Garde (France); Grenier, Charles; Ferraro, Dario; Degiovanni, Pascal [Universite de Lyon, Federation de Physique Andre Marie Ampere, CNRS - Laboratoire de Physique de l' Ecole Normale Superieure de Lyon, Lyon (France)
2014-01-15
The edge channels of the quantum Hall effect provide one dimensional chiral and ballistic wires along which electrons can be guided in an optics-like setup. Electronic propagation can then be analyzed using concepts and tools derived from optics. After a brief review of electron optics experiments performed using stationary current sources which continuously emit electrons in the conductor, this paper focuses on triggered sources, which can generate on-demand a single particle state. It first outlines the electron optics formalism and its analogies and differences with photon optics and then turns to the presentation of single electron emitters and their characterization through the measurements of the average electrical current and its correlations. This is followed by a discussion of electron quantum optics experiments in the Hanbury-Brown and Twiss geometry where two-particle interferences occur. Finally, Coulomb interactions effects and their influence on single electron states are considered. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Electron quantum optics in ballistic chiral conductors
International Nuclear Information System (INIS)
Bocquillon, Erwann; Freulon, Vincent; Parmentier, Francois D.; Berroir, Jean-Marc; Placais, Bernard; Feve, Gwendal; Wahl, Claire; Rech, Jerome; Jonckheere, Thibaut; Martin, Thierry; Grenier, Charles; Ferraro, Dario; Degiovanni, Pascal
2014-01-01
The edge channels of the quantum Hall effect provide one dimensional chiral and ballistic wires along which electrons can be guided in an optics-like setup. Electronic propagation can then be analyzed using concepts and tools derived from optics. After a brief review of electron optics experiments performed using stationary current sources which continuously emit electrons in the conductor, this paper focuses on triggered sources, which can generate on-demand a single particle state. It first outlines the electron optics formalism and its analogies and differences with photon optics and then turns to the presentation of single electron emitters and their characterization through the measurements of the average electrical current and its correlations. This is followed by a discussion of electron quantum optics experiments in the Hanbury-Brown and Twiss geometry where two-particle interferences occur. Finally, Coulomb interactions effects and their influence on single electron states are considered. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Quantum algebras in nuclear structure
International Nuclear Information System (INIS)
Bonatsos, D.; Daskaloyannis, C.
1995-01-01
Quantum algebras is a mathematical tool which provides us with a class of symmetries wider than that of Lie algebras, which are contained in the former as a special case. After a self-contained introduction through the necessary mathematical tools (q-numbers, q-analysis, q-oscillators, q-algebras), the su q (2) rotator model and its extensions, the construction of deformed exactly soluble models (Interacting Boson Model, Moszkowski model), the use of deformed bosons in the description of pairing correlations, and the symmetries of the anisotropic quantum harmonic oscillator with rational ratios of frequencies, which underline the structure of superdeformed and hyperdeformed nuclei are discussed in some details. A brief description of similar applications to molecular structure and an outlook are also given. (author) 2 Tabs., 324 Refs
A quantum field theory of the extended electron
International Nuclear Information System (INIS)
Salesi, Giovanni; Recami, Erasmo; Universidade Estadual de Campinas, SP
1993-12-01
In a recent paper, the classical model of Barut and Zanghi (BZ) for the electron spin which interpreted the Zitterbewegung (zbw) motion along helical paths and its quantum version have been investigated by using the language of Clifford algebras. In also doing, a new non-linear Dirac-like equation (NDE) was derived. We want to readdress the whole subject, and complete it, by adopting - for the sake of physical clarity - the ordinary tensorial language. In particular, we re-derive here the NDE for the electron quantum field, show it to be associated with a new conserved probability current, and stress its importance for a quantum field theory of spin 1/2 fermions. Actually, we propose this equation in substitution for the Dirac equation, which comes from the former by averaging over a zbw cycle. We then derive a new equation of motion for the quantum field velocity, which will allow us to regard the electron as an extended object, with a classically intelligible internal structure (thus overcoming some known, long-standing problems). We carefully the solutions of the NDE; with special attention to those implying (at the classical limit) light-like helical motions, since these appear to be the most adequate equations for the electron description, from the kinematical and physical points of view, and do cope with the electron electromagnetic properties (such as Coulomb field and intrinsic magnetic moment). (author). 18 refs
A quantum field theory of the extended electron
Energy Technology Data Exchange (ETDEWEB)
Salesi, Giovanni [Universita Statale di Catania (Italy). Dipt. di Fisica; Recami, Erasmo [Universita Statale di Bergamo, Dalmine, BG (Italy). Facolta di Ingegneria; [Universidade Estadual de Campinas, SP (Brazil). Dept. de Matematica Aplicada
1993-12-01
In a recent paper, the classical model of Barut and Zanghi (BZ) for the electron spin which interpreted the Zitterbewegung (zbw) motion along helical paths and its quantum version have been investigated by using the language of Clifford algebras. In also doing, a new non-linear Dirac-like equation (NDE) was derived. We want to readdress the whole subject, and complete it, by adopting - for the sake of physical clarity - the ordinary tensorial language. In particular, we re-derive here the NDE for the electron quantum field, show it to be associated with a new conserved probability current, and stress its importance for a quantum field theory of spin 1/2 fermions. Actually, we propose this equation in substitution for the Dirac equation, which comes from the former by averaging over a zbw cycle. We then derive a new equation of motion for the quantum field velocity, which will allow us to regard the electron as an extended object, with a classically intelligible internal structure (thus overcoming some known, long-standing problems). We carefully the solutions of the NDE; with special attention to those implying (at the classical limit) light-like helical motions, since these appear to be the most adequate equations for the electron description, from the kinematical and physical points of view, and do cope with the electron electromagnetic properties (such as Coulomb field and intrinsic magnetic moment). (author). 18 refs.
Wang, Hai; Barceló, Irene; Lana-Villarreal, Teresa; Gómez, Roberto; Bonn, Mischa; Cánovas, Enrique
2014-10-08
We quantify the rate and efficiency of picosecond electron transfer (ET) from PbS nanocrystals, grown by successive ionic layer adsorption and reaction (SILAR), into a mesoporous SnO2 support. Successive SILAR deposition steps allow for stoichiometry- and size-variation of the QDs, characterized using transmission electron microscopy. Whereas for sulfur-rich (p-type) QD surfaces substantial electron trapping at the QD surface occurs, for lead-rich (n-type) QD surfaces, the QD trapping channel is suppressed and the ET efficiency is boosted. The ET efficiency increase achieved by lead-rich QD surfaces is found to be QD-size dependent, increasing linearly with QD surface area. On the other hand, ET rates are found to be independent of both QD size and surface stoichiometry, suggesting that the donor-acceptor energetics (constituting the driving force for ET) are fixed due to Fermi level pinning at the QD/oxide interface. Implications of our results for QD-sensitized solar cell design are discussed.
Optical properties of the semiconductor quantum structure
International Nuclear Information System (INIS)
Haratizadeh, H.; Holtz, P.O.; Monemar, B.; Karlsoon, K.F.; Moskalenko, E.S.; Amano, H.; Akasaki, I.; Schoenfeld, W.V.; Garcia, J.M.; Petroff, P.M.
2004-01-01
Optical properties of the quantum structures have been discussed with emphasize of the AlGaN/GaN multiple quantum wells and InAs/GaAs quantum dot structures. We report on a detailed study of low temperature photoluminescence in Al 0 .07Ga 0 .93 N/GaN multiple quantum wells. The structures were nominally undoped multiple quantum well grown on sapphire substrate. The structure from discrete well width variations is here resolved in photoluminescence spectra. The results demonstrate that the theoretically estimated fields in this work are consistent with the experimental spectra
Electronic structure of spin systems
Energy Technology Data Exchange (ETDEWEB)
Saha-Dasgupta, Tanusri
2016-04-15
Highlights: • We review the theoretical modeling of quantum spin systems. • We apply the Nth order muffin-tin orbital electronic structure method. • The method shows the importance of chemistry in the modeling. • CuTe{sub 2}O{sub 5} showed a 2-dimensional coupled spin dimer behavior. • Ti substituted Zn{sub 2}VO(PO{sub 4}){sub 2} showed spin gap behavior. - Abstract: Low-dimensional quantum spin systems, characterized by their unconventional magnetic properties, have attracted much attention. Synthesis of materials appropriate to various classes within these systems has made this field very attractive and a site of many activities. The experimental results like susceptibility data are fitted with the theoretical model to derive the underlying spin Hamiltonian. However, often such a fitting procedure which requires correct guess of the assumed spin Hamiltonian leads to ambiguity in deciding the representative model. In this review article, we will describe how electronic structure calculation within the framework of Nth order muffin-tin orbital (NMTO) based Wannier function technique can be utilized to identify the underlying spin model for a large number of such compounds. We will show examples from compounds belonging to vanadates and cuprates.
Graph-based linear scaling electronic structure theory
Energy Technology Data Exchange (ETDEWEB)
Niklasson, Anders M. N., E-mail: amn@lanl.gov; Negre, Christian F. A.; Cawkwell, Marc J.; Swart, Pieter J.; Germann, Timothy C.; Bock, Nicolas [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Mniszewski, Susan M.; Mohd-Yusof, Jamal; Wall, Michael E.; Djidjev, Hristo [Computer, Computational, and Statistical Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Rubensson, Emanuel H. [Division of Scientific Computing, Department of Information Technology, Uppsala University, Box 337, SE-751 05 Uppsala (Sweden)
2016-06-21
We show how graph theory can be combined with quantum theory to calculate the electronic structure of large complex systems. The graph formalism is general and applicable to a broad range of electronic structure methods and materials, including challenging systems such as biomolecules. The methodology combines well-controlled accuracy, low computational cost, and natural low-communication parallelism. This combination addresses substantial shortcomings of linear scaling electronic structure theory, in particular with respect to quantum-based molecular dynamics simulations.
Electron transport in quantum wires: possible current instability mechanism
International Nuclear Information System (INIS)
Sablikov, V.A.
2001-01-01
The electrons nonlinear and dynamic transition in quantum wires connecting the electron reservoirs, are studies with an account of the Coulomb interaction distribution of electron density between the reservoirs and the wire. It is established that there exist two processes, leading to electrical instability in such structure. One of them is expressed in form of multistability of the charge accumulated in the wire, and negative differential conductivity. The other one is connected with origination of negative dynamic conductivity in the narrow frequency range near the resonance frequency of the charge waves on the wire length [ru
Energy Technology Data Exchange (ETDEWEB)
Lingerfelt, David B.; Lestrange, Patrick J.; Radler, Joseph J.; Brown-Xu, Samantha E.; Kim, Pyosang; Castellano, Felix N.; Chen, Lin X.; Li, Xiaosong
2017-02-24
Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a binuclear platinum complex, where a persistent periodic beating in the transient absorption signal’s anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of binuclear platinum complexes exhibiting a range of interplatinum distances. Results suggest that the long-lived coherence can only result when competitive electronic couplings are in balance. At longer Pt-Pt distances, the electronic couplings between the two halves of the binuclear system weaken, and exciton localization and recombination is favored on short time scales. For short Pt-Pt distances, electronic couplings between the states in the coherent superposition are stronger than the coupling with other excitonic states, leading to long-lived coherence.
Many electron effects in semiconductor quantum dots
Indian Academy of Sciences (India)
Semiconductor quantum dots (QDs) exhibit shell structures, very similar to atoms. Termed as 'artificial atoms' by some, they are much larger (1 100 nm) than real atoms. One can study a variety of manyelectron effects in them, which are otherwise difficult to observe in a real atom. We have treated these effects within the ...
Exact diagonalization library for quantum electron models
Iskakov, Sergei; Danilov, Michael
2018-04-01
We present an exact diagonalization C++ template library (EDLib) for solving quantum electron models, including the single-band finite Hubbard cluster and the multi-orbital impurity Anderson model. The observables that can be computed using EDLib are single particle Green's functions and spin-spin correlation functions. This code provides three different types of Hamiltonian matrix storage that can be chosen based on the model.
Ubiquitous Quantum Structure From Psychology to Finance
Khrennikov, Andrei Y
2010-01-01
Quantum-like structure is present practically everywhere. Quantum-like (QL) models, i.e. models based on the mathematical formalism of quantum mechanics and its generalizations can be successfully applied to cognitive science, psychology, genetics, economics, finances, and game theory. This book is not about quantum mechanics as a physical theory. The short review of quantum postulates is therefore mainly of historical value: quantum mechanics is just the first example of the successful application of non-Kolmogorov probabilities, the first step towards a contextual probabilistic description of natural, biological, psychological, social, economical or financial phenomena. A general contextual probabilistic model (Växjö model) is presented. It can be used for describing probabilities in both quantum and classical (statistical) mechanics as well as in the above mentioned phenomena. This model can be represented in a quantum-like way, namely, in complex and more general Hilbert spaces. In this way quantum prob...
Helical quantum states in HgTe quantum dots with inverted band structures.
Chang, Kai; Lou, Wen-Kai
2011-05-20
We investigate theoretically the electron states in HgTe quantum dots (QDs) with inverted band structures. In sharp contrast to conventional semiconductor quantum dots, the quantum states in the gap of the HgTe QD are fully spin-polarized and show ringlike density distributions near the boundary of the QD and spin-angular momentum locking. The persistent charge currents and magnetic moments, i.e., the Aharonov-Bohm effect, can be observed in such a QD structure. This feature offers us a practical way to detect these exotic ringlike edge states by using the SQUID technique.
International Nuclear Information System (INIS)
Badi, F.; Louhibi, S.; Aced, M.R.; Mehnane, N.; Sekkal, N.
2008-05-01
This paper reports first principle investigations of structural and electronic properties of both bulk and superlattice (SL) systems of cuprous halides. The obtained structural data for bulks compares well with literature while data for SL is not compared because unavailable (to our knowledge). The electronic structure of bulks and also of (001) and (110) growth axis superlattices (SLs) are calculated and it is shown that at the reverse of the IV-IV and III-V systems, the (110) growth axis impacts the electronic structure which indicates a great influence of the d-orbital. (author)
Energy Technology Data Exchange (ETDEWEB)
Sauerwald, Andres
2008-05-27
Aim of this thesis was to apply the analytical methods of the scanning transmission electron microscopy to the study of self-organized In(Ga)As quantum structures. With the imaging methods Z contrast and bright field (position resolutions in the subnanometer range) and especially with the possibilities of the quantitative chemical EELS analysis of the scanning transmission electron microscope (STEM) fundamental questions concerning morphology and chemical properties of self-organized quantum structures should be answered. By the high position resolution of the STEM among others essentail morphological and structural parameters in the growth behaviour of 'dot in a well' (DWell) structures and of vertically correlated quantum dots (QDs) could be analyzed. For the optimization of DWell structures samples were studied, the nominal InAs-QD growth position was directedly varied within the embedding InGaAs quantum wells. The STEM offers in connection with the EELS method a large potential for the chemical analysis of quantum structures. Studied was a sample series of self-organized InGaAs/GaAs structures on GaAs substrate, the stress of which was changed by varying the Ga content of the INGaAs material between 2.4 % and 4.3 %. [German] Ziel dieser Arbeit war es, die analytischen Methoden der Raster-Transmissionselektronenmikroskopie zur Untersuchung selbstorganisierter In(Ga)As-Quantenstrukturen anzuwenden. Mit den abbildenden Methoden Z-Kontrast und Hellfeld (Ortsaufloesungen im Subnanometerbereich) und insbesondere mit den Moeglichkeiten der quantitativen chemischen EELS-Analyse des Raster-Transmissionselektronenmikroskops (RTEMs) sollten grundsaetzliche Fragestellungen hinsichtlich der Morphologie und der chemischen Eigenschaften selbstorganisierter Quantenstrukturen beantwortet werden. Durch die hohe Ortsaufloesung des RTEMs konnten u.a. essentielle morphologische und strukturelle Parameter im Wachstumsverhalten von 'Dot in a Well
Fundamental Structure of Loop Quantum Gravity
Han, Muxin; Ma, Yongge; Huang, Weiming
In the recent twenty years, loop quantum gravity, a background independent approach to unify general relativity and quantum mechanics, has been widely investigated. The aim of loop quantum gravity is to construct a mathematically rigorous, background independent, non-perturbative quantum theory for a Lorentzian gravitational field on a four-dimensional manifold. In the approach, the principles of quantum mechanics are combined with those of general relativity naturally. Such a combination provides us a picture of, so-called, quantum Riemannian geometry, which is discrete on the fundamental scale. Imposing the quantum constraints in analogy from the classical ones, the quantum dynamics of gravity is being studied as one of the most important issues in loop quantum gravity. On the other hand, the semi-classical analysis is being carried out to test the classical limit of the quantum theory. In this review, the fundamental structure of loop quantum gravity is presented pedagogically. Our main aim is to help non-experts to understand the motivations, basic structures, as well as general results. It may also be beneficial to practitioners to gain insights from different perspectives on the theory. We will focus on the theoretical framework itself, rather than its applications, and do our best to write it in modern and precise langauge while keeping the presentation accessible for beginners. After reviewing the classical connection dynamical formalism of general relativity, as a foundation, the construction of the kinematical Ashtekar-Isham-Lewandowski representation is introduced in the content of quantum kinematics. The algebraic structure of quantum kinematics is also discussed. In the content of quantum dynamics, we mainly introduce the construction of a Hamiltonian constraint operator and the master constraint project. At last, some applications and recent advances are outlined. It should be noted that this strategy of quantizing gravity can also be extended to
Bend-imitating theory and electron scattering in sharply-bent quantum nanowires
International Nuclear Information System (INIS)
Vakhnenko, O.O.
2011-01-01
The concept of bend-imitating description as applied to the one-electron quantum mechanics in sharply-bent ideal electron waveguides and its development into a self consistent theory are presented. In the framework of bend-imitating approach, the investigation of the electron scattering in a doubly-bent 2D quantum wire with S-like bend has been made, and the explicit dependences of the transmission and reflection coefficients on geometrical parameters of a structure, as well as on the electron energy, have been obtained. The total elimination of the mixing between the scattering channels of a S-like bent quantum wire is predicted.
Probabilistic structure of quantum theory
International Nuclear Information System (INIS)
Burzynski, A.
1989-01-01
The fundamental ideas of quantum theory are presented. It is shown that two approaches to quantum theory: Heisenberg's matrix mechanics and Schroedinger's wave mechanics, can be formulated by means of the theory of operators in Hilbert space. Some remarks on Hilbert spaces, diadic and projection operators are done. States, probabilities and observables of quantum systems are discussed and time evolution of quantum states is analysed. Some remarks on two-component systems and symmetries are given. 21 refs. (M.F.W.)
Electronic properties of assemblies of zno quantum dots
Roest, Aarnoud Laurens
2003-01-01
Electron transport in an assembly of ZnO quantum dots has been studied using an electrochemically gated transistor. The electron mobility shows a step-wise increase as a function of the electron occupation per quantum dot. When the occupation number is below two, transport occurs by tunnelling
Electronic structure of silicene
International Nuclear Information System (INIS)
Voon, L. C. Lew Yan
2015-01-01
In this topical review, we discuss the electronic structure of free-standing silicene by comparing results obtained using different theoretical methods. Silicene is a single atomic layer of silicon similar to graphene. The interest in silicene is the same as for graphene, in being two-dimensional and possessing a Dirac cone. One advantage of silicene is due to its compatibility with current silicon electronics. Both empirical and first-principles techniques have been used to study the electronic properties of silicene. We will provide a brief overview of the parameter space for first-principles calculations. However, since the theory is standard, no extensive discussion will be included. Instead, we will emphasize what empirical methods can provide to such investigations and the current state of these theories. Finally, we will review the properties computed using both types of theories for free-standing silicene, with emphasis on areas where we have contributed. Comparisons to graphene is provided throughout. (topical review)
International Nuclear Information System (INIS)
Zozoulenko, I V; Ihnatsenka, S
2008-01-01
We have developed a mean-field first-principles approach for studying electronic and transport properties of low dimensional lateral structures in the integer quantum Hall regime. The electron interactions and spin effects are included within the spin density functional theory in the local density approximation where the conductance, the density, the effective potentials and the band structure are calculated on the basis of the Green's function technique. In this paper we present a systematic review of the major results obtained on the energetics, spin polarization, effective g factor, magnetosubband and edge state structure of split-gate and cleaved-edge overgrown quantum wires as well as on the conductance of quantum point contacts (QPCs) and open quantum dots. In particular, we discuss how the spin-resolved subband structure, the current densities, the confining potentials, as well as the spin polarization of the electron and current densities in quantum wires and antidots evolve when an applied magnetic field varies. We also discuss the role of the electron interaction and spin effects in the conductance of open systems focusing our attention on the 0.7 conductance anomaly in the QPCs. Special emphasis is given to the effect of the electron interaction on the conductance oscillations and their statistics in open quantum dots as well as to interpretation of the related experiments on the ultralow temperature saturation of the coherence time in open dots
International Nuclear Information System (INIS)
Grosso, G.
1986-01-01
The aim of this chapter is to present, in detail, some theoretical methods used to calculate electronic band structures in crystals. The basic strategies employed to attack the problem of electronic-structure calculations are presented. Successive sections present the basic formulations of the tight-binding, orthogonalized-plane-wave, Green'sfunction, and pseudopotential methods with a discussion of their application to perfect solids. Exemplifications in the case of a few selected problems provide further insight by the author into the physical aspects of the different methods and are a guide to the use of their mathematical techniques. A discussion is offered of completely a priori Hartree-Fock calculations and attempts to extend them. Special aspects of the different methods are also discussed in light of recently published related work
Overview of nuclear structure with electrons
International Nuclear Information System (INIS)
Geesaman, D. F.
1999-01-01
Following a broad summary of the author's view of nuclear structure in 1974, he will discuss the key elements they have learned in the past 25 years from the research at the M.I.T. Bates Linear Accelerator center and its sister electron accelerator laboratories. Electron scattering has provided the essential measurements for most of the progress. The future is bright for nuclear structure research as their ability to realistically calculate nuclear structure observables has dramatically advanced and they are increasingly able to incorporate an understanding of quantum chromodynamics into their picture of the nucleus
International Nuclear Information System (INIS)
Kozlovskii, Vladimir I; Korostelin, Yurii V; Skasyrsky, Yan K; Shapkin, P V; Trubenko, P A; Dianov, Evgenii M
1998-01-01
The method of molecular beam epitaxy on a ZnSe substrate was used to grow a ZnCdSe/ZnSe structure with 115 quantum wells. This structure was made up into a cavity which included part of the substrate. Lasing was excited by longitudinal pumping with a scanning electron beam of E e = 40 - 70 keV energy. At T = 80 K for E e = 65 keV the threshold current density was 60 A cm -2 and the output power was 0.15 W at the 465 nm wavelength. At T= 300 K the lasing (λ= 474 nm) occurred in the ZnSe substrate. (lasers)
Quantum revivals in the motion of electron in magnetic field
International Nuclear Information System (INIS)
Filipowicz, P.; Mostowski, J.
1981-01-01
We show that the motion of a relativistic electron in constant homogeneous magnetic field exhibits quasiperiodic behaviour (quantum revivals) and discuss the possibility of their observation. (author)
EPR and development of quantum electronics
International Nuclear Information System (INIS)
Manenkov, A A
2011-01-01
A role of electron paramagnetic resonance in development of quantum electronics is discussed. Basic principles and history of masers are briefly described. Spin-levels of paramagnetic ions in crystals as a very suitable object for active media of solid-state masers (called as EPR-masers) and physical processes in EPR-masers (population inversion of energy states) are analyzed. This analysis demonstrates a significant role of relaxation processes in multi-level spin-systems for efficient maser action. In this context peculiarities of spin-lattice and spin-spin cross relaxation processes in multi-level systems are analyzed. Development of EPR-masers and their application in radioastronomy and far-space communication systems are briefly described.
Quantum computation in semiconductor quantum dots of electron-spin asymmetric anisotropic exchange
International Nuclear Information System (INIS)
Hao Xiang; Zhu Shiqun
2007-01-01
The universal quantum computation is obtained when there exists asymmetric anisotropic exchange between electron spins in coupled semiconductor quantum dots. The asymmetric Heisenberg model can be transformed into the isotropic model through the control of two local unitary rotations for the realization of essential quantum gates. The rotations on each qubit are symmetrical and depend on the strength and orientation of asymmetric exchange. The implementation of the axially symmetric local magnetic fields can assist the construction of quantum logic gates in anisotropic coupled quantum dots. This proposal can efficiently use each physical electron spin as a logical qubit in the universal quantum computation
Epitaxial graphene electronic structure and transport
International Nuclear Information System (INIS)
De Heer, Walt A; Berger, Claire; Wu Xiaosong; Sprinkle, Mike; Hu Yike; Ruan Ming; First, Phillip N; Stroscio, Joseph A; Haddon, Robert; Piot, Benjamin; Faugeras, Clement; Potemski, Marek; Moon, Jeong-Sun
2010-01-01
Since its inception in 2001, the science and technology of epitaxial graphene on hexagonal silicon carbide has matured into a major international effort and is poised to become the first carbon electronics platform. A historical perspective is presented and the unique electronic properties of single and multilayered epitaxial graphenes on electronics grade silicon carbide are reviewed. Early results on transport and the field effect in Si-face grown graphene monolayers provided proof-of-principle demonstrations. Besides monolayer epitaxial graphene, attention is given to C-face grown multilayer graphene, which consists of electronically decoupled graphene sheets. Production, structure and electronic structure are reviewed. The electronic properties, interrogated using a wide variety of surface, electrical and optical probes, are discussed. An overview is given of recent developments of several device prototypes including resistance standards based on epitaxial graphene quantum Hall devices and new ultrahigh frequency analogue epitaxial graphene amplifiers.
Quantum mechanical effects in plasmonic structures with subnanometre gaps.
Zhu, Wenqi; Esteban, Ruben; Borisov, Andrei G; Baumberg, Jeremy J; Nordlander, Peter; Lezec, Henri J; Aizpurua, Javier; Crozier, Kenneth B
2016-06-03
Metallic structures with nanogap features have proven highly effective as building blocks for plasmonic systems, as they can provide a wide tuning range of operating frequencies and large near-field enhancements. Recent work has shown that quantum mechanical effects such as electron tunnelling and nonlocal screening become important as the gap distances approach the subnanometre length-scale. Such quantum effects challenge the classical picture of nanogap plasmons and have stimulated a number of theoretical and experimental studies. This review outlines the findings of many groups into quantum mechanical effects in nanogap plasmons, and discusses outstanding challenges and future directions.
Quantum entanglement in electron optics generation, characterization, and applications
Chandra, Naresh
2013-01-01
This monograph forms an interdisciplinary study in atomic, molecular, and quantum information (QI) science. Here a reader will find that applications of the tools developed in QI provide new physical insights into electron optics as well as properties of atoms & molecules which, in turn, are useful in studying QI both at fundamental and applied levels. In particular, this book investigates entanglement properties of flying electronic qubits generated in some of the well known processes capable of taking place in an atom or a molecule following the absorption of a photon. Here, one can generate Coulombic or fine-structure entanglement of electronic qubits. The properties of these entanglements differ not only from each other, but also from those when spin of an inner-shell photoelectron is entangled with the polarization of the subsequent fluorescence. Spins of an outer-shell electron and of a residual photoion can have free or bound entanglement in a laboratory.
Interpreting Quantum Logic as a Pragmatic Structure
Garola, Claudio
2017-12-01
Many scholars maintain that the language of quantum mechanics introduces a quantum notion of truth which is formalized by (standard, sharp) quantum logic and is incompatible with the classical (Tarskian) notion of truth. We show that quantum logic can be identified (up to an equivalence relation) with a fragment of a pragmatic language LGP of assertive formulas, that are justified or unjustified rather than trueor false. Quantum logic can then be interpreted as an algebraic structure that formalizes properties of the notion of empirical justification according to quantum mechanics rather than properties of a quantum notion of truth. This conclusion agrees with a general integrationist perspective that interprets nonstandard logics as theories of metalinguistic notions different from truth, thus avoiding incompatibility with classical notions and preserving the globality of logic.
Few electron quantum dot coupling to donor implanted electron spins
Rudolph, Martin; Harvey-Collard, Patrick; Neilson, Erik; Gamble, John; Muller, Richard; Jacobson, Toby; Ten-Eyck, Greg; Wendt, Joel; Pluym, Tammy; Lilly, Michael; Carroll, Malcolm
2015-03-01
Donor-based Si qubits are receiving increased interest because of recent demonstrations of high fidelity electron or nuclear spin qubits and their coupling. Quantum dot (QD) mediated interactions between donors are of interest for future coupling of two donors. We present experiment and modeling of a polysilicon/Si MOS QD, charge-sensed by a neighboring many electron QD, capable of coupling to one or two donor implanted electron spins (D) while tuned to the few electron regime. The unique design employs two neighboring gated wire FETs and self-aligned implants, which supports many configurations of implanted donors. We can access the (0,1) ⇔(1,0) transition between the D and QD, as well as the resonance condition between the few electron QD and two donors ((0,N,1) ⇔(0,N +1,0) ⇔(1,N,0)). We characterize capacitances and tunnel rate behavior combined with semi-classical and full configuration interaction simulations to study the energy landscape and kinetics of D-QD transitions. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE, Office of Basic Energy Sciences user facility. The work was supported by the Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000.
Quantum mechanical force field for water with explicit electronic polarization.
Han, Jaebeom; Mazack, Michael J M; Zhang, Peng; Truhlar, Donald G; Gao, Jiali
2013-08-07
A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensed-phase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen- and hydrogen-containing compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a three-point charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with three-point-charge potential) model, is suitable for modeling both gas-phase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 10(6) self-consistent-field calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across
The electronic structures of solids
Coles, B R
2013-01-01
The Electronic Structures of Solids aims to provide students of solid state physics with the essential concepts they will need in considering properties of solids that depend on their electronic structures and idea of the electronic character of particular materials and groups of materials. The book first discusses the electronic structure of atoms, including hydrogen atom and many-electron atom. The text also underscores bonding between atoms and electrons in metals. Discussions focus on bonding energies and structures in the solid elements, eigenstates of free-electron gas, and electrical co
DEFF Research Database (Denmark)
Uskov, Alexander; Protsenko, Igor E.; Mortensen, N. Asger
2014-01-01
We present a quantum mechanical approach to calculate broadening of plasmonic resonances in metallic nanostructures due to collisions of electrons with the surface of the structure. The approach is applicable if the characteristic size of the structure is much larger than the de Broglie electron...
About the structure of quantum intermediate state of superconductors
International Nuclear Information System (INIS)
Ledenev, O.P.
2008-01-01
The calculation of spatial structure of a quantum intermediate state in Type I superconductors is completed. Theoretical model of thermodynamics of considered state was proposed by Andreev. It is shown, that in a quantum case, the period of structure appears significantly smaller and has different dependence on both the magnetic field and temperature than in the classical intermediate Landau state. The decrease of thickness of normal layers results in increase of characteristic distance between the quantum Andreev levels of electronic excitations, and the transition to the quantum intermediate from classical state is realized at higher temperatures ∼1 K, than it was supposed in previous works. The comparison of calculation data with experimental results, for example using the sample of mono-crystal gallium, is conducted
Electronic quantum noise and microwave photons
International Nuclear Information System (INIS)
Bize-Reydellet, L.H.
2003-06-01
This work is devoted to the experimental study of quantum electronic noise in mesoscopic conductors. In the first part of this thesis, we studied shot noise in a one-dimensional ballistic conductor: a quantum point contact (QPC). We showed experimentally that, when one of the QPC contacts is irradiated with microwave photons, we observe partition noise in the absence of net current flowing through the sample. Thus, we validate the scattering theory of photo-assisted shot noise first by measuring the Fano factor without bias voltage across the conductor, and then by measuring shot noise in the doubly non equilibrium situation, where both a bias voltage and a microwave modulation are applied. In the second part, we realized the first tests of a new experimental set-up which will be able to measure high frequency noise of a mesoscopic conductor and the photon statistics emitted by this conductor in the measurement circuit. These tests consist in realizing Hanbury-Brown and Twiss type experiments (intensity interferometry) with two kinds of microwave photon source. First, we used a thermal incoherent source (macroscopic 50 Ohms resistor). It showed super-Poissonian noise, since the power fluctuations are proportional to the square of the mean photon power. Secondly, we studied a classical monochromatic source, which shows a Poissonian statistics. The giant Fano factor measured is perfectly explained by the attenuator and amplifier noise. (author)
Confined quantum systems: spectral properties of two-electron quantum dots
International Nuclear Information System (INIS)
Sako, T; Diercksen, G H F
2003-01-01
The spectrum, electron-density distribution and ground-state correlation energy of two electrons confined by an anisotropic harmonic oscillator potential have been studied for different confinement strengths ω by using the quantum chemical configuration interaction (CI) method employing a large Cartesian anisotropic Gaussian basis set and a full CI wavefunction. Energy level diagrams and electron-density distributions are displayed for selected electronic states and confinement parameters. The total energy and spacing between energy levels increase in all cases with increasing ω. The energy level structure cannot be matched by scaling with respect to ω. The correlation energy of the ground state is comparable in magnitude to that of the helium atom. It increases for increasing ω. The percentage of the correlation energy with respect to the total energy of the ground state is considerably larger than that of the helium atom
Polarized electrons, trions, and nuclei in charged quantum dots
Bracker, A. S.; Tischler, J. G.; Korenev, V. L.; Gammon, D.
2003-07-01
We have investigated spin polarization in GaAs quantum dots. Excitons and trions are polarized directly by optical excitation and studied through polarization of photoluminescence. Electrons and nuclei are polarized indirectly through subsequent relaxation processes. Polarized electrons are identified by the Hanle effect for exciton and trion photoluminescence, while polarized nuclei are identified through the Overhauser effect in individual charged quantum dots.
Quantum Hall Effect: proposed multi-electron tunneling experiment
International Nuclear Information System (INIS)
Kostadinov, I.Z.
1985-11-01
Here we propose a tunneling experiment for the fractional and Integral Quantum Hall Effect. It may demonstrate multi-electron tunneling and may provide information about the nature of the macroscopic quantum states of 2D electronic liquid or solid. (author)
Robust Optimal Design of Quantum Electronic Devices
Directory of Open Access Journals (Sweden)
Ociel Morales
2018-01-01
Full Text Available We consider the optimal design of a sequence of quantum barriers, in order to manufacture an electronic device at the nanoscale such that the dependence of its transmission coefficient on the bias voltage is linear. The technique presented here is easily adaptable to other response characteristics. There are two distinguishing features of our approach. First, the transmission coefficient is determined using a semiclassical approximation, so we can explicitly compute the gradient of the objective function. Second, in contrast with earlier treatments, manufacturing uncertainties are incorporated in the model through random variables; the optimal design problem is formulated in a probabilistic setting and then solved using a stochastic collocation method. As a measure of robustness, a weighted sum of the expectation and the variance of a least-squares performance metric is considered. Several simulations illustrate the proposed technique, which shows an improvement in accuracy over 69% with respect to brute-force, Monte-Carlo-based methods.
Ubiquitous quantum structure. From psychology to finance
International Nuclear Information System (INIS)
Khrennikov, Andrei
2010-01-01
Quantum-like structure is present practically everywhere. Quantum-like (QL) models, i.e. models based on the mathematical formalism of quantum mechanics and its generalizations can be successfully applied to cognitive science, psychology, genetics, economics, finances, and game theory. This book is not about quantum mechanics as a physical theory. The short review of quantum postulates is therefore mainly of historical value: quantum mechanics is just the first example of the successful application of non-Kolmogorov probabilities, the first step towards a contextual probabilistic description of natural, biological, psychological, social, economical or financial phenomena. A general contextual probabilistic model (Vaexjoemodel) is presented. It can be used for describing probabilities in both quantum and classical (statistical) mechanics as well as in the above mentioned phenomena. This model can be represented in a quantum-like way, namely, in complex and more general Hilbert spaces. In this way quantum probability is totally demystified: Born's representation of quantum probabilities by complex probability amplitudes, wave functions, is simply a special representation of this type. (orig.)
Ubiquitous quantum structure. From psychology to finance
Energy Technology Data Exchange (ETDEWEB)
Khrennikov, Andrei [University of Vaexjoe (Sweden). International Center for Mathematical Modeling in Physics and Cognitive Science
2010-07-01
Quantum-like structure is present practically everywhere. Quantum-like (QL) models, i.e. models based on the mathematical formalism of quantum mechanics and its generalizations can be successfully applied to cognitive science, psychology, genetics, economics, finances, and game theory. This book is not about quantum mechanics as a physical theory. The short review of quantum postulates is therefore mainly of historical value: quantum mechanics is just the first example of the successful application of non-Kolmogorov probabilities, the first step towards a contextual probabilistic description of natural, biological, psychological, social, economical or financial phenomena. A general contextual probabilistic model (Vaexjoemodel) is presented. It can be used for describing probabilities in both quantum and classical (statistical) mechanics as well as in the above mentioned phenomena. This model can be represented in a quantum-like way, namely, in complex and more general Hilbert spaces. In this way quantum probability is totally demystified: Born's representation of quantum probabilities by complex probability amplitudes, wave functions, is simply a special representation of this type. (orig.)
Shanker, A.; Bhowmik, D.; Bhattacharya, T. K.
2010-01-01
We aim to analytically arrive at a beam splitter formulation for electron waves. The electron beam splitter is an essential component of quantum logical devices. To arrive at the beam splitter structure, the electrons are treated as waves, i.e. we assume the transport to be ballistic. Ballistic electrons are electrons that travel over such short distances that their phase coherence is maintained. For mesoscopic devices with size smaller than the mean free path, the phase relaxation length and...
Quantum logic gates based on coherent electron transport in quantum wires.
Bertoni, A; Bordone, P; Brunetti, R; Jacoboni, C; Reggiani, S
2000-06-19
It is shown that the universal set of quantum logic gates can be realized using solid-state quantum bits based on coherent electron transport in quantum wires. The elementary quantum bits are realized with a proper design of two quantum wires coupled through a potential barrier. Numerical simulations show that (a) a proper design of the coupling barrier allows one to realize any one-qbit rotation and (b) Coulomb interaction between two qbits of this kind allows the implementation of the CNOT gate. These systems are based on a mature technology and seem to be integrable with conventional electronics.
Fluorinated graphene films with graphene quantum dots for electronic applications
Energy Technology Data Exchange (ETDEWEB)
Antonova, I. V., E-mail: antonova@isp.nsc.ru [Rzhanov Institute of Semiconductor Physics, Russian Academy of Sciences, Siberian Branch, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Nebogatikova, N. A.; Prinz, V. Ya. [Rzhanov Institute of Semiconductor Physics, Russian Academy of Sciences, Siberian Branch, Novosibirsk 630090 (Russian Federation)
2016-06-14
This work analyzes carrier transport, the relaxation of non-equilibrium charge, and the electronic structure of fluorinated graphene (FG) films with graphene quantum dots (GQDs). The FG films with GQDs were fabricated by means of chemical functionalization in an aqueous solution of hydrofluoric acid. High fluctuations of potential relief inside the FG barriers have been detected in the range of up to 200 mV. A phenomenological expression that describes the dependence of the time of non-equilibrium charge emission from GQDs on quantum confinement levels and film thickness (potential barrier parameters between GQDs) is suggested. An increase in the degree of functionalization leads to a decrease in GQD size, the removal of the GQD effect on carrier transport, and the relaxation of non-equilibrium charge. The study of the electronic properties of FG films with GQDs has revealed a unipolar resistive switching effect in the films with a relatively high degree of fluorination and a high current modulation (up to ON/OFF ∼ 10{sup 4}–10{sup 5}) in transistor-like structures with a lower degree of fluorination. 2D films with GQDs are believed to have considerable potential for various electronic applications (nonvolatile memory, 2D connections with optical control and logic elements).
Probing quantum coherence in single-atom electron spin resonance
Willke, Philip; Paul, William; Natterer, Fabian D.; Yang, Kai; Bae, Yujeong; Choi, Taeyoung; Fernández-Rossier, Joaquin; Heinrich, Andreas J.; Lutz, Christoper P.
2018-01-01
Spin resonance of individual spin centers allows applications ranging from quantum information technology to atomic-scale magnetometry. To protect the quantum properties of a spin, control over its local environment, including energy relaxation and decoherence processes, is crucial. However, in most existing architectures, the environment remains fixed by the crystal structure and electrical contacts. Recently, spin-polarized scanning tunneling microscopy (STM), in combination with electron spin resonance (ESR), allowed the study of single adatoms and inter-atomic coupling with an unprecedented combination of spatial and energy resolution. We elucidate and control the interplay of an Fe single spin with its atomic-scale environment by precisely tuning the phase coherence time T2 using the STM tip as a variable electrode. We find that the decoherence rate is the sum of two main contributions. The first scales linearly with tunnel current and shows that, on average, every tunneling electron causes one dephasing event. The second, effective even without current, arises from thermally activated spin-flip processes of tip spins. Understanding these interactions allows us to maximize T2 and improve the energy resolution. It also allows us to maximize the amplitude of the ESR signal, which supports measurements even at elevated temperatures as high as 4 K. Thus, ESR-STM allows control of quantum coherence in individual, electrically accessible spins. PMID:29464211
Quantum tunneling and field electron emission theories
Liang, Shi-Dong
2013-01-01
Quantum tunneling is an essential issue in quantum physics. Especially, the rapid development of nanotechnology in recent years promises a lot of applications in condensed matter physics, surface science and nanodevices, which are growing interests in fundamental issues, computational techniques and potential applications of quantum tunneling. The book involves two relevant topics. One is quantum tunneling theory in condensed matter physics, including the basic concepts and methods, especially for recent developments in mesoscopic physics and computational formulation. The second part is the f
Quantum tunneling resonant electron transfer process in Lorentzian plasmas
International Nuclear Information System (INIS)
Hong, Woo-Pyo; Jung, Young-Dae
2014-01-01
The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed
International Nuclear Information System (INIS)
Babinski, A; Korkusinski, M; Hawrylak, P; Wasilewski, Z R; Potemski, M
2013-01-01
Magnetic-field dispersion of the multiexcitons related to the p shell of a single quantum dot (QD) is analysed in this work. The reduced cyclotron effective mass of carriers is determined from the energy splitting between the p + - and p − - related multiexcitonic emission lines. The reduced mass in the occupied QD was found to be larger than the mass related to the QD's single particle structure. The apparent increase of the reduced mass with increasing excitonic occupation of the dot is related to the mass renoralization due to electron-electron interactions within a multiexcitonic droplet
Sinha, Leena; Karabacak, Mehmet; Narayan, V.; Cinar, Mehmet; Prasad, Onkar
2013-05-01
Gabapentin (GP), structurally related to the neurotransmitter GABA (gamma-aminobutyric acid), mimics the activity of GABA and is also widely used in neurology for the treatment of peripheral neuropathic pain. It exists in zwitterionic form in solid state. The present communication deals with the quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of GP using density functional (DFT/B3LYP) method with 6-311++G(d,p) basis set. In view of the fact that amino acids exist as zwitterions as well as in the neutral form depending on the environment (solvent, pH, etc.), molecular properties of both the zwitterionic and neutral form of GP have been analyzed. The fundamental vibrational wavenumbers as well as their intensities were calculated and compared with experimental FT-IR and FT-Raman spectra. The fundamental assignments were done on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method. The electric dipole moment, polarizability and the first hyperpolarizability values of the GP have been calculated at the same level of theory and basis set. The nonlinear optical (NLO) behavior of zwitterionic and neutral form has been compared. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization has been analyzed using natural bond orbital analysis. Ultraviolet-visible (UV-Vis) spectrum of the title molecule has also been calculated using TD-DFT method. The thermodynamic properties of both the zwitterionic and neutral form of GP at different temperatures have been calculated.
Quantum-Dynamical Theory of Electron Exchange Correlation
Directory of Open Access Journals (Sweden)
Burke Ritchie
2013-01-01
aggregate, is elucidated. The relationship depends on the use of spin-dependent quantum trajectories (SDQT to evaluate Coulomb’s law between any two electrons as an instantaneous interaction in space and time rather than as a quantum-mean interaction in the form of screening and exchange potentials. Hence FDS depends in an ab initio sense on the inference of SDQT from Dirac’s equation, which provides for relativistic Lorentz invariance and a permanent magnetic moment (or spin in the electron’s equation of motion. Schroedinger’s time-dependent equation can be used to evaluate the SDQT in the nonrelativistic regime of electron velocity. Remarkably FDS is a relativistic property of an ensemble of electron, even though it is of order c0 in the nonrelativistic limit, in agreement with experimental observation. Finally it is shown that covalent versus separated-atoms limits can be characterized by the SDQT. As an example of the use of SDQT in a canonical structure problem, the energies of the 1Σg and 3Σu states of H2 are calculated and compared with the accurate variational energies of Kolos and Wolniewitz.
International Nuclear Information System (INIS)
Da Silva, Robson; Hoff, Diego A; Rego, Luis G C
2015-01-01
Charge and excitonic-energy transfer phenomena are fundamental for energy conversion in solar cells as well as artificial photosynthesis. Currently, much interest is being paid to light-harvesting and energy transduction processes in supramolecular structures, where nuclear dynamics has a major influence on electronic quantum dynamics. For this reason, the simulation of long range electron transfer in supramolecular structures, under environmental conditions described within an atomistic framework, has been a difficult problem to study. This work describes a coupled quantum mechanics/molecular mechanics method that aims at describing long range charge transfer processes in supramolecular systems, taking into account the atomistic details of large molecular structures, the underlying nuclear motion, and environmental effects. The method is applied to investigate the relevance of electron–nuclei interaction on the mechanisms for photo-induced electron–hole pair separation in dye-sensitized interfaces as well as electronic dynamics in molecular structures. (paper)
Adiabatic quantum search algorithm for structured problems
International Nuclear Information System (INIS)
Roland, Jeremie; Cerf, Nicolas J.
2003-01-01
The study of quantum computation has been motivated by the hope of finding efficient quantum algorithms for solving classically hard problems. In this context, quantum algorithms by local adiabatic evolution have been shown to solve an unstructured search problem with a quadratic speedup over a classical search, just as Grover's algorithm. In this paper, we study how the structure of the search problem may be exploited to further improve the efficiency of these quantum adiabatic algorithms. We show that by nesting a partial search over a reduced set of variables into a global search, it is possible to devise quantum adiabatic algorithms with a complexity that, although still exponential, grows with a reduced order in the problem size
Mode structure of a quantum cascade laser
Bogdanov, A. A.; Suris, R. A.
2011-03-01
We analyze the mode structure of a quantum cascade laser (QCL) cavity considering the surface plasmon-polariton modes and familiar modes of hollow resonator jointly, within a single model. We present a comprehensive mode structure analysis of the laser cavity, varying its geometric parameters and free electron concentration inside cavity layers within a wide range. Our analysis covers, in particular, the cases of metal-insulator-metal and insulator-metal-insulator waveguides. We discuss the phenomenon of negative dispersion for eigenmodes in detail and explain the nature of this phenomenon. We specify a waveguide parameters domain in which negative dispersion exists. The mode structure of QCL cavity is considered in the case of the anisotropic electrical properties of the waveguide materials. We show that anisotropy of the waveguide core results in propagation of Langmuir modes that are degenerated in the case of the isotropic core. Comparative analysis of optical losses due to free carrier absorption is presented for different modes within the frequency range from terahertz to ultraviolet frequencies.
International Nuclear Information System (INIS)
Yumatov, V.D.; Il'inchik, E.A.; Murakhtanov, V.V.; Dunaev, S.T.; Volkov, V.V.
1993-01-01
Electron structure of 6.9-bis-(ammonia)-nide-decarborane(12), that is, B 10 H 12 (NH 3 ) 2 , is studied by means of ultrasoft X-ray spectroscopy using nitrogen and boron atoms. Calculations of MNDO and ab initio are conducted. Electron structure of ammonia and of /B 10 H 12 / cluster is studied and its variation at complex formation is investigated, as well. On the basis of calculations one shows, that some vacant orbitals belonging to borane cluster participate into chemical bond of donor-acceptor type among the fragments. Presence of π-component of bond between NH 3 and /B 10 H 12 / and occurrence of four-central bound in borane cluster are detected
Strong quantum-confined stark effect in germanium quantum-well structures on silicon
International Nuclear Information System (INIS)
Kuo, Y.; Lee, Y. K.; Gei, Y.; Ren, S; Roth, J. E.; Miller, D. A.; Harris, J. S.
2006-01-01
Silicon is the dominant semiconductor for electronics, but there is now a growing need to integrate such component with optoelectronics for telecommunications and computer interconnections. Silicon-based optical modulators have recently been successfully demonstrated but because the light modulation mechanisms in silicon are relatively weak, long (for example, several millimeters) devices or sophisticated high-quality-factor resonators have been necessary. Thin quantum-well structures made from III-V semiconductors such as GaAs, InP and their alloys exhibit the much stronger Quantum-Confined Stark Effect (QCSE) mechanism, which allows modulator structures with only micrometers of optical path length. Such III-V materials are unfortunately difficult to integrate with silicon electronic devices. Germanium is routinely integrated with silicon in electronics, but previous silicon-germanium structures have also not shown strong modulation effects. Here we report the discovery of the QCSE, at room temperature, in thin germanium quantum-well structures grown on silicon. The QCSE here has strengths comparable to that in III-V materials. Its clarity and strength are particularly surprising because germanium is an indirect gap semiconductor, such semiconductors often display much weak optical effects than direct gap materials (such as the III-V materials typically used for optoelectronics). This discovery is very promising for small, high-speed, low-power optical output devices fully compatible with silicon electronics manufacture. (author)
Electron Raman scattering in asymmetrical multiple quantum wells
International Nuclear Information System (INIS)
Betancourt-Riera, R; Rosas, R; Marin-Enriquez, I; Riera, R; Marin, J L
2005-01-01
Optical properties of asymmetrical multiple quantum wells for the construction of quantum cascade lasers are calculated, and expressions for the electronic states of asymmetrical multiple quantum wells are presented. The gain and differential cross-section for an electron Raman scattering process are obtained. Also, the emission spectra for several scattering configurations are discussed, and the corresponding selection rules for the processes involved are studied; an interpretation of the singularities found in the spectra is given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers
Nonequilibrium Electron Transport Through a Quantum Dot from Kubo Formula
International Nuclear Information System (INIS)
Lue Rong; Zhang Guangming
2005-01-01
Based on the Kubo formula for an electron tunneling junction, we revisit the nonequilibrium transport properties through a quantum dot. Since the Fermi level of the quantum dot is set by the conduction electrons of the leads, we calculate the electron current from the left side by assuming the quantum dot coupled to the right lead as another side of the tunneling junction, and the other way round is used to calculate the current from the right side. By symmetrizing these two currents, an effective local density states on the dot can be obtained, and is discussed at high and low temperatures, respectively.
In situ electron-beam polymerization stabilized quantum dot micelles.
Travert-Branger, Nathalie; Dubois, Fabien; Renault, Jean-Philippe; Pin, Serge; Mahler, Benoit; Gravel, Edmond; Dubertret, Benoit; Doris, Eric
2011-04-19
A polymerizable amphiphile polymer containing PEG was synthesized and used to encapsulate quantum dots in micelles. The quantum dot micelles were then polymerized using a "clean" electron beam process that did not require any post-irradiation purification. Fluorescence spectroscopy revealed that the polymerized micelles provided an organic coating that preserved the quantum dot fluorescence better than nonpolymerized micelles, even under harsh conditions. © 2011 American Chemical Society
Substantially Enhancing Quantum Coherence of Electrons in Graphene via Electron-Plasmon Coupling.
Cheng, Guanghui; Qin, Wei; Lin, Meng-Hsien; Wei, Laiming; Fan, Xiaodong; Zhang, Huayang; Gwo, Shangjr; Zeng, Changgan; Hou, J G; Zhang, Zhenyu
2017-10-13
The interplays between different quasiparticles in solids lay the foundation for a wide spectrum of intriguing quantum effects, yet how the collective plasmon excitations affect the quantum transport of electrons remains largely unexplored. Here we provide the first demonstration that when the electron-plasmon coupling is introduced, the quantum coherence of electrons in graphene is substantially enhanced with the quantum coherence length almost tripled. We further develop a microscopic model to interpret the striking observations, emphasizing the vital role of the graphene plasmons in suppressing electron-electron dephasing. The novel and transformative concept of plasmon-enhanced quantum coherence sheds new insight into interquasiparticle interactions, and further extends a new dimension to exploit nontrivial quantum phenomena and devices in solid systems.
Photon-Electron Interactions in Dirac Quantum Materials
Energy Technology Data Exchange (ETDEWEB)
Xu, Xiaodong [Univ. of Washington, Seattle, WA (United States). Dept. of Material Science and Engineering
2017-11-10
The objective of this proposal was to explore the fundamental light-matter interactions in a new class of Dirac quantum materials, atomically thin transition metal dichalcogenides (TMDs). Monolayer TMDs are newly discovered two-dimensional semiconductors with direct bandgap. Due to their hexagonal lattice structure, the band edge localizes at corner of Brillouin zone, i.e. “Dirac valleys”. This gives the corresponding electron states a “valley index” (or pseudospin) in addition to the real spin. Remarkably, the valley pseudospins have circularly polarized optical selection rules, providing the first solid state system for dynamic control of the valley degree of freedom. During this award, we have developed a suite of advanced nano-optical spectroscopy tools in the investigation and manipulation of charge, spin, and valley degrees of freedom in monolayer semiconductors. Emerging physical phenomena, such as quantum coherence between valley pseudospins, have been demonstrated for the first time in solids. In addition to monolayers, we have developed a framework in engineering, formulating, and understanding valley pseudospin physics in 2D heterostructures formed by different monolayer semiconductors. We demonstrated long-lived valley-polarized interlayer excitons with valley-dependent many-body interaction effects. These works push the research frontier in understanding the light-matter interactions in atomically-thin quantum materials for protentional transformative energy technologies.
Electron transport and coherence in semiconductor quantum dots and rings
Van der Wiel, W.G.
2002-01-01
A number of experiments on electron transport and coherence in semiconductor vertical and lateral quantum dots and semiconductor rings is described. Quantum dots are often referred to as "artificial atoms", because of their similarities with real atoms. Examples of such atom-like properties that
Quantum Electronic Matter in Two Dimensions
Energy Technology Data Exchange (ETDEWEB)
Eisenstein, James [California Inst. of Technology (CalTech), Pasadena, CA (United States)
2015-01-27
-layer cousins. In particular, the exotic collective (and deeply quantum mechanical) electronic phases which develop when a large magnetic field is applied have been a major focus of effort. Significant results have been obtained from both ordinary electrical measurements and from more sophisticated thermoelectric studies of such systems. Related studies of few-layer graphenes have elucidated the transition from the two- to three-dimensional electrical properties of carbon-based conductors. Investigations like these expand our understanding of electronic materials general. While there are certainly immediate fundamental scientific pay-offs, it is also true that research of this kind ultimately leads to technological breakthroughs in the long term. By way of example, superconductivity was undoubtedly regarded as a useless novelty when it was discovered in 1911. Who could have known then that it would become crucial to the medical revolution brought about by magnetic resonance imaging decades later?
Effect of structural disorder on quantum oscillations in graphite
Energy Technology Data Exchange (ETDEWEB)
Camargo, B. C., E-mail: b.c-camargo@yahoo.com.br; Kopelevich, Y. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, Unicamp 13083-970, Campinas, São Paulo (Brazil); Usher, A.; Hubbard, S. B. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)
2016-01-18
We have studied the effect of structural disorder on the de Haas van Alphen and Shubnikov de Haas quantum oscillations measured in natural, Kish, and highly oriented pyrolytic graphite samples at temperatures down to 30 mK and at magnetic fields up to 14 T. The measurements were performed on different samples characterized by means of x-ray diffractometry, transmission electron microscopy, and atomic-force microscopy techniques. Our results reveal a correlation between the amplitude of quantum oscillations and the sample surface roughness.
Influence of scattering processes on electron quantum states in nanowires
Directory of Open Access Journals (Sweden)
Pozdnyakov Dmitry
2007-01-01
Full Text Available AbstractIn the framework of quantum perturbation theory the self-consistent method of calculation of electron scattering rates in nanowires with the one-dimensional electron gas in the quantum limit is worked out. The developed method allows both the collisional broadening and the quantum correlations between scattering events to be taken into account. It is an alternativeper seto the Fock approximation for the self-energy approach based on Green’s function formalism. However this approach is free of mathematical difficulties typical to the Fock approximation. Moreover, the developed method is simpler than the Fock approximation from the computational point of view. Using the approximation of stable one-particle quantum states it is proved that the electron scattering processes determine the dependence of electron energy versus its wave vector.
Gated-controlled electron pumping in connected quantum rings
International Nuclear Information System (INIS)
Lima, R.P.A.; Domínguez-Adame, F.
2014-01-01
We study the electronic transport across connected quantum rings attached to leads and subjected to time-harmonic side-gate voltages. Using the Floquet formalism, we calculate the net pumped current generated and controlled by the side-gate voltage. The control of the current is achieved by varying the phase shift between the two side-gate voltages as well as the Fermi energy. In particular, the maximum current is reached when the side-gate voltages are in quadrature. This new design based on connected quantum rings controlled without magnetic fields can be easily integrated in standard electronic devices. - Highlights: • We introduce and study a minimal setup to pump electrons through connected quantum rings. • Quantum pumping is achieved by time-harmonic side-gate voltages instead of the more conventional time-dependent magnetic fluxes. • Our new design could be easily integrated in standard electronic devices
Nonequilibrium electron transport through quantum dots in the Kondo regime
DEFF Research Database (Denmark)
Wölfle, Peter; Paaske, Jens; Rosch, Achim
2005-01-01
Electron transport at large bias voltage through quantum dots in the Kondo regime is described within the perturbative renormalization group extended to nonequilibrium. The conductance, local magnetization, dynamical spin susceptibility and local spectral function are calculated. We show how...
Structure of conduction electrons on polysilanes
Energy Technology Data Exchange (ETDEWEB)
Ichikawa, Tsuneki [Hokkaido Univ., Sapporo (Japan); Kumagai, Jun
1998-10-01
The orbital structures of conduction electrons on permethylated oligosilane, Si{sub 2n}(CH{sub 3}){sub 2n+2}(n = 2 - 8), and poly(cyclohexylmethylsilane) have been determined by the electron spin-echo envelope modulation signals of the radical anions of these silanes in a deuterated rigid matrix at 77 K. The conduction electron on permethylated oligosilane is delocalized over the entire main chain, whereas that on poly(cyclohexylmethylsilane) is localized on a part of the main chain composed of about six Si atoms. Quantum-chemical calculations suggest that Anderson localization due to fluctuation of {sigma} conjugation by conformational disorder of the main chain is responsible for the localization of both the conduction electron and the hole. (author)
Three short distance structures from quantum algebras
International Nuclear Information System (INIS)
Kempf, A.
1997-01-01
Known results are reviewed and new results are given on three types of short distance structures of observables which typically appear in studies of quantum group related algebras. In particular, one of the short distance structures is shown to suggest a new mechanism for the introduction of internal symmetries
Data Structures in Classical and Quantum Computing
M.J. Fillinger (Max)
2013-01-01
textabstractThis survey summarizes several results about quantum computing related to (mostly static) data structures. First, we describe classical data structures for the set membership and the predecessor search problems: Perfect Hash tables for set membership by Fredman, Koml\\'{o}s and
Inhomogeneous effects in the quantum free electron laser
International Nuclear Information System (INIS)
Piovella, N.; Bonifacio, R.
2006-01-01
We include inhomogeneous effects in the quantum model of a free electron laser taking into account the initial energy spread of the electron beam. From a linear analysis, we obtain a generalized dispersion relation, from which the exponential gain can be explicitly calculated. We determine the maximum allowed initial energy spread in the quantum exponential regime and we discuss the limit of large energy spread
Electron-electron interactions in graphene field-induced quantum dots in a high magnetic field
DEFF Research Database (Denmark)
Orlof, A.; Shylau, Artsem; Zozoulenko, I. V.
2015-01-01
We study the effect of electron-electron interaction in graphene quantum dots defined by an external electrostatic potential and a high magnetic field. To account for the electron-electron interaction, we use the Thomas-Fermi approximation and find that electron screening causes the formation...... of compressible strips in the potential profile and the electron density. We numerically solve the Dirac equations describing the electron dynamics in quantum dots, and we demonstrate that compressible strips lead to the appearance of plateaus in the electron energies as a function of the magnetic field. Finally...
Two-dimensional electron gas in monolayer InN quantum wells
International Nuclear Information System (INIS)
Pan, W.; Wang, G. T.; Dimakis, E.; Moustakas, T. D.; Tsui, D. C.
2014-01-01
We report in this letter experimental results that confirm the two-dimensional nature of the electron systems in a superlattice structure of 40 InN quantum wells consisting of one monolayer of InN embedded between 10 nm GaN barriers. The electron density and mobility of the two-dimensional electron system (2DES) in these InN quantum wells are 5 × 10 15 cm −2 (or 1.25 × 10 14 cm −2 per InN quantum well, assuming all the quantum wells are connected by diffused indium contacts) and 420 cm 2 /Vs, respectively. Moreover, the diagonal resistance of the 2DES shows virtually no temperature dependence in a wide temperature range, indicating the topological nature of the 2DES
Controllable continuous evolution of electronic states in a single quantum ring
Chakraborty, Tapash; Manaselyan, Aram; Barseghyan, Manuk; Laroze, David
2018-02-01
An intense terahertz laser field is shown to have a profound effect on the electronic and optical properties of quantum rings where the isotropic and anisotropic quantum rings can now be treated on equal footing. We have demonstrated that in isotropic quantum rings the laser field creates unusual Aharonov-Bohm oscillations that are usually expected in anisotropic rings. Furthermore, we have shown that intense laser fields can restore the isotropic physical properties in anisotropic quantum rings. In principle, all types of anisotropies (structural, effective masses, defects, etc.) can evolve as in isotropic rings in our present approach. Most importantly, we have found a continuous evolution of the energy spectra and intraband optical characteristics of structurally anisotropic quantum rings to those of isotropic rings in a controlled manner with the help of a laser field.
Michalski, J.; Bryndal, I.; Lorenc, J.; Hermanowicz, K.; Janczak, J.; Hanuza, J.
2018-02-01
The crystal and molecular structures of 6-methyl-3,5-dinitro-2-[(E)-phenyldiazenyl]pyridine have been determined by X-ray diffraction and quantum chemical DFT calculations. The crystal is monoclinic, space group Cc (No. 9) with Z = 4 with the unit cell parameters: a = 12.083(7), b = 12.881(6), c = 8.134(3) Å and β = 97.09(5)°. The azo-bridge appears in the trans conformation in which C2-N2-N2‧-C1‧ torsion angle takes a value - 178.6(3)°, whereas the dihedral angle between the planes of the phenyl and pyridine rings is 3.5(2)°. The IR and Raman spectra measured in the temperature range 80-350 K and quantum chemical calculations with the use of B3LYP/6-311G(2d,2p) approach confirmed the trans configuration of the azo-bridge as the most stable energetically and allowed determination of the energy other virtual structures. The observed effects were used in the discussion of vibrational dynamics of the studied compound. The energy gap between cis and trans conformers equals to 1.054 eV (0.03873 Hartree). The electron absorption and emission spectra have been measured and analyzed on the basis of DFT calculations. The life time of the excited state is 12 μs and the Stokes shift is close to 5470 cm- 1.
Quantum integrals from coalgebra structure
International Nuclear Information System (INIS)
Post, S; Riglioni, D
2015-01-01
Quantum versions of the hydrogen atom and the harmonic oscillator are studied on non Euclidean spaces of dimension N. 2N−1 integrals, of arbitrary order, are constructed via a multi-dimensional version of the factorization method, thus confirming the conjecture of Riglioni (2013 J. Phys. A: Math. Theor. 46 265207). The systems are extended via coalgebra extension of sl(2) representations, although not all integrals are expressible in these generators. As an example, dimensional reduction is applied to four-dimensional systems to obtain extension and new proofs of the superintegrability of known families of Hamiltonians. (paper)
Electronic transient processes and optical spectra in quantum dots for quantum computing
Czech Academy of Sciences Publication Activity Database
Král, Karel; Zdeněk, Petr; Khás, Zdeněk
2004-01-01
Roč. 3, č. 1 (2004), s. 17-25 ISSN 1536-125X R&D Projects: GA AV ČR IAA1010113 Institutional research plan: CEZ:AV0Z1010914 Keywords : depopulation * electronic relaxation * optical spectra * quantum dots * self-assembled quantum dots * upconversion Subject RIV: BE - Theoretical Physics Impact factor: 3.176, year: 2004
Quantum mechanical simulations of polymers for molecular electronics and photonics
International Nuclear Information System (INIS)
Dupuis, M.; Villar, H.O.; Clementi, E.
1987-01-01
Ab initio quantum mechanical studies can play an important role in obtaining a detailed understanding of the electronic structure of existing materials, and in predicting the properties of new ones. In this article the authors give a general outline of their research activity in two areas dealing with new materials, specifically, conducting polymers and polymers with non-linear optical properties. The authors present the strategy followed for the study of these molecular systems, and an overview of their findings concerning the structure of the prototypical conducting polymer, i.e. pure and doped polyacetylene (PA). They focused attention on vibrational spectra and infrared and Raman intensities. The results of self-consistent-field (SCF) calculations on charged soliton-like molecules are consistent with experimental observation. In particular, they show that the theoretically established accidental mutual exclusion of infrared and Raman bands invalidates the requirement formulated on the basis of the interpretation of experimental data, that defects in PA must have local C/sub 2h/ symmetry. These conclusions are derived from extensive calculations for which supercomputer performance was imperative and carried out on the parallel supercomputer assembled at IBM-Kingston as a loosely coupled array of processors (LCAP). The authors briefly describe this computer system which has proven to be ideally suited to the methods of ab initio quantum chemistry
Terahertz Plasma Waves in Two Dimensional Quantum Electron Gas with Electron Scattering
International Nuclear Information System (INIS)
Zhang Liping
2015-01-01
We investigate the Terahertz (THz) plasma waves in a two-dimensional (2D) electron gas in a nanometer field effect transistor (FET) with quantum effects, the electron scattering, the thermal motion of electrons and electron exchange-correlation. We find that, while the electron scattering, the wave number along y direction and the electron exchange-correlation suppress the radiation power, but the thermal motion of electrons and the quantum effects can amplify the radiation power. The radiation frequency decreases with electron exchange-correlation contributions, but increases with quantum effects, the wave number along y direction and thermal motion of electrons. It is worth mentioning that the electron scattering has scarce influence on the radiation frequency. These properties could be of great help to the realization of practical THz plasma oscillations in nanometer FET. (paper)
Electronic structure of superlattices
International Nuclear Information System (INIS)
Altarelli, M.
1987-01-01
Calculations of electronic states in semiconductor superlattices are briefly reviewed, with emphasis on the envelope-function method and on comparison with experiments. The energy levels in presence of external magnetic fields are discussed and compared to magneto-optical experiments. (author) [pt
FTL Quantum Models of the Photon and the Electron
International Nuclear Information System (INIS)
Gauthier, Richard F.
2007-01-01
A photon is modeled by an uncharged superluminal quantum moving at 1.414c along an open 45-degree helical trajectory with radius R = λ/2π (where λ is the helical pitch or wavelength). A mostly superluminal spatial model of an electron is composed of a charged pointlike quantum circulating at an extremely high frequency ( 2.5 x 1020 hz) in a closed, double-looped hehcal trajectory whose helical pitch is one Compton wavelength h/mc. The quantum has energy and momentum but not rest mass, so its speed is not limited by c. sThe quantum's speed is superluminal 57% of the time and subluminal 43% of the time, passing through c twice in each trajectory cycle. The quantum's maximum speed in the electron's rest frame is 2.515c and its minimum speed is .707c. The electron model's helical trajectory parameters are selected to produce the electron's spin (ℎ/2π)/2 and approximate (without small QED corrections) magnetic moment e(ℎ/2π)/2m (the Bohr magneton μB) as well as its Dirac equation-related 'jittery motion' angular frequency 2mc2/(ℎ/2π), amplitude (ℎ/2π)/2mc and internal speed c. The two possible helicities of the electron model correspond to the electron and the positron. With these models, an electron is like a closed circulating photon. The electron's inertia is proposed to be related to the electron model's circulating internal Compton momentum mc. The internal superluminalily of the photon model, the internal superluminahty/subluminality of the electron model, and the proposed approach to the electron's inertia as ''momentum at rest'' within the electron, could be relevant to possible mechanisms of superluminal communication and transportation
Quantum phase transitions of strongly correlated electron systems
International Nuclear Information System (INIS)
Imada, Masatoshi
1998-01-01
Interacting electrons in solids undergo various quantum phase transitions driven by quantum fluctuations. The quantum transitions take place at zero temperature by changing a parameter to control quantum fluctuations rather than thermal fluctuations. In contrast to classical phase transitions driven by thermal fluctuations, the quantum transitions have many different features where quantum dynamics introduces a source of intrinsic fluctuations tightly connected with spatial correlations and they have been a subject of recent intensive studies as we see below. Interacting electron systems cannot be fully understood without deep analyses of the quantum phase transitions themselves, because they are widely seen and play essential roles in many phenomena. Typical and important examples of the quantum phase transitions include metal-insulator transitions, (2, 3, 4, 5, 6, 7, 8, 9) metal-superconductor transitions, superconductor-insulator transitions, magnetic transitions to antiferromagnetic or ferromagnetic phases in metals as well as in Mott insulators, and charge ordering transitions. Here, we focus on three different types of transitions
Classical behavior of few-electron parabolic quantum dots
International Nuclear Information System (INIS)
Ciftja, O.
2009-01-01
Quantum dots are intricate and fascinating systems to study novel phenomena of great theoretical and practical interest because low dimensionality coupled with the interplay between strong correlations, quantum confinement and magnetic field creates unique conditions for emergence of fundamentally new physics. In this work we consider two-dimensional semiconductor quantum dot systems consisting of few interacting electrons confined in an isotropic parabolic potential. We study the many-electron quantum ground state properties of such systems in presence of a perpendicular magnetic field as the number of electrons is varied using exact numerical diagonalizations and other approaches. The results derived from the calculations of the quantum model are then compared to corresponding results for a classical model of parabolically confined point charges who interact with a Coulomb potential. We find that, for a wide range of parameters and magnetic fields considered in this work, the quantum ground state energy is very close to the classical energy of the most stable classical configuration under the condition that the classical energy is properly adjusted to incorporate the quantum zero point motion.
Energy Technology Data Exchange (ETDEWEB)
Tran, Quoc Tri; Tran, Van Tan, E-mail: tvtan@dthu.edu.vn [Theoretical and Physical Chemistry Division, Dong Thap University, 783-Pham Huu Lau, Cao Lanh City, Ward 6, Dong Thap (Viet Nam)
2016-06-07
The geometrical and electronic structures of ScSi{sub 3}{sup −/0} clusters have been studied with the B3LYP, CCSD(T), and CASPT2 methods. The ground state of the anionic cluster was evaluated to be the {sup 1}A{sub 1} of rhombic η{sup 2}-(Si{sub 3})Sc{sup −} isomer, whereas that of the neutral cluster was computed to be the {sup 2}A{sub 1} of the same isomer. All features in the 266 and 193 nm photoelectron spectra of ScSi{sub 3}{sup −} cluster were interpreted by the one- and two-electron detachments from the {sup 1}A{sub 1} of rhombic η{sup 2}-(Si{sub 3})Sc{sup −} isomer. The Franck-Condon factor simulation results show that the first broad band starting at 1.78 eV in the spectra comprises several vibrational progression peaks of two totally symmetric modes with the corresponding frequencies of 296 and 354 cm{sup −1}.
Identifying Quantum Structures in the Ellsberg Paradox
Aerts, Diederik; Sozzo, Sandro; Tapia, Jocelyn
2014-10-01
Empirical evidence has confirmed that quantum effects occur frequently also outside the microscopic domain, while quantum structures satisfactorily model various situations in several areas of science, including biological, cognitive and social processes. In this paper, we elaborate a quantum mechanical model which faithfully describes the Ellsberg paradox in economics, showing that the mathematical formalism of quantum mechanics is capable to represent the ambiguity present in this kind of situations, because of the presence of contextuality. Then, we analyze the data collected in a concrete experiment we performed on the Ellsberg paradox and work out a complete representation of them in complex Hilbert space. We prove that the presence of quantum structure is genuine, that is, interference and superposition in a complex Hilbert space are really necessary to describe the conceptual situation presented by Ellsberg. Moreover, our approach sheds light on `ambiguity laden' decision processes in economics and decision theory, and allows to deal with different Ellsberg-type generalizations, e.g., the Machina paradox.
Electronic structure of alloys
International Nuclear Information System (INIS)
Ehrenreich, H.; Schwartz, L.M.
1976-01-01
The description of electronic properties of binary substitutional alloys within the single particle approximation is reviewed. Emphasis is placed on a didactic exposition of the equilibrium properties of the transport and magnetic properties of such alloys. Topics covered include: multiple scattering theory; the single band alloy; formal extensions of the theory; the alloy potential; realistic model state densities; the s-d model; and the muffin tin model. 43 figures, 3 tables, 151 references
Measurement of quantum noise in a single-electron transistor near the quantum limit
Xue, W. W.; Ji, Z.; Pan, Feng; Stettenheim, Joel; Blencowe, M. P.; Rimberg, A. J.
2009-09-01
Quantum measurement has challenged physicists for almost a century. Classically, there is no lower bound on the noise a measurement may add. Quantum mechanically, however, measuring a system necessarily perturbs it. When applied to electrical amplifiers, this means that improved sensitivity requires increased backaction that itself contributes noise. The result is a strict quantum limit on added amplifier noise. To approach this limit, a quantum-limited amplifier must possess an ideal balance between sensitivity and backaction; furthermore, its noise must dominate that of subsequent classical amplifiers. Here, we report the first complete and quantitative measurement of the quantum noise of a superconducting single-electron transistor (S-SET) near a double Cooper-pair resonance predicted to have the right combination of sensitivity and backaction. A simultaneous measurement of our S-SET's charge sensitivity indicates that it operates within a factor of 3.6 of the quantum limit, a fourfold improvement over the nearest comparable results.
Electron self-trapping at quantum and classical critical points
Auslender, M.I.; Katsnelson, M.I.
2006-01-01
Using Feynman path integral technique estimations of the ground state energy have been found for a conduction electron interacting with order parameter fluctuations near quantum critical points. In some cases only singular perturbation theory in the coupling constant emerges for the electron ground
Phonon excess heating in electronic relaxation theory in quantum dots
Czech Academy of Sciences Publication Activity Database
Král, Karel; Lin, Ch. Y.
2008-01-01
Roč. 22, č. 20 (2008), s. 3439-3460 ISSN 0217-9792 R&D Projects: GA MŠk ME 866 Institutional research plan: CEZ:AV0Z10100520 Keywords : quantum dots * electron -phonon interaction * electron ic transport Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.558, year: 2008
Quantum electron transfer processes induced by thermo-coherent ...
Indian Academy of Sciences (India)
WINTEC
Thermo-coherent state; electron transfer; quantum rate. 1. Introduction. The study ... two surfaces,16 namely, one electron two-centered exchange problem,7–10 many ... temperature classical regime for the single and the two-mode cases have ...
Quantum-mechanical treatment of an electron undergoing synchrotron radiation.
White, D.
1972-01-01
The problem of an electron moving perpendicular to an intense magnetic field is approached from the framework of quantum mechanics. A numerical solution to the related rate equations describing the probabilities of occupation of the electron's energy states is put forth along with the expected errors involved. The quantum-mechanical approach is found to predict a significant amount of energy broadening with time for an initially monoenergetic electron beam entering a region of an intense magnetic field as long as the product of initial energy and magnetic field is of order 50 MG BeV or larger.
The quantum structure of black holes
International Nuclear Information System (INIS)
Mathur, Samir D
2006-01-01
We give an elementary review of black holes in string theory. We discuss black hole entropy from string microstates and Hawking radiation from these states. We then review the structure of two-charge microstates and explore how 'fractionation' can lead to quantum effects over macroscopic length scales of the order of the horizon radius. (topical review)
Quantum synchrotron spectra from semirelativistic electrons in teragauss magnetic fields
International Nuclear Information System (INIS)
Brainerd, J.J.
1987-01-01
Synchrotron spectra are calculated from quantum electrodynamic transition rates for thermal and power-law electron distributions. It is shown that quantum effects appear in thermal spectra when the photon energy is greater than the electron temperature, and in power-law spectra when the electron energy in units of the electron rest mass times the magnetic field strength in units of the critical field strength is of order unity. These spectra are compared with spectra calculated from the ultrarelativistic approximation for synchrotron emission. It is found that the approximation for the power-law spectra is good, and the approximation for thermal spectra produces the shape of the spectrum accurately but fails to give the correct normalization. Single photon pair creation masks the quantum effects for power-law distributions, so only modifications to thermal spectra are important for gamma-ray bursts. 13 references
Electronics for Piezoelectric Smart Structures
Warkentin, D. J.; Tani, J.
1997-01-01
This paper briefly presents work addressing some of the basic considerations for the electronic components used in smart structures incorporating piezoelectric elements. After general remarks on the application of piezoelectric elements to the problem of structural vibration control, three main topics are described. Work to date on the development of techniques for embedding electronic components within structural parts is presented, followed by a description of the power flow and dissipation requirements of those components. Finally current work on the development of electronic circuits for use in an 'active wall' for acoustic noise is introduced.
International Nuclear Information System (INIS)
Reboredo, F.A.; Hood, R.Q.; Kent, P.C.
2009-01-01
We develop a formalism and present an algorithm for optimization of the trial wave-function used in fixed-node diffusion quantum Monte Carlo (DMC) methods. The formalism is based on the DMC mixed estimator of the ground state probability density. We take advantage of a basic property of the walker configuration distribution generated in a DMC calculation, to (i) project-out a multi-determinant expansion of the fixed node ground state wave function and (ii) to define a cost function that relates the interacting-ground-state-fixed-node and the non-interacting trial wave functions. We show that (a) locally smoothing out the kink of the fixed-node ground-state wave function at the node generates a new trial wave function with better nodal structure and (b) we argue that the noise in the fixed-node wave function resulting from finite sampling plays a beneficial role, allowing the nodes to adjust towards the ones of the exact many-body ground state in a simulated annealing-like process. Based on these principles, we propose a method to improve both single determinant and multi-determinant expansions of the trial wave function. The method can be generalized to other wave function forms such as pfaffians. We test the method in a model system where benchmark configuration interaction calculations can be performed and most components of the Hamiltonian are evaluated analytically. Comparing the DMC calculations with the exact solutions, we find that the trial wave function is systematically improved. The overlap of the optimized trial wave function and the exact ground state converges to 100% even starting from wave functions orthogonal to the exact ground state. Similarly, the DMC total energy and density converges to the exact solutions for the model. In the optimization process we find an optimal non-interacting nodal potential of density-functional-like form whose existence was predicted in a previous publication (Phys. Rev. B 77 245110 (2008)). Tests of the method are
Integrable structures in quantum field theory
International Nuclear Information System (INIS)
Negro, Stefano
2016-01-01
This review was born as notes for a lecture given at the Young Researchers Integrability School (YRIS) school on integrability in Durham, in the summer of 2015. It deals with a beautiful method, developed in the mid-nineties by Bazhanov, Lukyanov and Zamolodchikov and, as such, called BLZ. This method can be interpreted as a field theory version of the quantum inverse scattering, also known as the algebraic Bethe ansatz. Starting with the case of conformal field theories (CFTs) we show how to build the field theory analogues of commuting transfer T matrices and Baxter Q -operators of integrable lattice models. These objects contain the complete information of the integrable structure of the theory, viz. the integrals of motion, and can be used, as we will show, to derive the thermodynamic Bethe ansatz and nonlinear integral equations. This same method can be easily extended to the description of integrable structures of certain particular massive deformations of CFTs; these, in turn, can be described as quantum group reductions of the quantum sine-Gordon model and it is an easy step to include this last theory in the framework of BLZ approach. Finally we show an interesting and surprising connection of the BLZ structures with classical objects emerging from the study of classical integrable models via the inverse scattering transform method. This connection goes under the name of ODE/IM correspondence and we will present it for the specific case of quantum sine-Gordon model only. (topical review)
Logic and algebraic structures in quantum computing
Eskandarian, Ali; Harizanov, Valentina S
2016-01-01
Arising from a special session held at the 2010 North American Annual Meeting of the Association for Symbolic Logic, this volume is an international cross-disciplinary collaboration with contributions from leading experts exploring connections across their respective fields. Themes range from philosophical examination of the foundations of physics and quantum logic, to exploitations of the methods and structures of operator theory, category theory, and knot theory in an effort to gain insight into the fundamental questions in quantum theory and logic. The book will appeal to researchers and students working in related fields, including logicians, mathematicians, computer scientists, and physicists. A brief introduction provides essential background on quantum mechanics and category theory, which, together with a thematic selection of articles, may also serve as the basic material for a graduate course or seminar.
Classical-quantum correspondence in electron-positron pair creation
International Nuclear Information System (INIS)
Chott, N. I.; Su, Q.; Grobe, R.
2007-01-01
We examine the creation of electron-positron pairs in a very strong force field. Using numerical solutions to quantum field theory we calculate the spatial and momentum probability distributions for the created particles. A comparison with classical mechanical phase space calculations suggests that despite the fully relativistic and quantum mechanical nature of the matter creation process, most aspects can be reproduced accurately in terms of classical mechanics
Contactless measurement of alternating current conductance in quantum Hall structures
Energy Technology Data Exchange (ETDEWEB)
Drichko, I. L.; Diakonov, A. M.; Malysh, V. A.; Smirnov, I. Yu.; Ilyinskaya, N. D.; Usikova, A. A. [A. F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Galperin, Y. M. [Department of Physics, University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo (Norway); A. F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Kummer, M.; Känel, H. von [Laboratorium für Festkörperphysik ETH Zürich, CH-8093 Zürich (Switzerland)
2014-10-21
We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods—acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use the fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized p-SiGe/Ge/SiGe heterostructure.
Quantum theory of the electron liquid
National Research Council Canada - National Science Library
Giuliani, Gabriele; Vignale, Giovanni
2005-01-01
... to the Wigner crystal, from the Luttinger liquid to the quantum Hall liquid, are extensively discussed. Both static and time-dependent density functional theory are presented in detail. Although the emphasis is on the development of the basic physical ideas and on a critical discussion of the most useful approximations, the formal derivation of the r...
Quantum correlations and light localization in disordered nanophotonic structures
DEFF Research Database (Denmark)
Smolka, Stephan
This thesis reports results on quantum properties of light in multiple-scattering nano-structured materials. Spatial quantum correlations of photons are demonstrated experimentally that are induced by multiple scattering of squeezed light and of purely quantum origin. By varying the quantum state...
Field emission from finite barrier quantum structures
Energy Technology Data Exchange (ETDEWEB)
Biswas Sett, Shubhasree, E-mail: shubhasree24@gmail.com [The Institution of Engineers - India, 8, Gokhale Road, Kolkata 700 020 (India); Bose, Chayanika, E-mail: chayanikab@ieee.org [Electronics and Telecommunication Engg. Dept., Jadavpur University, Kolkata 700 032 (India)
2014-10-01
We study field emission from various finite barrier quasi-low dimensional structures, taking image force into account. To proceed, we first formulate an expression for field emission current density from a quantum dot. Transverse dimensions of the dot are then increased in turn, to obtain current densities respectively from quantum wire and quantum well with infinite potential energy barriers. To find out field emission from finite barrier structures, the above analysis is followed with a correction in the energy eigen values. In course, variations of field emission current density with strength of the applied electric field and structure dimensions are computed considering n-GaAs and n-GaAs/Al{sub x}Ga{sub 1−x}As as the semiconductor materials. In each case, the current density is found to increase exponentially with the applied field, while it oscillates with structure dimensions. The magnitude of the emission current is less when the image force is not considered, but retains the similar field dependence. In all cases, the field emission from infinite barrier structures exceeds those from respective finite barrier ones.
Physics of Quantum Structures in Photovoltaic Devices
Raffaelle, Ryne P.; Andersen, John D.
2005-01-01
There has been considerable activity recently regarding the possibilities of using various nanostructures and nanomaterials to improve photovoltaic conversion of solar energy. Recent theoretical results indicate that dramatic improvements in device efficiency may be attainable through the use of three-dimensional arrays of zero-dimensional conductors (i.e., quantum dots) in an ordinary p-i-n solar cell structure. Quantum dots and other nanostructured materials may also prove to have some benefits in terms of temperature coefficients and radiation degradation associated with space solar cells. Two-dimensional semiconductor superlattices have already demonstrated some advantages in this regard. It has also recently been demonstrated that semiconducting quantum dots can also be used to improve conversion efficiencies in polymeric thin film solar cells. Improvement in thin film cells utilizing conjugated polymers has also be achieved through the use of one-dimensional quantum structures such as carbon nanotubes. It is believed that carbon nanotubes may contribute to both the disassociation as well as the carrier transport in the conjugated polymers used in certain thin film photovoltaic cells. In this paper we will review the underlying physics governing some of the new photovoltaic nanostructures being pursued, as well as the the current methods being employed to produce III-V, II-VI, and even chalcopyrite-based nanomaterials and nanostructures for solar cells.
Quantum Electron Tunneling in Respiratory Complex I1
Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.
2014-01-01
We have simulated the atomistic details of electronic wiring of all Fe/S clusters in complex I, a key enzyme in the respiratory electron transport chain. The tunneling current theory of many-electron systems is applied to the broken-symmetry (BS) states of the protein at the ZINDO level. One-electron tunneling approximation is found to hold in electron tunneling between the anti-ferromagnetic binuclear and tetranuclear Fe/S clusters with moderate induced polarization of the core electrons. Calculated tunneling energy is about 3 eV higher than Fermi level in the band gap of the protein, which supports that the mechanism of electron transfer is quantum mechanical tunneling, as in the rest of electron transport chain. Resulting electron tunneling pathways consist of up to three key contributing protein residues between neighboring Fe/S clusters. A distinct signature of the wave properties of electrons is observed as quantum interferences when multiple tunneling pathways exist. In N6a-N6b, electron tunnels along different pathways depending on the involved BS states, suggesting possible fluctuations of the tunneling pathways driven by the local protein environment. The calculated distance dependence of the electron transfer rates with internal water molecules included are in good agreement with a reported phenomenological relation. PMID:21495666
Single electron probes of fractional quantum hall states
Venkatachalam, Vivek
electrometer, we measure the local charge of the nu = 5/2 FQH state. An immediate consequence of measuring fractionally quantized conductance plateaus is that the charge of local excitations should be a fraction of e, the charge of an electron. The simplest charge that would be expected at nu = 5/2 would e/2. However, if the charged particles that condense into the nu = 5/2 FQH state are paired, the expected local charge becomes e/4. By watching these local charges being added to compressible puddles at nu = 5/2 and nu = 7/3, we find that the local charge at nu = 5/2 is indeed e/4, indicating that objects of charge e are pairing to form the ground state of the system. This has implications for the future possibility of detecting non-Abelian braiding statistics in this state, and is described in detail in Chapter 2. By further monitoring how eagerly these e/4 particles enter puddles as we increase the temperature, we can attempt to identify the presence of some excess entropy related to an unconventional degeneracy of their ground state. Such an entropy would be expected if the nu = 5/2 state exhibited non-Abelian braiding statistics. Progress on these experiments and prospects for building a quantum computer are presented in Chapter 3. Next, by operating the SET as a thermometer, we monitor heat flow along the compressible edge and through the bulk of IQH and FQH states. As an edge is heated and charge on that edge is swept downstream by the external magnetic field, we expect that charge to carry the injected energy in the same downstream direction. However, for certain FQH states, this is not the case. By heating an edge with a quantum point contact (QPC) and monitoring the heat transported upstream and downstream, we find that heat can be transported upstream when the edge contains structure related to nu = 2/3 FQH physics. Surprisingly, this can be present even when the bulk is in a conventional insulating (IQH) state. Additionally, we unexpectedly find that the nu = 1 bulk
Single electron-spin memory with a semiconductor quantum dot
International Nuclear Information System (INIS)
Young, Robert J; Dewhurst, Samuel J; Stevenson, R Mark; Atkinson, Paola; Bennett, Anthony J; Ward, Martin B; Cooper, Ken; Ritchie, David A; Shields, Andrew J
2007-01-01
We show storage of the circular polarization of an optical field, transferring it to the spin-state of an individual electron confined in a single semiconductor quantum dot. The state is subsequently read out through the electronically-triggered emission of a single photon. The emitted photon shares the same polarization as the initial pulse but has a different energy, making the transfer of quantum information between different physical systems possible. With an applied magnetic field of 2 T, spin memory is preserved for at least 1000 times more than the exciton's radiative lifetime
Electronic structure of defects in semiconductor heterojunctions
International Nuclear Information System (INIS)
Haussy, Bernard; Ganghoffer, Jean Francois
2002-01-01
Full text.heterojunctions and semiconductors and superlattices are well known and well used by people interested in optoelectronics communications. Components based on the use of heterojunctions are interesting for confinement of light and increase of quantum efficiency. An heterojunction is the contact zone between two different semiconductors, for example GaAs and Ga 1-x Al x As. Superlattices are a succession of heterojunctions (up to 10 or 20). These systems have been the subjects of many experiments ao analyse the contact between semiconductors. They also have been theoretically studied by different types of approach. The main result of those studies is the prediciton of band discontinuities. Defects in heterojunctions are real traps for charge carriers; they can affect the efficiency of the component decreasing the currents and the fluxes in it. the knowledge of their electronic structure is important, a great density of defects deeply modifies the electronic structure of the whole material creating real new bands of energy in the band structure of the component. in the first part of this work, we will describe the heterostructure and the defect in terms of quantum wells and discrete levels. This approach allows us to show the role of the width of the quantum well describing the structure but induces specific behaviours due to the one dimensional modelling. Then a perturbative treatment is proposed using the Green's functions formalism. We build atomic chains with different types of atoms featuring the heterostructure and the defect. Densities of states of a structure with a defect and levels associated to the defect are obtained. Results are comparable with the free electrons work, but the modelling do not induce problems due to a one dimensional approach. To extend our modelling, a three dimensions approach, based on a cavity model, is investigated. The influence of the defect, - of hydrogenoid type - introduced in the structure, is described by a cavity
Computation of quantum electron transport with local current conservation using quantum trajectories
International Nuclear Information System (INIS)
Alarcón, A; Oriols, X
2009-01-01
A recent proposal for modeling time-dependent quantum electron transport with Coulomb and exchange correlations using quantum (Bohm) trajectories (Oriols 2007 Phys. Rev. Lett. 98 066803) is extended towards the computation of the total (particle plus displacement) current in mesoscopic devices. In particular, two different methods for the practical computation of the total current are compared. The first method computes the particle and the displacement currents from the rate of Bohm particles crossing a particular surface and the time-dependent variations of the electric field there. The second method uses the Ramo–Shockley theorem to compute the total current on that surface from the knowledge of the Bohm particle dynamics in a 3D volume and the time-dependent variations of the electric field on the boundaries of that volume. From a computational point of view, it is shown that both methods achieve local current conservation, but the second is preferred because it is free from 'spurious' peaks. A numerical example, a Bohm trajectory crossing a double-barrier tunneling structure, is presented, supporting the conclusions
Projected quasiparticle theory for molecular electronic structure
Scuseria, Gustavo E.; Jiménez-Hoyos, Carlos A.; Henderson, Thomas M.; Samanta, Kousik; Ellis, Jason K.
2011-09-01
We derive and implement symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations and apply them to the molecular electronic structure problem. All symmetries (particle number, spin, spatial, and complex conjugation) are deliberately broken and restored in a self-consistent variation-after-projection approach. We show that the resulting method yields a comprehensive black-box treatment of static correlations with effective one-electron (mean-field) computational cost. The ensuing wave function is of multireference character and permeates the entire Hilbert space of the problem. The energy expression is different from regular HFB theory but remains a functional of an independent quasiparticle density matrix. All reduced density matrices are expressible as an integration of transition density matrices over a gauge grid. We present several proof-of-principle examples demonstrating the compelling power of projected quasiparticle theory for quantum chemistry.
Electronic structure of silicon superlattices
International Nuclear Information System (INIS)
Krishnamurthy, S.; Moriarty, J.A.
1984-01-01
Utilizing a new complex-band-structure technique, the electronic structure of model Si-Si/sub 1-x/Ge/sub x/ and MOS superlattices has been obtained over a wide range of layer thickness d (11 less than or equal to d less than or equal to 110 A). For d greater than or equal to 44 A, it is found that these systems exhibit a direct fundamental band gap. Further calculations of band-edge effective masses and impurity scattering rates suggest the possibility of a band-structure-driven enhancement in electron mobility over bulk silicon
Entanglement transfer from electrons to photons in quantum dots: an open quantum system approach
International Nuclear Information System (INIS)
Budich, Jan C; Trauzettel, Bjoern
2010-01-01
We investigate entanglement transfer from a system of two spin-entangled electron-hole pairs, each placed in a separate single mode cavity, to the photons emitted due to cavity leakage. Dipole selection rules and a splitting between the light hole and the heavy hole subbands are the crucial ingredients establishing a one-to-one correspondence between electron spins and circular photon polarizations. To account for the measurement of the photons as well as dephasing effects, we choose a stochastic Schroedinger equation and a conditional master equation approach, respectively. The influence of interactions with the environment as well as asymmetries in the coherent couplings on the photon entanglement is analysed for two concrete measurement schemes. The first one is designed to violate the Clauser-Horne-Shimony-Holt (CHSH) inequality, while the second one employs the visibility of interference fringes to prove the entanglement of the photons. Because of the spatial separation of the entangled electronic system over two quantum dots, a successful verification of entangled photons emitted by this system would imply the detection of nonlocal spin entanglement of massive particles in a solid state structure.
Atomistic theory of excitonic fine structure in InAs/InP nanowire quantum dot molecules
Świderski, M.; Zieliński, M.
2017-03-01
Nanowire quantum dots have peculiar electronic and optical properties. In this work we use atomistic tight binding to study excitonic spectra of artificial molecules formed by a double nanowire quantum dot. We demonstrate a key role of atomistic symmetry and nanowire substrate orientation rather than cylindrical shape symmetry of a nanowire and a molecule. In particular for [001 ] nanowire orientation we observe a nonvanishing bright exciton splitting for a quasimolecule formed by two cylindrical quantum dots of different heights. This effect is due to interdot coupling that effectively reduces the overall symmetry, whereas single uncoupled [001 ] quantum dots have zero fine structure splitting. We found that the same double quantum dot system grown on [111 ] nanowire reveals no excitonic fine structure for all considered quantum dot distances and individual quantum dot heights. Further we demonstrate a pronounced, by several orders of magnitude, increase of the dark exciton optical activity in a quantum dot molecule as compared to a single quantum dot. For [111 ] systems we also show spontaneous localization of single particle states in one of nominally identical quantum dots forming a molecule, which is mediated by strain and origins from the lack of the vertical inversion symmetry in [111 ] nanostructures of overall C3 v symmetry. Finally, we study lowering of symmetry due to alloy randomness that triggers nonzero excitonic fine structure and the dark exciton optical activity in realistic nanowire quantum dot molecules of intermixed composition.
Controlling electron quantum dot qubits by spin-orbit interactions
International Nuclear Information System (INIS)
Stano, P.
2007-01-01
Single electron confined in a quantum dot is studied. A special emphasis is laid on the spin properties and the influence of spin-orbit interactions on the system. The study is motivated by a perspective exploitation of the spin of the confined electron as a qubit, a basic building block of in a foreseen quantum computer. The electron is described using the single band effective mass approximation, with parameters typical for a lateral electrostatically defined quantum dot in a GaAs/AlGaAs heterostructure. The stemming data for the analysis are obtained by numerical methods of exact diagonalization, however, all important conclusions are explained analytically. The work focuses on three main areas -- electron spectrum, phonon induced relaxation and electrically and magnetically induced Rabi oscillations. It is shown, how spin-orbit interactions influence the energy spectrum, cause finite spin relaxation and allow for all-electrical manipulation of the spin qubit. Among the main results is the discovery of easy passages, where the spin relaxation is unusually slow and the qubit is protected against parasitic electrical fields connected with manipulation by resonant electromagnetic fields. The results provide direct guide for manufacturing quantum dots with much improved properties, suitable for realizing single electron spin qubits. (orig.)
Controlling electron quantum dot qubits by spin-orbit interactions
Energy Technology Data Exchange (ETDEWEB)
Stano, P.
2007-01-15
Single electron confined in a quantum dot is studied. A special emphasis is laid on the spin properties and the influence of spin-orbit interactions on the system. The study is motivated by a perspective exploitation of the spin of the confined electron as a qubit, a basic building block of in a foreseen quantum computer. The electron is described using the single band effective mass approximation, with parameters typical for a lateral electrostatically defined quantum dot in a GaAs/AlGaAs heterostructure. The stemming data for the analysis are obtained by numerical methods of exact diagonalization, however, all important conclusions are explained analytically. The work focuses on three main areas -- electron spectrum, phonon induced relaxation and electrically and magnetically induced Rabi oscillations. It is shown, how spin-orbit interactions influence the energy spectrum, cause finite spin relaxation and allow for all-electrical manipulation of the spin qubit. Among the main results is the discovery of easy passages, where the spin relaxation is unusually slow and the qubit is protected against parasitic electrical fields connected with manipulation by resonant electromagnetic fields. The results provide direct guide for manufacturing quantum dots with much improved properties, suitable for realizing single electron spin qubits. (orig.)
Complex dynamics in planar two-electron quantum dots
International Nuclear Information System (INIS)
Schroeter, Sebastian Josef Arthur
2013-01-01
Quantum dots play an important role in a wide range of recent experimental and technological developments. In particular they are promising candidates for realisations of quantum bits and further applications in quantum information theory. The harmonically confined Hooke's atom model is experimentally verified and separates in centre-of-mass and relative coordinates. Findings that are contradictory to this separability call for an extension of the model, in particular changing the confinement potential. In order to study effects of an anharmonic confinement potential on spectral properties of planar two-electron quantum dots a sophisticated numerical approach is developed. Comparison between the Helium atom, Hooke's atom and an anharmonic potential model are undertaken in order to improve the description of quantum dots. Classical and quantum features of complexity and chaos are investigated and used to characterise the dynamics of the system to be mixed regular-chaotic. Influence of decoherence can be described by quantum fidelity, which measures the effect of a perturbation on the time evolution. The quantum fidelity of eigenstates of the system depends strongly on the properties of the perturbation. Several methods for solving the time-dependent Schrödinger equation are implemented and a high level of accuracy for long time evolutions is achieved. The concept of offset entanglement, the entanglement of harmonic models in the noninteracting limit, is introduced. This concept explains different questions raised in the literature for harmonic quantum dot models, recently. It shows that only in the groundstate the electrons are not entangled in the fermionic sense. The applicability, validity, and origin of Hund's first rule in general quantum dot models is further addressed. In fact Hund's first rule is only applicable, and in this case also valid, for one pair of singlet and triplet states in Hooke's atom. For more realistic models of two-electron quantum dots an
Complex dynamics in planar two-electron quantum dots
Energy Technology Data Exchange (ETDEWEB)
Schroeter, Sebastian Josef Arthur
2013-06-25
Quantum dots play an important role in a wide range of recent experimental and technological developments. In particular they are promising candidates for realisations of quantum bits and further applications in quantum information theory. The harmonically confined Hooke's atom model is experimentally verified and separates in centre-of-mass and relative coordinates. Findings that are contradictory to this separability call for an extension of the model, in particular changing the confinement potential. In order to study effects of an anharmonic confinement potential on spectral properties of planar two-electron quantum dots a sophisticated numerical approach is developed. Comparison between the Helium atom, Hooke's atom and an anharmonic potential model are undertaken in order to improve the description of quantum dots. Classical and quantum features of complexity and chaos are investigated and used to characterise the dynamics of the system to be mixed regular-chaotic. Influence of decoherence can be described by quantum fidelity, which measures the effect of a perturbation on the time evolution. The quantum fidelity of eigenstates of the system depends strongly on the properties of the perturbation. Several methods for solving the time-dependent Schrödinger equation are implemented and a high level of accuracy for long time evolutions is achieved. The concept of offset entanglement, the entanglement of harmonic models in the noninteracting limit, is introduced. This concept explains different questions raised in the literature for harmonic quantum dot models, recently. It shows that only in the groundstate the electrons are not entangled in the fermionic sense. The applicability, validity, and origin of Hund's first rule in general quantum dot models is further addressed. In fact Hund's first rule is only applicable, and in this case also valid, for one pair of singlet and triplet states in Hooke's atom. For more realistic models of two-electron
Thermodynamics and the structure of quantum theory
International Nuclear Information System (INIS)
Krumm, Marius; Müller, Markus P; Barnum, Howard; Barrett, Jonathan
2017-01-01
Despite its enormous empirical success, the formalism of quantum theory still raises fundamental questions: why is nature described in terms of complex Hilbert spaces, and what modifications of it could we reasonably expect to find in some regimes of physics? Here we address these questions by studying how compatibility with thermodynamics constrains the structure of quantum theory. We employ two postulates that any probabilistic theory with reasonable thermodynamic behaviour should arguably satisfy. In the framework of generalised probabilistic theories, we show that these postulates already imply important aspects of quantum theory, like self-duality and analogues of projective measurements, subspaces and eigenvalues. However, they may still admit a class of theories beyond quantum mechanics. Using a thought experiment by von Neumann, we show that these theories admit a consistent thermodynamic notion of entropy, and prove that the second law holds for projective measurements and mixing procedures. Furthermore, we study additional entropy-like quantities based on measurement probabilities and convex decomposition probabilities, and uncover a relation between one of these quantities and Sorkin’s notion of higher-order interference. (paper)
The structure of states and maps in quantum theory
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 73; Issue 3. The structure of states and maps in quantum theory. Sudhavathani Simon S P ... The structure of statistical state spaces in the classical and quantum theories are compared in an interesting and novel manner. Quantum state spaces and maps on them ...
Quantum waveguide theory of a fractal structure
International Nuclear Information System (INIS)
Lin Zhiping; Hou Zhilin; Liu Youyan
2007-01-01
The electronic transport properties of fractal quantum waveguide networks in the presence of a magnetic field are studied. A Generalized Eigen-function Method (GEM) is used to calculate the transmission and reflection coefficients of the studied systems unto the fourth generation Sierpinski fractal network with node number N=123. The relationship among the transmission coefficient T, magnetic flux Φ and wave vector k is investigated in detail. The numerical results are shown by the three-dimensional plots and contour maps. Some resonant-transmission features and the symmetry of the transmission coefficient T to flux Φ are observed and discussed, and compared with the results of the tight-binding model
Electronic properties of asymmetrical quantum dots dressed by laser field
Energy Technology Data Exchange (ETDEWEB)
Kibis, O.V. [Department of Applied and Theoretical Physics, Novosibirsk State Technical University, Karl Marx Avenue 20, 630092 Novosibirsk (Russian Federation); Slepyan, G.Ya.; Maksimenko, S.A. [Institute for Nuclear Problems, Belarus State University, Bobruyskaya St. 11, 220050 Minsk (Belarus); Hoffmann, A. [Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)
2012-05-15
In the present paper, we demonstrate theoretically that the strong non-resonant interaction between asymmetrical quantum dots (QDs) and a laser field results in harmonic oscillations of their band gap. It is shown that such oscillations change the spectrum of elementary electron excitations in QDs: in the absence of the laser pumping there is only one resonant electron frequency, but QDs dressed by the laser field have a set of electron resonant frequencies. One expects that this modification of elementary electron excitations in QDs can be observable in optical experiments. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
From quantum transitions to electronic motions
Krausz, Ferenc
2017-01-01
Laser spectroscopy and chromoscopy permit precision measurement of quantum transitions and captures atomic-scale dynamics, respectively. Frequency- and time-domain metrology ranks among the supreme laser disciplines in fundamental science. For decades, these fields evolved independently, without interaction and synergy between them. This has changed profoundly with controlling the position of the equidistant frequency spikes of a mode-locked laser oscillator. By the self-referencing technique invented by Theodor Hänsch, the comb can be coherently linked to microwaves and used for precision measurements of energy differences between quantum states. The resultant optical frequency synthesis has revolutionized precision spectroscopy. Locking the comb lines to the resonator round-trip frequency by the same approach has given rise to laser pulses with controlled field oscillations. This article reviews, from a personal perspective, how the bridge between frequency- and time-resolved metrology emerged on the turn of the millennium and how synthesized several-cycle laser fields have been instrumental in establishing the basic tools and techniques for attosecond science.
Electron energy spectrum in core-shell elliptic quantum wire
Directory of Open Access Journals (Sweden)
V.Holovatsky
2007-01-01
Full Text Available The electron energy spectrum in core-shell elliptic quantum wire and elliptic semiconductor nanotubes are investigated within the effective mass approximation. The solution of Schrodinger equation based on the Mathieu functions is obtained in elliptic coordinates. The dependencies of the electron size quantization spectrum on the size and shape of the core-shell nanowire and nanotube are calculated. It is shown that the ellipticity of a quantum wire leads to break of degeneration of quasiparticle energy spectrum. The dependences of the energy of odd and even electron states on the ratio between semiaxes are of a nonmonotonous character. The anticrosing effects are observed at the dependencies of electron energy spectrum on the transversal size of the core-shell nanowire.
Henderson, Gregory Newell
Semiconductor device dimensions are rapidly approaching a fundamental limit where drift-diffusion equations and the depletion approximation are no longer valid. In this regime, quantum effects can dominate device response. To increase further device density and speed, new devices must be designed that use these phenomena to positive advantage. In addition, quantum effects provide opportunities for a new class of devices which can perform functions previously unattainable with "conventional" semiconductor devices. This thesis has described research in the analysis of electron wave effects in semiconductors and the development of methods for the design, fabrication, and characterization of quantum devices based on these effects. First, an exact set of quantitative analogies are presented which allow the use of well understood optical design and analysis tools for the development of electron wave semiconductor devices. Motivated by these analogies, methods are presented for modeling electron wave grating diffraction using both an exact rigorous coupled-wave analysis and approximate analyses which are useful for grating design. Example electron wave grating switch and multiplexer designs are presented. In analogy to thin-film optics, the design and analysis of electron wave Fabry-Perot interference filters are also discussed. An innovative technique has been developed for testing these (and other) electron wave structures using Ballistic Electron Emission Microscopy (BEEM). This technique uses a liquid-helium temperature scanning tunneling microscope (STM) to perform spectroscopy of the electron transmittance as a function of electron energy. Experimental results show that BEEM can resolve even weak quantum effects, such as the reflectivity of a single interface between materials. Finally, methods are discussed for incorporating asymmetric electron wave Fabry-Perot filters into optoelectronic devices. Theoretical and experimental results show that such structures could
Imaging electron wave functions inside open quantum rings.
Martins, F; Hackens, B; Pala, M G; Ouisse, T; Sellier, H; Wallart, X; Bollaert, S; Cappy, A; Chevrier, J; Bayot, V; Huant, S
2007-09-28
Combining scanning gate microscopy (SGM) experiments and simulations, we demonstrate low temperature imaging of the electron probability density |Psi|(2)(x,y) in embedded mesoscopic quantum rings. The tip-induced conductance modulations share the same temperature dependence as the Aharonov-Bohm effect, indicating that they originate from electron wave function interferences. Simulations of both |Psi|(2)(x,y) and SGM conductance maps reproduce the main experimental observations and link fringes in SGM images to |Psi|(2)(x,y).
Electronic properties of excited states in single InAs quantum dots
International Nuclear Information System (INIS)
Warming, Till
2009-01-01
The application of quantum-mechanical effects in semiconductor nanostructures enables the realization of novel opto-electronic devices. Examples are given by single-photon emitters and emitters of entangled photon pairs, both being essential for quantum cryptography, or for qubit systems as needed for quantum computing. InAs/GaAs quantum dots are one of the most promising candidates for such applications. A detailed knowledge of the electronic properties of quantum dots is a prerequisite for this development. The aim of this work is an experimental access to the detailed electronic structure of the excited states in single InAs/GaAs quantum dots including few-particle effects and in particular exchange interaction. The experimental approach is micro photoluminescence excitation spectroscopy (μPLE). One of the main difficulties using μPLE to probe single QDs is the unambiguous assignment of the observed resonances in the spectrum to specific transitions. By comparing micro photoluminescence (μPL) and μPLE spectra, the identification of the main resonances becomes possible. The key is given by the fine structure of the hot trion. Excitation spectroscopy on single charged QDs enables for the first time the complete observation of a non-trivial fine structure of an excitonic complex in a QD, the hot trion. Modelling based on eight-band k.p theory in combination with a configuration interaction scheme is in excellent agreement. Therewith the simulation also enables realistic predictions on the fine structure of the ground-state exciton which is of large importance for single quantum dot devices. Theory concludes from the observed transitions that the structural symmetry of the QDs is broken. Micro photoluminescence excitation spectroscopy combined with resonantly excited micro photoluminescence enables an optical access to the single particle states of the hole without the influence of few-particle coulomb interactions. Based on this knowledge the exciton binding
Electron Energy Level Statistics in Graphene Quantum Dots
De Raedt, H.; Katsnellson, M. I.; Katsnelson, M.I.
2008-01-01
Motivated by recent experimental observations of size quantization of electron energy levels in graphene quantum dots [7] we investigate the level statistics in the simplest tight-binding model for different dot shapes by computer simulation. The results are in a reasonable agreement with the
Hot electrons in superlattices: quantum transport versus Boltzmann equation
DEFF Research Database (Denmark)
Wacker, Andreas; Jauho, Antti-Pekka; Rott, S.
1999-01-01
A self-consistent solution of the transport equation is presented for semiconductor superlattices within different approaches: (i) a full quantum transport model based on nonequilibrium Green functions, (ii) the semiclassical Boltzmann equation for electrons in a miniband, and (iii) Boltzmann...
Quantum noise in a terahertz hot electron bolometer mixer
Zhang, W.; Khosropanah, P.; Gao, J. R.; Kollberg, E. L.; Yngvesson, K. S.; Bansal, T.; Barends, R.; Klapwijk, T. M.
2010-01-01
We have measured the noise temperature of a single, sensitive superconducting NbN hot electron bolometer (HEB) mixer in a frequency range from 1.6 to 5.3 THz, using a setup with all the key components in vacuum. By analyzing the measured receiver noise temperature using a quantum noise (QN) model
Stark-like electron transfer between quantum wells
International Nuclear Information System (INIS)
Dubovis, S.A.; Voronko, A.N.; Basharov, A.M.
2008-01-01
The Stark-like mechanism of electron transfer between two energy subband localized in remote quantum wells is examined theoretically. Estimations of major parameters of the problem in case of delta-function-wells model are adduced. Schematic model allowing experimental study of Stark-like transfer is proposed
The quantum mechanical analysis of the free electron laser
International Nuclear Information System (INIS)
Dattoli, G.; Renieri, A.
1985-01-01
A quantum analysis of the Free Electron Laser is presented. The theory is developed both in single and longitudinal multimode regimes. Finally a self-consistent procedure to study the growth of the laser signal from the vacuum to the macroscopic level is presented
Applied nonlinear optics in the journal 'Quantum Electronics'
International Nuclear Information System (INIS)
Grechin, Sergei G; Dmitriev, Valentin G; Chirkin, Anatolii S
2011-01-01
A brief historical review of the experimental and theoretical works on nonlinear optical frequency conversion (generation of harmonics, up- and down-conversion, parametric oscillation), which have been published in the journal 'Quantum Electronics' for the last 40 years, is presented.
Distribution of tunnelling times for quantum electron transport
International Nuclear Information System (INIS)
Rudge, Samuel L.; Kosov, Daniel S.
2016-01-01
In electron transport, the tunnelling time is the time taken for an electron to tunnel out of a system after it has tunnelled in. We define the tunnelling time distribution for quantum processes in a dissipative environment and develop a practical approach for calculating it, where the environment is described by the general Markovian master equation. We illustrate the theory by using the rate equation to compute the tunnelling time distribution for electron transport through a molecular junction. The tunnelling time distribution is exponential, which indicates that Markovian quantum tunnelling is a Poissonian statistical process. The tunnelling time distribution is used not only to study the quantum statistics of tunnelling along the average electric current but also to analyse extreme quantum events where an electron jumps against the applied voltage bias. The average tunnelling time shows distinctly different temperature dependence for p- and n-type molecular junctions and therefore provides a sensitive tool to probe the alignment of molecular orbitals relative to the electrode Fermi energy.
Quantum simulations of small electron-hole complexes
International Nuclear Information System (INIS)
Lee, M.A.; Kalia, R.K.; Vashishta, P.D.
1984-09-01
The Green's Function Monte Carlo method is applied to the calculation of the binding energies of electron-hole complexes in semiconductors. The quantum simulation method allows the unambiguous determination of the ground state energy and the effects of band anisotropy on the binding energy. 22 refs., 1 fig
Mathematical Structure in Quantum Systems and applications
International Nuclear Information System (INIS)
Cavero-Pelaez, I.; Clemente-Gallardo, J.; Marmo, G.; Muñoz--Castañeda, J.M.
2013-01-01
This volume contains most of the contributions presented at the Conference 'Mathematical Structures in Quantum Systems and applications', held at the Centro de Ciencias de Benasque 'Pedro Pascual', Benasque (Spain) from 8-14 July 2012. The aim of the Conference was to bring together physicists working on different applications of mathematical methods to quantum systems in order to enable the different communities to become acquainted with other approaches and techniques that could be used in their own fields of expertise. We concentrated on three main subjects: – the geometrical description of Quantum Mechanics; – the Casimir effect and its mathematical implications; – the Quantum Zeno Effect and Open system dynamics. Each of these topics had a set of general lectures, aimed at presenting a global view on the subject, and other more technical seminars. We would like to thank all participants for their contribution to creating a wonderful scientific atmosphere during the Conference. We would especially like to thank the speakers and the authors of the papers contained in this volume, the members of the Scientific Committee for their guidance and support and, of course, the referees for their generous work. Special thanks are also due to the staff of the Centro de Ciencias de Benasque 'Pedro Pascual' who made this successful meeting possible. On behalf of the organising committee and the authors we would also like to acknowledge the partial support provided by the ESF-CASIMIR network ('New Trends and Applications of the Casimir Effect'), the QUITEMAD research Project (“Quantum technologies at Madrid”, Ref. Comunidad de Madrid P2009/ESP-1594), the MICINN Project (MTM2011-16027-E) and the Government from Arag´on (DGA) (DGA, Department of Industry and Innovation and the European Social Fund, DGA-Grant 24/1) who made the Conference and this Proceedings volume possible.
Empirical pseudo-potential studies on electronic structure
Indian Academy of Sciences (India)
Theoretical investigations of electronic structure of quantum dots is of current interest in nanophase materials. Empirical theories such as effective mass approximation, tight binding methods and empirical pseudo-potential method are capable of explaining the experimentally observed optical properties. We employ the ...
Energy Technology Data Exchange (ETDEWEB)
Gladysiewicz, M.; Wartak, M. S. [Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5 (Canada); Kudrawiec, R. [Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)
2015-08-07
The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ≤ 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n < 5 × 10{sup 18 }cm{sup −3}, material gain spectra calculated within 8- and 14-band kp Hamiltonians are similar. It means that the 8-band kp model can be used to calculate material gain in dilute bismides QWs. Therefore, it can be applied to analyze QWs containing new dilute bismides for which the VBAC parameters are unknown. Thus, the energy gap and electron effective mass for Bi-containing materials are used instead of VBAC parameters. The electronic band structure and material gain have been calculated for 8 nm wide GaInAsBi QWs on GaAs and InP substrates with various compositions. In these QWs, Bi concentration was varied from 0% to 5% and indium concentration was tuned in order to keep the same compressive strain (ε = 2%) in QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 μm. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 μm and 1.55 μm) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga{sub 0.47}In{sub 0.53}As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 μm, i.e., at the wavelengths that are not available in current InP-based lasers.
Electron-electron scattering and mobilities in semiconductors and quantum wells
International Nuclear Information System (INIS)
Lyo, S.K.
1986-01-01
The effect of electron-electron scattering on the mobility in semiconductors and semiconductor quantum wells is examined. A general exact formula is derived for the mobility, when the electron-electron collision rate is much faster than other scattering rates such as those by ionized impurities and phonons. In this limit, the transport relaxation rate is independent of the carrier's energy and contributions to the inverse mobility from individual scattering mechanism add up. The mobility becomes significantly reduced from its value in the absence of electron-electron scattering. When the collision rates are not necessarily dominated by electron-electron scattering, the mobility is calculated by the Kohler-Sondheimer variational method in the presence of ionized-impurity scattering and acoustic-phonon scattering in a nondegenerate two-dimensional quantum well
Quantum state propagation in linear photonic bandgap structures
International Nuclear Information System (INIS)
Severini, S; Tricca, D; Sibilia, C; Bertolotti, M; Perina, Jan
2004-01-01
In this paper we investigate the propagation of a generic quantum state in a corrugated waveguide, which reproduces a photonic bandgap structure. We find the conditions that assure the outcoming state to preserve the quantum properties of the incoming state. Then, focusing on a particular quantum state (realized by two counter-propagating coherent states), we study the possibility of preserving the quantum properties of this particular double coherent state even in the presence of absorption phenomena during propagation in the structure
Parallel magnetotransport in multiple quantum well structures
International Nuclear Information System (INIS)
Sheregii, E.M.; Ploch, D.; Marchewka, M.; Tomaka, G.; Kolek, A.; Stadler, A.; Mleczko, K.; Strupinski, W.; Jasik, A.; Jakiela, R.
2004-01-01
The results of investigations of parallel magnetotransport in AlGaAs/GaAs and InGaAs/InAlAs/InP multiple quantum wells structures (MQW's) are presented in this paper. The MQW's were obtained by metalorganic vapour phase epitaxy with different shapes of QW, numbers of QW and levels of doping. The magnetotransport measurements were performed in wide region of temperatures (0.5-300 K) and at high magnetic fields up to 30 T (B is perpendicular and current is parallel to the plane of the QW). Three types of observed effects are analyzed: quantum Hall effect and Shubnikov-de Haas oscillations at low temperatures (0.5-6 K) as well as magnetophonon resonance at higher temperatures (77-300 K)
Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin
He, Yu; He, Yu-Ming; Wei, Yu-Jia; Jiang, Xiao; Chen, Kai; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Höfling, Sven
2017-08-01
Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of 0.796 ±0.020 . Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path, and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 m. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axes on the Bloch sphere, with an average fidelity of 78.5%.
Electron-longitudinal-acoustic-phonon scattering in double-quantum-dot based quantum gates
International Nuclear Information System (INIS)
Zhao Peiji; Woolard, Dwight L.
2008-01-01
We propose a nanostructure design which can significantly suppress longitudinal-acoustic-phonon-electron scattering in double-quantum-dot based quantum gates for quantum computing. The calculated relaxation rates vs. bias voltage exhibit a double-peak feature with a minimum approaching 10 5 s -1 . In this matter, the energy conservation law prohibits scattering contributions from phonons with large momenta; furthermore, increasing the barrier height between the double quantum dots reduces coupling strength between the dots. Hence, the joint action of the energy conservation law and the decoupling greatly reduces the scattering rates. The degrading effects of temperatures can be reduced simply by increasing the height of the barrier between the dots
Electronic structure and correlation effects in actinides
International Nuclear Information System (INIS)
Albers, R.C.
1998-01-01
This report consists of the vugraphs given at a conference on electronic structure. Topics discussed are electronic structure, f-bonding, crystal structure, and crystal structure stability of the actinides and how they are inter-related
Wang, Hongyue; Lhuillier, Emmanuel; Yu, Qian; Mottaghizadeh, Alireza; Ulysse, Christian; Zimmers, Alexandre; Dubertret, Benoit; Aubin, Herve
2015-03-01
We present a tunnel spectroscopy study of the electronic spectrum of single PbS Quantum Dots (QDs) trapped between nanometer-spaced electrodes, measured at low temperature T=5 K. The carrier filling of the QD can be controlled either by the drain voltage in the shell filling regime or by a gate voltage. In the empty QD, the tunnel spectrum presents the expected signature of the 8x degenerated excited levels. In the drain controlled shell filling regime, the levels degeneracies are lifted by the global electrostatic Coulomb energy of the QD; in the gate controlled shell filling regime, the levels degeneracies are lifted by the intra-Coulomb interactions. In the charged quantum dot, electron-phonons interactions lead to the apparition of Franck-Condon side bands on the single excited levels and possibly Franck Condon blockade at low energy. The sharpening of excited levels at higher gate voltage suggests that the magnitude of electron-phonon interactions is decreased upon increasing the electron filling in the quantum dot. This work was supported by the French ANR Grants 10-BLAN-0409-01, 09-BLAN-0388-01, by the Region Ile-de-France in the framework of DIM Nano-K and by China Scholarship Council.
Ballistic transport and electronic structure
Schep, Kees M.; Kelly, Paul J.; Bauer, Gerrit E.W.
1998-01-01
The role of the electronic structure in determining the transport properties of ballistic point contacts is studied. The conductance in the ballistic regime is related to simple geometrical projections of the Fermi surface. The essential physics is first clarified for simple models. For real
The Electronic Structure of Calcium
DEFF Research Database (Denmark)
Jan, J.-P.; Skriver, Hans Lomholt
1981-01-01
The electronic structure of calcium under pressure is re-examined by means of self-consistent energy band calculations based on the local density approximation and using the linear muffin-tin orbitals (LMTO) method with corrections to the atomic sphere approximation included. At zero pressure...
Quantum effects in biological electron transfer
Czech Academy of Sciences Publication Activity Database
de la Lande, A.; Babcock, N. S.; Řezáč, Jan; Levy, B.; Sanders, B. C.; Salahub, D.
2012-01-01
Roč. 14, č. 17 (2012), s. 5902-5918 ISSN 1463-9076 Institutional research plan: CEZ:AV0Z40550506 Keywords : electron transfer * tunnelling * decoherence * semi-classical molecular dynamics * density functional theory Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.829, year: 2012
Electronic structure of metal clusters
International Nuclear Information System (INIS)
Wertheim, G.K.
1989-01-01
Photoemission spectra of valence electrons in metal clusters, together with threshold ionization potential measurements, provide a coherent picture of the development of the electronic structure from the isolated atom to the large metallic cluster. An insulator-metal transition occurs at an intermediate cluster size, which serves to define the boundary between small and large clusters. Although the outer electrons may be delocalized over the entire cluster, a small cluster remains insulating until the density of states near the Fermi level exceeds 1/kT. In large clusters, with increasing cluster size, the band structure approaches that of the bulk metal. However, the bands remain significantly narrowed even in a 1000-atom cluster, giving an indication of the importance of long-range order. The core-electron binding-energy shifts of supported metal clusters depend on changes in the band structure in the initial state, as well as on various final-state effects, including changes in core hole screening and the coulomb energy of the final-state charge. For cluster supported on amorphous carbon, this macroscopic coulomb shift is often dominant, as evidenced by the parallel shifts of the core-electron binding energy and the Fermi edge. Auger data confirm that final-state effects dominate in cluster of Sn and some other metals. Surface atom core-level shifts provide a valuable guide to the contributions of initial-state changes in band structure to cluster core-electron binding energy shifts, especially for Au and Pt. The available data indicate that the shift observed in supported, metallic clusters arise largely from the charge left on the cluster by photoemission. As the metal-insulator transition is approached from above, metallic screening is suppressed and the shift is determined by the local environment. (orig.)
Electronic Structures of LNA Phosphorothioate Oligonucleotides
Directory of Open Access Journals (Sweden)
Henrik G. Bohr
2017-09-01
Full Text Available Important oligonucleotides in anti-sense research have been investigated in silico and experimentally. This involves quantum mechanical (QM calculations and chromatography experiments on locked nucleic acid (LNA phosphorothioate (PS oligonucleotides. iso-potential electrostatic surfaces are essential in this study and have been calculated from the wave functions derived from the QM calculations that provide binding information and other properties of these molecules. The QM calculations give details of the electronic structures in terms of e.g., energy and bonding, which make them distinguish or differentiate between the individual PS diastereoisomers determined by the position of sulfur atoms. Rules are derived from the electronic calculations of these molecules and include the effects of the phosphorothioate chirality and formation of electrostatic potential surfaces. Physical and electrochemical descriptors of the PS oligonucleotides are compared to the experiments in which chiral states on these molecules can be distinguished. The calculations demonstrate that electronic structure, electrostatic potential, and topology are highly sensitive to single PS configuration changes and can give a lead to understanding the activity of the molecules. Keywords: LNA phosphorothioate, DNA/LNA oligonucleotide, diastereoisomers, Hartree-Fock calculations, iso-potential surface, anion chromatograms
Electron localization and optical absorption of polygonal quantum rings
Sitek, Anna; Serra, Llorenç; Gudmundsson, Vidar; Manolescu, Andrei
2015-06-01
We investigate theoretically polygonal quantum rings and focus mostly on the triangular geometry where the corner effects are maximal. Such rings can be seen as short core-shell nanowires, a generation of semiconductor heterostructures with multiple applications. We show how the geometry of the sample determines the electronic energy spectrum, and also the localization of electrons, with effects on the optical absorption. In particular, we show that irrespective of the ring shape low-energy electrons are always attracted by corners and are localized in their vicinity. The absorption spectrum in the presence of a magnetic field shows only two peaks within the corner-localized state domain, each associated with different circular polarization. This picture may be changed by an external electric field which allows previously forbidden transitions, and thus enables the number of corners to be determined. We show that polygonal quantum rings allow absorption of waves from distant ranges of the electromagnetic spectrum within one sample.
Electron Spin Optical Orientation in Charged Quantum Dots
Shabaev, A.; Gershoni, D.; Korenev, V. L.
2005-03-01
We present a theory of nonresonant optical orientation of electron spins localized in quantum dots. This theory explains the negative circularly polarized photoluminescence of singlet trions localized in quantum dots previously observed in experiments where trion polarization changed to negative with time and where the degree of the negative polarization increased with intensity of pumping light. We have shown that this effect can be explained by the accumulation of dark excitons that occurs due to the spin blocking of the singlet trion formation - the major mechanism of dark exciton recombination. The accumulation of dark excitons results from a lack of electrons with a spin matching the exciton polarization. The electron spin lifetime is shortened by a transverse magnetic field or a temperature increase. This takes the block off the dark exciton recombination and restores the positive degree of trion polarization. The presented theory gives good agreement with experimental data.
Quantum noise in a terahertz hot electron bolometer mixer
Zhang, W.; Khosropanah, P.; Gao, J. R.; Kollberg, E. L.; Yngvesson, K. S.; Bansal, T.; Barends, R.; Klapwijk, T. M.
2010-01-01
We have measured the noise temperature of a single, sensitive superconducting NbN hot electron bolometer (HEB) mixer in a frequency range from 1.6 to 5.3 THz, using a setup with all the key components in vacuum. By analyzing the measured receiver noise temperature using a quantum noise (QN) model for HEB mixers, we confirm the effect of QN. The QN is found to be responsible for about half of the receiver noise at the highest frequency in our measurements. The ?-factor (the quantum efficiency ...
Solid state lasers: a major direction in quantum electronics
International Nuclear Information System (INIS)
Shcherbakov, I.A.
2004-01-01
The aim of the report is to analyze development of solid-state lasers (SSL) as one of the most important avenues of the quantum electronics. The obtained intensity of a laser radiation at the focus equal to 5x10 1 0 W/cm 2 (the field intensity equal to about 5x10 1 0 V/cm 2 ) is noted to enable to observe nonlinear quantum- electrodynamic effects. Besides, one managed to increase the SSL efficiency conventionally equal to maximum 3% up to 48-50%. Paper describes new types of SSLs, namely, the crystalline fiber lasers with the lateral gradient of the index of refraction [ru
Two Electron States in a Quantum Ring on a Sphere
International Nuclear Information System (INIS)
Kazaryan, Eduard M.; Shahnazaryan, Vanik A.; Sarkisyan, Hayk A.
2014-01-01
Two electron states in a quantum ring on a spherical surface are discussed. The problem is discussed within the frameworks of Russell–Saunders coupling scheme, that is, the spin–orbit coupling is neglected. Treating Coulomb interaction as a perturbation, the energy correction for different states is calculated. The dependence of the Coulomb interaction energy on external polar boundary angle of quantum ring is obtained. In analogue with the helium atom the concept of states exchange time is introduced, and its dependence on geometrical parameters of the ring is shown. (author)
Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer
Duan, Hong-Guang; Prokhorenko, Valentyn I.; Cogdell, Richard J.; Ashraf, Khuram; Stevens, Amy L.; Thorwart, Michael; Miller, R. J. Dwayne
2017-08-01
During the first steps of photosynthesis, the energy of impinging solar photons is transformed into electronic excitation energy of the light-harvesting biomolecular complexes. The subsequent energy transfer to the reaction center is commonly rationalized in terms of excitons moving on a grid of biomolecular chromophores on typical timescales Olson protein, in which interference oscillatory signals up to 1.5 ps were reported and interpreted as direct evidence of exceptionally long-lived electronic quantum coherence. Here, we show that the optical 2D photon echo spectra of this complex at ambient temperature in aqueous solution do not provide evidence of any long-lived electronic quantum coherence, but confirm the orthodox view of rapidly decaying electronic quantum coherence on a timescale of 60 fs. Our results can be considered as generic and give no hint that electronic quantum coherence plays any biofunctional role in real photoactive biomolecular complexes. Because in this structurally well-defined protein the distances between bacteriochlorophylls are comparable to those of other light-harvesting complexes, we anticipate that this finding is general and directly applies to even larger photoactive biomolecular complexes.
Quantum algebraic representation of localization and motion of a Dirac electron
International Nuclear Information System (INIS)
Jaekel, Marc-Thierry; Reynaud, Serge
2001-01-01
Quantum algebraic observables representing localization in space-time of a Dirac electron are defined. Inertial motion of the electron is represented in the quantum algebra with electron mass acting as the generator of motion. Since transformations to uniformly accelerated frames are naturally included in this conformally invariant description, the quantum algebra is also able to deal with uniformly accelerated motion
Field dependence of the electron spin relaxation in quantum dots.
Calero, Carlos; Chudnovsky, E M; Garanin, D A
2005-10-14
The interaction of the electron spin with local elastic twists due to transverse phonons is studied. The universal dependence of the spin-relaxation rate on the strength and direction of the magnetic field is obtained in terms of the electron gyromagnetic tensor and macroscopic elastic constants of the solid. The theory contains no unknown parameters and it can be easily tested in experiment. At high magnetic field it provides a parameter-free lower bound on the electron spin relaxation in quantum dots.
Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures
2018-02-19
AFRL-AFOSR-JP-TR-2018-0012 Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures PHILIP Kim HARVARD COLLEGE PRESIDENT...21-02-2018 2. REPORT TYPE Final 3. DATES COVERED (From - To) 15 Aug 2015 to 14 Feb 2017 4. TITLE AND SUBTITLE Nano Electronics on...NOTES 14. ABSTRACT We report molecular beam epitaxial growth and electronic transport properties of high quality topological insulator Bi2Se3 thin films
Natural occupation numbers in two-electron quantum rings.
Tognetti, Vincent; Loos, Pierre-François
2016-02-07
Natural orbitals (NOs) are central constituents for evaluating correlation energies through efficient approximations. Here, we report the closed-form expression of the NOs of two-electron quantum rings, which are prototypical finite-extension systems and new starting points for the development of exchange-correlation functionals in density functional theory. We also show that the natural occupation numbers for these two-electron paradigms are in general non-vanishing and follow the same power law decay as atomic and molecular two-electron systems.
Natural occupation numbers in two-electron quantum rings
Energy Technology Data Exchange (ETDEWEB)
Tognetti, Vincent, E-mail: vincent.tognetti@univ-rouen.fr [Normandy Univ., COBRA UMR 6014 & FR 3038, Université de Rouen, INSA Rouen, CNRS, 1 rue Tesniére, 76821 Mont Saint Aignan, Cedex (France); Loos, Pierre-François [Research School of Chemistry, Australian National University, Canberra ACT 2601 (Australia)
2016-02-07
Natural orbitals (NOs) are central constituents for evaluating correlation energies through efficient approximations. Here, we report the closed-form expression of the NOs of two-electron quantum rings, which are prototypical finite-extension systems and new starting points for the development of exchange-correlation functionals in density functional theory. We also show that the natural occupation numbers for these two-electron paradigms are in general non-vanishing and follow the same power law decay as atomic and molecular two-electron systems.
Electron confinement in thin metal films. Structure, morphology and interactions
Energy Technology Data Exchange (ETDEWEB)
Dil, J.H.
2006-05-15
This thesis investigates the interplay between reduced dimensionality, electronic structure, and interface effects in ultrathin metal layers (Pb, In, Al) on a variety of substrates (Si, Cu, graphite). These layers can be grown with such a perfection that electron confinement in the direction normal to the film leads to the occurrence of quantum well states in their valence bands. These quantum well states are studied in detail, and their behaviour with film thickness, on different substrates, and other parameters of growth are used here to characterise a variety of physical properties of such nanoscale systems. The sections of the thesis deal with a determination of quantum well state energies for a large data set on different systems, the interplay between film morphology and electronic structure, and the influence of substrate electronic structure on their band shape; finally, new ground is broken by demonstrating electron localization and correlation effects, and the possibility to measure the influence of electron-phonon coupling in bulk bands. (orig.)
Electronic structure of single crystal C60
International Nuclear Information System (INIS)
Wu, J.; Shen, Z.X.; Dessau, D.S.; Cao, R.; Marshall, D.S.; Pianetta, P.; Lindau, I.; Yang, X.; Terry, J.; King, D.M.; Wells, B.O.; Elloway, D.; Wendt, H.R.; Brown, C.A.; Hunziker, H.; Vries, M.S. de
1992-01-01
We report angle-resolved photoemission data from single crystals of C 60 cleaved in UHV. Unlike the other forms of pure carbon, the valence band spectrum of C 60 consists of many sharp features that can be essentially accounted for by the quantum chemical calculations describing individual molecules. This suggests that the electronic structure of solid C 60 is mainly determined by the bonding interactions within the individual molecules. We also observe remarkable intensity modulations of the photoemission features as a function of photon energy, suggesting strong final state effects. Finally, we address the issue of the band width of the HOMO state of C 60 . We assert that the width of the photoemission peak of C 60 does not reflect the intrinsic band width because it is broadened by the non 0-0 transitions via the Franck-Condon principle. Our view point provides a possible reconciliation between these photoemission data and those measured by other techniques. (orig.)
Hlavacek, Nikolaus C.; McAnally, Michael O.; Drucker, Stephen
2013-02-01
The cavity ringdown absorption spectrum of acrolein (propenal, CH2=CH—CH=O) was recorded near 412 nm, under bulk-gas conditions at room temperature and in a free-jet expansion. The measured spectral region includes the 0^0_0 band of the T1(n, π*) ← S0 system. We analyzed the 0^0_0 rotational contour by using the STROTA computer program [R. H. Judge et al., J. Chem. Phys. 103, 5343 (1995)], 10.1063/1.470569, which incorporates an asymmetric rotor Hamiltonian for simulating and fitting singlet-triplet spectra. We used the program to fit T1(n, π*) inertial constants to the room-temperature contour. The determined values (cm-1), with 2σ confidence intervals, are A = 1.662 ± 0.003, B = 0.1485 ± 0.0006, C = 0.1363 ± 0.0004. Linewidth analysis of the jet-cooled spectrum yielded a value of 14 ± 2 ps for the lifetime of isolated acrolein molecules in the T1(n, π*), v = 0 state. We discuss the observed lifetime in the context of previous computational work on acrolein photochemistry. The spectroscopically derived inertial constants for the T1(n, π*) state were used to benchmark a variety of computational methods. One focus was on complete active space methods, such as complete active space self-consistent field (CASSCF) and second-order perturbation theory with a CASSCF reference function (CASPT2), which are applicable to excited states. We also examined the equation-of-motion coupled-cluster and time-dependent density function theory excited-state methods, and finally unrestricted ground-state techniques, including unrestricted density functional theory and unrestricted coupled-cluster theory with single and double and perturbative triple excitations. For each of the above methods, we or others [O. S. Bokareva et al., Int. J. Quantum Chem. 108, 2719 (2008)], 10.1002/qua.21803 used a triple zeta-quality basis set to optimize the T1(n, π*) geometry of acrolein. We find that the multiconfigurational methods provide the best agreement with fitted inertial
Subband structure comparison between n- and p- type double delta-doped Ga As quantum wells
International Nuclear Information System (INIS)
Rodriguez V, I.; Gaggero S, L.M.
2004-01-01
We compute the electron level structure (n-type) and the hole subband structure (p-type) of double -doped GaAs (DDD) quantum wells, considering exchange effects. The Thomas-Fermi (TF), and Thomas-Fermi-Dirac (TFD) approximations have been applied in order to describe the bending of the conduction and valence band, respectively. The electron and the hole subband structure study indicates that exchange effects are more important in p-type DDD quantum wells than in n-type DDD Also our results agree with the experimental data available. (Author) 33 refs., 2 tabs., 5 figs
Spin relaxation in quantum dots due to electron exchange with leads.
Vorontsov, A B; Vavilov, M G
2008-11-28
We calculate spin relaxation rates in lateral quantum dot systems due to electron exchange between dots and leads. Using rate equations, we develop a theoretical description of the experimentally observed electric current in the spin blockade regime of double quantum dots. A single expression fits the entire current profile and describes the structure of both the conduction peaks and the suppressed ("valley") region. Extrinsic rates calculated here have to be taken into account for accurate extraction of intrinsic relaxation rates due to the spin-orbit and hyperfine spin scattering mechanisms from spin blockade measurements.
Coherent Electron Scattering Captured by an Attosecond Quantum Stroboscope
International Nuclear Information System (INIS)
Mauritsson, J.; Johnsson, P.; Mansten, E.; Swoboda, M.; Ruchon, T.; L'Huillier, A.; Schafer, K. J.
2008-01-01
We demonstrate a quantum stroboscope based on a sequence of identical attosecond pulses that are used to release electrons into a strong infrared (IR) laser field exactly once per laser cycle. The resulting electron momentum distributions are recorded as a function of time delay between the IR laser and the attosecond pulse train using a velocity map imaging spectrometer. Because our train of attosecond pulses creates a train of identical electron wave packets, a single ionization event can be studied stroboscopically. This technique has enabled us to image the coherent electron scattering that takes place when the IR field is sufficiently strong to reverse the initial direction of the electron motion causing it to rescatter from its parent ion
The Structural Foundations of Quantum Gravity
International Nuclear Information System (INIS)
Rovelli, Carlo
2007-01-01
The core of the collection of papers that form the book originates from a workshop on 'Structural Aspects of Quantum Gravity' held in Milwaukee, WI, in 2002. But the collection also includes contributions from philosophers and scientists who did not attend the meeting. The book is presented with a structuralist agenda: to emphasize the idea that 'relational structures are of equal or more fundamental ontological status than objects'. The goal of the editors is, as they put it, to 'suggest' a possible 'interpretative and ontological perspective from which to view quantum gravity physics'. Attention to structure rather than objects is a long-standing tradition. It played a major role in anthropology and linguistics, from which it fertilized numerous other disciplines. In the recent philosophy of science, when criticism of the dominant positivism of the beginning of the century has begun to pile up, several thinkers have steered towards more realist positions. The conceptual problems of quantum gravity are illustrated and discussed in detail throughout the book, often from different perspectives, and sometimes with discordant conclusions. At times, the book reads almost as a dialogue, where different thinkers present different sides of the issue. Perhaps it is our full conceptualization of reality that evolves, not just its ontology: our knowledge of the world's structures (and equations) persists and changes historically as much as our knowledge of the world's objects. Efforts to find a fixed ground on which to anchor our beliefs often fail; I think the scientific picture of the world is credible because it captures the best that we know today, not because it captures something definitive. Still, I find the ideas underlying the structural proposal challenging and very intriguing. Notions such as object, entity or substance keep playing a fundamental role in physics, but continue also to show their limits: a physicist often thinks that the prototypical 'object' is
Electron Raman scattering in semiconductor quantum wire in an external magnetic field
International Nuclear Information System (INIS)
Betancourt-Riera, Ri; Nieto Jalil, J M; Riera, R; Betancourt-Riera, Re; Rosas, R
2008-01-01
The differential cross-section for an electron Raman scattering process in a semiconductor quantum wire in the presence of an external magnetic field perpendicular to the plane of confinement is calculated. We assume a single parabolic conduction band. The emission spectra for different scattering configurations and the selection rules for the processes are studied. Singularities in the spectra are found and interpreted. The electron Raman scattering studied here can be used to provide direct information about the electron band and subband structure of these confinement systems. The magnetic field distribution is considered constant with value B 0 inside the wire and zero outside
Direct Identification of Atomic-Like Electronic Levels in InAs Nano crystal Quantum Dots
International Nuclear Information System (INIS)
Millo, O.; Katz, D.
1999-01-01
The size dependent level structure of InAs nano crystals in the range 2-7 nm in diameter is investigated using both tunneling and optical spectroscopies. The tunneling measurements are performed using a cryogenic scanning tunneling microscope on individual nano crystals that, are attached to a gold substrate via dithiol molecules. The tunneling I-V characteristics manifest an interplay between single electron charging and quantum size effects. We are able to directly identify quantum confined states of isolated InAs nano crystals having s and p symmetries. These states are observed in the I-V curves as two and six-fold single electron charging multiplets. Excellent agreement is found between the strongly allowed optical transitions [1] and the spacing of levels detected in the tunneling experiment. This correlation provides new information on the quantum-dot level structure, from which we conclude that the top-most valence band state has both s and p characteristics. The interplay between level structure singles electron charging of the nano crystals obeys an atomic-like Aufbau sequential electron level occupation
Deep learning and the electronic structure problem
Mills, Kyle; Spanner, Michael; Tamblyn, Isaac
In the past decade, the fields of artificial intelligence and computer vision have progressed remarkably. Supported by the enthusiasm of large tech companies, as well as significant hardware advances and the utilization of graphical processing units to accelerate computations, deep neural networks (DNN) are gaining momentum as a robust choice for many diverse machine learning applications. We have demonstrated the ability of a DNN to solve a quantum mechanical eigenvalue equation directly, without the need to compute a wavefunction, and without knowledge of the underlying physics. We have trained a convolutional neural network to predict the total energy of an electron in a confining, 2-dimensional electrostatic potential. We numerically solved the one-electron Schrödinger equation for millions of electrostatic potentials, and used this as training data for our neural network. Four classes of potentials were assessed: the canonical cases of the harmonic oscillator and infinite well, and two types of randomly generated potentials for which no analytic solution is known. We compare the performance of the neural network and consider how these results could lead to future advances in electronic structure theory.
Energy Technology Data Exchange (ETDEWEB)
Carroll, Malcolm S.; rochette, sophie; Rudolph, Martin; Roy, A. -M.; Curry, Matthew Jon; Ten Eyck, Gregory A.; Manginell, Ronald P.; Wendt, Joel R.; Pluym, Tammy; Carr, Stephen M; Ward, Daniel Robert; Lilly, Michael; pioro-ladriere, michel
2017-07-01
We introduce a silicon metal-oxide-semiconductor quantum dot structure that achieves dot-reservoir tunnel coupling control without a dedicated barrier gate. The elementary structure consists of two accumulation gates separated spatially by a gap, one gate accumulating a reservoir and the other a quantum dot. Control of the tunnel rate between the dot and the reservoir across the gap is demonstrated in the single electron regime by varying the reservoir accumulation gate voltage while compensating with the dot accumulation gate voltage. The method is then applied to a quantum dot connected in series to source and drain reservoirs, enabling transport down to the single electron regime. Finally, tuning of the valley splitting with the dot accumulation gate voltage is observed. This split accumulation gate structure creates silicon quantum dots of similar characteristics to other realizations but with less electrodes, in a single gate stack subtractive fabrication process that is fully compatible with silicon foundry manufacturing.
Electron Acceptor Materials Engineering in Colloidal Quantum Dot Solar Cells
Liu, Huan
2011-07-15
Lead sulfide colloidal quantum dot (CQD) solar cells with a solar power conversion efficiency of 5.6% are reported. The result is achieved through careful optimization of the titanium dioxide electrode that serves as the electron acceptor. Metal-ion-doped sol-gel-derived titanium dioxide electrodes produce a tunable-bandedge, well-passivated materials platform for CQD solar cell optimization. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Designing quantum information processing via structural physical approximation.
Bae, Joonwoo
2017-10-01
In quantum information processing it may be possible to have efficient computation and secure communication beyond the limitations of classical systems. In a fundamental point of view, however, evolution of quantum systems by the laws of quantum mechanics is more restrictive than classical systems, identified to a specific form of dynamics, that is, unitary transformations and, consequently, positive and completely positive maps to subsystems. This also characterizes classes of disallowed transformations on quantum systems, among which positive but not completely maps are of particular interest as they characterize entangled states, a general resource in quantum information processing. Structural physical approximation offers a systematic way of approximating those non-physical maps, positive but not completely positive maps, with quantum channels. Since it has been proposed as a method of detecting entangled states, it has stimulated fundamental problems on classifications of positive maps and the structure of Hermitian operators and quantum states, as well as on quantum measurement such as quantum design in quantum information theory. It has developed efficient and feasible methods of directly detecting entangled states in practice, for which proof-of-principle experimental demonstrations have also been performed with photonic qubit states. Here, we present a comprehensive review on quantum information processing with structural physical approximations and the related progress. The review mainly focuses on properties of structural physical approximations and their applications toward practical information applications.
Bobrov, B. D.
1991-07-01
Experimental results are used to show that circular interferograms are of interest in studies of screw dislocations of speckle-distorted laser beams because of a close correspondence between the symmetry of these interferograms and defects. The presence of dislocations transforms a system of the usual rings into a split network. Typical structure elements of such interferograms are right- and left-handed spirals connecting singular points of dislocations. Spiral fragments can be used in the diagnostics of dislocations regarded as independent defects. A method is suggested for the formation of highly directed optical beams with a low level of the usual aberrations, but with a complex phase surface topology. Screw dislocations are shown to be a natural analog of helical waves known in optics and capable of deliberate generation.
Quantum mechanics of electronic-rotational energy transfer in F(2P) + H2 collisions
International Nuclear Information System (INIS)
Wyatt, R.E.; Walker, R.B.
1977-01-01
A theoretical study is made of electronic-rotational energy transfer in F( 2 P) + H 2 three-dimensional collisions, with electronic matrix elements from DIM theory. The quantum close-coupled equations are integrated via the R-matrix propagation method. Inelastic quenching probabilities are emphasized, with and without simulated open reaction channels. Interweaving patterns in the transition probability for even and odd nuclear parity vs. J (total angular momentum quantum number) are analyzed in terms of avoided crossing structure in the electrotational energy correlation diagrams. Localized regions where electronic quenching is dominant are identified in the correlation diagrams, and are confirmed in separate calculations which neglect interchannel mixing in local regions of the atom-molecule separation. Open reaction channels are found to have little influence on the quenching probabilities in these low energy calculations
Numerical simulation of electronic properties of coupled quantum dots on wetting layers
International Nuclear Information System (INIS)
Betcke, M M; Voss, H
2008-01-01
Self-assembled quantum dots are grown on wetting layers and frequently in an array-like assembly of many similar but not exactly equal dots. Nevertheless, most simulations disregard these structural conditions and restrict themselves to simulating a pure single quantum dot. For reasons of numerical efficiency we advocate the effective one-band Hamiltonian with energy- and position-dependent effective mass approximation and a finite height hard-wall 3D confinement potential for computation of the energy levels of the electrons in the conduction band. Within this model we investigate the geometrical effects mentioned above on the electronic structure of a pyramidal InAs quantum dot embedded in a GaAs matrix. We find that the presence of a wetting layer may affect the electronic structure noticeably. Furthermore, we establish that, in spite of the large bandgap of the InAs/GaAs heterostructure, if the dots in a vertically aligned array are sufficiently close stacked there is considerable interaction between their eigenfunctions. Moreover, the eigenfunctions of such an array are quite sensitive to certain structural perturbations
Pico-femtosecond image-tube photography in quantum electronics
International Nuclear Information System (INIS)
Schelev, M Ya
2001-01-01
The possibility of experimental achievement of the time resolution of image-converter tubes (ICTs) corresponding to the theoretical limit of 10 fs is considered as applied to quantum electronics problems. A new generation of ICTs with a temporal resolution of 200 - 500 fs has been developed for recording femtosecond laser radiation. The entirely new devices based on time-analysing ICTs such as femtosecond photoelectronic diffractometers, have been created for studying the dynamics of phase transitions in substances using diffrac-tion of electrons with energies ranging from 20 to 40 keV. (femtosecond technologies)
Characterization of encapsulated quantum dots via electron channeling contrast imaging
Energy Technology Data Exchange (ETDEWEB)
Deitz, Julia I.; McComb, David W. [Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Carnevale, Santino D. [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); De Graef, Marc [Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Grassman, Tyler J., E-mail: grassman.5@osu.edu [Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)
2016-08-08
A method for characterization of encapsulated epitaxial quantum dots (QD) in plan-view geometry using electron channeling contrast imaging (ECCI) is presented. The efficacy of the method, which requires minimal sample preparation, is demonstrated with proof-of-concept data from encapsulated (sub-surface) epitaxial InAs QDs within a GaAs matrix. Imaging of the QDs under multiple diffraction conditions is presented, establishing that ECCI can provide effectively identical visualization capabilities as conventional two-beam transmission electron microscopy. This method facilitates rapid, non-destructive characterization of sub-surface QDs giving immediate access to valuable nanostructural information.
Electronic structure of lanthanide scandates
Mizzi, Christopher A.; Koirala, Pratik; Marks, Laurence D.
2018-02-01
X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and density functional theory calculations were used to study the electronic structure of three lanthanide scandates: GdSc O3,TbSc O3 , and DySc O3 . X-ray photoelectron spectra simulated from first-principles calculations using a combination of on-site hybrid and GGA +U methods were found to be in good agreement with experimental x-ray photoelectron spectra. The hybrid method was used to model the ground state electronic structure and the GGA +U method accounted for the shift of valence state energies due to photoelectron emission via a Slater-Janak transition state approach. From these results, the lanthanide scandate valence bands were determined to be composed of Ln 4 f ,O 2 p , and Sc 3 d states, in agreement with previous work. However, contrary to previous work the minority Ln 4 f states were found to be located closer to, and in some cases at, the valence band maximum. This suggests that minority Ln 4 f electrons may play a larger role in lanthanide scandate properties than previously thought.
International Nuclear Information System (INIS)
Bodek, K.; Rozpędzik, D.; Zejma, J.; Caban, P.; Rembieliński, J.; Włodarczyk, M.; Ciborowski, J.; Enders, J.; Köhler, A.; Kozela, A.
2013-01-01
The Polish-German project QUEST aims at studying relativistic quantum spin correlations of the Einstein-Rosen-Podolsky-Bohm type, through measurement of the correlation function and the corresponding probabilities for relativistic electron pairs. The results will be compared to theoretical predictions obtained by us within the framework of relativistic quantum mechanics, based on assumptions regarding the form of the relativistic spin operator. Agreement or divergence will be interpreted in the context of non-uniqueness of the relativistic spin operator in quantum mechanics as well as dependence of the correlation function on the choice of observables representing the spin. Pairs of correlated electrons will originate from the Mo/ller scattering of polarized 15 MeV electrons provided by the superconducting Darmstadt electron linear accelerator S-DALINAC, TU Darmstadt, incident on a Be target. Spin projections will be determined using the Mott polarimetry technique. Measurements (starting 2013) are planned for longitudinal and transverse beam polarizations and different orientations of the beam polarization vector w.r.t. the Mo/ller scattering plane. This is the first project to study relativistic spin correlations for particles with mass
Artificially Structured Semiconductors to Model Novel Quantum Phenomena
Energy Technology Data Exchange (ETDEWEB)
Pinczuk, Aron [Columbia Univ., New York, NY (United States). Dept. of Applied Physics and Applied Mathematics; Wind, Shalom J. [Columbia Univ., New York, NY (United States). Dept. of Applied Physics and Applied Mathematics
2018-01-13
Award Period: September 1st, 2013 through February 15th, 2017 Submitted to the USDOE Office of Basic Energy Sciences By Aron Pinczuk and Shalom J. Wind Department of Applied Physics and Applied Mathematics Columbia University New York, NY 10027 January 2017 Award # DE-SC0010695 ABSTRACT Research in this project seeks to design, create and study a class of tunable artificial quantum structures in order to extend the range and scope of new and exciting physical phenomena and to explore the potential for new applications. Advanced nanofabrication was used to create an external potential landscape that acts as a lattice of confinement sites for electrons (and/or holes) in a two-dimensional electron gas in a high perfection semiconductor in such a manner that quantum interactions between different sites dictate the significant physics. Our current focus is on ‘artificial graphene’ (AG) in which a set of quantum dots (or sites) are patterned in a honeycomb lattice. The combination of leading edge nanofabrication with ultra-pure semiconductor materials in this project extends the frontier for small period, low-disorder AG systems, enabling the exploration of graphene physics in a semiconductor platform. TECHNICAL DESCRIPTION Contemporary condensed matter science has entered an era of discovery of new low-dimensional materials, such as graphene and other atomically thin materials, that exhibit exciting new physical phenomena that were previously inaccessible. Concurrent with the discovery and development of these new materials are impressive advancements in nanofabrication, which offer an ever-expanding toolbox for creating a myriad of high quality patterns at nanoscale dimensions. This project started about four years ago. Among its major achievements are the realizations of very small period artificial lattices with honeycomb topology in GaAs quantum wells. In our most recent work the periods of the ‘artificial graphene’ (AG) lattices extend down to 40 nm. These
Energy Technology Data Exchange (ETDEWEB)
Vetere, V
2002-09-15
This thesis is related to comparative studies of the chemical properties of molecular complexes containing lanthanide or actinide trivalent cations, in the context of the nuclear waste disposal. More precisely, our aim was a quantum chemical analysis of the metal-ligand bonding in such species. Various theoretical approaches were compared, for the inclusion of correlation (density functional theory, multiconfigurational methods) and of relativistic effects (relativistic scalar and 2-component Hamiltonians, relativistic pseudopotentials). The performance of these methods were checked by comparing computed structural properties to published experimental data, on small model systems: lanthanide and actinide tri-halides and on X{sub 3}M-L species (X=F, Cl; M=La, Nd, U; L = NH{sub 3}, acetonitrile, CO). We have thus shown the good performance of density functionals combined with a quasi-relativistic method, as well as of gradient-corrected functionals associated with relativistic pseudopotentials. In contrast, functionals including some part of exact exchange are less reliable to reproduce experimental trends, and we have given a possible explanation for this result . Then, a detailed analysis of the bonding has allowed us to interpret the discrepancies observed in the structural properties of uranium and lanthanides complexes, based on a covalent contribution to the bonding, in the case of uranium(III), which does not exist in the lanthanide(III) homologues. Finally, we have examined more sizeable systems, closer to experimental species, to analyse the influence of the coordination number, of the counter-ions and of the oxidation state of uranium, on the metal-ligand bonding. (author)
The quantum dynamics of electronically nonadiabatic chemical reactions
Truhlar, Donald G.
1993-01-01
Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally
Spin fine structure of optically excited quantum dot molecules
Scheibner, M.; Doty, M. F.; Ponomarev, I. V.; Bracker, A. S.; Stinaff, E. A.; Korenev, V. L.; Reinecke, T. L.; Gammon, D.
2007-06-01
The interaction between spins in coupled quantum dots is revealed in distinct fine structure patterns in the measured optical spectra of InAs/GaAs double quantum dot molecules containing zero, one, or two excess holes. The fine structure is explained well in terms of a uniquely molecular interplay of spin-exchange interactions, Pauli exclusion, and orbital tunneling. This knowledge is critical for converting quantum dot molecule tunneling into a means of optically coupling not just orbitals but also spins.
Physics of lateral triple quantum-dot molecules with controlled electron numbers.
Hsieh, Chang-Yu; Shim, Yun-Pil; Korkusinski, Marek; Hawrylak, Pawel
2012-11-01
We review the recent progress in theory and experiments with lateral triple quantum dots with controlled electron numbers down to one electron in each dot. The theory covers electronic and spin properties as a function of topology, number of electrons, gate voltage and external magnetic field. The orbital Hund's rules and Nagaoka ferromagnetism, magnetic frustration and chirality, interplay of quantum interference and electron-electron interactions and geometrical phases are described and related to charging and transport spectroscopy. Fabrication techniques and recent experiments are covered, as well as potential applications of triple quantum-dot molecule in coherent control, spin manipulation and quantum computation.
Scattering and structures essentials and analogies in quantum physics
Povh, Bogdan
2017-01-01
Quantum physics may appear complicated, especially if one forgets the "big picture" and gets lost in the details. However, it can become clearer and less tangled if one applies a few fundamental concepts so that simplified approaches can emerge and estimated orders of magnitude become clear. Povh and Rosina’s Scattering and Structures presents the properties of quantum systems (elementary particles, nucleons, atoms, molecules, quantum gases, quantum liquids, stars, and early universe) with the help of elementary concepts and analogies between these seemingly different systems. In this new edition, sections on quantum gases and an up to date overview of elementary particles have been added.
Wei, Hai-Rui; Deng, Fu-Guo
2014-01-13
We present some compact quantum circuits for a deterministic quantum computing on electron-spin qubits assisted by quantum dots inside single-side optical microcavities, including the CNOT, Toffoli, and Fredkin gates. They are constructed by exploiting the giant optical Faraday rotation induced by a single-electron spin in a quantum dot inside a single-side optical microcavity as a result of cavity quantum electrodynamics. Our universal quantum gates have some advantages. First, all the gates are accomplished with a success probability of 100% in principle. Second, our schemes require no additional electron-spin qubits and they are achieved by some input-output processes of a single photon. Third, our circuits for these gates are simple and economic. Moreover, our devices for these gates work in both the weak coupling and the strong coupling regimes, and they are feasible in experiment.
Pseudorandom binary injection of levitons for electron quantum optics
Glattli, D. C.; Roulleau, P.
2018-03-01
The recent realization of single-electron sources lets us envision performing electron quantum optics experiments, where electrons can be viewed as flying qubits propagating in a ballistic conductor. To date, all electron sources operate in a periodic electron injection mode, leading to energy spectrum singularities in various physical observables which sometimes hide the bare nature of physical effects. To go beyond this, we propose a spread-spectrum approach where electron flying qubits are injected in a nonperiodic manner following a pseudorandom binary bit pattern. Extending the Floquet scattering theory approach from periodic to spread-spectrum drive, the shot noise of pseudorandom binary sequences of single-electron injection can be calculated for leviton and nonleviton sources. Our new approach allows us to disentangle the physics of the manipulated excitations from that of the injection protocol. In particular, the spread-spectrum approach is shown to provide better knowledge of electronic Hong-Ou-Mandel correlations and to clarify the nature of the pulse train coherence and the role of the dynamical orthogonality catastrophe for noninteger charge injection.
Resonance fluorescence and electron spin in semiconductor quantum dots
Energy Technology Data Exchange (ETDEWEB)
Zhao, Yong
2009-11-18
The work presented in this dissertation contains the first observation of spin-resolved resonance fluorescence from a single quantum dot and its application of direct measurement of electron spin dynamics. The Mollow triplet and the Mollow quintuplet, which are the hallmarks of resonance fluorescence, are presented as the non-spin-resolved and spin-resolved resonance fluorescence spectrum, respectively. The negligible laser background contribution, the near pure radiative broadened spectrum and the anti-bunching photon statistics imply the sideband photons are background-free and near transform-limited single photons. This demonstration is a promising step towards the heralded single photon generation and electron spin readout. Instead of resolving spectrum, an alternative spin-readout scheme by counting resonance fluorescence photons under moderate laser power is demonstrated. The measurements of n-shot time-resolved resonance fluorescence readout are carried out to reveal electron spin dynamics of the measurement induced back action and the spin relaxation. Hyperfine interaction and heavy-light hole mixing are identified as the relevant mechanisms for the back action and phonon-assistant spin-orbit interaction dominates the spin relaxation. After a detailed discussion on charge-spin configurations in coupled quantum dots system, the single-shot readout on electron spin are proposed. (orig.)
Resonance fluorescence and electron spin in semiconductor quantum dots
International Nuclear Information System (INIS)
Zhao, Yong
2009-01-01
The work presented in this dissertation contains the first observation of spin-resolved resonance fluorescence from a single quantum dot and its application of direct measurement of electron spin dynamics. The Mollow triplet and the Mollow quintuplet, which are the hallmarks of resonance fluorescence, are presented as the non-spin-resolved and spin-resolved resonance fluorescence spectrum, respectively. The negligible laser background contribution, the near pure radiative broadened spectrum and the anti-bunching photon statistics imply the sideband photons are background-free and near transform-limited single photons. This demonstration is a promising step towards the heralded single photon generation and electron spin readout. Instead of resolving spectrum, an alternative spin-readout scheme by counting resonance fluorescence photons under moderate laser power is demonstrated. The measurements of n-shot time-resolved resonance fluorescence readout are carried out to reveal electron spin dynamics of the measurement induced back action and the spin relaxation. Hyperfine interaction and heavy-light hole mixing are identified as the relevant mechanisms for the back action and phonon-assistant spin-orbit interaction dominates the spin relaxation. After a detailed discussion on charge-spin configurations in coupled quantum dots system, the single-shot readout on electron spin are proposed. (orig.)
Electron scattering and nuclear structure
International Nuclear Information System (INIS)
Frois, B.
1987-01-01
The search for the appropriate degrees of freedom to describe nuclei is the central focus of nuclear physics today. Therefore the authors explore in this review their current understanding of nuclear structure as defined by electromagnetic data. The precision of the electromagnetic probe allows us to define accurately the limits of present theoretical descriptions. The authors review here a broad range of subjects that have been addressed by recent experiments, from the study of meson exchange currents and single-particle distributions to collective excitations in heavy nuclei. However, they do not discuss elastic magnetic scattering, inelastic excitation of discrete states, or single-nucleon knockout reactions since these reactions were recently reviewed. The principal aim of this review is to offer a fresh perspective on nuclear structure, based on the new generation of electron scattering data presented here and in the above-mentioned articles
Fine structure and optical pumping of spins in individual semiconductor quantum dots
Bracker, Allan S.; Gammon, Daniel; Korenev, Vladimir L.
2008-11-01
We review spin properties of semiconductor quantum dots and their effect on optical spectra. Photoluminescence and other types of spectroscopy are used to probe neutral and charged excitons in individual quantum dots with high spectral and spatial resolution. Spectral fine structure and polarization reveal how quantum dot spins interact with each other and with their environment. By taking advantage of the selectivity of optical selection rules and spin relaxation, optical spin pumping of the ground state electron and nuclear spins is achieved. Through such mechanisms, light can be used to process spins for use as a carrier of information.
Fine structure and optical pumping of spins in individual semiconductor quantum dots
International Nuclear Information System (INIS)
Bracker, Allan S; Gammon, Daniel; Korenev, Vladimir L
2008-01-01
We review spin properties of semiconductor quantum dots and their effect on optical spectra. Photoluminescence and other types of spectroscopy are used to probe neutral and charged excitons in individual quantum dots with high spectral and spatial resolution. Spectral fine structure and polarization reveal how quantum dot spins interact with each other and with their environment. By taking advantage of the selectivity of optical selection rules and spin relaxation, optical spin pumping of the ground state electron and nuclear spins is achieved. Through such mechanisms, light can be used to process spins for use as a carrier of information
Two dimensional electron systems for solid state quantum computation
Mondal, Sumit
Two dimensional electron systems based on GaAs/AlGaAs heterostructures are extremely useful in various scientific investigations of recent times including the search for quantum computational schemes. Although significant strides have been made over the past few years to realize solid state qubits on GaAs/AlGaAs 2DEGs, there are numerous factors limiting the progress. We attempt to identify factors that have material and design-specific origin and develop ways to overcome them. The thesis is divided in two broad segments. In the first segment we describe the realization of a new field-effect induced two dimensional electron system on GaAs/AlGaAs heterostructure where the novel device-design is expected to suppress the level of charge noise present in the device. Modulation-doped GaAs/AlGaAs heterostructures are utilized extensively in the study of quantum transport in nanostructures, but charge fluctuations associated with remote ionized dopants often produce deleterious effects. Electric field-induced carrier systems offer an attractive alternative if certain challenges can be overcome. We demonstrate a field-effect transistor in which the active channel is locally devoid of modulation-doping, but silicon dopant atoms are retained in the ohmic contact region to facilitate low-resistance contacts. A high quality two-dimensional electron gas is induced by a field-effect that is tunable over a density range of 6.5x10 10cm-2 to 2.6x1011cm-2 . Device design, fabrication, and low temperature (T=0.3K) characterization results are discussed. The demonstrated device-design overcomes several existing limitations in the fabrication of field-induced 2DEGs and might find utility in hosting nanostructures required for making spin qubits. The second broad segment describes our effort to correlate transport parameters measured at T=0.3K to the strength of the fractional quantum Hall state observed at nu=5/2 in the second Landau level of high-mobility GaAs/AlGaAs two dimensional
Quantum-Sequencing: Fast electronic single DNA molecule sequencing
Casamada Ribot, Josep; Chatterjee, Anushree; Nagpal, Prashant
2014-03-01
A major goal of third-generation sequencing technologies is to develop a fast, reliable, enzyme-free, high-throughput and cost-effective, single-molecule sequencing method. Here, we present the first demonstration of unique ``electronic fingerprint'' of all nucleotides (A, G, T, C), with single-molecule DNA sequencing, using Quantum-tunneling Sequencing (Q-Seq) at room temperature. We show that the electronic state of the nucleobases shift depending on the pH, with most distinct states identified at acidic pH. We also demonstrate identification of single nucleotide modifications (methylation here). Using these unique electronic fingerprints (or tunneling data), we report a partial sequence of beta lactamase (bla) gene, which encodes resistance to beta-lactam antibiotics, with over 95% success rate. These results highlight the potential of Q-Seq as a robust technique for next-generation sequencing.
On the structure of the quantum-mechanical probability models
International Nuclear Information System (INIS)
Cufaro-Petroni, N.
1992-01-01
In this paper the role of the mathematical probability models in the classical and quantum physics in shortly analyzed. In particular the formal structure of the quantum probability spaces (QPS) is contrasted with the usual Kolmogorovian models of probability by putting in evidence the connections between this structure and the fundamental principles of the quantum mechanics. The fact that there is no unique Kolmogorovian model reproducing a QPS is recognized as one of the main reasons of the paradoxical behaviors pointed out in the quantum theory from its early days. 8 refs
Physics of lateral triple quantum-dot molecules with controlled electron numbers
International Nuclear Information System (INIS)
Hsieh, Chang-Yu; Shim, Yun-Pil; Korkusinski, Marek; Hawrylak, Pawel
2012-01-01
We review the recent progress in theory and experiments with lateral triple quantum dots with controlled electron numbers down to one electron in each dot. The theory covers electronic and spin properties as a function of topology, number of electrons, gate voltage and external magnetic field. The orbital Hund's rules and Nagaoka ferromagnetism, magnetic frustration and chirality, interplay of quantum interference and electron–electron interactions and geometrical phases are described and related to charging and transport spectroscopy. Fabrication techniques and recent experiments are covered, as well as potential applications of triple quantum-dot molecule in coherent control, spin manipulation and quantum computation. (review article)
Strain and Quantum Dots Manipulation in Nitride Compounds for Opto-electronic Devices
National Research Council Canada - National Science Library
Bedair, S. M; El-Masry, N. A
2008-01-01
Activities during the project period can be divided into two main areas. The first dealt with quantum structure and optical properties of light sources based on GaInN/AlInGaN quantum well structures...
Structured electron beams from nano-engineered cathodes
Energy Technology Data Exchange (ETDEWEB)
Lueangaramwong, A. [NICADD, DeKalb; Mihalcea, D. [NICADD, DeKalb; Andonian, G. [RadiaBeam Tech.; Piot, P. [Fermilab
2017-03-07
The ability to engineer cathodes at the nano-scale have open new possibilities such as enhancing quantum eciency via surface-plasmon excitation, forming ultra-low-emittance beams, or producing structured electron beams. In this paper we present numerical investigations of the beam dynamics associated to this class of cathode in the weak- and strong-field regimes.We finally discuss the possible applications of some of the achievable cathode patterns when coupled with other phase space manipulations.
Exploring semiconductor quantum dots and wires by high resolution electron microscopy
Energy Technology Data Exchange (ETDEWEB)
Molina, S I [Departamento de Ciencia de los Materiales e Ing Metalurgica y Q. Inorganica, F. de Ciencias, Universidad de Cadiz, Campus Rio San Pedro. 11510 Puerto Real (Cadiz) (Spain); Galindo, P L [Departamento de Lenguajes y Sistemas Informaticos, CASEM, Universidad de Cadiz, Campus Rio San Pedro. 11510 Puerto Real (Cadiz) (Spain); Gonzalez, L; Ripalda, J M [Instituto de Microelectronica de Madrid (CNM, CSIC), Isaac Newton 8, 28760 Tres Cantos, Madrid (Spain); Varela, M; Pennycook, S J, E-mail: sergio.molina@uca.e [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge TN 37831 (United States)
2010-02-01
We review in this communication our contribution to the structural characterisation of semiconductor quantum dots and wires by high resolution electron microscopy, both in phase-contrast and Z-contrast modes. We show how these techniques contribute to predict the preferential sites of nucleation of these nanostructures, and also determine the compositional distribution in 1D and 0D nanostructures. The results presented here were produced in the framework of the European Network of Excellence entitled {sup S}elf-Assembled semiconductor Nanostructures for new Devices in photonics and Electronics (SANDiE){sup .}
Electronic structure of point defects in semiconductors
International Nuclear Information System (INIS)
Bruneval, Fabien
2014-01-01
trace concentration (of the order of one part per million). However, owing to the heavy burden of the quantum-mechanical electronic structure calculations, which grow very rapidly with the number of electrons, the present day simulations do not easily exceed a few hundred atoms nowadays. This induces effective defect concentrations of the order of one percent which are very far from the diluted defects observed in the experiments. The extrapolation of high concentrations to low concentrations is difficult because defects in semiconductors often bear a net electric charge which induces long-range interactions between the spuriously interacting charged defects. The first part of my work presents the techniques available in this area, improvements in the techniques and some understanding of these spurious interactions. The second topic addressed in this memoir focuses on improving the electronic structure of defects in semiconductors and insulators. Defects in these materials introduce discrete electronic levels within the band gap of the pristine bulk material. These electronic levels correspond to the electrons involved in the defect states. Their wave function is more or less localized around the defect region and the filling of the state may also vary with the thermodynamic conditions (Fermi level). These levels inside the band gap govern the modification of the properties of electronic and optical transport. Unfortunately the standard ab initio approaches, in the context of Density Functional Theory (DFT), are unable to get the correct band gaps of semiconductors and insulators. This is why many defect properties cannot be predicted with certainty within these approaches. This second part demonstrates how the introduction of the many-body perturbation theory in the so-called GW approximation solves the problem of band gaps and thus allows one to obtain more reliable defect properties. Of course, the field of ab initio electronic structure for defects is far from being
Hybridization of electron states in a step quantum well in a magnetic field
International Nuclear Information System (INIS)
Barseghyan, M.G.; Kirakosyan, A.A.
2005-01-01
The quantum states and energy levels of an electrion in a rectangular step quantum well in a magnetic field parallel to the plane of two-dimentional electron gas are investigated. It is shown that the joint effect of the magnetic field and confining potential of the quantum well results in redical change of the electron spectrum. The dependence of the electron energy levels on the quantum well parameters, magnetic field induction and projection of the wave-vector along the magnetic field induction are calculated. Numerical calculations are carried out for a AlAs/GaAlAs/GaAs/AlAs step quantum well
Optical properties of semiconductors quantum microcavity structures
International Nuclear Information System (INIS)
Afshar, A.M.
1996-12-01
The principal phenomenon investigated in this thesis is vacuum Rabi coupling in semiconductor microcavity structures. In these structures quantum well excitons are embedded in a Fabry - Perot like cavity, defined by two semiconductor dielectric mirrors. In such a system the coupled exciton and cavity photon mode form a mixed - mode polariton, where on - resonance there are two branches, each having 50% exciton and 50% photon character. The separation between the upper and lower branches is a measure of the coupling strength where the strength is dependent on the exciton oscillator strength. This interaction is known as vacuum Rabi coupling, and clear anticrossing is seen when the exciton is tuned through the cavity. In our reflectivity experiments we demonstrate control of the coupling between the cavity mode and the exciton by varying temperature, applied electric or magnetic field. Modelling of the reflectivity spectra and the tuning was done using a Transfer Matrix Reflectivity (TMR) model or a linear dispersion model, where in both cases the excitons are treated as Lorentz oscillators. Temperature tuning is achieved because exciton energy decreases with temperature at a much faster rate than the cavity mode. We have demonstrated vacuum Rabi coupling of the cavity mode with both the heavy - hole and light - hole excitons. Electric field tuning is achieved via the quantum confined Stark effect which decreases the exciton energy with increasing field, whilst at the same time the cavity mode energy remains constant. A study of how the electric field reduction of exciton oscillator strength reduces the vacuum Rabi coupling strength is performed. We report the first observation in a semiconductor structure of motional narrowing, seen in both electric field and in temperature tuning experiments at high magnetic field. In magnetic field studies we show how magnetic field induced increase in exciton oscillator strength affects the vacuum Rabi coupling. We also show by
Interferometry of Klein tunnelling electrons in graphene quantum rings
de Sousa, D. J. P.; Chaves, Andrey; Pereira, J. M.; Farias, G. A.
2017-01-01
We theoretically study a current switch that exploits the phase acquired by a charge carrier as it tunnels through a potential barrier in graphene. The system acts as an interferometer based on an armchair graphene quantum ring, where the phase difference between interfering electronic wave functions for each path can be controlled by tuning either the height or the width of a potential barrier in the ring arms. By varying the parameters of the potential barriers, the interference can become completely destructive. We demonstrate how this interference effect can be used for developing a simple graphene-based logic gate with a high on/off ratio.
Electronic States and Persistent Currents in Nanowire Quantum Ring
Kokurin, I. A.
2018-04-01
The new model of a quantum ring (QR) defined inside a nanowire (NW) is proposed. The one-particle Hamiltonian for electron in [111]-oriented NW QR is constructed taking into account both Rashba and Dresselhaus spin-orbit coupling (SOC). The energy levels as a function of magnetic field are found using the exact numerical diagonalization. The persistent currents (both charge and spin) are calculated. The specificity of SOC and arising anticrossings in energy spectrum lead to unusual features in persistent current behavior. The variation of magnetic field or carrier concentration by means of gate can lead to pure spin persistent current with the charge current being zero.
Quantum theory of the optical and electronic properties of semiconductors
Haug, Hartmut
1990-01-01
The current technological revolution in the development of computing devices has created a demand for a textbook on the quantum theory of the electronic and optical properties of semiconductors and semiconductor devices. This book successfully fulfills this need. Based on lectures given by the authors, it is a comprehensive introduction for researchers or graduate-level students to the subject. Certain sections can also serve as a graduate-level textbook for use in solid state physics courses or for more specialized courses. The final chapters establish a direct link to current research in sem
Electronic structure of semiconductor interfaces
Energy Technology Data Exchange (ETDEWEB)
Herman, F
1983-02-01
The study of semiconductor interfaces is one of the most active and exciting areas of current semiconductor research. Because interfaces play a vital role in modern semiconductor technology (integrated circuits, heterojunction lasers, solar cells, infrared detectors, etc.), there is a strong incentive to understand interface properties at a fundamental level and advance existing technology thereby. At the same time, technological advances such as molecular beam epitaxy have paved the way for the fabrication of semiconductor heterojunctions and superlattices of novel design which exhibit unusual electronic, optical, and magnetic properties and offer unique opportunities for fundamental scientific research. A general perspective on this subject is offered treating such topics as the atomic and electronic structure of semiconductor surfaces and interfaces; oxidation and oxide layers; semiconductor heterojunctions and superlattices; rectifying metal-semiconductor contacts; and interface reactions. Recent progress is emphasized and some future directions are indicated. In addition, the role that large-scale scientific computation has played in furthering our theoretical understanding of semiconductor surfaces and interfaces is discussed. Finally, the nature of theoretical models, and the role they play in describing the physical world is considered.
Electronic structure of semiconductor interfaces
International Nuclear Information System (INIS)
Herman, F.
1983-01-01
The study of semiconductor interfaces is one of the most active and exciting areas of current semiconductor research. Because interfaces play a vital role in modern semiconductor technology (integrated circuits, heterojunction lasers, solar cells, infrared detectors, etc.), there is a strong incentive to understand interface properties at a fundamental level and advance existing technology thereby. At the same time, technological advances such as molecular beam epitaxy have paved the way for the fabrication of semiconductor heterojunctions and superlattices of novel design which exhibit unusual electronic, optical, and magnetic properties and offer unique opportunities for fundamental scientific research. A general perspective on this subject is offered treating such topics as the atomic and electronic structure of semiconductor surfaces and interfaces; oxidation and oxide layers; semiconductor heterojunctions and superlattices; rectifying metal-semiconductor contacts; and interface reactions. Recent progress is emphasized and some future directions are indicated. In addition, the role that large-scale scientific computation has played in furthering our theoretical understanding of semiconductor surfaces and interfaces is discussed. Finally, the nature of theoretical models, and the role they play in describing the physical world is considered. (Author) [pt
Effects of Electric Field on the Valence-Bond Property of an Electron in a Quantum-Dot Molecule
Institute of Scientific and Technical Information of China (English)
王立民; 罗莹; 马本堃
2002-01-01
The electronic structure of the quantum-dot molecules in an electric field is investigated by the finite element method with the effective mass approximation. The numerical calculation results show that the valence bond of the quantum-dot molecule alternates between covalent bonds and ionic bonds as the electric field increases. The valence-bond property can be reflected by the oscillator strength of the intraband transition. The bound state with the highest energy level in the quantum-dot molecule gradually changes into a quasibound state when the electric field increases.
Tomonaga-Luttinger physics in electronic quantum circuits.
Jezouin, S; Albert, M; Parmentier, F D; Anthore, A; Gennser, U; Cavanna, A; Safi, I; Pierre, F
2013-01-01
In one-dimensional conductors, interactions result in correlated electronic systems. At low energy, a hallmark signature of the so-called Tomonaga-Luttinger liquids is the universal conductance curve predicted in presence of an impurity. A seemingly different topic is the quantum laws of electricity, when distinct quantum conductors are assembled in a circuit. In particular, the conductances are suppressed at low energy, a phenomenon called dynamical Coulomb blockade. Here we investigate the conductance of mesoscopic circuits constituted by a short single-channel quantum conductor in series with a resistance, and demonstrate a proposed link to Tomonaga-Luttinger physics. We reformulate and establish experimentally a recently derived phenomenological expression for the conductance using a wide range of circuits, including carbon nanotube data obtained elsewhere. By confronting both conductance data and phenomenological expression with the universal Tomonaga-Luttinger conductance curve, we demonstrate experimentally the predicted mapping between dynamical Coulomb blockade and the transport across a Tomonaga-Luttinger liquid with an impurity.
Optical manipulation of electron spin in quantum dot systems
Villas-Boas, Jose; Ulloa, Sergio; Govorov, Alexander
2006-03-01
Self-assembled quantum dots (QDs) are of particular interest for fundamental physics because of their similarity with atoms. Coupling two of such dots and addressing them with polarized laser light pulses is perhaps even more interesting. In this paper we use a multi-exciton density matrix formalism to model the spin dynamics of a system with single or double layers of QDs. Our model includes the anisotropic electron-hole exchange in the dots, the presence of wetting layer states, and interdot tunneling [1]. Our results show that it is possible to switch the spin polarization of a single self-assembled quantum dot under elliptically polarized light by increasing the laser intensity. In the nonlinear mechanism described here, intense elliptically polarized light creates an effective exchange channel between the exciton spin states through biexciton states, as we demonstrate by numerical and analytical methods. We further show that the effect persists in realistic ensembles of dots, and we propose alternative ways to detect it. We also extend our study to a double layer of quantum dots, where we find a competition between Rabi frequency and tunneling oscillations. [1] J. M. Villas-Boas, S. E. Ulloa, and A. O. Govorov, Phys. Rev. Lett. 94, 057404 (2005); Phys. Rev. B 69, 125342 (2004).
Schaibley, J R; Burgers, A P; McCracken, G A; Duan, L-M; Berman, P R; Steel, D G; Bracker, A S; Gammon, D; Sham, L J
2013-04-19
The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this Letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to a single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot's excited state. We obtain a lower bound on the fidelity of entanglement of 0.59±0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement-based spin-spin entanglement which does not require sub-nanosecond timing resolution, we estimate that this system would enable near ideal performance. The inferred (usable) entanglement generation rate is 3×10(3) s(-1). This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network.
Capacitance-voltage characteristics of quantum well structures
Moon, C R; Choe, B D
1999-01-01
The characteristics of the apparent carrier distribution (ACD) of quantum well (QW) structures are investigated using the self-consistent simulation and the capacitance-voltage (C-V) profiling techniques. The simulation results on the differential carrier distribution show that the change of position expectation value of two-dimensional electrons determines the full width at half maximum of 100 K ACD peaks when conduction band offset is DELTA E sub c = 160 meV and the QW width t sub w is greater than 120 A. The contribution of Debye averaging effects to the ACD peaks becomes important as t sub w and DELTA E sub c values decrease and the temperature is increased. The influence of Debye averaging effects on ACD peaks appears differently according to the location of each well in multiple QWs. These results indicate that the extraction of QW parameters from the C-V profile should be done with caution.
Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Bădescu, Ş. C.; Lyanda-Geller, Y.; Reinecke, T. L.
2005-10-01
We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions.
Non-quantum electronic responses of zinc oxide nanomaterials
International Nuclear Information System (INIS)
Kim, Hansoo; Kim, Younghyun
2013-01-01
The influence of the high surface-to-volume ratio of ZnO nanomaterials, whose sizes are large enough to exclude the quantum effect, on electronic properties was investigated by spatially resolved valence electron energy loss spectroscopy. ZnO nanowires, nanoplates, and nanotubes with different sizes were fabricated and characterized. Both the reduced volume and the increased surface area of the large ZnO nanomaterials were found to be able to modify electronic properties significantly. Hence, a nanoplate and a nanotube with very small volumes show unique energy loss functions and dielectric functions different from those of bulk ZnO at all the probe points. On the other hand, a nanowire with a relatively large diameter (70 nm) has electronic properties similar to those of bulk ZnO at the center. However, they are dissimilar at the edge of the nanowire due to the component of surface parallel to the electron path and the reduced interaction volume. Moreover, some interband transitions shift positions and bulk plasmons change oscillator strength depending upon the size of the volume and the geometry of the surface. These empirical results demonstrate that semiconducting nanomaterials larger than the exciton Bohr radius can still behave differently from bulk materials due to the high ratio between surface area and volume. (paper)
Response of a relativistic quantum magnetized electron gas
International Nuclear Information System (INIS)
Melrose, Donald B; Weise, Jeanette I
2009-01-01
The response 4-tensor is derived for a spin-independent, relativistic magnetized quantum electron gas. The sum over spins is carried out both directly and using a procedure due to Ritus. The 4-tensor components are written in terms of a sum over the two solutions of the resonance condition for the particle 4-momentum. It is shown that the dispersive properties may be described in terms of a single plasma dispersion function, for arbitrary occupation numbers for electrons and positrons in each Landau level. The plasma dispersion function is evaluated explicitly in the completely degenerate and nondegenerate thermal limits. The perpendicular wave number appears in the arguments of J-functions, which are proportional to generalized Laguerre polynomials, but not in the plasma dispersion function. The result generalizes a known form for the response tensor for parallel propagation (in the completely degenerate case), when the J-functions are either zero or unity, to arbitrary angles of propagation.
Quantum Kinetic Theory and Applications Electrons, Photons, Phonons
Vasko, Fedir T
2006-01-01
This lecture-style monograph is addressed to several categories of readers. First, it will be useful for graduate students studying theory. Second, the topics covered should be interesting for postgraduate students of various specializations. Third, the researchers who want to understand the background of modern theoretical issues in more detail can find a number of useful results here. The phenomena covered involve kinetics of electron, phonon, and photon systems in solids. The dynamical properties and interactions of electrons, phonons, and photons are briefly described in Chapter 1. Further, in Chapters 2-8, the authors present the main theoretical methods: linear response theory, various kinetic equations for the quasiparticles under consideration, and diagram technique. The presentation of the key approaches is always accompanied by solutions of concrete problems to illustrate ways to apply the theory. The remaining chapters are devoted to various manifestations of quantum transport in solids. The choice...
SPAD electronics for high-speed quantum communications
Bienfang, Joshua C.; Restelli, Alessandro; Migdall, Alan
2011-01-01
We discuss high-speed electronics that support the use of single-photon avalanche diodes (SPADs) in gigahertz singlephoton communications systems. For InGaAs/InP SPADs, recent work has demonstrated reduced afterpulsing and count rates approaching 500 MHz can be achieved with gigahertz periodic-gating techniques designed to minimize the total avalanche charge to less than 100 fC. We investigate afterpulsing in this regime and establish a connection to observations using more conventional techniques. For Si SPADs, we report the benefits of improved timing electronics that enhance the temporal resolution of Si SPADs used in a free-space quantum key distribution (QKD) system operating in the GHz regime. We establish that the effects of count-rate fluctuations induced by daytime turbulent scintillation are significantly reduced, benefitting the performance of the QKD system.
Optical and Micro-Structural Characterization of MBE Grown Indium Gallium Nitride Polar Quantum Dots
El Afandy, Rami
2011-07-07
Gallium nitride and related materials have ushered in scientific and technological breakthrough for lighting, mass data storage and high power electronic applications. These III-nitride materials have found their niche in blue light emitting diodes and blue laser diodes. Despite the current development, there are still technological problems that still impede the performance of such devices. Three-dimensional nanostructures are proposed to improve the electrical and thermal properties of III-nitride optical devices. This thesis consolidates the characterization results and unveils the unique physical properties of polar indium gallium nitride quantum dots grown by molecular beam epitaxy technique. In this thesis, a theoretical overview of the physical, structural and optical properties of polar III-nitrides quantum dots will be presented. Particular emphasis will be given to properties that distinguish truncated-pyramidal III-nitride quantum dots from other III-V semiconductor based quantum dots. The optical properties of indium gallium nitride quantum dots are mainly dominated by large polarization fields, as well as quantum confinement effects. Hence, the experimental investigations for such quantum dots require performing bandgap calculations taking into account the internal strain fields, polarization fields and confinement effects. The experiments conducted in this investigation involved the transmission electron microscopy and x-ray diffraction as well as photoluminescence spectroscopy. The analysis of the temperature dependence and excitation power dependence of the PL spectra sheds light on the carrier dynamics within the quantum dots, and its underlying wetting layer. A further analysis shows that indium gallium nitride quantum dots through three-dimensional confinements are able to prevent the electronic carriers from getting thermalized into defects which grants III-nitrides quantum dot based light emitting diodes superior thermally induced optical
Oriented matroids—combinatorial structures underlying loop quantum gravity
Brunnemann, Johannes; Rideout, David
2010-10-01
We analyze combinatorial structures which play a central role in determining spectral properties of the volume operator (Ashtekar A and Lewandowski J 1998 Adv. Theor. Math. Phys. 1 388) in loop quantum gravity (LQG). These structures encode geometrical information of the embedding of arbitrary valence vertices of a graph in three-dimensional Riemannian space and can be represented by sign strings containing relative orientations of embedded edges. We demonstrate that these signature factors are a special representation of the general mathematical concept of an oriented matroid (Ziegler G M 1998 Electron. J. Comb.; Björner A et al 1999 Oriented Matroids (Cambridge: Cambridge University Press)). Moreover, we show that oriented matroids can also be used to describe the topology (connectedness) of directed graphs. Hence, the mathematical methods developed for oriented matroids can be applied to the difficult combinatorics of embedded graphs underlying the construction of LQG. As a first application we revisit the analysis of Brunnemann and Rideout (2008 Class. Quantum Grav. 25 065001 and 065002), and find that enumeration of all possible sign configurations used there is equivalent to enumerating all realizable oriented matroids of rank 3 (Ziegler G M 1998 Electron. J. Comb.; Björner A et al 1999 Oriented Matroids (Cambridge: Cambridge University Press)), and thus can be greatly simplified. We find that for 7-valent vertices having no coplanar triples of edge tangents, the smallest non-zero eigenvalue of the volume spectrum does not grow as one increases the maximum spin jmax at the vertex, for any orientation of the edge tangents. This indicates that, in contrast to the area operator, considering large jmax does not necessarily imply large volume eigenvalues. In addition we give an outlook to possible starting points for rewriting the combinatorics of LQG in terms of oriented matroids.
Numerical simulations of time-resolved quantum electronics
International Nuclear Information System (INIS)
Gaury, Benoit; Weston, Joseph; Santin, Matthieu; Houzet, Manuel; Groth, Christoph; Waintal, Xavier
2014-01-01
Numerical simulation has become a major tool in quantum electronics both for fundamental and applied purposes. While for a long time those simulations focused on stationary properties (e.g. DC currents), the recent experimental trend toward GHz frequencies and beyond has triggered a new interest for handling time-dependent perturbations. As the experimental frequencies get higher, it becomes possible to conceive experiments which are both time-resolved and fast enough to probe the internal quantum dynamics of the system. This paper discusses the technical aspects–mathematical and numerical–associated with the numerical simulations of such a setup in the time domain (i.e. beyond the single-frequency AC limit). After a short review of the state of the art, we develop a theoretical framework for the calculation of time-resolved observables in a general multiterminal system subject to an arbitrary time-dependent perturbation (oscillating electrostatic gates, voltage pulses, time-varying magnetic fields, etc.) The approach is mathematically equivalent to (i) the time-dependent scattering formalism, (ii) the time-resolved non-equilibrium Green’s function (NEGF) formalism and (iii) the partition-free approach. The central object of our theory is a wave function that obeys a simple Schrödinger equation with an additional source term that accounts for the electrons injected from the electrodes. The time-resolved observables (current, density, etc.) and the (inelastic) scattering matrix are simply expressed in terms of this wave function. We use our approach to develop a numerical technique for simulating time-resolved quantum transport. We find that the use of this wave function is advantageous for numerical simulations resulting in a speed up of many orders of magnitude with respect to the direct integration of NEGF equations. Our technique allows one to simulate realistic situations beyond simple models, a subject that was until now beyond the simulation
A surface-gated InSb quantum well single electron transistor
International Nuclear Information System (INIS)
Orr, J M S; Buckle, P D; Fearn, M; Storey, C J; Buckle, L; Ashley, T
2007-01-01
Single electron charging effects in a surface-gated InSb/AlInSb QW structure are reported. This material, due to its large g-factor and light effective mass, offers considerable advantages over more commonly used materials, such as GaAs, for quantum information processing devices. However, differences in material and device technology result in significant processing challenges. Simple Coulomb blockade and quantized confinement models are considered to explain the observation of conductance oscillations in these structures. The charging energy (e 2 /C) is found to be comparable with the energy spectrum for single particle states (ΔE)
Poly-silicon quantum-dot single-electron transistors
International Nuclear Information System (INIS)
Kang, Kwon-Chil; Lee, Joung-Eob; Lee, Jung-Han; Lee, Jong-Ho; Shin, Hyung-Cheol; Park, Byung-Gook
2012-01-01
For operation of a single-electron transistors (SETs) at room temperature, we proposed a fabrication method for a SET with a self-aligned quantum dot by using polycrystalline silicon (poly-Si). The self-aligned quantum dot is formed by the selective etching of a silicon nanowire on a planarized surface and the subsequent deposition and etch-back of poly-silicon or chemical mechanical polishing (CMP). The two tunneling barriers of the SET are fabricated by thermal oxidation. Also, to decrease the leakage current and control the gate capacitance, we deposit a hard oxide mask layer. The control gate is formed by using an electron beam and photolithography on chemical vapor deposition (CVD). Owing to the small capacitance of the narrow control gate due to the tetraethyl orthosilicate (TEOS) hard mask, we observe clear Coulomb oscillation peaks and differential trans-conductance curves at room temperature. The clear oscillation period of the fabricated SET is 2.0 V.
Quasiparticle GW calculations within the GPAW electronic structure code
DEFF Research Database (Denmark)
Hüser, Falco
The GPAW electronic structure code, developed at the physics department at the Technical University of Denmark, is used today by researchers all over the world to model the structural, electronic, optical and chemical properties of materials. They address fundamental questions in material science...... and use their knowledge to design new materials for a vast range of applications. Todays hottest topics are, amongst many others, better materials for energy conversion (e.g. solar cells), energy storage (batteries) and catalysts for the removal of environmentally dangerous exhausts. The mentioned...... properties are to a large extent governed by the physics on the atomic scale, that means pure quantum mechanics. For many decades, Density Functional Theory has been the computational method of choice, since it provides a fairly easy and yet accurate way of determining electronic structures and related...
Quantum Effects in Inverse Opal Structures
Bleiweiss, Michael; Datta, Timir; Lungu, Anca; Yin, Ming; Iqbal, Zafar; Palm, Eric; Brandt, Bruce
2002-03-01
Properties of bismuth inverse opals and carbon opal replicas were studied. The bismuth nanostructures were fabricated by pressure infiltration into porous artificial opal, while the carbon opal replicas were created via CVD. These structures form a regular three-dimensional network in which the bismuth and carbon regions percolate in all directions between the close packed spheres of SiO_2. The sizes of the conducting regions are of the order of tens of nanometers. Static susceptibility of the bismuth inverse opal showed clear deHaas-vanAlphen oscillations. Transport measurements, including Hall, were done using standard ac four and six probe techniques in fields up to 17 T* and temperatures between 4.2 and 200 K. Observations of Shubnikov-deHaas oscillations in magnetoresistance, one-dimensional weak localization, quantum Hall and other effects will be discussed. *Performed at the National High Magnetic Field Lab (NHMFL) FSU, Tallahassee, FL. This work was partially supported by grants from DARPA-nanothermoelectrics, NASA-EPSCOR and the USC nanocenter.
Electron Raman scattering in semiconductor quantum well wire of cylindrical ring geometry
International Nuclear Information System (INIS)
Betancourt-Riera, Re.; Betancourt-Riera, Ri.; Nieto Jalil, J. M.; Riera, R.
2015-01-01
We study the electron states and the differential cross section for an electron Raman scattering process in a semiconductor quantum well wire of cylindrical ring geometry. The electron Raman scattering developed here can be used to provide direct information about the electron band structures of these confinement systems. We assume that the system grows in a GaAs/Al 0.35 Ga 0.65 As matrix. The system is modeled by considering T = 0 K and also a single parabolic conduction band, which is split into a sub-band system due to the confinement. The emission spectra are discussed for different scattering configurations, and the selection rules for the processes are also studied. Singularities in the spectra are found and interpreted. (paper)
International Nuclear Information System (INIS)
Gilmore, Joel; McKenzie, Ross H
2005-01-01
We give a theoretical treatment of the interaction of electronic excitations (excitons) in biomolecules and quantum dots with the surrounding polar solvent. Significant quantum decoherence occurs due to the interaction of the electric dipole moment of the solute with the fluctuating electric dipole moments of the individual molecules in the solvent. We introduce spin boson models which could be used to describe the effects of decoherence on the quantum dynamics of biomolecules which undergo light-induced conformational change and on biomolecules or quantum dots which are coupled by Foerster resonant energy transfer
Wu, Feng; Sun, Haiding; Ajia, Idris A.; Roqan, Iman S.; Zhang, Daliang; Dai, Jiangnan; Chen, Changqing; Feng, Zhe Chuan; Li, Xiaohang
2017-01-01
Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.
Wu, Feng
2017-05-03
Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.
International Nuclear Information System (INIS)
Birkholz, Jens Eiko
2008-01-01
We study the influence of the spin-orbit interaction on the electronic transport through quantum dots and quantum wires of correlated electrons. Starting with a one-dimensional infinite continuum model without Coulomb interaction, we analyze the interplay of the spin-orbit interaction, an external magnetic field, and an external potential leading to currents with significant spin-polarization in appropriate parameter regimes. Since lattice models are known to often be superior to continuum models in describing the experimental situation of low-dimensional mesoscopic systems, we construct a lattice model which exhibits the same low-energy physics in terms of energy dispersion and spin expectation values. Confining the lattice to finite length and connecting it to two semi-infinite noninteracting Fermi liquid leads, we calculate the zero temperature linear conductance using the Landauer-Bttiker formalism and show that spin-polarization effects also evolve for the lattice model by adding an adequate potential structure and can be controlled by tuning the overall chemical potential of the system (quantum wire and leads). Next, we allow for a finite Coulomb interaction and use the functional renormalization group (fRG) method to capture correlation effects induced by the Coulomb interaction. The interacting system is thereby transformed into a noninteracting system with renormalized system parameters. For short wires (∝100 lattice sites), we show that the energy regime in which spin polarization is found is strongly affected by the Coulomb interaction. For long wires (>1000 lattice sites), we find the power-law suppression of the total linear conductance on low energy scales typical for inhomogeneous Luttinger liquids while the degree of spin polarization stays constant. Considering quantum dots which consist of two lattice sites, we observe the well-known Kondo effect and analyze, how the Kondo temperature is affected by the spin-orbit interaction. Moreover, we show
Associated quantum vector bundles and symplectic structure on a quantum space
International Nuclear Information System (INIS)
Coquereaux, R.; Garcia, A.O.; Trinchero, R.
2000-01-01
We define a quantum generalization of the algebra of functions over an associated vector bundle of a principal bundle. Here the role of a quantum principal bundle is played by a Hopf-Galois extension. Smash products of an algebra times a Hopf algebra H are particular instances of these extensions, and in these cases we are able to define a differential calculus over their associated vector bundles without requiring the use of a (bicovariant) differential structure over H. Moreover, if H is coquasitriangular, it coacts naturally on the associated bundle, and the differential structure is covariant. We apply this construction to the case of the finite quotient of the SL q (2) function Hopf algebra at a root of unity (q 3 = 1) as the structure group, and a reduced 2-dimensional quantum plane as both the 'base manifold' and fibre, getting an algebra which generalizes the notion of classical phase space for this quantum space. We also build explicitly a differential complex for this phase space algebra, and find that levels 0 and 2 support a (co)representation of the quantum symplectic group. On this phase space we define vector fields, and with the help of the Sp q structure we introduce a symplectic form relating 1-forms to vector fields. This leads naturally to the introduction of Poisson brackets, a necessary step to do 'classical' mechanics on a quantum space, the quantum plane. (author)
Polarized fine structure in the excitation spectrum of a negatively charged quantum dot
Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Badescu, S. C.; Lyanda-Geller, Y.; Reinecke, T. L.
2005-01-01
We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of qua...
Alignment creation by elastic electron scattering. A quantum treatment
International Nuclear Information System (INIS)
Csanak, G.; Kilcrease, D.P.; Fursa, D.V.; Bray, I.
2004-01-01
Alignment creation by elastic heavy particle scattering has been studied by many authors. A formula for the alignment creation cross section by elastic scattering is obtained by quantum-mechanical methods. The formula obtained differs from the analogous formula relevant for inelastic electron scattering. In the case of a J=1 to J=1 transition according to the inelastic formula, the alignment created is proportional to the quantity σ (1) - σ (0) where σ (M) is the excitation cross section of the M magnetic sublevel and thus σ (1) = (σ 1-1 + σ 10 + σ 11 )/3 and σ (0) = (σ 0-1 +σ 00 + σ 01 )/3 where σ MM' refers to the cross section of the electron impact induced M' to M transition. In the elastic scattering alignment creation formula obtained in the case of a J=1 to J=1 elastic scattering, the alignment created is proportional to the quantity q(1) - q(0) where q(1) σ (1) - σ 11 /3 and q(0) = σ 00 /3. Thus in obtaining q(M), the elastic scattering cross section by the M magnetic sublevel, σ MM' , is subtracted. This derivation considered only direct scattering, i.e. the incident electron was considered distinguishable from the target electrons. (Y.Kazumata)
Quantum dynamics and electronic spectroscopy within the framework of wavelets
International Nuclear Information System (INIS)
Toutounji, Mohamad
2013-01-01
This paper serves as a first-time report on formulating important aspects of electronic spectroscopy and quantum dynamics in condensed harmonic systems using the framework of wavelets, and a stepping stone to our future work on developing anharmonic wavelets. The Morlet wavelet is taken to be the mother wavelet for the initial state of the system of interest. This work reports daughter wavelets that may be used to study spectroscopy and dynamics of harmonic systems. These wavelets are shown to arise naturally upon optical electronic transition of the system of interest. Natural birth of basis (daughter) wavelets emerging on exciting an electronic two-level system coupled, both linearly and quadratically, to harmonic phonons is discussed. It is shown that this takes place through using the unitary dilation and translation operators, which happen to be part of the time evolution operator of the final electronic state. The corresponding optical autocorrelation function and linear absorption spectra are calculated to test the applicability and correctness of the herein results. The link between basis wavelets and the Liouville space generating function is established. An anharmonic mother wavelet is also proposed in the case of anharmonic electron–phonon coupling. A brief description of deriving anharmonic wavelets and the corresponding anharmonic Liouville space generating function is explored. In conclusion, a mother wavelet (be it harmonic or anharmonic) which accounts for Duschinsky mixing is suggested. (paper)
Huang, Danhong; Iurov, Andrii; Gao, Fei; Gumbs, Godfrey; Cardimona, D. A.
2018-02-01
The effects of point defects on the loss of either energies of ballistic electron beams or incident photons are studied by using a many-body theory in a multi-quantum-well system. This theory includes the defect-induced vertex correction to a bare polarization function of electrons within the ladder approximation, and the intralayer and interlayer screening of defect-electron interactions is also taken into account in the random-phase approximation. The numerical results of defect effects on both energy-loss and optical-absorption spectra are presented and analyzed for various defect densities, numbers of quantum wells, and wave vectors. The diffusion-reaction equation is employed for calculating distributions of point defects in a layered structure. For completeness, the production rate for Frenkel-pair defects and their initial concentration are obtained based on atomic-level molecular-dynamics simulations. By combining the defect-effect, diffusion-reaction, and molecular-dynamics models with an available space-weather-forecast model, it will be possible in the future to enable specific designing for electronic and optoelectronic quantum devices that will be operated in space with radiation-hardening protection and, therefore, effectively extend the lifetime of these satellite onboard electronic and optoelectronic devices. Specifically, this theory can lead to a better characterization of quantum-well photodetectors not only for high quantum efficiency and low dark current density but also for radiation tolerance or mitigating the effects of the radiation.
Computer-automated tuning of semiconductor double quantum dots into the single-electron regime
Energy Technology Data Exchange (ETDEWEB)
Baart, T. A.; Vandersypen, L. M. K. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Eendebak, P. T. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Netherlands Organisation for Applied Scientific Research (TNO), P.O. Box 155, 2600 AD Delft (Netherlands); Reichl, C.; Wegscheider, W. [Solid State Physics Laboratory, ETH Zürich, 8093 Zürich (Switzerland)
2016-05-23
We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the double quantum dots into the single-electron regime. The algorithm only requires (1) prior knowledge of the gate design and (2) the pinch-off value of the single gate T that is shared by all the quantum dots. This work significantly alleviates the user effort required to tune multiple quantum dot devices.
Logical and mathematical structures of quantum mechanics
International Nuclear Information System (INIS)
Beltrametti, E.G.; Cassinelli, G.
1976-01-01
The logic associated with a physical system is first analysed, and the general properties of observable and states are discussed. The logic of the Hilbert-space formulation of quantum mechanics and of pure, ideal measurements is described
Nonlinearity in structural and electronic materials
International Nuclear Information System (INIS)
Bishop, A.R.; Beardmore, K.M.; Ben-Naim, E.
1997-01-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project strengthens a nonlinear technology base relevant to a variety of problems arising in condensed matter and materials science, and applies this technology to those problems. In this way the controlled synthesis of, and experiments on, novel electronic and structural materials provide an important focus for nonlinear science, while nonlinear techniques help advance the understanding of the scientific principles underlying the control of microstructure and dynamics in complex materials. This research is primarily focused on four topics: (1) materials microstructure: growth and evolution, and porous media; (2) textures in elastic/martensitic materials; (3) electro- and photo-active polymers; and (4) ultrafast photophysics in complex electronic materials. Accomplishments included the following: organization of a ''Nonlinear Materials'' seminar series and international conferences including ''Fracture, Friction and Deformation,'' ''Nonequilibrium Phase Transitions,'' and ''Landscape Paradigms in Physics and Biology''; invited talks at international conference on ''Synthetic Metals,'' ''Quantum Phase Transitions,'' ''1996 CECAM Euroconference,'' and the 1995 Fall Meeting of the Materials Research Society; large-scale simulations and microscopic modeling of nonlinear coherent energy storage at crack tips and sliding interfaces; large-scale simulation and microscopic elasticity theory for precursor microstructure and dynamics at solid-solid diffusionless phase transformations; large-scale simulation of self-assembling organic thin films on inorganic substrates; analysis and simulation of smoothing of rough atomic surfaces; and modeling and analysis of flux pattern formation in equilibrium and nonequilibrium Josephson junction arrays and layered superconductors
High-fidelity quantum gates on quantum-dot-confined electron spins in low-Q optical microcavities
Li, Tao; Gao, Jian-Cun; Deng, Fu-Guo; Long, Gui-Lu
2018-04-01
We propose some high-fidelity quantum circuits for quantum computing on electron spins of quantum dots (QD) embedded in low-Q optical microcavities, including the two-qubit controlled-NOT gate and the multiple-target-qubit controlled-NOT gate. The fidelities of both quantum gates can, in principle, be robust to imperfections involved in a practical input-output process of a single photon by converting the infidelity into a heralded error. Furthermore, the influence of two different decay channels is detailed. By decreasing the quality factor of the present microcavity, we can largely increase the efficiencies of these quantum gates while their high fidelities remain unaffected. This proposal also has another advantage regarding its experimental feasibility, in that both quantum gates can work faithfully even when the QD-cavity systems are non-identical, which is of particular importance in current semiconductor QD technology.
Evaluation of quantum-chemical methods of radiolysis stability for macromolecular structures
International Nuclear Information System (INIS)
Postolache, Cristian; Matei, Lidia
2005-01-01
The behavior of macromolecular structures in ionising fields was analyzed by quantum-chemical methods. In this study the primary radiolytic effect was analyzed using a two-step radiolytic mechanism: a) ionisation of molecule and spatial redistribution of atoms in order to reach a minimum value of energy, characteristic to the quantum state; b) neutralisation of the molecule by electron capture and its rapid dissociation into free radicals. Chemical bonds suspected to break are located in the distribution region of LUMO orbital and have minimal homolytic dissociation energies. Representative polymer structures (polyethylene, polypropylene, polystyrene, poly α and β polystyrene, polyisobutylene, polytetrafluoroethylene, poly methylsiloxanes) were analyzed. (authors)
Elafandy, Rami T.
2011-12-01
Comparison between indium rich (27%) InGaN/GaN quantum dots (QDs) and their underlying wetting layer (WL) is performed by means of optical and structural characterizations. With increasing temperature, micro-photoluminescence (μPL) study reveals the superior ability of QDs to prevent carrier thermalization to nearby traps compared to the two dimensional WL. Thus, explaining the higher internal quantum efficiency of the QD nanostructure compared to the higher dimensional WL. Structural characterization (X-ray diffraction (XRD)) and transmission electron microscopy (TEM)) reveal an increase in the QD indium content over the WL indium content which is due to strain induced drifts. © 2011 IEEE.
International Nuclear Information System (INIS)
Nozawa, Tomohiro; Arakawa, Yasuhiko
2014-01-01
The intraband transitions which are essential for quantum dot intermediate band solar cells (QD IBSCs) are theoretically investigated by estimating the matrix elements from a ground bound state, which is often regarded as an intermediate band (IB), to conduction band (CB) states for a structure with a quantum dot (QD) embedded in a matrix (a QD/matrix structure). We have found that the QD pushes away the electron envelope functions (probability densities) from the QD region in almost all quantum states above the matrix CB minimum. As a result, the matrix elements of the intraband transitions in the QD/matrix structure are largely reduced, compared to those calculated assuming the envelope functions of free electrons (i.e., plane-wave envelope functions) in a matrix structure as the final states of the intraband transitions. The result indicates the strong influence of the QD itself on the intraband transitions from the IB to the CB states in QD IBSC devices. This work will help in better understanding the problem of the intraband transitions and give new insight, that is, engineering of quantum states is indispensable for the realization of QD IBSCs with high solar energy conversion efficiencies. (paper)
From structure to spectra. Tight-binding theory of InGaAs quantum dots
International Nuclear Information System (INIS)
Goldmann, Elias
2014-01-01
Self-assembled semiconductor quantum dots have raised considerable interest in the last decades due to a multitude of possible applications ranging from carrier storage to light emitters, lasers and future quantum communication devices. Quantum dots offer unique electronic and photonic properties due to the three-dimensional confinement of charge carriers and the coupling to a quasi-continuum of wetting layer and barrier states. In this work we investigate the electronic structure of In x Ga 1-x As quantum dots embedded in GaAs, considering realistic quantum dot geometries and Indium concentrations. We utilize a next-neighbour sp 3 s * tight-binding model for the calculation of electronic single-particle energies and wave functions bound in the nanostructure and account for strain arising from lattice mismatch of the constituent materials atomistically. With the calculated single-particle wave functions we derive Coulomb matrix elements and include them into a configuration interaction treatment, yielding many-particle states and energies of the interacting many-carrier system. Also from the tight-binding single-particle wave functions we derive dipole transition strengths to obtain optical quantum dot emission and absorption spectra with Fermi's golden rule. Excitonic fine-structure splittings are obtained, which play an important role for future quantum cryptography and quantum communication devices for entanglement swapping or quantum repeating. For light emission suited for long-range quantum-crypted fiber communication InAs quantum dots are embedded in an In x Ga 1-x As strain-reducing layer, shifting the emission wavelength into telecom low-absorption windows. We investigate the influence of the strain-reducing layer Indium concentration on the excitonic finestructure splitting. The fine-structure splitting is found to saturate and, in some cases, even reduce with strain-reducing layer Indium concentration, a result being counterintuitively. Our result
From structure to spectra. Tight-binding theory of InGaAs quantum dots
Energy Technology Data Exchange (ETDEWEB)
Goldmann, Elias
2014-07-23
Self-assembled semiconductor quantum dots have raised considerable interest in the last decades due to a multitude of possible applications ranging from carrier storage to light emitters, lasers and future quantum communication devices. Quantum dots offer unique electronic and photonic properties due to the three-dimensional confinement of charge carriers and the coupling to a quasi-continuum of wetting layer and barrier states. In this work we investigate the electronic structure of In{sub x}Ga{sub 1-x}As quantum dots embedded in GaAs, considering realistic quantum dot geometries and Indium concentrations. We utilize a next-neighbour sp{sup 3}s{sup *} tight-binding model for the calculation of electronic single-particle energies and wave functions bound in the nanostructure and account for strain arising from lattice mismatch of the constituent materials atomistically. With the calculated single-particle wave functions we derive Coulomb matrix elements and include them into a configuration interaction treatment, yielding many-particle states and energies of the interacting many-carrier system. Also from the tight-binding single-particle wave functions we derive dipole transition strengths to obtain optical quantum dot emission and absorption spectra with Fermi's golden rule. Excitonic fine-structure splittings are obtained, which play an important role for future quantum cryptography and quantum communication devices for entanglement swapping or quantum repeating. For light emission suited for long-range quantum-crypted fiber communication InAs quantum dots are embedded in an In{sub x}Ga{sub 1-x}As strain-reducing layer, shifting the emission wavelength into telecom low-absorption windows. We investigate the influence of the strain-reducing layer Indium concentration on the excitonic finestructure splitting. The fine-structure splitting is found to saturate and, in some cases, even reduce with strain-reducing layer Indium concentration, a result being
Gap Structure and Gapless Structure in Fractional Quantum Hall Effect
Directory of Open Access Journals (Sweden)
Shosuke Sasaki
2012-01-01
Full Text Available Higher-order composite fermion states are correlated with many quasiparticles. The energy calculations are very complicated. We develop the theory of Tao and Thouless to explain them. The total Hamiltonian is (+, where includes Landau energies and classical Coulomb energies. We find the most uniform electron configuration in Landau states which has the minimum energy of . At =(2−1/(2, all the nearest electron pairs are forbidden to transfer to any empty states because of momentum conservation. Therefore, perturbation energies of the nearest electron pairs are zero in all order of perturbation. At =/(2−1, /(2+1, all the nearest electron (or hole pairs can transfer to all hole (or electron states. At =4/11, 4/13, 5/13, 5/17, 6/17, only the specific nearest hole pairs can transfer to all electron states. For example, the nearest-hole-pair energy at =4/11 is lower than the limiting energies from both sides (the left side =(4+1/(11+3 and the right side =(4−1/(11−3 for infinitely large . Thus, the nearest-hole-pair energy at specific is different from the limiting values from both sides. The property yields energy gap for the specific . Also gapless structure appears at other filling factors (e.g., at =1/2.
Deo, Vincent; Zhang, Yao; Soghomonian, Victoria; Heremans, Jean J.
2015-03-01
Quantum interference is used to measure the spin interactions between an InAs surface electron system and the iron center in the biomolecule hemin in nanometer proximity in a bio-organic/semiconductor device structure. The interference quantifies the influence of hemin on the spin decoherence properties of the surface electrons. The decoherence times of the electrons serve to characterize the biomolecule, in an electronic complement to the use of spin decoherence times in magnetic resonance. Hemin, prototypical for the heme group in hemoglobin, is used to demonstrate the method, as a representative biomolecule where the spin state of a metal ion affects biological functions. The electronic determination of spin decoherence properties relies on the quantum correction of antilocalization, a result of quantum interference in the electron system. Spin-flip scattering is found to increase with temperature due to hemin, signifying a spin exchange between the iron center and the electrons, thus implying interactions between a biomolecule and a solid-state system in the hemin/InAs hybrid structure. The results also indicate the feasibility of artificial bioinspired materials using tunable carrier systems to mediate interactions between biological entities.
Structure and reactions of quantum halos
International Nuclear Information System (INIS)
Jensen, A.S.; Riisager, K.; Fedorov, D.V.; Garrido, E.
2004-01-01
This article provides an overview of the basic principles of the physics of quantum halo systems, defined as bound states of clusters of particles with a radius extending well into classically forbidden regions. Exploiting the consequences of this definition, the authors derive the conditions for occurrence in terms of the number of clusters, binding energy, angular momentum, cluster charges, and excitation energy. All these quantities must be small. The article discusses the transitions between different cluster divisions and the importance of thresholds for cluster or particle decay, with particular attention to the Efimov effect and the related exotic states. The pertinent properties can be described by the use of dimensionless variables. Then universal and specific properties can be distinguished, as shown in a series of examples selected from nuclear, atomic, and molecular systems. The neutron dripline is especially interesting for nuclei and negative ions for atoms. For molecules, in which the cluster division comes naturally, a wider range of possibilities exists. Halos in two dimensions have very different properties, and their states are easily spatially extended, whereas Borromean systems are unlikely and spatially confined. The Efimov effect and the Thomas collapse occur only for dimensions between 2.3 and 3.8 and thus not for 2. High-energy reactions directly probe the halo structure. The authors discuss the reaction mechanisms for high-energy nuclear few-body halo breakup on light, intermediate, and heavy nuclear targets. For light targets, the strong interaction dominates, while for heavy targets, the Coulomb interaction dominates. For intermediate targets these processes are of comparable magnitude. As in atomic and molecular physics, a geometric impact-parameter picture is very appropriate. Finally, the authors briefly consider the complementary processes involving electroweak probes available through beta decay, electromagnetic transitions, and
Ligand-assisted fabrication, structure, and luminescence properties of Fe:ZnSe quantum dots
International Nuclear Information System (INIS)
Xie, Ruishi; Zhang, Xingquan; Liu, Haifeng
2014-01-01
Highlights: • A green route is developed for synthesis of water-soluble and fluorescent Fe:ZnSe quantum dots. • Tunable luminescence intensity can be realized with different ligand-to-Zn molar ratios. • The obtained quantum dots are in the so-called “quantum confinement regime”. -- Abstract: Here, we report a synthetic route for highly emissive Fe:ZnSe quantum dots in aqueous media using the mercaptoacetic acid ligand as stabilizing agent. The structural, morphological, componential, and optical properties of the resulting quantum dots were explored by the X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence and UV–visible absorption spectroscopies. The average crystallite size was calculated to be about ca., 4.0 nm using the Scherrer equation, which correlates well with the value obtained from the transmission electron microscopy analysis. The obtained water-soluble Fe:ZnSe quantum dots in the so-called “quantum confinement regime” are spherical shaped, possess the cubic sphalerite crystal structure, and exhibit tunable luminescence properties. The presence of mercaptoacetic acid on the surface of Fe:ZnSe quantum dots was confirmed by the Fourier transform infrared spectroscopy measurements. As the ligand/Zn molar ratio increases from 1.3 to 2.8, there is little shift in the absorption peak of the Fe:ZnSe sample, indicating that the particle size of the obtained quantum dots is not changed during the synthetic process. The photoluminescence quantum yield of the as-prepared water-soluble Fe:ZnSe quantum dots can be up to 39%. The molar ratio of ligand-to-Zn plays a crucial role in determining the final luminescence properties of the resulting quantum dots, and the maximum PL intensity appears as the ligand-to-Zn molar ratio is 2.2. In addition, the underlying mechanism for
Ligand-assisted fabrication, structure, and luminescence properties of Fe:ZnSe quantum dots
Energy Technology Data Exchange (ETDEWEB)
Xie, Ruishi, E-mail: rxie@foxmail.com; Zhang, Xingquan; Liu, Haifeng
2014-03-15
Highlights: • A green route is developed for synthesis of water-soluble and fluorescent Fe:ZnSe quantum dots. • Tunable luminescence intensity can be realized with different ligand-to-Zn molar ratios. • The obtained quantum dots are in the so-called “quantum confinement regime”. -- Abstract: Here, we report a synthetic route for highly emissive Fe:ZnSe quantum dots in aqueous media using the mercaptoacetic acid ligand as stabilizing agent. The structural, morphological, componential, and optical properties of the resulting quantum dots were explored by the X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence and UV–visible absorption spectroscopies. The average crystallite size was calculated to be about ca., 4.0 nm using the Scherrer equation, which correlates well with the value obtained from the transmission electron microscopy analysis. The obtained water-soluble Fe:ZnSe quantum dots in the so-called “quantum confinement regime” are spherical shaped, possess the cubic sphalerite crystal structure, and exhibit tunable luminescence properties. The presence of mercaptoacetic acid on the surface of Fe:ZnSe quantum dots was confirmed by the Fourier transform infrared spectroscopy measurements. As the ligand/Zn molar ratio increases from 1.3 to 2.8, there is little shift in the absorption peak of the Fe:ZnSe sample, indicating that the particle size of the obtained quantum dots is not changed during the synthetic process. The photoluminescence quantum yield of the as-prepared water-soluble Fe:ZnSe quantum dots can be up to 39%. The molar ratio of ligand-to-Zn plays a crucial role in determining the final luminescence properties of the resulting quantum dots, and the maximum PL intensity appears as the ligand-to-Zn molar ratio is 2.2. In addition, the underlying mechanism for
Relativity, symmetry and the structure of quantum theory
Klink, William H; Schweiger, Wolfgang
Quantum theory is one of the most successful of all physical theories. Our everyday world is dominated by devices that function because of knowledge of the quantum world. Yet many, physicists and non-physicists alike, find the theory which explains the behavior of the quantum world baffling and strange. This book is the first in a series of three that argues that relativity and symmetry determine the structure of quantum theory. That is to say, the structure of quantum theory is what it is because of relativity and symmetry. There are different types of relativity, each leading to a particular type of quantum theory. This book deals specifically with what we call Newton relativity, the form of relativity built into Newtonian mechanics, and the quantum theory to which it gives rise, which we call Galilean (often misleadingly called non-relativistic) quantum theory. Key Features: • Meaning and significance of the term of relativity; discussion of the principle of relativity. • Relation of symmetry to relati...
Impact of Relativistic Electron Beam on Hole Acoustic Instability in Quantum Semiconductor Plasmas
Siddique, M.; Jamil, M.; Rasheed, A.; Areeb, F.; Javed, Asif; Sumera, P.
2018-01-01
We studied the influence of the classical relativistic beam of electrons on the hole acoustic wave (HAW) instability exciting in the semiconductor quantum plasmas. We conducted this study by using the quantum-hydrodynamic model of dense plasmas, incorporating the quantum effects of semiconductor plasma species which include degeneracy pressure, exchange-correlation potential and Bohm potential. Analysis of the quantum characteristics of semiconductor plasma species along with relativistic effect of beam electrons on the dispersion relation of the HAW is given in detail qualitatively and quantitatively by plotting them numerically. It is worth mentioning that the relativistic electron beam (REB) stabilises the HAWs exciting in semiconductor (GaAs) degenerate plasma.
Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire
International Nuclear Information System (INIS)
Munguía-Rodríguez, M; Riera, R; Betancourt-Riera, Ri; Betancourt-Riera, Re; Nieto Jalil, J M
2016-01-01
The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire is calculated, and expressions for the electronic states are presented. The system is modeled by considering T = 0 K and also with a single parabolic conduction band, which is split into a subband system due to the confinement. The gain and differential cross-section for an electron Raman scattering process are obtained. In addition, the emission spectra for several scattering configurations are discussed, and interpretations of the singularities found in the spectra are given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers. (paper)
Quantum criticality around metal-insulator transitions of strongly correlated electron systems
Misawa, Takahiro; Imada, Masatoshi
2007-03-01
Quantum criticality of metal-insulator transitions in correlated electron systems is shown to belong to an unconventional universality class with violation of the Ginzburg-Landau-Wilson (GLW) scheme formulated for symmetry breaking transitions. This unconventionality arises from an emergent character of the quantum critical point, which appears at the marginal point between the Ising-type symmetry breaking at nonzero temperatures and the topological transition of the Fermi surface at zero temperature. We show that Hartree-Fock approximations of an extended Hubbard model on square lattices are capable of such metal-insulator transitions with unusual criticality under a preexisting symmetry breaking. The obtained universality is consistent with the scaling theory formulated for Mott transitions and with a number of numerical results beyond the mean-field level, implying that preexisting symmetry breaking is not necessarily required for the emergence of this unconventional universality. Examinations of fluctuation effects indicate that the obtained critical exponents remain essentially exact beyond the mean-field level. It further clarifies the whole structure of singularities by a unified treatment of the bandwidth-control and filling-control transitions. Detailed analyses of the criticality, containing diverging carrier density fluctuations around the marginal quantum critical point, are presented from microscopic calculations and reveal the nature as quantum critical “opalescence.” The mechanism of emerging marginal quantum critical point is ascribed to a positive feedback and interplay between the preexisting gap formation present even in metals and kinetic energy gain (loss) of the metallic carrier. Analyses of crossovers between GLW type at nonzero temperature and topological type at zero temperature show that the critical exponents observed in (V,Cr)2O3 and κ-ET -type organic conductors provide us with evidence for the existence of the present marginal
Correlative Light- and Electron Microscopy Using Quantum Dot Nanoparticles.
Killingsworth, Murray C; Bobryshev, Yuri V
2016-08-07
A method is described whereby quantum dot (QD) nanoparticles can be used for correlative immunocytochemical studies of human pathology tissue using widefield fluorescence light microscopy and transmission electron microscopy (TEM). To demonstrate the protocol we have immunolabeled ultrathin epoxy sections of human somatostatinoma tumor using a primary antibody to somatostatin, followed by a biotinylated secondary antibody and visualization with streptavidin conjugated 585 nm cadmium-selenium (CdSe) quantum dots (QDs). The sections are mounted on a TEM specimen grid then placed on a glass slide for observation by widefield fluorescence light microscopy. Light microscopy reveals 585 nm QD labeling as bright orange fluorescence forming a granular pattern within the tumor cell cytoplasm. At low to mid-range magnification by light microscopy the labeling pattern can be easily recognized and the level of non-specific or background labeling assessed. This is a critical step for subsequent interpretation of the immunolabeling pattern by TEM and evaluation of the morphological context. The same section is then blotted dry and viewed by TEM. QD probes are seen to be attached to amorphous material contained in individual secretory granules. Images are acquired from the same region of interest (ROI) seen by light microscopy for correlative analysis. Corresponding images from each modality may then be blended to overlay fluorescence data on TEM ultrastructure of the corresponding region.
Directory of Open Access Journals (Sweden)
Manvir S. Kushwaha
2012-09-01
Full Text Available The most fundamental approach to an understanding of electronic, optical, and transport phenomena which the condensed matter physics (of conventional as well as nonconventional systems offers is generally founded on two experiments: the inelastic electron scattering and the inelastic light scattering. This work embarks on providing a systematic framework for the theory of inelastic electron scattering and of inelastic light scattering from the electronic excitations in GaAs/Ga1−xAlxAs quantum wells. To this end, we start with the Kubo's correlation function to derive the generalized nonlocal, dynamic dielectric function, and the inverse dielectric function within the framework of Bohm-Pines’ random-phase approximation. This is followed by a thorough development of the theory of inelastic electron scattering and of inelastic light scattering. The methodological part is then subjected to the analytical diagnoses which allow us to sense the subtlety of the analytical results and the importance of their applications. The general analytical results, which know no bounds regarding, e.g., the subband occupancy, are then specified so as to make them applicable to practicality. After trying and testing the eigenfunctions, we compute the density of states, the Fermi energy, the full excitation spectrum made up of intrasubband and intersubband – single-particle and collective (plasmon – excitations, the loss functions for all the principal geometries envisioned for the inelastic electron scattering, and the Raman intensity, which provides a measure of the real transitions induced by the (laser probe, for the inelastic light scattering. It is found that the dominant contribution to both the loss peaks and the Raman peaks comes from the collective (plasmon excitations. As to the single-particle peaks, the analysis indicates a long-lasting lack of quantitative comparison between theory and experiments. It is inferred that the inelastic electron
Energy Technology Data Exchange (ETDEWEB)
Rozhkov, A.V., E-mail: arozhkov@gmail.co [Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 (Japan); Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, 125412, Moscow (Russian Federation); Giavaras, G. [Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 (Japan); Bliokh, Yury P. [Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 (Japan); Department of Physics, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Freilikher, Valentin [Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 (Japan); Department of Physics, Bar-Ilan University, Ramat-Gan 52900 (Israel); Nori, Franco [Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 (Japan); Department of Physics, University of Michigan, Ann Arbor, MI 48109-1040 (United States)
2011-06-15
This brief review discusses electronic properties of mesoscopic graphene-based structures. These allow controlling the confinement and transport of charge and spin; thus, they are of interest not only for fundamental research, but also for applications. The graphene-related topics covered here are: edges, nanoribbons, quantum dots, pn-junctions, pnp-structures, and quantum barriers and waveguides. This review is partly intended as a short introduction to graphene mesoscopics.
Coupled electron-phonon transport from molecular dynamics with quantum baths
DEFF Research Database (Denmark)
Lu, Jing Tao; Wang, J. S.
2009-01-01
Based on generalized quantum Langevin equations for the tight-binding wavefunction amplitudes and lattice displacements, electron and phonon quantum transport are obtained exactly using molecular dynamics (MD) in the ballistic regime. The electron-phonon interactions can be handled with a quasi...
Towards quantum optics and entanglement with electron spin ensembles in semiconductors
van der Wal, Caspar H.; Sladkov, Maksym
We discuss a technique and a material system that enable the controlled realization of quantum entanglement between spin-wave modes of electron ensembles in two spatially separated pieces of semiconductor material. The approach uses electron ensembles in GaAs quantum wells that are located inside
Direct Observation of Electron-to-Hole Energy Transfer in CdSe Quantum Dots
Hendry, E.; Koeberg, M.; Wang, F.; Zhang, H.; de Mello Donega, C.; Vanmaekelbergh, D.; Bonn, M.
2006-01-01
We independently determine the subpicosecond cooling rates for holes and electrons in CdSe quantum dots. Time-resolved luminescence and terahertz spectroscopy reveal that the rate of hole cooling, following photoexcitation of the quantum dots, depends critically on the electron excess energy. This
Fabrication of a novel silicon single electron transistor for Si:P quantum computer devices
International Nuclear Information System (INIS)
Angus, S.J.; Smith, C.E.A.; Gauja, E.; Dzurak, A.S.; Clark, R.G.; Snider, G.L.
2004-01-01
Full text: Quantum computation relies on the successful measurement of quantum states. Single electron transistors (SETs) are known to be able to perform fast and sensitive charge measurements of solid state qubits. However, due to their sensitivity, SETs are also very susceptible to random charge fluctuations in a solid-state materials environment. In previous dc transport measurements, silicon-based SETs have demonstrated greater charge stability than A1/A1 2 O 3 SETs. We have designed and fabricated a novel silicon SET architecture for a comparison of the noise characteristics of silicon and aluminium based devices. The silicon SET described here is designed for controllable and reproducible low temperature operation. It is fabricated using a novel dual gate structure on a silicon-on-insulator substrate. A silicon quantum wire is formed in a 100nm thick high-resistivity superficial silicon layer using reactive ion etching. Carriers are induced in the silicon wire by a back gate in the silicon substrate. The tunnel barriers are created electrostatically, using lithographically defined metallic electrodes (∼40nm width). These tunnel barriers surround the surface of the quantum wire, thus producing excellent electrostatic confinement. This architecture provides independent control of tunnel barrier height and island occupancy, thus promising better control of Coulomb blockade oscillations than in previously investigated silicon SETs. The use of a near intrinsic silicon substrate offers compatibility with Si:P qubits in the longer term
Fundamental length, bubble electrons and non-local quantum electrodynamics
International Nuclear Information System (INIS)
Hsu, J.P.; Mac, E.
1977-06-01
Based on the concept of a bubble electron and the approach of Pais and Uhlenbeck, one constructs a finite quantum electrodynamics which is relativistically invariant, macro-causal and unitary. In this model, fields and their interaction are local, but the action function of free fields is nonlocal. The propagators are modified so that a fundamental length L is naturally introduced to physics. The modified static potential is given by V(r) = e/r for r greater than L and V(r) = 0 for r less than L, which is produced by the bubble source r -1 ddelta(r-L)/dr rather than a point source. It is found that L less than 4 x 10 -15 cm. Experimental consequences and modifications of strict causality at short distances, vertical bars 2 vertical bar approximately L 2 , are discussed
Does the Finite Size of Electrons Affect Quantum Noise in Electronic Devices?
International Nuclear Information System (INIS)
Colomés, E; Marian, D; Oriols, X
2015-01-01
Quantum transport is commonly studied with the use of quasi-particle infinite- extended states. This leads to a powerful formalism, the scattering-states theory, able to capture in compact formulas quantities of interest, such as average current, noise, etc.. However, when investigating the spatial size-dependence of quasi-particle wave packets in quantum noise with exchange and tunneling, unexpected new terms appear in the quantum noise expression. For this purpose, the two particle transmission and reflection probabilities for two initial one-particle wave packets (with opposite central momentums) spatially localized at each side of a potential barrier are studied. After the interaction, each wave packet splits into a transmitted and a reflected component. It can be shown that the probability of detecting two (identically injected) electrons at the same side of the barrier is different from zero in very common (single or double barrier) scenarios. This originates an increase of quantum noise which cannot be obtained through the scattering states formalism. (paper)
Energy Technology Data Exchange (ETDEWEB)
Gamble, John King [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Nielsen, Erik [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Baczewski, Andrew David [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Moussa, Jonathan Edward [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Gao, Xujiao [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Salinger, Andrew G. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Muller, Richard P. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2017-07-01
This paper describes our work over the past few years to use tools from quantum chemistry to describe electronic structure of nanoelectronic devices. These devices, dubbed "artificial atoms", comprise a few electrons, con ned by semiconductor heterostructures, impurities, and patterned electrodes, and are of intense interest due to potential applications in quantum information processing, quantum sensing, and extreme-scale classical logic. We detail two approaches we have employed: nite-element and Gaussian basis sets, exploring the interesting complications that arise when techniques that were intended to apply to atomic systems are instead used for artificial, solid-state devices.
Structure and unity. Trancendence-philosophical interpretation of quantum physics
International Nuclear Information System (INIS)
Lambrecht, Juergen
2013-01-01
Since their beginnings at the begin of the 20th century quantum physics in the ontological and epistemological interpretation of their results is facing persistent difficulties, which could not be satisfactorily solved to this day. Some quantum phenomena are beyond of both our everyday understanding of the world and the classical-physical picture of the world, which is essentially based on the mechanics of Isaac Newton. They exceed our imagination and seem at least partly contradict logical and space-time laws. Transcendence-philosophical thinking, which exhibits a close structural relation to the logics of Georg Wilhelm Friedrich Hegel and to the philosophical systems analysis, provides a set of methodological instruments, which can help to avoid some problems of quantum-theoretical interpretation, which are in striking contrast to the mathematically consistent formulation of quantum theory. This is paradigmatically shown by selected main themes of the quantum-theoretical discussion.
Energy Technology Data Exchange (ETDEWEB)
Clark, R.G.; Ford, R.A.; Haynes, S.R.; Ryan, J.F.; Turberfield, A.J.; Wright, P.A. (Clarendon Lab., Univ. of Oxford (UK)); Williams, F.I.B.; Deville, G.; Glattli, D.C. (CEN de Saclay, 91 - Gif-sur-Yvette (France)); Mallett, J.R.; Oswald, P.M.W. (Clarendon Lab., Univ. of Oxford (UK) Katholieke Univ. Leuven (Belgium)); Burgt, M. van der; Herlach, F. (Katholieke Univ. Leuven (Belgium)); Foxon, C.T.; Harris, J.J. (Philips Research Labs., Redhill (UK))
1991-02-01
Our recent optical detection of the integer and fractional quantum Hall effects in GaAs, by intrinsic band-gap photoluminescence at dilution refrigerator temperatures, is reviewed. This work has been extended to the extreme quantum limit where a photoluminescence peak develops close to Landau level filling factor {nu}=1/5 which correlates both with the onset of threshold behaviour in current-voltage characteristics of the two-dimensional electron system and a resonant radio-frequency absorption; the latter are quantitatively accounted for by a model of crystalline electronic structure broken up into domains. Preliminary mK transport experiments in intense, pulsed magnetic fields are also described, which establish a basis to access the electron solid phase transition in a hitherto unattainable region of the (B,T) plane. (orig.).
Dimension-dependent stimulated radiative interaction of a single electron quantum wavepacket
Gover, Avraham; Pan, Yiming
2018-06-01
In the foundation of quantum mechanics, the spatial dimensions of electron wavepacket are understood only in terms of an expectation value - the probability distribution of the particle location. One can still inquire how the quantum electron wavepacket size affects a physical process. Here we address the fundamental physics problem of particle-wave duality and the measurability of a free electron quantum wavepacket. Our analysis of stimulated radiative interaction of an electron wavepacket, accompanied by numerical computations, reveals two limits. In the quantum regime of long wavepacket size relative to radiation wavelength, one obtains only quantum-recoil multiphoton sidebands in the electron energy spectrum. In the opposite regime, the wavepacket interaction approaches the limit of classical point-particle acceleration. The wavepacket features can be revealed in experiments carried out in the intermediate regime of wavepacket size commensurate with the radiation wavelength.
Quantum algebra structure of certain Jackson integrals
International Nuclear Information System (INIS)
Matsuo, Atsushi
1993-01-01
The q-difference system satisfied by Jackson integrals with a configuration of A-type root system is studied. We explicitly construct some linear combination of Jackson integrals, which satisfies the quantum Knizhnik-Zamolodchikov equation for the 2-point correlation function of q-vertex operators, introduced by Frenkel and Reshetik hin, for the quantum affine algebra U q (sl 2 ). The expression of integrands for the n-point case is conjectured, and a set of linear relations for the corresponding Jackson integrals is proved. (orig.)
Interacting Electrons and Holes in Quasi-2D Quantum Dots in Strong Magnetic Fields
Hawrylak, P.; Sheng, W.; Cheng, S.-J.
2004-09-01
Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and of excitonic quantum Hall droplets at a filling factorν=2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons.
Interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields
International Nuclear Information System (INIS)
Hawrylak, P.; Sheng, W.; Cheng, S.-J.
2004-01-01
Theory of optical properties of interacting electrons and holes in quasi-2D quantum dots in strong magnetic fields is discussed. In two dimensions and the lowest Landau level, hidden symmetries control the interaction of the interacting system with light. By confining electrons and holes into quantum dots hidden symmetries can be removed and the excitation spectrum of electrons and excitons can be observed. We discuss a theory electronic and excitonic quantum Hall droplets at a filling factor υ = 2. For an excitonic quantum Hall droplet the characteristic emission spectra are predicted to be related to the total spin of electron and hole configurations. For the electronic droplet the excitation spectrum of the droplet can be mapped out by measuring the emission for increasing number of electrons. (author)
THE QUANTUM-WELL STRUCTURES OF SELF ELECTROOPTIC-EFFECT DEVICES AND GALLIUM-ARSENIDE
Directory of Open Access Journals (Sweden)
Mustafa TEMİZ
1996-02-01
Full Text Available Multiple quantum-well (MQW electroabsorptive self electro optic-effect devices (SEEDs are being extensively studied for use in optical switching and computing. The self electro-optic-effect devices which has quantum-well structures is a new optoelectronic technology with capability to obtain both optical inputs and outputs for Gallium-Arsenide/Aluminum Gallium-Arsenide (GaAs/AlGaAs electronic circuits. The optical inputs and outputs are based on quantum-well absorptive properties. These quantum-well structures consist of many thin layers of semiconductors materials of GaAs/AlGaAs which have emerged some important directions recently. The most important advance in the physics of these materials since the early days has been invention of the heterojunction structures which is based at present on GaAs technology. GaAs/AlGaAs structures present some important advantages to relevant band gap and index of refraction which allow to form the quantum-well structures and also to make semiconductor lasers, dedectors and waveguide optical switches.
Dai, Peng; Jiang, Nan; Tan, Ren-Xiang
2016-01-01
Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.
Energy Technology Data Exchange (ETDEWEB)
Wang, Liancheng, E-mail: wanglc@semi.ac.cn, E-mail: lzq@semi.ac.cn, E-mail: zh.zhang@hebut.edu.cn [Engineering Product Development Pillar (EPD), Singapore University of Technology & Design (SUTD), 8 Somapah Road, Singapore 487372 (Singapore); Semiconductor Lighting Technology Research and Development Center, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Mind Star (Beijing) Technology Co., Ltd., Zhongguancun South Street, Haidian District, No. 45 Hing Fat Building 1001, Beijing 100872 (China); Liu, Zhiqiang, E-mail: wanglc@semi.ac.cn, E-mail: lzq@semi.ac.cn, E-mail: zh.zhang@hebut.edu.cn; Tian, Ying Dong; Yi, Xiaoyan; Wang, Junxi; Li, Jinmin; Wang, Guohong [Semiconductor Lighting Technology Research and Development Center, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Zhang, Zi-Hui, E-mail: wanglc@semi.ac.cn, E-mail: lzq@semi.ac.cn, E-mail: zh.zhang@hebut.edu.cn [Key Laboratory of Electronic Materials and Devices of Tianjin, School of Electronics and Information Engineering, Hebei University of Technology, Tianjin 300401 (China)
2016-04-14
The effects of graphene on the optical properties of active system, e.g., the InGaN/GaN multiple quantum wells, are thoroughly investigated and clarified. Here, we have investigated the mechanisms accounting for the photoluminescence reduction for the graphene covered GaN/InGaN multiple quantum wells hybrid structure. Compared to the bare multiple quantum wells, the photoluminescence intensity of graphene covered multiple quantum wells showed a 39% decrease after excluding the graphene absorption losses. The responsible mechanisms have been identified with the following factors: (1) the graphene two dimensional hole gas intensifies the polarization field in multiple quantum wells, thus steepening the quantum well band profile and causing hole-electron pairs to further separate; (2) a lower affinity of graphene compared to air leading to a weaker capability to confine the excited hot electrons in multiple quantum wells; and (3) exciton transfer through non-radiative energy transfer process. These factors are theoretically analysed based on advanced physical models of semiconductor devices calculations and experimentally verified by varying structural parameters, such as the indium fraction in multiple quantum wells and the thickness of the last GaN quantum barrier spacer layer.
International Nuclear Information System (INIS)
Tyszka, K.; Moraru, D.; Samanta, A.; Mizuno, T.; Tabe, M.; Jabłoński, R.
2015-01-01
We comparatively study donor-induced quantum dots in Si nanoscale-channel transistors for a wide range of doping concentration by analysis of single-electron tunneling transport and surface potential measured by Kelvin probe force microscopy (KPFM). By correlating KPFM observations of donor-induced potential landscapes with simulations based on Thomas-Fermi approximation, it is demonstrated that single-electron tunneling transport at lowest gate voltages (for smallest coverage of screening electrons) is governed most frequently by only one dominant quantum dot, regardless of doping concentration. Doping concentration, however, primarily affects the internal structure of the quantum dot. At low concentrations, individual donors form most of the quantum dots, i.e., “donor-atom” quantum dots. In contrast, at high concentrations above metal-insulator transition, closely placed donors instead of individual donors form more complex quantum dots, i.e., “donor-cluster” quantum dots. The potential depth of these “donor-cluster” quantum dots is significantly reduced by increasing gate voltage (increasing coverage of screening electrons), leading to the occurrence of multiple competing quantum dots
International Nuclear Information System (INIS)
Hege, Hans-Christian; Manz, Joern; Marquardt, Falko; Paulus, Beate; Schild, Axel
2010-01-01
Graphical abstract: In the limit of coherent tunneling, double bond shifting (DBS) of cyclooctatetraene from a reactant (R) to a product (P) is associated with pericyclic electron fluxes from double to single bonds, corresponding to a pincer-motion-type set of arrows in the Lewis structures, each representing a transfer of 0.19 electrons. - Abstract: Pericyclic rearrangement of cyclooctatetraene proceeds from equivalent sets of two reactants to two products. In the ideal limit of coherent tunneling, these reactants and products may tunnel to each other by ring inversions and by double bond shifting (DBS). We derive simple cosinusoidal or sinusoidal time evolutions of the bond-to-bond electron fluxes and yields during DBS, for the tunneling scenario. These overall yields and fluxes may be decomposed into various contributions for electrons in so called pericyclic, other valence, and core orbitals. Pericyclic orbitals are defined as the subset of valence orbitals which describe the changes of Lewis structures during the pericyclic reaction. The quantum dynamical results are compared with the traditional scheme of fluxes of electrons in pericyclic orbitals, as provided by arrows in Lewis structures.
Nanosecond-timescale spin transfer using individual electrons in a quadruple-quantum-dot device
Energy Technology Data Exchange (ETDEWEB)
Baart, T. A.; Jovanovic, N.; Vandersypen, L. M. K. [QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Reichl, C.; Wegscheider, W. [Solid State Physics Laboratory, ETH Zürich, 8093 Zürich (Switzerland)
2016-07-25
The ability to coherently transport electron-spin states between different sites of gate-defined semiconductor quantum dots is an essential ingredient for a quantum-dot-based quantum computer. Previous shuttles using electrostatic gating were too slow to move an electron within the spin dephasing time across an array. Here, we report a nanosecond-timescale spin transfer of individual electrons across a quadruple-quantum-dot device. Utilizing enhanced relaxation rates at a so-called hot spot, we can upper bound the shuttle time to at most 150 ns. While actual shuttle times are likely shorter, 150 ns is already fast enough to preserve spin coherence in, e.g., silicon based quantum dots. This work therefore realizes an important prerequisite for coherent spin transfer in quantum dot arrays.
Coulomb drag: a probe of electron interactions in coupled quantum wells
DEFF Research Database (Denmark)
Jauho, Antti-Pekka
1996-01-01
As semiconductor devices shrink in size and in dimensionality, interactions between charge carriers become more and more important. There is a simple physical reason behind this behavior: fewer carriers lead to less effective screening, and hence stronger effective interactions. A point in case...... are one-dimensional systems (quantum wires): there electron-electron interactions may lead to a behavior, which is qualitatively different from the standard Fermi liquid picture (Luttinger liquids). Electron-electron interactions also play a central role in the fractional quantum Hall effect, which...... be the study of quantum wires: there the interactions may lead to even more dramatic effects...
International Nuclear Information System (INIS)
Sakly, A.; Safta, N.; Mejri, H.; Lamine, A. Ben
2011-01-01
Research highlights: → This paper is dedicated to structures based on Cd 1-x Zn x S. - Abstract: The present work reports on a theoretical investigation of superlattices based on Cd 1-x Zn x S quantum dots embedded in an insulating material. The system to model is assumed to be a series of flattened cylindrical quantum dots with a finite barrier at the boundary and is studied using a sinusoidal potential. The electronic states of both Γ 1 - (ground) and Γ 2 - (first excited) minibands have been computed as a function of inter-quantum dot separation and Zn composition. An analysis of the results shows that the widths of Γ 1 - and Γ 2 - minibands decrease as the superlattice period and Zn content increase separately. Moreover, the sinusoidal shape of the confining potential accounts for the coupling between quantum dots quantitatively less than the Kronig-Penney potential model.
Electronic structure studies of fullerites and fullerides
International Nuclear Information System (INIS)
Merkel, M.; Sohmen, E.; Masaki, A.; Romberg, H.; Alexander, M.; Knupfer, M.; Golden, M.S.; Adelmann, P.; Renker, B.; Fink, J.
1993-01-01
The electronic structure of fullerites and fullerides has been investigated by high-resolution photoemission and by high-energy electron energy-loss spectroscopy in transmission. Information on the occupied Π and σ bands, on the unoccupied Π * and σ * bands, and on the joint density of states has been obtained. In particular, we report on the changes of the electronic structure of fullerides as a function of dopant concentration. (orig.)
Solvated electron structure in glassy matrices
International Nuclear Information System (INIS)
Kevan, L.
1981-01-01
Current knowledge of the detailed geometrical structure of solvated electrons in aqueous and organic media is summarized. The geometry of solvated electrons in glassy methanol, ethanol, and 2-methyltetrahydrofuran is discussed. Advanced electron magnetic resonance methods and development of new methods of analysis of electron spin echo modulation patterns, second moment line shapes, and forbidden photon spin-flip transitions for paramagnetic species in these disordered systems are discussed. 66 references are cited
Structure an dynamics in cavity quantum electrodynamics
International Nuclear Information System (INIS)
Kimble, H.J.
1994-01-01
Much of the theoretical background related to the radiative processes for atoms in the presence of boundaries comes from two often disjoint areas, namely cavity quantum electrodynamics and optical bistability with two-state atoms. While the former of these areas has been associated to a large degree with studies in a perturbative domain of altered associated to a large degree with studies in a perturbative domain of altered emission processes in the presence of boundaries other than those of free space, the latter is often viewed from the perspective of hysteresis cycles and device applications. With the exception of the laser, however, perhaps the most extensive investigations of quantum statistical processes in quantum optics are to be found in the literature on bistability with two-state atoms and on cavity QED. Unfortunately, the degree of overlap of these two areas has not always been fully appreciated. This circumstance is perhaps due in part to the fact that the investigation of dynamical processes in cavity QED has had as its cornerstone the Jaynes-Cummings problem, with extensions to include, for example, small amounts of dissipation. On the other hand, a principle aspect of the bistability literature has been the study of quantum fluctuations in open systems for which dissipation plays a central role, but for which the coherent quantum dynamics of the Haynes-Cummings model are to a large measure lost due to the usual assumption of large system size and weak coupling (as in the standard theory of the laser). 132 refs., 26 figs., 1 tab
Electronic structure and tautomerism of thioamides
Energy Technology Data Exchange (ETDEWEB)
Novak, Igor, E-mail: inovak@csu.edu.au [Charles Sturt University, POB 883, Orange, NSW 2800 (Australia); Klasinc, Leo, E-mail: klasinc@irb.hr [Physical Chemistry Department, Ruđer Bošković Institute, HR-10002 Zagreb (Croatia); McGlynn, Sean P., E-mail: sean.mcglynn@chemgate.chem.lsu.edu [Louisiana State University, Baton Rouge, LA 70803 (United States)
2016-05-15
Highlights: • Electronic structure of thioamide group and its relation to Lewis basicity. • Tautomerism of the (thio)amide groups. • Substituent effects on the electronic structure of (thio)amide group. - Abstract: The electronic structures of several thioamides have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of thioamide derivatives are discussed. The predominant tautomers in the gas phase are of keto–(thio)keto form. The addition of cyclohexanone moiety to the thioamide group enhances the Lewis base character of the sulfur atom. The addition of phenyl group to the (thio)amide group significantly affects its electronic structure.
Photoelectron spectra and electronic structure of some spiroborate complexes
Energy Technology Data Exchange (ETDEWEB)
Vovna, V.I.; Tikhonov, S.A.; Lvov, I.B., E-mail: lvov.ib@dvfu.ru; Osmushko, I.S.; Svistunova, I.V.; Shcheka, O.L.
2014-12-15
Highlights: • The electronic structure of three spiroborate complexes—boron 1,2-dioxyphenylene β-diketonates has been investigated. • UV and X-ray photoelectron spectra have been interpreted. • DFT calculations have been used for interpretation of spectral bands. • The binding energy of nonequivalent carbon and oxygen atoms were measured. • The structure of X-ray photoelectron spectra of the valence electrons is in good agreement with the energies and composition of Kohn–Sham orbitals. - Abstract: The electronic structure of the valence and core levels of three spiroborate complexes – boron 1,2-dioxyphenylene β-diketonates – has been investigated by methods of UV and X-ray photoelectron spectroscopy and quantum chemical density functional theory. The ionization energy of π- and n-orbitals of the dioxyphenylene fragment and β-diketonate ligand were measured from UV photoelectron spectra. This made it possible to determine the effect of substitution of one or two methyl groups by the phenyl in diketone on the electronic structure of complexes. The binding energy of nonequivalent carbon and oxygen atoms were measured from X-ray photoelectron spectra. The results of calculations of the energy of the valence orbitals of complexes allowed us to refer bands observed in the spectra of the valence electrons to the 2s-type levels of carbon and oxygen.
Si quantum dots for nano electronics: From materials to applications
International Nuclear Information System (INIS)
Lombardo, S.; Spinella, C.; Rimini, E.
2005-01-01
This paper reviews the subject of Si quantum dots embedded in dielectric and its application to the realization of non volatile semiconductor memories. In the first part of the paper various approaches for the analysis of the materials through transmission electron microscopy (TEM) are critically discussed. The advantages coming from an innovative application of energy filtered TEM are put in clear evidence. The paper then focuses on the synthesis of the materials: two different methodologies for the realization of the dots, both based on chemical vapor deposition are described in detail, and physical models providing some understanding of the observed phenomenology are reported. We then discuss the application of this nano technology to the realization of the storage nodes in non volatile semiconductor memories. The following sections describe the electrical characteristics found in the test devices and some key aspects are described in terms of quantitative models. The test devices show several performance advantages, indicating that the approach is an excellent candidate for the realization of Flash memories of the nano electronic era
Revealing electronic open quantum systems with subsystem TDDFT
Krishtal, Alisa; Pavanello, Michele
2016-03-01
Open quantum systems (OQSs) are perhaps the most realistic systems one can approach through simulations. In recent years, describing OQSs with Density Functional Theory (DFT) has been a prominent avenue of research with most approaches based on a density matrix partitioning in conjunction with an ad-hoc description of system-bath interactions. We propose a different theoretical approach to OQSs based on partitioning of the electron density. Employing the machinery of subsystem DFT (and its time-dependent extension), we provide a novel way of isolating and analyzing the various terms contributing to the coupling between the system and the surrounding bath. To illustrate the theory, we provide numerical simulations on a toy system (a molecular dimer) and on a condensed phase system (solvated excimer). The simulations show that non-Markovian dynamics in the electronic system-bath interactions are important in chemical applications. For instance, we show that the superexchange mechanism of transport in donor-bridge-acceptor systems is a non-Markovian interaction between the donor-acceptor (OQS) with the bridge (bath) which is fully characterized by real-time subsystem time-dependent DFT.
Free-electron laser and related quantum beams
International Nuclear Information System (INIS)
Minehara, Eisuke J.
2003-01-01
Past, present and future development programs of the JAERI super-conducting rf linac-based FELs and light sources with and without energy recovery have been discussed and introduced briefly. The JAERI FEL group has successfully discovered, and realized the brand-new FEL lasing mode of 255 fs ultra fast pulse, 6-9% high-efficiency, one GW high peak power, a few kW average power, and wide tunability of medium and far infrared wavelength regions at the same time. Using the new lasing, we could realize a powerful and efficient free-electron laser (FEL) for industrial uses near future. In order to realize such a tunable, ultra-short-pulse, high averaged-power FEL, we have needed the efficient and powerful CW FEL driver of the JAERI compact, stand-alone and zero-boil-off super-conducting rf linac with an energy-recovery geometry. The JAERI energy-recovery and/or super-conducting rf linac driver has been developed to use as an industrial electron irradiator, and millimeter-wave, far-infrared, mid-infrared, near-infrared and shorter wavelength quantum beam sources. (author)
Free-electron laser and related quantum beams
Energy Technology Data Exchange (ETDEWEB)
Minehara, Eisuke J [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2003-07-01
Past, present and future development programs of the JAERI super-conducting rf linac-based FELs and light sources with and without energy recovery have been discussed and introduced briefly. The JAERI FEL group has successfully discovered, and realized the brand-new FEL lasing mode of 255 fs ultra fast pulse, 6-9% high-efficiency, one GW high peak power, a few kW average power, and wide tunability of medium and far infrared wavelength regions at the same time. Using the new lasing, we could realize a powerful and efficient free-electron laser (FEL) for industrial uses near future. In order to realize such a tunable, ultra-short-pulse, high averaged-power FEL, we have needed the efficient and powerful CW FEL driver of the JAERI compact, stand-alone and zero-boil-off super-conducting rf linac with an energy-recovery geometry. The JAERI energy-recovery and/or super-conducting rf linac driver has been developed to use as an industrial electron irradiator, and millimeter-wave, far-infrared, mid-infrared, near-infrared and shorter wavelength quantum beam sources. (author)
Revealing electronic open quantum systems with subsystem TDDFT.
Krishtal, Alisa; Pavanello, Michele
2016-03-28
Open quantum systems (OQSs) are perhaps the most realistic systems one can approach through simulations. In recent years, describing OQSs with Density Functional Theory (DFT) has been a prominent avenue of research with most approaches based on a density matrix partitioning in conjunction with an ad-hoc description of system-bath interactions. We propose a different theoretical approach to OQSs based on partitioning of the electron density. Employing the machinery of subsystem DFT (and its time-dependent extension), we provide a novel way of isolating and analyzing the various terms contributing to the coupling between the system and the surrounding bath. To illustrate the theory, we provide numerical simulations on a toy system (a molecular dimer) and on a condensed phase system (solvated excimer). The simulations show that non-Markovian dynamics in the electronic system-bath interactions are important in chemical applications. For instance, we show that the superexchange mechanism of transport in donor-bridge-acceptor systems is a non-Markovian interaction between the donor-acceptor (OQS) with the bridge (bath) which is fully characterized by real-time subsystem time-dependent DFT.
International Nuclear Information System (INIS)
Rousseau, E.
2006-12-01
An electron on helium presents a quantized energy spectrum. The interaction with the environment is considered sufficiently weak in order to allow the realization of a quantum bit (qubit) by using the first two energy levels. The first stage in the realization of this qubit was to trap and control a single electron. This is carried out thanks to a set of micro-fabricated electrodes defining a well of potential in which the electron is trapped. We are able with such a sample to trap and detect a variables number of electrons varying between one and around twenty. This then allowed us to study the static behaviour of a small number of electrons in a trap. They are supposed to crystallize and form structures called Wigner molecules. Such molecules have not yet been observed yet with electrons above helium. Our results bring circumstantial evidence for of Wigner crystallization. We then sought to characterize the qubit more precisely. We sought to carry out a projective reading (depending on the state of the qubit) and a measurement of the relaxation time. The results were obtained by exciting the electron with an incoherent electric field. A clean measurement of the relaxation time would require a coherent electric field. The conclusion cannot thus be final but it would seem that the relaxation time is shorter than calculated theoretically. That is perhaps due to a measurement of the relaxation between the oscillating states in the trap and not between the states of the qubit. (author)
Time-dependent quantum chemistry of laser driven many-electron molecules
International Nuclear Information System (INIS)
Nguyen-Dang, Thanh-Tung; Couture-Bienvenue, Étienne; Viau-Trudel, Jérémy; Sainjon, Amaury
2014-01-01
A Time-Dependent Configuration Interaction approach using multiple Feshbach partitionings, corresponding to multiple ionization stages of a laser-driven molecule, has recently been proposed [T.-T. Nguyen-Dang and J. Viau-Trudel, J. Chem. Phys. 139, 244102 (2013)]. To complete this development toward a fully ab-initio method for the calculation of time-dependent electronic wavefunctions of an N-electron molecule, we describe how tools of multiconfiguration quantum chemistry such as the management of the configuration expansion space using Graphical Unitary Group Approach concepts can be profitably adapted to the new context, that of time-resolved electronic dynamics, as opposed to stationary electronic structure. The method is applied to calculate the detailed, sub-cycle electronic dynamics of BeH 2 , treated in a 3–21G bound-orbital basis augmented by a set of orthogonalized plane-waves representing continuum-type orbitals, including its ionization under an intense λ = 800 nm or λ = 80 nm continuous-wave laser field. The dynamics is strongly non-linear at the field-intensity considered (I ≃ 10 15 W/cm 2 ), featuring important ionization of an inner-shell electron and strong post-ionization bound-electron dynamics
Spacetime structure of an evaporating black hole in quantum gravity
International Nuclear Information System (INIS)
Bonanno, A.; Reuter, M.
2006-01-01
The impact of the leading quantum gravity effects on the dynamics of the Hawking evaporation process of a black hole is investigated. Its spacetime structure is described by a renormalization group improved Vaidya metric. Its event horizon, apparent horizon, and timelike limit surface are obtained by taking the scale dependence of Newton's constant into account. The emergence of a quantum ergosphere is discussed. The final state of the evaporation process is a cold, Planck size remnant
Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles
DEFF Research Database (Denmark)
Iida, Daisuke; Fadil, Ahmed; Chen, Yuntian
2015-01-01
We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhance......We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density...
The equation of motion of an electron: a debate in classical and quantum physics
International Nuclear Information System (INIS)
Kim, K.-J.
1999-01-01
The current status of understanding of the equation of motion of an electron is summarized. Classically, a consistent, linearized theory exists for an electron of finite extent, as long as the size of the electron is larger than the classical electron radius. Nonrelativistic quantum mechanics seems to offer a tine theory even in the point-particle limit
Transmission electron microscopy study of vertical quantum dots molecules grown by droplet epitaxy
Energy Technology Data Exchange (ETDEWEB)
Hernandez-Maldonado, D., E-mail: david.hernandez@uca.es [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Herrera, M.; Sales, D.L. [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Alonso-Gonzalez, P.; Gonzalez, Y.; Gonzalez, L. [Instituto de Microelectronica de Madrid (CNM-CSIC), Isaac Newton 8 (PTM), 28760 Tres Cantos, Madrid (Spain); Pizarro, J.; Galindo, P.L. [Departamento de Lenguajes y Sistemas Informaticos, CASEM, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Molina, S.I. [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain)
2010-07-01
The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition.
Transmission electron microscopy study of vertical quantum dots molecules grown by droplet epitaxy
International Nuclear Information System (INIS)
Hernandez-Maldonado, D.; Herrera, M.; Sales, D.L.; Alonso-Gonzalez, P.; Gonzalez, Y.; Gonzalez, L.; Pizarro, J.; Galindo, P.L.; Molina, S.I.
2010-01-01
The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition.
Localized polarons and doorway vibrons in finite quantum structures
Czech Academy of Sciences Publication Activity Database
Fehske, H.; Wellein, G.; Loos, Jan; Bishop, A. R.
2008-01-01
Roč. 77, č. 8 (2008), 085117/1-085117/6 ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100521 Keywords : quantum dots * electron - phonon interaction * polarons Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.322, year: 2008
Enhanced Emission of Quantum System in Si-Ge Nanolayer Structure.
Huang, Zhong-Mei; Huang, Wei-Qi; Dong, Tai-Ge; Wang, Gang; Wu, Xue-Ke
2016-12-01
It is very interesting that the enhanced peaks near 1150 and 1550 nm are observed in the photoluminescence (PL) spectra in the quantum system of Si-Ge nanolayer structure, which have the emission characteristics of a three-level system with quantum dots (QDs) pumping and emission of quasi-direct-gap band, in our experiment. In the preparing process of Si-Ge nanolayer structure by using a pulsed laser deposition method, it is discovered that the nanocrystals of Si and Ge grow in the (100) and (111) directions after annealing or electron beam irradiation. The enhanced PL peaks with multi-longitudinal-mode are measured at room temperature in the super-lattice of Si-Ge nanolayer quantum system on SOI.
Electron scattering and nuclear structure
International Nuclear Information System (INIS)
Wolynec, E.
1985-01-01
A review of the historical development and the theory necessary to the interpretation of the experimental results is made. Some measurement techniques, experimental results and the technique of analysis of these data are presented. Future perspectives, due to the appearence of continous electron current accelerators, in this field of study are discussed. (L.C.) [pt
Electron gun controlled smart structure
Martin, Jeffrey W.; Main, John Alan; Redmond, James M.; Henson, Tammy D.; Watson, Robert D.
2001-01-01
Disclosed is a method and system for actively controlling the shape of a sheet of electroactive material; the system comprising: one or more electrodes attached to the frontside of the electroactive sheet; a charged particle generator, disposed so as to direct a beam of charged particles (e.g. electrons) onto the electrode; a conductive substrate attached to the backside of the sheet; and a power supply electrically connected to the conductive substrate; whereby the sheet changes its shape in response to an electric field created across the sheet by an accumulation of electric charge within the electrode(s), relative to a potential applied to the conductive substrate. Use of multiple electrodes distributed across on the frontside ensures a uniform distribution of the charge with a single point of e-beam incidence, thereby greatly simplifying the beam scanning algorithm and raster control electronics, and reducing the problems associated with "blooming". By placing a distribution of electrodes over the front surface of a piezoelectric film (or other electroactive material), this arrangement enables improved control over the distribution of surface electric charges (e.g. electrons) by creating uniform (and possibly different) charge distributions within each individual electrode. Removal or deposition of net electric charge can be affected by controlling the secondary electron yield through manipulation of the backside electric potential with the power supply. The system can be used for actively controlling the shape of space-based deployable optics, such as adaptive mirrors and inflatable antennae.
Quantum Ising model on hierarchical structures
International Nuclear Information System (INIS)
Lin Zhifang; Tao Ruibao.
1989-11-01
A quantum Ising chain with both the exchange couplings and the transverse fields arranged in a hierarchical way is considered. Exact analytical results for the critical line and energy gap are obtained. It is shown that when R 1 not= R 2 , where R 1 and R 2 are the hierarchical parameters for the exchange couplings and the transverse fields, respectively, the system undergoes a phase transition in a different universality class from the pure quantum Ising chain with R 1 =R 2 =1. On the other hand, when R 1 =R 2 =R, there exists a critical value R c dependent on the furcating number of the hierarchy. In case of R > R c , the system is shown to exhibit as Ising-like critical point with the critical behaviour the same as in the pure case, while for R c the system belongs to another universality class. (author). 19 refs, 2 figs
Quasiparticle properties of a coupled quantum-wire electron-phonon system
DEFF Research Database (Denmark)
Hwang, E. H.; Hu, Ben Yu-Kuang; Sarma, S. Das
1996-01-01
We study leading-order many-body effects of longitudinal-optical phonons on electronic properties of one-dimensional quantum-wire systems. We calculate the quasiparticle properties of a weakly polar one-dimensional electron gas in the presence of both electron-phonon and electron-electron interac......We study leading-order many-body effects of longitudinal-optical phonons on electronic properties of one-dimensional quantum-wire systems. We calculate the quasiparticle properties of a weakly polar one-dimensional electron gas in the presence of both electron-phonon and electron......-electron interactions, The leading-order dynamical screening approximation (GW approximation) is used to obtain the electron self-energy, the quasiparticle spectral function, and the quasiparticle damping rate in our calculation by treating electrons and phonons on an equal footing. Our theory includes effects (within...... theoretical results for quasiparticle properties....
Size-dependent electronic eigenstates of multilayer organic quantum wells
International Nuclear Information System (INIS)
Nguyen Ba An; Hanamura, E.
1995-09-01
A detailed theoretical treatment is given eigenfunctions and eigenenergies of a multilayer organic quantum well sandwiched between two different dielectric media. The abrupt change of dielectric constants at the interfaces distorts the wave function and results in possible surface states in addition to propagating states. The proper boundary conditions are accounted for by the method of image charges. Analytic criteria for existence of surface states are established using the nearest layers approximation, which depend not only on the intralayer parameters but also on the number of layers. The size dependence together with the dependence on signs and relative magnitudes of the structure parameters fully determine the energy spectrum of propagating states as well as the number and the location of surface states. (author). 28 refs, 10 figs, 2 tabs
Electronic structure of p type Delta doped systems
International Nuclear Information System (INIS)
Gaggero S, L.M.; Perez A, R.
1998-01-01
We summarize of the results obtained for the electronic structure of quantum wells that consist in an atomic layer doped with impurities of p type. The calculations are made within the frame worth of the wrapper function approach to independent bands and with potentials of Hartree. We study the cases reported experimentally (Be in GaAs and B in Si). We present the levels of energy, the wave functions and the rate of the electronic population between the different subbands, as well as the dependence of these magnitudes with the density of impurities in the layer. The participation of the bans of heavy holes is analysed, light and split-off band in the total electronic population. The effect of the temperature is discussed and we give a possible qualitative explanation of the experimental optical properties. (Author)
International Nuclear Information System (INIS)
Shen Jianqi
2011-01-01
Quantum vacuum mode structure can be changed due to length scale fluctuation of the cross section of a metallic waveguide. Such a structure change in vacuum modes (particularly in cutoff vacuum modes) would lead to dramatic enhancement or inhibition of spontaneous emission decay of atoms and, if the waveguide is filled with a dilute atomic vapor consisting of quantum-coherent atoms of a four-level tripod-configuration system, an optical wave propagating inside the waveguide can be coherently manipulated by tunable constructive and destructive quantum interference between two control transitions (driven by two control fields) in a quite unusual way (e.g., the optical response, in which a three-level dark state is involved, is sensitive to the waveguide dimension variations at certain positions of resonance of the atomic spontaneous emission decay rate). Therefore, an intriguing effect that can be employed to designs of new photonic and quantum optical devices could be achieved based on the present mechanisms of quantum-vacuum manipulation and quantum coherence control.
Chakrabarti, S; Chatterjee, B; Debbarma, S; Ghatak, K P
2015-09-01
In this paper we study the influence of strong electric field on the two dimensional (2D)effective electron mass (EEM) at the Fermi level in quantum wells of III-V, ternary and quaternary semiconductors within the framework of k x p formalism by formulating a new 2D electron energy spectrum. It appears taking quantum wells of InSb, InAs, Hg(1-x)Cd(x)Te and In(1-x)Ga(x)As(1-y)P(y) lattice matched to InP as examples that the EEM increases with decreasing film thickness, increasing electric field and increases with increasing surface electron concentration exhibiting spikey oscillations because of the crossing over of the Fermi level by the quantized level in quantum wells and the quantized oscillation occurs when the Fermi energy touches the sub-band energy. The electric field makes the mass quantum number dependent and the oscillatory mass introduces quantum number dependent mass anisotropy in addition to energy. The EEM increases with decreasing alloy composition where the variations are totally band structure dependent. Under certain limiting conditions all the results for all the cases get simplified into the well-known parabolic energy bands and thus confirming the compatibility test. The content of this paper finds three applications in the fields of nano-science and technology.
Putz, Mihai V
2009-11-10
The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr's quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions - all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems.
Directory of Open Access Journals (Sweden)
Mihai V. Putz
2009-11-01
Full Text Available The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr’s quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions – all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving many-electronic systems.
Energy Technology Data Exchange (ETDEWEB)
Sun, Yuming, E-mail: ymsun@ytu.edu.cn; Su, Yuehua; Dai, Zhenhong; Wang, WeiTian
2016-10-20
Photosynthesis is driven by electron transfer in reaction centers in which the functional unit is composed of several simple molecules C{sub 2}-symmetrically arranged into two branches. In view of quantum mechanism, both branches are possible pathways traversed by the transferred electron. Due to different evolution of spin state along two pathways in transmembrane electric potential (TEP), quantum state of the transferred electron at the bridged site acquires a geometric phase difference dependent on TEP, the most efficient electron transport takes place in a specific range of TEP beyond which electron transfer is dramatically suppressed. What’s more, reaction center acts like elaborately designed quantum device preparing polarized spin dependent on TEP for the transferred electron to regulate the reduction potential at bridged site. In brief, electron transfer generates the TEP, reversely, TEP modulates the efficiency of electron transfer. This may be an important approach to maintaining an appreciable pH environment in photosynthesis.
Irregular Aharonov–Bohm effect for interacting electrons in a ZnO quantum ring
International Nuclear Information System (INIS)
Chakraborty, Tapash; Manaselyan, Aram; Barseghyan, Manuk
2017-01-01
The electronic states and optical transitions of a ZnO quantum ring containing few interacting electrons in an applied magnetic field are found to be very different from those in a conventional semiconductor system, such as a GaAs ring. The strong Zeeman interaction and the Coulomb interaction of the ZnO system, two important characteristics of the electron system in ZnO, exert a profound influence on the electron states and on the optical properties of the ring. In particular, our results indicate that the Aharonov–Bohm (AB) effect in a ZnO quantum ring strongly depends on the electron number. In fact, for two electrons in the ZnO ring, the AB oscillations become aperiodic, while for three electrons (interacting) the AB oscillations completely disappear. Therefore, unlike in conventional quantum ring topology, here the AB effect (and the resulting persistent current) can be controlled by varying the electron number. (paper)
STRUCTURAL STABILITY AND ELECTRONIC STRUCTURE OF ...
African Journals Online (AJOL)
2012-12-31
Dec 31, 2012 ... may be applications at high temperature strength and corrosion ... B2 structure, like that found in cesium-chloride (CsCl) and chemical formula RM, where R denotes a rare - earth element and M denotes a late transition metal ...
Design of Carborane Molecular Architectures via Electronic Structure Computations
International Nuclear Information System (INIS)
Oliva, J.M.; Serrano-Andres, L.; Klein, D.J.; Schleyer, P.V.R.; Mich, J.
2009-01-01
Quantum-mechanical electronic structure computations were employed to explore initial steps towards a comprehensive design of poly carborane architectures through assembly of molecular units. Aspects considered were (i) the striking modification of geometrical parameters through substitution, (ii) endohedral carboranes and proposed ejection mechanisms for energy/ion/atom/energy storage/transport, (iii) the excited state character in single and dimeric molecular units, and (iv) higher architectural constructs. A goal of this work is to find optimal architectures where atom/ion/energy/spin transport within carborane superclusters is feasible in order to modernize and improve future photo energy processes.
Quantum theory of the optical and electronic properties of semiconductors
Haug, Hartmut
2009-01-01
This invaluable textbook presents the basic elements needed to understand and research into semiconductor physics. It deals with elementary excitations in bulk and low-dimensional semiconductors, including quantum wells, quantum wires and quantum dots. The basic principles underlying optical nonlinearities are developed, including excitonic and many-body plasma effects. Fundamentals of optical bistability, semiconductor lasers, femtosecond excitation, the optical Stark effect, the semiconductor photon echo, magneto-optic effects, as well as bulk and quantum-confined Franz-Keldysh effects, are covered. The material is presented in sufficient detail for graduate students and researchers with a general background in quantum mechanics.This fifth edition includes an additional chapter on 'Quantum Optical Effects' where the theory of quantum optical effects in semiconductors is detailed. Besides deriving the 'semiconductor luminescence equations' and the expression for the stationary luminescence spectrum, the resu...
Relationship between electronic structure and radioprotective activity of some indazoles
International Nuclear Information System (INIS)
Sokolov, Yu.A.
2000-01-01
The quantum-chemical study of electronic structure of 29 indasoles with complete optimization of geometry and search of quantitative link between the established characteristics and radioprotective activity (RPA) was carried out through the MNDO method with application of multiple linear and nonlinear regression analysis and the basic component method. The equations of correlation relationship between the RPA and electronic characteristics are presented. 10 indasole structures, the forecasted RPA values whereof (survival rate, %) equal 50% and above, are selected. The statistic significance of the obtained correlation equations and their regression coefficients make it possible to conclude, that the established relationships are not accidental and are prospective for forecasting RPA of other close compounds of the indasole series [ru
Electronic structure of metallic glasses
International Nuclear Information System (INIS)
Oelhafen, P.; Lapka, R.; Gubler, U.; Krieg, J.; DasGupta, A.; Guentherodt, H.J.; Mizoguchi, T.; Hague, C.; Kuebler, J.; Nagel, S.R.
1981-01-01
This paper is organized in six sections and deals with (1) the glassy transition metal alloys, their d-band structure, the d-band shifts on alloying and their relation to the alloy heat of formation (ΔH) and the glass forming ability, (2) the glass to crystal phase transition viewed by valence band spectroscopy, (3) band structure calculations, (4) metallic glasses prepared by laser glazing, (5) glassy normal metal alloys, and (6) glassy hydrides
Electronic structure and tautomerism of aryl ketones
International Nuclear Information System (INIS)
Novak, Igor; Klasinc, Leo; Šket, Boris; McGlynn, S.P.
2015-01-01
Graphical abstract: Photoelectron spectroscopy, tautomerism. - Highlights: • UV photoelectron spectroscopy of aryl ketones. • The relative stability of tautomers and their electronic structures. • The factors influencing tautomerism. - Abstract: The electronic structures of several aryl ketones (AK) and their α-halo derivatives have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of the AK derivatives are discussed
Phenomenology of the electron structure function
International Nuclear Information System (INIS)
Slominski, W.; Szwed, J.
2001-01-01
The advantages of introducing the electron structure function (ESF) in electron induced processes are demonstrated. Contrary to the photon structure function it is directly measured in such processes. At present energies, a simultaneous analysis of both the electron and the photon structure functions gives an important test of the experimentally applied methods. Estimates of the ESF at LEP momenta are given. At very high momenta contributions from W and Z bosons together with γ-Z interference can be observed. Predictions for the next generation of experiments are given. (orig.)
Electronic structure and tautomerism of aryl ketones
Energy Technology Data Exchange (ETDEWEB)
Novak, Igor, E-mail: inovak@csu.edu.au [Charles Sturt University, POB 883, Orange, NSW 2800 (Australia); Klasinc, Leo, E-mail: klasinc@irb.hr [Physical Chemistry Department, Ruđer Bošković Institute, HR-10002 Zagreb (Croatia); Šket, Boris, E-mail: Boris.Sket@fkkt.uni-lj.si [Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 (Slovenia); McGlynn, S.P., E-mail: sean.mcglynn@chemgate.chem.lsu.edu [Louisiana State University, Baton Rouge, LA 70803 (United States)
2015-07-15
Graphical abstract: Photoelectron spectroscopy, tautomerism. - Highlights: • UV photoelectron spectroscopy of aryl ketones. • The relative stability of tautomers and their electronic structures. • The factors influencing tautomerism. - Abstract: The electronic structures of several aryl ketones (AK) and their α-halo derivatives have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of the AK derivatives are discussed.
Quantum A∞-structures for open-closed topological strings
International Nuclear Information System (INIS)
Herbst, M.
2006-02-01
We study factorizations of topological string amplitudes on higher genus Riemann surfaces with multiple boundary components and find quantum A ∞ -relations, which are the higher genus analog of the (classical) A ∞ -relations on the disk. For topological strings with c=3 the quantum A ∞ -relations are trivially satisfied on a single D-brane, whereas in a multiple D-brane configuration they may be used to compute open higher genus amplitudes recursively from disk amplitudes. This can be helpful in open Gromov-Witten theory in order to determine open string higher genus instanton corrections. Finally, we find that the quantum A ∞ -structure cannot quite be recast into a quantum master equation on the open string moduli space. (orig.)
International Nuclear Information System (INIS)
Brainerd, J.J.; Petrosian, V.
1987-01-01
Calculations are performed numerically and analytically of synchrotron spectra for thermal and power-law electron distributions using the single-particle synchrotron power spectrum derived from quantum electrodynamics. It is found that the photon energy at which quantum effects appear is proportional to temperature and independent of field strength for thermal spectra; quantum effects introduce an exponential roll-off away from the classical spectra. For power law spectra, the photon energy at which quantum effects appear is inversely proportional to the magnetic field strength; quantum effects produce a steeper power law than is found classically. The results are compared with spectra derived from the classical power spectrum with an energy cutoff ensuring conservation of energy. It is found that an energy cutoff is generally an inadequate approximation of quantum effects for low photon energies and for thermal spectra, but gives reasonable results for high-energy emission from power-law electron distributions. 17 references
Makarewicz, Emilia; Gordon, Agnieszka J; Mierzwicki, Krzysztof; Latajka, Zdzislaw; Berski, Slawomir
2014-06-05
Quantum chemistry methods have been applied to study the influence of the Xe atom inserted into the hydrogen-bromine bond (HBr → HXeBr), particularly on the nature of atomic interactions in the HBr···CO2 and HXeBr···CO2 complexes. Detailed analysis of the nature of chemical bonds has been carried out using topological analysis of the electron localization function, while topological analysis of electron density was used to gain insight into the nature of weak nonbonding interactions. Symmetry-adapted perturbation theory within the orbital approach was applied for greater understanding of the physical contributions to the total interaction energy.
Physics colloquium: Electron counting in quantum dots in and out of equilibrium
Geneva University
2011-01-01
GENEVA UNIVERSITY Ecole de physique Département de physique nucléaire et corspusculaire 24, quai Ernest-Ansermet 1211 Genève 4 Tél.: (022) 379 62 73 Fax: (022) 379 69 92olé Lundi 31 octobre 2011 17h00 - Ecole de Physique, Auditoire Stueckelberg PHYSICS COLLOQUIUM « Electron counting in quantum dots in and out of equilibrium » Prof. Klaus Ensslin Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland Electron transport through quantum dots is governed by Coulomb blockade. Using a nearby quantum point contact the time-dependent charge flow through quantum dots can be monitored on the basis of single electrons. This way electron transport has been investigated in equilibrium as well as out of equilibrium. Recently it has become possible to experimentally verify the fluctuation theorem. The talk will also address electron counting experiments in grapheme. Une verrée ...
Two-electron states in double quantum dot in direct electric field
International Nuclear Information System (INIS)
Burdov, V.A.
2001-01-01
One determined analytically the wave functions of stationary states and the spectrum of two-electron system in symmetric binary quantum point. It is shown that in the normal state at the absence of external electric field the electrons due to the Coulomb blockade can not be collectively in one quantum point. In the external electric field the situation changes. When a certain critical value of field intensity is reached the probability of detection of both electrons in one quantum point by a jump increases from zero up to 1 [ru
Quantum Dot Detectors with Plasmonic Structures
2015-05-15
configuration of polarization and propagation is depicted (E, H , and k denote electric field, magnetic field, and wave vector, respectively) are available in...4. G. T. Liu, A. Stintz, H . Li, T. C. Newell, G. L. Gray, P. M. Varangis, K. J. Malloy, and L. F. Lester, “The Influence of Quantum-Well Composition...A. Barve, J. Montoya , W.-Y. Jang, S. R. J. Brueck, M. Sundaram, A. Reisinger, S. Krishna, and S. K. Noh, “A monolithically integrated plasmonic
Tailoring quantum structures for active photonic crystals
DEFF Research Database (Denmark)
Kuznetsova, Nadezda
demonstrated various trench profiles along the [0-1-1] and [0-11] crystallographic directions. Selectively grown InGaAs/InP quantum wells (QWs) possessed distinct geometrical and optical properties in the cases of directly grown InGaAs and when an InP buffer was deposited underneath. The fabrication process...... consumption for on-chip and chip-to-chip optical communication. In order to develop metal-organic vapor phase epitaxial selective area etching and growth, a mask was fabricated in the HSQ e-beam resist including optimization of exposure and development conditions. By use of CBr4 as an etchant, in situ etching...
Controllable Continuous evolution of electronic states in a single quantum ring
Chakraborty, Tapash; Manaselyan, Aram; Barseghyan, Manuk; Laroze, David
2017-01-01
Intense terahertz laser field is shown to have a profound effect on the electronic and optical properties of quantum rings, where the isotropic and anisotropic quantum rings can now be treated on equal footing. We have demonstrated that in isotropic quantum rings the laser field creates irregular AB oscillations that are usually expected in anisotropic rings. Further, we have shown for the first time that intense laser fields can restore the {\\it isotropic} physical properties in anisotropic ...
Electron spin relaxation in a transition-metal dichalcogenide quantum dot
Pearce, Alexander J.; Burkard, Guido
2017-06-01
We study the relaxation of a single electron spin in a circular quantum dot in a transition-metal dichalcogenide monolayer defined by electrostatic gating. Transition-metal dichalcogenides provide an interesting and promising arena for quantum dot nano-structures due to the combination of a band gap, spin-valley physics and strong spin-orbit coupling. First we will discuss which bound state solutions in different B-field regimes can be used as the basis for qubits states. We find that at low B-fields combined spin-valley Kramers qubits to be suitable, while at large magnetic fields pure spin or valley qubits can be envisioned. Then we present a discussion of the relaxation of a single electron spin mediated by electron-phonon interaction via various different relaxation channels. In the low B-field regime we consider the spin-valley Kramers qubits and include impurity mediated valley mixing which will arise in disordered quantum dots. Rashba spin-orbit admixture mechanisms allow for relaxation by in-plane phonons either via the deformation potential or by piezoelectric coupling, additionally direct spin-phonon mechanisms involving out-of-plane phonons give rise to relaxation. We find that the relaxation rates scale as \\propto B 6 for both in-plane phonons coupling via deformation potential and the piezoelectric effect, while relaxation due to the direct spin-phonon coupling scales independant to B-field to lowest order but depends strongly on device mechanical tension. We will also discuss the relaxation mechanisms for pure spin or valley qubits formed in the large B-field regime.
Electronic properties and optical absorption of a phosphorene quantum dot
Liang, F. X.; Ren, Y. H.; Zhang, X. D.; Jiang, Z. T.
2018-03-01
Using the tight-binding Hamiltonian approach, we theoretically study the electronic and optical properties of a triangular phosphorene quantum dot (PQD) including one normal zigzag edge and two skewed armchair edges (ZAA-PQD). It is shown that the energy spectrum can be classified into the filled band (FB), the zero-energy band (ZB), and the unfilled band (UB). Numerical calculations of the FB, ZB, and UB probability distributions show that the FB and the UB correspond to the bulk states, while the ZB corresponds to the edge states, which appear on all of the three edges of the ZAA-PQD sharply different from the other PQDs. We also find that the strains and the electric fields can affect the energy levels inhomogeneously. Then the optical properties of the ZAA-PQD are investigated. There appear some strong low-energy optical absorption peaks indicating its sensitive low-energy optical response that is absent in other PQDs. Moreover, the strains and the electric fields can make inhomogeneous influences on the optical spectrum of the ZAA-PQD. This work may provide a useful reference for designing the electrical, mechanical, and optical PQD devices.
Detection of electromagnetic radiation using micromechanical multiple quantum wells structures
Datskos, Panagiotis G [Knoxville, TN; Rajic, Slobodan [Knoxville, TN; Datskou, Irene [Knoxville, TN
2007-07-17
An apparatus and method for detecting electromagnetic radiation employs a deflectable micromechanical apparatus incorporating multiple quantum wells structures. When photons strike the quantum-well structure, physical stresses are created within the sensor, similar to a "bimetallic effect." The stresses cause the sensor to bend. The extent of deflection of the sensor can be measured through any of a variety of conventional means to provide a measurement of the photons striking the sensor. A large number of such sensors can be arranged in a two-dimensional array to provide imaging capability.
Tuning of few-electron states and optical absorption anisotropy in GaAs quantum rings.
Wu, Zhenhua; Li, Jian; Li, Jun; Yin, Huaxiang; Liu, Yu
2017-11-15
The electronic and optical properties of a GaAs quantum ring (QR) with few electrons in the presence of the Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction (DSOI) have been investigated theoretically. The configuration interaction (CI) method is employed to calculate the eigenvalues and eigenstates of the multiple-electron QR accurately. Our numerical results demonstrate that the symmetry breaking induced by the RSOI and DSOI leads to an anisotropic distribution of multi-electron states. The Coulomb interaction offers additional modulation of the electron distribution and thus the optical absorption indices in the quantum rings. By tuning the magnetic/electric fields and/or electron numbers in a quantum ring, one can change its optical properties significantly. Our theory provides a new way to control the multi-electron states and optical properties of a QR by hybrid modulations or by electrical means only.
Directory of Open Access Journals (Sweden)
Hong-Quan ZHao
2012-01-01
Full Text Available One-dimensional nanowire quantum devices and basic quantum logic AND and OR unit on hexagonal nanowire units controlled by wrap gate (WPG were designed and fabricated on GaAs-based one-dimensional electron gas (1-DEG regular nanowire network with hexagonal topology. These basic quantum logic units worked correctly at 35 K, and clear quantum conductance was achieved on the node device, logic AND circuit unit, and logic OR circuit unit. Binary-decision-diagram- (BDD- based arithmetic logic unit (ALU is realized on GaAs-based regular nanowire network with hexagonal topology by the same fabrication method as that of the quantum devices and basic circuits. This BDD-based ALU circuit worked correctly at room temperature. Since these quantum devices and circuits are basic units of the BDD ALU combinational circuit, the possibility of integrating these quantum devices and basic quantum circuits into the BDD-based quantum circuit with more complicated structures was discussed. We are prospecting the realization of quantum BDD combinational circuitries with very small of energy consumption and very high density of integration.
Optical pumping of electron and nuclear spin in a negatively-charged quantum dot
Bracker, Allan; Gershoni, David; Korenev, Vladimir
2005-03-01
We report optical pumping of electron and nuclear spins in an individual negatively-charged quantum dot. With a bias-controlled heterostructure, we inject one electron into the quantum dot. Intense laser excitation produces negative photoluminescence polarization, which is easily erased by the Hanle effect, demonstrating optical pumping of a long-lived resident electron. The electron spin lifetime is consistent with the influence of nuclear spin fluctuations. Measuring the Overhauser effect in high magnetic fields, we observe a high degree of nuclear spin polarization, which is closely correlated to electron spin pumping.
On the quantum Landau collision operator and electron collisions in dense plasmas
Energy Technology Data Exchange (ETDEWEB)
Daligault, Jérôme, E-mail: daligaul@lanl.gov [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2016-03-15
The quantum Landau collision operator, which extends the widely used Landau/Fokker-Planck collision operator to include quantum statistical effects, is discussed. The quantum extension can serve as a reference model for including electron collisions in non-equilibrium dense plasmas, in which the quantum nature of electrons cannot be neglected. In this paper, the properties of the Landau collision operator that have been useful in traditional plasma kinetic theory and plasma transport theory are extended to the quantum case. We outline basic properties in connection with the conservation laws, the H-theorem, and the global and local equilibrium distributions. We discuss the Fokker-Planck form of the operator in terms of three potentials that extend the usual two Rosenbluth potentials. We establish practical closed-form expressions for these potentials under local thermal equilibrium conditions in terms of Fermi-Dirac and Bose-Einstein integrals. We study the properties of linearized quantum Landau operator, and extend two popular approximations used in plasma physics to include collisions in kinetic simulations. We apply the quantum Landau operator to the classic test-particle problem to illustrate the physical effects embodied in the quantum extension. We present useful closed-form expressions for the electron-ion momentum and energy transfer rates. Throughout the paper, similarities and differences between the quantum and classical Landau collision operators are emphasized.
On the quantum Landau collision operator and electron collisions in dense plasmas
Daligault, Jérôme
2016-03-01
The quantum Landau collision operator, which extends the widely used Landau/Fokker-Planck collision operator to include quantum statistical effects, is discussed. The quantum extension can serve as a reference model for including electron collisions in non-equilibrium dense plasmas, in which the quantum nature of electrons cannot be neglected. In this paper, the properties of the Landau collision operator that have been useful in traditional plasma kinetic theory and plasma transport theory are extended to the quantum case. We outline basic properties in connection with the conservation laws, the H-theorem, and the global and local equilibrium distributions. We discuss the Fokker-Planck form of the operator in terms of three potentials that extend the usual two Rosenbluth potentials. We establish practical closed-form expressions for these potentials under local thermal equilibrium conditions in terms of Fermi-Dirac and Bose-Einstein integrals. We study the properties of linearized quantum Landau operator, and extend two popular approximations used in plasma physics to include collisions in kinetic simulations. We apply the quantum Landau operator to the classic test-particle problem to illustrate the physical effects embodied in the quantum extension. We present useful closed-form expressions for the electron-ion momentum and energy transfer rates. Throughout the paper, similarities and differences between the quantum and classical Landau collision operators are emphasized.
Quantum spin-glass transition in the two-dimensional electron gas
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 58; Issue 2 ... Spin glasses; quantum phase transition; ferromagnetism; electron gas. ... We argue that a quantum transition involving the destruction of the spin-glass order in an applied in-plane magnetic ﬁeld offers a natural explanation of some features of recent ...
Learning nitrogen-vacancy electron spin dynamics on a silicon quantum photonic simulator
Wang, J.; Paesani, S.; Santagati, R.; Knauer, S.; Gentile, A. A.; Wiebe, N.; Petruzzella, M.; Laing, A.; Rarity, J. G.; O'Brien, J. L.; Thompson, M. G.
2017-01-01
We present the experimental demonstration of quantum Hamiltonian learning. Using an integrated silicon-photonics quantum simulator with the classical machine learning technique, we successfully learn the Hamiltonian dynamics of a diamond nitrogen-vacancy center's electron ground-state spin.
Giant electron-hole transport asymmetry in ultra-short quantum transistors
McRae, A. C.; Tayari, V.; Porter, J. M.; Champagne, A. R.
2017-01-01
Making use of bipolar transport in single-wall carbon nanotube quantum transistors would permit a single device to operate as both a quantum dot and a ballistic conductor or as two quantum dots with different charging energies. Here we report ultra-clean 10 to 100 nm scale suspended nanotube transistors with a large electron-hole transport asymmetry. The devices consist of naked nanotube channels contacted with sections of tube under annealed gold. The annealed gold acts as an n-doping top gate, allowing coherent quantum transport, and can create nanometre-sharp barriers. These tunnel barriers define a single quantum dot whose charging energies to add an electron or a hole are vastly different (e−h charging energy asymmetry). We parameterize the e−h transport asymmetry by the ratio of the hole and electron charging energies ηe−h. This asymmetry is maximized for short channels and small band gap tubes. In a small band gap device, we demonstrate the fabrication of a dual functionality quantum device acting as a quantum dot for holes and a much longer quantum bus for electrons. In a 14 nm-long channel, ηe−h reaches up to 2.6 for a device with a band gap of 270 meV. The charging energies in this device exceed 100 meV. PMID:28561024