Chen, Y. F.; Tung, J. C.; Tuan, P. H.; Yu, Y. T.; Liang, H. C.; Huang, K. F.
2017-01-01
A general method is developed to characterize the family of classical periodic orbits from the quantum Green's function for the two-dimensional (2D) integrable systems. A decomposing formula related to the beta function is derived to link the quantum Green's function with the individual classical periodic orbits. The practicality of the developed formula is demonstrated by numerically analyzing the 2D commensurate harmonic oscillators and integrable quantum billiards. Numerical analyses reveal that the emergence of the classical features in quantum Green's functions principally comes from the superposition of the degenerate states for 2D harmonic oscillators. On the other hand, the damping factor in quantum Green's functions plays a critical role to display the classical features in mesoscopic regime for integrable quantum billiards, where the physical function of the damping factor is to lead to the coherent superposition of the nearly degenerate eigenstates.
A model of the two-dimensional quantum harmonic oscillator in an $AdS_3$ background
Frick, Rudolf
2016-01-01
In this paper we study a model of the two-dimensional quantum harmonic oscillator in a 3-dimensional anti-de Sitter background. We use a generalized Schr\\"odinger picture in which the analogs of the Schr\\"odinger operators of the particle are independent of both the time and the space coordinates in different representations. The spacetime independent operators of the particle induce the Lie algebra of Killing vector fields of the $AdS_3$ spacetime. In this picture, we have a metamorphosis of the Heisenberg's uncertainty relations.
A model of the two-dimensional quantum harmonic oscillator in an AdS{sub 3} background
Energy Technology Data Exchange (ETDEWEB)
Frick, R. [Universitaet zu Koeln, Institut fuer Theoretische Physik, Cologne (Germany)
2016-10-15
In this paper we study a model of the two-dimensional quantum harmonic oscillator in a three-dimensional anti-de Sitter background. We use a generalized Schroedinger picture in which the analogs of the Schroedinger operators of the particle are independent of both the time and the space coordinates in different representations. The spacetime independent operators of the particle induce the Lie algebra of Killing vector fields of the AdS{sub 3} spacetime. In this picture, we have a metamorphosis of the Heisenberg uncertainty relations. (orig.)
Two-dimensional quantum repeaters
Wallnöfer, J.; Zwerger, M.; Muschik, C.; Sangouard, N.; Dür, W.
2016-11-01
The endeavor to develop quantum networks gave rise to a rapidly developing field with far-reaching applications such as secure communication and the realization of distributed computing tasks. This ultimately calls for the creation of flexible multiuser structures that allow for quantum communication between arbitrary pairs of parties in the network and facilitate also multiuser applications. To address this challenge, we propose a two-dimensional quantum repeater architecture to establish long-distance entanglement shared between multiple communication partners in the presence of channel noise and imperfect local control operations. The scheme is based on the creation of self-similar multiqubit entanglement structures at growing scale, where variants of entanglement swapping and multiparty entanglement purification are combined to create high-fidelity entangled states. We show how such networks can be implemented using trapped ions in cavities.
Supersymmetry and the constants of motion of the two-dimensional isotropic harmonic oscillator
Energy Technology Data Exchange (ETDEWEB)
Torres del Castillo, G.F. [Departamento de Fisica Matematica, Instituto de Ciencias, Universidad Autonoma de Puebla, 72570 Puebla (Mexico); Tepper G, T. [Escuela de Ciencias, Departamento de Fisica y Matematicas, Universidad de Las Americas-Puebla, Santa Catarina Martir, 72820 Cholula, Puebla (Mexico)
2002-07-01
It is shown that the constants of motion of the two-dimensional isotropic harmonic oscillator not related to the rotational invariance of the Hamiltonian can be derived using the ideas of supersymmetric quantum mechanics. (Author)
Bound states of two-dimensional relativistic harmonic oscillators
Institute of Scientific and Technical Information of China (English)
Qiang Wen-Chao
2004-01-01
We give the exact normalized bound state wavefunctions and energy expressions of the Klein-Gordon and Dirac equations with equal scalar and vector harmonic oscillator potentials in the two-dimensional space.
Energy Technology Data Exchange (ETDEWEB)
Mota, R.D. [Unidad Profesional Interdisciplinaria de Ingenieria y Tecnologias Avanzadas, Mexico DF (Mexico)]. E-mail: mota@gina.esfm.ipn.mx; ravelo@esfm.ipn.mx; Granados, V.D.; Queijeiro, A.; Garcia, J. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, Mexico DF (Mexico)
2002-03-29
For the quantum two-dimensional isotropic harmonic oscillator we show that the Infeld-Hull radial operators, as well as those of the supersymmetric approach for the radial equation, are contained in the constants of motion of the problem. (author)
Quantum computation with two-dimensional graphene quantum dots
Institute of Scientific and Technical Information of China (English)
Li Jie-Sen; Li Zhi-Bing; Yao Dao-Xin
2012-01-01
We study an array of graphene nano sheets that form a two-dimensional S =1/2 Kagome spin lattice used for quantum computation.The edge states of the graphene nano sheets axe used to form quantum dots to confine electrons and perform the computation.We propose two schemes of bang-bang control to combat decoherence and realize gate operations on this array of quantum dots.It is shown that both schemes contain a great amount of information for quantum computation.The corresponding gate operations are also proposed.
A two-dimensional spin liquid in quantum kagome ice.
Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G
2015-06-22
Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials.
Directory of Open Access Journals (Sweden)
Sameer M. Ikhdair
2013-01-01
Full Text Available The Klein-Gordon (KG equation for the two-dimensional scalar-vector harmonic oscillator plus Cornell potentials in the presence of external magnetic and Aharonov-Bohm (AB flux fields is solved using the wave function ansatz method. The exact energy eigenvalues and the wave functions are obtained in terms of potential parameters, magnetic field strength, AB flux field, and magnetic quantum number. The results obtained by using different Larmor frequencies are compared with the results in the absence of both magnetic field (ωL = 0 and AB flux field (ξ=0 cases. Effect of external fields on the nonrelativistic energy eigenvalues and wave function solutions is also precisely presented. Some special cases like harmonic oscillator and Coulombic fields are also studied.
Quantum entanglement in a two-dimensional ion trap
Institute of Scientific and Technical Information of China (English)
王成志; 方卯发
2003-01-01
In this paper, we investigate the quantum entanglement in a two-dimensional ion trap system. We discuss the quantum entanglement between the ion and phonons by using reduced entropy, and that between two degrees of freedom of the vibrational motion along x and y directions by using quantum relative entropy. We discuss also the influence of initial state of the system on the quantum entanglement and the relation between two entanglements in the trapped ion system.
Two-dimensional localized structures in harmonically forced oscillatory systems
Ma, Y.-P.; Knobloch, E.
2016-12-01
Two-dimensional spatially localized structures in the complex Ginzburg-Landau equation with 1:1 resonance are studied near the simultaneous presence of a steady front between two spatially homogeneous equilibria and a supercritical Turing bifurcation on one of them. The bifurcation structures of steady circular fronts and localized target patterns are computed in the Turing-stable and Turing-unstable regimes. In particular, localized target patterns grow along the solution branch via ring insertion at the core in a process reminiscent of defect-mediated snaking in one spatial dimension. Stability of axisymmetric solutions on these branches with respect to axisymmetric and nonaxisymmetric perturbations is determined, and parameter regimes with stable axisymmetric oscillons are identified. Direct numerical simulations reveal novel depinning dynamics of localized target patterns in the radial direction, and of circular and planar localized hexagonal patterns in the fully two-dimensional system.
Spin dynamics in a two-dimensional quantum gas
DEFF Research Database (Denmark)
Pedersen, Poul Lindholm; Gajdacz, Miroslav; Deuretzbacher, Frank
2014-01-01
We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimp......We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions...
Freely configurable quantum simulator based on a two-dimensional array of individually trapped ions
Mielenz, Manuel; Wittemer, Matthias; Hakelberg, Frederick; Schmied, Roman; Blain, Matthew; Maunz, Peter; Leibfried, Dietrich; Warring, Ulrich; Schaetz, Tobias
2015-01-01
A custom-built and precisely controlled quantum system may offer access to a fundamental understanding of another, less accessible system of interest. A universal quantum computer is currently out of reach, but an analog quantum simulator that makes the relevant observables, interactions, and states of a quantum model accessible could permit experimental insight into complex quantum dynamics that are intractable on conventional computers. Several platforms have been suggested and proof-of-principle experiments have been conducted. Here we characterise two-dimensional arrays of three ions trapped by radio-frequency fields in individually controlled harmonic wells forming equilateral triangles with side lengths 40 and 80 micrometer. In our approach, which is scalable to arbitrary two dimensional lattices, we demonstrate individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as tuning of crucial couplings be...
Non perturbative methods in two dimensional quantum field theory
Abdalla, Elcio; Rothe, Klaus D
1991-01-01
This book is a survey of methods used in the study of two-dimensional models in quantum field theory as well as applications of these theories in physics. It covers the subject since the first model, studied in the fifties, up to modern developments in string theories, and includes exact solutions, non-perturbative methods of study, and nonlinear sigma models.
Quantum skyrmions in two-dimensional chiral magnets
Takashima, Rina; Ishizuka, Hiroaki; Balents, Leon
2016-10-01
We study the quantum mechanics of magnetic skyrmions in the vicinity of the skyrmion-crystal to ferromagnet phase boundary in two-dimensional magnets. We show that the skyrmion excitation has an energy dispersion that splits into multiple bands due to the combination of magnus force and the underlying lattice. Condensation of the skyrmions can give rise to an intermediate phase between the skyrmion crystal and ferromagnet: a quantum liquid, in which skyrmions are not spatially localized. We show that the critical behavior depends on the spin size S and the topological number of the skyrmion. Experimental signatures of quantum skyrmions in inelastic neutron-scattering measurements are also discussed.
Institute of Scientific and Technical Information of China (English)
Sameer M.Ikhdair; Majid Hamzavi
2012-01-01
We study the effects of the perpendicular magnetic and Aharonov Bohm (AB) flux fields on the energy levels of a two-dimensional (2D) Klein-Gordon (KG) particle subjected to an equal scalar and vector pseudo-harmonic oscillator (PHO).We calculate the exact energy eigenvalues and normalized wave functions in terms of chemical potential parameter,magnetic field strength,AB flux field,and magnetic quantum number by means of the Nikiforov-Uvarov (NU) method.The non-relativistic limit,PHO,and harmonic oscillator solutions in the existence and absence of external fields are also obtained.
Multiple Potts Models Coupled to Two-Dimensional Quantum Gravity
Baillie, C F
1992-01-01
We perform Monte Carlo simulations using the Wolff cluster algorithm of {\\it multiple} $q=2,3,4$ state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the $c>1$ region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for $c>1$. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for $c>1$.
Multiple Potts models coupled to two-dimensional quantum gravity
Baillie, C. F.; Johnston, D. A.
1992-07-01
We perform Monte Carlo simulations using the Wolff cluster algorithm of multiple q=2, 3, 4 state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the c>1 region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for c>1. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for c>1.
Topological Quantum Optics in Two-Dimensional Atomic Arrays
Perczel, J.; Borregaard, J.; Chang, D. E.; Pichler, H.; Yelin, S. F.; Zoller, P.; Lukin, M. D.
2017-07-01
We demonstrate that two-dimensional atomic emitter arrays with subwavelength spacing constitute topologically protected quantum optical systems where the photon propagation is robust against large imperfections while losses associated with free space emission are strongly suppressed. Breaking time-reversal symmetry with a magnetic field results in gapped photonic bands with nontrivial Chern numbers and topologically protected, long-lived edge states. Due to the inherent nonlinearity of constituent emitters, such systems provide a platform for exploring quantum optical analogs of interacting topological systems.
Entropic Barriers for Two-Dimensional Quantum Memories
Brown, Benjamin J.; Al-Shimary, Abbas; Pachos, Jiannis K.
2014-03-01
Comprehensive no-go theorems show that information encoded over local two-dimensional topologically ordered systems cannot support macroscopic energy barriers, and hence will not maintain stable quantum information at finite temperatures for macroscopic time scales. However, it is still well motivated to study low-dimensional quantum memories due to their experimental amenability. Here we introduce a grid of defect lines to Kitaev's quantum double model where different anyonic excitations carry different masses. This setting produces a complex energy landscape which entropically suppresses the diffusion of excitations that cause logical errors. We show numerically that entropically suppressed errors give rise to superexponential inverse temperature scaling and polynomial system size scaling for small system sizes over a low-temperature regime. Curiously, these entropic effects are not present below a certain low temperature. We show that we can vary the system to modify this bound and potentially extend the described effects to zero temperature.
Quantum creep in a highly crystalline two-dimensional superconductor
Saito, Yu; Kasahara, Yuichi; Ye, Jianting; Iwasa, Yoshihiro; Nojima, Tsutomu
Conventional studies on quantum phase transitions, especially on superconductor-insulator or superconductor-metal-insulator transitions have been performed in deposited metallic thin films such as Bismuth or MoGe. Although the techniques of thin films deposition have been considerably improved, unintentional disorder such as impurities and deficiencies, generating the pinning centers, seems to still exist in such systems. The mechanical exfoliated highly crystalline two-dimensional material can be a good candidate to realize a less-disordered 2D superconductor with extremely weak pinning, combined with transfer method or ionic-liquid gating. We report on the quantum metal, namely, magnetic-field-induced metallic state observed in an ion-gated two-dimensional superconductor based on an ultra-highly crystalline layered band insulator, ZrNCl. We found that the superconducting state is extremely fragile against external magnetic fields; that is, zero resistance state immediately disappears, once an external magnetic field switches on. This is because the present system is relatively clean and the pinning potential is extremely weak, which cause quantum tunneling and flux flow of vortices, resulting in metallic ground state.
The XY model coupled to two-dimensional quantum gravity
Baillie, C. F.; Johnston, D. A.
1992-09-01
We perform Monte Carlo simulations using the Wolff cluster algorithm of the XY model on both fixed and dynamical phi-cubed graphs (i.e. without and with coupling to two-dimensional quantum gravity). We compare the numerical results with the theoretical expectation that the phase transition remains of KT type when the XY model is coupled to gravity. We also examine whether the universality we discovered in our earlier work on various Potts models with the same value of the central charge, c, carries over to the XY model, which has c=1.
Magnetic quantum dot in two-dimensional topological insulators
Li, Guo; Zhu, Jia-Lin; Yang, Ning
2017-03-01
Magnetic quantum dots in two-dimensional band and topological insulators are studied by solving the modified Dirac model under nonuniform magnetic fields. The Landau levels split into discrete states with certain angular momentum. The states splitting from the zero Landau levels lie in the energy gap for topological insulators but are out of the gap for band insulators. It is found that the ground states oscillate between the spin-up and spin-down states when the magnetic field or the dot size changes. The oscillation manifests itself as changes of sign and strength of charge currents near the dot's edge.
The XY Model Coupled to Two-Dimensional Quantum Gravity
Baillie, C F; 10.1016/0370-2693(92)91037-A
2009-01-01
We perform Monte Carlo simulations using the Wolff cluster algorithm of the XY model on both fixed and dynamical phi-cubed graphs (i.e. without and with coupling to two-dimensional quantum gravity). We compare the numerical results with the theoretical expectation that the phase transition remains of KT type when the XY model is coupled to gravity. We also examine whether the universality we discovered in our earlier work on various Potts models with the same value of the central charge, $c$, carries over to the XY model, which has $c=1$.
Spin from defects in two-dimensional quantum field theory
Novak, Sebastian
2015-01-01
We build two-dimensional quantum field theories on spin surfaces starting from theories on oriented surfaces with networks of topological defect lines and junctions. The construction uses a combinatorial description of the spin structure in terms of a triangulation equipped with extra data. The amplitude for the spin surfaces is defined to be the amplitude for the underlying oriented surface together with a defect network dual to the triangulation. Independence of the triangulation and of the other choices follows if the line defect and junctions are obtained from a Delta-separable Frobenius algebra with involutive Nakayama automorphism in the monoidal category of topological defects. For rational conformal field theory we can give a more explicit description of the defect category, and we work out two examples related to free fermions in detail: the Ising model and the so(n) WZW model at level 1.
Soliton nanoantennas in two-dimensional arrays of quantum dots
Gligorić, G; Hadžievski, Lj; Slepyan, G Ya; Malomed, B A
2015-01-01
We consider two-dimensional (2D) arrays of self-organized semiconductor quantum dots (QDs) strongly interacting with electromagnetic field in the regime of Rabi oscillations. The QD array built of two-level states is modelled by two coupled systems of discrete nonlinear Schr\\"{o}dinger equations. Localized modes in the form of single-peaked fundamental and vortical stationary Rabi solitons and self-trapped breathers have been found. The results for the stability, mobility and radiative properties of the Rabi modes suggest a concept of a self-assembled 2D \\textit{% soliton-based nano-antenna}, which should be stable against imperfections In particular, we discuss the implementation of such a nano-antenna in the form of surface plasmon solitons in graphene, and illustrate possibilities to control their operation by means of optical tools.
Ultrabroadband two-quantum two-dimensional electronic spectroscopy
Gellen, Tobias A.; Bizimana, Laurie A.; Carbery, William P.; Breen, Ilana; Turner, Daniel B.
2016-08-01
A recent theoretical study proposed that two-quantum (2Q) two-dimensional (2D) electronic spectroscopy should be a background-free probe of post-Hartree-Fock electronic correlations. Testing this theoretical prediction requires an instrument capable of not only detecting multiple transitions among molecular excited states but also distinguishing molecular 2Q signals from nonresonant response. Herein we describe a 2Q 2D spectrometer with a spectral range of 300 nm that is passively phase stable and uses only beamsplitters and mirrors. We developed and implemented a dual-chopping balanced-detection method to resolve the weak molecular 2Q signals. Experiments performed on cresyl violet perchlorate and rhodamine 6G revealed distinct 2Q signals convolved with nonresonant response. Density functional theory computations helped reveal the molecular origin of these signals. The experimental and computational results demonstrate that 2Q electronic spectra can provide a singular probe of highly excited electronic states.
Crossed Andreev effects in two-dimensional quantum Hall systems
Hou, Zhe; Xing, Yanxia; Guo, Ai-Min; Sun, Qing-Feng
2016-08-01
We study the crossed Andreev effects in two-dimensional conductor/superconductor hybrid systems under a perpendicular magnetic field. Both a graphene/superconductor hybrid system and an electron gas/superconductor one are considered. It is shown that an exclusive crossed Andreev reflection, with other Andreev reflections being completely suppressed, is obtained in a high magnetic field because of the chiral edge states in the quantum Hall regime. Importantly, the exclusive crossed Andreev reflection not only holds for a wide range of system parameters, e.g., the size of system, the width of central superconductor, and the quality of coupling between the graphene and the superconductor, but also is very robust against disorder. When the applied bias is within the superconductor gap, a robust Cooper-pair splitting process with high-efficiency can be realized in this system.
Quantum magnetotransport in a modulated two-dimensional electron gas
Park, Tae-ik; Gumbs, Godfrey
1997-09-01
Quantum mechanical calculations of the magnetotransport coefficients of a modulated two-dimensional electron gas in a perpendicular magnetic field are presented using the Kubo method. The model modulation potential used is such that the effect of the steepness of the potential and its strength on the band part of the longitudinal resistivity ρxxand the Hall resistivity ρxycould be studied. In the extreme limit of a very steep potential, a two-dimensional square array of antidots is simulated. Impurity scattering is included in the self-consistent t-matrix approximation. The results show that for a strong lateral superlattice potential, ρxyis quenched in the low magnetic field regime and as the magnetic field increases there is a large negative Hall resistivity. The intensity of this negative peak is suppressed as the strength of the modulation potential is decreased. It is also shown that the height of the negative peak depends on the steepness of the potential. The longitudinal resistivity also has some interesting features. There are Aharonov-Bohm oscillations and a double peak structure which depends on both the strength of the modulation potential as well as its slope. The numerical results show that the position and intensity of the lower peak is not very sensitive to a change in the strength of the lattice potential or its steepness. However, the upper peak is greatly reduced when the lattice potential is diminished in strength. The double peak feature in ρxxand the negative peak and quenching of the Hall effect at low magnetic fields have been observed experimentally for antidots in both the quasiclassical and quantum regimes.
Criticality in Two-Dimensional Quantum Systems: Tensor Network Approach
Ran, Shi-Ju; Li, Wei; Lewenstein, Maciej; Su, Gang
2016-01-01
Determination and characterization of criticality in two-dimensional (2D) quantum many-body systems belong to the most important challenges and problems of quantum physics. In this paper we propose an efficient scheme to solve this problem by utilizing the infinite projected entangled pair state (iPEPS), and tensor network (TN) representations. We show that the criticality of a 2D state is faithfully reproduced by the ground state (dubbed as boundary state) of a one-dimensional effective Hamiltonian constructed from its iPEPS representation. We demonstrate that for a critical state the correlation length and the entanglement spectrum of the boundary state are essentially different from those of a gapped iPEPS. This provides a solid indicator that allows to identify the criticality of the 2D state. Our scheme is verified on the resonating valence bond (RVB) states on kagom\\'e and square lattices, where the boundary state of the honeycomb RVB is found to be described by a $c=1$ conformal field theory. We apply ...
Quantum holographic encoding in a two-dimensional electron gas
Energy Technology Data Exchange (ETDEWEB)
Moon, Christopher
2010-05-26
The advent of bottom-up atomic manipulation heralded a new horizon for attainable information density, as it allowed a bit of information to be represented by a single atom. The discrete spacing between atoms in condensed matter has thus set a rigid limit on the maximum possible information density. While modern technologies are still far from this scale, all theoretical downscaling of devices terminates at this spatial limit. Here, however, we break this barrier with electronic quantum encoding scaled to subatomic densities. We use atomic manipulation to first construct open nanostructures - 'molecular holograms' - which in turn concentrate information into a medium free of lattice constraints: the quantum states of a two-dimensional degenerate Fermi gas of electrons. The information embedded in the holograms is transcoded at even smaller length scales into an atomically uniform area of a copper surface, where it is densely projected into both two spatial degrees of freedom and a third holographic dimension mapped to energy. In analogy to optical volume holography, this requires precise amplitude and phase engineering of electron wavefunctions to assemble pages of information volumetrically. This data is read out by mapping the energy-resolved electron density of states with a scanning tunnelling microscope. As the projection and readout are both extremely near-field, and because we use native quantum states rather than an external beam, we are not limited by lensing or collimation and can create electronically projected objects with features as small as {approx}0.3 nm. These techniques reach unprecedented densities exceeding 20 bits/nm{sup 2} and place tens of bits into a single fermionic state.
Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots
Energy Technology Data Exchange (ETDEWEB)
Cundiff, Steven T. [Univ. of Colorado, Boulder, CO (United States)
2016-05-03
This final report describes the activities undertaken under grant "Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots". The goal of this program was to implement optical 2-dimensional Fourier transform spectroscopy and apply it to electronic excitations, including excitons, in semiconductors. Specifically of interest are quantum wells that exhibit disorder due to well width fluctuations and quantum dots. In both cases, 2-D spectroscopy will provide information regarding coupling among excitonic localization sites.
Temperature dependence of universal fluctuations in the two-dimensional harmonic XY model.
Palma, G
2006-04-01
We compute exact analytical expressions for the skewness and kurtosis in the two-dimensional harmonic XY model. These quantities correspond to the third and fourth normalized moments of the probability density function (PDF) of the magnetization of the model. From their behavior, we conclude that they depend explicitly on the system temperature even in the thermodynamic limit, and hence the PDF itself must depend on it. Our results correct the hypothesis called universal fluctuations, they confirm and extend previous results which showed a T dependence of the PDF, including perturbative expansions within the XY model up to first order in temperature.
Zhang, Yiqi; Liu, Xing; Belić, Milivoj R; Zhong, Weiping; Wen, Feng; Zhang, Yanpeng
2015-08-15
We analytically and numerically investigate an anharmonic propagation of two-dimensional beams in a harmonic potential. We pick noncentrosymmetric beams of common interest that carry orbital angular momentum. The examples studied include superposed Bessel-Gauss (BG), Laguerre-Gauss (LG), and circular Airy (CA) beams. For the BG beams, periodic inversion, phase transition, and rotation with periodic angular velocity are demonstrated during propagation. For the LG and CA beams, periodic inversion and variable rotation are still there but not the phase transition. On the whole, the "center of mass" and the orbital angular momentum of a beam exhibit harmonic motion, but the motion of the beam intensity distribution in detail is subject to external and internal torques and forces, causing it to be anharmonic. Our results are applicable to other superpositions of finite circularly asymmetric beams.
Low-Lying States of the A+B-A+B- Coulomb Systems in Two-Dimensional Quantum Dots
Institute of Scientific and Technical Information of China (English)
XIE Wen-Fang
2001-01-01
The features of the low-lying spectra of four-body A+B-A+B- systems have been deduced based on symmetry. Using the method of few-body physics, we calculate the energy spectra of A + B- A + B- systems in a harmonic quantum dot. We find that the biexciton in a two-dimensional quantum dot may have other bound excited states and the quantum mechanical symmetry plays a crucialrole in determining the energy levels and structures of the low-lying states.
Multifarious topological quantum phase transitions in two-dimensional topological superconductors
Liu, Xiao-Ping; Zhou, Yuan; Wang, Yi-Fei; Gong, Chang-De
2016-06-01
We study the two-dimensional topological superconductors of spinless fermions in a checkerboard-lattice Chern-insulator model. With the short-range p-wave superconducting pairing, multifarious topological quantum phase transitions have been found and several phases with high Chern numbers have been observed. We have established a rich phase diagram for these topological superconducting states. A finite-size checkerboard-lattice cylinder with a harmonic trap potential has been further investigated. Based upon the self-consistent numerical calculations of the Bogoliubov-de Gennes equations, various phase transitions have also been identified at different regions of the system. Multiple pairs of Majorana fermions are found to be well-separated and localized at the phase boundaries between the phases characterized by different Chern numbers.
One- and Two-Dimensional Nuclear Magnetic Resonance Spectroscopy with a Diamond Quantum Sensor
Boss, J. M.; Chang, K.; Armijo, J.; Cujia, K.; Rosskopf, T.; Maze, J. R.; Degen, C. L.
2016-05-01
We report on Fourier spectroscopy experiments performed with near-surface nitrogen-vacancy centers in a diamond chip. By detecting the free precession of nuclear spins rather than applying a multipulse quantum sensing protocol, we are able to unambiguously identify the NMR species devoid of harmonics. We further show that, by engineering different Hamiltonians during free precession, the hyperfine coupling parameters as well as the nuclear Larmor frequency can be selectively measured with up to five digits of precision. The protocols can be combined to demonstrate two-dimensional Fourier spectroscopy. Presented techniques will be useful for mapping nuclear coordinates in molecules deposited on diamond sensor chips, en route to imaging their atomic structure.
Multifarious topological quantum phase transitions in two-dimensional topological superconductors
Liu, Xiao-Ping; Zhou, Yuan; Wang, Yi-Fei; Gong, Chang-De
2016-01-01
We study the two-dimensional topological superconductors of spinless fermions in a checkerboard-lattice Chern-insulator model. With the short-range p-wave superconducting pairing, multifarious topological quantum phase transitions have been found and several phases with high Chern numbers have been observed. We have established a rich phase diagram for these topological superconducting states. A finite-size checkerboard-lattice cylinder with a harmonic trap potential has been further investigated. Based upon the self-consistent numerical calculations of the Bogoliubov-de Gennes equations, various phase transitions have also been identified at different regions of the system. Multiple pairs of Majorana fermions are found to be well-separated and localized at the phase boundaries between the phases characterized by different Chern numbers. PMID:27329219
Spin dynamics and magnetic correlation length in two-dimensional quantum heisenberg antiferromagnets
Carretta; Ciabattoni; Cuccoli; Mognaschi; Rigamonti; Tognetti; Verrucchi
2000-01-10
The correlated spin dynamics and temperature dependence of the correlation length xi(T) in two-dimensional quantum (S = 1/2) Heisenberg antiferromagnets (2DQHAF) on a square lattice are discussed in light of experimental results of proton spin lattice relaxation in copper formiate tetradeuterate. In this compound the exchange constant is much smaller than the one in recently studied 2DQHAF, such as La2CuO4 and Sr2CuO2Cl2. Thus the spin dynamics can be probed in detail over a wider temperature range. The NMR relaxation rates turn out to be in excellent agreement with a theoretical mode-coupling calculation. The deduced temperature behavior of xi(T) is in agreement with high-temperature expansions, quantum Monte Carlo simulations, and the pure quantum self-consistent harmonic approximation. Contrary to the predictions of the theories based on the nonlinear sigma model, no evidence of crossover between different quantum regimes is observed.
Deformed oscillator algebras for two dimensional quantum superintegrable systems
Bonatsos, Dennis; Kokkotas, K D; Bonatsos, Dennis
1994-01-01
Quantum superintegrable systems in two dimensions are obtained from their classical counterparts, the quantum integrals of motion being obtained from the corresponding classical integrals by a symmetrization procedure. For each quantum superintegrable systema deformed oscillator algebra, characterized by a structure function specific for each system, is constructed, the generators of the algebra being functions of the quantum integrals of motion. The energy eigenvalues corresponding to a state with finite dimensional degeneracy can then be obtained in an economical way from solving a system of two equations satisfied by the structure function, the results being in agreement to the ones obtained from the solution of the relevant Schrodinger equation. The method shows how quantum algebraic techniques can simplify the study of quantum superintegrable systems, especially in two dimensions.
Quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$
Wang, Kefeng; Graf, D.; Petrovic, C.
2016-01-01
We report quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$. The band structure shows several narrow bands with nearly linear energy dispersion and Dirac-cone-like points at the Fermi level. The quantum oscillation experiments revealed one quasi-two-dimensional Fermi pocket and another complex pocket with small cyclotron resonant mass. The in-plane transverse magnetoresistance exhibits a crossover at a critical field $B^*$ from semiclassical weak-field $B^2$ dep...
Two-dimensional ion trap lattice on a microchip for quantum simulation
Sterling, R C; Weidt, S; Lake, K; Srinivasan, P; Webster, S C; Kraft, M; Hensinger, W K
2013-01-01
Using a controllable quantum system it is possible to simulate other highly complex quantum systems efficiently overcoming an in-principle limitation of classical computing. Trapped ions constitute such a highly controllable quantum system. So far, no dedicated architectures for the simulation of two-dimensional spin lattices using trapped ions in radio-frequency ion traps have been produced, limiting the possibility of carrying out such quantum simulations on a large scale. We report the operation of a two-dimensional ion trap lattice integrated in a microchip capable of implementing quantum simulations of two-dimensional spin lattices. Our device provides a scalable microfabricated architecture for trapping such ion lattices with coupling strengths between neighbouring ions sufficient to provide a powerful platform for the implementation of quantum simulations. In order to realize this device we developed a specialist fabrication process that allows for the application of very large voltages. We fabricated ...
Quantum search on the two-dimensional lattice using the staggered model with Hamiltonians
Portugal, R.; Fernandes, T. D.
2017-04-01
Quantum search on the two-dimensional lattice with one marked vertex and cyclic boundary conditions is an important problem in the context of quantum algorithms with an interesting unfolding. It avails to test the ability of quantum walk models to provide efficient algorithms from the theoretical side and means to implement quantum walks in laboratories from the practical side. In this paper, we rigorously prove that the recent-proposed staggered quantum walk model provides an efficient quantum search on the two-dimensional lattice, if the reflection operators associated with the graph tessellations are used as Hamiltonians, which is an important theoretical result for validating the staggered model with Hamiltonians. Numerical results show that on the two-dimensional lattice staggered models without Hamiltonians are not as efficient as the one described in this paper and are, in fact, as slow as classical random-walk-based algorithms.
Dipolar quantum electrodynamics of the two-dimensional electron gas
Todorov, Yanko
2015-03-01
Similarly to a previous work on the homogeneous electron gas [Y. Todorov, Phys. Rev. B 89, 075115 (2014), 10.1103/PhysRevB.89.075115], we apply the Power-Zienau-Wooley (PZW) formulation of the quantum electrodynamics to the case of an electron gas quantum confined by one-dimensional potential. We provide a microscopic description of all collective plasmon modes of the gas, oscillating both along and perpendicular to the direction of quantum confinement. Furthermore, we study the interaction of the collective modes with a photonic structure, planar metallic waveguide, by using the full expansion of the electromagnetic field into normal modes. We show how the boundary conditions for the electromagnetic field influence both the transverse light-matter coupling and the longitudinal particle-particle interactions. The PZW descriptions appear thus as a convenient tool to study semiconductor quantum optics in geometries where quantum-confined particles interact with strongly confined electromagnetic fields in microresonators, such as the ones used to achieve the ultrastrong light-matter coupling regime.
Laser driven impurity states in two-dimensional quantum dots and quantum rings
Laroze, D.; Barseghyan, M.; Radu, A.; Kirakosyan, A. A.
2016-11-01
The hydrogenic donor impurity states in two-dimensional GaAs/Ga0.7Al0.3As quantum dot and quantum ring have been investigated under the action of intense laser field. A laser dressed effect on both electron confining and electron-impurity Coulomb interaction potentials has been considered. The single electron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. The accidental degeneracy of the impurity states have been observed for different positions of the impurity and versus values of the laser field parameter. The obtained theoretical results indicate a novel opportunity to tune the performance of quantum dots and quantum rings and to control their specific properties by means of laser field.
Two-dimensional lattice gauge theories with superconducting quantum circuits
Energy Technology Data Exchange (ETDEWEB)
Marcos, D., E-mail: david.marcos@me.com [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Widmer, P. [Albert Einstein Center, Institute for Theoretical Physics, Bern University, CH-3012, Bern (Switzerland); Rico, E. [IPCMS (UMR 7504) and ISIS (UMR 7006), University of Strasbourg and CNRS, 67000 Strasbourg (France); Hafezi, M. [Joint Quantum Institute, NIST/University of Maryland, College Park 20742 (United States); Department of Electrical Engineering and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742 (United States); Rabl, P. [Institute of Atomic and Subatomic Physics, TU Wien, Stadionallee 2, 1020 Wien (Austria); Wiese, U.-J. [Albert Einstein Center, Institute for Theoretical Physics, Bern University, CH-3012, Bern (Switzerland); Zoller, P. [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria)
2014-12-15
A quantum simulator of U(1) lattice gauge theories can be implemented with superconducting circuits. This allows the investigation of confined and deconfined phases in quantum link models, and of valence bond solid and spin liquid phases in quantum dimer models. Fractionalized confining strings and the real-time dynamics of quantum phase transitions are accessible as well. Here we show how state-of-the-art superconducting technology allows us to simulate these phenomena in relatively small circuit lattices. By exploiting the strong non-linear couplings between quantized excitations emerging when superconducting qubits are coupled, we show how to engineer gauge invariant Hamiltonians, including ring-exchange and four-body Ising interactions. We demonstrate that, despite decoherence and disorder effects, minimal circuit instances allow us to investigate properties such as the dynamics of electric flux strings, signaling confinement in gauge invariant field theories. The experimental realization of these models in larger superconducting circuits could address open questions beyond current computational capability.
Quantum vortex dynamics in two-dimensional neutral superfluids
Wang, C. -C J.; Duine, R.A.; MacDonald, A.H.
2010-01-01
We derive an effective action for the vortex-position degree of freedom in a superfluid by integrating out condensate phase- and density-fluctuation environmental modes. When the quantum dynamics of environmental fluctuations is neglected, we confirm the occurrence of the vortex Magnus force and
Two-Dimensional Arrays of Neutral Atom Quantum Gates
2012-10-20
Isenhower, X. Zhang, A. Gill, T. Walker, M. Saffman. Deterministic entanglement of two neutral atoms via Rydberg blockade, Physical Review A, (09 2010...squeezing of atomic ensembles by multicolor quantum nondemolition measurements, Physical Review A, (02 2009): 0. doi: 10.1103/PhysRevA.79.023831 10/19/2012...collective encoding in holmium atoms, Physical Review A, (07 2008): 0. doi: 10.1103/PhysRevA.78.012336 10/19/2012 10.00 M Saffman, X L Zhang, A T
Twisted Conformal Algebra and Quantum Statistics of Harmonic Oscillators
Directory of Open Access Journals (Sweden)
J. Naji
2014-01-01
Full Text Available We consider noncommutative two-dimensional quantum harmonic oscillators and extend them to the case of twisted algebra. We obtained modified raising and lowering operators. Also we study statistical mechanics and thermodynamics and calculated partition function which yields the free energy of the system.
Quantum mechanical treatment of a constrained particle on two dimensional sphere
Jahangiri, L.; Panahi, H.
2016-12-01
In this work, we study the motion of a particle on two dimensional sphere. By writing the Schrodinger equation, we obtain the wave function and energy spectra for three dimensional harmonic oscillator potential plus trigonometric Rosen-Morse non-central potential. By letting three special cases for intertwining operator, we investigate the energy spectra and wave functions for Smorodinsky-Winternitz potential model.
Non-linear excitation of quantum emitters in two-dimensional hexagonal boron nitride
Schell, Andreas W; Takashima, Hideaki; Takeuchi, Shigeki; Aharonovich, Igor
2016-01-01
Two-photon absorption is an important non-linear process employed for high resolution bio-imaging and non-linear optics. In this work we realize two-photon excitation of a quantum emitter embedded in a two-dimensional material. We examine defects in hexagonal boron nitride and show that the emitters exhibit similar spectral and quantum properties under one-photon and two-photon excitation. Furthermore, our findings are important to deploy two-dimensional hexagonal boron nitride for quantum non-linear photonic applications.
Calculating Two-Dimensional Spectra with the Mixed Quantum-Classical Ehrenfest Method
van der Vegte, C. P.; Dijkstra, A. G.; Knoester, J.; Jansen, T. L. C.
2013-01-01
We present a mixed quantum-classical simulation approach to calculate two-dimensional spectra of coupled two-level electronic model systems. We include the change in potential energy of the classical system due to transitions in the quantum system using the Ehrenfest method. We study how this
Ge, Yingbin
2016-01-01
Hands-on exercises are designed for undergraduate physical chemistry students to derive two-dimensional quantum chemistry from scratch for the H atom and H[subscript 2] molecule, both in the ground state and excited states. By reducing the mathematical complexity of the traditional quantum chemistry teaching, these exercises can be completed…
Calculating Two-Dimensional Spectra with the Mixed Quantum-Classical Ehrenfest Method
van der Vegte, C. P.; Dijkstra, A. G.; Knoester, J.; Jansen, T. L. C.
2013-01-01
We present a mixed quantum-classical simulation approach to calculate two-dimensional spectra of coupled two-level electronic model systems. We include the change in potential energy of the classical system due to transitions in the quantum system using the Ehrenfest method. We study how this feedba
Exact two-body solutions and quantum defect theory of two-dimensional dipolar quantum gas
Jie, Jianwen; Qi, Ran
2016-10-01
In this paper, we provide the two-body exact solutions of the two-dimensional (2D) Schrödinger equation with isotropic +/- 1/{r}3 interactions. An analytic quantum defect theory is constructed based on these solutions and it is applied to investigate the scattering properties as well as two-body bound states of an ultracold polar molecules confined in a quasi-2D geometry. Interestingly, we find that for the attractive case, the scattering resonance happens simultaneously in all partial waves, which has not been observed in other systems. The effect of this feature on the scattering phase shift across such resonances is also illustrated.
Tanimura, Y; Steffen, T
2000-01-01
The relaxation processes in a quantum system nonlinearly coupled to a harmonic Gaussian-Markovian heat bath are investigated by the quantum Fokker-Planck equation in the hierarchy form. This model describes frequency fluctuations in the quantum system with an arbitrary correlation time and thus
Steffen, T; Tanimura, Y
2000-01-01
The quantum Fokker-Planck equation is derived for a system nonlinearly coupled to a harmonic oscillator bath. The system-bath interaction is assumed to be linear in the bath coordinates but quadratic in the system coordinate. The relaxation induced dynamics of a harmonic system are investigated by s
Emergent topology and dynamical quantum phase transitions in two-dimensional closed quantum systems
Bhattacharya, Utso; Dutta, Amit
2017-07-01
Dynamical quantum phase transitions (DQPTs) manifested in the nonanalyticities in the temporal evolution of a closed quantum system generated by the time-independent final Hamiltonian, following a quench (or ramping) of a parameter of the Hamiltonian, is an emerging frontier of nonequilibrium quantum dynamics. We, here, introduce the notion of a dynamical topological order parameter (DTOP) that characterizes these DQPTs occurring in quenched (or ramped) two-dimensional closed quantum systems; this is quite a nontrivial generalization of the notion of DTOP introduced in Budich and Heyl [Phys. Rev. B 93, 085416 (2016), 10.1103/PhysRevB.93.085416] for one-dimensional situations. This DTOP is obtained from the "gauge-invariant" Pancharatnam phase extracted from the Loschmidt overlap, i.e., the modulus of the overlap between the initially prepared state and its time-evolved counterpart reached following a temporal evolution generated by the time-independent final Hamiltonian. This generic proposal is illustrated considering DQPTs occurring in the subsequent temporal evolution following a sudden quench of the staggered mass of the topological Haldane model on a hexagonal lattice where it stays fixed to zero or unity and makes a discontinuous jump between these two values at critical times at which DQPTs occur. What is remarkable is that while the topology of the equilibrium model is characterized by the Chern number, the emergent topology associated with the DQPTs is characterized by a generalized winding number.
Origin of the inverse energy cascade in two-dimensional quantum turbulence
Skaugen, Audun
2016-01-01
We unravel the intimate connection between fundamental characteristics of two dimensional turbulence, i.e. the large-scale coherent structures and the inverse energy cascade. We propose a driven, dissipative point vortex model that is able to capture the dynamics of two-dimensional quantum turbulence by the emergent clustering of same-sign vortices, which form a non-equilibrium analogue of Onsager vortex equilibria. The inverse energy cascade developing in a statistically neutral system originates from this clustering of co-rotating and counter-rotating vortices. The Kolmogorov energy spectrum $k^{-5/3}$ is attributed to the scale-free correlations in the vorticity field fluctuations, here measured by the weighted pair correlation function that has a power-law decay as $r^{-4/3}$ on inertial separation lengthscales $r$. This scale-invariant statistics of vorticity, attributed to a conformal symmetry of two-dimensional classical turbulence, draws further analogies between classical and quantum turbulence beyon...
Two-dimensional quantum compass model in a staggered field: some rigorous results
Institute of Scientific and Technical Information of China (English)
He Pei-Song; You Wen-Long; Tian Guang-Shan
2011-01-01
We study the properties of the two-dimensional quantum compass model in a staggered field. Using the PerronFr(o)enius theorem and the reflection positivity method, we rigorously determine the low energy spectrum of this model and its global ground state Ψ0. Furthermore, we show that Ψ0 has a directional long-range order.
Expectation value of composite field $T{\\bar T}$ in two-dimensional quantum field theory
Zamolodchikov, Alexander B.
2004-01-01
I show that the expectation value of the composite field $T{\\bar T}$, built from the components of the energy-momentum tensor, is expressed exactly through the expectation value of the energy-momentum tensor itself. The relation is derived in two-dimensional quantum field theory under broad assumptions, and does not require integrability.
Quantum computing via defect states in two-dimensional antidot lattices.
Flindt, Christian; Mortensen, Niels Asger; Jauho, Antti-Pekka
2005-12-01
We propose a new structure suitable for quantum computing in a solid-state environment: designed defect states in antidot lattices superimposed on a two-dimensional electron gas at a semiconductor heterostructure. State manipulation can be obtained with gate control. Model calculations indicate that it is feasible to fabricate structures whose energy level structure is robust against thermal dephasing.
Scaling dimensions of manifestly generally covariant operators in two-dimensional quantum gravity
Nishimura, J; Tsuchiya, A; Jun Nishimura; Shinya Tamura; Asato Tsuchiya
1994-01-01
Using (2+$\\epsilon$)-dimensional quantum gravity recently formulated by Kawai, Kitazawa and Ninomiya, we calculate the scaling dimensions of manifestly generally covariant operators in two-dimensional quantum gravity coupled to $(p,q)$ minimal conformal matter. In the spectrum appear all the scaling dimensions of the scaling operators in the matrix model except the boundary operators, while there are also many others which have no corresponding scaling dimensions in the matrix model.
Spin transport in the two-dimensional quantum disordered anisotropic Heisenberg model
Energy Technology Data Exchange (ETDEWEB)
Lima, L.S. [Departamento de Física e Matemática, Centro Federal de Educação Tecnológica de Minas Gerais, 30510-000 Belo Horizonte, MG (Brazil); Pires, A.S.T.; Costa, B.V. [Departamento de Física ICEx, UFMG, CP 702, 31270-901 Belo Horizonte, MG (Brazil)
2014-12-15
We use the self consistent harmonic approximation together with the Linear Response Theory to study the effect of nonmagnetic disorder on spin transport in the quantum diluted two-dimensional anisotropic Heisenberg model with spin S=1 in a square lattice. The model has a BKT transition at zero dilution. We calculate the regular part of the spin conductivity σ{sup reg}(ω) and the Drude weight D{sub S}(T) as a function of the non-magnetic concentration, x. Our calculations show that the spin conductivity drops abruptly to zero at x{sub c}{sup SCHA}≈0.5 indicating that the system changes from an ideal spin conductor state to an insulator. This value is far above the site percolation threshold x{sub c}{sup site}≈0.41. Although the SCHA fails in determining precisely the percolation threshold, both the spin conductivity and the Drude weight show a quite regular behavior inside 0≤x≤x{sub c}{sup SCHA} indicating that the transition stays in the same universality class all along the interval. - Highlights: • The site dilution generates a large influence on regular part of the spin conductivity, σ{sup reg}(ω), and in the Drude weight, D(T). • In a concentration of impurities about x≈0.5, the regular part of the spin conductivity and the Drude weight fall to zero. • In this point we have a change in the state of the system from an ideal spin conductor to a spin insulator.
Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor
Branny, Artur; Kumar, Santosh; Proux, Raphaël; Gerardot, Brian D
2017-01-01
An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor. We create point-like strain perturbations in mono- and bi-layer WSe2 which locally modify the band-gap, leading to efficient funnelling of excitons towards isolated strain-tuned quantum emitters that exhibit high-purity single photon emission. We achieve near unity emitter creation probability and a mean positioning accuracy of 120±32 nm, which may be improved with further optimization of the nanopillar dimensions. PMID:28530219
Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor
Branny, Artur; Kumar, Santosh; Proux, Raphaël; Gerardot, Brian D.
2017-05-01
An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor. We create point-like strain perturbations in mono- and bi-layer WSe2 which locally modify the band-gap, leading to efficient funnelling of excitons towards isolated strain-tuned quantum emitters that exhibit high-purity single photon emission. We achieve near unity emitter creation probability and a mean positioning accuracy of 120+/-32 nm, which may be improved with further optimization of the nanopillar dimensions.
Bipartite entanglement entropy in massive two-dimensional quantum field theory.
Doyon, Benjamin
2009-01-23
Recently, Cardy, Castro Alvaredo, and the author obtained the first exponential correction to saturation of the bipartite entanglement entropy at large region lengths in massive two-dimensional integrable quantum field theory. It depends only on the particle content of the model, and not on the way particles scatter. Based on general analyticity arguments for form factors, we propose that this result is universal, and holds for any massive two-dimensional model (also out of integrability). We suggest a link of this result with counting pair creations far in the past.
Po, Hoi Chun; Zhou, Qi
2015-08-13
Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems.
Quantum Hall effect in black phosphorus two-dimensional electron system.
Li, Likai; Yang, Fangyuan; Ye, Guo Jun; Zhang, Zuocheng; Zhu, Zengwei; Lou, Wenkai; Zhou, Xiaoying; Li, Liang; Watanabe, Kenji; Taniguchi, Takashi; Chang, Kai; Wang, Yayu; Chen, Xian Hui; Zhang, Yuanbo
2016-07-01
The development of new, high-quality functional materials has been at the forefront of condensed-matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the materials base of two-dimensional electron systems (2DESs). Here, we report the observation of the integer quantum Hall effect in a high-quality black phosphorus 2DES. The high quality is achieved by embedding the black phosphorus 2DES in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DES and brings the carrier Hall mobility up to 6,000 cm(2) V(-1) s(-1). The exceptional mobility enabled us to observe the quantum Hall effect and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime.
Nonlinear low-frequency electrostatic wave dynamics in a two-dimensional quantum plasma
Energy Technology Data Exchange (ETDEWEB)
Ghosh, Samiran, E-mail: sran_g@yahoo.com [Department of Applied Mathematics, University of Calcutta, 92, Acharya Prafulla Chandra Road, Kolkata-700 009 (India); Chakrabarti, Nikhil, E-mail: nikhil.chakrabarti@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064 (India)
2016-08-15
The problem of two-dimensional arbitrary amplitude low-frequency electrostatic oscillation in a quasi-neutral quantum plasma is solved exactly by elementary means. In such quantum plasmas we have treated electrons quantum mechanically and ions classically. The exact analytical solution of the nonlinear system exhibits the formation of dark and black solitons. Numerical simulation also predicts the possible periodic solution of the nonlinear system. Nonlinear analysis reveals that the system does have a bifurcation at a critical Mach number that depends on the angle of propagation of the wave. The small-amplitude limit leads to the formation of weakly nonlinear Kadomstev–Petviashvili solitons.
On Relations between One-Dimensional Quantum and Two-Dimensional Classical Spin Systems
Directory of Open Access Journals (Sweden)
J. Hutchinson
2015-01-01
Full Text Available We exploit mappings between quantum and classical systems in order to obtain a class of two-dimensional classical systems characterised by long-range interactions and with critical properties equivalent to those of the class of one-dimensional quantum systems treated by the authors in a previous publication. In particular, we use three approaches: the Trotter-Suzuki mapping, the method of coherent states, and a calculation based on commuting the quantum Hamiltonian with the transfer matrix of a classical system. This enables us to establish universality of certain critical phenomena by extension from the results in the companion paper for the classical systems identified.
Energy Spectra of Vortex Distributions in Two-Dimensional Quantum Turbulence
Directory of Open Access Journals (Sweden)
Ashton S. Bradley
2012-10-01
Full Text Available We theoretically explore key concepts of two-dimensional turbulence in a homogeneous compressible superfluid described by a dissipative two-dimensional Gross-Pitaeveskii equation. Such a fluid supports quantized vortices that have a size characterized by the healing length ξ. We show that, for the divergence-free portion of the superfluid velocity field, the kinetic-energy spectrum over wave number k may be decomposed into an ultraviolet regime (k≫ξ^{-1} having a universal k^{-3} scaling arising from the vortex core structure, and an infrared regime (k≪ξ^{-1} with a spectrum that arises purely from the configuration of the vortices. The Novikov power-law distribution of intervortex distances with exponent -1/3 for vortices of the same sign of circulation leads to an infrared kinetic-energy spectrum with a Kolmogorov k^{-5/3} power law, which is consistent with the existence of an inertial range. The presence of these k^{-3} and k^{-5/3} power laws, together with the constraint of continuity at the smallest configurational scale k≈ξ^{-1}, allows us to derive a new analytical expression for the Kolmogorov constant that we test against a numerical simulation of a forced homogeneous, compressible, two-dimensional superfluid. The numerical simulation corroborates our analysis of the spectral features of the kinetic-energy distribution, once we introduce the concept of a clustered fraction consisting of the fraction of vortices that have the same sign of circulation as their nearest neighboring vortices. Our analysis presents a new approach to understanding two-dimensional quantum turbulence and interpreting similarities and differences with classical two-dimensional turbulence, and suggests new methods to characterize vortex turbulence in two-dimensional quantum fluids via vortex position and circulation measurements.
Interactions of a Charged Particle with Parallel Two-Dimensional Quantum Electron Gases
Institute of Scientific and Technical Information of China (English)
LI Chun-Zhi; SONG Yuan-Hong; WANG You-Nian
2008-01-01
@@ By using the linearized quantum hydrodynamic (QHD) theory, electronic excitations induced by a charged particle moving between or over two parallel two-dimensional quantum electron gases (2DQEG) are investigated. The calculation shows that the influence of the quantum effects on the interaction process should be taken into account. Including the quantum statistical and quantum diffraction effects, the general expressions of the induced potential and the stopping power are obtained. Our simulation results indicate that a V-shaped oscillatory wake potential exists in the electron gases during the test charge intrusion. Meanwhile, double peaks will occur in the stopping power when the distance of two surfaces is smaller and the test charge gets closer to any one of the two sheets.
Wenzel, Sandro; Bogacz, Leszek; Janke, Wolfhard
2008-09-19
The two-dimensional J-J' dimerized quantum Heisenberg model is studied on the square lattice by means of (stochastic series expansion) quantum Monte Carlo simulations as a function of the coupling ratio alpha=J'/J. The critical point of the order-disorder quantum phase transition in the J-J' model is determined as alpha_c=2.5196(2) by finite-size scaling for up to approximately 10 000 quantum spins. By comparing six dimerized models we show, contrary to the current belief, that the critical exponents of the J-J' model are not in agreement with the three-dimensional classical Heisenberg universality class. This lends support to the notion of nontrivial critical excitations at the quantum critical point.
Ultraviolet finiteness of Chiral Perturbation Theory for two-dimensional Quantum Electrodynamics
Paston, S A; Franke, V A
2003-01-01
We consider the perturbation theory in the fermion mass (chiral perturbation theory) for the two-dimensional quantum electrodynamics. With this aim, we rewrite the theory in the equivalent bosonic form in which the interaction is exponential and the fermion mass becomes the coupling constant. We reformulate the bosonic perturbation theory in the superpropagator language and analyze its ultraviolet behavior. We show that the boson Green's functions without vacuum loops remain finite in all orders of the perturbation theory in the fermion mass.
Quantum Monte Carlo simulation of a two-dimensional Majorana lattice model
Hayata, Tomoya; Yamamoto, Arata
2017-07-01
We study interacting Majorana fermions in two dimensions as a low-energy effective model of a vortex lattice in two-dimensional time-reversal-invariant topological superconductors. For that purpose, we implement ab initio quantum Monte Carlo simulation to the Majorana fermion system in which the path-integral measure is given by a semipositive Pfaffian. We discuss spontaneous breaking of time-reversal symmetry at finite temperatures.
Gopinath, T; Kumar, Anil
2006-12-01
Hadamard spectroscopy has earlier been used to speed-up multi-dimensional NMR experiments. In this work, we speed-up the two-dimensional quantum computing scheme, by using Hadamard spectroscopy in the indirect dimension, resulting in a scheme which is faster and requires the Fourier transformation only in the direct dimension. Two and three qubit quantum gates are implemented with an extra observer qubit. We also use one-dimensional Hadamard spectroscopy for binary information storage by spatial encoding and implementation of a parallel search algorithm.
Quantum spin-glass transition in the two-dimensional electron gas
Indian Academy of Sciences (India)
Subir Sachdev
2002-02-01
We discuss the possibility of spin-glass order in the vicinity of the unexpected metallic state of the two-dimensional electron gas in zero applied magnetic ﬁeld. An average ferromagnetic moment may also be present, and the spin-glass order then resides in the plane orthogonal to the ferromagnetic moment. 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 magnetoconductance measurements. We present a quantum ﬁeld theory for such a transition and compute its mean ﬁeld properties.
Unconventional critical activated scaling of two-dimensional quantum spin glasses
Matoz-Fernandez, D. A.; Romá, F.
2016-07-01
We study the critical behavior of two-dimensional short-range quantum spin glasses by numerical simulations. Using a parallel tempering algorithm, we calculate the Binder cumulant for the Ising spin glass in a transverse magnetic field with two different short-range bond distributions, the bimodal and the Gaussian ones. Through an exhaustive finite-size analysis, we show that the cumulant probably follows an unconventional activated scaling, which we interpret as new evidence supporting the hypothesis that the quantum critical behavior is governed by an infinite randomness fixed point.
Two-dimensional distributed-phase-reference protocol for quantum key distribution
DEFF Research Database (Denmark)
Bacco, Davide; Christensen, Jesper Bjerge; Usuga Castaneda, Mario A.;
2016-01-01
Quantum key distribution (QKD) and quantum communication enable the secure exchange of information between remote parties. Currently, the distributed-phase-reference (DPR) protocols, which are based on weak coherent pulses, are among the most practical solutions for long-range QKD. During the last...... 10 years, long-distance fiber-based DPR systems have been successfully demonstrated, although fundamental obstacles such as intrinsic channel losses limit their performance. Here, we introduce the first two-dimensional DPR-QKD protocol in which information is encoded in the time and phase of weak...
Three-body recombination in a quasi-two-dimensional quantum gas
Huang, Bo; Zenesini, Alessandro; Grimm, Rudolf
2016-05-01
Quantum three-body recombination in three-dimensional systems is influenced by a series of weakly bound trimers known as Efimov states, which are induced by short-range interactions and exhibit a discrete scaling symmetry. On the other hand, two-dimensional systems with contact interactions are characterized by continuous scale invariance and support no Efimov physics. This raises questions about the behaviour of three-body recombination in the transition from three to two dimensions. We use ultracold caesium atoms trapped in anisotropic potentials formed by a pair of counter-propagating laser beams to experimentally investigate three-body recombination in quasi-two-dimensional systems with tunable confinement and tunable interactions. In our recent experiments, we observed a smooth transition of the three-body recombination rate coefficient from a three-dimensional to a deeply quasi-two-dimensional system. A comparison between the results obtained near two Feshbach resonances indicates a universal behaviour of three-body recombination in the quasi-two-dimensional regime. Austrian Science Fund FWF within project P23106.
DEFF Research Database (Denmark)
Dahl, Jens Peder; Schleich, W. P.
2009-01-01
For a closed quantum system the state operator must be a function of the Hamiltonian. When the state is degenerate, additional constants of the motion enter the play. But although it is the Weyl transform of the state operator, the Wigner function is not necessarily a function of the Weyl...
Extraordinary behaviors in a two-dimensional decoherent alternative quantum walk
Chen, Tian; Zhang, Xiangdong
2016-07-01
We reveal the quantum and classical behaviors of the two-dimensional (2D) alternative quantum walk (AQW) in the presence of decoherence. For different kinds of decoherence, the analytic expressions for the moments of position distribution of the AQW are obtained. Taking the broken line noise and coin decoherence as examples of decoherence, we find that when decoherence emerges in only one direction, the anisotropic position distribution pattern appears, and not all the motions of the walker exhibit the transition from quantum to classical behaviors. Considering the effect of decoherence, we reveal the anisotropic correlations between the x (y ) position of the 2D walker and the state of the coin in 2D AQWs.
Tunable band topology reflected by fractional quantum Hall States in two-dimensional lattices.
Wang, Dong; Liu, Zhao; Cao, Junpeng; Fan, Heng
2013-11-01
Two-dimensional lattice models subjected to an external effective magnetic field can form nontrivial band topologies characterized by nonzero integer band Chern numbers. In this Letter, we investigate such a lattice model originating from the Hofstadter model and demonstrate that the band topology transitions can be realized by simply introducing tunable longer-range hopping. The rich phase diagram of band Chern numbers is obtained for the simple rational flux density and a classification of phases is presented. In the presence of interactions, the existence of fractional quantum Hall states in both |C| = 1 and |C| > 1 bands is confirmed, which can reflect the band topologies in different phases. In contrast, when our model reduces to a one-dimensional lattice, the ground states are crucially different from fractional quantum Hall states. Our results may provide insights into the study of new fractional quantum Hall states and experimental realizations of various topological phases in optical lattices.
Levanony, Dana
2010-01-01
We study the internal structure of a two-dimensional dilatonic evaporating black hole, based on the CGHS model. At the semiclassical level, a (weak) spacelike singularity was previously found to develop inside the black hole. We employ here a simplified quantum formulation of spacetime dynamics in the neighborhood of this singularity, using a minisuperspace-like approach. Quantum evolution is found to be regular and well-defined at the semiclassical singularity. A well-localized initial wave-packet propagating towards the singularity bounces off the latter and retains its well-localized form. Our simplified quantum treatment thus suggests that spacetime may extend semiclassically beyond the singularity, and also signifies the specific extension.
Evidence of two-dimensional quantum Wigner Crystal in a zero magnetic field
Huang, Jian; Pfeiffer, Loren; West, Ken
2014-03-01
In disorder-dominated cases, Anderson localization occurs as a result of destructive interference effects caused by (short-ranged) random disorders. On the other hand, in interaction-dominated scenarios, striking manifestations of quantum physics emerge in response to strong inter-particle Coulomb energy (EC). The most prominent interaction-driven effect is the Wigner crystallization (WC) of electrons, an electron solid made up with spatially separated charges settling in a form of a lattice. The classical version of the crystallization, with the Debye temperature ΘD
Test of quantum thermalization in the two-dimensional transverse-field Ising model
Blaß, Benjamin; Rieger, Heiko
2016-12-01
We study the quantum relaxation of the two-dimensional transverse-field Ising model after global quenches with a real-time variational Monte Carlo method and address the question whether this non-integrable, two-dimensional system thermalizes or not. We consider both interaction quenches in the paramagnetic phase and field quenches in the ferromagnetic phase and compare the time-averaged probability distributions of non-conserved quantities like magnetization and correlation functions to the thermal distributions according to the canonical Gibbs ensemble obtained with quantum Monte Carlo simulations at temperatures defined by the excess energy in the system. We find that the occurrence of thermalization crucially depends on the quench parameters: While after the interaction quenches in the paramagnetic phase thermalization can be observed, our results for the field quenches in the ferromagnetic phase show clear deviations from the thermal system. These deviations increase with the quench strength and become especially clear comparing the shape of the thermal and the time-averaged distributions, the latter ones indicating that the system does not completely lose the memory of its initial state even for strong quenches. We discuss our results with respect to a recently formulated theorem on generalized thermalization in quantum systems.
Bonatsos, Dennis; Kolokotronis, P; Lenis, D; Bonatsos, Dennis
1994-01-01
The symmetry algebra of the two-dimensional quantum harmonic oscillator with rational ratio of frequencies is identified as a non-linear extension of the u(2) algebra. The finite dimensional representation modules of this algebra are studied and the energy eigenvalues are determined using algebraic methods of general applicability to quantum superintegrable systems.
Quantum State Transfer in a Two-dimensional Regular Spin Lattice of Triangular Shape
Miki, Hiroshi; Vinet, Luc; Zhedanov, Alexei
2012-01-01
Quantum state transfer in a triangular domain of a two-dimensional, equally-spaced, spin lat- tice with non-homogeneous nearest-neighbor couplings is analyzed. An exact solution of the one- excitation dynamics is provided in terms of 2-variable Krawtchouk orthogonal polynomials that have been recently defined. The probability amplitude for an excitation to transit from one site to another is given. For some values of the parameters, perfect transfer is shown to take place from the apex of the lattice to the boundary hypotenuse.
Modeling A.C. Electronic Transport through a Two-Dimensional Quantum Point Contact
Energy Technology Data Exchange (ETDEWEB)
Aronov, I.E.; Beletskii, N.N.; Berman, G.P.; Campbell, D.K.; Doolen, G.D.; Dudiy, S.V.
1998-12-07
We present the results on the a.c. transport of electrons moving through a two-dimensional (2D) semiconductor quantum point contact (QPC). We concentrate our attention on the characteristic properties of the high frequency admittance ({omega}{approximately}0 - 50 GHz), and on the oscillations of the admittance in the vicinity of the separatrix (when a channel opens or closes), in presence of the relaxation effects. The experimental verification of such oscillations in the admittance would be a strong confirmation of the semi-classical approach to the a.c. transport in a QPC, in the separatrix region.
Institute of Scientific and Technical Information of China (English)
JI An-Chun; TIAN Guang-Shan
2006-01-01
In the present paper, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuation in a two-dimensional spatially anisotropic Heisenberg antiferromagnet with integer spin S. Previously, someauthors computed this quantity by the mean-field theory based on the Schwinger boson representation of spin operators.However, for S = 1, their result is much less than the one derived by numerical calculations. By taking the effect ofquantum spin fluctuation into consideration, we are able to produce a greatly improved result.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Jun [School of Physics, Beijing Institute of Technology and Beijing Key Laboratory of Fractional Signals and Systems, Beijing 100081 (China); College of Physics and Electronic Engineering, Henan Normal University, 453007 Xinxiang, Henan (China); Zhang, Xiangdong, E-mail: zhangxd@bit.edu.cn [School of Physics, Beijing Institute of Technology and Beijing Key Laboratory of Fractional Signals and Systems, Beijing 100081 (China)
2015-09-28
Simultaneous negative refraction for both the fundamental frequency (FF) and second-harmonic (SH) fields in two-dimensional nonlinear photonic crystals have been found through both the physical analysis and exact numerical simulation. By combining such a property with the phase-matching condition and strong second-order susceptibility, we have designed a SH lens to realize focusing for both the FF and SH fields at the same time. Good-quality non-near field images for both FF and SH fields have been observed. The physical mechanism for such SH focusing phenomena has been disclosed, which is different from the backward SH generation as has been pointed out in the previous investigations. In addition, the effect of absorption losses on the phenomena has also been discussed. Thus, potential applications of these phenomena to biphotonic microscopy technique are anticipated.
Nonequilibrium Phase Transition in a Two-Dimensional Driven Open Quantum System
Directory of Open Access Journals (Sweden)
G. Dagvadorj
2015-11-01
Full Text Available The Berezinskii-Kosterlitz-Thouless mechanism, in which a phase transition is mediated by the proliferation of topological defects, governs the critical behavior of a wide range of equilibrium two-dimensional systems with a continuous symmetry, ranging from spin systems to superconducting thin films and two-dimensional Bose fluids, such as liquid helium and ultracold atoms. We show here that this phenomenon is not restricted to thermal equilibrium, rather it survives more generally in a dissipative highly nonequilibrium system driven into a steady state. By considering a quantum fluid of polaritons of an experimentally relevant size, in the so-called optical parametric oscillator regime, we demonstrate that it indeed undergoes a phase transition associated with a vortex binding-unbinding mechanism. Yet, the exponent of the power-law decay of the first-order correlation function in the (algebraically ordered phase can exceed the equilibrium upper limit: this shows that the ordered phase of driven-dissipative systems can sustain a higher level of collective excitations before the order is destroyed by topological defects. Our work suggests that the macroscopic coherence phenomena, observed recently in interacting two-dimensional light-matter systems, result from a nonequilibrium phase transition of the Berezinskii-Kosterlitz-Thouless rather than the Bose-Einstein condensation type.
Numerical study for the c-dependence of fractal dimension in two-dimensional quantum gravity
Kawamoto, N; Kawamoto, Noboru; Yotsuji, Kenji
2002-01-01
We numerically investigate the fractal structure of two-dimensional quantum gravity coupled to matter central charge c for $-2 \\leq c \\leq 1$. We reformulate Q-state Potts model into the model which can be identified as a weighted percolation cluster model and can make continuous change of Q, which relates c, on the dynamically triangulated lattice. The c-dependence of the critical coupling is measured from the percolation probability and susceptibility. The c-dependence of the string susceptibility of the quantum surface is evaluated and has very good agreement with the theoretical predictions. The c-dependence of the fractal dimension based on the finite size scaling hypothesis is measured and has excellent agreement with one of the theoretical predictions previously proposed except for the region near $c\\approx 1$.
Huard; Cox; Saminadayar; Arnoult; Tatarenko
2000-01-01
The dependence of the optical absorption spectrum of a semiconductor quantum well on two-dimensional electron concentration n(e) is studied using CdTe samples. The trion peak (X-) seen at low n(e) evolves smoothly into the Fermi edge singularity at high n(e). The exciton peak (X) moves off to high energy, weakens, and disappears. The X,X- splitting is linear in n(e) and closely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn0.002Te quantum wells in a magnetic field, the X,X- splitting reflects unequal Fermi energies for M = +/-1/2 electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects.
Kallin, Ann B; Hyatt, Katharine; Singh, Rajiv R P; Melko, Roger G
2013-03-29
We develop a method to calculate the bipartite entanglement entropy of quantum models, in the thermodynamic limit, using a numerical linked-cluster expansion (NLCE) involving only rectangular clusters. It is based on exact diagonalization of all n×m rectangular clusters at the interface between entangled subsystems A and B. We use it to obtain the Renyi entanglement entropy of the two-dimensional transverse field Ising model, for arbitrary real Renyi index α. Extrapolating these results as a function of the order of the calculation, we obtain universal pieces of the entanglement entropy associated with lines and corners at the quantum critical point. They show NLCE to be one of the few methods capable of accurately calculating universal properties of arbitrary Renyi entropies at higher dimensional critical points.
Two-dimensional distributed-phase-reference protocol for quantum key distribution
Bacco, Davide; Christensen, Jesper Bjerge; Castaneda, Mario A. Usuga; Ding, Yunhong; Forchhammer, Søren; Rottwitt, Karsten; Oxenløwe, Leif Katsuo
2016-12-01
Quantum key distribution (QKD) and quantum communication enable the secure exchange of information between remote parties. Currently, the distributed-phase-reference (DPR) protocols, which are based on weak coherent pulses, are among the most practical solutions for long-range QKD. During the last 10 years, long-distance fiber-based DPR systems have been successfully demonstrated, although fundamental obstacles such as intrinsic channel losses limit their performance. Here, we introduce the first two-dimensional DPR-QKD protocol in which information is encoded in the time and phase of weak coherent pulses. The ability of extracting two bits of information per detection event, enables a higher secret key rate in specific realistic network scenarios. Moreover, despite the use of more dimensions, the proposed protocol remains simple, practical, and fully integrable.
Cavity quantum electrodynamics with many-body states of a two-dimensional electron gas.
Smolka, Stephan; Wuester, Wolf; Haupt, Florian; Faelt, Stefan; Wegscheider, Werner; Imamoglu, Ataç
2014-10-17
Light-matter interaction has played a central role in understanding as well as engineering new states of matter. Reversible coupling of excitons and photons enabled groundbreaking results in condensation and superfluidity of nonequilibrium quasiparticles with a photonic component. We investigated such cavity-polaritons in the presence of a high-mobility two-dimensional electron gas, exhibiting strongly correlated phases. When the cavity was on resonance with the Fermi level, we observed previously unknown many-body physics associated with a dynamical hole-scattering potential. In finite magnetic fields, polaritons show distinct signatures of integer and fractional quantum Hall ground states. Our results lay the groundwork for probing nonequilibrium dynamics of quantum Hall states and exploiting the electron density dependence of polariton splitting so as to obtain ultrastrong optical nonlinearities.
Phase diagram and correlation functions of the two-dimensional dissipative quantum XY model
Hou, Changtao; Varma, Chandra M.
2016-11-01
The two-dimensional quantum XY model, with a Caldeira-Leggett form of dissipation, is applicable to the quantum-critical properties of diverse experimental systems, ranging from superconductor to insulator transitions, ferromagnetic and antiferromagnetic transitions in metals, to the loop-current order transition in cuprates. We solve the reexpression of this model in terms of orthogonal topological excitations, vortices, and a variety of instantons, by renormalization group methods. The calculations explain the extraordinary properties of the model discovered in Monte Carlo calculations: the product form of the quantum-critical fluctuations in space and time, a spatial correlation length proportional to the logarithm of the temporal correlation length near the transition from a disordered to a fully ordered state, and the occurrence of a phase with spatial order without temporal order. They are intimately related to the flow of the metric of time in relation to the metric of space, i.e., of the dynamical critical exponent z . These properties appear to be essential in understanding the strange metallic phase found in a variety of quantum-critical transitions as well as the accompanying high-temperature superconductivity.
Shabani, Javad
2016-10-01
Theory suggests that the interface between a one-dimensional semiconductor (Sm) with strong spin-orbit coupling and a superconductor (S) hosts Majorana modes with nontrivial topological properties. A key challenge in fabrication of such hybrid devices is forming highly transparent contacts between the active electrons in the semiconductor and the superconducting metal. Recently, it has been shown that a near perfect interface and a highly transparent contact can be achieved using epitaxial growth of aluminum on InAs nanowires. In this work, we present the first two-dimensional epitaxial superconductor-semiconductor material system that can serve as a platform for topological superconductivity. We show that our material system, Al-InAs, satisfies all the requirements necessary to reach into the topological superconducting regime by individual characterization of the semiconductor two dimensional electron system, superconductivity of Al and performance of S-Sm-S junctions. This exciting development might lead to a number of useful applications ranging from spintronics to quantum computing.
Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid
Yu, Xiaoquan; Nian, Jun; Reeves, Matthew T; Bradley, Ashton S
2016-01-01
Clustering of like-sign vortices in a planar bounded domain is known to occur at negative temperature, a phenomenon that Onsager demonstrated to be a consequence of bounded phase space. In a confined superfluid, quantized vortices can support such an ordered phase, provided they evolve as an almost isolated subsystem containing sufficient energy. A detailed theoretical understanding of the statistical mechanics of such states thus requires a microcanonical approach. Here we develop an analytical theory of the vortex clustering transition in a neutral system of quantum vortices confined to a two-dimensional disk geometry, within the microcanonical ensemble. As the system energy increases above a critical value, the system develops global order via the emergence of a macroscopic dipole structure from the homogeneous phase of vortices, spontaneously breaking the Z2 symmetry associated with invariance under vortex circulation exchange, and the rotational SO(2) symmetry due to the disk geometry. The dipole structu...
Magnetoelectronic transport of the two-dimensional electron gas in CdSe single quantum wells
Indian Academy of Sciences (India)
P K Ghosh; A Ghosal; D Chattopadhyay
2009-02-01
Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are calculated with a numerical iterative technique in the framework of Fermi–Dirac statistics. Lattice scatterings due to polar-mode longitudinal optic (LO) phonons, and acoustic phonons via deformation potential and piezoelectric couplings, are considered together with background and remote ionized impurity interactions. The parallel mode of piezoelectric scattering is found to contribute more than the perpendicular mode. We observe that the Hall mobility decreases with increasing temperature but increases with increasing channel width. The magnetoresistance coefficient is found to decrease with increasing temperature and increase with increasing magnetic field in the classical region.
Donor-bound electron states in a two-dimensional quantum ring under uniform magnetic field
Institute of Scientific and Technical Information of China (English)
Jia Bo-Yong; Yu Zhong-Yuan; Liu Yu-Min; Han Li-Hong; Yao Wen-Jie; Feng Hao; Ye Han
2011-01-01
The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring.The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.
Properties of two-dimensional electron gas containing self-organized quantum antidots
Vasilyev, Yu.; Suchalkin, S.; Zundel, M.; Heisenberg, D.; Eberl, K.; von Klitzing, K.
1999-11-01
A nonuniform two-dimensional electron gas in a heterojunction with inserted self-organized electrically inactive dots (acting as antidots) has been fabricated by molecular-beam epitaxy of AlGaAs/AlInAs/GaAs layer sequences. Transport measurements give the ratio of the transport mobility to the quantum mobility less than four, which suggests that the dominant scattering at low magnetic fields is the short-range scattering from the lateral potential of the antidots. Far-infrared cyclotron resonance (CR) spectra show an absorption mode as narrow as 0.5 cm-1 at high magnetic fields associated with the high-mobility electron gas formed between the antidot islands and confined in the lateral directions. The confinement energy of 14 cm-1 is derived from the CR spectra.
Unbinding of mutually avoiding random walks and two-dimensional quantum gravity
Carlon, Enrico; Baiesi, Marco
2004-12-01
We analyze the unbinding transition for a two-dimensional lattice polymer in which the constituent strands are mutually avoiding random walks. At low temperatures the strands are bound and form a single self-avoiding walk. We show that unbinding in this model is a strong first order transition. The entropic exponents associated with denaturated loops and end-segment distributions show sharp differences at the transition point and in the high temperature phase. Their values can be deduced from some exact arguments relying on a conformal mapping of copolymer networks into a fluctuating geometry, i.e., in the presence of quantum gravity. An excellent agreement between analytical and numerical estimates is observed for all cases analyzed.
Reflectance measurement of two-dimensional photonic crystal nanocavities with embedded quantum dots
Stumpf, Wolfgang C; Kojima, Takanori; Fujita, Masayuki; Tanaka, Yoshinori; Noda, Susumu
2010-01-01
The spectra of two-dimensional photonic crystal slab nanocavities with embedded InAs quantum dots are measured by photoluminescence and reflectance. In comparing the spectra taken by these two different methods, consistency with the nanocavities' resonant wavelengths is found. Furthermore, it is shown that the reflectance method can measure both active and passive cavities. Q-factors of nanocavities, whose resonant wavelengths range from 1280 to 1620 nm, are measured by the reflectance method in cross polarization. Experimentally, Q-factors decrease for longer wavelengths and the intensity, reflected by the nanocavities on resonance, becomes minimal around 1360 nm. The trend of the Q-factors is explained by the change of the slab thickness relative to the resonant wavelength, showing a good agreement between theory and experiment. The trend of reflected intensity by the nanocavities on resonance can be understood as effects that originate from the PC slab and the underlying air cladding thickness. In addition...
Quantum Phase Transition in the Two-Dimensional Random Transverse-Field Ising Model
Pich, C.; Young, A. P.
1998-03-01
We study the quantum phase transition in the random transverse-field Ising model by Monte Carlo simulations. In one-dimension it has been established that this system has the following striking behavior: (i) the dynamical exponent is infinite, and (ii) the exponents for the divergence of the average and typical correlation lengths are different. An important issue is whether this behavior is special to one-dimension or whether similar behavior persists in higher dimensions. Here we attempt to answer this question by studies of the two-dimensional model. Our simulations use the Wolff cluster algorithm and the results are analyzed by anisotropic finite size scaling, paying particular attention to the Binder ratio of moments of the order parameter distribution and the distribution of the spin-spin correlation functions for various distances.
Measurement of the quantum capacitance of two-dimensional vanadium dioxide films
Wu, Zhe; Knighton, Talbot; Tarquini, Vinicio; Huang, Jian; Sepúlveda, Nelson; Department of Physics; Astronomy, Wayne State University Collaboration; Department of Electrical; Computer Engineering, Michigan State University Collaboration
2015-03-01
With a homebuilt ac bridge, we have performed capacitance measurement of quasi two-dimensional vanadium dioxide films grown on silicon-dioxide/p-doped silicon substrate. The out-phase-signal, which corresponds to the resistivity variation, is superior to the four-terminal measurement result of the temperature dependence of the resistivity which varies by four orders of magnitude from 360K to 310K. The hysteretic behavior shows an overlap of two distinctive features that indicate a shifted structural transition relative to the Mott transition. In addition, the quantum capacitance is obtained through the in-phase signals so that d μ/dn, the inverse of the density of states, is determined as a function of temperature. This has resulted in a diverging compressibility below the critical temperature by four orders of magnitude, consistent with a Mott transition influenced by Peierls transition.
Two-dimensional topological crystalline insulator phase in quantum wells of trivial insulators
Niu, Chengwang; Buhl, Patrick M.; Bihlmayer, Gustav; Wortmann, Daniel; Blügel, Stefan; Mokrousov, Yuriy
2016-06-01
The realization of two-dimensional (2D) topological insulators (TIs) in HgTe/CdTe quantum wells (QWs) has generated an explosion of research on TIs and novel topologically nontrivial phases. Here we predict, based on first-principles calculations, that the newly discovered 2D topological crystalline insulators (TCIs) phase exists even in the QWs of trivial insulators, e.g. (Sn/Pb)Te and Na(Cl/Br), with mirror Chern number {n}{{M}}=-2. Tunable nontrivial energy gaps ranging from 4 to 238 meV are obtained, guaranteeing further room-temperature observations and applications. The combined effect of strain and electrostatic interaction that can be engineered by the cladding layers leads to a band inversion, resulting in the phase transition from trivial insulator to 2D TCIs. Our work provides a new strategy for engineering topological states in 2D materials.
Energy Technology Data Exchange (ETDEWEB)
Sukhanov, Aleksei A.
2017-05-15
We study the energy spectra of bound states in quantum dots (QDs) formed by an electrostatic potential in two-dimensional topological insulator (TI) and their transformation with changes in QD depth and radius. It is found that, unlike a trivial insulator, the energy difference between the levels of the ground state and first excited state can decrease with decreasing the radius and increasing the depth of the QD so that these levels intersect under some critical condition. The crossing of the levels results in unusual features of optical properties caused by intraceneter electron transitions. In particular, it leads to significant changes of light absorption due to electron transitions between such levels and to the transient electroluminescence induced by electrical tuning of QD and TI parameters. In the case of magnetic TIs, the polarization direction of the absorbed or emitted circularly polarized light is changed due to the level crossing.
Size Effect of a Negatively Charged Exciton in a Two-Dimensional Quantum Dot
Institute of Scientific and Technical Information of China (English)
LIU Chao; XIE Wen-Fang
2009-01-01
In this paper we study a negatively charged exciton (NCE), which is trapped by a two-dimensional (2D) parabolic potential.By using matrix diagonalization techniques, the correlation energies of the low-lying states with L = O, 1, and 2 are calculated as a function of confinement strength.We find that the size effects of different states are different.This phenomenon can be explained as a hidden symmetry, which is originated purely from symmetry.Based on symmetry, the features of the low-lying states are discussed in the influence of the 2D parabolic potential well.It is found that the confinement may cause accidental degeneracies between levels with different low-excited states.It is shown that the effect of quantum confinement on the binding energy of the heavy hole is stronger than that of a light hole.
Song, Xiang-Xiang; Liu, Di; Mosallanejad, Vahid; You, Jie; Han, Tian-Yi; Chen, Dian-Teng; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guang-Can; Guo, Guo-Ping
2015-10-28
Two-dimensional layered materials, such as transition metal dichalcogenides (TMDCs), are promising materials for future electronics owing to their unique electronic properties. With the presence of a band gap, atomically thin gate defined quantum dots (QDs) can be achieved on TMDCs. Herein, standard semiconductor fabrication techniques are used to demonstrate quantum confined structures on WSe2 with tunnel barriers defined by electric fields, therefore eliminating the edge states induced by etching steps, which commonly appear in gapless graphene QDs. Over 40 consecutive Coulomb diamonds with a charging energy of approximately 2 meV were observed, showing the formation of a QD, which is consistent with the simulations. The size of the QD could be tuned over a factor of 2 by changing the voltages applied to the top gates. These results shed light on a way to obtain smaller quantum dots on TMDCs with the same top gate geometry compared to traditional GaAs/AlGaAs heterostructures with further research.
Two-dimensional quantum percolation with binary non-zero hopping integrals
Dillon Thomas, Brianna; Nakanishi, Hisao
In a previous work [Dillon and Nakanishi, Eur.Phys.J B 87, 286 (2014)], we calculated the transmission coefficient of the two-dimensional quantum percolation problem and mapped out in detail the three regimes of localization, i.e., exponentially localized, power-law localized, and delocalized which had been proposed earlier [Islam and Nakanishi, Phys.Rev. E 77, 061109 (2008)]. We now consider a variation on quantum percolation in which the hopping integral (Vdiluted) associated with bonds that connect to at least one diluted site is non-zero but a fraction of the hopping integral (Vfull=1) between non-diluted sites. We study the latter model by calculating quantities such as the transmission coefficient and the inverse participation ratio and find the original quantum percolation results to be stable over a wide range of energy. In particular, except in the immediate neighborhood of the band center (where increasing Vdiluted to just 0.02*Vfull appears to eliminate localization effects), increasing Vdiluted only shifts the boundaries between the 3 regimes but does not eliminate them until the Vdiluted reaches 20
Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal
Energy Technology Data Exchange (ETDEWEB)
Wosnitza, J; Ignatchik, O; Bergk, B [Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden (Germany); Gvozdikov, V M [Max-Planck-Institut fuer Physik komplexer Systeme, D-01187 Dresden (Germany); Hagel, J [Institut fuer Festkoerperphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany); Meeson, P J [H H Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom); Schlueter, J A [Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Davis, H; Winter, R W; Gard, G L [Department of Chemistry, Portland State University, Portland, OR 97207 (United States)], E-mail: J.Wosnitza@fzd.de
2008-08-15
We report on an anomalous behavior of the spin-splitting zeros in the de Haas-van Alphen (dHvA) signal of a quasi-two-dimensional organic superconductor. The zeros as well as the angular dependence of the amplitude of the second harmonic deviate remarkably from the standard Lifshitz-Kosevich (LK) prediction. In contrast, the angular dependence of the fundamental dHvA amplitude as well as the spin-splitting zeros of the Shubnikov-de Haas (SdH) signal follow the LK theory. We can explain this behavior of the dHvA signal by small chemical-potential (CP) oscillations and find a very good agreement between theory and experiment. A detailed wave-shape analysis of the dHvA oscillations corroborates the existence of an oscillating CP. We discuss the absence of the above spin-zero effect in the SdH signal and argue that in {beta}-prime-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} it can be explained by an incoherent variable range hopping interlayer transport which is insensitive to the small CP oscillations.
Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal.
Energy Technology Data Exchange (ETDEWEB)
Wosnitza, J.; Gvozdikov, V. M.; Hagel, J.; Meeson, P. J.; Schlueter, J. A.; Ignatchick, O.; Winter, R. W.; Gard, G. L.; Davis, H.; Bergk, B.; Materials Science Division; Technische Univ. Dresden; Max-Planck Inst. Phys. Complex Systems; Univ. Bristol; Portland State Univ.
2008-01-01
We report on an anomalous behavior of the spin-splitting zeros in the de Haas-van Alphen (dHvA) signal of a quasi-two-dimensional organic superconductor. The zeros as well as the angular dependence of the amplitude of the second harmonic deviate remarkably from the standard Lifshitz-Kosevich (LK) prediction. In contrast, the angular dependence of the fundamental dHvA amplitude as well as the spin-splitting zeros of the Shubnikov-de Haas (SdH) signal follow the LK theory. We can explain this behavior of the dHvA signal by small chemical-potential (CP) oscillations and find a very good agreement between theory and experiment. A detailed wave-shape analysis of the dHvA oscillations corroborates the existence of an oscillating CP. We discuss the absence of the above spin-zero effect in the SdH signal and argue that in {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} it can be explained by an incoherent variable range hopping interlayer transport which is insensitive to the small CP oscillations.
Energy Technology Data Exchange (ETDEWEB)
Nevedomskiy, V. N., E-mail: nevedom@mail.ioffe.ru; Bert, N. A.; Chaldyshev, V. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Preobrazhernskiy, V. V.; Putyato, M. A.; Semyagin, B. R. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation)
2015-12-15
A single molecular-beam epitaxy process is used to produce GaAs-based heterostructures containing two-dimensional arrays of InAs semiconductor quantum dots and AsSb metal quantum dots. The twodimensional array of AsSb metal quantum dots is formed by low-temperature epitaxy which provides a large excess of arsenic in the epitaxial GaAs layer. During the growth of subsequent layers at a higher temperature, excess arsenic forms nanoinclusions, i.e., metal quantum dots in the GaAs matrix. The two-dimensional array of such metal quantum dots is created by the δ doping of a low-temperature GaAs layer with antimony which serves as a precursor for the heterogeneous nucleation of metal quantum dots and accumulates in them with the formation of AsSb metal alloy. The two-dimensional array of InAs semiconductor quantum dots is formed via the Stranski–Krastanov mechanism at the GaAs surface. Between the arrays of metal and semiconductor quantum dots, a 3-nm-thick AlAs barrier layer is grown. The total spacing between the arrays of metal and semiconductor quantum dots is 10 nm. Electron microscopy of the structure shows that the arrangement of metal quantum dots and semiconductor quantum dots in the two-dimensional arrays is spatially correlated. The spatial correlation is apparently caused by elastic strain and stress fields produced by both AsSb metal and InAs semiconductor quantum dots in the GaAs matrix.
Two-dimensional hole systems in indium-based quantum well heterostructures
Energy Technology Data Exchange (ETDEWEB)
Loher, Josef
2016-08-01
The complex spin-orbit interaction (SOI) of two-dimensional hole gas (2DHG) systems - the relativistic coupling of the hole spin degree of freedom to their movement in an electric field - is of fundamental interest in spin physics due to its key role for spin manipulation in spintronic devices. In this work, we were able to evaluate the tunability of Rashba-SOI-related parameters in the 2DHG system of InAlAs/InGaAs/InAs:Mn quantum well heterostructures experimentally by analyzing the hole density evolution of quantum interference effects at low magnetic fields. We achieved to cover a significant range of hole densities by the joint action of the variation of the manganese modulation doping concentration during molecular beam epitaxy and external field-effect-mediated manipulation of the 2D carrier density in Hall bar devices by a metallic topgate. Within these magnetotransport experiments, a reproducible phenomenon of remarkable robustness emerged in the transverse Hall magnetoresistivity of the indium 2DHG systems which are grown on a special InAlAs step-graded metamorphic buffer layer structure to compensate crystal lattice mismatch. As a consequence of the strain relaxation process, these material systems are characterized by anisotropic properties along different crystallographic directions. We identify a puzzling offset phenomenon in the zero-field Hall magnetoresistance and demonstrate it to be a universal effect in systems with spatially anisotropic transport properties.
Atomistic Analysis of Room Temperature Quantum Coherence in Two-Dimensional CdSe Nanostructures.
Pal, Sougata; Nijjar, Parmeet; Frauenheim, Thomas; Prezhdo, Oleg V
2017-03-02
Recent experiments on CdSe nanoplatelets synthesized with precisely controlled thickness that eliminates ensemble disorder have allowed accurate measurement of quantum coherence at room temperature. Matching exactly the CdSe cores of the experimentally studied particles and considering several defects, we establish the atomistic origins of the loss of coherence between heavy and light hole excitations in two-dimensional CdSe and CdSe/CdZnS core/shell structures. The coherence times obtained using molecular dynamics based on tight-binding density functional theory are in excellent agreement with the measured values. We show that a long coherence time is a consequence of both small fluctuations in the energy gap between the excited state pair, which is much less than thermal energy, and a slow decay of correlation between the energies of the two states. Anionic defects at the core/shell interface have little effect on the coherence lifetime, while cationic defects strongly perturb the electronic structure, destroying the experimentally observed coherence. By coupling to the same phonon modes, the heavy and light holes synchronize their energy fluctuations, facilitating long-lived coherence. We further demonstrate that the electronic excitations are localized close to the surface of these narrow nanoscale systems, and therefore, they couple most strongly to surface acoustic phonons. The established features of electron-phonon coupling and the influence of defects, surfaces, and core/shell interfaces provide important insights into quantum coherence in nanoscale materials in general.
Excited states of two-dimensional hydrogen atom in tilted magnetic field: Quantum chaos
Koval, Eugene A.; Koval, Oksana A.
2017-09-01
The aim of the current work is the research of the influence of a tilted magnetic field direction on the spectrum and the energy level spacing distribution of a two-dimensional (2D) hydrogen atom and of an exciton in GaAs/Al0.33Ga0.67As quantum well. It was discovered that the quantum chaos (QC) is initiated with an increasing angle α between the magnetic field direction and the normal to the atomic plane. It is characterized by the repulsion of levels leading to the eliminating of the shell structure and by changing the spectrum statistical properties. The statement about the initiation of chaos and its dominance over regular motion with increasing angle α is confirmed by the results of our calculations of the classical dynamics presented in this paper. The evolution of the spatial distribution of the square of the absolute value of the wave function at an increasing angle α was observed. The differences of calculated dependencies of energies for various excited states on the tilt angle at a wide range of the magnetic field strength were described.
Polarized heat current generated by quantum pumping in two-dimensional topological insulators
Ronetti, F.; Carrega, M.; Ferraro, D.; Rech, J.; Jonckheere, T.; Martin, T.; Sassetti, M.
2017-03-01
We consider the transport properties of a two-dimensional topological insulator in a double quantum point contact geometry in the presence of a time-dependent external field. In the proposed setup an external gate is placed above a single constriction and it couples only with electrons belonging to the top edge. This asymmetric configuration and the presence of an ac signal allow for a quantum pumping mechanism, which, in turn, can generate finite heat and charge currents in an unbiased device configuration. A microscopic model for coupling with the external time-dependent gate potential is developed and the induced finite heat and charge currents are investigated. We demonstrate that in the noninteracting case, heat flow is associated with a single spin component, due to the helical nature of the edge states, and therefore a finite and polarized heat current is obtained in this configuration. The presence of e -e interchannel interactions strongly affects the current signal, lowering the degree of polarization of the system. Finally, we also show that separate heat and charge flows can be achieved, varying the amplitude of the external gate.
Czarnik, Piotr; Dziarmaga, Jacek; Oleś, Andrzej M.
2016-05-01
Progress in describing thermodynamic phase transitions in quantum systems is obtained by noticing that the Gibbs operator e-β H for a two-dimensional (2D) lattice system with a Hamiltonian H can be represented by a three-dimensional tensor network, the third dimension being the imaginary time (inverse temperature) β . Coarse graining the network along β results in a 2D projected entangled-pair operator (PEPO) with a finite bond dimension D . The coarse graining is performed by a tree tensor network of isometries. The isometries are optimized variationally, taking into account full tensor environment, to maximize the accuracy of the PEPO. The algorithm is applied to the isotropic quantum compass model on an infinite square lattice near a symmetry-breaking phase transition at finite temperature. From the linear susceptibility in the symmetric phase and the order parameter in the symmetry-broken phase, the critical temperature is estimated at Tc=0.0606 (4 ) J , where J is the isotropic coupling constant between S =1/2 pseudospins.
Laser driven intraband optical transitions in two-dimensional quantum dots and quantum rings
Barseghyan, M. G.; Kirakosyan, A. A.; Laroze, D.
2017-01-01
The intraband optical absorption have been investigated in the presence of hydrogenic donor impurity in GaAs/GaAlAs quantum dot and quantum ring in the intense laser field. The single electron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. Different selection rules are obtained for intraband transitions depending on the direction of incident light polarization. Due to the accidental degeneracy of the laser dressed impurity states the crossings of the curves of the threshold energies and the dipole matrix elements on laser field parameter have been observed. The intraband absorption coefficient is calculated for different locations of hydrogenic donor impurity and different values of intense laser field parameter. The obtained results show that the absorption spectrum can exhibit either a blue- or redshift depending on the impurity location, values of the laser field parameter and direction of incident light polarization. The obtained theoretical results indicate a novel opportunity to tune the performance of new devices, based on the quantum dots and quantum rings and to control their specific properties by means of intense laser and hydrogenic donor impurity.
Tunable two-dimensional arrays of single Rydberg atoms for realizing quantum Ising models.
Labuhn, Henning; Barredo, Daniel; Ravets, Sylvain; de Léséleuc, Sylvain; Macrì, Tommaso; Lahaye, Thierry; Browaeys, Antoine
2016-06-30
Spin models are the prime example of simplified many-body Hamiltonians used to model complex, strongly correlated real-world materials. However, despite the simplified character of such models, their dynamics often cannot be simulated exactly on classical computers when the number of particles exceeds a few tens. For this reason, quantum simulation of spin Hamiltonians using the tools of atomic and molecular physics has become a very active field over the past years, using ultracold atoms or molecules in optical lattices, or trapped ions. All of these approaches have their own strengths and limitations. Here we report an alternative platform for the study of spin systems, using individual atoms trapped in tunable two-dimensional arrays of optical microtraps with arbitrary geometries, where filling fractions range from 60 to 100 per cent. When excited to high-energy Rydberg D states, the atoms undergo strong interactions whose anisotropic character opens the way to simulating exotic matter. We illustrate the versatility of our system by studying the dynamics of a quantum Ising-like spin-1/2 system in a transverse field with up to 30 spins, for a variety of geometries in one and two dimensions, and for a wide range of interaction strengths. For geometries where the anisotropy is expected to have small effects on the dynamics, we find excellent agreement with ab initio simulations of the spin-1/2 system, while for strongly anisotropic situations the multilevel structure of the D states has a measurable influence. Our findings establish arrays of single Rydberg atoms as a versatile platform for the study of quantum magnetism.
Electronic transport in two-dimensional systems in the quantum hall regime
Tarquini, Vinicio
The integer and the fractional quantum Hall effects are essential to the exploration of quantum matters characterized by topological phases. A quantum Hall system hosts one-dimensional (1D) chiral edge channels that manifest zero magnetoresistance, dissipationless due to the broken time reversal symmetry, and quantized Hall resistance vhe2 with v being the topological invariant (or Chern number). The 1-1 correspondence between the conducting gapless edge channels to the gapped incompressible bulk states is a defining character of a topological insulator (TI). Understanding this correspondence in real systems, especially the origin of its robustness (in terms of the limit of breakdown), is important both fundamentally and practically (i.e. in relation to spintronics). However, the breakdown mechanism, especially in light of the edge-bulk correlation, is still an open question. We adopt GaAs two-dimensional (2D) high-mobility hole systems confined in a 20 nm wide (100)-GaAs quantum wells and have perform transport measurement for a range of charge densities between 4 and 5 x 1010 cm -2 with a carrier mobility of 2 - 4 x 106 cm 2/V·s down to millikelvin temperatures. Systematic characterization of the 2D systems through Shubnikov-de Haas (SdH) oscillations yields an effective mass between 0.30 and 0.50me, in good agreement with the cyclotron resonance results. We then modify a regular Hall bar system into a unique anti-Hall bar geometry that provides an extra set of independent chiral edge channels without altering the topological invariant. We perform systematic measurement of quantum oscillations via chiral edges while simultaneously probing the bulk dynamics, through measuring across independent edges, in respond to the edge excitations. The edge-bulk correspondence reveals a non-equilibrium dynamical development of the incompressible bulk states that leads to a novel asymmetrical 1-0 Hall potential distribution. Moreover, probing the breakdown via inner and outer
Quantum anomaly, universal relations, and breathing mode of a two-dimensional Fermi gas.
Hofmann, Johannes
2012-05-01
In this Letter, we show that the classical SO(2,1) symmetry of a harmonically trapped Fermi gas in two dimensions is broken by quantum effects. The anomalous correction to the symmetry algebra is given by a two-body operator that is well known as the contact. Taking into account this modification, we are able to derive the virial theorem for the system and a universal relation for the pressure of a homogeneous gas. The existence of an undamped breathing mode is associated with the classical symmetry. We provide an estimate for the anomalous frequency shift of this oscillation at zero temperature and compare the result with a recent experiment by [E. Vogt et al., Phys. Rev. Lett. 108, 070404 (2012)]. Discrepancies are attributed to finite temperature effects.
Experimental study of two-dimensional quantum Wigner solid in zero magnetic field
Energy Technology Data Exchange (ETDEWEB)
Huang, Jian [Department of Physics and Astronomy, Wayne State University, Detroit, MI 48201 (United States); Pfeiffer, L. N.; West, K. W. [Department of Electrical Engineering, Princeton University, Princeton, NJ 08544 (United States)
2014-03-31
At temperatures T → 0, strongly interacting two-dimensional (2D) electron systems manifest characteristic insulating behaviors that are key for understanding the nature of the ground state in light of the interplay between disorder and electron-electron interaction. In contrast to the hopping conductance demonstrated in the insulating side of the metal-to-insulator transition, the ultra-high quality 2D systems exhibit nonactivated T-dependence of the conductivity even for dilute carrier concentrations down to 7×10{sup 8} cm{sup −2}. The apparent metal-to-insulator transition (MIT) occurs for a large r{sub s} value around 40 for which a Wigner Crystalllization is expected. The magnetoresistance for a series of carrier densities in the vicinity of the transition exhibits a characteristic sign change in weak perpendicular magnetic field. Within the Wigner Crystallization regime (with r{sub s} > 40), we report an experimental observation of a characteristic nonlinear threshold behavior from a high-resolution dc dynamical response as an evidence for aWigner crystallization in high-purity GaAs 2D hole systems in zero magnetic field. The system under an increasing current drive exhibits voltage oscillations with negative differential resistance. They confirm the coexistence of a moving crystal along with striped edge states as observed for electrons on helium surfaces. Moreover, the threshold is well below the typical classical levels due to a different pinning and depinning mechanism that is possibly related to quantum processes.
Experimental study of two-dimensional quantum Wigner solid in zero magnetic field
Huang, Jian; Pfeiffer, L. N.; West, K. W.
2014-03-01
At temperatures T → 0, strongly interacting two-dimensional (2D) electron systems manifest characteristic insulating behaviors that are key for understanding the nature of the ground state in light of the interplay between disorder and electron-electron interaction. In contrast to the hopping conductance demonstrated in the insulating side of the metal-to-insulator transition, the ultra-high quality 2D systems exhibit nonactivated T-dependence of the conductivity even for dilute carrier concentrations down to 7×108 cm-2. The apparent metal-to-insulator transition (MIT) occurs for a large rs value around 40 for which a Wigner Crystalllization is expected. The magnetoresistance for a series of carrier densities in the vicinity of the transition exhibits a characteristic sign change in weak perpendicular magnetic field. Within the Wigner Crystallization regime (with rs > 40), we report an experimental observation of a characteristic nonlinear threshold behavior from a high-resolution dc dynamical response as an evidence for aWigner crystallization in high-purity GaAs 2D hole systems in zero magnetic field. The system under an increasing current drive exhibits voltage oscillations with negative differential resistance. They confirm the coexistence of a moving crystal along with striped edge states as observed for electrons on helium surfaces. Moreover, the threshold is well below the typical classical levels due to a different pinning and depinning mechanism that is possibly related to quantum processes.
Zhou, Jian; Jena, Puru
2017-02-01
While most of the two-dimensional (2D) topological crystalline insulators (TCIs) belong to group IV-VI narrow-band-gap semiconductors in a square lattice, in the present work we predict a TCI family based on transition metal intercalated compounds in a hexagonal lattice. First-principles calculations combined with a substrate-fixed globally optimal structural search technique show that a layer of Os prefers a uniform distribution between two graphene sheets. Band dispersion calculations reveal a Dirac point and a Dirac nodal ring near the Fermi level. The Dirac point is ascribed to the hybridization of e2 and e2* orbitals, and the Dirac ring is formed due to dispersion of s and e1* orbitals. Upon inclusion of spin-orbit coupling, these Dirac states open topologically nontrivial local band gaps, which are characterized by nonzero mirror Chern numbers. The quantum spin Hall effect is also observed by integrating the spin Berry curvature in the Brillouin zone. In contrast to the 2D group IV-VI TCIs whose band inversions at X and Y points are "locked" by C4 rotation symmetry, here the relative energy of two local band gaps can be manipulated by in-plane biaxial strains. Some other similar intercalation compounds are also shown to be topologically nontrivial. Our work extends the 2D TCI family into a hexagonal lattice composed of transition metals.
An, Taeyang; Cha, Min-Chul
2013-03-01
We study the superfluid-insulator quantum phase transition in a disordered two-dimensional quantum rotor model with random on-site interactions in the presence of particle-hole symmetry. Via worm-algorithm Monte Carlo calculations of superfluid density and compressibility, we find the dynamical critical exponent z ~ 1 . 13 (2) and the correlation length critical exponent 1 / ν ~ 1 . 1 (1) . These exponents suggest that the insulating phase is a incompressible Mott glass rather than a Bose glass.
Kwac, Kijeong; Lee, Chewook; Jung, Yousung; Han, Jaebeom; Kwak, Kyungwon; Zheng, Junrong; Fayer, M D; Cho, Minhaeng
2006-12-28
Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared vibrational echo spectrum as a function of time, which directly displays the formation and dissociation of the complex through the growth of off-diagonal peaks, and the linear absorption spectrum, which displays two hydroxyl stretch peaks, one for the complex and one for the free phenol. The results of the simulations are compared to previously reported experimental data and are found to be in quite reasonable agreement. The electronic structure calculations show that the complex is T shaped. The classical potential used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level of the electronic structure calculations. A variety of other features is extracted from the simulations including the relationship between the structure and the projection of the electric field on the hydroxyl group. The fluctuating electric field is used to determine the hydroxyl stretch frequency-frequency correlation function (FFCF). The simulations are also used to examine the number distribution of benzene and CCl4 molecules in the first solvent shell around the phenol. It is found that the distribution is not that of the solvent mole fraction of benzene. There are substantial probabilities of finding a phenol in either a pure benzene environment or a pure CCl4 environment. A conjecture is made that relates the FFCF to the local number of benzene molecules in phenol's first solvent shell.
Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid
Yu, Xiaoquan; Billam, Thomas P.; Nian, Jun; Reeves, Matthew T.; Bradley, Ashton S.
2016-08-01
Clustering of like-sign vortices in a planar bounded domain is known to occur at negative temperature, a phenomenon that Onsager demonstrated to be a consequence of bounded phase space. In a confined superfluid, quantized vortices can support such an ordered phase, provided they evolve as an almost isolated subsystem containing sufficient energy. A detailed theoretical understanding of the statistical mechanics of such states thus requires a microcanonical approach. Here we develop an analytical theory of the vortex clustering transition in a neutral system of quantum vortices confined to a two-dimensional disk geometry, within the microcanonical ensemble. The choice of ensemble is essential for identifying the correct thermodynamic limit of the system, enabling a rigorous description of clustering in the language of critical phenomena. As the system energy increases above a critical value, the system develops global order via the emergence of a macroscopic dipole structure from the homogeneous phase of vortices, spontaneously breaking the Z2 symmetry associated with invariance under vortex circulation exchange, and the rotational SO (2 ) symmetry due to the disk geometry. The dipole structure emerges characterized by the continuous growth of the macroscopic dipole moment which serves as a global order parameter, resembling a continuous phase transition. The critical temperature of the transition, and the critical exponent associated with the dipole moment, are obtained exactly within mean-field theory. The clustering transition is shown to be distinct from the final state reached at high energy, known as supercondensation. The dipole moment develops via two macroscopic vortex clusters and the cluster locations are found analytically, both near the clustering transition and in the supercondensation limit. The microcanonical theory shows excellent agreement with Monte Carlo simulations, and signatures of the transition are apparent even for a modest system of 100
Degenerate ground states and multiple bifurcations in a two-dimensional q-state quantum Potts model.
Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T; Zhou, Huan-Qiang
2014-06-01
We numerically investigate the two-dimensional q-state quantum Potts model on the infinite square lattice by using the infinite projected entangled-pair state (iPEPS) algorithm. We show that the quantum fidelity, defined as an overlap measurement between an arbitrary reference state and the iPEPS ground state of the system, can detect q-fold degenerate ground states for the Z_{q} broken-symmetry phase. Accordingly, a multiple bifurcation of the quantum ground-state fidelity is shown to occur as the transverse magnetic field varies from the symmetry phase to the broken-symmetry phase, which means that a multiple-bifurcation point corresponds to a critical point. A (dis)continuous behavior of quantum fidelity at phase transition points characterizes a (dis)continuous phase transition. Similar to the characteristic behavior of the quantum fidelity, the magnetizations, as order parameters, obtained from the degenerate ground states exhibit multiple bifurcation at critical points. Each order parameter is also explicitly demonstrated to transform under the Z_{q} subgroup of the symmetry group of the Hamiltonian. We find that the q-state quantum Potts model on the square lattice undergoes a discontinuous (first-order) phase transition for q=3 and q=4 and a continuous phase transition for q=2 (the two-dimensional quantum transverse Ising model).
Roslyak, O.; Gumbs, Godfrey; Mukamel, S.
2012-05-01
We study the localization of dressed Dirac electrons in a cylindrical quantum dot (QD) formed on monolayer and bilayer graphene by spatially different potential profiles. Short lived excitonic states which are too broad to be resolved in linear spectroscopy are revealed by cross peaks in the photon-echo nonlinear technique. Signatures of the dynamic gap in the two-dimensional spectra are discussed. The effect of the Coulomb induced exciton-exciton scattering and the formation of biexciton molecules are demonstrated.
Sikkenk, Tycho S.; Coester, Kris; Buhrandt, Stefan; Fritz, Lars; Schmidt, Kai P.
2017-02-01
The classical Ising model on the frustrated three-dimensional (3D) swedenborgite lattice has disordered spin liquid ground states for all ratios of inter- and intraplanar couplings. Quantum fluctuations due to a transverse field give rise to several exotic phenomena. In the limit of weakly coupled kagome layers we find a 3D version of disorder by disorder degeneracy lifting. For large out-of-plane couplings one-dimensional macrospins are formed, which realize a disordered macrospin liquid phase on an emerging two-dimensional triangular lattice. We speculate about a possibly exotic version of quantum criticality that connects the polarized phase to the macrospin liquid.
Das, A; Das, A; Wotzasek, C
1995-01-01
We study a supersymmetric 2-dimensional harmonic oscillator which carries a representation of the general graded Lie algebra GL(2\\vert1) formulate it on the superspace, and discuss its physical spectrum.
Anomalous Dissipative Quantum Harmonic Oscillator
Institute of Scientific and Technical Information of China (English)
CHEN Dian-Yong; BAI Zhan-Wu; DONG Yu-Bing
2008-01-01
We investigate the low-temperature statistical properties of a harmonic oscillator coupled to a heat bath, where the low-frequency spectrum vanishes. We obtain the exact result of the zero point energy. Due to the low frequency shortage of environmental oscillators' spectral density, the coordinate and momentum correlation functions decay as r-4and r-6 respectively at zero temperature, where T is the correlation time. The low-temperature behavior of the mean energy does not violate the third law of thermodynamics, but differs largely from the Ohmic spectrum case.
Institute of Scientific and Technical Information of China (English)
WEI Gao-Feng; LONG Chao-Yun; LONG Zheng-Wen; QIN Shui-Jie
2008-01-01
In this paper,the isotropic charged harmonic oscillator in uniform magnetic field is researched in the non-commutative phase space;the corresponding exact energy is obtained,and the analytic eigenfunction is presented in terms of the confluent hypergeometric function.It is shown that in the non-commutative space,the isotropic charged harmonic oscillator in uniform magnetic field has the similar behaviors to the Landau problem.
Quantum-corrected two-dimensional Horava-Lifshitz black hole entropy
Anacleto, M A; Brito, F A; Mota-Silva, J C
2015-01-01
In this paper we focus on the Halmiton-Jacobi method to determine the temperature and the entropy of a two-dimensional Horava-Lifshitz black hole by using the generalized uncertainty principles (GUP). We also address the product of horizons, mainly concerning the event, Cauchy, cosmological and virtual horizons.
Quantum-Corrected Two-Dimensional Horava-Lifshitz Black Hole Entropy
Directory of Open Access Journals (Sweden)
M. A. Anacleto
2016-01-01
Full Text Available We focus on the Hamilton-Jacobi method to determine several thermodynamic quantities such as temperature, entropy, and specific heat of two-dimensional Horava-Lifshitz black holes by using the generalized uncertainty principles (GUP. We also address the product of horizons, mainly concerning the event, Cauchy, and cosmological and virtual horizons.
Coherent electron focusing with quantum point contacts in a two-dimensional electron gas
Houten, H. van; Beenakker, C.W.J.; Williamson, J.G.; Broekaart, M.E.I.; Loosdrecht, P.H.M. van; Wees, B.J. van; Mooij, J.E.; Foxon, C.T.; Harris, J.J.
1989-01-01
Transverse electron focusing in a two-dimensional electron gas is investigated experimentally and theoretically for the first time. A split Schottky gate on top of a GaAs-AlxGa1–xAs heterostructure defines two point contacts of variable width, which are used as injector and collector of ballistic el
Two new integrable cases of two-dimensional quantum mechanics with a magnetic field
Marikhin, V. G.
2016-04-01
Two integrable cases of two-dimensional Schrödinger equation with a magnetic field are proposed. Using the polar coordinates and the symmetrical gauge, we will obtain solutions of these equations through biconfluent and confluent Heun functions. The quantization rules will be derived for both systems under consideration.
Bakke, K.; Belich, H.
2014-07-01
We study the effects of the Lorentz symmetry violation in the nonrelativistic quantum dynamics of a spin-1/2 neutral particle interacting with external fields confined to a two-dimensional quantum ring (W.-C. Tan, J.C. Inkson, Semicond. Sci. Technol. 11, 1635 (1996)). We show a possible scenario for the Lorentz symmetry breaking that permits us to make an analogy with the Landau-Aharonov-Casher system (M. Ericsson, E. Sjöqvist, Phys. Rev. A 65, 013607 (2001)), where a change in the angular frequency characteristic of the confinement of a quantum particle to a two-dimensional ring is obtained. Then, we show that an upper bound for the Lorentz symmetry breaking parameters may be set up. Besides, we analyse another possible scenario of the Lorentz symmetry violation by showing the presence of an analogue of the Coulomb potential. We obtain the bound states solutions to the Schrödinger-Pauli equation and discuss a quantum effect characterized by the dependence of the angular frequency on the quantum numbers of the system.
Collective modes of a two-dimensional spin-1/2 Fermi gas in a harmonic trap
DEFF Research Database (Denmark)
Baur, Stefan; Vogt, Enrico; Köhl, Michael
2013-01-01
We derive analytical expressions for the frequency and damping of the lowest collective modes of a two-dimensional Fermi gas using kinetic theory. For strong coupling, we furthermore show that pairing correlations overcompensate the effects of Pauli blocking on the collision rate for a large rang...... the experimental bounds results in a damping of the breathing mode which is comparable to what is observed, even for a scale-invariant system....
Quantum Spectra and Classical Orbits in Two-Dimensional Equilateral Triangular Billiards
Institute of Scientific and Technical Information of China (English)
LIN Sheng-Lu; GAO Feng; HONG Zheng-Pin; DU Meng-Li
2005-01-01
@@ We study the correspondence between quantum spectra and classical orbits in the equilateral triangular billiards. The eigenstates of such systems are not separable functions of two variables even though the problem is exactlysolvable. We calculate the Fourier transform of a quantum spectral function and find that the positions of thepeaks match well with the lengths of the classical orbits. This is another example showing that the quantum spectral function provides a bridge between quantum and classical mechanics.
Construction of two-dimensional quantum field models through Longo-Witten endomorphisms
Tanimoto, Yoh
2013-01-01
We present a procedure to construct families of local, massive and interacting Haag-Kastler nets on the two-dimensional spacetime through an operator-algebraic method. An existence proof of local observable is given without relying on modular nuclearity. By a similar technique, another family of wedge-local nets is constructed using certain endomorphisms of conformal nets recently studied by Longo and Witten.
Quantum dynamics of the damped harmonic oscillator
Philbin, T G
2012-01-01
The quantum theory of the damped harmonic oscillator has been a subject of continual investigation since the 1930s. The obstacle to quantization created by the dissipation of energy is usually dealt with by including a discrete set of additional harmonic oscillators as a reservoir. But a discrete reservoir cannot directly yield dynamics such as Ohmic damping (proportional to velocity) of the oscillator of interest. By using a continuum of oscillators as a reservoir, we canonically quantize the harmonic oscillator with Ohmic damping and also with general damping behaviour. The dynamics of a damped oscillator is determined by an arbitrary effective susceptibility that obeys Kramers-Kronig relations. This approach offers an alternative description of nano-mechanical oscillators and opto-mechanical systems.
Kreider, Kevin L.; Baumeister, Kenneth J.
1996-01-01
An explicit finite difference real time iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for future large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable for a harmonic monochromatic sound field, a parabolic (in time) approximation is introduced to reduce the order of the governing equation. The analysis begins with a harmonic sound source radiating into a quiescent duct. This fully explicit iteration method then calculates stepwise in time to obtain the 'steady state' harmonic solutions of the acoustic field. For stability, applications of conventional impedance boundary conditions requires coupling to explicit hyperbolic difference equations at the boundary. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
Edén, Mattias
2010-05-01
Three two-dimensional (2D) NMR homonuclear correlation techniques invoking double-quantum (2Q) filtration of the central transitions of half-integer spins are evaluated numerically and experimentally. They correlate directly detected single-quantum (1Q) coherences in the t(2) domain with either of 1Q, two-spin 2Q or single-spin multiple-quantum coherence-evolutions in the indirect (t(1)) dimension. We employ experimental (23)Na and (27)Al NMR on sodium sulfite and the natural mineral sillimanite (SiAl(2)O(5)), in conjunction with simulated 2D spectra from pairs of dipolar-recoupled spins-3/2 and 5/2 at different external magnetic fields, to compare the correlation strategies from the viewpoints of 2D spectral resolution, signal sensitivity, implementational aspects and their relative merits for establishing internuclear proximities and quadrupolar tensor orientations.
Wang, Yunhua; Liu, Yulan; Wang, Biao
2017-01-01
Periodically driven nontrivial quantum states open another door to engineer topological phases in solid systems by light. Here we show, based on the Floquet-Bloch theory, that the on-resonant linearly and circularly polarized infrared light brings in the exotic Floquet quantum spin Hall state and half-metal in two-dimensional Metal-organic frameworks (2D MOFs) because of the unbroken and broken time-reversal symmetry, respectively. We also observe that the off-resonant light triggers topological quantum phase transitions and induces semimetals with pseudospin-1 Dirac-Weyl fermions via the photon-dressed topological band structures of 2D MOFs. This work paves a way to design light-controlled spintronics and optoelectronics based on 2D MOFs. PMID:28134315
Wang, Yunhua; Liu, Yulan; Wang, Biao
2017-01-01
Periodically driven nontrivial quantum states open another door to engineer topological phases in solid systems by light. Here we show, based on the Floquet-Bloch theory, that the on-resonant linearly and circularly polarized infrared light brings in the exotic Floquet quantum spin Hall state and half-metal in two-dimensional Metal-organic frameworks (2D MOFs) because of the unbroken and broken time-reversal symmetry, respectively. We also observe that the off-resonant light triggers topological quantum phase transitions and induces semimetals with pseudospin-1 Dirac-Weyl fermions via the photon-dressed topological band structures of 2D MOFs. This work paves a way to design light-controlled spintronics and optoelectronics based on 2D MOFs.
Ma, Xuedan; Diroll, Benjamin T; Cho, Wooje; Fedin, Igor; Schaller, Richard D; Talapin, Dmitri V; Gray, Stephen K; Wiederrecht, Gary P; Gosztola, David J
2017-09-05
Quasi-two-dimensional nanoplatelets (NPLs) possess fundamentally different excitonic properties from zero-dimensional quantum dots. We study lateral size-dependent photon emission statistics and carrier dynamics of individual NPLs using second-order photon correlation (g((2))(τ)) spectroscopy and photoluminescence (PL) intensity-dependent lifetime analysis. Room-temperature radiative lifetimes of NPLs can be derived from maximum PL intensity periods in PL time traces. It first decreases with NPL lateral size and then stays constant, deviating from the electric dipole approximation. Analysis of the PL time traces further reveals that the single exciton quantum yield in NPLs decreases with NPL lateral size and increases with protecting shell thickness, indicating the importance of surface passivation on NPL emission quality. Second-order photon correlation (g((2))(τ)) studies of single NPLs show that the biexciton quantum yield is strongly dependent on the lateral size and single exciton quantum yield of the NPLs. In large NPLs with unity single exciton quantum yield, the corresponding biexciton quantum yield can reach unity. These findings reveal that by careful growth control and core-shell material engineering, NPLs can be of great potential for light amplification and integrated quantum photonic applications.
The quantum spectral analysis of the two-dimensional annular billiard system
Institute of Scientific and Technical Information of China (English)
Zhang Yan-Hui; Zhang Ji-Ouan; Xu Xue-You; Lin Sheng-Lu
2009-01-01
Based on the extended closed-orbit theory together with spectral analysis, this paper studies the correspondence between quantum mechanics and the classical counterpart in a two-dimeusional annular billiard. The results demonstrate that the Fourier-transformed quantum spectra are in very good accordance with the lengths of the classical ballistic trajectories, whereas spectral strength is intimately associated with the shapes of possible open orbits connecting arbitrary two points in the annular cavity. This approach facilitates an intuitive understanding of basic quantum features such as quantum interference, locations of the wavefunctions, and allows quantitative calculations in the range of high energies, where full quantum calculations may become impractical in general. This treatment provides a thread to explore the properties of microjunction transport and even quantum chaos under the much more general system.
Loop equations and Virasoro constraints in non-perturbative two-dimensional quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Dijkgraaf, R.; Verlinde, H. (Princeton Univ., NJ (USA). Joseph Henry Labs.); Verlinde, E. (Institute for Advanced Study, Princeton, NJ (USA). School of Natural Sciences)
1991-01-21
We give a derivation of the loop equation for two-dimensional gravity from the KdV equations and the string equation of the one-matrix model. We find that the loop equation is equivalent to an infinite set of linear constraints on the square root of the partition function satisfying the Virasoro algebra. We give an interpretation of these equations in topological gravity and discuss their extension to multi-matrix models. For the multi-critical models the loop equation naturally singles out the operators corresponding to the primary fields of the minimal models. (orig.).
Loop Equations and Virasoro Constraints in Non-Perturbative Two-Dimensional Quantum Gravity
Dijkgraaf, Robbert; Verlinde, Herman; Verlinde, Erik
We give a derivation of the loop equation for two-dimensional gravity from the KdV equations and the string equation of the one-matrix model. We find that the loop equation is equivalent to an infinite set of linear constraints on the square root of the partition function satisfying the Virasoro algebra. We give an interpretation of these equations in topological gravity and discuss their extension to multi-matrix models. For the multi-critical models the loop equation naturally singles out the operators corresponding to the primary fields of the minimal models.
Spin-Orbit Splitting in Semiconductor Quantum Dots with a Two-Dimensional Ring Model
Institute of Scientific and Technical Information of China (English)
FENG Jun-Sheng; LIU Zheng
2009-01-01
We present a theoretical study of the energy levels with two-dimensional ring confining potential in the presence of the Rashba spin-orbit interaction.The features of some low-lying states in various strengths of the Rashba spin-orbit interaction are investigated.The Rashba spin-orbit splitting can also be influenced by the width of the potential barrier.The computed results show that the spin-polarized electronic states can be more easily achieved in a weakly confined dot when the confinement strength for the Rashba spin-orbit interaction is larger than a critical value.
Institute of Scientific and Technical Information of China (English)
Song Ya-Feng; Lü Yan-Wu; Wen Wei; Liu Xiang-Lin; Yang Shao-Yan; Zhu Qin-Sheng; Wang Zhan-Guo
2012-01-01
The collective charge density excitations in a free-standing nanorod with a two-dimensional parabolic quantum well are investigated within the framework of Bohm-Pine's random-phase approximation in the two-subband model.The new simplified analytical expressions of the Coulomb interaction matrix elements and dielectric functions are derived and numerically discussed.In addition,the electron density and temperature dependences of dispersion features are also investigated.We find that in the two-dimensional parabolic quantum well,the intrasubband upper branch is coupled with the intersubband mode,which is quite different from other quasi-one-dimensional systems like a cylindrical quantum wire with an infinite rectangular potential.In addition,we also find that higher temperature results in the intersubband mode(with an energy of 12 meV(～3 THz))becoming totally damped,which agrees well with the experimental results of Raman scattering in the literature.These interesting properties may provide useful references to the design of free-standing nanorod based devices.
Chern, Li Ern; Hwang, Kyusung; Mizoguchi, Tomonari; Huh, Yejin; Kim, Yong Baek
2017-07-01
The Kagome-lattice-based material, volborthite, Cu3V2O7(OH) 2.2 H2O , has been considered as a promising platform for discovery of unusual quantum ground states due to the frustrated nature of spin interaction. We explore possible quantum spin liquid and magnetically ordered phases in a two-dimensional nonsymmorphic lattice, which is described by the plane group p 2 g g , consistent with the spatial anisotropy of the spin model derived from density functional theory (DFT) for volborthite. Using the projective symmetry group (PSG) analysis and Schwinger boson mean field theory, we classify possible spin liquid phases with bosonic spinons and investigate magnetically ordered phases connected to such states. It is shown, in general, that only translationally invariant mean field spin liquid ansatzes are allowed in two-dimensional nonsymmorphic lattices. We study the mean field phase diagram of the DFT-derived spin model and find that possible quantum spin liquid phases are connected to two types of magnetically ordered phases, a coplanar incommensurate (q ,0 ) spiral order as the ground state and a closely competing coplanar commensurate (π ,π ) spin density wave order. In addition, periodicity enhancement of the two-spinon continuum, a consequence of symmetry fractionalization, is found in the spin liquid state connected to the (π ,π ) spin density wave order. We discuss relevance of these results to recent and future experiments on volborthite.
Topology Change and the Emergence of Geometry in Two Dimensional Causal Quantum Gravity
Westra, W.
2007-01-01
Despite many attempts, gravity has vigorously resisted a unification with the laws of quantum mechanics. Besides a plethora of technical issues, one is also faced with many interesting conceptual problems. The study of quantum gravity in lower dimensional models ameliorates the technical difficultie
Hilbert-Schmidt Geometry of n-Level Jakobczyk-Siennicki Two-Dimensional Quantum Systems
Slater, P B
2005-01-01
Jakobczyk and Siennicki studied two-dimensional sections of a set of Bloch vectors corresponding to n x n density matrices of two-qubit systems (that is, the case n=4). They found essentially five different types of (nontrivial) separability regimes. We compute the Euclidean/Hilbert-Schmidt (HS) separability probabilities assigned to these regimes, and conduct parallel two-dimensional section analyses for the cases n=6,8,9 and 10. We obtain a very wide variety of exact HS-probabilities. For n>6, the probabilities are those of having a partial positive transpose (PPT). For the n=6 case, we also obtain biseparability probabilities; in the n=8,9 instances, bi-PPT probabilities; and for n=8, tri-PPT probabilities. By far, the most frequently recorded probability for n>4 is Pi/4 = 0.785398$. We also conduct a number of related analyses, pertaining to the (one-dimensional) boundaries (both exterior and interior) of the separability and PPT domains, and discuss some exact calculations pertaining to the 9-dimensional...
Energy Technology Data Exchange (ETDEWEB)
Radozycki, Tomasz [Cardinal Stefan Wyszynski University, Faculty of Mathematics and Natural Sciences, College of Sciences, Warsaw (Poland)
2015-09-15
The Lorentz transformation properties of the equal-time bound-state Bethe-Salpeter amplitude in the two-dimensional massless quantum electrodynamics (the so-called Schwinger model) are considered. It is shown that while boosting a bound state (a 'meson') this amplitude is subject to approximate Lorentz contraction. The effect is exact for large separations of constituent particles ('quarks'), while for small distances the deviation is more significant. For this phenomenon to appear, the full function, i.e. with the inclusion of all instanton contributions, has to be considered. The amplitude in each separate topological sector does not exhibit such properties. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Radożycki, Tomasz, E-mail: t.radozycki@uksw.edu.pl [Faculty of Mathematics and Natural Sciences, College of Sciences, Cardinal Stefan Wyszyński University, Wóycickiego 1/3, 01-938, Warsaw (Poland)
2015-09-24
The Lorentz transformation properties of the equal-time bound-state Bethe–Salpeter amplitude in the two-dimensional massless quantum electrodynamics (the so-called Schwinger model) are considered. It is shown that while boosting a bound state (a ‘meson’) this amplitude is subject to approximate Lorentz contraction. The effect is exact for large separations of constituent particles (‘quarks’), while for small distances the deviation is more significant. For this phenomenon to appear, the full function, i.e. with the inclusion of all instanton contributions, has to be considered. The amplitude in each separate topological sector does not exhibit such properties.
Institute of Scientific and Technical Information of China (English)
JI An-Chun; TIAN Guang-Shan
2007-01-01
In the present paper, we investigate the quantum phase transition in a spatially anisotropic antiferromagnetic Heisenberg model of S = 1 with single-ion energy anisotropy. By using the Schwinger boson representation, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuations. We find that, for the positive single-ion energy, a nonzero value of Jc⊥ is always needed to stabilize the antiferromagnetic long-range order in this model. It resolves a difference among literature and shows clearly that the effect of quantum fluctuations may qualitatively change a result obtained by the mean-field theories on lower-dimensional systems.
Quantum Poincare Section of a Two-Dimensional hamiltonian in a Coherent State Representation
Institute of Scientific and Technical Information of China (English)
金迎新; 贺凯芬
2002-01-01
We study the quantum behaviour of a quasi-integrable Hamiltonian. The unperturbed Hamiltonian displays degeneracies of energy levels, which become avoided crossings under a nonintegrable perturbation. In this twodimensional system, the quantum Poincaré section plot is constructed in the coherent state representation with the restriction that the centres of the wavepackets are confined at the classical surface of constant energy. It is found that the quantum Poincaré section plot obtained in this way provides an evident counterpart of the classical system.
Deep Learning the Quantum Phase Transitions in Random Two-Dimensional Electron Systems
Ohtsuki, Tomoki; Ohtsuki, Tomi
2016-12-01
Random electron systems show rich phases such as Anderson insulator, diffusive metal, quantum Hall and quantum anomalous Hall insulators, Weyl semimetal, as well as strong/weak topological insulators. Eigenfunctions of each matter phase have specific features, but owing to the random nature of systems, determining the matter phase from eigenfunctions is difficult. Here, we propose the deep learning algorithm to capture the features of eigenfunctions. Localization-delocalization transition, as well as disordered Chern insulator-Anderson insulator transition, is discussed.
Two-dimensional models as testing ground for principles and concepts of local quantum physics
Schroer, Bert
2006-02-01
In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g., chiral models, factorizing models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work, I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: (1) a modular interpretation of the chiral model Diff( S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime and (2) a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) for rational chiral theories. The SL (2, Z) modular Verlinde relation is a special case of this thermal duality and (within the family of rational models) the matrix S appearing in the thermal duality relation becomes identified with the statistics character matrix S. The relevant angular "Euclideanization" is done in the setting of the Tomita-Takesaki modular formalism of operator algebras. I find it appropriate to dedicate this work to the memory of J.A. Swieca with whom I shared the interest in two-dimensional models as a testing ground for QFT for more than one decade. This is a significantly extended version of an "Encyclopedia of Mathematical Physics" contribution hep-th/0502125.
Two-dimensional models as testing ground for principles and concepts of local quantum physics
Energy Technology Data Exchange (ETDEWEB)
Schroer, Bert [FU Berlin (Germany). Institut fuer Theoretische Physik
2005-04-15
In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g. chiral models, factoring models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: (1) a modular interpretation of the chiral model Diff(S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime and (2) a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) for rational chiral theories. The SL(2,Z) modular Verlinde relation is a special case of this thermal duality and (within the family of rational models) the matrix S appearing in the thermal duality relation becomes identified with the statistics character matrix S. The relevant angular 'Euclideanization' is done in the setting of the Tomita-Takesaki modular formalism of operator algebras. I find it appropriate to dedicate this work to the memory of J. A. Swieca with whom I shared the interest in two-dimensional models as a testing ground for QFT for more than one decade. This is a significantly extended version of an 'Encyclopedia of Mathematical Physics' contribution hep-th/0502125. (author)
Zeng, Shengwei; Lü, Weiming; Huang, Zhen; Liu, Zhiqi; Han, Kun; Gopinadhan, Kalon; Li, Changjian; Guo, Rui; Zhou, Wenxiong; Ma, Haijiao Harsan; Jian, Linke; Venkatesan, Thirumalai; Ariando
2016-04-26
Electric field effect in electronic double layer transistor (EDLT) configuration with ionic liquids as the dielectric materials is a powerful means of exploring various properties in different materials. Here, we demonstrate the modulation of electrical transport properties and extremely high mobility of two-dimensional electron gas at LaAlO3/SrTiO3 (LAO/STO) interface through ionic liquid-assisted electric field effect. With a change of the gate voltages, the depletion of charge carrier and the resultant enhancement of electron mobility up to 19 380 cm(2)/(V s) are realized, leading to quantum oscillations of the conductivity at the LAO/STO interface. The present results suggest that high-mobility oxide interfaces, which exhibit quantum phenomena, could be obtained by ionic liquid-assisted field effect.
Sandvik, Anders W
2007-06-01
Using ground-state projector quantum Monte Carlo simulations in the valence-bond basis, it is demonstrated that nonfrustrating four-spin interactions can destroy the Néel order of the two-dimensional S=1/2 Heisenberg antiferromagnet and drive it into a valence-bond solid (VBS) phase. Results for spin and dimer correlations are consistent with a single continuous transition, and all data exhibit finite-size scaling with a single set of exponents, z=1, nu=0.78+/-0.03, and eta=0.26+/-0.03. The unusually large eta and an emergent U(1) symmetry, detected using VBS order parameter histograms, provide strong evidence for a deconfined quantum critical point.
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.
Quantum dots and etch-induced depletion of a silicon two-dimensional electron gas
Klein, L. J.; Lewis, K. L. M.; Slinker, K. A.; Goswami, Srijit; van der Weide, D. W.; Blick, R. H.; Mooney, P. M.; Chu, J. O.; Coppersmith, S. N.; Friesen, Mark; Eriksson, M. A.
2006-01-01
The controlled depletion of electrons in semiconductors is the basis for numerous devices. Reactive-ion etching provides an effective technique for fabricating both classical and quantum devices. However, Fermi-level pinning must be carefully considered in the development of small devices, such as quantum dots. Because of depletion, the electrical size of the device is reduced in comparison with its physical dimension. To investigate this issue in modulation-doped silicon single-electron transistors, we fabricate several types of devices in silicon-germanium heterostructures using two different etches, CF4 and SF6. We estimate the depletion width associated with each etch by two methods: (i) conductance measurements in etched wires of decreasing thickness (to determine the onset of depletion), and (ii) capacitance measurements of quantum dots (to estimate the size of the active region). We find that the SF6 etch causes a much smaller depletion width, making it more suitable for device fabrication.
Quantum limit for two-dimensional resolution of two incoherent optical point sources
Ang, Shan Zheng; Tsang, Mankei
2016-01-01
We obtain the multiple-parameter quantum Cram\\'er-Rao bound for estimating the Cartesian components of the centroid and separation of two incoherent optical point sources using an imaging system with finite spatial bandwidth. Under quite general and realistic assumptions on the point-spread function of the imaging system, and for weak source strengths, we show that the Cram\\'er-Rao bounds for the x and y components of the separation are independent of the values of those components, which may be well-below the conventional Rayleigh resolution limit. We also propose two linear optics-based measurement methods that approach the quantum bound for the estimation of the Cartesian components of the separation once the centroid has been located. One of the methods is an interferometric scheme that approaches the quantum bound for sub-Rayleigh separations. The other method uses fiber coupling to attain the bound regardless of the distance between the two sources.
Spin correlations in the two-dimensional quantum s=1/2 XY model
Sznajd, J.
1995-08-01
A quantum version of the Niemeijer-van Leeuwen real-space renormalization-group method is used to study the temperature dependence of the two- and four-spin correlations in the quantum XY model on the triangular lattice. The first-order cumulant expansion results suggest, similarly to other methods, a low-temperature phase of an essentially different kind from that predicted for the classical model. The possible explanation of the origin of the spurious 2D Heisenberg-like nontrivial fixed point in some renormalization-group calculations is also proposed.
Two-Dimensional GaAs/AlGaAs Multiple Quantum Well Spatial Light Modulators
Institute of Scientific and Technical Information of China (English)
Qin Wang; Jan Borglind; Smilja Becanovic; Stéphane Junique; Daniel (A)gren; Bertrand Noharet; Linda H(o)glund; Olof (O)berg; Erik Petrini; Jan Y. Andersson; Hedda Malm
2003-01-01
Multiple quantum well spatial light modulators with 128x128 array in 38μm pitch are fabricated using two pproaches, one with an attachment of an optical substrate and another one without. These two fabrication processes are described and compared.
Two-dimensional time-dependent quantum-mechanical scattering event
Energy Technology Data Exchange (ETDEWEB)
Galbraith, I.; Ching, Y.S.; Abraham, E.
1984-01-01
Nonrelativistic quantum-mechanical scattering in two dimensions is studied numerically by integrating the time-dependent Schroedinger equation. A partial-wave analysis is used to discuss the numerical results. A potential barrier, a square well and a single slit are considered as the scattering potentials.
Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures
Weber, W.; Golub, L. E.; Danilov, S. N.; Karch, J.; Reitmaier, C.; Wittmann, B.; Bel' kov, V. V.; Ivchenko, E. L.; Kvon, Z. D.; Vinh, N. Q.; van der Meer, A. F. G.; Murdin, B.; Ganichev, S. D.
2008-01-01
Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are relat
Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures
Weber, W.; Golub, L. E.; Danilov, S. N.; Karch, J.; Reitmaier, C.; Wittmann, B.; Bel'Kov, V. V.; Ivchenko, E. L.; Kvon, Z. D.; Vinh, N. Q.; van der Meer, A. F. G.; Murdin, B.; Ganichev, S. D.
2008-06-01
Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are related to the lack of an inversion center in the GaN-based heterojunctions.
Two-dimensional models as testing ground for principles and concepts of local quantum physics
Schrör, B
2005-01-01
In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g. chiral models, factorizing models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) and a modular interpretation of the chiral model Diff(S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime. As a special case of the thermal duality, the SL(2,Z) modular Verlinde relation is thus a consequence of the principles of thermal QFT togeth...
Ground-state properties of two-dimensional quantum fluid helium and hydrogen mixtures
Um, C I; Oh, H G
1998-01-01
Using a variational Jastrow wavefunction extended to include a three-body correlation function and a hypernetted chain scheme with the contributions of elementary diagrams, we analyze the ground-state energies and the structural properties of two-dimensional H- sup 4 He and H sub 2 - sup 4 He mixtures. The mixtures are in equilibrium at a lower density compared to a pure sup 4 He system because of the large zero-point energies of the hydrogen atom and molecule. We evaluate the lowering of the ground-state energies as a function of the impurity concentration and total density of mixtures. Comparing the result with boson sup 3 He- sup 4 He mixtures, we show that the shifts of energy mainly come from the difference of the zero-point energies of the impurities rather than from the interatomic potentials.We also analyze the enthalpies to study the miscibility and conclude that boson-boson mixtures are completely phase separated in their equilibria.
Second-harmonic imaging of semiconductor quantum dots
DEFF Research Database (Denmark)
Østergaard, John Erland; Bozhevolnyi, Sergey I.; Pedersen, Kjeld;
2000-01-01
Resonant second-harmonic generation is observed at room temperature in reflection from self-assembled InAlGaAs quantum dots grown on a GaAs (001) substrate. The detected second-harmonic signal peaks at a pump wavelength of similar to 885 nm corresponding to the quantum-dot photoluminescence maximum....... In addition, the second-harmonic spectrum exhibits another smaller but well-pronounced peak at 765 nm not found in the linear experiments. We attribute this peak to the generation of second-harmonic radiation in the AlGaAs spacer layer enhanced by the local symmetry at the quantum-dot interface. We further...... observe that second-harmonic images of the quantum-dot surface structure show wavelength-dependent spatial variations. Imaging at different wavelength is used to demonstrate second-harmonic generation from the semiconductor quantum dots. (C) 2000 American Institute of Physics....
General model for a entanglement-enhanced composed quantum game on a two-dimensional lattice
Miszczak, Jarosław Adam; Sładkowski, Jan
2013-01-01
We introduce a method of analyzing entanglement enhanced quantum games on regular lattices of agents. Our method is valid for setups with periodic and non-periodic boundary conditions. To demonstrate our approach we study two different types games, namely the prisoner's dilemma game and a cooperative Parrondo's game. In both cases we obtain results showing, that entanglement is a crucial resource necessary for the agents to achieve positive capital gain.
Sarkar, Subhajit; Chaudhury, Ranjan; Paul, Samir K.
2017-01-01
The available results from the inelastic neutron scattering experiment performed on the quasi-two dimensional spin 1/2 anti-ferromagnetic material La2CuO4 have been analysed theoretically. The formalism of ours is based on a semi-classical like treatment involving a model of an ideal gas of mobile vortices and anti-vortices built on the background of the Néel state, using the bipartite classical spin configuration corresponding to an XY-anisotropic Heisenberg anti-ferromagnet on a square lattice. The results for the integrated intensities for our spin 1/2 model corresponding to different temperatures, show occurrence of vigorous unphysical oscillations, when convoluted with a realistic spectral window function. These results indicate failure of the conventional semi-classical theoretical model of ideal vortex/anti-vortex gas arising in the Berezinskii-Kosterlitz-Thouless theory for the low spin magnetic systems. A full fledged quantum mechanical formalism and calculations seem crucial for the understanding of topological excitations in such low spin systems. Furthermore, a severe disagreement is found to occur at finite values of energy transfer between the integrated intensities obtained theoretically from the conventional formalism and those obtained experimentally. This further suggests strongly that the full quantum treatment should also incorporate the interaction between the fragile-magnons and the topological excitations. This is quite plausible in view of the recent work establishing such a process in XXZ quantum ferromagnet on 2D lattice. The high spin XXZ quasi-two dimensional antiferromagnet like MnPS3 however follows the conventional theory quite well.
Quantum critical response function in quasi-two-dimensional itinerant antiferromagnets
Varma, C. M.; Zhu, Lijun; Schröder, Almut
2015-10-01
We reexamine the experimental results for the magnetic response function χ''(q ,E ,T ) for q around the antiferromagnetic vectors Q , in the quantum-critical region, obtained by inelastic neutron scattering, on an Fe-based superconductor and on a heavy-fermion compound. The motivation is to compare the results with a recent theory, which shows that the fluctuations in a generic antiferromagnetic model for itinerant fermions map to those in the universality class of the dissipative quantum-XY model. The quantum-critical fluctuations in this model, in a range of parameters, are given by the correlations of spatial and temporal topological defects. The theory predicts a χ''(q ,E ,T ) (i) which is a separable function of (q -Q ) and of (E ,T ) , (ii) at criticality, the energy-dependent part is ∝tanh(E /2 T ) below a cutoff energy, (iii) the correlation time departs from its infinite value at criticality on the disordered side by an essential singularity, and (iv) the correlation length depends logarithmically on the correlation time, so that the dynamical critical exponent z is ∞ . The limited existing experimental results are found to be consistent with the first two unusual predictions from which the linear dependence of the resistivity on T and the T lnT dependence of the entropy also follow. More experiments are suggested, especially to test the theory of variations on the correlation time and length on the departure from criticality.
Otsuka, Yuichi; Yunoki, Seiji; Sorella, Sandro
2016-01-01
The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.
Effective mass theory of a two-dimensional quantum dot in the presence of magnetic field
Indian Academy of Sciences (India)
Himanshu Asnani; Raghu Mahajan; Praveen Pathak; Vijay A Singh
2009-09-01
The effective mass of electrons in low-dimensional semiconductors is position-dependent. The standard kinetic energy operator of quantum mechanics for this position-dependent mass is non-Hermitian and needs to be modified. This is achieved by imposing the BenDaniel–Duke (BDD) boundary condition. We have investigated the role of this boundary condition for semiconductor quantum dots (QDs) in one, two and three dimensions. In these systems the effective mass m i inside the dot of size R is different from the mass m o outside. Hence a crucial factor in determining the electronic spectrum is the mass discontinuity factor = /} . We have proposed a novel quantum scale, , which is a dimensionless parameter proportional to 220, where 0 represents the barrier height. We show both by numerical calculations and asymptotic analysis that the ground state energy and the surface charge density, (ρ()), can be large and dependent on . We also show that the dependence of the ground state energy on the size of the dot is infraquadratic. We also study the system in the presence of magnetic field . The BDD condition introduces a magnetic length-dependent term $(\\sqrt{\\hbar /eB})$ into and hence the ground state energy. We demonstrate that the significance of BDD condition is pronounced at large and large magnetic fields. In many cases the results using the BDD condition is significantly different from the non-Hermitian treatment of the problem.
Efficient Blue Electroluminescence Using Quantum-Confined Two-Dimensional Perovskites.
Kumar, Sudhir; Jagielski, Jakub; Yakunin, Sergii; Rice, Peter; Chiu, Yu-Cheng; Wang, Mingchao; Nedelcu, Georgian; Kim, Yeongin; Lin, Shangchao; Santos, Elton J G; Kovalenko, Maksym V; Shih, Chih-Jen
2016-10-03
Solution-processed hybrid organic-inorganic lead halide perovskites are emerging as one of the most promising candidates for low-cost light-emitting diodes (LEDs). However, due to a small exciton binding energy, it is not yet possible to achieve an efficient electroluminescence within the blue wavelength region at room temperature, as is necessary for full-spectrum light sources. Here, we demonstrate efficient blue LEDs based on the colloidal, quantum-confined 2D perovskites, with precisely controlled stacking down to one-unit-cell thickness (n = 1). A variety of low-k organic host compounds are used to disperse the 2D perovskites, effectively creating a matrix of the dielectric quantum wells, which significantly boosts the exciton binding energy by the dielectric confinement effect. Through the Förster resonance energy transfer, the excitons down-convert and recombine radiatively in the 2D perovskites. We report room-temperature pure green (n = 7-10), sky blue (n = 5), pure blue (n = 3), and deep blue (n = 1) electroluminescence, with record-high external quantum efficiencies in the green-to-blue wavelength region.
Directory of Open Access Journals (Sweden)
Yuichi Otsuka
2016-03-01
Full Text Available The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.
Quantum control of harmonic oscillator networks
Genoni, Marco G; Kim, M S; Burgarth, Daniel
2011-01-01
Controllability -- the possibility of performing any target dynamics by applying a set of available operations -- is a fundamental requirement for the practical use of any physical system. For finite-dimensional systems, as for instance spin systems, precise criterions to establish controllability, such as the so called rank criterion, are well known. However most physical systems require a description in terms of an infinite-dimensional Hilbert space whose controllability properties are poorly understood. Here, we investigate infinite-dimensional bosonic quantum systems -- encompassing quantum light, ensembles of bosonic atoms, motional degrees of freedom of ions, and nano-mechanical oscillators -- governed by quadratic Hamiltonians (such that their evolution is analogous to coupled harmonic oscillators). After having highlighted the intimate connection between controllability and recurrence in the Hilbert space, we prove that, for coupled oscillators, a simple extra condition has to be fulfilled to extend t...
Van Gorder, Robert A.
2016-05-01
Very recent experimental work has demonstrated the existence of Kelvin waves along quantized vortex filaments in superfluid helium. The possible configurations and motions of such filaments is of great physical interest, and Svistunov previously obtained a Hamiltonian formulation for the dynamics of quantum vortex filaments in the low-temperature limit under the assumption that the vortex filament is essentially aligned along one axis, resulting in a two-dimensional (2D) problem. It is standard to approximate the dynamics of thin filaments by employing the local induction approximation (LIA), and we show that by putting the two-dimensional LIA into correspondence with the first equation in the integrable Wadati-Konno-Ichikawa-Schimizu (WKIS) hierarchy, we immediately obtain solutions to the two-dimensional LIA, such as helix, planar, and self-similar solutions. These solutions are obtained in a rather direct manner from the WKIS equation and then mapped into the 2D-LIA framework. Furthermore, the approach can be coupled to existing inverse scattering transform results from the literature in order to obtain solitary wave solutions including the analog of the Hasimoto one-soliton for the 2D-LIA. One large benefit of the approach is that the correspondence between the 2D-LIA and the WKIS allows us to systematically obtain vortex filament solutions directly in the Cartesian coordinate frame without the need to solve back from curvature and torsion. Implications of the results for the physics of experimentally studied solitary waves, Kelvin waves, and postvortex reconnection events are mentioned.
Two-dimensional spin liquids with Z2 topological order in an array of quantum wires
Patel, Aavishkar A.; Chowdhury, Debanjan
2016-11-01
Insulating Z2 spin liquids are a phase of matter with bulk anyonic quasiparticle excitations and ground-state degeneracies on manifolds with nontrivial topology. We construct a time-reversal symmetric Z2 spin liquid in two spatial dimensions using an array of quantum wires. We identify the anyons as kinks in the appropriate Luttinger-liquid description, compute their mutual statistics, and construct local operators that transport these quasiparticles. We also present a construction of a fractionalized Fermi liquid (FL*) by coupling the spin sector of the Z2 spin liquid to a Fermi liquid via a Kondo-like coupling.
Zhao, Li-Ming; Zhou, Yun-Song; Wang, Ai-Hua
2017-02-01
Second harmonic generation (SHG) in a two-dimensional (2D) nonlinear photonic crystal (NPC) with finite width along z-direction that is embedded in air is investigated, without adopting the traditional approximations such as a plane-wave approximation (PWA) and slowly varying amplitude approximation (SVAA). The so-called quasi-phase-matching (QPM) and the corresponding SHG conversion efficiency can be modulated significantly by the field of fundamental wave (FW). It is assumed that the incident light, along z-direction, is normally launched upon the surface of the sample, and QPM for different directions is investigated. It is found that the QPM shows significant differences, compared with the traditional QPM along the two different directions: in the direction of finite width of the sample, the peak value of SHG conversion efficiency is deviated from the traditional case and it gets to its peak values when the transmittance resonance occurs. However, in the other direction, the deviation from the traditional QPM arises from the field modulation of the second harmonic wave (SHW) and in this direction, it is investigated that the full width at half maximum of QPM is much wider than that in the direction of finite width of the sample. These results can be used to provide a theoretical guidance for achieving QPM SHG.
Szyniszewski, M.; Mostaani, E.; Drummond, N. D.; Fal'ko, V. I.
2017-02-01
Excitonic effects play a particularly important role in the optoelectronic behavior of two-dimensional (2D) semiconductors. To facilitate the interpretation of experimental photoabsorption and photoluminescence spectra we provide statistically exact diffusion quantum Monte Carlo binding-energy data for Mott-Wannier models of excitons, trions, and biexcitons in 2D semiconductors. We also provide contact pair densities to allow a description of contact (exchange) interactions between charge carriers using first-order perturbation theory. Our data indicate that the binding energy of a trion is generally larger than that of a biexciton in 2D semiconductors. We provide interpolation formulas giving the binding energy and contact density of 2D semiconductors as functions of the electron and hole effective masses and the in-plane polarizability.
Experimental apparatus for quantum simulation with two-dimensional 9Be + Coulomb crystals
Pyka, Karsten; Ball, Harrison; McRae, Terry; Edmunds, Claire; Lee, Michael W.; Henderson, Samuel; Biercuk, Michael J.; Quantum Control Lab Team
2015-03-01
We report on the development of a new experimental setup designed for Quantum Simulation studies at a computationally relevant scale using laser-cooled 9Be + ion-crystals in a Penning trap. The trap geometry is optimized using numerical calculations for trapping large ion crystals with enhanced optical access and reduced anharmonic perturbations. Separate loading and spectroscopy zones prevent long term drifts of the trapping parameters due to contamination of the trap electrodes with Be deposits. Our customized superconducting magnet provides a homogenous (dB/B telecom wavelength fiber laser systems in the IR via nonlinear conversion. Our new approach employs high-efficiency telecom modulators and mode-selecting cavities to generate multiple beamlines from a single Sum-frequency-Generation step. Ultimately, this newly developed setup will allow for studies of many-body spin systems with tuneable interaction strength from infinite-range to nearest-neighbour type interaction.
Two-Dimensional Dirac Fermions in a Topological Insulator: Transport in the Quantum Limit
Energy Technology Data Exchange (ETDEWEB)
Analytis, J.G.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab /Stanford U., Appl. Phys. Dept.; McDonald, R.D.; /Los Alamos; Riggs, S.C.; /Natl. High Mag. Field Lab.; Chu, J.-H.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab /Stanford U., Appl. Phys. Dept.; Boebinger, G.S.; /Natl. High Mag. Field Lab.; Fisher, I.R.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab /Stanford U., Appl. Phys. Dept.
2011-08-12
Pulsed magnetic fields of up to 55T are used to investigate the transport properties of the topological insulator Bi{sub 2}Se{sub 3} in the extreme quantum limit. For samples with a bulk carrier density of n = 2.9 x 10{sup 16} cm{sup -3}, the lowest Landau level of the bulk 3D Fermi surface is reached by a field of 4T. For fields well beyond this limit, Shubnikov-de Haas oscillations arising from quantization of the 2D surface state are observed, with the {nu} = 1 Landau level attained by a field of {approx} 35T. These measurements reveal the presence of additional oscillations which occur at fields corresponding to simple rational fractions of the integer Landau indices.
Shear viscosity at the Ising-nematic quantum critical point in two dimensional metals
Patel, Aavishkar A; Sachdev, Subir
2016-01-01
In a strongly interacting quantum liquid without quasiparticles, general scaling arguments imply that the dimensionless ratio $(k_B /\\hbar)\\, \\eta/s$, where $\\eta$ is the shear viscosity and $s$ is the entropy density, is a universal number. We compute the shear viscosity of the Ising-nematic critical point of metals in spatial dimension $d=2$ by an expansion below $d=5/2$. The anisotropy associated with directions parallel and normal to the Fermi surface leads to a violation of the scaling expectations: $\\eta$ scales in the same manner as a chiral conductivity, and the ratio $\\eta/s$ diverges as $T^{-2/z}$, where $z$ is the dynamic critical exponent for fermionic excitations dispersing normal to the Fermi surface.
Virial Theorem for a Class of Quantum Nonlinear Harmonic Oscillators
Institute of Scientific and Technical Information of China (English)
王雪红; 郭军义; 李艳
2012-01-01
In this paper,the Virial Theorem based on a class of quantum nonlinear harmonic oscillators is presented.This relationship has to do with parameter λ and ?/?λ,where the λ is a real number.When λ=0,the nonlinear harmonic oscillator naturally reduces to the usual quantum linear harmonic oscillator,and the Virial Theorem also reduces to the usual Virial Theorem.
Xu, Cenke
Several examples of quantum spin systems and pseudo spin systems have been studied, and unconventional states of matters and phase transitions have been realized in all these systems under consideration. In the p +/- ip superconductor Josephson lattice and the p--band cold atomic system trapped in optical lattices, novel phases which behave similarly to 1+1 dimensional systems are realized, despite the fact that the real physical systems are in two or three dimensional spaces. For instance, by employing a spin-wave analysis together with a new duality transformation, we establish the existence and stability of a novel gapless "critical phase", which we refer to as a "bond algebraic liquid". This novel critical phase is analogous to the 1+1 dimensional algebraic boson liquid phase. The reason for the novel physics is that there is a quasilocal gauge symmetry in the effective low energy Hamiltonian. In a spin-1 system on the kagome lattice, and a hard-core boson system on the honeycomb lattice, the low energy physics is controlled by two components of compact U(1) gauge symmetries that emerge at low energy. Making use of the confinement nature of the 2+1 dimensional compact gauge theories and the powerful duality between gauge theories and height field theories, the crystalline phase diagrams are studied for both systems, and the transitions to other phases are also considered. These phase diagrams might be accessible in strongly correlated materials, or atomic systems in optical lattices. A novel quantum ground state of matter is realized in a bosonic model on three dimensional fcc lattice with emergent low energy excitations. The novel phase obtained is a stable gapless boson liquid phase, with algebraic boson density correlations. The stability of this phase is protected against the instanton effect and superfluidity by self-duality and large gauge symmetries on both sides of the duality. The gapless collective excitations of this phase closely resemble the
High-field studies of quantum oscillations in quasi-two-dimensional organic metals
Sandhu, Pravindrajit
frequencies in the dHvA signal is found to be a quantum mechanical effect arising from differences in field dependence of the states in the two partially occupied bands near the Fermi level.
Irie, Hiroshi; Todt, Clemens; Kumada, Norio; Harada, Yuichi; Sugiyama, Hiroki; Akazaki, Tatsushi; Muraki, Koji
2016-10-01
We study coherent transport and bound state formation of Bogoliubov quasiparticles in a high-mobility I n0.75G a0.25As two-dimensional electron gas (2DEG) coupled to a superconducting Nb electrode by means of a quantum point contact (QPC) as a tunable single-mode probe. Below the superconducting critical temperature of Nb, the QPC shows a single-channel conductance greater than the conductance quantum 2 e2/h at zero bias, which indicates the presence of Andreev-reflected quasiparticles, time-reversed states of the injected electron, returning back through the QPC. The marked sensitivity of the conductance enhancement to voltage bias and perpendicular magnetic field suggests a mechanism analogous to reflectionless tunneling—a hallmark of phase-coherent transport, with the boundary of the 2DEG cavity playing the role of scatterers. When the QPC transmission is reduced to the tunneling regime, the differential conductance vs bias voltage probes the single-particle density of states in the proximity area. Measured conductance spectra show a double peak within the superconducting gap of Nb, demonstrating the formation of Andreev bound states in the 2DEG. Both of these results, obtained in the open and closed geometries, underpin the coherent nature of quasiparticles, i.e., phase-coherent Andreev reflection at the InGaAs/Nb interface and coherent propagation in the ballistic 2DEG.
Tollerud, Jonathan O
2016-01-01
We identify carrier scattering at densities below which it has previously been observed in semiconductor quantum wells. These effects are evident in the peakshapes of 2D double-quantum spectra, which change as a function of excitation density. At high excitation densities ($\\geq 10^{9}$ carriers/,cm$^{-2}$) we observe untilted peaks similar to those reported in previous experiments. At low excitation densities (<$10^{8}$ carriers cm$^{-2}$) we observe narrower, tilted peaks. Using a simple simulation, we show that tilted peak-shapes are expected in double-quantum spectra when inhomogeneous broadening is much larger than homogeneous broadening, and that fast pure-decoherence of the double-quantum coherence can obscure this peak tilt. These results show that carrier interactions are important at lower densities than previously expected, and that the `natural' double-quantum peakshapes are hidden by carrier interactions at the excitation densities typically used. Furthermore, these results demonstrate that an...
Britton, Joseph W; Sawyer, Brian C; Keith, Adam C; Wang, C-C Joseph; Freericks, James K; Uys, Hermann; Biercuk, Michael J; Bollinger, John J
2012-04-25
The presence of long-range quantum spin correlations underlies a variety of physical phenomena in condensed-matter systems, potentially including high-temperature superconductivity. However, many properties of exotic, strongly correlated spin systems, such as spin liquids, have proved difficult to study, in part because calculations involving N-body entanglement become intractable for as few as N ≈ 30 particles. Feynman predicted that a quantum simulator--a special-purpose 'analogue' processor built using quantum bits (qubits)--would be inherently suited to solving such problems. In the context of quantum magnetism, a number of experiments have demonstrated the feasibility of this approach, but simulations allowing controlled, tunable interactions between spins localized on two- or three-dimensional lattices of more than a few tens of qubits have yet to be demonstrated, in part because of the technical challenge of realizing large-scale qubit arrays. Here we demonstrate a variable-range Ising-type spin-spin interaction, J(i,j), on a naturally occurring, two-dimensional triangular crystal lattice of hundreds of spin-half particles (beryllium ions stored in a Penning trap). This is a computationally relevant scale more than an order of magnitude larger than previous experiments. We show that a spin-dependent optical dipole force can produce an antiferromagnetic interaction J(i,j) proportional variant d(-a)(i,j), where 0 ≤ a ≤ 3 and d(i,j) is the distance between spin pairs. These power laws correspond physically to infinite-range (a = 0), Coulomb-like (a = 1), monopole-dipole (a = 2) and dipole-dipole (a = 3) couplings. Experimentally, we demonstrate excellent agreement with a theory for 0.05 ≲ a ≲ 1.4. This demonstration, coupled with the high spin count, excellent quantum control and low technical complexity of the Penning trap, brings within reach the simulation of otherwise computationally intractable problems in quantum magnetism.
Kamali Tafreshi, Azadeh; Barış Top, Can; Güneri Gençer, Nevzat
2017-06-01
Harmonic motion microwave Doppler imaging (HMMDI) is a novel imaging modality for imaging the coupled electrical and mechanical properties of body tissues. In this paper, we used two experimental systems with different receiver configurations to obtain HMMDI images from tissue-mimicking phantoms at multiple vibration frequencies between 15 Hz and 35 Hz. In the first system, we used a spectrum analyzer to obtain the Doppler data in the frequency domain, while in the second one, we used a homodyne receiver that was designed to acquire time-domain data. The developed phantoms mimicked the elastic and dielectric properties of breast fat tissue, and included a 14~\\text{mm}× 9 mm cylindrical inclusion representing the tumor. A focused ultrasound probe was mechanically scanned in two lateral dimensions to obtain two-dimensional HMMDI images of the phantoms. The inclusions were resolved inside the fat phantom using both experimental setups. The image resolution increased with increasing vibration frequency. The designed receiver showed higher sensitivity than the spectrum analyzer measurements. The results also showed that time-domain data acquisition should be used to fully exploit the potential of the HMMDI method.
Zhukovsky, V. Ch.; Krevchik, V. D.; Semenov, M. B.; Krevchik, P. V.; Zaytsev, R. V.; Egorov, I. A.
2016-11-01
The field and temperature dependence of the probability of two-dimensional dissipative tunneling is studied in the framework of one-instanton approximation for a model double-well oscillator potential in an external electric field at finite temperature with account for the influence of two local phonon modes for quantum dots in a system of a combined atomic force and a scanning tunneling microscope. It is demonstrated that in the mode of synchronous parallel transfer of tunneling particles from the cantilever tip to the quantum dot the two local phonon modes result in the occurrence of two stable peaks in the curve of the 2D dissipative tunneling probability as a function of the field. Qualitative comparison of the theoretical curve in the limit of weak dissociation and the experimental current-voltage characteristic for quantum dots that grow from colloidal gold under a cantilever tip at the initial stage of quantum-dot formation when the quantum dot size does not exceed 10 nm is performed. It is established that one of the two stable peaks that correspond to interaction of tunneling particles with two local phonon modes in the temperature dependence of the 2D dissipative tunneling probability can be split in two, which corresponds to the tunneling channel interference mechanism. It is found that the theoretically predicted and experimentally observed mode of quantum beats occurs near the bifurcation point.
Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J.; Atkin, Paul; Berean, Kyle J.; Clark, Rhiannon M.; Cole, Ivan S.; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh
2016-06-01
Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4]2- anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications.Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of
Brézin, E
1992-01-01
In the usual matrix-model approach to random discretized two-dimensional manifolds, one introduces n Ising spins on each cell, i.e. a discrete version of 2D quantum gravity coupled to matter with a central charge n/2. The matrix-model consists then of an integral over $2^{n}$ matrices, which we are unable to solve for $n>1$. However for a fixed genus we can expand in the cosmological constant g for arbitrary values of n, and a simple minded analysis of the series yields for n=0,1 and 2 the expected results for the exponent $\\gamma_{string}$ with an amazing precision given the small number of terms that we considered. We then proceed to larger values of n. Simple tests of universality are successfully applied; for instance we obtain the same exponents for n=3 or for one Ising model coupled to a one dimensional target space. The calculations are easily extended to states Potts models, through an integration over $q^{n}$ matrices. We see no sign of the tachyonic instability of the theory, but we have only consid...
Kim, Ju H.; Han, S. Y.; Brooks, J. S.
1999-08-01
We investigate the phenomenon of magnetic breakdown in quasi-two-dimensional organic conductors such as α-(ET)2KHg(SCN)4 and κ-(ET)2Cu(NCS)2 by constructing a tight-binding model based on a realistic band structure which is derived from the crystallographic data. We solve the model numerically to compute the magnetic field dependence of the magnetization and show that the present model accounts naturally for the experimentally observed magnetization oscillation frequencies that are forbidden in the semiclassical picture. The computed values of the fundamental and magnetic breakdown frequencies with no adjustable parameters are close to the experimentally measured values. For completeness, we carry out the computation for both canonical (fixed number of particles) and grand canonical (fixed chemical potential) ensembles, and show that the forbidden frequencies appear in both cases. Hence, the appearance of anomalous frequencies in the de Haas-van Alphen effect has a quantum-mechanical origin and arises from the interplay of electronic states from two partially occupied bands near the Fermi energy as a function of magnetic field. We also compute the temperature dependence of the magnetization and apply ad hoc the Lifshitz-Kosevich analysis to the amplitudes of the Fourier components at moderately high temperatures. This yields effective mass values for α-(ET)2KHg(SCN)4 in good agreement with experimental values.
Effect of phase transition on quantum transport in group-IV two-dimensional U-shape device
Energy Technology Data Exchange (ETDEWEB)
Sadi, Mohammad Abdullah; Gupta, Gaurav, E-mail: a0089293@nus.edu.sg; Liang, Gengchiau [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore)
2014-10-21
The effect of phase-transition from the quantum-spin-hall to the band-insulator phase on the transport through a three-terminal U-shape spin-separator has been computationally investigated via non-equilibrium green function formalism. Two-dimensional group-IV elements have been comprehensively appraised as the device material. The device separates the unpolarized current injected at the source-terminal into nearly 100% spin-polarized currents of the opposite polarities at the two drain terminals. The phase-transition activated by the electric-field orthogonal to the device is shown to extensively influence the current magnitude and its spin-polarization, and the effect is stronger for materials with smaller intrinsic spin-orbit coupling. Moreover, the device length and the area under field are shown to critically affect the device characteristics on phase change. It is shown that the same device can be operated as a spin-filter by inducing phase-transition selectively in the channel. The results are important for designing spin-devices from Group-IV monolayers.
Qin, Mingpu; Zhang, Shiwei
2016-01-01
Ground state properties of the Hubbard model on a two-dimensional square lattice are studied by the auxiliary-field quantum Monte Carlo method. Accurate results for energy, double occupancy, effective hopping, magnetization, and momentum distribution are calculated for interaction strengths of U/t from 2 to 8, for a range of densities including half-filling and n = 0.3, 0.5, 0.6, 0.75, and 0.875. At half-filling, the results are numerically exact. Away from half-filling, the constrained path Monte Carlo method is employed to control the sign problem. Our results are obtained with several advances in the computational algorithm, which are described in detail. We discuss the advantages of generalized Hartree-Fock trial wave functions and its connection to pairing wave functions, as well as the interplay with different forms of Hubbard-Stratonovich decompositions. We study the use of different twist angle sets when applying the twist averaged boundary conditions. We propose the use of quasi-random sequences, whi...
Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J; Atkin, Paul; Berean, Kyle J; Clark, Rhiannon M; Cole, Ivan S; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh
2016-06-16
Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4](2-) anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications.
Wu, Wei; Xu, Jing-Bo
2016-08-01
We investigate the quantum phase transitions of spin systems in one and two dimensions by employing trace distance and multipartite entanglement along with the real-space quantum renormalization group method. As illustration examples, a one-dimensional and a two-dimensional XY models are considered. It is shown that the quantum phase transitions of these spin-chain systems can be revealed by the singular behaviors of the first derivatives of renormalized trace distance and multipartite entanglement in the thermodynamics limit. Moreover, we find that the renormalized trace distance and multipartite entanglement obey certain universal exponential-type scaling laws in the vicinity of the quantum critical points.
Institute of Scientific and Technical Information of China (English)
Zhai Zhi-Yuan; Li Yu-Qi; Pan Xiao-Yin
2012-01-01
We investigate the effects due to anisotropy and magnetic field interaction for a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot.The specific heat is studied with varying temperature,anisotropy,and magnetic field strength.The cases without and with the inclusion of the spin Zeeman interaction are considered.
Mesoscopic quantum interference experiments in InGaAs and GaAs two-dimensional systems
Ren, Shaola
The study of quantum interference in solid-state systems yields insight in fundamental properties of mesoscopic systems. Electron quantum interference constitutes an important method to explore mesoscopic physics and quantum decoherence. This dissertation focuses on two-dimensional (2D) electron systems in delta-Si doped n-type In0:64Ga0:36As/In 0:45Al0:55As, 2D hole systems in Si-doped p-type GaAs/Al 0:35Ga0:65As and C-doped p-type GaAs/Al0:24Ga 0:76As heterostructures. The low temperature experiments study the magnetotransport of nano- and micro-scale lithographically defined devices fabricated on the heterostructures. These devices include a single ring interferometer and a ring interferometer array in 2D electron system, Hall bar geometries and narrow wires in 2D hole systems. The single ring interferometer yields pronounced Aharonov-Bohm (AB) oscillations with magnetic flux periodicity of h/e over a wide range of magnetic field. The periodicity was confirmed by Fourier transformation of the oscillations. The AB oscillation amplitude shows a quasi-periodic modulation over applied magnetic field due to local magnetic flux threading through the interferometer arms. Further study of current and temperature dependence of the amplitude of the oscillations indicates that the Thouless energy forms the measure of excitation energies giving quantum decoherence. An in-plane magnetic field was applied to the single ring interferometer to study the Berry's phase and the Aharonov-Casher effect. The ring interferometer array yields both AB oscillations and Altshuler-Aronov-Spivak (AAS) oscillations, the latter with magnetic flux periodicity of h/2e. The AAS oscillations require time-reversal symmetry and hence can be used to qualify time-reversal symmetry breaking. More importantly, the fundamental mesoscopic dephasing length associated with time-reversal symmetry breaking under applied magnetic field, an effective magnetic length, can be obtained by the analysis of the AAS
de Forges de Parny, L.; Rousseau, V. G.
2017-01-01
We study the ground state and the thermal phase diagram of a two-species Bose-Hubbard model, with U(1 ) ×Z2 symmetry, describing atoms and molecules on a two-dimensional optical lattice interacting via a Feshbach resonance. Using quantum Monte Carlo simulations and mean-field theory, we show that the conversion between the two species, coherently coupling the atomic and molecular states, has a crucial impact on the Mott-superfluid transition and stabilizes an insulating phase with a gap controlled by the conversion term—the Feshbach insulator—instead of a standard Mott-insulating phase. Depending on the detuning between atoms and molecules, this model exhibits three phases: the Feshbach insulator, a molecular condensate coexisting with noncondensed atoms, and a mixed atomic-molecular condensate. Employing finite-size scaling analysis, we observe three-dimensional (3D) X Y (3D Ising) transition when U(1 ) (Z2) symmetry is broken, whereas the transition is first order when both U(1 ) and Z2 symmetries are spontaneously broken. The finite-temperature phase diagram is also discussed. The thermal disappearance of the molecular superfluid leads to a Berezinskii-Kosterlitz-Thouless transition with unusual universal jump in the superfluid density. The loss of the quasi-long-range coherence of the mixed atomic and molecular superfluid is more subtle since only atoms exhibit conventional Berezinskii-Kosterlitz-Thouless criticality. We also observe a signal compatible with a classical first-order transition between the mixed superfluid and the normal Bose liquid at low temperature.
Introduction to classical and quantum harmonic oscillators
Bloch, Sylvan C
2013-01-01
From conch shells to lasers . harmonic oscillators, the timeless scientific phenomenon As intriguing to Galileo as they are to scientists today, harmonic oscillators have provided a simple and compelling paradigm for understanding the complexities that underlie some of nature's and mankind's most fascinating creations. From early string and wind instruments fashioned from bows and seashells to the intense precision of lasers, harmonic oscillators have existed in various forms, as objects of beauty and scientific use. And harmonic oscillation has endured as one of science's most fascinating con
Energy Technology Data Exchange (ETDEWEB)
Campione, Salvatore, E-mail: sncampi@sandia.gov [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Center for Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Department of Electrical Engineering and Computer Science, University of California Irvine, Irvine, California 92697 (United States); Benz, Alexander; Brener, Igal, E-mail: ibrener@sandia.gov [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Center for Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Sinclair, Michael B. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Capolino, Filippo [Department of Electrical Engineering and Computer Science, University of California Irvine, Irvine, California 92697 (United States)
2014-03-31
We theoretically analyze the second harmonic generation capacity of two-dimensional periodic metamaterials comprising sub-wavelength resonators strongly coupled to intersubband transitions in quantum wells (QWs) at mid-infrared frequencies. The metamaterial is designed to support a fundamental resonance at ∼30 THz and an orthogonally polarized resonance at the second harmonic frequency (∼60 THz), while the asymmetric quantum well structure is designed to provide a large second order susceptibility. Upon continuous wave illumination at the fundamental frequency we observe second harmonic signals in both the forward and backward directions, with the forward efficiency being larger. We calculate the overall second harmonic conversion efficiency of the forward wave to be ∼1.3 × 10{sup −2} W/W{sup 2}—a remarkably large value, given the deep sub-wavelength dimensions of the QW structure (about 1/15th of the free space wavelength of 10 μm). The results shown in this Letter provide a strategy for designing easily fabricated sources across the entire infrared spectrum through proper choice of QW and resonator designs.
Schreiber, K. A.; Samkharadze, N.; Gardner, G. C.; Biswas, Rudro R.; Manfra, M. J.; Csáthy, G. A.
2017-07-01
Under hydrostatic pressure, the ground state of a two-dimensional electron gas at ν =5 /2 changes from a fractional quantum Hall state to the stripe phase. By measuring the energy gap of the fractional quantum Hall state and of the onset temperature of the stripe phase, we mapped out a phase diagram of these competing phases in the pressure-temperature plane. Our data highlight the dichotomy of two descriptions of the half-filled Landau level near the quantum critical point: one based on electrons and another on composite fermions.
Energy Technology Data Exchange (ETDEWEB)
Van Gorder, Robert A., E-mail: Robert.VanGorder@maths.ox.ac.uk [Mathematical Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG (United Kingdom)
2015-09-15
In a recent paper, we give a study of the purely rotational motion of general stationary states in the two-dimensional local induction approximation (2D-LIA) governing superfluid turbulence in the low-temperature limit [B. Svistunov, “Superfluid turbulence in the low-temperature limit,” Phys. Rev. B 52, 3647 (1995)]. Such results demonstrated that variety of stationary configurations are possible from vortex filaments exhibiting purely rotational motion in addition to commonly discussed configurations such as helical or planar states. However, the filaments (or, more properly, waves along these filaments) can also exhibit translational motion along the axis of orientation. In contrast to the study on vortex configurations for purely rotational stationary states, the present paper considers non-stationary states which exhibit a combination of rotation and translational motions. These solutions can essentially be described as waves or disturbances which ride along straight vortex filament lines. As expected from our previous work, there are a number of types of structures that can be obtained under the 2D-LIA. We focus on non-stationary states, as stationary states exhibiting translation will essentially take the form of solutions studied in [R. A. Van Gorder, “General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation,” Phys. Fluids 26, 065105 (2014)], with the difference being translation along the reference axis, so that qualitative appearance of the solution geometry will be the same (even if there are quantitative differences). We discuss a wide variety of general properties of these non-stationary solutions and derive cases in which they reduce to known stationary states. We obtain various routes to Kelvin waves along vortex filaments and demonstrate that if the phase and amplitude of a disturbance both propagate with the same wave speed, then Kelvin waves will result. We also consider the self
Deformed quantum harmonic oscillator with diffusion and dissipation
Isar, A
2002-01-01
A master equation for the deformed quantum harmonic oscillator interacting with a dissipative environment, in particular with a thermal bath, is derived in the microscopic model by using perturbation theory. The coefficients of the master equation and of equations of motion for observables depend on the deformation function. The steady state solution of the equation for the density matrix in the number representation is obtained and the equilibrium energy of the deformed harmonic oscillator is calculated in the approximation of small deformation.
Deformed quantum harmonic oscillator with diffusion and dissipation
Isar, A.; Scheid, W.
2002-07-01
A master equation for the deformed quantum harmonic oscillator interacting with a dissipative environment, in particular with a thermal bath, is derived in the microscopic model by using perturbation theory. The coefficients of the master equation and of equations of motion for observables depend on the deformation function. The steady-state solution of the equation for the density matrix in the number representation is obtained and the equilibrium energy of the deformed harmonic oscillator is calculated in the approximation of small deformation.
Energy Technology Data Exchange (ETDEWEB)
Nakra Mohajer, Soukaina; El Harouny, El Hassan [Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences, Université Abdelmalek Essaadi, B.P. 2121 M’Hannech II, 93030 Tétouan (Morocco); Ibral, Asmaa [Equipe d’Optique et Electronique du Solide, Département de Physique, Faculté des Sciences, Université Chouaïb Doukkali, B. P. 20 El Jadida Principale, El Jadida (Morocco); Laboratoire d’Instrumentation, Mesure et Contrôle, Département de Physique, Faculté des Sciences, Université Chouaïb Doukkali, B. P. 20 El Jadida Principale, El Jadida (Morocco); El Khamkhami, Jamal [Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences, Université Abdelmalek Essaadi, B.P. 2121 M’Hannech II, 93030 Tétouan (Morocco); and others
2016-09-15
Eigenvalues equation solutions of a hydrogen-like donor impurity, confined in a hemispherical quantum dot deposited on a wetting layer and capped by an insulating matrix, are determined in the framework of the effective mass approximation. Conduction band alignments at interfaces between quantum dot and surrounding materials are described by infinite height barriers. Ground and excited states energies and wave functions are determined analytically and via one-dimensional finite difference approach in case of an on-center donor. Donor impurity is then moved from center to pole of hemispherical quantum dot and eigenvalues equation is solved via Ritz variational principle, using a trial wave function where Coulomb attraction between electron and ionized donor is taken into account, and by two-dimensional finite difference approach. Numerical codes developed enable access to variations of donor total energy, binding energy, Coulomb correlation parameter, spatial extension and radial probability density with respect to hemisphere radius and impurity position inside the quantum dot.
Energy Technology Data Exchange (ETDEWEB)
Dasgupta, Shivaji
2009-02-15
In this work two-dimensional electron systems (2DESs) based on AlAs/AlGaAs heterostructures doped with Si are investigated. The electrons are confined in AlAs quantum wells (QWs) sandwiched between AlGaAs buffers. Analytical calculations and simulations for AlAs QWs are presented in the first chapter. The results show a cross-over width, above which the wide (001)-oriented QWs show double valley occupancy and wide (110)-oriented QWs show single valley occupancy. We solve the Schroedinger equation analytically for anisotropic masses. The solution shows the orientation dependence of the elliptical cyclotron orbit due to the anisotropic mass. We also present an introduction to the Landau level crossings based on g{sup *}m{sup *} product. In the next chapter, we present experimental results for the double-valley (001)-oriented AlAs QWs. We present the different structures of the deep AlAs QWs along with the low temperature magnetotransport data for these QWs. Thereafter, we present the results on shallow AlAs QWs. We achieved a mobility of 4.2 x 10{sup 5} cm{sup 2}/Vs at 330 mK for the deep backside doped AlAs QW. For the shallow QWs, we achieved a mobility of2.3 x 10{sup 5} cm{sup 2}/Vs at 330 mK, for a density of 2.9 x 10{sup 11} cm{sup -2}. From the magneto-transport data, we see evidence of the double-valley occupation for the (001)-oriented AlAs wide QWs. In the next chapter, we present experimental results for the single-valley (110)-oriented AlAs QWs. We deduced the donor binding energy and the doping efficiency for this facet from a doping series of double-sided doped QWs. Thereafter, we designed different structures for the (110)-oriented AlAs QWs, which we present along with their respective low temperature magneto-transport data. We measured one of the double-sided doped AlAs QWs at very high magnetic fields and low temperatures, down to 60 mK. At the end of the chapter, we present a spike feature observed in the magneto-transport data of these QWs. This
Large- quantum chromodynamics and harmonic sums
Indian Academy of Sciences (India)
Eduardo De Rafael
2012-06-01
In the large- limit of QCD, two-point functions of local operators become harmonic sums. I review some properties which follow from this fact and which are relevant for phenomenological applications. This has led us to consider a class of analytic number theory functions as toy models of large- QCD which also is discussed.
Second-harmonic scanning optical microscopy of semiconductor quantum dots
DEFF Research Database (Denmark)
Vohnsen, B.; Bozhevolnyi, S.I.; Pedersen, K.;
2001-01-01
Second-harmonic (SH) optical imaging of self-assembled InAlGaAs quantum dots (QD's) grown on a GaAs(0 0 1) substrate has been accomplished at room temperature by use of respectively a scanning far-field optical microscope in reflection mode and a scanning near-field optical microscope...
Quantum Harmonic Oscillator Algebra and Link Invariants
Gómez, C
1991-01-01
The $q$--deformation $U_q (h_4)$ of the harmonic oscillator algebra is defined and proved to be a Ribbon Hopf algebra.Associated with this Hopf algebra we define an infinite dimensional braid group representation on the Hilbert space of the harmonic oscillator, and an extended Yang--Baxter system in the sense of Turaev. The corresponding link invariant is computed in some particular cases and coincides with the inverse of the Alexander--Conway polynomial. The $R$ matrix of $U_q (h_4)$ can be interpreted as defining a baxterization of the intertwiners for semicyclic representations of $SU(2)_q$ at $q=e^{2 \\pi i/N}$ in the $N \\rightarrow \\infty$ limit.Finally we define new multicolored braid group representations and study their relation to the multivariable Alexander--Conway polynomial.
Dissipative quantum trajectories in complex space: Damped harmonic oscillator
Chou, Chia-Chun
2016-10-01
Dissipative quantum trajectories in complex space are investigated in the framework of the logarithmic nonlinear Schrödinger equation. The logarithmic nonlinear Schrödinger equation provides a phenomenological description for dissipative quantum systems. Substituting the wave function expressed in terms of the complex action into the complex-extended logarithmic nonlinear Schrödinger equation, we derive the complex quantum Hamilton-Jacobi equation including the dissipative potential. It is shown that dissipative quantum trajectories satisfy a quantum Newtonian equation of motion in complex space with a friction force. Exact dissipative complex quantum trajectories are analyzed for the wave and solitonlike solutions to the logarithmic nonlinear Schrödinger equation for the damped harmonic oscillator. These trajectories converge to the equilibrium position as time evolves. It is indicated that dissipative complex quantum trajectories for the wave and solitonlike solutions are identical to dissipative complex classical trajectories for the damped harmonic oscillator. This study develops a theoretical framework for dissipative quantum trajectories in complex space.
DEFF Research Database (Denmark)
Julsgaard, Brian; Johansen, Jeppe; Stobbe, Søren
2008-01-01
We have performed time-resolved spectroscopy on InAs quantum dot ensembles in photonic crystal membranes. The influence of the photonic crystal is investigated by varying the lattice constant systematically. We observe a strong slow down of the quantum dots’ spontaneous emission rates as the two-...... the bandgap in good agreement with local density of states calculations.......We have performed time-resolved spectroscopy on InAs quantum dot ensembles in photonic crystal membranes. The influence of the photonic crystal is investigated by varying the lattice constant systematically. We observe a strong slow down of the quantum dots’ spontaneous emission rates as the two...
Tracking dynamics of two-dimensional continuous attractor neural networks
Fung, C. C. Alan; Wong, K. Y. Michael; Wu, Si
2009-12-01
We introduce an analytically solvable model of two-dimensional continuous attractor neural networks (CANNs). The synaptic input and the neuronal response form Gaussian bumps in the absence of external stimuli, and enable the network to track external stimuli by its translational displacement in the two-dimensional space. Basis functions of the two-dimensional quantum harmonic oscillator in polar coordinates are introduced to describe the distortion modes of the Gaussian bump. The perturbative method is applied to analyze its dynamics. Testing the method by considering the network behavior when the external stimulus abruptly changes its position, we obtain results of the reaction time and the amplitudes of various distortion modes, with excellent agreement with simulation results.
Du, Ling-Ling; Li, Peng-Cheng; Zhou, Xiao-Xin
2017-08-01
We present the role of quantum trajectories on high-order harmonic generation (HHG) related to the various internuclear distances in hydrogen molecule ions in an intense laser field by solving two-dimensional time-dependent Schrödinger equation. We find that the contribution of the long trajectories in HHG is dominant at smaller internuclear distances, but the contribution of the short trajectories is dominant at larger internuclear distances, it implies that the role of quantum trajectories closes to those HHG of the atom. In addition, the HHG spectrum of hydrogen molecule ions exhibits an internuclear distance-dependent double plateau structure which is related to the electron migrating from one nucleus to another one. Combining with the Morlet transform of quantum time-frequency spectrum and an extended semiclassical analysis, the role of quantum trajectories on HHG with the various internuclear distance are clarified.
DEFF Research Database (Denmark)
Petersen, Christian Leth; Hansen, Ole Per
1996-01-01
We have investigated the AC conductivity elements in the quantum Hall regime of two-dimensional electron gases coupled capacitively to electrodes with Corbino geometry. The samples are GaAlAs/GaAs single heterostructures, and the measurements are made at low frequencies, up to 20 kHz. The diagonal...... conductivity is derived from magnetocapacitance measurements. It increases with increasing frequency according to a power law at integer filling factors. The exponent of the power law depends on both temperature and filling factor. Ratios between Hall conductivities at different filling factors are obtained...
Kurilovich, P. D.; Kurilovich, V. D.; Burmistrov, I. S.
2016-10-01
We study indirect exchange interaction between magnetic impurities in the (001) CdTe/HgTe/CdTe symmetric quantum well. We consider low temperatures and the case of the chemical potential placed in the energy gap of the two-dimensional quasiparticle spectrum. We find that the indirect exchange interaction is suppressed exponentially with the distance between magnetic impurities. The presence of inversion asymmetry results in oscillations of the indirect exchange interaction with the distance and generates additional terms which are noninvariant under rotations in the (001) plane. The indirect exchange interaction matrix has complicated structure with some terms proportional to the sign of the energy gap.
Quantum-spin-liquid states in the two-dimensional kagome antiferromagnets ZnxCu4-x(OD)6Cl2.
Lee, S-H; Kikuchi, H; Qiu, Y; Lake, B; Huang, Q; Habicht, K; Kiefer, K
2007-11-01
A three-dimensional system of interacting spins typically develops static long-range order when it is cooled. If the spins are quantum (S=1/2), however, novel quantum paramagnetic states may appear. The most highly sought state among them is the resonating-valence-bond state, in which every pair of neighbouring quantum spins forms an entangled spin singlet (valence bonds) and these singlets are quantum mechanically resonating among themselves. Here we provide an experimental indication for such quantum paramagnetic states existing in frustrated antiferromagnets, Zn(x)Cu(4-x)(OD)(6)Cl(2), where the S=1/2 magnetic Cu2+ moments form layers of a two-dimensional kagome lattice. We find that in Cu(4)(OD)(6)Cl(2), where distorted kagome planes are weakly coupled, a dispersionless excitation mode appears in the magnetic excitation spectrum below approximately 20 K, whose characteristics resemble those of quantum spin singlets in a solid state, known as a valence-bond solid, that breaks translational symmetry. Doping with non-magnetic Zn2+ ions reduces the distortion of the kagome lattice, and weakens the interplane coupling but also dilutes the magnetic occupancy of the kagome lattice. The valence-bond-solid state is suppressed, and for ZnCu(3)(OD)(6)Cl(2), where the kagome planes are undistorted and 90% occupied by the Cu2+ ions, the low-energy spin fluctuations become featureless.
Hadamard States and Two-dimensional Gravity
Salehi, H
2001-01-01
We have used a two-dimensional analog of the Hadamard state-condition to study the local constraints on the two-point function of a linear quantum field conformally coupled to a two-dimensional gravitational background. We develop a dynamical model in which the determination of the state of the quantum field is essentially related to the determination of a conformal frame. A particular conformal frame is then introduced in which a two-dimensional gravitational equation is established.
Institute of Scientific and Technical Information of China (English)
ZHAI Zhi-Yuan; YANG Tao; PAN Xiao-Yin
2012-01-01
The propagator for an anisotropic two-dimension charged harmonic oscillator in the presence of a constant external magnetic field and a time-dependent electric field is exactly evaluated. Various special cases appearing in the literature can be obtained by properly setting the values of the parameters in our results.%The propagator for an anisotropic two-dimension charged harmonic oscillator in the presence of a constant external magnetic field and a time-dependent electric field is exactly evaluated.Various special cases appearing in the literature can be obtained by properly setting the values of the parameters in our results.
Two dimensional unstable scar statistics.
Energy Technology Data Exchange (ETDEWEB)
Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)
2006-12-01
This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.
Isar, Aurelian
1995-01-01
The harmonic oscillator with dissipation is studied within the framework of the Lindblad theory for open quantum systems. By using the Wang-Uhlenbeck method, the Fokker-Planck equation, obtained from the master equation for the density operator, is solved for the Wigner distribution function, subject to either the Gaussian type or the delta-function type of initial conditions. The obtained Wigner functions are two-dimensional Gaussians with different widths. Then a closed expression for the density operator is extracted. The entropy of the system is subsequently calculated and its temporal behavior shows that this quantity relaxes to its equilibrium value.
Karanikolas, Vasilios D.; Marocico, Cristian A.; Eastham, Paul R.; Bradley, A. Louise
2016-11-01
The total spontaneous emission rate of a quantum emitter in the presence of an infinite MoS2 monolayer is enhanced by several orders of magnitude, compared to its free-space value, due to the excitation of surface exciton polariton modes and lossy modes. The spectral and distance dependence of the spontaneous emission rate are analyzed and the lossy surface wave, surface exciton polariton mode and radiative contributions are identified. The transverse magnetic and transverse electric exciton polariton modes can be excited for different emission frequencies of the quantum emitter, and their contributions to the total spontaneous emission rate are different. To calculate these different decay rates we use the non-Hermitian description of light-matter interactions, employing a Green's tensor formalism. The distance dependence follows different trends depending on the emission energy of the quantum emitter. For the case of the lossy surface waves, the distance dependence follows a z-n,n =2 ,3 ,4 , trend. When transverse magnetic exciton polariton modes are excited, they dominate and characterize the distance dependence of the spontaneous emission rate of a quantum emitter in the presence of the MoS2 layers. The interaction between a quantum emitter and a MoS2 superlattice is investigated, and we observe a splitting of the modes supported by the superlattice. Moreover, a blueshift of the peak values of the spontaneous emission rate of a quantum emitter is observed as the number of layers is increased. The field distribution profiles, created by a quantum emitter, are used to explain this behavior.
Distance-dependent energy transfer between CdSe/CdS quantum dots and a two-dimensional semiconductor
Energy Technology Data Exchange (ETDEWEB)
Goodfellow, Kenneth M.; Vamivakas, A. Nick, E-mail: nick.vamivakas@rochester.edu [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Chakraborty, Chitraleema [Materials Science, University of Rochester, Rochester, New York 14627 (United States); Sowers, Kelly [Department of Chemistry, University of Rochester, Rochester, New York 14627 (United States); Waduge, Pradeep; Wanunu, Meni [Department of Physics, Northeastern University, Boston, Massachusetts 02115 (United States); Krauss, Todd [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Department of Chemistry, University of Rochester, Rochester, New York 14627 (United States); Driscoll, Kristina [Department of Physics, Rochester Institute of Technology, Rochester, New York 14627 (United States)
2016-01-11
Atomically thin semiconductors, such as the transition metal dichalcogenides, show great potential for nanoscale photodetection, energy harvesting, and nanophotonics. Here, we investigate the efficiency of energy transfer between colloidal quantum dots with a cadmium selenide core and cadmium sulfide shell and monolayer molybdenum diselenide (MoSe{sub 2}). We show that MoSe{sub 2} effectively quenches the fluorescence of quantum dots when the two materials are in contact. We then separate the MoSe{sub 2} and quantum dots by inserting variable thickness hexagonal boron nitride (h-BN) spacers and show that the efficiency at which the MoSe{sub 2} quenches fluorescence decreases as the h-BN thickness is increased. For distances d, this trend can be modeled by a 1/d{sup 4} decay, in agreement with theory and recent studies involving graphene.
Quantum kicked harmonic oscillator in contact with a heat bath
Prado Reynoso, M. Á.; López Vázquez, P. C.; Gorin, T.
2017-02-01
We consider the quantum harmonic oscillator in contact with a finite-temperature bath, modeled by the Caldeira-Leggett master equation. Applying periodic kicks to the oscillator, we study the system in different dynamical regimes between classical integrability and chaos, on the one hand, and ballistic or diffusive energy absorption, on the other. We then investigate the influence of the heat bath on the oscillator in each case. Phase-space techniques allow us to simulate the evolution of the system efficiently. In this way, we calculate high-resolution Wigner functions at long times, where the system approaches a quasistationary cyclic evolution. Thereby, we perform an accurate study of the thermodynamic properties of a nonintegrable, quantum chaotic system in contact with a heat bath at finite temperature. In particular, we find that the heat transfer between harmonic oscillator and heat bath is governed by Fourier's law.
Quantum Harmonic Oscillator State Control in a Squeezed Fock Basis
Kienzler, D.; Lo, H.-Y.; Negnevitsky, V.; Flühmann, C.; Marinelli, M.; Home, J. P.
2017-07-01
We demonstrate control of a trapped-ion quantum harmonic oscillator in a squeezed Fock state basis, using engineered Hamiltonians analogous to the Jaynes-Cummings and anti-Jaynes-Cummings forms. We demonstrate that for squeezed Fock states with low n the engineered Hamiltonians reproduce the √{n } scaling of the matrix elements which is typical of Jaynes-Cummings physics, and also examine deviations due to the finite wavelength of our control fields. Starting from a squeezed vacuum state, we apply sequences of alternating transfer pulses which allow us to climb the squeezed Fock state ladder, creating states up to excitations of n =6 with up to 8.7 dB of squeezing, as well as demonstrating superpositions of these states. These techniques offer access to new sets of states of the harmonic oscillator which may be applicable for precision metrology or quantum information science.
Institute of Scientific and Technical Information of China (English)
Zheng Rui; Liu Bang-Gui
2012-01-01
In order to gain a deeper understanding of the quantum criticality in the explicitly staggered dimerized Heisenberg models,we study a generalized staggered dimer model named the J0 J1-J2 model,which corresponds to the staggered J J’ model on a square lattice and a honeycomb lattice when J1/J0 equals 1 and 0,respectively.Using the quantum Monte Carlo method,we investigate all the quantum critical points of these models with J1/J0 changing from 0 to 1as a function of coupling ratio α =J2/J0.We extract all the critical values of the coupling ratio αc for these models,and we also obtain the critical exponents v,β/v,and η using different finite-size scaling ans(a)tz,.All these exponents are not consistent with the three-dimensional Heisenberg universality class,indicating some unconventional quantum ciritcial points in these models.
Franzrahe, K.; Henseler, P.; Ricci, A.; Strepp, W.; Sengupta, S.; Dreher, M.; Kircher, Chr.; Lohrer, M.; Quester, W.; Binder, K.; Nielaba, P.
2005-07-01
Quantum effects, structures and phase transitions in Nano-systems have been analyzed. An overview is given on the results of our computations on structural and elastic properties of model colloids, on phase transitions of model colloids in external fields, and on structural and electronic properties of stretched atomic wires.
Unitary approach to the quantum forced harmonic oscillator
2014-01-01
In this paper we introduce an alternative approach to studying the evolution of a quantum harmonic oscillator subject to an arbitrary time dependent force. With the purpose of finding the evolution operator, certain unitary transformations are applied successively to Schr\\"odinger's equation reducing it to its simplest form. Therefore, instead of solving the original Schr\\"odinger's partial differential equation in time and space the problem is replaced by a system of ordinary differential eq...
Dynamically self-regular quantum harmonic black holes
Directory of Open Access Journals (Sweden)
Euro Spallucci
2015-04-01
Full Text Available The recently proposed UV self-complete quantum gravity program is a new and very interesting way to envision Planckian/trans-Planckian physics. In this new framework, high energy scattering is dominated by the creation of micro black holes, and it is experimentally impossible to probe distances shorter than the horizon radius. In this letter we present a model which realizes this idea through the creation of self-regular quantum black holes admitting a minimal size extremal configuration. Their radius provides a dynamically generated minimal length acting as a universal short-distance cutoff. We propose a quantization scheme for this new kind of microscopic objects based on a Bohr-like approach, which does not require a detailed knowledge of quantum gravity. The resulting black hole quantum picture resembles the energy spectrum of a quantum harmonic oscillator. The mass of the extremal configuration plays the role of zero-point energy. Large quantum number re-establishes the classical black hole description. Finally, we also formulate a “quantum hoop conjecture” which is satisfied by all the mass eigenstates and sustains the existence of quantum black holes sourced by Gaussian matter distributions.
Ma, Yandong; Kou, Liangzhi; Li, Xiao; Dai, Ying; Heine, Thomas
2016-01-01
So far, several transition metal dichalcogenide (TMDC)-based two-dimensional (2D) topological insulators (TIs) have been discovered, all of them based on a tetragonal lattice. However, in 2D crystals, the hexagonal rather than the tetragonal symmetry is the most common motif. Here, based on first principles calculations, we propose a class of stable 2D TMDCs of composition MX2(M =Mo ,W ;X =S ,Se ,Te ) with a hexagonal lattice. They are all in the same stability range as other 2D TMDC allotropes that have been demonstrated experimentally, and they are identified to be practical 2D TIs with large band gaps ranging from 41 to 198 meV, making them suitable for applications at room temperature. Besides, in contrast to tetragonal 2D TMDCs, their hexagonal lattice will greatly facilitate the integration of theses novel TI state van der Waals crystals with other hexagonal or honeycomb materials and thus provide a route for 2D material-based devices for wider nanoelectronic and spintronic applications. The nontrivial band gaps of both WS e2 and WT e2 2D crystals are 198 meV, which are larger than that in any previously reported TMDC-based TIs. These large band gaps entirely stem from the strong spin orbit coupling strength within the d orbitals of Mo/W atoms near the Fermi level. Our findings broaden the scientific and technological impact of both 2D TIs and TMDCs.
Hsieh, Y. H.; Yu, Y. T.; Tuan, P. H.; Tung, J. C.; Huang, K. F.; Chen, Y. F.
2017-02-01
The trajectory equations for classical periodic orbits in the equilateral-triangular and circular billiards are systematically extracted from quantum stationary coherent states. The relationship between the phase factors of quantum stationary coherent states and the initial positions of classical periodic orbits is analytically derived. In addition, the stationary coherent states with noncoprime parametric numbers are shown to correspond to the multiple periodic orbits, which cannot be explicable in the one-particle picture. The stationary coherent states are further verified to be linked to the resonant modes that are generally observed in the experimental wave system excited by a localized and unidirectional source. The excellent agreement between the resonant modes and the stationary coherent states not only manifests the importance of classical features in experimental systems but also paves the way to manipulate the mesoscopic wave functions localized on the periodic orbits for applications.
Masuda, Hidetoshi; Sakai, Hideaki; Tokunaga, Masashi; Yamasaki, Yuichi; Miyake, Atsushi; Shiogai, Junichi; Nakamura, Shintaro; Awaji, Satoshi; Tsukazaki, Atsushi; Nakao, Hironori; Murakami, Youichi; Arima, Taka-hisa; Tokura, Yoshinori; Ishiwata, Shintaro
2016-01-01
For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.
Ross, Matthew R.
The primary focus of this work is the development of a mid-infrared pulse shaping system. The primary motivation for this system is for two-dimensional infrared (2DIR) spectroscopy, however, the mid-infrared pulse shaper also allows for more sophisticated spectroscopic experiments not previously attempted in the mid-infrared. Moreover, many can be implemented without changes or realignment of the optical setup. Example spectra are presented along with a discussion of capabilities and diagnostics. A second major project presented is 2DIR spectroscopy of iron pentacarbonyl, Fe(CO)5, a small metal carbonyl. This molecule undergoes Berry pseudorotation, a form of fluxtionality. This fast exchange of ligands mixes axial and equatorial modes and occurs on a timescale of picoseconds, too fast for NMR and other methods of measuring chemical structure and isomerization. Ultrafast chemical exchange spectroscopy, a measurement within 2DIR spectroscopy, is capable of resolving the time scales of this motion. We found that this process is affected by the solvent environment, specifically the solvent viscosity in alkanes and hydrogen bonding environments in alcohols. Lastly, a study is presented in which a series of synthetic metalloenzymes with a metal active site are studied by 2DIR spectroscopy. In this case a carbonyl is ligated to a copper-I atom in the active site, which then serves as our spectroscopic probe. We find, unexpectedly, that the shape of the carbonyl vibrational potential, as measured by the anharmonicity, is time-dependent. We attribute this to a geometrical rearrangement and are able to suggest that this effect is dependent on local site structure and dynamics and not significantly affected by electric potential near the peptide.
CSIR Research Space (South Africa)
Britton, JW
2012-04-01
Full Text Available apparatus, laser-cooled 9Be+ ions natu- rally form a stable 2D Coulomb crystal on a triangular lattice with 300 spins (Fig. 1). Each ion is spin-1/2 system (qubit) over which we exert high fidelity quantum control [26]. In this paper we demonstrate... as a function of the electric field intensity IR = ceo 2 jELj 2 = ceo2 jEU j 2 at the cen- ter of the laser beams. For qR = 4:8 and IR = 1 W/cm2 , Fo = 1:4 10 23 N. Stronger forces can be generated after experimental mod- ification to our...
The Two-Dimensional MnO2/Graphene Interface: Half-metallicity and Quantum Anomalous Hall State
Gan, Liyong
2015-10-07
We explore the electronic properties of the MnO2/graphene interface by first-principles calculations, showing that MnO2 becomes half-metallic. MnO2 in the MnO2/graphene/MnO2 system provides time-reversal and inversion symmetry breaking. Spin splitting by proximity occurs at the Dirac points and a topologically nontrivial band gap is opened, enabling a quantum anomalous Hall state. The half-metallicity, spin splitting, and size of the band gap depend on the interfacial interaction, which can be tuned by strain engineering.
Quantum optics. Quantum harmonic oscillator state synthesis by reservoir engineering.
Kienzler, D; Lo, H-Y; Keitch, B; de Clercq, L; Leupold, F; Lindenfelser, F; Marinelli, M; Negnevitsky, V; Home, J P
2015-01-02
The robust generation of quantum states in the presence of decoherence is a primary challenge for explorations of quantum mechanics at larger scales. Using the mechanical motion of a single trapped ion, we utilize reservoir engineering to generate squeezed, coherent, and displaced-squeezed states as steady states in the presence of noise. We verify the created state by generating two-state correlated spin-motion Rabi oscillations, resulting in high-contrast measurements. For both cooling and measurement, we use spin-oscillator couplings that provide transitions between oscillator states in an engineered Fock state basis. Our approach should facilitate studies of entanglement, quantum computation, and open-system quantum simulations in a wide range of physical systems. Copyright © 2015, American Association for the Advancement of Science.
A quantum mechanical model of "dark matter"
Belokurov, V V
2014-01-01
The role of singular solutions in some simple quantum mechanical models is studied. The space of the states of two-dimensional quantum harmonic oscillator is shown to be separated into sets of states with different properties.
Torrielli, Alessandro
2003-01-01
The results of our research on noncommutative perturbative quantum field theory and its relation to string theory are exposed with details. 1) We give an introduction to noncommutative quantum field theory and its derivation from open string theory in an antisymmetric background. 2) We perform a perturbative Wilson loop calculation for 2D NCYM. We compare the LCG results for the WML and the PV prescription. With WML the loop is well-defined and regular in the commutative limit. With PV the result is singular. This is intriguing: in the commutative theory their difference is related to topological excitations, moreover PV provides a point-like potential. 3) Commutative 2D YM exhibits an interplay between geometrical and U(N) gauge properties: in the exact expression of a Wilson loop with n windings a scaling intertwines n and N. In the NC case the interplay becomes tighter due to the merging of space-time and ``internal'' symmetries. Surprisingly, in our up to O(g^6) (and beyond) crossed graphs calculations the scaling we mentioned occurs for large n, N and theta. 4) We discuss the breakdown of perturbative unitarity of noncommutative electric-type QFT in the light of strings. We consider the analytic structure of string loop two-point functions suitably continuing them off-shell, and then study the Seiberg-Witten limit. In this way we pick up how the unphysical tachyonic branch cut appears in the NC field theory.
Torrielli, A
2003-01-01
The results of our research on noncommutative perturbative quantum field theory and its relation to string theory are exposed with details. 1) We give an introduction to noncommutative quantum field theory and its derivation from open string theory in an antisymmetric background. 2) We perform a perturbative Wilson loop calculation for 2D NCYM. We compare the LCG results for the WML and the PV prescription. With WML the loop is well-defined and regular in the commutative limit. With PV the result is singular. This is intriguing: in the commutative theory their difference is related to topological excitations, moreover PV provides a point-like potential. 3) Commutative 2D YM exhibits an interplay between geometrical and U(N) gauge properties: in the exact expression of a Wilson loop with n windings a scaling intertwines n and N. In the NC case the interplay becomes tighter due to the merging of space-time and ``internal'' symmetries. Surprisingly, in our up to O(g^6) (and beyond) crossed graphs calculations th...
Excitation with quantum light. I. Exciting a harmonic oscillator
Carreño, J. C. López; Laussy, F. P.
2016-12-01
We present a two-part study of the excitation of an optical target by quantum light. In this first part, we introduce the problematic and address the first case of interest, that of exciting the quantum harmonic oscillator, corresponding to, e.g., a single-mode passive cavity or a noninteracting bosonic field. We introduce a mapping of the Hilbert space that allows to chart usefully the accessible regions. We then consider the quantum excitation from single-photon sources in the form of a two-level system under various regimes of (classical) pumping: incoherent, coherent, and in the Mollow triplet regime. We close this first part with an overview of the material to be covered in the subsequent work.
Zhou, Liujiang; Shi, Wujun; Sun, Yan; Shao, Bin; Felser, Claudia; Yan, Binghai; Frauenheim, Thomas
2016-09-01
Quantum spin Hall (QSH) insulates exist in special two-dimensional (2D) semiconductors, possessing the quantized spin-Hall conductance that are topologically protected from backscattering. Based on the first-principles calculations, we predict a novel family of QSH insulators in 2D tantalum carbide halides TaCX (X = Cl, Br, and I) with unique rectangular lattice and large direct energy gaps. The mechanism for 2D QSH effect originates from an intrinsic d-d band inversion in the process of chemical bonding. Further, stain and intrinsic electric field can be used to tune the electronic structure and enhance the energy gap. TaCX nanoribbon, which has the single-Dirac-cone edge states crossing the bulk band gap, exhibits a linear dispersion with a high Fermi velocity comparable to that of graphene. These 2D materials with considerable nontrivial gaps promise great application potential in the new generation of dissipationless electronics and spintronics.
O2- -to-F- substitution on the quasi-two-dimensional quantum antiferromagnet (CuCl)LaNb2O7
Tassel, C.; Kobayashi, Y.; Mitsuoka, S.; Takeiri, F.; Ajiro, Y.; Kageyama, H.
2011-09-01
We present the preparation of the electron-doped quasi-two dimensional quantum antiferromagnet (CuCl)LaNb2O7 by two step-wise topochemical reactions. The first step involves a reductive fluorination of the insulating layered perovskite RbLaNb2O7 using polytetrafluoroethylene that allows electric conduction in the perovskite blocks. The product RbLaNb2O6F was then ion-exchanged with copper dichloride to yield (CuCl)LaNb2O6F. The synchrotron x-ray diffraction study indicates that the structure of the final compound is different from that of the pure (CuCl)LaNb2O7.
Exchange enhancement of the electron g-factor in a two-dimensional semimetal in HgTe quantum wells
Energy Technology Data Exchange (ETDEWEB)
Bovkun, L. S., E-mail: bovkun@ipmras.ru; Krishtopenko, S. S.; Zholudev, M. S.; Ikonnikov, A. V.; Spirin, K. E. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Dvoretsky, S. A.; Mikhailov, N. N. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Teppe, F.; Knap, W. [Universite Montpellier II, Laboratoire Charles Coulomb (L2C), UMR CNRS 5221, GIS-TERALAB (France); Gavrilenko, V. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)
2015-12-15
The exchange enhancement of the electron g-factor in perpendicular magnetic fields to 12 T in HgTe/CdHgTe quantum wells 20 nm wide with a semimetal band structure is studied. The electron effective mass and g-factor at the Fermi level are determined by analyzing the temperature dependence of the amplitude of Shubnikov–de Haas oscillation in weak fields and near odd Landau-level filling factors ν ≤ 9. The experimental values are compared with theoretical calculations performed in the one-electron approximation using the eight-band kp Hamiltonian. The found dependence of g-factor enhancement on the electron concentration is explained by changes in the contributions of hole- and electron-like states to exchange corrections to the Landau-level energies in the conduction band.
Finite-temperature scaling close to Ising-nematic quantum critical points in two-dimensional metals
Punk, Matthias
2016-11-01
We study finite-temperature properties of metals close to an Ising-nematic quantum critical point in two spatial dimensions. In particular we show that at any finite temperature there is a regime where order parameter fluctuations are characterized by a dynamical critical exponent z =2 , in contrast to z =3 found at zero temperature. Our results are based on a simple Eliashberg-type approach, which gives rise to a boson self-energy proportional to Ω /γ (T ) at small momenta, where γ (T ) is the temperature dependent fermion scattering rate. These findings might shed some light on recent Monte Carlo simulations at finite temperature, where results consistent with z =2 were found.
Directory of Open Access Journals (Sweden)
E Taghizdehsiskht
2013-09-01
Full Text Available In recent years, semiconductor nanostructures have become the model systems of choice for investigation of electrical conduction on short length scales. Quantum transport is studied in a two dimensional electron gas because of the combination of a large Fermi wavelength and large mean free path. In the present work, a numerical method is implemented in order to contribute to the understanding of quantum transport in narrow channels in different conditions of disorder and magnetic fields. We have used an approach that has proved to be very useful in describing mesoscopic transport. We have assumed zero temperature and phase coherent transport. By using the trick that a conductor connected to infinite leads can be replaced by a finite conductor with the effect of the leads incorporated through a 'self-energy' function, a convenient method was provided for evaluating the Green's function of the whole device numerically. Then, Fisher-Lee relations was used for calculating the transmission coefficients through coherent mesoscopic conductors. Our calculations were done in a model system with Hard-wall boundary conditions in the transverse direction, and the Anderson model of disorder was used in disordered samples. We have presented the results of quantum transport for different strengths of disorder and introduced magnetic fields. Our results confirmed the Landauer formalism for calculation of electronic transport. We observed that weak localization effect can be removed by application of a weak perpendicular magnetic field. Finally, we numerically showed the transition to the integral quantum Hall effect regime through the suppression of backscattering on a disordered model system by calculating the two terminal conductance of a quasi-one-dimensional quantum conductor as a strong magnetic field is applied. Our results showed that this regime is entered when there is a negligible overlap between electron edge states localized at opposite sides of
Dynamically self-regular quantum harmonic black holes
Spallucci, Euro
2015-01-01
The recently proposed UV self-complete quantum gravity program is a new and very interesting way to envision Planckian/trans-Planckian physics. in this new framework, high energy scattering is dominated by the creation of micro black holes, and it is experimentally impossible to probe distances shorter than the horizon radius. In this letter we present a model which realizes this idea through the creation of self-regular quantum black holes admitting a minimal size extremal configuration. Their radius provides a dynamically generated minimal length acting as a universal short-distance cut-off. We propose a quantisation scheme for this new kind of microscopic objects based on a Bohr-like approach, which does not require a detailed knowledge of quantum gravity. The resulting black hole quantum picture resembles the energy spectrum of a quantum harmonic oscillator. The mass of the extremal configuration plays the role of zero-point energy. Large quantum number re-establish the classical black hole description. F...
Nonequilibrium quantum fluctuation relations for harmonic systems in nonthermal environments
Pagel, D.; Nalbach, P.; Alvermann, A.; Fehske, H.; Thorwart, M.
2013-10-01
We formulate exact generalized nonequilibrium fluctuation relations for the quantum mechanical harmonic oscillator coupled to multiple harmonic baths. Each of the different baths is prepared in its own individual (in general nonthermal) state. Starting from the exact solution for the oscillator dynamics we study fluctuations of the oscillator position as well as of the energy current through the oscillator under general nonequilibrium conditions. In particular, we formulate a fluctuation-dissipation relation for the oscillator position autocorrelation function that generalizes the standard result for the case of a single bath at thermal equilibrium. Moreover, we show that the generating function for the position operator fulfils a generalized Gallavotti-Cohen-like relation. For the energy transfer through the oscillator, we determine the average energy current together with the current fluctuations. Finally, we discuss the generalization of the cumulant generating function for the energy transfer to nonthermal bath preparations.
Quantum Energy Teleportation with a Linear Harmonic Chain
Nambu, Yasusada
2010-01-01
A protocol of quantum energy teleportation is proposed for a one-dimensional harmonic chain. A coherent-state POVM measurement is performed to coupled oscillators of the chain in the ground state accompanied by energy infusion to the system. This measurement consumes a part of ground state entanglement. Depending on the measurement result, a displacement operation is performed on a distant oscillator accompanied by energy extraction from the zero-point fluctuation of the oscillator. We find that the amount of consumed entanglement is bounded from below by a positive value that is proportional to the amount of teleported energy.
Elementary derivation of the quantum propagator for the harmonic oscillator
Shao, Jiushu
2016-10-01
Operator algebra techniques are employed to derive the quantum evolution operator for the harmonic oscillator. The derivation begins with the construction of the annihilation and creation operators and the determination of the wave function for the coherent state as well as its time-dependent evolution, and ends with the transformation of the propagator in a mixed position-coherent-state representation to the desired one in configuration space. Throughout the entire procedure, besides elementary operator manipulations, it is only necessary to solve linear differential equations and to calculate Gaussian integrals.
Non-Markovian quantum Brownian motion of a harmonic oscillator
Energy Technology Data Exchange (ETDEWEB)
Tang, J.
1994-02-01
We apply the density-matrix method to the study of quantum Brownian motion of a harmonic oscillator coupled to a heat bath, a system investigated previously by Caldeira and Leggett using a different method. Unlike the earlier work, in our derivation of the master equation the non-Markovian terms are maintained. Although the same model of interaction is used, discrepancy is found between their results and our equation in the Markovian limit. We also point out that the particular interaction model used by both works cannot lead to the phenomenological generalized Langevin theory of Kubo.
Pakmehr, Mehdi; Bruene, Christoph; Buhmann, Hartmut; Molenkamp, Laurens; McCombe, Bruce
2015-03-01
HgTe quantum wells (QWs) have shown a number of interesting phenomena over the past 20 years, most recently the first two-dimensional topological insulating state. We have studied thermoelectric photovoltages of 2D electrons in a 6.1 nm wide HgTe quantum well induced by cyclotron resonance absorption (B = 2 - 5 T) of a focused THz laser beam. We have estimated thermo-power coefficients by detailed analysis of the beam profile at the sample surface and the photovoltage signals developed across various contacts of a large Hall bar structure at a bath temperature of 1.6 K. We obtain reasonable values of the magneto-thermopower coefficients. Work at UB was supported by NSF DMR 1008138 and the Office of the Provost, and at the University of Wuerzburg by DARPA MESO Contract N6601-11-1-4105, by DFG Grant HA5893/4-1 within SPP 1666 and the Leibnitz Program, and the EU ERC-AG Program (Project 3-TOP.
Energy Technology Data Exchange (ETDEWEB)
Zhu, Rui, E-mail: rzhu@scut.edu.cn; Dai, Jiao-Hua [Department of Physics, South China University of Technology, Guangzhou 510641 (China); Guo, Yong [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)
2015-04-28
Interference between different quantum paths can generate Fano resonance. One of the examples is transport through a quasibound state driven by a time-dependent scattering potential. Previously it is found that Fano resonance occurs as a result of energy matching in one-dimensional systems. In this work, we demonstrate that when transverse motion is present, Fano resonance occurs precisely at the wavevector matching situation. Using the Floquet scattering theory, we considered the transport properties of a nonadiabatic time-dependent well both in a two-dimensional electron gas and monolayer graphene structure. Dispersion of the quasibound state of a static quantum well is obtained with transverse motion present. We found that Fano resonance occurs when the wavevector in the transport direction of one of the Floquet sidebands is exactly identical to that of the quasibound state in the well at equilibrium and follows the dispersion pattern of the latter. To observe the Fano resonance phenomenon in the transmission spectrum, we also considered the pumped shot noise properties when time and spatial symmetry secures vanishing current in the considered configuration. Prominent Fano resonance is found in the differential pumped shot noise with respect to the reservoir Fermi energy.
Bonatsos, Dennis; Kolokotronis, P; Lenis, D; Bonatsos, Dennis
1994-01-01
The symmetry algebra of the two-dimensional anisotropic quantum harmonic oscillator with rational ratio of frequencies, which is characterizing ``pancake'' nuclei, is identified as a non-linear extension of the u(2) algebra. The finite dimensional representation modules of this algebra are studied and the energy eigenvalues are determined using algebraic methods of general applicability to quantum superintegrable systems. For labelling the degenerate states an ``angular momentum'' operator is introduced, the eigenvalues of which are roots of appropriate generalized Hermite polynomials. In the special case with frequency ratio 2:1 the resulting algebra is identified as the finite W algebra W_3^{(2)}.
Energy Technology Data Exchange (ETDEWEB)
Bankura, Arindam; Chandra, Amalendu, E-mail: amalen@iitk.ac.in [Department of Chemistry, Indian Institute of Technology, Kanpur 208016 (India)
2015-01-28
The dynamics of proton transfer (PT) through hydrogen bonds in a two-dimensional water layer confined between two graphene sheets at room temperature are investigated through ab initio and quantum-classical simulations. The excess proton is found to be mostly solvated as an Eigen cation where the hydronium ion donates three hydrogen bonds to the neighboring water molecules. In the solvation shell of the hydronium ion, the three coordinated water molecules with two donor hydrogen bonds are found to be properly presolvated to accept a proton. Although no hydrogen bond needs to be broken for transfer of a proton to such presolvated water molecules from the hydronium ion, the PT rate is still found to be not as fast as it is for one-dimensional chains. Here, the PT is slowed down as the probability of finding a water with two donor hydrogen bonds in the solvation shell of the hydronium ion is found to be only 25%-30%. The hydroxide ion is found to be solvated mainly as a complex anion where it accepts four H-bonds through its oxygen atom and the hydrogen atom of the hydroxide ion remains free all the time. Here, the presolvation of the hydroxide ion to accept a proton requires that one of its hydrogen bonds is broken and the proton comes from a neighboring water molecule with two acceptor and one donor hydrogen bonds. The coordination number reduction by breaking of a hydrogen bond is a slow process, and also the population of water molecules with two acceptor and one donor hydrogen bonds is only 20%-25% of the total number of water molecules. All these factors together tend to slow down the hydroxide ion migration rate in two-dimensional water layers compared to that in three-dimensional bulk water.
Bankura, Arindam; Chandra, Amalendu
2015-01-01
The dynamics of proton transfer (PT) through hydrogen bonds in a two-dimensional water layer confined between two graphene sheets at room temperature are investigated through ab initio and quantum-classical simulations. The excess proton is found to be mostly solvated as an Eigen cation where the hydronium ion donates three hydrogen bonds to the neighboring water molecules. In the solvation shell of the hydronium ion, the three coordinated water molecules with two donor hydrogen bonds are found to be properly presolvated to accept a proton. Although no hydrogen bond needs to be broken for transfer of a proton to such presolvated water molecules from the hydronium ion, the PT rate is still found to be not as fast as it is for one-dimensional chains. Here, the PT is slowed down as the probability of finding a water with two donor hydrogen bonds in the solvation shell of the hydronium ion is found to be only 25%-30%. The hydroxide ion is found to be solvated mainly as a complex anion where it accepts four H-bonds through its oxygen atom and the hydrogen atom of the hydroxide ion remains free all the time. Here, the presolvation of the hydroxide ion to accept a proton requires that one of its hydrogen bonds is broken and the proton comes from a neighboring water molecule with two acceptor and one donor hydrogen bonds. The coordination number reduction by breaking of a hydrogen bond is a slow process, and also the population of water molecules with two acceptor and one donor hydrogen bonds is only 20%-25% of the total number of water molecules. All these factors together tend to slow down the hydroxide ion migration rate in two-dimensional water layers compared to that in three-dimensional bulk water.
Quantum chaos for two-dimensional Sinai billiard%二维Sinai台球系统的量子混沌研究
Institute of Scientific and Technical Information of China (English)
秦陈陈; 杨双波
2014-01-01
We study the classical and quantum correspondence for a two-dimensional Sinai billiard system. By using the Stationary state expansion method and Gutzwiller’s periodic orbit theory, we analyze the quantum length spectrum obtained through the Fourier transformation of the quantum density of state for the Sinai billiard system, and by comparing the peak position with the length of the classical periodic orbit we find their excellent correspondence. We observe that some quantum states are localized near some short period orbits, forming the quantum scarred states or superscarred states. In this paper we also investigate the nearest-neighbor spacing distribution of levels for both concentric and nonconcentric Sinai billiard systems, and find that the concentric Sinai billiard system is nearintegrable, and for the nonconcentric Sinai billiard system withϑ=3π/8 its nearest-neighbor spacing distribution of levels transits from nearintegrable to the Wigner distribution as the distance between the two centers increases.%研究了二维Sinai台球系统的经典与量子的对应关系，运用定态展开法和Gutzwiller的周期轨道理论对Sinai台球系统的态密度经傅里叶变换得到的量子长度谱进行分析，并把量子长度谱中峰的位置与其所对应的经典体系的周期轨道长度做对比，发现两者之间存在很好的对应关系。观察到了一些量子态局域在短周期轨道附近形成量子scarred态或量子superscarred态。还研究了同心与非同心Sinai台球系统的能级最近邻间距分布，发现同心Sinai台球系统是近可积的，非同心Sinai台球系统在θ=3π/8下，随两中心间距离的增加，能级最近邻间距分布将由近可积向维格那分布过渡。
Quantum Encoding and Entanglement in Terms of Phase Operators Associated with Harmonic Oscillator
Singh, Manu Pratap; Rajput, B. S.
2016-10-01
Realization of qudit quantum computation has been presented in terms of number operator and phase operators associated with one-dimensional harmonic oscillator and it has been demonstrated that the representations of generalized Pauli group, viewed in harmonic oscillator operators, allow the qudits to be explicitly encoded in such systems. The non-Hermitian quantum phase operators contained in decomposition of the annihilation and creation operators associated with harmonic oscillator have been analysed in terms of semi unitary transformations (SUT) and it has been shown that the non-vanishing analytic index for harmonic oscillator leads to an alternative class of quantum anomalies. Choosing unitary transformation and the Hermitian phase operator free from quantum anomalies, the truncated annihilation and creation operators have been obtained for harmonic oscillator and it has been demonstrated that any attempt of removal of quantum anomalies leads to absence of minimum uncertainty.
Energy Technology Data Exchange (ETDEWEB)
Griesbeck, Michael
2012-11-22
Since many years there has been great effort to explore the spin dynamics in low-dimensional electron systems embedded in GaAs/AlGaAs based heterostructures for the purpose of quantum computation and spintronics applications. Advances in technology allow for the design of high quality and well-defined two-dimensional electron systems (2DES), which are perfectly suited for the study of the underlying physics that govern the dynamics of the electron spin system. In this work, spin dynamics in high-mobility 2DES is studied by means of the all-optical time-resolved Kerr/Faraday rotation technique. In (001)-grown 2DES, a strong in-plane spin dephasing anisotropy is studied, resulting from the interference of comparable Rashba and Dresselhaus contributions to the spin-orbit field (SOF). The dependence of this anisotropy on parameters like the confinement length of the 2DES, the sample temperature, as well as the electron density is demonstrated. Furthermore, coherent spin dynamics of an ensemble of ballistically moving electrons is studied without and within an applied weak magnetic field perpendicular to the sample plane, which forces the electrons to move on cyclotron orbits. Finally, strongly anisotropic spin dynamics is investigated in symmetric (110)-grown 2DES, using the resonant spin amplification method. Here, extremely long out-of-plane spin dephasing times can be achieved, in consequence of the special symmetry of the Dresselhaus SOF.
Okada, Makiko; Tanaka, Hidekazu; Kurita, Nobuyuki; Johmoto, Kohei; Uekusa, Hidehiro; Miyake, Atsushi; Tokunaga, Masashi; Nishimoto, Satoshi; Nakamura, Masaaki; Jaime, Marcelo; Radtke, Guillaume; Saúl, Andrés
2016-09-01
We synthesized single crystals of composition Ba2CuSi2O6Cl2 and investigated their quantum magnetic properties. The crystal structure is closely related to that of the quasi-two-dimensional (2D) dimerized magnet BaCuSi2O6 also known as Han purple. Ba2CuSi2O6Cl2 has a singlet ground state with an excitation gap of Δ /kB=20.8 K. The magnetization curves for two different field directions almost perfectly coincide when normalized by the g factor except for a small jump anomaly for a magnetic field perpendicular to the c axis. The magnetization curve with a nonlinear slope above the critical field is in excellent agreement with exact-diagonalization calculations based on a 2D coupled spin-dimer model. Individual exchange constants are also evaluated using density functional theory (DFT). The DFT results demonstrate a 2D exchange network and weak frustration between interdimer exchange interactions, supported by weak spin-lattice coupling implied from our magnetostriction data. The magnetic-field-induced spin ordering in Ba2CuSi2O6Cl2 is described as the quasi-2D Bose-Einstein condensation of triplets.
Phase-space treatment of the driven quantum harmonic oscillator
Indian Academy of Sciences (India)
DIÓGENES CAMPOS
2017-03-01
A recent phase-space formulation of quantum mechanics in terms of the Glauber coherent states is applied to study the interaction of a one-dimensional harmonic oscillator with an arbitrary time-dependent force. Wave functions of the simultaneous values of position q and momentum p are deduced, which in turn give the standard position and momentum wave functions, together with expressions for the ηth derivatives with respect to q and p, respectively. Afterwards, general formulae for momentum, position and energy expectation values are obtained, and the Ehrenfest theorem is verified. Subsequently, general expressions for the cross-Wigner functions are deduced. Finally, a specific example is considered to numerically and graphically illustrate some results.
Repulsively interacting fermions in a two-dimensional deformed trap with spin-orbit coupling
DEFF Research Database (Denmark)
Marchukov, O. V.; Fedorov, D. V.; Jensen, A. S.
2015-01-01
We investigate a two-dimensional system of fermions with two internal (spin) degrees of freedom. It is confined by a deformed harmonic trap and subject to a Zeeman field, Rashba or Dresselhaus one-body spin-orbit couplings and two-body short range repulsion. We obtain self-consistent mean-field $...... that cold atoms may be used to study quantum chaos both in the presence and absence of interactions....
Quantum, classical and semiclassical analyses of photon statistics in harmonic generation
Bajer, J; Bajer, Jiri; Miranowicz, Adam
2001-01-01
In this review, we compare different descriptions of photon-number statistics in harmonic generation processes within quantum, classical and semiclassical approaches. First, we study the exact quantum evolution of the harmonic generation by applying numerical methods including those of Hamiltonian diagonalization and global characteristics. We show explicitly that the harmonic generations can indeed serve as a source of nonclassical light. Then, we demonstrate that the quasi-stationary sub-Poissonian light can be generated in these quantum processes under conditions corresponding to the so-called no-energy-transfer regime known in classical nonlinear optics. By applying method of classical trajectories, we demonstrate that the analytical predictions of the Fano factors are in good agreement with the quantum results. On comparing second and higher harmonic generations in the no-energy-transfer regime, we show that the highest noise reduction is achieved in third-harmonic generation with the Fano-factor of the ...
Tokuhisa, Atsushi; Taka, Junichiro; Kono, Hidetoshi; Go, Nobuhiro
2012-01-01
A new two-step algorithm is developed for reconstructing the three-dimensional diffraction intensity of a globular biological macromolecule from many experimentally measured quantum-noise-limited two-dimensional X-ray laser diffraction patterns, each for an unknown orientation. The first step is classification of the two-dimensional patterns into groups according to the similarity of direction of the incident X-rays with respect to the molecule and an averaging within each group to reduce the noise. The second step is detection of common intersecting circles between the signal-enhanced two-dimensional patterns to identify their mutual location in the three-dimensional wavenumber space. The newly developed algorithm enables one to detect a signal for classification in noisy experimental photon-count data with as low as ∼0.1 photons per effective pixel. The wavenumber of such a limiting pixel determines the attainable structural resolution. From this fact, the resolution limit due to the quantum noise attainable by this new method of analysis as well as two important experimental parameters, the number of two-dimensional patterns to be measured (the load for the detector) and the number of pairs of two-dimensional patterns to be analysed (the load for the computer), are derived as a function of the incident X-ray intensity and quantities characterizing the target molecule. PMID:22514069
The Large-Volume Limit of a Quantum Tetrahedron is a Quantum Harmonic Oscillator
Schliemann, John
2013-01-01
It is shown that the volume operator of a quantum tetrahedron is, in the sector of large eigenvalues, accurately described by a quantum harmonic oscillator. This result relies on the fact that (i) the volume operator couples only neighboring states of its standard basis, and (ii) its matrix elements show a unique maximum as a function of internal angular momentum quantum numbers. These quantum numbers, considered as a continuous variable, are the coordinate of the oscillator describing its quadratic potential, while the corresponding derivative defines a momentum operator. We also analyze the scaling properties of the oscillator parameters as a function of the size of the tetrahedron, and the role of different angular momentum coupling schemes.
On quantum harmonic oscillator being subjected to absolute potential state
Indian Academy of Sciences (India)
SWAMI NITYAYOGANANDA
2017-01-01
In a quantum harmonic oscillator (QHO), the energy of the oscillator increases with increased frequency. In this paper, assuming a boundary condition that the product of momentum and position, or the product of energy density and position remains constant in the QHO, it is established that a particle subjected to increasing frequencies becomes gradually subtler to transform into a very high dormant potential energy. This very high dormant potential energy is referred to as ‘like-potential’ energy in this paper. In the process a new wave function is generated. This new function, which corresponds to new sets of particles, has scope to raise the quantum oscillator energy (QOE) up to infinity. It is proposed to show that this high energy does not get cancelled but remainsdormant. Further, it is proposed that the displacement about the equilibrium goes to zero when the vibration of the oscillator stops and then the QOE becomes infinity – this needs further research. The more the QOE, the greaterwill be the degree of dormancy. A simple mathematical model has been derived here to discuss the possibilities that are involved in the QHO under the above-mentioned boundary conditions.
On quantum harmonic oscillator being subjected to absolute potential state
Nityayogananda, Swami
2017-01-01
In a quantum harmonic oscillator (QHO), the energy of the oscillator increases with increased frequency. In this paper, assuming a boundary condition that the product of momentum and position, or the product of energy density and position remains constant in the QHO, it is established that a particle subjected to increasing frequencies becomes gradually subtler to transform into a very high dormant potential energy. This very high dormant potential energy is referred to as `like-potential' energy in this paper. In the process a new wave function is generated. This new function, which corresponds to new sets of particles, has scope to raise the quantum oscillator energy (QOE) up to infinity. It is proposed to show that this high energy does not get cancelled but remains dormant. Further, it is proposed that the displacement about the equilibrium goes to zero when the vibration of the oscillator stops and then the QOE becomes infinity - this needs further research. The more the QOE, the greater will be the degree of dormancy. A simple mathematical model has been derived here to discuss the possibilities that are involved in the QHO under the above-mentioned boundary conditions.
Chou, C H; Yu, T; Chou, Chung-Hsien; Yu, Ting
2007-01-01
In this paper we derive an exact master equation for two coupled quantum harmonic oscillators interacting via bilinear coupling with a common environment made up of many harmonic oscillators at arbitrary temperature for a general spectral density function. We first show a simple derivation based on the observation that the two harmonic oscillator model can be effectively mapped into that of a single harmonic oscillator in a general environment plus a free harmonic oscillator. Since the exact one harmonic oscillator master equation is known [Hu, Paz and Zhang, Phys. Rev. D \\textbf{45}, 2843 (1992)], the exact master equation with all its coefficients for this two harmonic oscillator model can be easily deduced from the known results of the single harmonic oscillator case. In the second part we give an influence functional treatment of this model and provide explicit expressions for the evolution operator of the reduced density matrix which are useful for the study of decoherence and disentanglement issues. We ...
Effect of the shape of quantum dots on the third-harmonic generations
Li, Keyin; Guo, Kangxian; Liang, Litao
2017-02-01
The effect of the shape of quantum dots on the third-harmonic generations is theoretically investigated. Using the effective-mass approximation, calculations are performed employing methods of both the compact-density-matrix and the matrix diagonalization. We discuss the properties of the third-harmonic generations (THG) coefficients as a function of the incident photon frequency in elliptic and triangular shaped quantum dots. The results reveal that the shape of quantum dots has a great influence on the third-harmonic generations.
Ikhdair, Sameer M
2012-01-01
We study the effects of the perpendicular magnetic and Aharonov-Bohm (AB) flux fields on the energy levels of a two-dimensional (2D) Klein-Gordon (KG) particle subjects to equal scalar and vector pseudo-harmonic oscillator (PHO). We calculate the exact energy eigenvalues and normalized wave functions in terms of chemical potential parameter, magnetic field strength, AB flux field and magnetic quantum number by means of the Nikiforov-Uvarov (NU) method. The non-relativistic limit, PHO and harmonic oscillator solutions in the existence and absence of external fields are also obtained.
Harmonic oscillator in Snyder space: The classical case and the quantum case
Indian Academy of Sciences (India)
Carlos Leiva
2010-02-01
The harmonic oscillator in Snyder space is investigated in its classical and quantum versions. The classical trajectory is obtained and the semiclassical quantization from the phase space trajectories is discussed. An effective cut-off to high frequencies is found. The quantum version is developed and an equivalent usual harmonic oscillator is obtained through an effective mass and an effective frequency introduced in the model. This modified parameters give us a modified energy spectrum also.
Osserman, Robert
2011-01-01
The basic component of several-variable calculus, two-dimensional calculus is vital to mastery of the broader field. This extensive treatment of the subject offers the advantage of a thorough integration of linear algebra and materials, which aids readers in the development of geometric intuition. An introductory chapter presents background information on vectors in the plane, plane curves, and functions of two variables. Subsequent chapters address differentiation, transformations, and integration. Each chapter concludes with problem sets, and answers to selected exercises appear at the end o
Juday, Richard D. (Inventor)
1992-01-01
A two-dimensional vernier scale is disclosed utilizing a cartesian grid on one plate member with a polar grid on an overlying transparent plate member. The polar grid has multiple concentric circles at a fractional spacing of the spacing of the cartesian grid lines. By locating the center of the polar grid on a location on the cartesian grid, interpolation can be made of both the X and Y fractional relationship to the cartesian grid by noting which circles coincide with a cartesian grid line for the X and Y direction.
Spin transport of the frustrated quasi-two-dimensional XY-like antiferromagnet
Lima, L. S.
2017-01-01
We use the Self Consistent Harmonic Approximation together with the Kubo formalism of the Linear Response Theory to study the spin transport in the two-dimensional frustrated Heisenberg antiferromagnet in a square lattice with easy-plane ion single anisotropy. The regular part of the spin conductivity σreg(ω) is determined for several values of the critical ion single parameter Dc, that separates the low D region from the large D quantum paramagnetic phase. We have obtained an abrupt change in the spin conductivity in the discontinuity points of the graphic Dc vs. η, where the system presents a quantum phase transition.
Harmonic bath averaged Hamiltonian: an efficient tool to capture quantum effects of large systems.
Yang, Yonggang; Liu, Xiaomeng; Meuwly, Markus; Xiao, Liantuan; Jia, Suotang
2012-11-26
Starting from a reaction path Hamiltonian, a suitably reduced harmonic bath averaged Hamiltonian is derived by averaging over all the normal mode coordinates. Generalization of the harmonic bath averaged Hamiltonian to any dimensions are performed and the feasibility to use a linear reaction path/surface are investigated and discussed. By use of a harmonic bath averaged Hamiltonian, the tunneling splitting and proton transfer dynamics of malonaldehyde is briefly discussed and shows that the harmonic bath averaged Hamiltonian is an efficient tool to capture quantum effects in larger systems.
Phase diagram of a two-dimensional liquid in GaAs/AlxGa1-xAs biased double quantum wells
DEFF Research Database (Denmark)
Timofeev, V. B.; Larionov, A. V.; Alessi, M. G.;
2000-01-01
densities, P, and temperatures, T. For increasing P or decreasing T, a sharp transition from two gases of photoexcited electrons and holes, spatially separated and confined in the two wells, to two two-dimensional (2D) liquids has been observed. The gas-to-2D-liquid transition is evidenced by a strong...
Quantum Electrodynamics Basis of Classical-Field High-Harmonic Generation Theory
Institute of Scientific and Technical Information of China (English)
王兵兵; 高靓辉; 傅盘铭; 郭东升; R. R. Freeman
2001-01-01
From the nonperturbative quantum electrodynamics theory, we derive the Landau-Dykhne formula which represents the quantum-mechanical formulation of the three-step model. These studies provide a basis for the classical-field approaches to high-order harmonic generation and justify some assumptions used in classical-field modelling.
Chou, Chung-Hsien; Yu, Ting; Hu, B L
2008-01-01
In this paper we derive an exact master equation for two coupled quantum harmonic oscillators interacting via bilinear coupling with a common environment at arbitrary temperature made up of many harmonic oscillators with a general spectral density function. We first show a simple derivation based on the observation that the two harmonic oscillator model can be effectively mapped into that of a single harmonic oscillator in a general environment plus a free harmonic oscillator. Since the exact one harmonic oscillator master equation is available [B. L. Hu, J. P. Paz, and Y. Zhang, Phys. Rev. D 45, 2843 (1992)], the exact master equation with all its coefficients for this two harmonic oscillator model can be easily deduced from the known results of the single harmonic oscillator case. In the second part we give an influence functional treatment of this model and provide explicit expressions for the evolutionary operator of the reduced density matrix which are useful for the study of decoherence and disentanglement issues. We show three applications of this master equation: on the decoherence and disentanglement of two harmonic oscillators due to their interaction with a common environment under Markovian approximation, and a derivation of the uncertainty principle at finite temperature for a composite object, modeled by two interacting harmonic oscillators. The exact master equation for two, and its generalization to N, harmonic oscillators interacting with a general environment are expected to be useful for the analysis of quantum coherence, entanglement, fluctuations, and dissipation of mesoscopic objects toward the construction of a theoretical framework for macroscopic quantum phenomena.
Phase-dependent quantum interference between different pathways in bichromatic harmonic generation
Institute of Scientific and Technical Information of China (English)
Cai Jun; Wang Li-Ming; Qiao Hao-Xue
2009-01-01
This paper studies the harmonic generation of the hydrogen atom subjected to a collinear bichromatic laser field by numerically solving the time-dependent Schr(o)dinger equation using the split-operator pseudo-spectral method.By adding a frequency variation to the additional field,the contributions of different pathways to particular order harmonic generation can be isolated.The quantum interference pattern between harmonic pathways,which influences the harmonic intensity,is found to be either constructive or destructive with respect to different relative phase of the two field components.Detailed description of up to the 35th-order harmonics and the harmonic pathways for a wide range of field parameters is presented.
The performance characteristics of an irreversible quantum Otto harmonic refrigeration cycle
Institute of Scientific and Technical Information of China (English)
HE JiZhou; HE Xian; TANG Wei
2009-01-01
In this paper,an irreversible quantum Otto refrigeration cycle working with harmonic systems is estab-lished.Base on Heisenberg quantum master equation,the equations of motion for the set of harmonic systems thermodynamic observables are derived.The simulated diagrams of the quantum Otto refrig-eration cycle are plotted.The relationship between average power of friction,cooling rate,power input,and the time of adiabatic process is analyzed by using numerical calculation.Moreover,the influence of the heat conductance and the time of iso-frequency process on the performance of the cycle is dis-cussed.
The performance characteristics of an irreversible quantum Otto harmonic refrigeration cycle
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In this paper, an irreversible quantum Otto refrigeration cycle working with harmonic systems is established. Base on Heisenberg quantum master equation, the equations of motion for the set of harmonic systems thermodynamic observables are derived. The simulated diagrams of the quantum Otto refrigeration cycle are plotted. The relationship between average power of friction, cooling rate, power input, and the time of adiabatic process is analyzed by using numerical calculation. Moreover, the influence of the heat conductance and the time of iso-frequency process on the performance of the cycle is discussed.
Two-dimensional optical spectroscopy
Cho, Minhaeng
2009-01-01
Discusses the principles and applications of two-dimensional vibrational and optical spectroscopy techniques. This book provides an account of basic theory required for an understanding of two-dimensional vibrational and electronic spectroscopy.
(3+1)-Dimensional Quantum Mechanics from Monte Carlo Hamiltonian: Harmonic Oscillator
Institute of Scientific and Technical Information of China (English)
LUO Xiang-Qian; XU Hao; YANG Jie-Chao; WANG Yu-Li; CHANG Di; LIN Yin; Helmut Kroger
2001-01-01
In Lagrangian formulation, it is extremely difficult to compute the excited spectrum and wavefunctions ora quantum theory via Monte Carlo methods. Recently, we developed a Monte Carlo Hamiltonian method for investigating this hard problem and tested the algorithm in quantum-mechanical systems in 1+1 and 2t1 dimensions. In this paper we apply it to the study of thelow-energy quantum physics of the (3+1)-dimensional harmonic oscillator.``
On the Bandgap quantum coupler and the harmonic oscillator interacting with a reservoir
Quijas, P C G
2007-01-01
In order to be able to study dissipation, the interaction between a single system and their environment was introduced in quantum mechanics. Master and quantum Langeving equations was derived and, also, decoherence was studied using this approach. One of the most used model in this field of research is a single harmonic oscillator interacting with an infinite number of harmonic oscillators. In this work we analytically solve, with the evolution operator method, the Schrodinger equation for this model in the case of resonance. Also we address a different aspect of the quantum computing with linear optics. That is, we propose the linear bandgap quantum coupler, in the cases N=2 and N=3, to generate a new phase operator $U_{dp}^{\\pi} $ working on the two and three qubits basis like an alternative realization of a quantum phase gate.
Exact diagonalization of the D-dimensional spatially confined quantum harmonic oscillator
Directory of Open Access Journals (Sweden)
Kunle Adegoke
2016-01-01
Full Text Available In the existing literature various numerical techniques have been developed to quantize the confined harmonic oscillator in higher dimensions. In obtaining the energy eigenvalues, such methods often involve indirect approaches such as searching for the roots of hypergeometric functions or numerically solving a differential equation. In this paper, however, we derive an explicit matrix representation for the Hamiltonian of a confined quantum harmonic oscillator in higher dimensions, thus facilitating direct diagonalization.
Quantum-orbit analysis of high-order harmonic generation by resonant plasmon field enhancement
Shaaran, T; Lewenstein, M
2012-01-01
We perform a detailed analysis of high-order harmonic generation (HHG) in atoms within the strong field approximation (SFA) by considering spatially inhomogeneous monochromatic laser fields. We investigate how the individual pairs of quantum orbits contribute to the harmonic spectra. We show that in the case of inhomogeneous fields, the electron tunnels with two different canonical momenta. One of them leads to a higher cutoff and the other one develops a lower cutoff. Furthermore, we demonstrate that the quantum orbits have a very different behavior in comparison to the homogeneous field. We also conclude that in the case of the inhomogeneous fields, both odd and even harmonics are present in the HHG spectra. Within our model, we show that the HHG cutoff extends far beyond the semiclassical cutoff as a function of inhomogeneity strength. Our findings are in good agreement both with quantum mechanical and classical models.
Ground-state isolation and discrete flows in a rationally extended quantum harmonic oscillator
Cariñena, José F
2016-01-01
Ladder operators for the simplest version of a rationally extended quantum harmonic oscillator (REQHO) are constructed by applying a Darboux transformation to the quantum harmonic oscillator system. It is shown that the physical spectrum of the REQHO carries a direct sum of a trivial and an infinite-dimensional irreducible representation of the polynomially deformed bosonized osp(1|2) superalgebra. In correspondence with this the ground state of the system is isolated from other physical states but can be reached by ladder operators via non-physical energy eigenstates, which belong to either an infinite chain of similar eigenstates or to the chains with generalized Jordan states. We show that the discrete chains of the states generated by ladder operators and associated with physical energy levels include six basic generalized Jordan states, in comparison with the two basic Jordan states entering in analogous discrete chains for the quantum harmonic oscillator.
Spatiotemporal separation of high harmonic radiation into two quantum path components
Energy Technology Data Exchange (ETDEWEB)
Gaarde, M. B.; Salin, F.; Constant, E.; Balcou, Ph.; Schafer, K. J.; Kulander, K. C.; L’Huillier, A.
1999-02-01
We present a spatio-temporal analysis of high harmonic generation, showing evidence for the presence of several quantum path contributions to the atomic dipole moment. We show that the harmonic radiation can largely be described as a sum of two fields having a phase proportional to the intensity of the generating field. We compare our results to recent experimental results demonstrating this separation. We show how the temporal and spatial coherence properties are influenced by this effect, and discuss how it could be used to obtain better control of the generated harmonic radiation.
A diffusion quantum Monte Carlo study of geometries and harmonic frequencies of molecules
Lu, Shih-I.
2004-01-01
This article describes an approach in determination of equilibrium geometries and harmonic frequencies of molecules by the Ornstein-Uhlenbeck diffusion quantum Monte Carlo method based on the floating spherical Gaussians. In conjunction with a projected and renormalized Hellmann-Feynman gradient and an electronic energy at variational Monte Carlo and diffusion quantum Monte Carlo, respectively, the quasi-Newton algorithm implemented with the Broyden-Fletcher-Goldfarb-Shanno updated Hessian was used to find the optimized molecular geometry. We applied this approach to N2 and H2O molecules. The geometry and harmonic frequencies calculated were consistent with some sophisticated ab initio calculated values within reasonable statistical uncertainty.
Andrews, David L.; Romero, Luciana C. Davila
2009-01-01
The dynamical behaviour of simple harmonic motion can be found in numerous natural phenomena. Within the quantum realm of atomic, molecular and optical systems, two main features are associated with harmonic oscillations: a finite ground-state energy and equally spaced quantum energy levels. Here it is shown that there is in fact a one-to-one…
Energy Technology Data Exchange (ETDEWEB)
Mohammadkhani, R., E-mail: rmkhani@znu.ac.ir; Hassanloo, Gh.
2014-11-01
We have studied the tunneling conductance of a clean two dimensional electron gas/p- wave superconductor junction with Rashba spin–orbit coupling (RSOC) which is present in the normal layer and at the interface. Using the extended Blonder–Tinkham–Klapwijk formalism we have found that the subgap conductance peaks are shifted to a nonzero bias by RSOC at the interface which are the same as Ref. [1]. It is shown that for low insulating barrier and in the absence of the interface RSOC, the tunneling conductance decreases within energy gap with increasing of the RSOC in the normal layer while for high insulating barrier it enhances by increase of the RSOC. We have also shown that the RSOC inside the normal cannot affect the location of the subgap conductance peaks shifted by the interface RSOC.
On a Hidden Symmetry of Quantum Harmonic Oscillators
Lopez, Raquel M; Vega-Guzman, Jose M
2011-01-01
We present a six parameter family of the square integrable wave functions for the linear harmonic oscillator, which cannot be obtained by the standard separation of variables. They are found by the action of corresponding maximal kinematical invariance group on the standard solutions. Some possible applications are briefly discussed.
López-Ruiz, F. F.; Guerrero, J.; Aldaya, V.; Cossío, F.
2012-08-01
Using a quantum version of the Arnold transformation of classical mechanics, all quantum dynamical systems whose classical equations of motion are non-homogeneous linear second-order ordinary differential equations (LSODE), including systems with friction linear in velocity such as the damped harmonic oscillator, can be related to the quantum free-particle dynamical system. This implies that symmetries and simple computations in the free particle can be exported to the LSODE-system. The quantum Arnold transformation is given explicitly for the damped harmonic oscillator, and an algebraic connection between the Caldirola-Kanai model for the damped harmonic oscillator and the Bateman system will be sketched out.
Falomir, H.; Pisani, P. A. G.; Vega, F.; Cárcamo, D.; Méndez, F.; Loewe, M.
2016-02-01
We study two-dimensional Hamiltonians in phase space with noncommutativity both in coordinates and momenta. We consider the generator of rotations on the noncommutative plane and the Lie algebra generated by Hermitian rotationally invariant quadratic forms of noncommutative dynamical variables. We show that two quantum phases are possible, characterized by the Lie algebras {sl}(2,{{R}}) or su(2) according to the relation between the noncommutativity parameters, with the rotation generator related with the Casimir operator. From this algebraic perspective, we analyze the spectrum of some simple models with nonrelativistic rotationally invariant Hamiltonians in this noncommutative phase space, such as the isotropic harmonic oscillator, the Landau problem and the cylindrical well potential.
Falomir, H; Vega, F; Cárcamo, D; Méndez, F; Loewe, M
2015-01-01
We study two-dimensional Hamiltonians in phase space with noncommutativity both in coordinates and momenta. We consider the generator of rotations on the noncommutative plane and the Lie algebra generated by Hermitian rotationally invariant quadratic forms of noncommutative dynamical variables. We show that two quantum phases are possible, characterized by the Lie algebras $sl(2,\\mathbb{R})$ or $su(2)$ according to the relation between the noncommutativity parameters. From this perspective, we analyze the spectrum of some simple models with nonrelativistic rotationally invariant Hamiltonians in this noncommutative phase space, as the isotropic harmonic oscillator, the Landau problem and the cylindrical well potential.
Abdelmadjid Maireche
2015-01-01
The paper describes the deformed Hamiltonian for Schrödinger equation with mixed harmonic potential known by sextic potential and the corresponding spectrum of energies which depended with 3-new quantum numbers (j = l ± 1/2, l) and s = 1/2 in the non-commutativity infinitesimal parameter θ.
Steuernagel, Ole
2014-06-01
In quantum physics the free particle and the harmonically trapped particle are arguably the most important systems a physicist needs to know about. It is little known that, mathematically, they are one and the same. This knowledge helps us to understand either from the viewpoint of the other. Here we show that all general time-dependent solutions of the free-particle Schrödinger equation can be mapped to solutions of the Schrödinger equation for harmonic potentials, both the trapping oscillator and the inverted "oscillator". This map is fully invertible and therefore induces an isomorphism between both types of system, they are equivalent. A composition of the map and its inverse allows us to map from one harmonic oscillator to another with a different spring constant and different center position. The map is independent of the state of the system, consisting only of a coordinate transformation and multiplication by a form factor, and can be chosen such that the state is identical in both systems at one point in time. This transition point in time can be chosen freely, the wave function of the particle evolving in time in one system before the transition point can therefore be linked up smoothly with the wave function for the other system and its future evolution after the transition point. Such a cut-and-paste procedure allows us to describe the instantaneous changes of the environment a particle finds itself in. Transitions from free to trapped systems, between harmonic traps of different spring constants or center positions, or, from harmonic binding to repulsive harmonic potentials are straightforwardly modelled. This includes some time-dependent harmonic potentials. The mappings introduced here are computationally more efficient than either state-projection or harmonic oscillator propagator techniques conventionally employed when describing instantaneous (non-adiabatic) changes of a quantum particle's environment.
Directory of Open Access Journals (Sweden)
Xiaowei Liu, Lingen Chen, Feng Wu, Fengrui Sun
2015-01-01
Full Text Available The optimal performance of an irreversible quantum Carnot refrigerator with working medium consisting of many non-interacting harmonic oscillators is investigated in this paper. The quantum refrigerator cycle is composed of two isothermal processes and two irreversible adiabatic processes, and the irreversibilities of heat resistance, internal friction and bypass heat leakage are considered. By using the quantum master equation, semi-group approach and finite time thermodynamics (FTT, this paper derives the cooling load and coefficient of performance (COP of the quantum refrigeration cycle and provides detailed numerical examples. At high temperature limit, the cooling load versus COP characteristic curves are plotted, and effects of internal friction and bypass heat leakage on the optimal performance of the quantum refrigerator are discussed. Three special cases, i.e., endoreversible, frictionless and without bypass heat leakage, are discussed in brief.
Energy Technology Data Exchange (ETDEWEB)
Bietenholz, Wolfgang, E-mail: wolbi@nucleares.unam.mx; Chryssomalakos, Chryssomalis, E-mail: chryss@nucleares.unam.mx; Salgado, Marcelo, E-mail: marcelo@nucleares.unam.mx [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A.P. 70-543, México D.F. 04510, México (Mexico)
2015-10-15
We comment on a fatal flaw in the analysis contained in the work of Martínez-y-Romero et al., [J. Math. Phys. 54, 053509 (2013)], which concerns the motion of a point particle in an inverse square potential, and show that most conclusions reached there are wrong. In particular, the manifestly senseless claim that, in the attractive potential case, no bounded orbits exist for negative energies, is traced to a sign error. Several more mistakes, both in the classical and the quantum cases, are pointed out.
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
A systematic theoretical approach is developed to study the electronic and transport properties of a twodimensional electron gas (2DEG) in the presence of spin-orbit interactions induced by the Rashba effect. The standard random-phase approximation is employed to calculate the screening length caused by electron-electron interaction in different transition channels. The quantum and transport mobilities in different spin branches are evaluated using the momentum-balance equation derived from the Boltzmann equation,in which the electron interactions with both the remote and background impurities are taken into account in an InAlAs/InGaAs heterojunction at low-temperatures.
Yuan, Jian-Hui; Chen, Ni; Mo, Hua; Zhang, Yan; Zhang, Zhi-Hai
2015-12-01
A detailed investigation of the second harmonic generation in symmetrical and asymmetrical Gaussian potential quantum wells under the influence of applied electric field by using the compact-density-matrix approach and the finite difference method. The results show that the second-harmonic generation susceptibility obtained in two cases can reach the magnitude of 10-4 m/V, which depend dramatically on the applied electric field and the structural parameters. Finally, the resonant peak and its corresponding to the resonant energy are also taken into account.
Van Diejen, J F
1997-01-01
Two families (type $A$ and type $B$) of confluent hypergeometric polynomials in several variables are studied. We describe the orthogonality properties, differential equations, and Pieri type recurrence formulas for these families. In the one-variable case, the polynomials in question reduce to the Hermite polynomials (type $A$) and the Laguerre polynomials (type $B$), respectively. The multivariable confluent hypergeometric families considered here may be used to diagonalize the rational quantum Calogero models with harmonic confinement (for the classical root systems) and are closely connected to the (symmetric) generalized spherical harmonics investigated by Dunkl.
Quantum properties of transverse pattern formation in second-harmonic generation
DEFF Research Database (Denmark)
Bache, Morten; Scotto, P.; Zambrini, R.;
2002-01-01
We investigate the spatial quantum noise properties of the one-dimensional transverse pattern formation instability in intracavity second-harmonic generation. The Q representation of a quasi-probability distribution is implemented in terms of nonlinear stochastic Langevin equations. We study...... these equations through extensive numerical simulations and analytically in the linearized limit. Our study, made below and above the threshold of pattern formation, is guided by a microscopic scheme of photon interaction underlying pattern formation in second-harmonic generation. Close to the threshold...
Energy Technology Data Exchange (ETDEWEB)
Cao Wei; Lu Peixiang; Lan Pengfei; Hong Weiyi; Wang Xinlin [Wuhan National Laboratory for Optoelectronics and School of Optoelectronics Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)
2007-03-14
The time-frequency properties of high harmonic generation (HHG) driven by a bichromatic field consisting of a fundamental and a weak third harmonic field are investigated. The selection of an individual quantum path contributing to harmonic generation can be achieved by adjusting the relative phase between the two components of the driving field. The classical trajectory simulation of the strong-field electron dynamics is performed to analyse the physical process. Our calculations show that it is the control of the ionization step that leads to the quantum path selection. This quantum selection can be used to generate regular and strong attosecond pulses.
Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.
Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron
2016-06-01
Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.
Kawamata, Shuichi; Hibino, Akira; Tanaka, Sho; Kawamura, Yuichi
2016-10-01
In order to develop optical devices for 2-3 μm wavelength regions, the InP-based InGaAs/GaAsSb type II multiple quantum well system has been investigated. By doping nitrogen into InGaAs layers, the system becomes effective in creating the optical devices with a longer wavelength. In this report, electrical transport properties are reported on the InGaAsN/GaAsSb type II system. The epitaxial layers with the single hetero or multiple quantum well structure on InP substrates are grown by the molecular beam epitaxy. The electrical resistance of samples with different nitrogen concentrations has been measured as a function of the magnetic field up to 9 Tesla at several temperatures between 2 and 6 K. The oscillation of the resistance due to the Shubnikov-de Haas (SdH) effect has been observed at each temperature. The effective mass is obtained from the temperature dependence of the amplitude of the SdH oscillations. The value of the effective mass increases from 0.048 for N = 0.0% to 0.062 for N = 1.2 and 1.5% as the nitrogen concentration increases. The mass enhancement occurs with corresponding to the reduction of the bandgap energy. These results are consistent with the band anticrossing model.
Two-dimensional discrete gap breathers in a two-dimensional discrete diatomic Klein-Gordon lattice
Institute of Scientific and Technical Information of China (English)
XU Quan; QIANG Tian
2009-01-01
We study the existence and stability of two-dimensional discrete breathers in a two-dimensional discrete diatomic Klein-Gordon lattice consisting of alternating light and heavy atoms, with nearest-neighbor harmonic coupling.Localized solutions to the corresponding nonlinear differential equations with frequencies inside the gap of the linear wave spectrum, i.e. two-dimensional gap breathers, are investigated numerically. The numerical results of the corresponding algebraic equations demonstrate the possibility of the existence of two-dimensional gap breathers with three types of symmetries, i.e., symmetric, twin-antisymmetric and single-antisymmetric. Their stability depends on the nonlinear on-site potential (soft or hard), the interaction potential (attractive or repulsive)and the center of the two-dimensional gap breather (on a light or a heavy atom).
Lu, Fangchao; Tang, Ning; Shang, Liangliang; Guan, Hongming; Xu, Fujun; Ge, Weikun; Shen, Bo
2017-01-01
Magnetic transport spectroscopy is investigated in quantum point contacts (QPCs) fabricated in Al0.25Ga0.75N/GaN heterostructures. The magnetic field perpendicular to the two-dimensional electron gas (2DEG) is shown to depopulate the quasi-one-dimensional energy levels in the first two-dimensional (2D) subband faster than those in the second one. In GaN based heterostructures, the energy levels in the second 2D subband is generally concealed in the fast course of depletion and hence rarely detected. The perpendicular magnetic field facilitates the observation of the second 2D subband, and provides a method to study the properties of these energy levels. A careful analysis on the rate of the magnetic depletion with respect to the level index and confinement is carried out, from which the profile of the lateral confinement in GaN based QPCs is found to be triangular. The stability diagram at T shows the energy separation between the first and second 2D subband to be in the range of 32 to 42 meV. PMID:28225042
High-harmonic spectroscopy of aligned molecules
Yun, Hyeok; Yun, Sang Jae; Lee, Gae Hwang; Nam, Chang Hee
2017-01-01
High harmonics emitted from aligned molecules driven by intense femtosecond laser pulses provide the opportunity to explore the structural information of molecules. The field-free molecular alignment technique is an expedient tool for investigating the structural characteristics of linear molecules. The underlying physics of field-free alignment, showing the characteristic revival structure specific to molecular species, is clearly explained from the quantum-phase analysis of molecular rotational states. The anisotropic nature of molecules is shown from the harmonic polarization measurement performed with spatial interferometry. The multi-orbital characteristics of molecules are investigated using high-harmonic spectroscopy, applied to molecules of N2 and CO2. In the latter case the two-dimensional high-harmonic spectroscopy, implemented using a two-color laser field, is applied to distinguish harmonics from different orbitals. Molecular high-harmonic spectroscopy will open a new route to investigate ultrafast dynamics of molecules.
Quantum harmonic Brownian motion in a general environment: A modified phase-space approach
Energy Technology Data Exchange (ETDEWEB)
Yeh, L. [Univ. of California, Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)
1993-06-23
After extensive investigations over three decades, the linear-coupling model and its equivalents have become the standard microscopic models for quantum harmonic Brownian motion, in which a harmonically bound Brownian particle is coupled to a quantum dissipative heat bath of general type modeled by infinitely many harmonic oscillators. The dynamics of these models have been studied by many authors using the quantum Langevin equation, the path-integral approach, quasi-probability distribution functions (e.g., the Wigner function), etc. However, the quantum Langevin equation is only applicable to some special problems, while other approaches all involve complicated calculations due to the inevitable reduction (i.e., contraction) operation for ignoring/eliminating the degrees of freedom of the heat bath. In this dissertation, the author proposes an improved methodology via a modified phase-space approach which employs the characteristic function (the symplectic Fourier transform of the Wigner function) as the representative of the density operator. This representative is claimed to be the most natural one for performing the reduction, not only because of its simplicity but also because of its manifestation of geometric meaning. Accordingly, it is particularly convenient for studying the time evolution of the Brownian particle with an arbitrary initial state. The power of this characteristic function is illuminated through a detailed study of several physically interesting problems, including the environment-induced damping of quantum interference, the exact quantum Fokker-Planck equations, and the relaxation of non-factorizable initial states. All derivations and calculations axe shown to be much simplified in comparison with other approaches. In addition to dynamical problems, a novel derivation of the fluctuation-dissipation theorem which is valid for all quantum linear systems is presented.
Two-Dimensional NMR Lineshape Analysis
Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John
2016-04-01
NMR titration experiments are a rich source of structural, mechanistic, thermodynamic and kinetic information on biomolecular interactions, which can be extracted through the quantitative analysis of resonance lineshapes. However, applications of such analyses are frequently limited by peak overlap inherent to complex biomolecular systems. Moreover, systematic errors may arise due to the analysis of two-dimensional data using theoretical frameworks developed for one-dimensional experiments. Here we introduce a more accurate and convenient method for the analysis of such data, based on the direct quantum mechanical simulation and fitting of entire two-dimensional experiments, which we implement in a new software tool, TITAN (TITration ANalysis). We expect the approach, which we demonstrate for a variety of protein-protein and protein-ligand interactions, to be particularly useful in providing information on multi-step or multi-component interactions.
A two-dimensional Dirac fermion microscope
Bøggild, Peter; Caridad, José M.; Stampfer, Christoph; Calogero, Gaetano; Papior, Nick Rübner; Brandbyge, Mads
2017-06-01
The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.
A two-dimensional Dirac fermion microscope.
Bøggild, Peter; Caridad, José M; Stampfer, Christoph; Calogero, Gaetano; Papior, Nick Rübner; Brandbyge, Mads
2017-06-09
The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.
Zhai, Wangjian
2014-12-01
Electric-field-induced second-harmonic generation in asymmetrical Gaussian potential quantum wells is investigated using the effective mass approximation employing the compact density matrix method and the iterative approach. Our results show that the absolute value, the real part and the imaginary part of second-harmonic generation are greatly affected by the height of the Gaussian potential quantum wells, the range of the Gaussian confinement potential and the applied electric field. The relationship between the absolute value and the imaginary part of second-harmonic generation together with the relationship between the absolute value and the real part of second-harmonic generation is studied. It is found that no matter how the height of the Gaussian potential quantum wells, the range of the Gaussian confinement potential and the applied electric field vary, the resonant peaks of the absolute value of second-harmonic generation do not originate from the imaginary part but from the real part.
Yuan, Jian-Hui; Zhang, Yan; Mo, Hua; Chen, Ni; Zhang, Zhihai
2015-12-01
The second-harmonic generation susceptibility in semiparabolic quantum wells with applied electric field is investigated theoretically. For the same topic studied by Zhang and Xie [Phys. Rev. B 68 (2003) 235315] [1], some new and reliable results are obtained by us. It is easily observed that the second harmonic generation susceptibility decreases and the blue shift of the resonance is induced with increasing of the frequencies of the confined potential. Moreover, a transition from a two-photon resonance to two single-photon resonances will appear adjusted by the frequencies of the confined potential. Similar results can also be obtained by controlling the applied electric field. Surprisingly, the second harmonic generation susceptibility is weakened in the presence of the electric field, which is in contrast to the conventional case. Finally, the resonant peak and its corresponding resonant energy are also taken into account.
DEFF Research Database (Denmark)
Han, Yong-Chang; Madsen, Lars Bojer
2010-01-01
We solve the time-dependent Schrödinger equation for atomic hydrogen in an intense field using spherical coordinates with a radial grid and a spherical harmonic basis for the angular part. We present the high-order harmonic spectra based on three different forms, the dipole, dipole velocity......, and acceleration forms, and two gauges, the length and velocity gauges. The relationships among the harmonic phases obtained from the Fourier transform of the three forms are discussed in detail. Although quantum mechanics is gauge invariant and the length and velocity gauges should give identical results, the two...... gauges present different computation efficiencies, which reflects the different behavior in terms of characteristics of the physical couplings acting in the two gauges. In order to obtain convergence, more angular momentum states are required in the length gauge, while more grid points are required...
Suárez, I; Larrue, A; Rodríguez-Cantó, P J; Almuneau, G; Abargues, R; Chirvony, V S; Martínez-Pastor, J P
2014-08-15
In this Letter, we study a new kind of organic polymer waveguide numerically and experimentally by combining an ultrathin (10-50 nm) layer of compactly packed CdSe/ZnS core/shell colloidal quantum dots (QDs) sandwiched between two cladding poly(methyl methacrylate) (PMMA) layers. When a pumping laser beam is coupled into the waveguide edge, light is mostly confined around the QD layer, improving the efficiency of excitation. Moreover, the absence of losses in the claddings allows the propagation of the pumping laser beam along the entire waveguide length; hence, a high-intensity photoluminescence (PL) is produced. Furthermore, a novel fabrication technology is developed to pattern the PMMA into ridge structures by UV lithography in order to provide additional light confinement. The sandwich-type waveguide is analyzed in comparison to a similar one formed by a PMMA film homogeneously doped by the same QDs. A 100-fold enhancement in the waveguided PL is found for the sandwich-type case due to the higher concentration of QDs inside the waveguide.
Zhang, Bingpo; Lu, Ping; Liu, Henan; Jiao, Lin; Ye, Zhenyu; Jaime, M; Balakirev, F F; Yuan, Huiqiu; Wu, Huizhen; Pan, Wei; Zhang, Yong
2015-07-08
Quantum oscillations are observed in the 2DEG system at the interface of novel heterostructures, PbTe/CdTe (111), with nearly identical lattice parameters (a(PbTe) = 0.6462 nm, a(CdTe) = 0.648 nm) but very different lattice structures (PbTe: rock salt, CdTe: zinc blende). The 2DEG formation mechanism, a mismatch in the bonding configurations of the valence electrons at the interface, is uniquely different from the other known 2DEG systems. The aberration-corrected scanning transmission electron microscope (AC-STEM) characterization indicates an abrupt interface without cation interdiffusion due to a large miscibility gap between the two constituent materials. Electronic transport measurements under magnetic field up to 60 T, with the observation of Landau level filling factor ν = 1, unambiguously reveal a π Berry phase, suggesting the Dirac Fermion nature of the 2DEG at the heterostructure interface, and the PbTe/CdTe heterostructure being a new candidate for 2D topological crystalline insulators.
Camp, Seth; Gaarde, Mette B
2015-01-01
We present a theoretical study of the influence of resonant enhancement on quantum path dynamics in the generation of harmonics above and below the ionization threshold in helium. By varying the wavelength and intensity of the driving field from 425 nm to 500 nm and from 30 TW/cm${^2}$ to 140 TW/cm${^2}$, respectively, we identify enhancements of harmonics 7, 9, and 11 that correspond to multiphoton resonances between the ground state and the Stark shifted $1s2p$, $1s3p$, and $1s4p$ excited states. A time-frequency analysis of the emission shows that both the short and long quantum path contributions to the harmonic yield are enhanced through these bound state resonances. We analyze the sub-cycle time structure of the 9th harmonic yield in the vicinity of the resonances and find that on resonance the long trajectory contribution is phase shifted by approximately $\\pi/4$. Finally, we compare the single atom and the macroscopic response of a helium gas and find that while the sub-cycle time profiles are slightl...
Parnis, J. Mark; Thompson, Matthew G. K.
2004-01-01
An introductory undergraduate physical organic chemistry exercise that introduces the harmonic oscillator's use in vibrational spectroscopy is developed. The analysis and modeling exercise begins with the students calculating the stretching modes of common organic molecules with the help of the quantum mechanical harmonic oscillator (QMHO) model.
Vysotsky, Yu B; Fomina, E S; Belyaeva, E A; Aksenenko, E V; Vollhardt, D; Miller, R
2009-12-31
The semiempirical quantum-chemical PM3 method is used to calculate the thermodynamic parameters of clusterization of the S-form of alpha-amino acids with the general composition C(n)H(2n+1)CHNH(2)COOH (n = 5-15) at 278 and 298 K. It is shown that six stable conformations of monomers exist, for which the thermodynamic parameters (enthalpy and Gibbs' energy) of the formation and absolute entropy are calculated. The correlation dependencies of the calculated parameters on the alkyl chain length are found to be linear. The structures of the monomers are used to build larger clusters (dimers, tetramers, hexamers). For all small clusters (comprised of two to six molecules), the thermodynamic parameters of formation and clusterization are calculated. It is shown that for tetramers and hexamers the enthalpy, entropy, and Gibbs' energy of clusterization are linearly dependent on the alkyl chain length, whereas for the dimers these dependencies are stepwise. The thermodynamic characteristics of clusterization of associates tilted by angles of 9 and 30 degrees with respect to the normal to the interface are calculated. It is shown that the 30 degrees angle orientation is more energetically advantageous for this class of compounds. The geometric parameters of the unit cell characteristic for the infinite 2D film which corresponds to the most advantageous conformation of the monomer were calculated using the PM3 parametrization to be a = 4.57-4.71 A and b = 5.67-5.75 A, with the angle between the axes theta = 100-103 degrees . These values agree well with the available experimental data. Spontaneous clusterization of alpha-amino acids at the air/water interface at 278 K takes place if the alkyl chain length exceeds 11-12 carbon atoms, whereas for 298 K this clusterization threshold corresponds to 13-14 carbon atoms in the alkyl chain, also in agreement with the experimental data.
Vysotsky, Yu B; Fomina, E S; Belyaeva, E A; Aksenenko, E V; Fainerman, V B; Vollhardt, D; Miller, R
2011-03-17
The quantum-chemical semiempiric PM3 method is used to calculate the thermodynamic parameters of clusterization for the racemic α-amino acids C(n)H(2n+1)CHNH(2)COOH with n=5-15 at 278 and 298 K. Possible relative orientations of the monomers in the heterochiral clusters are considered. It is shown that, for the racemic mixtures of α-amino acids, the formation of heterochiral 2D films is most energetically preferable with the alternating (rather than "checkered") packing of the enantiomers with opposite specific rotation. The two enantiomeric forms of α-amino acids in the heterochiral 2D clusters are tilted with respect to the normal to the q direction at angles of φ(1)=20° and φ(2) = 33°, whereas the single enantiomeric forms are oriented at an angle of δ=9° with respect to the normal to the p direction. It is shown that the heterochiral 2D film based on the α-amino acid structures oriented at the angle φ(2)=33° with respect to the normal to the q direction possesses a rectangular unit cell with the geometric parameters a = 4.62 Å and b = 10.70 Å and the tilt angle of the alkyl chain of the molecule with respect to the interface t(2)=35°, which is in good agreement with the X-ray structural data a=4.80 Å, b=9.67 Å, and t(2)=37°. The parameters of the lattice structure of monolayers formed by amphiphilic amino acids are shown to be determined by the "a" type of the intermolecular H-H interactions, whereas the tilt angle of the molecules with respect to the interface depends on the volume and the structure of the functional groups involved in the hydrophilic part of the molecule. Spontaneous clusterization of the racemic form of α-amino acids at the air/water interface at 278 K takes place if the alkyl chain length is equal or higher than 12-13 carbon atoms, whereas for 298 K this clusterization threshold corresponds to 14 carbon atoms in the hydrocarbon chain. These values agree with the experimental data. © 2011 American Chemical Society
Binding energy of two-dimensional biexcitons
DEFF Research Database (Denmark)
Singh, Jai; Birkedal, Dan; Vadim, Lyssenko;
1996-01-01
Using a model structure for a two-dimensional (2D) biexciton confined in a quantum well, it is shown that the form of the Hamiltonian of the 2D biexciton reduces into that of an exciton. The binding energies and Bohr radii of a 2D biexciton in its various internal energy states are derived...... analytically using the fractional dimension approach. The ratio of the binding energy of a 2D biexciton to that of a 2D exciton is found to be 0.228, which agrees very well with the recent experimental value. The results of our approach are compared with those of earlier theories....
Topology optimization of two-dimensional elastic wave barriers
DEFF Research Database (Denmark)
Van Hoorickx, C.; Sigmund, Ole; Schevenels, M.
2016-01-01
Topology optimization is a method that optimally distributes material in a given design domain. In this paper, topology optimization is used to design two-dimensional wave barriers embedded in an elastic halfspace. First, harmonic vibration sources are considered, and stiffened material is insert...
Two-dimensional liquid chromatography
DEFF Research Database (Denmark)
Græsbøll, Rune
of this thesis is on online comprehensive two-dimensional liquid chromatography (online LC×LC) with reverse phase in both dimensions (online RP×RP). Since online RP×RP has not been attempted before within this research group, a significant part of this thesis consists of knowledge and experience gained...
Molecular internal dynamics studied by quantum path interferences in high order harmonic generation
Energy Technology Data Exchange (ETDEWEB)
Zaïr, Amelle, E-mail: azair@imperial.ac.uk [Imperial College London, Department of Physics, Blackett Laboratory Laser Consortium, London SW7 2AZ (United Kingdom); Siegel, Thomas; Sukiasyan, Suren; Risoud, Francois; Brugnera, Leonardo; Hutchison, Christopher [Imperial College London, Department of Physics, Blackett Laboratory Laser Consortium, London SW7 2AZ (United Kingdom); Diveki, Zsolt; Auguste, Thierry [Service des Photons, Atomes et Molécules, CEA-Saclay, 91191 Gif-sur-Yvette (France); Tisch, John W.G. [Imperial College London, Department of Physics, Blackett Laboratory Laser Consortium, London SW7 2AZ (United Kingdom); Salières, Pascal [Service des Photons, Atomes et Molécules, CEA-Saclay, 91191 Gif-sur-Yvette (France); Ivanov, Misha Y.; Marangos, Jonathan P. [Imperial College London, Department of Physics, Blackett Laboratory Laser Consortium, London SW7 2AZ (United Kingdom)
2013-03-12
Highlights: ► Electronic trajectories in high order harmonic generation encodes attosecond and femtosecond molecular dynamical information. ► The observation of these quantum paths allows us to follow nuclear motion after ionization. ► Quantum paths interference encodes a signature of superposition of ionization channels. ► Quantum paths interference encodes a signature of transfer of population between channels due to laser coupling. ► Quantum paths interference is a promising technique to resolve ultra-fast dynamical processes after ionization. - Abstract: We investigate how short and long electron trajectory contributions to high harmonic emission and their interferences give access to information about intra-molecular dynamics. In the case of unaligned molecules, we show experimental evidence that the long trajectory contribution is more dependent upon the molecular species than the short one, providing a high sensitivity to cation nuclear dynamics from 100’s of as to a few fs after ionisation. Using theoretical approaches based on the strong field approximation and numerical integration of the time dependent Schrödinger equation, we examine how quantum path interferences encode electronic motion when the molecules are aligned. We show that the interferences are dependent upon which ionisation channels are involved and any superposition between them. In particular, quantum path interferences can encode signatures of electron dynamics if the laser field drives a coupling between the channels. Hence, molecular quantum path interferences are a promising method for attosecond spectroscopy, allowing the resolution of ultra-fast charge migration in molecules after ionisation in a self-referenced manner.
MAVRI, J; LENSINK, M; BERENDSEN, HJC
1994-01-01
A density matrix evolution (DME) method (Berendsen, H. J. C., and Mavri, J., 1993, J. phys. Chem., 97, 13464) to simulate the dynamics of quantum systems embedded in a classical environment is applied to study the inelastic collisions of a classical particle with a five level quantum harmonic
Juday, Richard D.
1992-01-01
Modified vernier scale gives accurate two-dimensional coordinates from maps, drawings, or cathode-ray-tube displays. Movable circular overlay rests on fixed rectangular-grid overlay. Pitch of circles nine-tenths that of grid and, for greatest accuracy, radii of circles large compared with pitch of grid. Scale enables user to interpolate between finest divisions of regularly spaced rule simply by observing which mark on auxiliary vernier rule aligns with mark on primary rule.
Renormalization of two-dimensional quantum electrodynamics
Energy Technology Data Exchange (ETDEWEB)
Casana S, Rodolfo; Dias, Sebastiao A
1997-12-01
The Schwinger model, when quantized in a gauge non-invariant way exhibits a dependence on a parameter {alpha} (the Jackiw-Rajaraman parameter) in a way which is analogous to the case involving chiral fermions (the chiral Schwinger model). For all values of a {alpha}1, there are divergences in the fermionic Green`s functions. We propose a regularization of the generating functional Z [{eta}, {eta}, J] and we use it to renormalize the theory to one loop level, in a semi-perturbative sense. At the end of the renormalization procedure we find an implicit dependence of {alpha} on the renormalization scale {mu}. (author) 26 refs.
Saha, Anirban
2015-01-01
We investigate the quantum mechanical transitions, induced by the combined effect of Gravitational wave (GW) and noncommutative (NC) structure of space, among the states of a 2-dimensional harmonic oscillator. The phonon modes excited by the passing GW within the resonant bar-detector are formally identical to forced harmonic oscillator and they represent a length variation of roughly the same order of magnitude as the characteristic length-scale of spatial noncommutativity estimated from the phenomenological upper bound of the NC parameter. This motivates our present work. We employ a number of different GW wave-forms that are typically expected from possible astronomical sources. We find that the transition probablities are quite sensitive to the nature of polarization of the GW. We further elaborate on the particular type of sources of GW radiation which can induce transitions that can be used as effective probe of the spatial noncommutative structure.
Optimal analysis on the performance of an irreversible harmonic quantum Brayton refrigeration cycle.
Lin, Bihong; Chen, Jincan
2003-11-01
An irreversible model of a quantum refrigeration cycle working with many noninteracting harmonic oscillators is established. The refrigeration cycle consists of two adiabatic and two constant-frequency processes. The general performance characteristics of the cycle are investigated, based on the quantum master equation and the semigroup approach. The expressions for several important performance parameters such as the coefficient of performance, cooling rate, power input, and rate of entropy production are derived. By using numerical solutions, the cooling rate of the refrigeration cycle subject to finite cycle duration is optimized. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal region of the coefficient of performance and the optimal ranges of temperatures of the working substance and times spent on the two constant-frequency processes are determined. Moreover, the optimal performance of the cycle in the high-temperature limit is compared with that of a classical Brayton refrigerator working with an ideal gas. The results obtained here show that in the high-temperature limit a harmonic quantum Brayton cycle may be equivalent to a classical Brayton cycle.
Bhattacharjee, Suraka; Chaudhury, Ranjan
2016-11-01
The generalized spin stiffness constant for a doped quantum antiferromagnet has been investigated both analytically and numerically as a function of doping concentration at zero temperature, based on the strongly correlated t-J model on two-dimensional square lattice. The nature of the theoretical dependence of the stiffness constant on doping shows a striking similarity with that of the effective exchange constant, obtained from the combination of other theoretical and experimental techniques in the low doping region. This correspondence once again establishes that spin stiffness can very well play the role of an effective exchange constant even in the strongly correlated semi-itinerant systems. Our theoretical plot of the stiffness constant against doping concentration in the whole doping region exhibits the various characteristic features like a possible crossover in the higher doping regions and persistence of short range ordering even for very high doping with the complete vanishing of spin stiffness occurring only close to 100% doping. Our results receive very good support from various other theoretical approaches and also brings out a few limitations of some of them. Our detailed analysis highlights the crucial importance of the study of spin stiffness for the proper understanding of magnetic correlations in a semi-itinerant magnetic system described by the strongly correlated t-J model. Moreover, our basic formalism can also be utilized for determination of the effective exchange constant and magnetic correlations for itinerant magnetic systems, in general in a novel way.
Lu, Shih-I.
2004-06-01
Application of the Ornstein-Uhlenbeck diffusion quantum Monte Carlo method in combination with a trial wave function constructed from the floating spherical Gaussian orbitals and spherical Gaussian geminals to studies on the equilibrium structures and harmonic frequencies of ethane and ozone is presented. These Monte Carlo computed results are compared with those of experiments as well as the coupled cluster methods with the correlation consistent basis sets for the two molecules. For ozone, we also compare the Monte Carlo results with the results from multireference calculations.
Two-Variable Hermite Function as Quantum Entanglement of Harmonic Oscillator's Wave Functions
Institute of Scientific and Technical Information of China (English)
LU Hai-Liang; FAN Hong-Yi
2007-01-01
We reveal that the two-variable Hermite function hm,n, which is the generalized Bargmann representation of the two-mode Fock state, involves quantum entanglement of harmonic oscillator's wave functions.The Schmidt decomposition of hm,n is derived. It also turns out that hm,n can be generated by windowed Fourier transform of the single-variable Hermite functions. As an application, the wave function of the two-variable Hermite polynomial state S(r)Hm,n(μa1+, μa2+)|00〉, which is the minimum uncertainty state for sum squeezing, in 〈η| representation is calculated.
Two-dimensional liquid chromatography
DEFF Research Database (Denmark)
Græsbøll, Rune
Two-dimensional liquid chromatography has received increasing interest due to the rise in demand for analysis of complex chemical mixtures. Separation of complex mixtures is hard to achieve as a simple consequence of the sheer number of analytes, as these samples might contain hundreds or even...... dimensions. As a consequence of the conclusions made within this thesis, the research group has, for the time being, decided against further development of online LC×LC systems, since it was not deemed ideal for the intended application, the analysis of the polar fraction of oil. Trap-and...
Studies on the second-harmonic generations in cubical quantum dots with applied electric field
Energy Technology Data Exchange (ETDEWEB)
Shao Shuai [Department of Physics, College of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006 (China); Guo Kangxian, E-mail: axguo@sohu.co [Department of Physics, College of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006 (China); Zhang Zhihai; Li Ning; Peng Chao [Department of Physics, College of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006 (China)
2011-02-01
The second-harmonic generation (SHG) coefficient for cubical quantum dots (CQDs) with the applied electric field is theoretically investigated. Using the compact density-matrix approach and the iterative method, we get the analytical expression of the SHG coefficient. And the numerical calculations for the typical GaAs/AlAs CQDs are presented. The results show that the SHG coefficient can reach the magnitude of 10{sup -5} m/V, about two orders higher than that in spherical quantum dot system. More importantly, the SHG coefficient is not a monotonic function of the length L of CQDs as well as the applied field F. If we select suitable values of F and L, we will get a higher value of the SHG coefficient. In addition, the relaxation rate also affects the SHG coefficient obviously.
The optimal performance of a quantum refrigeration cycle working with harmonic oscillators
Lin Bi Hong; Hua Ben
2003-01-01
The cycle model of a quantum refrigeration cycle working with many non-interacting harmonic oscillators and consisting of two isothermal and two constant-frequency processes is established. Based on the quantum master equation and semi-group approach, the general performance of the cycle is investigated. Expressions for some important performance parameters, such as the coefficient of performance, cooling rate, power input, and rate of the entropy production, are derived. Several interesting cases are discussed and, especially, the optimal performance of the cycle at high temperatures is discussed in detail. Some important characteristic curves of the cycle, such as the cooling rate versus coefficient of performance curves, the power input versus coefficient of performance curves, the cooling rate versus power input curves, and so on, are presented. The maximum cooling rate and the corresponding coefficient of performance are calculated. Other optimal performances are also analysed. The results obtained here ...
Dynamical Relation between Quantum Squeezing and Entanglement in Coupled Harmonic Oscillator System
Directory of Open Access Journals (Sweden)
Lock Yue Chew
2014-04-01
Full Text Available In this paper, we investigate into the numerical and analytical relationship between the dynamically generated quadrature squeezing and entanglement within a coupled harmonic oscillator system. The dynamical relation between these two quantum features is observed to vary monotically, such that an enhancement in entanglement is attained at a fixed squeezing for a larger coupling constant. Surprisingly, the maximum attainable values of these two quantum entities are found to consistently equal to the squeezing and entanglement of the system ground state. In addition, we demonstrate that the inclusion of a small anharmonic perturbation has the effect of modifying the squeezing versus entanglement relation into a nonunique form and also extending the maximum squeezing to a value beyond the system ground state.
Two-dimensional capillary origami
Energy Technology Data Exchange (ETDEWEB)
Brubaker, N.D., E-mail: nbrubaker@math.arizona.edu; Lega, J., E-mail: lega@math.arizona.edu
2016-01-08
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid. - Highlights: • Full solution set of the two-dimensional capillary origami problem. • Fluid does not necessarily wet the entire plate. • Global energy approach provides exact differential equations satisfied by minimizers. • Bifurcation diagrams highlight three different regimes. • Conditions for spontaneous encapsulation are identified.
Nonlinear optical response of a two-dimensional atomic crystal.
Merano, Michele
2016-01-01
The theory of Bloembergen and Pershan for the light waves at the boundary of nonlinear media is extended to a nonlinear two-dimensional (2D) atomic crystal, i.e., a single planar atomic lattice, placed between linear bulk media. The crystal is treated as a zero-thickness interface, a real 2D system. Harmonic waves emanate from it. Generalization of the laws of reflection and refraction give the direction and the intensity of the harmonic waves. As a particular case that contains all the essential physical features, second-order harmonic generation is considered. The theory, due to its simplicity that stems from the special character of a single planar atomic lattice, is able to elucidate and explain the rich experimental details of harmonic generation from a 2D atomic crystal.
Gajić, A.; Radovanović, J.; Milanović, V.; Indjin, D.; Ikonić, Z.
2014-02-01
A computational model for the optimization of the second order optical nonlinearities in GaInAs/AlInAs quantum cascade laser structures is presented. The set of structure parameters that lead to improved device performance was obtained through the implementation of the Genetic Algorithm. In the following step, the linear and second harmonic generation power were calculated by self-consistently solving the system of rate equations for carriers and photons. This rate equation system included both stimulated and simultaneous double photon absorption processes that occur between the levels relevant for second harmonic generation, and material-dependent effective mass, as well as band nonparabolicity, were taken into account. The developed method is general, in the sense that it can be applied to any higher order effect, which requires the photon density equation to be included. Specifically, we have addressed the optimization of the active region of a double quantum well In0.53Ga0.47As/Al0.48In0.52As structure and presented its output characteristics.
ABC of ladder operators for rationally extended quantum harmonic oscillator systems
Cariñena, José F.; Plyushchay, Mikhail S.
2017-07-01
The problem of construction of ladder operators for rationally extended quantum harmonic oscillator (REQHO) systems of a general form is investigated in the light of existence of different schemes of the Darboux-Crum-Krein-Adler transformations by which such systems can be generated from the quantum harmonic oscillator. Any REQHO system is characterized by the number of separated states in its spectrum, the number of ‘valence bands’ in which the separated states are organized, and by the total number of the missing energy levels and their position. All these peculiarities of a REQHO system are shown to be detected and reflected by a trinity (A^+/- , B^+/- , C^+/-) of the basic (primary) lowering and raising ladder operators related between themselves by certain algebraic identities with coefficients polynomially-dependent on the Hamiltonian. We show that all the secondary, higher-order ladder operators are obtainable by a composition of the basic ladder operators of the trinity which form the set of the spectrum-generating operators. Each trinity, in turn, can be constructed from the intertwining operators of the two complementary minimal schemes of the Darboux-Crum-Krein-Adler transformations.
Optimal Power and Efficiency of Quantum Thermoacoustic Micro-cycle Working in 1D Harmonic Trap
E, Qing; Wu, Feng; Yin, Yong; Liu, XiaoWei
2017-10-01
Thermoacoustic engines (including heat engines and refrigerators) are energy conversion devices without moving part. They have great potential in aviation, new energy utilization, power technology, refrigerating and cryogenics. The thermoacoustic parcels, which compose the working fluid of a thermoacoustic engine, oscillate within the sound channel with a temperature gradient. The thermodynamic foundation of a thermoacoustic engine is the thermoacoustic micro-cycle (TAMC). In this paper, the theory of quantum mechanics is applied to the study of the actual thermoacoustic micro-cycle for the first time. A quantum mechanics model of the TAMC working in a 1D harmonic trap, which is named as a quantum thermoacoustic micro-cycle (QTAMC), is established. The QTAMC is composed of two constant force processes connected by two straight line processes. Analytic expressions of the power output and the efficiency for QTAMC have been derived. The effects of the trap width and the temperature amplitude on the power output and the thermal efficiency have been discussed. Some optimal characteristic curves of power output versus efficiency are plotted, and then the optimization region of QTAMC is given in this paper. The results obtained here not only enrich the thermoacoustic theory but also expand the application of quantum thermodynamics.
Two-dimensional capillary origami
Brubaker, N. D.; Lega, J.
2016-01-01
We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid.
Two-dimensional cubic convolution.
Reichenbach, Stephen E; Geng, Frank
2003-01-01
The paper develops two-dimensional (2D), nonseparable, piecewise cubic convolution (PCC) for image interpolation. Traditionally, PCC has been implemented based on a one-dimensional (1D) derivation with a separable generalization to two dimensions. However, typical scenes and imaging systems are not separable, so the traditional approach is suboptimal. We develop a closed-form derivation for a two-parameter, 2D PCC kernel with support [-2,2] x [-2,2] that is constrained for continuity, smoothness, symmetry, and flat-field response. Our analyses, using several image models, including Markov random fields, demonstrate that the 2D PCC yields small improvements in interpolation fidelity over the traditional, separable approach. The constraints on the derivation can be relaxed to provide greater flexibility and performance.
Institute of Scientific and Technical Information of China (English)
Xinru Li[1; Ying Dai[1; Yandong Ma[1; Wei Wei[1; Lin Yu[1; Baibiao Huang[2
2015-01-01
A new family of two-dimensional （2D） topological insulators （TIs） comprising g-TIA （A = N, P, As, and Sb） monolayers constructed by T1 and group-V elements is predicted by first-principles calculations and molecular-dynamics （MD） simulations. The geometric stability, band inversion, nontrivial edge states, and electric polarity are investigated to predict the large-gap quantum spin Hall insulator and Rashba-Dresselhaus effects. The MD results reveal that the g-T1A monolayers remain stable even at room temperature. The g-T1A （A = As, Sb） monolayers become TIs under the influence of strong spin-orbit couplings with large bulk bandgaps of 131 and 268 meV, respectively. A single band inversion is observed in each g-T1A （A = As, Sb） monolayer, indicating a nontrivial topological nature. Furthermore, the topological edge states are described by introducing a sufficiently wide zigzag-nanoribbon. A Dirac point in the middle of the bulk gap connects the valence- and conduction-band edges. The Fermi velocity near the Dirac point with a linear band dispersion is -0.51 × 106 m/s, which is comparable to that of many other 2D nanomaterials. More importantly, owing to the broken inversion symmetry normal to the plane of the g-T1A films, a promising Rashba-Dresselhaus effect with the parameter up to 0.85 eV-A is observed in the g-T1A （A = As, Sb） monolayers. Our findings regarding 2D topological g-T1A monolayers with room-temperature bandgaps, intriguing topological edge states, and a promising Rashba-Dresselhaus effect are of fundamental value and suggest potential applications in nanoelectronic devices.
Complex dynamical invariants for two-dimensional complex potentials
Indian Academy of Sciences (India)
J S Virdi; F Chand; C N Kumar; S C Mishra
2012-08-01
Complex dynamical invariants are searched out for two-dimensional complex potentials using rationalization method within the framework of an extended complex phase space characterized by $x = x_{1} + ip_{3}. y = x_{2} + ip_{4}, p_{x} = p_{1} + ix_{3}, p_{y} = p_{2} + ix_{4}$. It is found that the cubic oscillator and shifted harmonic oscillator admit quadratic complex invariants. THe obtained invariants may be useful for studying non-Hermitian Hamiltonian systems.
Energy Technology Data Exchange (ETDEWEB)
Butkus, Vytautas; Valkunas, Leonas [Department of Theoretical Physics, Faculty of Physics, Vilnius University, Sauletekio 9-III, 10222 Vilnius (Lithuania); Center for Physical Sciences and Technology, Gostauto 9, 01108 Vilnius (Lithuania); Abramavicius, Darius, E-mail: darius.abramavicius@ff.vu.lt [Department of Theoretical Physics, Faculty of Physics, Vilnius University, Sauletekio 9-III, 10222 Vilnius (Lithuania)
2014-01-21
A general theory of electronic excitations in aggregates of molecules coupled to intramolecular vibrations and the harmonic environment is developed for simulation of the third-order nonlinear spectroscopy signals. It is applied in studies of the time-resolved two-dimensional coherent spectra of four characteristic model systems: weakly/strongly vibronically coupled molecular dimers interacting with high/low frequency intramolecular vibrations. The results allow us to (i) classify and define the typical spectroscopic features of vibronically coupled molecules, (ii) separate the cases, when the long-lived quantum coherences due to vibrational lifetime borrowing should be expected, (iii) define when the complete exciton–vibrational mixing occurs, and (iv) when separation of excitonic and vibrational coherences is possible.
Classifying Two-dimensional Hyporeductive Triple Algebras
Issa, A Nourou
2010-01-01
Two-dimensional real hyporeductive triple algebras (h.t.a.) are investigated. A classification of such algebras is presented. As a consequence, a classification of two-dimensional real Lie triple algebras (i.e. generalized Lie triple systems) and two-dimensional real Bol algebras is given.
Two-dimensional topological photonic systems
Sun, Xiao-Chen; He, Cheng; Liu, Xiao-Ping; Lu, Ming-Hui; Zhu, Shi-Ning; Chen, Yan-Feng
2017-09-01
The topological phase of matter, originally proposed and first demonstrated in fermionic electronic systems, has drawn considerable research attention in the past decades due to its robust transport of edge states and its potential with respect to future quantum information, communication, and computation. Recently, searching for such a unique material phase in bosonic systems has become a hot research topic worldwide. So far, many bosonic topological models and methods for realizing them have been discovered in photonic systems, acoustic systems, mechanical systems, etc. These discoveries have certainly yielded vast opportunities in designing material phases and related properties in the topological domain. In this review, we first focus on some of the representative photonic topological models and employ the underlying Dirac model to analyze the edge states and geometric phase. On the basis of these models, three common types of two-dimensional topological photonic systems are discussed: 1) photonic quantum Hall effect with broken time-reversal symmetry; 2) photonic topological insulator and the associated pseudo-time-reversal symmetry-protected mechanism; 3) time/space periodically modulated photonic Floquet topological insulator. Finally, we provide a summary and extension of this emerging field, including a brief introduction to the Weyl point in three-dimensional systems.
Asymptotics for Two-dimensional Atoms
DEFF Research Database (Denmark)
Nam, Phan Thanh; Portmann, Fabian; Solovej, Jan Philip
2012-01-01
We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E^{\\TF}(\\lambd......We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E......^{\\TF}(\\lambda)$ is given by a Thomas-Fermi type variational problem and $c^{\\rm H}\\approx -2.2339$ is an explicit constant. We also show that the radius of a two-dimensional neutral atom is unbounded when $Z\\to \\infty$, which is contrary to the expected behavior of three-dimensional atoms....
Institute of Scientific and Technical Information of China (English)
王德华; 李红艳; 马晓光; 王美山; 杨传路
2007-01-01
Using the periodic orbit theory, we computed the quantum level density of a particle in the two-dimensional harmonic oscillator potential with and without the magnetic flux line for different cases. Especially discuss the influence of the magnetic flux line on the quantum level density. The results show when the frequency ratio of the two-dimensional harmonic potential is a rational number, the quantum level density is discrete. Each peak in the level density corresponds to one energy. However, when the frequency ratio is an irrational number, the level density is oscillating, when the magnetic flux is added, the amplitude of the oscillation decreased. This can be considered as a consequence of Aharonov-Bohm effect.%利用周期轨道理论,我们计算了在不同情况下,一个粒子在二维谐振子势中存在和不存在磁通量时的量子能级密度.重点讨论了磁通量对量子能级密度的影响.计算结果表明:当二维谐振子势的频率比值是有理数时,量子能级是分立的,能级密度中的每一条峰正好对应一个量子能级.然而,当频率比是无理数时,能级密度发生振荡,当加上磁通量后,振荡减小.这可以看作是Aharonov-Bohm效应的结果.
MAVRI, J; BERENDSEN, HJC
1994-01-01
A density-matrix evolution method [Berendsen and Mavri, J. Phys. Chem. 97, 13464 (1993)] coupled to a classical molecular dynamics simulation was applied to study a quantum harmonic oscillator immersed in a bath of Lennard-Jones particles. Eigenfunctions of the three, lowest levels of the unperturbe
MAVRI, J; BERENDSEN, HJC
1994-01-01
A density-matrix evolution method [Berendsen and Mavri, J. Phys. Chem. 97, 13464 (1993)] coupled to a classical molecular dynamics simulation was applied to study a quantum harmonic oscillator immersed in a bath of Lennard-Jones particles. Eigenfunctions of the three, lowest levels of the unperturbe
Bajer, Jirí; Miranowicz, Adam
2000-06-01
Second-harmonic generation in the no-energy-transfer regime can be a source of quasi-stationary sub-Poissonian light as was recently shown by Bajer et al (Bajer J, Haderka O and Perina J 1999 J. Opt. B: Quantum Semiclass. Opt. 1 529). We generalize their results for higher-harmonic generation by applying the numerical method of Hamiltonian diagonalization and the analytical semiclassical description of classical trajectories. The quasi-stationary behaviour of the sub-Poissonian photocount noise in the no-energy-transfer regime is explained. An approximate formula for the Fano factor is derived for arbitrary harmonics. It is predicted that the deepest quasi-stationary reduction of photocount noise in the no-energy-transfer regime is achieved in the third-harmonic generation.
Two-dimensional function photonic crystals
Wu, Xiang-Yao; Liu, Xiao-Jing; Liang, Yu
2016-01-01
In this paper, we have firstly proposed two-dimensional function photonic crystals, which the dielectric constants of medium columns are the functions of space coordinates $\\vec{r}$, it is different from the two-dimensional conventional photonic crystals constituting by the medium columns of dielectric constants are constants. We find the band gaps of two-dimensional function photonic crystals are different from the two-dimensional conventional photonic crystals, and when the functions form of dielectric constants are different, the band gaps structure should be changed, which can be designed into the appropriate band gaps structures by the two-dimensional function photonic crystals.
Quantum information entropies of ultracold atomic gases in a harmonic trap
Indian Academy of Sciences (India)
Tutul Biswas; Tarun Kanti Ghosh
2011-10-01
The position and momentum space information entropies of weakly interacting trapped atomic Bose–Einstein condensates and spin-polarized trapped atomic Fermi gases at absolute zero temperature are evaluated. We ﬁnd that sum of the position and momentum space information entropies of these quantum systems containing atoms conﬁned in a $D(≤ 3)$-dimensional harmonic trap has a universal form as $S^{(D)}_t = N(a D − b ln N)$, where ∼ 2.332 and = 2 for interacting bosonic systems and a ∼ 1.982 and = 1 for ideal fermionic systems. These results obey the entropic uncertainty relation given by Beckner, Bialynicki-Birula and Myceilski.
Energy Technology Data Exchange (ETDEWEB)
Thantu, Napoleon; Schley, Robert Scott; B. L. Justus
2003-05-01
Two-photon excited emission centered at 379-426 nm in photodarkening borosilicate glass doped with CuCl nanocrystalline quantum dots at room temperature has been observed. The emission is detected in the direction of the fundamental near-infrared beam. Time- and frequency-resolved measurements at room temperature and 77 K indicate that the emission is largely coherent light characteristic of second harmonic generation (SHG). An average conversion efficiency of ~10-10 is obtained for a 2 mm thick sample. The observed SHG can originate in the individual noncentrosymmetric nanocrystals, leading to a bulk-like contribution, and at the nanocrystal-glass interface, leading to a surface contribution. The bulk-like conversion efficiency is estimated using previously reported values of coherence length (5m) and bulk nonlinear susceptibility. This bulk-like conversion efficiency estimate is found to be smaller than the measured value, suggesting a more prominent surface contribution.
Directory of Open Access Journals (Sweden)
Andrea V. Bragas
2011-03-01
Full Text Available We report the enhancement of the optical second harmonic signal in non-centrosymmetric semiconductor CdS quantum dots, when they are placed in close contact with isolated silver nanoparticles. The intensity enhancement is about 1000. We also show that the enhancement increases when the incoming laser frequency $omega$ is tuned toward the spectral position of the silver plasmon at $2omega$, proving that the silver nanoparticle modifies the nonlinear emission.Received: 8 March 2011, Accepted: 30 May 2011; Edited by: L. Viña; Reviewed by: R. Gordon, Department of Electrical and Computer Engineering, University of Victoria, British Columbia, Canada; DOI: 10.4279/PIP.030002Cite as: P. M. Jais, C. von Bilderling, A. V. Bragas, Papers in Physics 3, 030002 (2011
Second-harmonic generation in asymmetric quantum dots in the presence of a static magnetic field
Institute of Scientific and Technical Information of China (English)
Li Xue-Chao; Wang An-Min; Wang Zhao-Liang; Yang Yang
2012-01-01
The second-harmonic generation (SHG) coefficient in an asymmetric quantum dot (QD) with a static magnetic field is theoretically investigated.Within the framework of the effective-mass approximation,we obtain the confined wave functions and energies of electrons in the QD.We also obtain the SHG coefficient by the compact-density-matrix approach and the iterative method.The numerical results for the typical GaAs/AlGaAs QD show that the SHG coefficient depends strongly on the magnitude of magnetic field,parameters of the asymmetric potential and the radius of the QD.The resonant peak shifts with the magnetic field or the radius of the QD changing.
Correlation effects on the energy spectra of quantum dot electrons with harmonic model interactions
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The low-lying excitation energy spectra of two, three and five quantum dot electrons with harmonic model interactions in a large magnetic field are calculated by the Hartree-Fock(HF) methods. Correlation effects on the energy level structures are investigated by comparing the HF results with the exact ones. It is found that the pure collective excitations(center-of-mass mode quanta) existing in the exact energy spectra do not appear in the HF energy spectra. The degeneracies of energy levels are also related to the correlation interactions, especially in the energy spectrum of two electrons. In the cases of more than two electrons, as the electron-electron interaction strength is increased the HF energy levels exhibit more complex crossings than the exact ones.
Evolution of a quantum harmonic oscillator coupled to a minimal thermal environment
Vidiella-Barranco, A.
2016-10-01
In this paper it is studied the influence of a minimal thermal environment on the dynamics of a quantum harmonic oscillator (labelled A), prepared in a coherent state. The environment itself consists of a second oscillator (labelled B), initially in a thermal state. Two types of interaction Hamiltonians are considered, and the time-evolution of the reduced density operator of oscillator A is compared to the one obtained from the usual master equation approach, i.e., assuming that oscillator A is coupled to a large reservoir. An analysis of the linear entropy evolution of oscillator A shows that simplified models may be able to describe important features related to the phenomenon of decoherence, such as the rapid growth of the linear entropy, as well as its dependence on the effective temperature of the environment.
Wang, Zhiguo; Liang, Zhenguo
2017-04-01
In this paper we prove an infinite dimensional KAM theorem, in which the assumptions on the derivatives of the perturbation in [24] are weakened from polynomial decay to logarithmic decay. As a consequence, we can apply it to 1D quantum harmonic oscillators and prove the reducibility of the linear harmonic oscillator, T=-\\frac{{{\\text{d}}2}}{\\text{d}{{x}2}}+{{x}2} , on {{L}2}≤ft({R}\\right) perturbed by the quasi-periodic in the time potential V(x,ω t;ω ) with logarithmic decay. This proves the pure-point nature of the spectrum of the Floquet operator K, where K:=‑i∑k=1nωk∂∂θk‑d2dx2+x2+εV(x,θω) is defined on {{L}2}≤ft({R}\\right)\\otimes {{L}2}≤ft({{{T}}n}\\right) , and the potential V(x,θ ;ω ) has logarithmic decay as well as its gradient in ω.
Role of quantum trajectory in high-order harmonic generation in the Keldysh multiphoton regime.
Li, Peng-Cheng; Jiao, Yuan-Xiang; Zhou, Xiao-Xin; Chu, Shih-I
2016-06-27
We present a systematic study of spectral and temporal structure of high-order harmonic generation (HHG) by solving accurately the time-dependent Schrödinger equation for a hydrogen atom in the multiphoton regime where the Keldysh parameter is greater unity. Combining with a time-frequency transform and an extended semiclassical analysis, we explore the role of quantum trajectory in HHG. We find that the time-frequency spectra of the HHG plateau near cutoff exhibit a decrease in intensity associated with the short- and long-trajectories when the ionization process is pushed from the multiphoton regime into the tunneling regime. This implies that the harmonic emission spectra in the region of the HHG plateau near and before the cutoff are suppressed. To see the generality of this prediction, we also present a time-dependent density-functional theoretical study of the effect of correlated multi-electron responses on the spectral and temporal structure of the HHG plateau of the Ar atom.
Tuset-Sanchis, Luis; Castro-Palacio, Juan C.; Gómez-Tejedor, José A.; Manjón, Francisco J.; Monsoriu, Juan A.
2015-01-01
A smartphone acceleration sensor is used to study two-dimensional harmonic oscillations. The data recorded by the free android application, Accelerometer Toy, is used to determine the periods of oscillation by graphical analysis. Different patterns of the Lissajous curves resulting from the superposition of harmonic motions are illustrated for…
Two-dimensional gas of massless Dirac fermions in graphene.
Novoselov, K S; Geim, A K; Morozov, S V; Jiang, D; Katsnelson, M I; Grigorieva, I V; Dubonos, S V; Firsov, A A
2005-11-10
Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.
Institute of Scientific and Technical Information of China (English)
许莹; 李晋斌
2012-01-01
采用随机级数展开的量子蒙特卡罗方法研究二维硬核的玻色-赫伯德模型的热力学性质.首先通过算符变换将模型映射成为二维反铁磁准海森伯模型.变换后的模型比通常的海森伯模型多一项,该项正比于系统的格点总数N,对于大粒子数的系统,该项使模拟耗时指数增加,所以难以计算大粒子数系统.采用非局域操作循环更新后,这个困难可以得到很好的解决,可使粒子数总数增大到几千个.研究结果表明,粒子数密度在0—0.5范围内增大时,能量呈递减趋势,并趋于某一定值,随着正方晶格系统尺度增大,能量也随之增大;正方晶格系统尺度一定时,能量和磁化强度随着温度的升高而增大,化学势的变化对能量和磁化强度没有影响,能量随着正方晶格系统尺度增大而增大,磁化强度却随之减小;正方晶格系统尺度一定时,化学势的增大对比热没有影响,随着温度的升高比热出现先增大后减小的趋势,最后趋于某个值,达到平衡,而正方晶格系统尺度越大,比热曲线增大部分的趋势越大,减小部分的趋势也更明显,参照朗道超流理论,本文模拟的能量和比热曲线趋势与朗道二流体模型下HeⅡ的理论研究一致;不同正方晶格系统尺度的影响不大,均匀磁化率倒数在0—0.5（J/k_B）的低温范围内有很小的波动,J为耦合能,k_B为玻尔兹曼常数,温度在0.5—2（J/k_B）的范围内,均匀磁化率的倒数随着温度的升高而增大,且曲线的趋势显示了一种类似近藤行为.%In this paper,the stochastic series expansion quantum Monte Carlo method is employed to investigate the thermodynamic properties of hardcore Bose-Hubbard model in two-dimensional space.The two-dimensional hardcore Bose-Hubbard model can be mapped into the two-dimensional antiferromagnetic quasi-Heisenberg model under transform of bosonic operators.There is an additional term which is proportional
A new look at the quantum mechanics of the harmonic oscillator
Energy Technology Data Exchange (ETDEWEB)
Kastrup, H.A.
2006-12-15
At first sight it is probably hard to believe that something new can be said about the harmonic oscillator (HO). But that is so indeed: Classically the Harmonic Oscillator (HO) is the generic example for the use of angle and action variables {phi} element of R mod 2{pi} and I>0. However, the transformation q= {radical}(2I)cos {phi}, p=-{radical}(2I)sin {phi} is only locally symplectic and singular for (q,p)=(0,0). Globally the phase space {l_brace}(q,p){r_brace} has the topological structure of the plane R{sup 2}, whereas the phase space {l_brace}({phi},I){r_brace} corresponds globally to the punctured plane R{sup 2}-(0,0) or to a simple cone S{sup 1} x R{sup +} with the tip deleted. This makes a qualitative difference as to the quantum theory of the two phase spaces: The quantizing canonical group for the plane R{sup 2} consists of the (centrally extended) translations generated by the Poisson Lie algebra basis {l_brace}q,p,1{r_brace}, whereas the corresponding canonical group of the phase space {l_brace}({phi},I){r_brace} is the group SO{up_arrow}(1,2)=Sp(2,R)/Z{sub 2}, where Sp(2,R) is the sympletic group of the plane, with the generating Poisson Lie algebra basis {l_brace}h{sub 0}=I,h{sub 1}=Icos{phi},h{sub 2}=-Isin{phi}{r_brace} which provides also the basic ''observables'' on {l_brace}({phi}, I){r_brace}. In the quantum mechanics of the ({phi},I)-model of the HO the three h{sub j} correspond to self-adjoint generators K{sub j}, j=0,1,2, of irreducible unitary representations from the positive discrete series of the group SO{up_arrow}(1,2) or one of its infinitely many covering groups, the representations parametrized by the Bargmann index k>0. This index k determines the ground state energy E{sub k,n=0}={Dirac_h}{omega}k of the ({phi},I)-Hamiltonian H(anti K)={Dirac_h}{omega}K{sub 0}. For an m-fold covering the lowest possible value for k is k=1/m, which can be made arbitrarily small by choosing m accordingly. This is not in contraction to
The nonlinear optical response of a two-dimensional atomic crystal
Merano, Michele
2015-01-01
The theory of Bloembergen and Persham for the light waves at the boundary of nonlinear media is applied to a nonlinear two-dimensional atomic crystal placed in between linear bulk media. The crystal is treated as a zero-thickness interface, a real two-dimensional system. Harmonic waves emanate from it. Generalization of the laws of reflection and refraction give the direction and the intensity of the harmonic waves. The nonlinear polarization of these special materials is very sensitive to the substrate on which they are deposited. Experiments on second harmonic generation of a $\\rm MoS_{2}$ monolayer are discussed to elucidate this point.
Davydov, Alexander
2010-01-01
It is accepted wisdom that language and formalism of classical physics are inadequate for description of quantum phenomena. Here I confront this point of view by showing that there exists a surprisingly accurate mapping between representation of some quantum phenomena in one dimension and behavior of a classical time-dependent harmonic oscillator. For the first time, I demonstrate that such quintessentially quantum effect as tunneling through a potential barrier can be described in terms of classical physics without violating the energy conservation law at any time instance. A formula is presented that generates a wide class of one-dimensional potential barrier shapes in analytic form with the desired reflection (transmission) coefficient and transmission phase shift along with the corresponding exact solutions of the time-independent Schr\\"odinger's equation. Based on these results and numerical evidence, I put forward a conjecture that a classical (macroscopic) harmonic oscillator disturbed by a parametric ...
Davydov, Alexander
2010-01-01
It is accepted wisdom that language and formalism of classical physics are inadequate for description of quantum phenomena. Here I confront this point of view by showing that there exists a surprisingly accurate mapping between representation of some quantum phenomena in one dimension and behavior of a classical time-dependent harmonic oscillator. For the first time, I demonstrate that such quintessentially quantum effect as tunneling through a potential barrier can be described in terms of classical physics without violating the energy conservation law at any time instance. A formula is presented that generates a wide class of one-dimensional potential barrier shapes in analytic form with the desired reflection (transmission) coefficient and transmission phase shift along with the corresponding exact solutions of the time-independent Schr\\"odinger's equation. Based on these results and numerical evidence, I put forward a conjecture that a classical (macroscopic) harmonic oscillator disturbed by a parametric ...
Directory of Open Access Journals (Sweden)
Ashkan Emami Ale Agha
2013-06-01
Full Text Available One of the most important concepts in multi programming Operating Systems is scheduling. It helps in choosing the processes for execution. Round robin method is one of the most important algorithms in scheduling. It is the most popular algorithm due to its fairness and starvation free nature towards the processes, which is achieved by using proper quantum time. The main challenge in this algorithm is selection of quantum time. This parameter affects on average Waiting Time and average Turnaround Time in execution queue. As the quantum time is static, it causes less context switching in case of high quantum time and high context switching in case of less quantum time. Increasing context switch leads to high average waiting time, high average turnaround time which is an overhead and degrades the system performance. With respect to these points, the algorithms should calculate proper value for the quantum time. Two main classes of algorithms that are proposed to calculate the quantum time include static and dynamic methods. In static methods quantum time is fixed during the scheduling. Dynamic algorithms are one of these methods that change the value of quantum time in each cycle. For example in one method the value of quantum time in each cycle is equal to the median of burst times of processes in ready queue and for another method this value is equal to arithmetic mean of burst times of ready processes.In this paper we proposed a new method to obtaining quantum time in each cycle based on arithmetic-harmonic mean (HARM. Harmonic mean is calculated by dividing the number of observations by the reciprocal of each number in the series. With examples we show that in some cases it can provides better scheduling criteria and improves the average Turnaround Time and average Waiting Time.
Thermodynamical analysis of a quantum heat engine based on harmonic oscillators
Insinga, Andrea; Andresen, Bjarne; Salamon, Peter
2016-07-01
Many models of heat engines have been studied with the tools of finite-time thermodynamics and an ensemble of independent quantum systems as the working fluid. Because of their convenient analytical properties, harmonic oscillators are the most frequently used example of a quantum system. We analyze different thermodynamical aspects with the final aim of the optimization of the performance of the engine in terms of the mechanical power provided during a finite-time Otto cycle. The heat exchange mechanism between the working fluid and the thermal reservoirs is provided by the Lindblad formalism. We describe an analytical method to find the limit cycle and give conditions for a stable limit cycle to exist. We explore the power production landscape as the duration of the four branches of the cycle are varied for short times, intermediate times, and special frictionless times. For short times we find a periodic structure with atolls of purely dissipative operation surrounding islands of divergent behavior where, rather than tending to a limit cycle, the working fluid accumulates more and more energy. For frictionless times the periodic structure is gone and we come very close to the global optimal operation. The global optimum is found and interestingly comes with a particular value of the cycle time.
Institute of Scientific and Technical Information of China (English)
ZHANG Li; XIE Hong-Jing
2003-01-01
Within the framework of the compact density matrix approach, the third-harmonic generation (THG) in an electric-field-biased semi-parabolic quantum well (QW) has been deduced and investigated. Via variant of displacement harmonic oscillation, the exact electronic states in the semi-parabolic QW with an applied electric field have also been obtained and discussed. Numerical results on typical GaAs material reveal that, electric fields and confined potential frequency of semi-parabolic Q W have obvious influences on the energy levels of electronic states and the THG in the semi-parabolic Q W systems.
Institute of Scientific and Technical Information of China (English)
ZHANGLi; XIEHong-Jing
2003-01-01
Within the framework of the compact density matrix approach, the third-harmonic generation (THG) in an electric-field-biased semi-parabolic quantum well (QW) has been deduced and investigated. Via variant of displacement harmonic oscillation, the exact electronic states in the semi-parabolic QW with an applied electric field have also been obtained and discussed. Numerical results on typical GaAs material reveal that, electric fields and confined potential frequency of semi-parabolic QW have obvious influences on the energy levels of electronic states and the THG in the semi-parabolic QW systems.
Predicting Two-Dimensional Silicon Carbide Monolayers.
Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I
2015-10-27
Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics.
Topological defects in two-dimensional crystals
Chen, Yong; Qi, Wei-Kai
2008-01-01
By using topological current theory, we study the inner topological structure of the topological defects in two-dimensional (2D) crystal. We find that there are two elementary point defects topological current in two-dimensional crystal, one for dislocations and the other for disclinations. The topological quantization and evolution of topological defects in two-dimensional crystals are discussed. Finally, We compare our theory with Brownian-dynamics simulations in 2D Yukawa systems.
Level crossings in complex two-dimensional potentials
Indian Academy of Sciences (India)
Qing-Hai Wang
2009-08-01
Two-dimensional $\\mathcal{PT}$-symmetric quantum-mechanical systems with the complex cubic potential 12 = 2 + 2 + 2 and the complex Hénon–Heiles potential HH = 2 + 2 + (2 − 3/3) are investigated. Using numerical and perturbative methods, energy spectra are obtained to high levels. Although both potentials respect the $\\mathcal{PT}$ symmetry, the complex energy eigenvalues appear when level crossing happens between same parity eigenstates.
Chronology Protection in Two-Dimensional Dilaton Gravity
Mishima, T; Mishima, Takashi; Nakamichi, Akika
1994-01-01
The global structure of 1 + 1 dimensional compact Universe is studied in two-dimensional model of dilaton gravity. First we give a classical solution corresponding to the spacetime in which a closed time-like curve appears, and show the instability of this spacetime due to the existence of matters. We also observe quantum version of such a spacetime having closed timelike curves never reappear unless the parameters are fine-tuned.
Tricritical behavior in a two-dimensional field theory
Hamber, Herbert
1980-05-01
The critical behavior of a two-dimensional scalar Euclidean field theory with a potential term that allows for three minima is analyzed using an approximate position-space renormalization-group transformation on the equivalent quantum spin Hamiltonian. The global phase diagram shows a tricritical point separating a critical line from a line of first-order transitions. Other critical properties are examined, and good agreement is found with results on classical spin models belonging to the same universality class.
Strongly interacting two-dimensional Dirac fermions
Lim, L.K.; Lazarides, A.; Hemmerich, Andreas; de Morais Smith, C.
2009-01-01
We show how strongly interacting two-dimensional Dirac fermions can be realized with ultracold atoms in a two-dimensional optical square lattice with an experimentally realistic, inherent gauge field, which breaks time reversal and inversion symmetries. We find remarkable phenomena in a temperature
Topology optimization of two-dimensional waveguides
DEFF Research Database (Denmark)
Jensen, Jakob Søndergaard; Sigmund, Ole
2003-01-01
In this work we use the method of topology optimization to design two-dimensional waveguides with low transmission loss.......In this work we use the method of topology optimization to design two-dimensional waveguides with low transmission loss....
Yoshino, Harukazu; Murata, Keizo; Nakanishi, Tsutomu; Li, Lin; Choi, Eun Sang; Graf, David; Brooks, James S.; Nogami, Yoshio; Papavassiliou, George C.
2005-01-01
The effect of thermal treatment on the transport properties is studied for a two-dimensional organic conductor τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y, (y ≤ 0.875). The temperature dependence of the electric resistivity below room temperature was found to be changed from metallic down to low temperature to semiconducting by heating up to 420 K. One of the two frequencies of Shubnikov--de Haas oscillations are found to be different between the non-heated and heated parts from a single crystal, while no evidence of structural change in X-ray photograph was observed. The present result clearly shows that nominal valence or band filling can be controlled by simple thermal treatment for the quasi-two-dimensional organic metal. The mechanism of the change in the band filling is discussed in terms of anion decomposition.
Perturbations and quantum relaxation
Kandhadai, Adithya
2016-01-01
We investigate whether small perturbations can cause relaxation to quantum equilibrium over very long timescales. We consider in particular a two-dimensional harmonic oscillator, which can serve as a model of a field mode on expanding space. We assume an initial wave function with small perturbations to the ground state. We present evidence that the trajectories are highly confined so as to preclude relaxation to equilibrium even over very long timescales. Cosmological implications are briefly discussed.
Quantum Diffusion on a Dynamically Disordered and Harmonically Driven Lattice with Static Bias:
Singh, Navinder; Kumar, N.
We revisit the problem of quantum diffusion of a particle moving on a lattice with dynamical disorder. Decoherence, essential for the diffusive motion, is introduced via a set of Lindblad operators, known to guarantee per se the positivity, Hermiticity and the trace-class nature of the reduced density matrix, are derived and solved analytically for several transport quantities of interest. For the special Hermitian choice of the Lindblad operators projected onto the lattice sites, we recover several known results, obtained by others, e.g. through the stochastic Liouville equation using phenomenological damping terms for the off-diagonal density-matrix elements. An interesting result that we obtained is for the case of a 1D lattice with static potential bias and a time-harmonic modulation (ac drive) of its transition-matrix element, where the diffusion coefficient shows an oscillatory behavior as function of the drive amplitude and frequency — clearly, a Wannier-Stark ladder signature. The question of dissipation is also briefly discussed.
Quadrupole second harmonic generation and sum-frequency generation in ZnO quantum dots
Energy Technology Data Exchange (ETDEWEB)
Maikhuri, Deepti; Purohit, S. P., E-mail: sppurohitjiit@gmail.com; Mathur, K. C. [Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida, U.P. 201307 (India)
2015-04-15
The second harmonic generation (SHG) and the sum frequency generation (SFG) processes are investigated in the conduction band states of the singly charged ZnO quantum dot (QD) embedded in the HfO{sub 2}, and the AlN matrices. With two optical fields of frequency ω{sub p} and ω{sub q} incident on the dot, we study the variation with frequency of the second order nonlinear polarization resulting in SHG and SFG, through the electric dipole and the electric quadrupole interactions of the pump fields with the electron in the dot. We obtain enhanced value of the second order nonlinear susceptibility in the dot compared to the bulk. The effective mass approximation with the finite confining barrier is used for obtaining the energy and wavefunctions of the quantized confined states of the electron in the conduction band of the dot. Our results show that both the SHG and SFG processes depend on the dot size, the surrounding matrix and the polarization states of the pump beams.
Saha, Surajit; Ghosh, Manas
2016-03-01
We perform a broad exploration of profiles of third harmonic generation (THG) susceptibility of impurity doped quantum dots (QDs) in the presence and absence of noise. We have invoked Gaussian white noise in the present study. A Gaussian impurity has been introduced into the QD. Noise has been applied to the system additively and multiplicatively. A perpendicular magnetic field emerges out as a confinement source and a static external electric field has been applied. The THG profiles have been pursued as a function of incident photon energy when several important parameters such as electric field strength, magnetic field strength, confinement energy, dopant location, Al concentration, dopant potential, relaxation time and noise strength assume different values. Moreover, the role of the pathway through which noise is applied (additive/multiplicative) on the THG profiles has also been deciphered. The THG profiles are found to be decorated with interesting observations such as shift of THG peak position and maximization/minimization of THG peak intensity. Presence of noise alters the characteristics of THG profiles and sometimes enhances the THG peak intensity. Furthermore, the mode of application of noise (additive/multiplicative) also regulates the THG profiles in a few occasions in contrasting manners. The observations highlight the possible scope of tuning the THG coefficient of doped QD systems in the presence of noise and bears tremendous technological importance.
Interaction of two-dimensional magnetoexcitons
Dumanov, E. V.; Podlesny, I. V.; Moskalenko, S. A.; Liberman, M. A.
2017-04-01
We study interaction of the two-dimensional magnetoexcitons with in-plane wave vector k→∥ = 0 , taking into account the influence of the excited Landau levels (ELLs) and of the external electric field perpendicular to the surface of the quantum well and parallel to the external magnetic field. It is shown that the account of the ELLs gives rise to the repulsion between the spinless magnetoexcitons with k→∥ = 0 in the Fock approximation, with the interaction constant g decreasing inverse proportional to the magnetic field strength B (g (0) ∼ 1 / B) . In the presence of the perpendicular electric field the Rashba spin-orbit coupling (RSOC), Zeeman splitting (ZS) and nonparabolicity of the heavy-hole dispersion law affect the Landau quantization of the electrons and holes. They move along the new cyclotron orbits, change their Coulomb interactions and cause the interaction between 2D magnetoexcitons with k→∥ = 0 . The changes of the Coulomb interactions caused by the electrons and by the holes moving with new cyclotron orbits are characterized by some coefficients, which in the absence of the electric field turn to be unity. The differences between these coefficients of the electron-hole pairs forming the magnetoexcitons determine their affinities to the interactions. The interactions between the homogeneous, semihomogeneous and heterogeneous magnetoexcitons forming the symmetric states with the same signs of their affinities are attractive whereas in the case of different sign affinities are repulsive. In the heterogeneous asymmetric states the interactions have opposite signs in comparison with the symmetric states. In all these cases the interaction constant g have the dependence g (0) 1 /√{ B} .
Two Dimensional Plasmonic Cavities on Moire Surfaces
Balci, Sinan; Kocabas, Askin; Karabiyik, Mustafa; Kocabas, Coskun; Aydinli, Atilla
2010-03-01
We investigate surface plasmon polariton (SPP) cavitiy modes on two dimensional Moire surfaces in the visible spectrum. Two dimensional hexagonal Moire surface can be recorded on a photoresist layer using Interference lithography (IL). Two sequential exposures at slightly different angles in IL generate one dimensional Moire surfaces. Further sequential exposure for the same sample at slightly different angles after turning the sample 60 degrees around its own axis generates two dimensional hexagonal Moire cavity. Spectroscopic reflection measurements have shown plasmonic band gaps and cavity states at all the azimuthal angles (omnidirectional cavity and band gap formation) investigated. The plasmonic band gap edge and the cavity states energies show six fold symmetry on the two dimensional Moire surface as measured in reflection measurements.
Two-dimensional function photonic crystals
Liu, Xiao-Jing; Liang, Yu; Ma, Ji; Zhang, Si-Qi; Li, Hong; Wu, Xiang-Yao; Wu, Yi-Heng
2017-01-01
In this paper, we have studied two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , that can become true easily by electro-optical effect and optical kerr effect. We calculated the band gap structures of TE and TM waves, and found the TE (TM) wave band gaps of function photonic crystals are wider (narrower) than the conventional photonic crystals. For the two-dimensional function photonic crystals, when the dielectric constant functions change, the band gaps numbers, width and position should be changed, and the band gap structures of two-dimensional function photonic crystals can be adjusted flexibly, the needed band gap structures can be designed by the two-dimensional function photonic crystals, and it can be of help to design optical devices.
Two-Dimensional Planetary Surface Lander
Hemmati, H.; Sengupta, A.; Castillo, J.; McElrath, T.; Roberts, T.; Willis, P.
2014-06-01
A systems engineering study was conducted to leverage a new two-dimensional (2D) lander concept with a low per unit cost to enable scientific study at multiple locations with a single entry system as the delivery vehicle.
Energy Technology Data Exchange (ETDEWEB)
Ibarra-Sierra, V.G.; Sandoval-Santana, J.C. [Departamento de Física, Universidad Autónoma Metropolitana Iztapalapa, Av. San Rafael Atlixco 186, Col. Vicentina, 09340 México D.F. (Mexico); Cardoso, J.L. [Área de Física Teórica y Materia Condensada, Universidad Autónoma Metropolitana Azcapotzalco, Av. San Pablo 180, Col. Reynosa-Tamaulipas, Azcapotzalco, 02200 México D.F. (Mexico); Kunold, A., E-mail: akb@correo.azc.uam.mx [Área de Física Teórica y Materia Condensada, Universidad Autónoma Metropolitana Azcapotzalco, Av. San Pablo 180, Col. Reynosa-Tamaulipas, Azcapotzalco, 02200 México D.F. (Mexico)
2015-11-15
We discuss the one-dimensional, time-dependent general quadratic Hamiltonian and the bi-dimensional charged particle in time-dependent electromagnetic fields through the Lie algebraic approach. Such method consists in finding a set of generators that form a closed Lie algebra in terms of which it is possible to express a quantum Hamiltonian and therefore the evolution operator. The evolution operator is then the starting point to obtain the propagator as well as the explicit form of the Heisenberg picture position and momentum operators. First, the set of generators forming a closed Lie algebra is identified for the general quadratic Hamiltonian. This algebra is later extended to study the Hamiltonian of a charged particle in electromagnetic fields exploiting the similarities between the terms of these two Hamiltonians. These results are applied to the solution of five different examples: the linear potential which is used to introduce the Lie algebraic method, a radio frequency ion trap, a Kanai–Caldirola-like forced harmonic oscillator, a charged particle in a time dependent magnetic field, and a charged particle in constant magnetic field and oscillating electric field. In particular we present exact analytical expressions that are fitting for the study of a rotating quadrupole field ion trap and magneto-transport in two-dimensional semiconductor heterostructures illuminated by microwave radiation. In these examples we show that this powerful method is suitable to treat quadratic Hamiltonians with time dependent coefficients quite efficiently yielding closed analytical expressions for the propagator and the Heisenberg picture position and momentum operators. -- Highlights: •We deal with the general quadratic Hamiltonian and a particle in electromagnetic fields. •The evolution operator is worked out through the Lie algebraic approach. •We also obtain the propagator and Heisenberg picture position and momentum operators. •Analytical expressions for a
Entanglement Entropy in Two-Dimensional String Theory.
Hartnoll, Sean A; Mazenc, Edward A
2015-09-18
To understand an emergent spacetime is to understand the emergence of locality. Entanglement entropy is a powerful diagnostic of locality, because locality leads to a large amount of short distance entanglement. Two-dimensional string theory is among the very simplest instances of an emergent spatial dimension. We compute the entanglement entropy in the large-N matrix quantum mechanics dual to two-dimensional string theory in the semiclassical limit of weak string coupling. We isolate a logarithmically large, but finite, contribution that corresponds to the short distance entanglement of the tachyon field in the emergent spacetime. From the spacetime point of view, the entanglement is regulated by a nonperturbative "graininess" of space.
Topological states in two-dimensional hexagon lattice bilayers
Zhang, Ming-Ming; Xu, Lei; Zhang, Jun
2016-10-01
We investigate the topological states of the two-dimensional hexagon lattice bilayer. The system exhibits a quantum valley Hall (QVH) state when the interlayer interaction t⊥ is smaller than the nearest neighbor hopping energy t, and then translates to a trivial band insulator state when t⊥ / t > 1. Interestingly, the system is found to be a single-edge QVH state with t⊥ / t = 1. The topological phase transition also can be presented via changing bias voltage and sublattice potential in the system. The QVH states have different edge modes carrying valley current but no net charge current. The bias voltage and external electric field can be tuned easily in experiments, so the present results will provide potential application in valleytronics based on the two-dimensional hexagon lattice.
Exact solution of a quantum forced time-dependent harmonic oscillator
Yeon, Kyu Hwang; George, Thomas F.; Um, Chung IN
1992-01-01
The Schrodinger equation is used to exactly evaluate the propagator, wave function, energy expectation values, uncertainty values, and coherent state for a harmonic oscillator with a time dependent frequency and an external driving time dependent force. These quantities represent the solution of the classical equation of motion for the time dependent harmonic oscillator.
Relativistic Harmonic Oscillators and Hadronic Structures in the Quantum-Mechanics Curriculum
Kim, Y. S.; Noz, Marilyn E.
1978-01-01
A relativistic harmonic-oscillator formalism which is mathematically simple as the nonrelativistic harmonic oscillator is given. In view of its effectiveness in describing Lorentz-deformed hadrons, the inclusion of this formalism in a first-year graduate course will make the results of high-energy experiments more understandable. (BB)
Energy Technology Data Exchange (ETDEWEB)
Arcos-Olalla, Rafael, E-mail: olalla@fisica.ugto.mx [Departamento de Física, DCI Campus León, Universidad de Guanajuato, Apdo. Postal E143, 37150 León, Gto. (Mexico); Reyes, Marco A., E-mail: marco@fisica.ugto.mx [Departamento de Física, DCI Campus León, Universidad de Guanajuato, Apdo. Postal E143, 37150 León, Gto. (Mexico); Rosu, Haret C., E-mail: hcr@ipicyt.edu.mx [IPICYT, Instituto Potosino de Investigacion Cientifica y Tecnologica, Apdo. Postal 3-74 Tangamanga, 78231 San Luis Potosí, S.L.P. (Mexico)
2012-10-01
We introduce an alternative factorization of the Hamiltonian of the quantum harmonic oscillator which leads to a two-parameter self-adjoint operator from which the standard harmonic oscillator, the one-parameter oscillators introduced by Mielnik, and the Hermite operator are obtained in certain limits of the parameters. In addition, a single Bernoulli-type parameter factorization, which is different from the one introduced by M.A. Reyes, H.C. Rosu, and M.R. Gutiérrez [Phys. Lett. A 375 (2011) 2145], is briefly discussed in the final part of this work. -- Highlights: ► Factorizations with operators which are not mutually adjoint are presented. ► New two-parameter and one-parameter self-adjoint oscillator operators are introduced. ► Their eigenfunctions are two- and one-parameter deformed Hermite functions.
Restrepo, R. L.; Kasapoglu, E.; Sakiroglu, S.; Ungan, F.; Morales, A. L.; Duque, C. A.
2017-09-01
The effects of electric and magnetic fields on the second and third harmonic generation coefficients in a Morse potential quantum well are theoretically studied. The energy levels and corresponding wave functions are obtained by solving the Schrödinger equation for the electron in the parabolic band scheme and effective mass approximations and the envelope function approach. The results show that both the electric and the magnetic fields have significant influence on the magnitudes and resonant peak energy positions of the second and third harmonic generation responses. In general, the Morse potential profile becomes wider and shallower as γ -parameter increases and so the energies of the bound states will be functions of this parameter. Therefore, we can conclude that the effects of the electric and magnetic fields can be used to tune and control the optical properties of interest in the range of the infrared electromagnetic spectrum.
Interpolation by two-dimensional cubic convolution
Shi, Jiazheng; Reichenbach, Stephen E.
2003-08-01
This paper presents results of image interpolation with an improved method for two-dimensional cubic convolution. Convolution with a piecewise cubic is one of the most popular methods for image reconstruction, but the traditional approach uses a separable two-dimensional convolution kernel that is based on a one-dimensional derivation. The traditional, separable method is sub-optimal for the usual case of non-separable images. The improved method in this paper implements the most general non-separable, two-dimensional, piecewise-cubic interpolator with constraints for symmetry, continuity, and smoothness. The improved method of two-dimensional cubic convolution has three parameters that can be tuned to yield maximal fidelity for specific scene ensembles characterized by autocorrelation or power-spectrum. This paper illustrates examples for several scene models (a circular disk of parametric size, a square pulse with parametric rotation, and a Markov random field with parametric spatial detail) and actual images -- presenting the optimal parameters and the resulting fidelity for each model. In these examples, improved two-dimensional cubic convolution is superior to several other popular small-kernel interpolation methods.
TWO-DIMENSIONAL TOPOLOGY OF COSMOLOGICAL REIONIZATION
Energy Technology Data Exchange (ETDEWEB)
Wang, Yougang; Xu, Yidong; Chen, Xuelei [Key Laboratory of Computational Astrophysics, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 China (China); Park, Changbom [School of Physics, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of); Kim, Juhan, E-mail: wangyg@bao.ac.cn, E-mail: cbp@kias.re.kr [Center for Advanced Computation, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of)
2015-11-20
We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two-dimensional genus curve for the early, middle, and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometre Array.
Two dimensional topology of cosmological reionization
Wang, Yougang; Xu, Yidong; Chen, Xuelei; Kim, Juhan
2015-01-01
We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two dimensional genus curve for the early, middle and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometer Array.
Energy Technology Data Exchange (ETDEWEB)
Mark, J. Abraham Hudson, E-mail: a.john.peter@gmail.com; Peter, A. John, E-mail: a.john.peter@gmail.com [Dept. of Physics, SSM Institute of Engineering and Technology, Dindigul-624002 (India)
2014-04-24
Third order susceptibility of third order harmonic generation is investigated in a Zn{sub 0.1}Mg{sub 0.9}Se/Zn{sub 0.8}Mg{sub 0.2}Se/Zn{sub 0.1}Mg{sub 0.9}Se quantum well in the presence of magnetic field strength. The confinement potential is considered as the addition of energy offsets of the conduction band (or valence band) and the strain-induced potential in our calculations. The material dependent effective mass is followed throughout the computation because it has a high influence on the electron energy levels in low dimensional semiconductor systems.
The q-DEFORMED SCHRÖDINGER Equation of the Harmonic Oscillator on the Quantum Euclidean Space
Carow-Watamura, Ursula; Watamura, Satoshi
We consider the q-deformed Schrödinger equation of the harmonic oscillator on the N-dimensional quantum Euclidean space. The creation and annihilation operators are found, which systematically produce all energy levels and eigenfunctions of the Schrödinger equation. In order to get the q series representation of the eigenfunction, we also give an alternative way to solve the Schrödinger equation which is based on the q analysis. We represent the Schrödinger equation by the q difference equation and solve it by using q polynomials and q exponential functions.
Two-dimensional x-ray diffraction
He, Bob B
2009-01-01
Written by one of the pioneers of 2D X-Ray Diffraction, this useful guide covers the fundamentals, experimental methods and applications of two-dimensional x-ray diffraction, including geometry convention, x-ray source and optics, two-dimensional detectors, diffraction data interpretation, and configurations for various applications, such as phase identification, texture, stress, microstructure analysis, crystallinity, thin film analysis and combinatorial screening. Experimental examples in materials research, pharmaceuticals, and forensics are also given. This presents a key resource to resea
Matching Two-dimensional Gel Electrophoresis' Spots
DEFF Research Database (Denmark)
Dos Anjos, António; AL-Tam, Faroq; Shahbazkia, Hamid Reza
2012-01-01
This paper describes an approach for matching Two-Dimensional Electrophoresis (2-DE) gels' spots, involving the use of image registration. The number of false positive matches produced by the proposed approach is small, when compared to academic and commercial state-of-the-art approaches. This ar......This paper describes an approach for matching Two-Dimensional Electrophoresis (2-DE) gels' spots, involving the use of image registration. The number of false positive matches produced by the proposed approach is small, when compared to academic and commercial state-of-the-art approaches...
Mobility anisotropy of two-dimensional semiconductors
Lang, Haifeng; Zhang, Shuqing; Liu, Zhirong
2016-12-01
The carrier mobility of anisotropic two-dimensional semiconductors under longitudinal acoustic phonon scattering was theoretically studied using deformation potential theory. Based on the Boltzmann equation with the relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was derived, showing that the influence of effective mass on mobility anisotropy is larger than those of deformation potential constant or elastic modulus. Parameters were collected for various anisotropic two-dimensional materials (black phosphorus, Hittorf's phosphorus, BC2N , MXene, TiS3, and GeCH3) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio is overestimated by the previously described method.
Towards two-dimensional search engines
Ermann, Leonardo; Chepelianskii, Alexei D.; Shepelyansky, Dima L.
2011-01-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way the ranking of nodes becomes two-dimensional that paves the way for development of two-dimensional search engines of new type. Statistical properties of inf...
Two-dimensionally confined topological edge states in photonic crystals
Barik, Sabyasachi; Miyake, Hirokazu; DeGottardi, Wade; Waks, Edo; Hafezi, Mohammad
2016-11-01
We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three-dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.
Two-Dimensionally Confined Topological Edge States in Photonic Crystals
Barik, Sabyasachi; DeGottardi, Wade; Waks, Edo; Hafezi, Mohammad
2016-01-01
We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.
Electronic Transmission Properties of Two-Dimensional Quasi-Lattice
Institute of Scientific and Technical Information of China (English)
侯志林; 傅秀军; 刘有延
2002-01-01
In the framework of the tight binding model, the electronic transmission properties of two-dimensional Penrose lattices with free boundary conditions are studied using the generalized eigenfunction method (Phys. Rev. B 60(1999)13444). The electronic transmission coefficients for Penrose lattices with different sizes and widths are calculated, and the result shows strong energy dependence because of the quasiperiodic structure and quantum coherent effect. Around the Fermi level E = 0, there is an energy region with zero transmission amplitudes,which suggests that the studied systems are insulating. The spatial distributions of several typical electronic states with different transmission coefficients are plotted to display the propagation process.
Two-dimensional chiral topological superconductivity in Shiba lattices
Li, Jian; Neupert, Titus; Wang, Zhijun; MacDonald, A. H.; Yazdani, A.; Bernevig, B. Andrei
2016-07-01
The chiral p-wave superconductor is the archetypal example of a state of matter that supports non-Abelian anyons, a highly desired type of exotic quasiparticle. With this, it is foundational for the distant goal of building a topological quantum computer. While some candidate materials for bulk chiral superconductors exist, they are subject of an ongoing debate about their actual paring state. Here we propose an alternative route to chiral superconductivity, consisting of the surface of an ordinary superconductor decorated with a two-dimensional lattice of magnetic impurities. We furthermore identify a promising experimental platform to realize this proposal.
Phase transitions in the two-dimensional Anisotropic Biquadratic Heisenberg Model
Energy Technology Data Exchange (ETDEWEB)
Moura, A.R., E-mail: armoura@infis.ufu.br [Universidade Federal de Uberlândia (Brazil); Pires, A.S.T., E-mail: antpires@fisica.ufmg.br [Universidade Federal de Minas Gerais (Brazil); Pereira, A.R., E-mail: apereira@ufv.br [Universidade Federal de Viçosa (Brazil)
2014-05-01
In this paper we study the influence of the single-ion anisotropy in the two-dimensional biquadratic Heisenberg model (ABHM) on the square lattice at zero and finite low temperatures. It is common to represent the bilinear and biquadratic terms by J{sub 1}=Jcosθ and J{sub 2}=Jsinθ, respectively, and the many phases present in the model as a function of θ are well documented. However we have adopted a constant value for the bilinear constant (J{sub 1}=1) and small values of the biquadratic term (|J{sub 2}|
Gonoskov, I A; Tsatrafyllis, N; Kominis, I K; Tzallas, P
2016-09-07
We analytically describe the strong-field light-electron interaction using a quantized coherent laser state with arbitrary photon number. We obtain a light-electron wave function which is a closed-form solution of the time-dependent Schrödinger equation (TDSE). This wave function provides information about the quantum optical features of the interaction not accessible by semi-classical theories. With this approach we can reveal the quantum optical properties of high harmonic generation (HHG) process in gases by measuring the photon statistics of the transmitted infrared (IR) laser radiation. This work can lead to novel experiments in high-resolution spectroscopy in extreme-ultraviolet (XUV) and attosecond science without the need to measure the XUV light, while it can pave the way for the development of intense non-classical light sources.
Noncommutative quantum mechanics
Gamboa, J.; Loewe, M.; Rojas, J. C.
2001-09-01
A general noncommutative quantum mechanical system in a central potential V=V(r) in two dimensions is considered. The spectrum is bounded from below and, for large values of the anticommutative parameter θ, we find an explicit expression for the eigenvalues. In fact, any quantum mechanical system with these characteristics is equivalent to a commutative one in such a way that the interaction V(r) is replaced by V=V(HHO,Lz), where HHO is the Hamiltonian of the two-dimensional harmonic oscillator and Lz is the z component of the angular momentum. For other finite values of θ the model can be solved by using perturbation theory.
Piezoelectricity in Two-Dimensional Materials
Wu, Tao
2015-02-25
Powering up 2D materials: Recent experimental studies confirmed the existence of piezoelectricity - the conversion of mechanical stress into electricity - in two-dimensional single-layer MoS2 nanosheets. The results represent a milestone towards embedding low-dimensional materials into future disruptive technologies. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
Kronecker Product of Two-dimensional Arrays
Institute of Scientific and Technical Information of China (English)
Lei Hu
2006-01-01
Kronecker sequences constructed from short sequences are good sequences for spread spectrum communication systems. In this paper we study a similar problem for two-dimensional arrays, and we determine the linear complexity of the Kronecker product of two arrays. Our result shows that similar good property on linear complexity holds for Kronecker product of arrays.
Two-Dimensional Toda-Heisenberg Lattice
Directory of Open Access Journals (Sweden)
Vadim E. Vekslerchik
2013-06-01
Full Text Available We consider a nonlinear model that is a combination of the anisotropic two-dimensional classical Heisenberg and Toda-like lattices. In the framework of the Hirota direct approach, we present the field equations of this model as a bilinear system, which is closely related to the Ablowitz-Ladik hierarchy, and derive its N-soliton solutions.
A novel two dimensional particle velocity sensor
Pjetri, Olti; Wiegerink, Remco J.; Lammerink, Theo S.; Krijnen, Gijs J.
2013-01-01
In this paper we present a two wire, two-dimensional particle velocity sensor. The miniature sensor of size 1.0x2.5x0.525 mm, consisting of only two crossed wires, shows excellent directional sensitivity in both directions, thus requiring no directivity calibration, and is relatively easy to fabrica
Two-dimensional microstrip detector for neutrons
Energy Technology Data Exchange (ETDEWEB)
Oed, A. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)
1997-04-01
Because of their robust design, gas microstrip detectors, which were developed at ILL, can be assembled relatively quickly, provided the prefabricated components are available. At the beginning of 1996, orders were received for the construction of three two-dimensional neutron detectors. These detectors have been completed. The detectors are outlined below. (author). 2 refs.
Two-dimensional magma-repository interactions
Bokhove, O.
2001-01-01
Two-dimensional simulations of magma-repository interactions reveal that the three phases --a shock tube, shock reflection and amplification, and shock attenuation and decay phase-- in a one-dimensional flow tube model have a precursor. This newly identified phase ``zero'' consists of the impact of
Two-dimensional subwavelength plasmonic lattice solitons
Ye, F; Hu, B; Panoiu, N C
2010-01-01
We present a theoretical study of plasmonic lattice solitons (PLSs) formed in two-dimensional (2D) arrays of metallic nanowires embedded into a nonlinear medium with Kerr nonlinearity. We analyze two classes of 2D PLSs families, namely, fundamental and vortical PLSs in both focusing and defocusing media. Their existence, stability, and subwavelength spatial confinement are studied in detai
A two-dimensional Dirac fermion microscope
DEFF Research Database (Denmark)
Bøggild, Peter; Caridad, Jose; Stampfer, Christoph
2017-01-01
in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2...
Energy Technology Data Exchange (ETDEWEB)
Mota, R D [Unidad Profesional Interdisciplinaria de IngenierIa y TecnologIas Avanzadas, IPN. Av. Instituto Politecnico Nacional 2580, Col. La Laguna Ticoman, 07340 Mexico DF (Mexico); Xicotencatl, M A [Departamento de Matematicas del Centro de Investigacion y Estudios Avanzados del IPN, Mexico DF, 07000 (Mexico); Granados, V D [Escuela Superior de FIsica y Matematicas, Instituto Politecnico Nacional, Ed. 9, Unidad Profesional Adolfo Lopez Mateos, 07738 Mexico DF (Mexico)
2004-02-20
In this work we introduce a generalization of the Jauch and Rohrlich quantum Stokes operators when the arrival direction from the source is unknown a priori. We define the generalized Stokes operators as the Jordan-Schwinger map of a triplet of harmonic oscillators with the Gell-Mann and Ne'eman matrices of the SU(3) symmetry group. We show that the elements of the Jordan-Schwinger map are the constants of motion of the three-dimensional isotropic harmonic oscillator. Also, we show that the generalized Stokes operators together with the Gell-Mann and Ne'eman matrices may be used to expand the polarization matrix. By taking the expectation value of the Stokes operators in a three-mode coherent state of the electromagnetic field, we obtain the corresponding generalized classical Stokes parameters. Finally, by means of the constants of motion of the classical 3D isotropic harmonic oscillator we describe the geometrical properties of the polarization ellipse.
Many body localization in two dimensional square and triangular lattices
Gonzalez-Garcia, L; Paredes, R
2016-01-01
Ultracold interacting Bose atoms placed in disordered two dimensional optical lattices with square and triangular symmetries are found to be localized above a certain disorder strength amplitude. From a Gross-Pitaevskii mean analysis we determine the localization length as a function of the disorder strength and investigate the energy spectrum in terms of the disorder magnitude. We found that the localization length is observed to decrease faster in triangular geometries than in square ones. In the presence of a harmonic confinement localization is observed at the center of the trap. The analysis of the energy spectrum reveals that discrete energy levels acquire a finite width that is always smaller than the distance among energy levels.
Collective Modes in Two Dimensional Binary Yukawa Systems
Kalman, Gabor J; Donko, Zoltan; Golden, Kenneth I; Kyrkos, Stamatios
2013-01-01
We analyze via theoretical approaches and molecular dynamics simulations the collective mode structure of strongly coupled two-dimensional binary Yukawa systems, for selected density, mass and charge ratios, both in the liquid and crystalline solid phases. Theoretically, the liquid phase is described through the Quasi-Localized Charge Approximation (QLCA) approach, while in the crystalline phase we study the centered honeycomb and the staggered rectangular crystal structures through the standard harmonic phonon approximation. We identify "longitudinal" and "transverse" acoustic and optic modes and find that the longitudinal acoustic mode evolves from its weakly coupled counterpart in a discontinuous non-perturbative fashion. The low frequency acoustic excitations are governed by the oscillation frequency of the average atom, while the high frequency optic excitation frequencies are related to the Einstein frequencies of the systems.
Creating tuneable microwave media from a two-dimensional lattice of re-entrant posts
Goryachev, Maxim; Tobar, Michael E.
2015-11-01
The potential capabilities of resonators based on two dimensional arrays of re-entrant posts is demonstrated. Such posts may be regarded as magnetically coupled lumped element microwave harmonic oscillators, arranged in a 2D lattices structure, which is enclosed in a 3D cavity. By arranging these elements in certain 2D patterns, we demonstrate how to achieve certain requirements with respect to field localisation and device spectra. Special attention is paid to symmetries of the lattices, mechanical tuning, design of areas of high localisation of magnetic energy; this in turn creates unique discrete mode spectra. We demonstrate analogies between systems designed on the proposed platform and well known physical phenomena such as polarisation, frustration, and Whispering Gallery Modes. The mechanical tunability of the cavity with multiple posts is analysed, and its consequences to optomechanical applications is calculated. One particular application to quantum memory is demonstrated with a cavity design consisting of separate resonators analogous to discrete Fabry-Pérot resonators. Finally, we propose a generalised approach to a microwave system design based on the concept of Programmable Cavity Arrays.
Creating tuneable microwave media from a two-dimensional lattice of re-entrant posts
Energy Technology Data Exchange (ETDEWEB)
Goryachev, Maxim; Tobar, Michael E. [ARC Centre of Excellence for Engineered Quantum Systems, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009 (Australia)
2015-11-28
The potential capabilities of resonators based on two dimensional arrays of re-entrant posts is demonstrated. Such posts may be regarded as magnetically coupled lumped element microwave harmonic oscillators, arranged in a 2D lattices structure, which is enclosed in a 3D cavity. By arranging these elements in certain 2D patterns, we demonstrate how to achieve certain requirements with respect to field localisation and device spectra. Special attention is paid to symmetries of the lattices, mechanical tuning, design of areas of high localisation of magnetic energy; this in turn creates unique discrete mode spectra. We demonstrate analogies between systems designed on the proposed platform and well known physical phenomena such as polarisation, frustration, and Whispering Gallery Modes. The mechanical tunability of the cavity with multiple posts is analysed, and its consequences to optomechanical applications is calculated. One particular application to quantum memory is demonstrated with a cavity design consisting of separate resonators analogous to discrete Fabry–Pérot resonators. Finally, we propose a generalised approach to a microwave system design based on the concept of Programmable Cavity Arrays.
Two-dimensional atom localization induced by a squeezed vacuum
Wang, Fei; Xu, Jun
2016-10-01
A scheme of two-dimensional (2D) atom localization induced by a squeezed vacuum is proposed, in which the three-level V-type atoms interact with two classical standing-wave fields. It is found that when the environment is changed from an ordinary vacuum to a squeezed vacuum, the 2D atom localization is realized by detecting the position-dependent resonance fluorescence spectrum. For comparison, we demonstrate that the atom localization originating from the quantum interference effect is distinct from that induced by a squeezed vacuum. Furthermore, the combined effects of the squeezed vacuum and quantum interference are also discussed under appropriate conditions. The internal physical mechanism is analyzed in terms of dressed-state representation. Project supported by the National Natural Science Foundation of China (Grant Nos. 11574179 and 11204099) and the Natural Science Foundation of Hubei Province, China (Grant No. 2014CFC1148).
Experimental evidence for a two-dimensional quantized Hall insulator
Hilke, M.; Shahar, D.; Song, S. H.; Tsui, D. C.; Xie, Y. H.; Monroe, Don
1998-10-01
The general theoretical definition of an insulator is a material in which the conductivity vanishes at the absolute zero of temperature. In classical insulators, such as materials with a band gap, vanishing conductivities lead to diverging resistivities. But other insulators can show more complex behaviour, particularly in the presence of a high magnetic field, where different components of the resistivity tensor can display different behaviours: the magnetoresistance diverges as the temperature approaches absolute zero, but the transverse (Hall) resistance remains finite. Such a system is known as a Hall insulator. Here we report experimental evidence for a quantized Hall insulator in a two-dimensional electron system-confined in a semiconductor quantum well. The Hall resistance is quantized in the quantum unit of resistance h/e2, where h is Planck's constant and e the electronic charge. At low fields, the sample reverts to being a normal Hall insulator.
Non-classical photon correlation in a two-dimensional photonic lattice
Gao, Jun; Lin, Xiao-Feng; Jiao, Zhi-Qiang; Feng, Zhen; Zhou, Zheng; Gao, Zhen-Wei; Xu, Xiao-Yun; Chen, Yuan; Tang, Hao; Jin, Xian-Min
2016-01-01
Quantum interference and quantum correlation, as two main features of quantum optics, play an essential role in quantum information applications, such as multi-particle quantum walk and boson sampling. While many experimental demonstrations have been done in one-dimensional waveguide arrays, it remains unexplored in higher dimensions due to tight requirement of manipulating and detecting photons in large-scale. Here, we experimentally observe non-classical correlation of two identical photons in a fully coupled two-dimensional structure, i.e. photonic lattice manufactured by three-dimensional femtosecond laser writing. Photon interference consists of 36 Hong-Ou-Mandel interference and 9 bunching. The overlap between measured and simulated distribution is up to $0.890\\pm0.001$. Clear photon correlation is observed in the two-dimensional photonic lattice. Combining with controllably engineered disorder, our results open new perspectives towards large-scale implementation of quantum simulation on integrated phot...
Time dependent quantum harmonic oscillator subject to a sudden change of mass: continuous solution
Energy Technology Data Exchange (ETDEWEB)
Moya C, H. [INAOE, Coordinacion de Optica, AP 51 y 216, 72000 Puebla (Mexico); Fernandez G, M. [Depto. de Fisica, CBI, Universidad Autonoma Metropolitana - Iztapalapa, 09340, Mexico, D.F. AP 55-534 (Mexico)
2007-07-01
We show that a harmonic oscillator subject to a sudden change of mass produces squeezed states. Our study is based on an approximate analytic solution to the time-dependent harmonic oscillator equation with a sub period function parameter. This continuous treatment differs from former studies that involve the matching of two time-independent solutions at the discontinuity. This formalism requires an ad hoc transformation of the original differential equation and is also applicable for rapid, although not necessarily instantaneous, mass variations. (Author)
Electronics based on two-dimensional materials.
Fiori, Gianluca; Bonaccorso, Francesco; Iannaccone, Giuseppe; Palacios, Tomás; Neumaier, Daniel; Seabaugh, Alan; Banerjee, Sanjay K; Colombo, Luigi
2014-10-01
The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.
Two-dimensional ranking of Wikipedia articles
Zhirov, A. O.; Zhirov, O. V.; Shepelyansky, D. L.
2010-10-01
The Library of Babel, described by Jorge Luis Borges, stores an enormous amount of information. The Library exists ab aeterno. Wikipedia, a free online encyclopaedia, becomes a modern analogue of such a Library. Information retrieval and ranking of Wikipedia articles become the challenge of modern society. While PageRank highlights very well known nodes with many ingoing links, CheiRank highlights very communicative nodes with many outgoing links. In this way the ranking becomes two-dimensional. Using CheiRank and PageRank we analyze the properties of two-dimensional ranking of all Wikipedia English articles and show that it gives their reliable classification with rich and nontrivial features. Detailed studies are done for countries, universities, personalities, physicists, chess players, Dow-Jones companies and other categories.
Towards two-dimensional search engines
Ermann, Leonardo; Shepelyansky, Dima L
2011-01-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way the ranking of nodes becomes two-dimensional that paves the way for development of two-dimensional search engines of new type. Information flow properties on PageRank-CheiRank plane are analyzed for networks of British, French and Italian Universities, Wikipedia, Linux Kernel, gene regulation and other networks. Methods of spam links control are also analyzed.
Toward two-dimensional search engines
Ermann, L.; Chepelianskii, A. D.; Shepelyansky, D. L.
2012-07-01
We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way, the ranking of nodes becomes two dimensional which paves the way for the development of two-dimensional search engines of a new type. Statistical properties of information flow on the PageRank-CheiRank plane are analyzed for networks of British, French and Italian universities, Wikipedia, Linux Kernel, gene regulation and other networks. A special emphasis is done for British universities networks using the large database publicly available in the UK. Methods of spam links control are also analyzed.
Two-Dimensional Scheduling: A Review
Directory of Open Access Journals (Sweden)
Zhuolei Xiao
2013-07-01
Full Text Available In this study, we present a literature review, classification schemes and analysis of methodology for scheduling problems on Batch Processing machine (BP with both processing time and job size constraints which is also regarded as Two-Dimensional (TD scheduling. Special attention is given to scheduling problems with non-identical job sizes and processing times, with details of the basic algorithms and other significant results.
Two dimensional fermions in four dimensional YM
Narayanan, R
2009-01-01
Dirac fermions in the fundamental representation of SU(N) live on a two dimensional torus flatly embedded in $R^4$. They interact with a four dimensional SU(N) Yang Mills vector potential preserving a global chiral symmetry at finite $N$. As the size of the torus in units of $\\frac{1}{\\Lambda_{SU(N)}}$ is varied from small to large, the chiral symmetry gets spontaneously broken in the infinite $N$ limit.
Two-dimensional Kagome photonic bandgap waveguide
DEFF Research Database (Denmark)
Nielsen, Jens Bo; Søndergaard, Thomas; Libori, Stig E. Barkou;
2000-01-01
The transverse-magnetic photonic-bandgap-guidance properties are investigated for a planar two-dimensional (2-D) Kagome waveguide configuration using a full-vectorial plane-wave-expansion method. Single-moded well-localized low-index guided modes are found. The localization of the optical modes...... is investigated with respect to the width of the 2-D Kagome waveguide, and the number of modes existing for specific frequencies and waveguide widths is mapped out....
String breaking in two-dimensional QCD
Hornbostel, K J
1999-01-01
I present results of a numerical calculation of the effects of light quark-antiquark pairs on the linear heavy-quark potential in light-cone quantized two-dimensional QCD. I extract the potential from the Q-Qbar component of the ground-state wavefunction, and observe string breaking at the heavy-light meson pair threshold. I briefly comment on the states responsible for the breaking.
Two-dimensional supramolecular electron spin arrays.
Wäckerlin, Christian; Nowakowski, Jan; Liu, Shi-Xia; Jaggi, Michael; Siewert, Dorota; Girovsky, Jan; Shchyrba, Aneliia; Hählen, Tatjana; Kleibert, Armin; Oppeneer, Peter M; Nolting, Frithjof; Decurtins, Silvio; Jung, Thomas A; Ballav, Nirmalya
2013-05-07
A bottom-up approach is introduced to fabricate two-dimensional self-assembled layers of molecular spin-systems containing Mn and Fe ions arranged in a chessboard lattice. We demonstrate that the Mn and Fe spin states can be reversibly operated by their selective response to coordination/decoordination of volatile ligands like ammonia (NH3). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Two dimensional echocardiographic detection of intraatrial masses.
DePace, N L; Soulen, R L; Kotler, M N; Mintz, G S
1981-11-01
With two dimensional echocardiography, a left atrial mass was detected in 19 patients. Of these, 10 patients with rheumatic mitral stenosis had a left atrial thrombus. The distinctive two dimensional echocardiographic features of left atrial thrombus included a mass of irregular nonmobile laminated echos within an enlarged atrial cavity, usually with a broad base of attachment to the posterior left atrial wall. Seven patients had a left atrial myxoma. Usually, the myxoma appeared as a mottled ovoid, sharply demarcated mobile mass attached to the interatrial septum. One patient had a right atrial angiosarcoma that appeared as a nonmobile mass extending from the inferior vena caval-right atrial junction into the right atrial cavity. One patient had a left atrial leiomyosarcoma producing a highly mobile mass attached to the lateral wall of the left atrium. M mode echocardiography detected six of the seven myxomas, one thrombus and neither of the other tumors. Thus, two dimensional echocardiography appears to be the technique of choice in the detection, localization and differentiation of intraatrial masses.
Continuous vs. discrete models for the quantum harmonic oscillator and the hydrogen atom
Lorente, M
2001-01-01
The Kravchuk and Meixner polynomials of discrete variable are introduced for the discrete models of the harmonic oscillator and hydrogen atom. Starting from Rodrigues formula we construct raising and lowering operators, commutation and anticommutation relations. The physical properties of discrete models are figured out through the equivalence with the continuous models obtained by limit process.
Continuous vs. discrete models for the quantum harmonic oscillator and the hydrogen atom
Lorente, Miguel
2001-07-01
The Kravchuk and Meixner polynomials of discrete variable are introduced for the discrete models of the harmonic oscillator and hydrogen atom. Starting from Rodrigues formula we construct raising and lowering operators, commutation and anticommutation relations. The physical properties of discrete models are figured out through the equivalence with the continuous models obtained by limit process.
Continuous vs. discrete models for the quantum harmonic oscillator and the hydrogen atom
Lorente, M.
2004-01-01
The Kravchuk and Meixner polynomials of discrete variable are introduced for the discrete models of the harmonic oscillator and hydrogen atom. Starting from Rodrigues formula we construct raising and lowering operators, commutation and anticommutation relations. The physical properties of discrete models are figured out through the equivalence with the continuous models obtained by limit process.
The two dimensional electron system as a nanoantenna in the microwave and terahertz bands
Iñarrea, Jesús
2011-12-01
We study the magnetoresistance of two-dimensional electron systems under several radiation sources of different frequencies for moderate power. We use the model of radiation-driven electron orbits extended to this regime. First, we consider the case of two different radiations and we find a regime of superposition or interference of harmonic motions, i.e., a modulated magnetoresistance response with pulses and beats. Finally, we consider a multiple photoexcitation case where we propose the two-dimensional electron system as a potential nanoantenna device or ultrasensitive detector for the microwave and terahertz bands. Thus, these results could be of special interest in nanophotonics and nanoelectronics.
Nonclassical phase-space trajectories for the damped harmonic quantum oscillator
Energy Technology Data Exchange (ETDEWEB)
Pachon, L.A. [Departamento de Fisica, Universidad Nacional de Colombia, Bogota D.C. (Colombia); Institut fuer Physik, Universitaet Augsburg, Universitaetsstrasse 1, D-86135 Augsburg (Germany); CeiBA - Complejidad, Bogota D.C. (Colombia); Ingold, G.-L., E-mail: gert.ingold@physik.uni-augsburg.de [Institut fuer Physik, Universitaet Augsburg, Universitaetsstrasse 1, D-86135 Augsburg (Germany); Dittrich, T. [Departamento de Fisica, Universidad Nacional de Colombia, Bogota D.C. (Colombia); CeiBA - Complejidad, Bogota D.C. (Colombia)
2010-10-05
Graphical abstract: The phase-space path-integral approach to the damped harmonic oscillator is analyzed beyond the Markovian approximation and the appearance of nonclassical trajectories is discussed. - Abstract: The phase-space path-integral approach to the damped harmonic oscillator is analyzed beyond the Markovian approximation. It is found that pairs of nonclassical trajectories contribute to the path-integral representation of the Wigner propagating function. Due to the linearity of the problem, the sum coordinate of a pair still satisfies the classical equation of motion. Furthermore, it is shown that the broadening of the Wigner propagating function of the damped oscillator arises due to the time-nonlocal interaction mediated by the heat bath.
Performance of a quantum heat engine cycle working with harmonic oscillator systems
Institute of Scientific and Technical Information of China (English)
2007-01-01
A cycle model of an irreversible heat engine working with harmonic systems is established in this paper. Based on the equation of motion of an operator in the Heisenberg picture and semi-group approach, the first law of thermodynamics for a harmonic system and the time evolution of the system are obtained. The general expressions for several important parameters, such as the work, efficiency, power output, and rate of entropy production are derived. By means of numerical analysis, the optimally operating regions and the optimal values of performance parameters of the cycle are determined under the condition of maximum power output. At last, some special cases, such as high temperature limit and frictionless case, are dis-cussed in brief.
Performance of a quantum heat engine cycle working with harmonic oscillator systems
Institute of Scientific and Technical Information of China (English)
WANG JianHui; HE JiZhou; MAO ZhiYuan
2007-01-01
A cycle model of an irreversible heat engine working with harmonic systems is established in this paper. Based on the equation of motion of an operator in the Heisenberg picture and semi-group approach, the first law of thermodynamics for a harmonic system and the time evolution of the system are obtained. The general expressions for several important parameters, such as the work, efficiency, power output, and rate of entropy production are derived. By means of numerical analysis, the optimally operating regions and the optimal values of performance parameters of the cycle are determined under the condition of maximum power output. At last, some special cases, such as high temperature limit and frictionless case, are discussed in brief.
Weakly disordered two-dimensional Frenkel excitons
Boukahil, A.; Zettili, Nouredine
2004-03-01
We report the results of studies of the optical properties of weakly disordered two- dimensional Frenkel excitons in the Coherent Potential Approximation (CPA). An approximate complex Green's function for a square lattice with nearest neighbor interactions is used in the self-consistent equation to determine the coherent potential. It is shown that the Density of States is very much affected by the logarithmic singularities in the Green's function. Our CPA results are in excellent agreement with previous investigations by Schreiber and Toyozawa using the Monte Carlo simulation.
Two-dimensional photonic crystal surfactant detection.
Zhang, Jian-Tao; Smith, Natasha; Asher, Sanford A
2012-08-07
We developed a novel two-dimensional (2-D) crystalline colloidal array photonic crystal sensing material for the visual detection of amphiphilic molecules in water. A close-packed polystyrene 2-D array monolayer was embedded in a poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel film. These 2-D photonic crystals placed on a mirror show intense diffraction that enables them to be used for visual determination of analytes. Binding of surfactant molecules attaches ions to the sensor that swells the PNIPAAm-based hydrogel. The resulting increase in particle spacing red shifts the 2-D diffracted light. Incorporation of more hydrophobic monomers increases the sensitivity to surfactants.
Theory of two-dimensional transformations
Kanayama, Yutaka J.; Krahn, Gary W.
1998-01-01
The article of record may be found at http://dx.doi.org/10.1109/70.720359 Robotics and Automation, IEEE Transactions on This paper proposes a new "heterogeneous" two-dimensional (2D) transformation group ___ to solve motion analysis/planning problems in robotics. In this theory, we use a 3×1 matrix to represent a transformation as opposed to a 3×3 matrix in the homogeneous formulation. First, this theory is as capable as the homogeneous theory, Because of the minimal size, its implement...
Two-dimensional ranking of Wikipedia articles
Zhirov, A O; Shepelyansky, D L
2010-01-01
The Library of Babel, described by Jorge Luis Borges, stores an enormous amount of information. The Library exists {\\it ab aeterno}. Wikipedia, a free online encyclopaedia, becomes a modern analogue of such a Library. Information retrieval and ranking of Wikipedia articles become the challenge of modern society. We analyze the properties of two-dimensional ranking of all Wikipedia English articles and show that it gives their reliable classification with rich and nontrivial features. Detailed studies are done for countries, universities, personalities, physicists, chess players, Dow-Jones companies and other categories.
Mobility anisotropy of two-dimensional semiconductors
Lang, Haifeng; Liu, Zhirong
2016-01-01
The carrier mobility of anisotropic two-dimensional (2D) semiconductors under longitudinal acoustic (LA) phonon scattering was theoretically studied with the deformation potential theory. Based on Boltzmann equation with relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was deduced, which shows that the influence of effective mass to the mobility anisotropy is larger than that of deformation potential constant and elastic modulus. Parameters were collected for various anisotropic 2D materials (black phosphorus, Hittorf's phosphorus, BC$_2$N, MXene, TiS$_3$, GeCH$_3$) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio was overestimated in the past.
Sums of two-dimensional spectral triples
DEFF Research Database (Denmark)
Christensen, Erik; Ivan, Cristina
2007-01-01
construct a sum of two dimensional modules which reflects some aspects of the topological dimensions of the compact metric space, but this will only give the metric back approximately. At the end we make an explicit computation of the last module for the unit interval in. The metric is recovered exactly......, the Dixmier trace induces a multiple of the Lebesgue integral but the growth of the number of eigenvalues is different from the one found for the standard differential operator on the unit interval....
Dynamics of film. [two dimensional continua theory
Zak, M.
1979-01-01
The general theory of films as two-dimensional continua are elaborated upon. As physical realizations of such a model this paper examines: inextensible films, elastic films, and nets. The suggested dynamic equations have enabled us to find out the characteristic speeds of wave propagation of the invariants of external and internal geometry and formulate the criteria of instability of their shape. Also included herein is a detailed account of the equation describing the film motions beyond the limits of the shape stability accompanied by the formation of wrinkles. The theory is illustrated by examples.
Zhang, Xiaoshi; Lytle, Amy L.; Cohen, Oren; Kapteyn, Henry C.; Murnane, Margaret M.
2010-11-09
All-optical quasi-phase matching (QPM) uses a train of counterpropagating pulses to enhance high-order harmonic generation (HHG) in a hollow waveguide. A pump pulse enters one end of the waveguide, and causes HHG in the waveguide. The counterpropagation pulses enter the other end of the waveguide and interact with the pump pulses to cause QPM within the waveguide, enhancing the HHG.
Self-starting harmonic frequency comb generation in a quantum cascade laser
Kazakov, Dmitry; Piccardo, Marco; Wang, Yongrui; Chevalier, Paul; Mansuripur, Tobias S.; Xie, Feng; Zah, Chung-En; Lascola, Kevin; Belyanin, Alexey; Capasso, Federico
2017-01-01
Optical frequency combs establish a rigid phase-coherent link between microwave and optical domains and are emerging as high-precision tools in an increasing number of applications. Frequency combs with large intermodal spacing are employed in the field of microwave photonics for radiofrequency arbitrary waveform synthesis and for generation of THz tones of high spectral purity in the future wireless communication networks. We demonstrate for the first time self-starting harmonic frequency co...
Energy Technology Data Exchange (ETDEWEB)
Thantu, Napoleon [Idaho National Engineering and Environmental Laboratory, 2525 Fremont Avenue, Idaho Falls, ID 83415 (United States)]. E-mail: Napoleon.Thantu@ngc.com
2005-01-01
We report two-photon excited emission in borosilicate glasses doped with ZnSe nanocrystalline quantum dots. The emission, predominantly near the two-photon energy and detected in the direction of the excitation beam, is in the visible, and the fundamental excitation is the near-infrared output of a tunable femtosecond laser. Depending on the two-photon energy, time- and frequency-resolved measurements at room temperature reveal that the emission largely consists of second harmonic generation (SHG) and two-photon luminescence upconversion, and a much smaller luminescence from redshifted, low-lying trap states and other trap levels residing near the semiconductor band edge. We discuss the SHG origin in terms of bulk-like and surface contributions from the nanocrystals and the two-photon resonant enhancement near the excitonic absorption.
Maldonado-Basilio, Ramón; Latkowski, Sylwester; Philippe, Severine; Landais, Pascal
2011-05-01
Synchronization of a 40 GHz quantum-dash mode-locked (ML) Fabry-Perot laser diode with optically injected pulse streams is experimentally studied. Injected signals consist of nonmodulated and modulated trains of 1.6 ps pulses at various repetition rates, ranging from 10 to 160 GHz and 10 to 160 Gbps, respectively. Subharmonic, fundamental, and harmonic synchronization of the ML laser allows retrieval of stable 40 GHz clock pulses featuring a width of 1.8 ps. Frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses when injecting signals at 10 and 20 GHz/Gbps. In addition, external synchronization of the laser with pulse streams at 80 and 160 GHz/Gbps is sustained despite the absence of significant components at or below 40 GHz.
Energy Technology Data Exchange (ETDEWEB)
Ayari, Taha; Li, Xin; Voss, Paul L.; Ougazzaden, Abdallah, E-mail: aougazza@georgiatech-metz.fr [School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Georgia Tech Lorraine, UMI 2958, Georgia Tech-CNRS, 57070 Metz (France); Sundaram, Suresh; El Gmili, Youssef [Georgia Tech Lorraine, UMI 2958, Georgia Tech-CNRS, 57070 Metz (France); Salvestrini, Jean Paul [Georgia Tech Lorraine, UMI 2958, Georgia Tech-CNRS, 57070 Metz (France); Université de Lorraine, LMOPS, EA 4423, 57070 Metz (France)
2016-04-25
Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure to be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production.
Ge, Xin-Lei
2016-06-01
We investigate high-harmonic generation (HHG) for the \\text{H}2+ molecular ion by solving a two-dimensional time-dependent Schrödinger equation in the combination of a circularly polarized laser pulse and a terahertz (THz) field. The results published recently by Ge et al (Opt. Express 23 8837-44) show that the harmonic intensity can be greatly enhanced when a THz field is added. Our work is an extension of Ge et al’s. We focus on considering the influence of THz field with different peak intensity, which shows that, with the increasing peak intensity of THz field, the cutoff of the harmonics can be remarkably extended, and the harmonic spectrum presents a two-plateau structure. The time-frequency analysis shows that the long trajectory makes a contribution to HHG when the intensity of THz field is low. With the increase of peak intensity of THz field, the long trajectory gradually disappears and the short trajectory makes the main contribution to HHG. We present the classical trajectory of the electron and the temporal evolution of the probability density of the electron wave packet to further understand the electron motion and the physical insight into HHG.
Two-dimensional gauge theoretic supergravities
Cangemi, D.; Leblanc, M.
1994-05-01
We investigate two-dimensional supergravity theories, which can be built from a topological and gauge invariant action defined on an ordinary surface. One is the N = 1 supersymmetric extension of the Jackiw-Teitelboim model presented by Chamseddine in a superspace formalism. We complement the proof of Montano, Aoaki and Sonnenschein that this extension is topological and gauge invariant, based on the graded de Sitter algebra. Not only do the equations of motion correspond to the supergravity ones and do gauge transformations encompass local supersymmetries, but we also identify the ∫-theory with the superfield formalism action written by Chamseddine. Next, we show that the N = 1 supersymmetric extension of string-inspired two-dimensional dilaton gravity put forward by Park and Strominger cannot be written as a ∫-theory. As an alternative, we propose two topological and gauge theories that are based on a graded extension of the extended Poincaré algebra and satisfy a vanishing-curvature condition. Both models are supersymmetric extensions of the string-inspired dilaton gravity.
Two-Dimensional Theory of Scientific Representation
Directory of Open Access Journals (Sweden)
A Yaghmaie
2013-03-01
Full Text Available Scientific representation is an interesting topic for philosophers of science, many of whom have recently explored it from different points of view. There are currently two competing approaches to the issue: cognitive and non-cognitive, and each of them claims its own merits over the other. This article tries to provide a hybrid theory of scientific representation, called Two-Dimensional Theory of Scientific Representation, which has the merits of the two accounts and is free of their shortcomings. To do this, we will argue that although scientific representation needs to use the notion of intentionality, such a notion is defined and realized in a simply structural form contrary to what cognitive approach says about intentionality. After a short introduction, the second part of the paper is devoted to introducing theories of scientific representation briefly. In the third part, the structural accounts of representation will be criticized. The next step is to introduce the two-dimensional theory which involves two key components: fixing and structural fitness. It will be argued that fitness is an objective and non-intentional relation, while fixing is intentional.
Two-dimensional shape memory graphene oxide
Chang, Zhenyue; Deng, Junkai; Chandrakumara, Ganaka G.; Yan, Wenyi; Liu, Jefferson Zhe
2016-06-01
Driven by the increasing demand for micro-/nano-technologies, stimuli-responsive shape memory materials at nanoscale have recently attracted great research interests. However, by reducing the size of conventional shape memory materials down to approximately nanometre range, the shape memory effect diminishes. Here, using density functional theory calculations, we report the discovery of a shape memory effect in a two-dimensional atomically thin graphene oxide crystal with ordered epoxy groups, namely C8O. A maximum recoverable strain of 14.5% is achieved as a result of reversible phase transition between two intrinsically stable phases. Our calculations conclude co-existence of the two stable phases in a coherent crystal lattice, giving rise to the possibility of constructing multiple temporary shapes in a single material, thus, enabling highly desirable programmability. With an atomic thickness, excellent shape memory mechanical properties and electric field stimulus, the discovery of a two-dimensional shape memory graphene oxide opens a path for the development of exceptional micro-/nano-electromechanical devices.
Two-dimensional nuclear magnetic resonance of quadrupolar systems
Energy Technology Data Exchange (ETDEWEB)
Wang, Shuanhu
1997-09-17
This dissertation describes two-dimensional nuclear magnetic resonance theory and experiments which have been developed to study quadruples in the solid state. The technique of multiple-quantum magic-angle spinning (MQMAS) is extensively reviewed and expanded upon in this thesis. Specifically, MQMAS is first compared with another technique, dynamic-angle spinning (DAS). The similarity between the two techniques allows us to extend much of the DAS work to the MQMAS case. Application of MQMAS to a series of aluminum containing materials is then presented. The superior resolution enhancement through MQMAS is exploited to detect the five- and six-coordinated aluminum in many aluminosilicate glasses. Combining the MQMAS method with other experiments, such as HETCOR, greatly expands the possibility of the use of MQMAS to study a large range of problems and is demonstrated in Chapter 5. Finally, the technique switching-angle spinning (SAS) is applied to quadrupolar nuclei to fully characterize a quadrupolar spin system in which all of the 8 NMR parameters are accurately determined. This dissertation is meant to demonstrate that with the combination of two-dimensional NMR concepts and new advanced spinning technologies, a series of multiple-dimensional NMR techniques can be designed to allow a detailed study of quadrupolar nuclei in the solid state.
Unpacking of a Crumpled Wire from Two-Dimensional Cavities.
Directory of Open Access Journals (Sweden)
Thiago A Sobral
Full Text Available The physics of tightly packed structures of a wire and other threadlike materials confined in cavities has been explored in recent years in connection with crumpled systems and a number of topics ranging from applications to DNA packing in viral capsids and surgical interventions with catheter to analogies with the electron gas at finite temperature and with theories of two-dimensional quantum gravity. When a long piece of wire is injected into two-dimensional cavities, it bends and originates in the jammed limit a series of closed structures that we call loops. In this work we study the extraction of a crumpled tightly packed wire from a circular cavity aiming to remove loops individually. The size of each removed loop, the maximum value of the force needed to unpack each loop, and the total length of the extracted wire were measured and related to an exponential growth and a mean field model consistent with the literature of crumpled wires. Scaling laws for this process are reported and the relationship between the processes of packing and unpacking of wire is commented upon.
Unpacking of a Crumpled Wire from Two-Dimensional Cavities.
Sobral, Thiago A; Gomes, Marcelo A F; Machado, Núbia R; Brito, Valdemiro P
2015-01-01
The physics of tightly packed structures of a wire and other threadlike materials confined in cavities has been explored in recent years in connection with crumpled systems and a number of topics ranging from applications to DNA packing in viral capsids and surgical interventions with catheter to analogies with the electron gas at finite temperature and with theories of two-dimensional quantum gravity. When a long piece of wire is injected into two-dimensional cavities, it bends and originates in the jammed limit a series of closed structures that we call loops. In this work we study the extraction of a crumpled tightly packed wire from a circular cavity aiming to remove loops individually. The size of each removed loop, the maximum value of the force needed to unpack each loop, and the total length of the extracted wire were measured and related to an exponential growth and a mean field model consistent with the literature of crumpled wires. Scaling laws for this process are reported and the relationship between the processes of packing and unpacking of wire is commented upon.
Photodetectors based on graphene, other two-dimensional materials and hybrid systems.
Koppens, F H L; Mueller, T; Avouris, Ph; Ferrari, A C; Vitiello, M S; Polini, M
2014-10-01
Graphene and other two-dimensional materials, such as transition metal dichalcogenides, have rapidly established themselves as intriguing building blocks for optoelectronic applications, with a strong focus on various photodetection platforms. The versatility of these material systems enables their application in areas including ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges. These detectors can be integrated with other photonic components based on the same material, as well as with silicon photonic and electronic technologies. Here, we provide an overview and evaluation of state-of-the-art photodetectors based on graphene, other two-dimensional materials, and hybrid systems based on the combination of different two-dimensional crystals or of two-dimensional crystals and other (nano)materials, such as plasmonic nanoparticles, semiconductors, quantum dots, or their integration with (silicon) waveguides.
Institute of Scientific and Technical Information of China (English)
XU Quan; TIAN Qiang
2007-01-01
Two-dimensional compact-like discrete breathers in discrete two-dimensional monatomic square lattices are investigated by discussing a generafized discrete two-dimensional monatomic model.It is proven that the twodimensional compact-like discrete breathers exist not only in two-dimensional soft Ф4 potentials but also in hard two-dimensional Ф4 potentials and pure two-dimensional K4 lattices.The measurements of the two-dimensional compact-like discrete breather cores in soft and hard two-dimensional Ф4 potential are determined by coupling parameter K4,while those in pure two-dimensional K4 lattices have no coupling with parameter K4.The stabilities of the two-dimensional compact-like discrete breathers correlate closely to the coupling parameter K4 and the boundary condition of lattices.
Flat Chern band in a two-dimensional organometallic framework.
Liu, Zheng; Wang, Zheng-Fei; Mei, Jia-Wei; Wu, Yong-Shi; Liu, Feng
2013-03-01
By combining exotic band dispersion with nontrivial band topology, an interesting type of band structure, namely, the flat Chern band, has recently been proposed to spawn high-temperature fractional quantum Hall states. Despite the proposal of several theoretical lattice models, however, it remains doubtful whether such a "romance of flatland" could exist in a real material. Here, we present a first-principles design of a two-dimensional indium-phenylene organometallic framework that realizes a nearly flat Chern band right around the Fermi level by combining lattice geometry, spin-orbit coupling, and ferromagnetism. An effective four-band model is constructed to reproduce the first-principles results. Our design, in addition, provides a general strategy to synthesize topologically nontrivial materials by virtue of organic chemistry and nanotechnology.
Superfluid phase transition in two-dimensional excitonic systems
Energy Technology Data Exchange (ETDEWEB)
Apinyan, V.; Kopeć, T.K., E-mail: kopec@int.pan.wroc.pl
2014-03-01
We study the superfluid phase transition in the two-dimensional (2D) excitonic system. Employing the extended Falicov–Kimball model (EFKM) and considering the local quantum correlations in the system composed of conduction band electrons and valence band holes we demonstrate the existence of the excitonic insulator (EI) state in the system. We show that at very low temperatures, the particle phase stiffness in the pure-2D excitonic system, governed by the non-local cross correlations, is responsible for the vortex–antivortex binding phase-field state, known as the Berezinskii–Kosterlitz–Thouless (BKT) superfluid state. We demonstrate that the existence of excitonic insulator phase is a necessary prerequisite, leading to quasi-long-range order in the 2D excitonic system.
Computationally Driven Two-Dimensional Materials Design: What Is Next?
Energy Technology Data Exchange (ETDEWEB)
Pan, Jie [Materials Science; Lany, Stephan [Materials Science; Qi, Yue [Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, United States
2017-07-17
Two-dimensional (2D) materials offer many key advantages to innovative applications, such as spintronics and quantum information processing. Theoretical computations have accelerated 2D materials design. In this issue of ACS Nano, Kumar et al. report that ferromagnetism can be achieved in functionalized nitride MXene based on first-principles calculations. Their computational results shed light on a potentially vast group of materials for the realization of 2D magnets. In this Perspective, we briefly summarize the promising properties of 2D materials and the role theory has played in predicting these properties. In addition, we discuss challenges and opportunities to boost the power of computation for the prediction of the 'structure-property-process (synthesizability)' relationship of 2D materials.
Isolated structures in two-dimensional optical superlattice
Zou, Xin-Hao; Yang, Bao-Guo; Xu, Xia; Tang, Peng-Ju; Zhou, Xiao-Ji
2017-10-01
Overlaying commensurate optical lattices with various configurations called superlattices can lead to exotic lattice topologies and, in turn, a discovery of novel physics. In this study, by overlapping the maxima of lattices, a new isolated structure is created, while the interference of minima can generate various "sublattice" patterns. Three different kinds of primitive lattices are used to demonstrate isolated square, triangular, and hexagonal "sublattice" structures in a two-dimensional optical superlattice, the patterns of which can be manipulated dynamically by tuning the polarization, frequency, and intensity of laser beams. In addition, we propose the method of altering the relative phase to adjust the tunneling amplitudes in "sublattices". Our configurations provide unique opportunities to study particle entanglement in "lattices" formed by intersecting wells and to implement special quantum logic gates in exotic lattice geometries.
Proximity Induced Superconducting Properties in One and Two Dimensional Semiconductors
DEFF Research Database (Denmark)
Kjærgaard, Morten
a voltage is passed through the Josephson junction, we observe multiple Andreev reflections and preliminary results point to a highly transmissive interface between the 2D electron gas and the superconductor. In the theoretical section we demonstrate analytically and numerically, that in a 1D nanowire......This report is concerned with the properties of one and two dimensional semiconducting materials when brought into contact with a superconductor. Experimentally we study the 2D electron gas in an InGaAs/InAs heterostructure with aluminum grown in situ on the surface, and theoretically we show...... that a superconducting 1D nanowire can harbor Majorana bound states in the absence of spin–orbit coupling. We fabricate and measure micrometer–sized mesoscopic devices demonstrating the inheritance of superconducting properties in the 2D electron gas. By placing a quantum point contact proximal to the interface between...
Quasi-Two-Dimensional Magnetism in Co-Based Shandites
Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki
2016-06-01
We report quasi-two-dimensional (Q2D) itinerant electron magnetism in the layered Co-based shandites. Comprehensive magnetization measurements were performed using single crystals of Co3Sn2-xInxS2 (0 ≤ x ≤ 2) and Co3-yFeySn2S2 (0 ≤ y ≤ 0.5). The magnetic parameters of both systems; the Curie temperature TC, effective moment peff and spontaneous moment ps; exhibit almost identical variations against the In- and Fe-concentrations, indicating significance of the electron count on the magnetism in the Co-based shandite. The ferromagnetic-nonmagnetic quantum phase transition is found around xc ˜ 0.8. Analysis based on the extended Q2D spin fluctuation theory clearly reveals the highly Q2D itinerant electron character of the ferromagnetism in the Co-based shandites.
Isolated Structures in Two-Dimensional Optical Superlattice
Zou, Xinhao; Xu, Xia; Tang, Pengju; Zhou, Xiaoji
2016-01-01
Overlaying commensurate optical lattices with various configurations called superlattices can lead to exotic lattice topologies and, in turn, a discovery of novel physics. In this study, by overlapping the maxima of lattices, a new isolated structure is created, while the interference of minima can generate various "sublattice" patterns. Three different kinds of primitive lattices are used to demonstrate isolated square, triangular, and hexagonal "sublattice" structures in a two-dimensional optical superlattice, the patterns of which can be manipulated dynamically by tuning the polarization, frequency, and intensity of laser beams. In addition, we propose the method of altering the relative phase to adjust the tunneling amplitudes in "sublattices." Our configurations provide unique opportunities to study particle entanglement in "lattices" formed by intersecting wells and to implement special quantum logic gates in exotic lattice geometries.
Curved Two-Dimensional Electron Systems in Semiconductor Nanoscrolls
Peters, Karen; Mendach, Stefan; Hansen, Wolfgang
The perfect control of strain and layer thickness in epitaxial semiconductor bilayers is employed to fabricate semiconductor nanoscrolls with precisely adjusted scroll diameter ranging between a few nanometers and several tens of microns. Furthermore, semiconductor heteroepitaxy allows us to incorporate quantum objects such as quantum wells, quantum dots, or modulation doped low-dimensional carrier systems into the nanoscrolls. In this review, we summarize techniques that we have developed to fabricate semiconductor nanoscrolls with well-defined location, orientation, geometry, and winding number. We focus on magneto-transport studies of curved two-dimensional electron systems in such nanoscrolls. An externally applied magnetic field results in a strongly modulated normal-to-surface component leading to magnetic barriers, reflection of edge channels, and local spin currents. The observations are compared to finite-element calculations and discussed on the basis of simple models taking into account the influence of a locally modulated state density on the conductivity. In particular, it is shown that the observations in high magnetic fields can be well described considering the transport in edge channels according to the Landauer-Büttiker model if additional magnetic field induced channels aligned along magnetic barriers are accounted for.
Prasad, C.; Ferry, D. K.; Wieder, H. H.
2004-04-01
We present Joule heating measurements carried out over a wide temperature range on two-dimensional electron gases (2DEGs) and quantum wires of varying widths fabricated in an In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As heterostructure system that has a 25 nm wide In0.53Ga0.47As quantum well region. The power dissipated per electron is extracted and the electron-phonon coupling processes in these systems are studied. The temperature decay of the power loss at the 2DEG points towards unscreened piezoelectric coupling to the acoustic modes over temperatures of 1-30 K, with boundary scattering in the ohmic contacts gaining importance at very low temperatures. In the wires, we observe different behaviour and the effect of wire width and carrier density on the observed energy-loss rates. Possible phonon confinement and exponential suppression in these structures are also looked at.
Two dimensional NMR of liquids and oriented molecules
Energy Technology Data Exchange (ETDEWEB)
Gochin, M.
1987-02-01
Chapter 1 discusses the quantum mechanical formalism used for describing the interaction between magnetic dipoles that dictates the appearance of a spectrum. The NMR characteristics of liquids and liquid crystals are stressed. Chapter 2 reviews the theory of multiple quantum and two dimensional NMR. Properties of typical spectra and phase cycling procedures are discussed. Chapter 3 describes a specific application of heteronuclear double quantum coherence to the removal of inhomogeneous broadening in liquids. Pulse sequences have been devised which cancel out any contribution from this inhomogeneity to the final spectrum. An interpretation of various pulse sequences for the case of /sup 13/C and /sup 1/H is given, together with methods of spectral editing by removal or retention of the homo- or heteronuclear J coupling. The technique is applied to a demonstration of high resolution in both frequency and spatial dimensions with a surface coil. In Chapter 4, multiple quantum filtered 2-D spectroscopy is demonstrated as an effective means of studying randomly deuterated molecules dissolved in a nematic liquid crystal. Magnitudes of dipole coupling constants have been determined for benzene and hexane, and their signs and assignments found from high order multiple quantum spectra. For the first time, a realistic impression of the conformation of hexane can be estimated from these results. Chapter 5 is a technical description of the MDB DCHIB-DR11W parallel interface which has been set up to transfer data between the Data General Nova 820 minicomputer, interfaced to the 360 MHz spectrometer, and the Vax 11/730. It covers operation of the boards, physical specifications and installation, and programs for testing and running the interface.
Quantum entanglement in coupled harmonic oscillator systems: from micro to macro
Kao, Jhih-Yuan; Chou, Chung-Hsien
2016-07-01
We investigate the entanglement dynamics of several models of coupled harmonic oscillators, whereby a number of properties concerning entanglement have been scrutinized, such as how the environment affects entanglement of a system, and death and revival of entanglement. Among them, there are two models for which we are able to vary their particle numbers easily by assuming identicalness, thereby examining how the particle number affects entanglement. We have found that the upper bound of entanglement between identical oscillators is approximately inversely proportional to the particle number.
Effects of Newtonian gravitational self-interaction in harmonically trapped quantum systems
Großardt, André; Ulbricht, Hendrik; Bassi, Angelo
2015-01-01
The Schr\\"odinger-Newton equation has gained attention in the recent past as a nonlinear modification of the Schr\\"odinger equation due to a gravitational self-interaction. Such a modification is expected from a fundamentally semi-classical theory of gravity, and can therefore be considered a test case for the necessity of the quantisation of the gravitational field. Here we provide a thorough study of the effects of the Schr\\"odinger-Newton equation for a micron-sized sphere trapped in a harmonic oscillator potential. We discuss both the effect on the energy eigenstates and the dynamical behaviour of squeezed states, covering the experimentally relevant parameter regimes.
Few-body, hyperspherical treatment of the quantum Hall effect
Directory of Open Access Journals (Sweden)
Wooten R. E.
2016-01-01
Full Text Available The quantum Hall effect arises from the quantum behavior of two-dimensional, strongly-interacting electrons exposed to a strong, perpendicular magnetic field [1, 2]. Conventionally treated from a many-body perspective, we instead treat the system from the few-body perspective using collective coordinates and the hyperspherical adiabatic technique developed originally for atomic systems [3]. The grand angular momentum K from K-harmonic few-body theory, is shown to be an approximate good collective quantum number in this system, and is shown to correlate with known fractional quantum Hall (FQH states at experimentally observed filling factors.
Mandal, Swapan
2017-03-01
The classical harmonic oscillator with time dependent mass and frequency is investigated to obtain a closed form exact analytical solution. It is found that the closed form analytical solutions are indeed possible if the time dependent mass of the oscillator is inversely proportional to the time dependent frequency. The scaled wronskian obtained from the linearly independent solutions of the equation of motion of the classical oscillator is used to obtain the solution corresponding to its quantum mechanical counterpart. The analytical solution of the present oscillator is used to obtain the squeezing effects of the input coherent light. In addition to the possibilities of getting the squeezed states, the present solution will be of use for investigating various quantum statistical properties of the radiation fields. As an example, we investigate the antibunching of the input thermal (chaotic) light coupled to the oscillator. Therefore, the appearance of the photon antibunching does not warrant the squeezing and vice-versa. The exact solution is obtained at the cost of the stringent condition where the product of time dependent mass and frequency of the oscillator is time invariant.
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Using a polarization method, the scattering problem for a two-dimensional inclusion embedded in infinite piezoelectric/piezomagnetic matrices is investigated. To achieve the purpose, the polarization method for a two-dimensional piezoelectric/piezo-magnetic "comparison body" is formulated. For simple harmonic motion, kernel of the polarization method reduces to a 2-D time-harmonic Green's function, which is ob-tained using the Radon transform. The expression is further simplified under condi-tions of low frequency of the incident wave and small diameter of the inclusion. Some analytical expressions are obtained. The analytical solutions for generalized piezoelec-tric/piezomagnetic anisotropic composites are given followed by simplified results for piezoelectric composites. Based on the latter results, two numerical results are provided for an elliptical cylindrical inclusion in a PZT-5H-matrix, showing the effect of different factors including size, shape, material properties, and piezoelectricity on the scattering cross-section.
Diffusion induced by bounded noise in a two-dimensional coupled memory system
Directory of Open Access Journals (Sweden)
Pengfei Xu
2014-01-01
Full Text Available The diffusion behavior driven by bounded noise under the influence of a coupled harmonic potential is investigated in a two-dimensional coupled-damped model. With the help of the Laplace analysis we obtain exact descriptions for a particle's two-time dynamics which is subjected to a coupled harmonic potential and a coupled damping. The time lag is used to describe the velocity autocorrelation function and mean square displacement of the diffusing particle. The diffusion behavior for the time lag is also discussed with respect to the coupled items and the amplitude of bounded noise.
Optimal excitation of two dimensional Holmboe instabilities
Constantinou, Navid C
2010-01-01
Highly stratified shear layers are rendered unstable even at high stratifications by Holmboe instabilities when the density stratification is concentrated in a small region of the shear layer. These instabilities may cause mixing in highly stratified environments. However these instabilities occur in tongues for a limited range of parameters. We perform Generalized Stability analysis of the two dimensional perturbation dynamics of an inviscid Boussinesq stratified shear layer and show that Holmboe instabilities at high Richardson numbers can be excited by their adjoints at amplitudes that are orders of magnitude larger than by introducing initially the unstable mode itself. We also determine the optimal growth that obtains for parameters for which there is no instability. We find that there is potential for large transient growth regardless of whether the background flow is exponentially stable or not and that the characteristic structure of the Holmboe instability asymptotically emerges for parameter values ...
Phonon hydrodynamics in two-dimensional materials.
Cepellotti, Andrea; Fugallo, Giorgia; Paulatto, Lorenzo; Lazzeri, Michele; Mauri, Francesco; Marzari, Nicola
2015-03-06
The conduction of heat in two dimensions displays a wealth of fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene and related materials. Here, we use density-functional perturbation theory and an exact, variational solution of the Boltzmann transport equation to study fully from first-principles phonon transport and heat conductivity in graphene, boron nitride, molybdenum disulphide and the functionalized derivatives graphane and fluorographene. In all these materials, and at variance with typical three-dimensional solids, normal processes keep dominating over Umklapp scattering well-above cryogenic conditions, extending to room temperature and more. As a result, novel regimes emerge, with Poiseuille and Ziman hydrodynamics, hitherto typically confined to ultra-low temperatures, characterizing transport at ordinary conditions. Most remarkably, several of these two-dimensional materials admit wave-like heat diffusion, with second sound present at room temperature and above in graphene, boron nitride and graphane.