Quantum teleportation from light beams to vibrational states of a macroscopic diamond
Hou, P.-Y.; Huang, Y.-Y.; Yuan, X.-X.; Chang, X.-Y.; Zu, C.; He, L.; Duan, L.-M.
2016-01-01
With the recent development of optomechanics, the vibration in solids, involving collective motion of trillions of atoms, gradually enters into the realm of quantum control. Here, building on the recent remarkable progress in optical control of motional states of diamonds, we report an experimental demonstration of quantum teleportation from light beams to vibrational states of a macroscopic diamond under ambient conditions. Through quantum process tomography, we demonstrate average teleportation fidelity (90.6±1.0)%, clearly exceeding the classical limit of 2/3. The experiment pushes the target of quantum teleportation to the biggest object so far, with interesting implications for optomechanical quantum control and quantum information science. PMID:27240553
Interception of excited vibrational quantum states by O2 in atmospheric association reactions.
Glowacki, David R; Lockhart, James; Blitz, Mark A; Klippenstein, Stephen J; Pilling, Michael J; Robertson, Struan H; Seakins, Paul W
2012-08-31
Bimolecular reactions in Earth's atmosphere are generally assumed to proceed between reactants whose internal quantum states are fully thermally relaxed. Here, we highlight a dramatic role for vibrationally excited bimolecular reactants in the oxidation of acetylene. The reaction proceeds by preliminary adduct formation between the alkyne and OH radical, with subsequent O(2) addition. Using a detailed theoretical model, we show that the product-branching ratio is determined by the excited vibrational quantum-state distribution of the adduct at the moment it reacts with O(2). Experimentally, we found that under the simulated atmospheric conditions O(2) intercepts ~25% of the excited adducts before their vibrational quantum states have fully relaxed. Analogous interception of excited-state radicals by O(2) is likely common to a range of atmospheric reactions that proceed through peroxy complexes.
Mukherjee, Nandini; Perreault, William E.; Zare, Richard N.
2017-07-01
We present a multi-color ladder excitation scheme that exploits Stark-induced adiabatic Raman passage to selectively populate a highly excited vibrational level of a molecule. We suggest that this multi-color coherent ladder excitation provides a practical way of accessing levels near the vibrational dissociation limit as well as the dissociative continuum, which would allow the generation of an entangled pair of fragments with near-zero relative kinetic energy. Specifically, we consider four- and six-photon coherent excitation of molecular hydrogen to high vibrational levels via intermediate vibrational levels, which are pairwise coupled by two-photon resonant interaction. Using a sequence of three partially overlapping, single-mode, nanosecond laser pulses we show that the sixth vibrational level of H2, which is too weakly coupled to be easily accessed by direct two-photon Raman excitation from the ground vibrational level, can be efficiently populated without leaving any population stranded in the intermediate level. Furthermore, we show that the fourteenth vibrational level of H2, which is the highest vibrational level in the ground electronic state with a binding energy of 22 meV, can be efficiently and selectively populated using a sequence of four pulses. The present technique offers the unique possibility of preparing entangled quantum states of H atoms without resorting to an ultracold system.
Poisson, Lionel; Maksimenska, Raman; Soep, Benoît; Mestdagh, Jean-Michel; Parker, David H; Nsangou, Mama; Hochlaf, Majdi
2010-03-11
In this paper we report an experimental study of the time-resolved response of the molecule 1,4-diazabicyclo[2.2.2]octane (DABCO) to 266.3 nm electronic excitation of the S(1) state with a femtosecond laser. Rotational decoherence and vibrational oscillation within the S(1) state are observed. We performed state-of-the-art ab initio calculations on the ground and low electronic states of the neutral molecule and the cation, which assist in the assignment of the observed photoelectron signals. Using our theoretical and spectroscopic data, the experimental findings are interpreted in terms of an unusual quantum interference between two different vibrational modes, with only the nu = 1 level of each mode being populated.
Energy Technology Data Exchange (ETDEWEB)
Hauer, Juergen; Buckup, Tiago [Fachbereich Chemie, Physikalische Chemie, Philipps-Universitaet Marburg, Hans-Meerwein-Strasse, D-35043 Marburg (Germany); Motzkus, Marcus [Fachbereich Chemie, Physikalische Chemie, Philipps-Universitaet Marburg, Hans-Meerwein-Strasse, D-35043 Marburg (Germany)], E-mail: motzkus@staff.uni-marburg.de
2008-06-23
Quantum control spectroscopy (QCS) is used as a tool to study, address selectively and enhance vibrational wavepacket motion in large solvated molecules. By contrasting the application of Fourier-limited and phase-modulated excitation on different electronic states, the interplay between the controllability of vibrational coherence and electronic resonance is revealed. We contrast control on electronic ground and excited state by introducing an additional pump beam prior to a DFWM-sequence (Pump-DFWM). Via phase modulation of this initial pump pulse, coherent control is extended to structural evolution on the vibrationally hot ground state (hot-S{sub 0}) and lowest lying excited state (S{sub 1}) of {beta}-carotene. In an open loop setup, the control scenarios for these different electronic states are compared in their effectiveness and mechanism.
Fujihashi, Yuta; Ishizaki, Akihito
2015-01-01
In 2D electronic spectroscopy studies, long-lived quantum beats have recently been observed in photosynthetic systems, and it has been suggested that the beats are produced by quantum mechanically mixed electronic and vibrational states. Concerning the electronic-vibrational quantum mixtures, the impact of protein-induced fluctuations was examined by calculating the 2D electronic spectra of a weakly coupled dimer with vibrational modes in the resonant condition [J. Chem. Phys. 142, 212403 (2015)]. This analysis demonstrated that quantum mixtures of the vibronic resonance are rather robust under the influence of the fluctuations at cryogenic temperatures, whereas the mixtures are eradicated by the fluctuations at physiological temperatures. However, this conclusion cannot be generalized because the magnitude of the coupling inducing the quantum mixtures is proportional to the inter-pigment coupling. In this study, we explore the impact of the fluctuations on electronic-vibrational quantum mixtures in a strongl...
Can Molecular Quantum Interference Effect Transistors Survive Vibration?
Chen, Shuguang; Zhou, WeiJun; Zhang, Qing; Kwok, YanHo; Chen, GuanHua; Ratner, Mark A
2017-10-19
Quantum interference in cross-conjugated molecules can be utilized to construct molecular quantum interference effect transistors. However, whether its application can be achieved depends on the survivability of the quantum interference under real conditions such as nuclear vibration. We use two simulation methods to investigate the effects of nuclear vibration on quantum interference in a meta-linked benzene system. The simulation results suggest that the quantum interference is robust against nuclear vibration not only in the steady state but also in its transient dynamics, and thus the molecular quantum interference effect transistors can be realized.
The Generalized Coherent State ansatz: Application to quantum electron-vibrational dynamics
Energy Technology Data Exchange (ETDEWEB)
Borrelli, Raffaele, E-mail: raffaele.borrelli@unito.it [DISAFA, Università di Torino, I-10095 Grugliasco (Italy); Gelin, Maxim F. [Departement of Chemistry, Technische Universität München, D-85747 Garching (Germany)
2016-12-20
A new ansatz for molecular vibronic wave functions based on a superposition of time-dependent Generalized Coherent States is developed and analysed. The methodology is specifically tailored to describe the time evolution of the wave function of a system in which several interacting electronic states are coupled to a bath of harmonic oscillators. The equations of motion for the wave packet parameters are obtained by using the Dirac–Frenkel time-dependent variational principle. The methodology is used to describe the quantum dynamical behavior of a model polaron system and its scaling and convergence properties are discussed and compared with numerically exact results.
Li, Bin; Bian, Wensheng
2008-07-01
Full-dimensional quantum calculations of vibrational states of C2H2 and C2D2 are performed in the high-energy region (above 20400cm-1 relative to the acetylene minimum). The theoretical scheme is a combination of several methods. To exploit the full parity and permutation symmetry, the CC-HH diatom-diatom Jacobi coordinates are chosen; phase space optimization in combination with physical considerations is used to obtain an efficient radial discrete variable representation, whereas a basis contraction scheme is applied for angular coordinates. The preconditioned inexact spectral transform method combined with an efficient preconditioner is employed to compute eigenstates within a desired spectral window. The computation is efficient. More definite assignments on vinylidene states than previous studies are acquired using the normal mode projection; in particular, a consistent analysis of the ν1 (symmetric CH stretch) state is provided. The computed vinylidene vibrational energy levels are in general good agreement with experiment, and several vinylidene states are reported for the first time.
Quantum dynamics of vibrational excitations and vibrational charge ...
Indian Academy of Sciences (India)
Quantum dynamics of vibrational excitations and vibrational charge transfer processes in H+ + O2 collisions at collision energy 23 eV ... The Fritz Haber Research Centre and The Department of Physical Chemisry, Hebrew University of Jerusalem, Jerusalem, Israel 91904; Department of Chemistry, Indian Institute of ...
Takayanagi, Toshiyuki
2017-11-08
We present the results of nonadiabatic quantum wave packet calculations to analyze the experimental transition state spectra for the I(2P3/2,1/2) + XI (X = H and D) hydrogen exchange reactions based on photodetachment of the IXI- anion. We developed (3 × 3) diabatic potential energy surfaces that can reasonably describe the nonadiabatic transitions induced by spin-orbit interactions. A good agreement was obtained between theory and experiment and it was found that nonadiabatic transitions play a role in the reaction dynamics. We also found that the calculated spectra showed very sharp resonance states with a vibrational bonding character, where the resonance wavefunctions are highly localized around the transition state region. Our calculated results suggest that one may experimentally detect these vibrational bonding resonances using time-domain transition state spectroscopy techniques since those states have picosecond-order lifetimes.
Dark states in quantum photosynthesis
Kozyrev, S V
2016-01-01
We discuss a model of quantum photosynthesis with degeneracy in the light-harvesting system. We consider interaction of excitons in chromophores with light and phonons (vibrations of environment). These interactions have dipole form but are different (are related to non-parallel vectors of "bright" states). We show that this leads to excitation of non-decaying "dark" states. We discuss relation of this model to the known from spectroscopical experiments phenomenon of existence of photonic echo in quantum photosynthesis.
Nuclear Quantum Vibrational Effects in Shock Hugoniot Temperatures
Energy Technology Data Exchange (ETDEWEB)
Goldman, N; Reed, E; Fried, L E
2009-07-23
We present a straightforward method for the inclusion of quantum nuclear vibrational effects in molecular dynamics calculations of shock Hugoniot temperatures. Using a Grueneisen equation of state and a quasiharmonic approximation to the vibrational energies, we derive a simple, post-processing method for calculation of the quantum corrected Hugoniot temperatures. We have used our novel technique on ab initio simulations of shock compressed water. Our results indicate significantly closer agreement with all available experimental temperature data. Our formalism and technique can be easily applied to a number of different shock compressed molecular liquids or solids.
Ergler, Th.; Feuerstein, B.; Rudenko, A.; Zrost, K.; Schröter, C. D.; Moshammer, R.; Ullrich, J.
2006-09-01
Applying 7 fs pump-probe pulses (780nm, 4×1014W/cm2) we observe electronic ground-state vibrational wave packets in neutral D2 with a period of T=11.101(70)fs by following the internuclear separation (R-)dependent ionization with a sensitivity of Δ⟨R⟩≤0.02Å. The absolute phase of the wave packet’s motion provides evidence for R-dependent depletion of the ground state by nonlinear ionization, to be the dominant preparation mechanism. A phase shift of about π found between pure ionization (D2+) and dissociation (D++D) channels opens a pathway of quantum control.
Takayanagi, Toshiyuki; Suzuki, Kento; Yoshida, Takahiko; Kita, Yukiumi; Tachikawa, Masanori
2017-05-01
We present computational results of vibrationally enhanced positron annihilation in the e+ + HCN/DCN collisions within a local complex potential model. Vibrationally elastic and inelastic cross sections and effective annihilation rates were calculated by solving a time-dependent complex-potential Schrödinger equation under the ab initio potential energy surface for the positron attached HCN molecule, [HCN; e+], with multi-component configuration interaction level (Kita and Tachikawa, 2014). We discuss the effect of vibrational excitation on the positron affinities from the obtained vibrational resonance features.
Quantum correlations and distinguishability of quantum states
Energy Technology Data Exchange (ETDEWEB)
Spehner, Dominique [Université Grenoble Alpes and CNRS, Institut Fourier, F-38000 Grenoble, France and Laboratoire de Physique et Modélisation des Milieux Condensés, F-38000 Grenoble (France)
2014-07-15
A survey of various concepts in quantum information is given, with a main emphasis on the distinguishability of quantum states and quantum correlations. Covered topics include generalized and least square measurements, state discrimination, quantum relative entropies, the Bures distance on the set of quantum states, the quantum Fisher information, the quantum Chernoff bound, bipartite entanglement, the quantum discord, and geometrical measures of quantum correlations. The article is intended both for physicists interested not only by collections of results but also by the mathematical methods justifying them, and for mathematicians looking for an up-to-date introductory course on these subjects, which are mainly developed in the physics literature.
Hardy, Lucien
2013-01-01
In this paper we consider theories in which reality is described by some underlying variables, λ. Each value these variables can take represents an ontic state (a particular state of reality). The preparation of a quantum state corresponds to a distribution over the ontic states, λ. If we make three basic assumptions, we can show that the distributions over ontic states corresponding to distinct pure states are nonoverlapping. This means that we can deduce the quantum state from a knowledge of the ontic state. Hence, if these assumptions are correct, we can claim that the quantum state is a real thing (it is written into the underlying variables that describe reality). The key assumption we use in this proof is ontic indifference — that quantum transformations that do not affect a given pure quantum state can be implemented in such a way that they do not affect the ontic states in the support of that state. In fact this assumption is violated in the Spekkens toy model (which captures many aspects of quantum theory and in which different pure states of the model have overlapping distributions over ontic states). This paper proves that ontic indifference must be violated in any model reproducing quantum theory in which the quantum state is not a real thing. The argument presented in this paper is different from that given in a recent paper by Pusey, Barrett and Rudolph. It uses a different key assumption and it pertains to a single copy of the system in question.
Furusawa, Akira
2015-01-01
This book explains what quantum states of light look like. Of special interest, a single photon state is explained by using a wave picture, showing that it corresponds to the complementarity of a quantum. Also explained is how light waves are created by photons, again corresponding to the complementarity of a quantum. The author shows how an optical wave is created by superposition of a "vacuum" and a single photon as a typical example. Moreover, squeezed states of light are explained as "longitudinal" waves of light and Schrödinger's cat states as macroscopic superposition states.
Sumner, Isaiah; Iyengar, Srinivasan S
2007-10-18
We have introduced a computational methodology to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach is based on the recently developed quantum wavepacket ab initio molecular dynamics method that combines quantum wavepacket dynamics with ab initio molecular dynamics. The computational efficiency of the dynamical procedure is drastically improved (by several orders of magnitude) through the utilization of wavelet-based techniques combined with the previously introduced time-dependent deterministic sampling procedure measure to achieve stable, picosecond length, quantum-classical dynamics of electrons and nuclei in clusters. The dynamical information is employed to construct a novel cumulative flux/velocity correlation function, where the wavepacket flux from the quantized particle is combined with classical nuclear velocities to obtain the vibrational density of states. The approach is demonstrated by computing the vibrational density of states of [Cl-H-Cl]-, inclusive of critical quantum nuclear effects, and our results are in good agreement with experiment. A general hierarchical procedure is also provided, based on electronic structure harmonic frequencies, classical ab initio molecular dynamics, computation of nuclear quantum-mechanical eigenstates, and employing quantum wavepacket ab initio dynamics to understand vibrational spectroscopy in hydrogen-bonded clusters that display large degrees of anharmonicities.
Kwac, Kijeong; Geva, Eitan
2013-11-21
The effect of vibrational excitation and relaxation of the hydroxyl stretch on the hydrogen-bond structure and dynamics of stereoselectively synthesized syn-tetrol and anti-tetrol dissolved in deuterated chloroform are investigated via a mixed quantum-classical molecular dynamics simulation. Emphasis is placed on the changes in hydrogen-bond structure upon photoexcitation and the nonequilibrium hydrogen-bond dynamics that follows the subsequent relaxation from the excited to the ground vibrational state. The propensity to form hydrogen bonds is shown to increase upon photoexcitation of the hydroxyl stretch, thereby leading to a sizable red-shift of the infrared emission spectra relative to the corresponding absorption spectra. The vibrational excited state lifetimes are calculated within the framework of Fermi's golden rule and the harmonic-Schofield quantum correction factor, and found to be sensitive reporters of the underlying hydrogen-bond structure. The energy released during the relaxation from the excited to the ground state is shown to break hydrogen bonds involving the relaxing hydroxyl. The spectral signature of this nonequilibrium relaxation process is analyzed in detail.
Zhang, Zhedong
2015-01-01
Recently the quantum nature in the energy transport in solar cell and light-harvesting complexes have attracted much attention, as being triggered by the experimental observations. We model the light-harvesting complex (i.e., PEB50 dimer) as a quantum heat engine (QHE) and study the effect of the undamped intra-molecule vibrational modes on the coherent energy transfer process and quantum transport. We find that the exciton-vibration interaction has non-trivial contribution to the promotion of quantum yield as well as transport properties of the quantum heat engine at steady state, by enhancing the quantum coherence quantified by entanglement entropy. The perfect quantum yield over 90% has been obtained, with theexciton-vibration coupling. We attribute these improvements to the renormalization of the electronic couplings effectively induced by exciton-vibration interaction and the subsequent delocalization of excitons. Finally we demonstrate that the thermal relaxation and dephasing can help the excitation en...
Hosten, O.; Krishnakumar, R.; Engelsen, N. J.; Kasevich, M.A.
2016-01-01
Quantum metrology exploits entangled states of particles to improve sensing precision beyond the limit achievable with uncorrelated particles. All previous methods required detection noise levels below this standard quantum limit to realize the benefits of the intrinsic sensitivity provided by these states. Remarkably, a recent proposal has shown that, in principle, such low-noise detection is not a necessary requirement. Here, we experimentally demonstrate a widely applicable method for enta...
Bădescu, Costin; O'Donnell, Ryan; Wright, John
2017-01-01
We consider the problem of quantum state certification, where one is given $n$ copies of an unknown $d$-dimensional quantum mixed state $\\rho$, and one wants to test whether $\\rho$ is equal to some known mixed state $\\sigma$ or else is $\\epsilon$-far from $\\sigma$. The goal is to use notably fewer copies than the $\\Omega(d^2)$ needed for full tomography on $\\rho$ (i.e., density estimation). We give two robust state certification algorithms: one with respect to fidelity using $n = O(d/\\epsilon...
Lockhart, Joshua; Guillén, Carlos E. González
2017-01-01
We consider a problem we call StateIsomorphism: given two quantum states of n qubits, can one be obtained from the other by rearranging the qubit subsystems? Our main goal is to study the complexity of this problem, which is a natural quantum generalisation of the problem StringIsomorphism. We show that StateIsomorphism is at least as hard as GraphIsomorphism, and show that these problems have a similar structure by presenting evidence to suggest that StateIsomorphism is an intermediate probl...
Quantum control of vibrational excitations in a heteronuclear ...
Indian Academy of Sciences (India)
WINTEC
Quantum control of vibrational excitations in a heteronuclear diatomic molecule. SITANSH SHARMA, PURSHOTAM SHARMA and HARJINDER SINGH* ... electric field is calculated and used for the subsequent quantum dynamics, within the dipole approxima- tion. ... properties of interference of dynamical paths to regulate ...
Zhang, Zhedong; Wang, Jin
2015-04-02
Recently, the quantum nature in the energy transport in solar cells and light-harvesting complexes has attracted much attention as being triggered by the experimental observations. We model the light-harvesting complex (i.e., PEB50 dimer) as a quantum heat engine (QHE) and study the effect of the undamped intramolecule vibrational modes on the coherent energy-transfer process and quantum transport. We find that the exciton-vibration interaction has nontrivial contribution to the promotion of quantum yield as well as transport properties of the QHE at steady state by enhancing the quantum coherence quantified by entanglement entropy. The perfect quantum yield over 90% has been obtained, with the exciton-vibration coupling. We attribute these improvements to the renormalization of the electronic couplings effectively induced by exciton-vibration interaction and the subsequent delocalization of excitons. Finally, we demonstrate that the thermal relaxation and dephasing can help the excitation energy transfer in the PEB50 dimer.
Quantum correlation dynamics in photosynthetic processes assisted by molecular vibrations
Energy Technology Data Exchange (ETDEWEB)
Giorgi, G.L., E-mail: g.giorgi@inrim.it [INRIM, Strada delle Cacce 91, I-10135 Torino (Italy); Roncaglia, M. [INRIM, Strada delle Cacce 91, I-10135 Torino (Italy); Raffa, F.A. [Politecnico di Torino, Dipartimento di Scienza Applicata e Tecnologia, Corso Duca degli Abruzzi 24, I-10129 Torino (Italy); Genovese, M. [INRIM, Strada delle Cacce 91, I-10135 Torino (Italy)
2015-10-15
During the long course of evolution, nature has learnt how to exploit quantum effects. In fact, recent experiments reveal the existence of quantum processes whose coherence extends over unexpectedly long time and space ranges. In particular, photosynthetic processes in light-harvesting complexes display a typical oscillatory dynamics ascribed to quantum coherence. Here, we consider the simple model where a dimer made of two chromophores is strongly coupled with a quasi-resonant vibrational mode. We observe the occurrence of wide oscillations of genuine quantum correlations, between electronic excitations and the environment, represented by vibrational bosonic modes. Such a quantum dynamics has been unveiled through the calculation of the negativity of entanglement and the discord, indicators widely used in quantum information for quantifying the resources needed to realize quantum technologies. We also discuss the possibility of approximating additional weakly-coupled off-resonant vibrational modes, simulating the disturbances induced by the rest of the environment, by a single vibrational mode. Within this approximation, one can show that the off-resonant bath behaves like a classical source of noise.
Brody, DC; Hughston, LP
2016-01-01
We propose an energy-driven stochastic master equation for the density matrix as a dynamical model for quantum state reduction. In contrast, most previous studies of state reduction have considered stochastic extensions of the Schr¨odinger equation, and have introduced the density matrix as the expectation of the random pure projection operator associated with the evolving state vector. After working out properties of the reduction process we construct a general solution to the energy- driven...
Xu, Yuntao; Xiong, Bo; Chang, Yih-Chung; Pan, Yi; Lo, Po Kam; Lau, Kai Chung; Ng, C Y
2017-04-12
We report detailed absolute integral cross sections (σ's) for the quantum-rovibrational-state-selected ion-molecule reaction in the center-of-mass collision energy (Ecm) range of 0.05-10.00 eV, where (vvv) = (000), (100), and (020), and . Three product channels, HCO+ + OH, HOCO+ + H, and CO+ + H2O, are identified. The measured σ(HCO+) curve [σ(HCO+) versus Ecm plot] supports the hypothesis that the formation of the HCO+ + OH channel follows an exothermic pathway with no potential energy barriers. Although the HOCO+ + H channel is the most exothermic, the σ(HOCO+) is found to be significantly lower than the σ(HCO+). The σ(HOCO+) curve is bimodal, indicating two distinct mechanisms for the formation of HOCO+. The σ(HOCO+) is strongly inhibited at Ecm 0.4 eV by (100) vibrational excitation. The Ecm onsets of σ(CO+) determined for the (000) and (100) vibrational states are in excellent agreement with the known thermochemical thresholds. This observation, along with the comparison of the σ(CO+) curves for the (100) and (000) states, shows that kinetic and vibrational energies are equally effective in promoting the CO+ channel. We have also performed high-level ab initio quantum calculations on the potential energy surface, intermediates, and transition state structures for the titled reaction. The calculations reveal potential barriers of ≈0.5-0.6 eV for the formation of HOCO+, and thus account for the low σ(HOCO+) and its bimodal profile observed. The Ecm enhancement for σ(HOCO+) at Ecm ≈ 0.5-5.0 eV can be attributed to the direct collision mechanism, whereas the formation of HOCO+ at low Ecm < 0.4 eV may involve a complex mechanism, which is mediated by the formation of a loosely sticking complex between HCO+ and OH. The direct collision and complex mechanisms proposed also allow the rationalization of the vibrational inhibition at low Ecm and the vibrational enhancement at high Ecm observed for the σ(HOCO+).
Rudolph, Terry; Spekkens, Robert W.
2004-11-01
We introduce a primitive for quantum cryptography that we term “state targeting.” We show that increasing one’s probability of success in this task above a minimum amount implies an unavoidable increase in the probability of a particular kind of failure. This is analogous to the unavoidable disturbance to a quantum state that results from gaining information about its identity, and can be shown to be a purely quantum effect. We solve various optimization problems for state targeting that are useful for the security analysis of two-party cryptographic tasks implemented between remote antagonistic parties. Although we focus on weak coin flipping, the results are significant for other two-party protocols, such as strong coin flipping, partially binding and concealing bit commitment, and bit escrow. Furthermore, the results have significance not only for the traditional notion of security in cryptography, that of restricting a cheater’s ability to bias the outcome of the protocol, but also for a different notion of security that arises only in the quantum context, that of cheat sensitivity. Finally, our analysis leads to some interesting secondary results, namely, a generalization of Uhlmann’s theorem and an operational interpretation of the fidelity between two mixed states.
Zhou, Yi; Kanoda, Kazushi; Ng, Tai-Kai
2017-04-01
This is an introductory review of the physics of quantum spin liquid states. Quantum magnetism is a rapidly evolving field, and recent developments reveal that the ground states and low-energy physics of frustrated spin systems may develop many exotic behaviors once we leave the regime of semiclassical approaches. The purpose of this article is to introduce these developments. The article begins by explaining how semiclassical approaches fail once quantum mechanics become important and then describe the alternative approaches for addressing the problem. Mainly spin-1 /2 systems are discussed, and most of the time is spent in this article on one particular set of plausible spin liquid states in which spins are represented by fermions. These states are spin-singlet states and may be viewed as an extension of Fermi liquid states to Mott insulators, and they are usually classified in the category of so-called S U (2 ), U (1 ), or Z2 spin liquid states. A review is given of the basic theory regarding these states and the extensions of these states to include the effect of spin-orbit coupling and to higher spin (S >1 /2 ) systems. Two other important approaches with strong influences on the understanding of spin liquid states are also introduced: (i) matrix product states and projected entangled pair states and (ii) the Kitaev honeycomb model. Experimental progress concerning spin liquid states in realistic materials, including anisotropic triangular-lattice systems [κ -(ET )2Cu2(CN )3 and EtMe3Sb [Pd (dmit )2]2 ], kagome-lattice system [ZnCu3(OH )6Cl2 ], and hyperkagome lattice system (Na4 Ir3 O8 ), is reviewed and compared against the corresponding theories.
Quantum engineering of continuous variable quantum states
Energy Technology Data Exchange (ETDEWEB)
Sabuncu, Metin
2009-10-29
Quantum information with continuous variables is a field attracting increasing attention recently. In continuous variable quantum information one makes use of the continuous information encoded into the quadrature of a quantized light field instead of binary quantities such as the polarization state of a single photon. This brand new research area is witnessing exciting theoretical and experimental achievements such as teleportation, quantum computation and quantum error correction. The rapid development of the field is mainly due higher optical data rates and the availability of simple and efficient manipulation tools in continuous-variable quantum information processing. We in this thesis extend the work in continuous variable quantum information processing and report on novel experiments on amplification, cloning, minimal disturbance and noise erasure protocols. The promising results we obtain in these pioneering experiments indicate that the future of continuous variable quantum information is bright and many advances can be foreseen. (orig.)
Quantum cobwebs: Universal entangling of quantum states
Indian Academy of Sciences (India)
Center for Philosophy and Foundation of Science, New Delhi, India ... Introduction. Quantum entanglement is generally regarded as a very useful resource for quantum infor- mation processing [1]. It can be used for teleportation [2], ... To achieve this, we introduce a class of entangled states calledzero sum amplitude(ZSA).
Multiphoton quantum optics and quantum state engineering
Energy Technology Data Exchange (ETDEWEB)
Dell' Anno, Fabio [Dipartimento di Fisica ' E. R. Caianiello' , Universita degli Studi di Salerno, CNISM and CNR-INFM Coherentia, and INFN Sezione di Napoli, Gruppo Collegato di Salerno, Via S. Allende, I-84081 Baronissi (Saudi Arabia) (Italy)]. E-mail: dellanno@sa.infn.it; De Siena, Silvio [Dipartimento di Fisica ' E. R. Caianiello' , Universita degli Studi di Salerno, CNISM and CNR-INFM Coherentia, and INFN Sezione di Napoli, Gruppo Collegato di Salerno, Via S. Allende, I-84081 Baronissi (SA) (Italy)]. E-mail: desiena@sa.infn.it; Illuminati, Fabrizio [Dipartimento di Fisica ' E. R. Caianiello' , Universita degli Studi di Salerno, CNISM and CNR-INFM Coherentia, and INFN Sezione di Napoli, Gruppo Collegato di Salerno, Via S. Allende, I-84081 Baronissi (SA) (Italy)]. E-mail: illuminati@sa.infn.it
2006-05-15
We present a review of theoretical and experimental aspects of multiphoton quantum optics. Multiphoton processes occur and are important for many aspects of matter-radiation interactions that include the efficient ionization of atoms and molecules, and, more generally, atomic transition mechanisms; system-environment couplings and dissipative quantum dynamics; laser physics, optical parametric processes, and interferometry. A single review cannot account for all aspects of such an enormously vast subject. Here we choose to concentrate our attention on parametric processes in nonlinear media, with special emphasis on the engineering of nonclassical states of photons and atoms that are relevant for the conceptual investigations as well as for the practical applications of forefront aspects of modern quantum mechanics. We present a detailed analysis of the methods and techniques for the production of genuinely quantum multiphoton processes in nonlinear media, and the corresponding models of multiphoton effective interactions. We review existing proposals for the classification, engineering, and manipulation of nonclassical states, including Fock states, macroscopic superposition states, and multiphoton generalized coherent states. We introduce and discuss the structure of canonical multiphoton quantum optics and the associated one- and two-mode canonical multiphoton squeezed states. This framework provides a consistent multiphoton generalization of two-photon quantum optics and a consistent Hamiltonian description of multiphoton processes associated to higher-order nonlinearities. Finally, we discuss very recent advances that by combining linear and nonlinear optical devices allow to realize multiphoton entangled states of the electromagnetic field, either in discrete or in continuous variables, that are relevant for applications to efficient quantum computation, quantum teleportation, and related problems in quantum communication and information.
Krasnoshchekov, Sergey V.; Stepanov, Nikolay F.
2013-11-01
In the theory of anharmonic vibrations of a polyatomic molecule, mixing the zero-order vibrational states due to cubic, quartic and higher-order terms in the potential energy expansion leads to the appearance of more-or-less isolated blocks of states (also called polyads), connected through multiple resonances. Such polyads of states can be characterized by a common secondary integer quantum number. This polyad quantum number is defined as a linear combination of the zero-order vibrational quantum numbers, attributed to normal modes, multiplied by non-negative integer polyad coefficients, which are subject to definition for any particular molecule. According to Kellman's method [J. Chem. Phys. 93, 6630 (1990)], the corresponding formalism can be conveniently described using vector algebra. In the present work, a systematic consideration of polyad quantum numbers is given in the framework of the canonical Van Vleck perturbation theory (CVPT) and its numerical-analytic operator implementation for reducing the Hamiltonian to the quasi-diagonal form, earlier developed by the authors. It is shown that CVPT provides a convenient method for the systematic identification of essential resonances and the definition of a polyad quantum number. The method presented is generally suitable for molecules of significant size and complexity, as illustrated by several examples of molecules up to six atoms. The polyad quantum number technique is very useful for assembling comprehensive basis sets for the matrix representation of the Hamiltonian after removal of all non-resonance terms by CVPT. In addition, the classification of anharmonic energy levels according to their polyad quantum numbers provides an additional means for the interpretation of observed vibrational spectra.
Coherent states in quantum mechanics
Rodrigues, R D L; Fernandes, D
2001-01-01
We present a review work on the coherent states is non-relativistic quantum mechanics analysing the quantum oscillators in the coherent states. The coherent states obtained via a displacement operator that act on the wave function of ground state of the oscillator and the connection with Quantum Optics which were implemented by Glauber have also been considered. A possible generalization to the construction of new coherent states it is point out.
Entangled states in quantum mechanics
Ruža, Jānis
2010-01-01
In some circles of quantum physicists, a view is maintained that the nonseparability of quantum systems-i.e., the entanglement-is a characteristic feature of quantum mechanics. According to this view, the entanglement plays a crucial role in the solution of quantum measurement problem, the origin of the “classicality” from the quantum physics, the explanation of the EPR paradox by a nonlocal character of the quantum world. Besides, the entanglement is regarded as a cornerstone of such modern disciplines as quantum computation, quantum cryptography, quantum information, etc. At the same time, entangled states are well known and widely used in various physics areas. In particular, this notion is widely used in nuclear, atomic, molecular, solid state physics, in scattering and decay theories as well as in other disciplines, where one has to deal with many-body quantum systems. One of the methods, how to construct the basis states of a composite many-body quantum system, is the so-called genealogical decomposition method. Genealogical decomposition allows one to construct recurrently by particle number the basis states of a composite quantum system from the basis states of its forming subsystems. These coupled states have a structure typical for entangled states. If a composite system is stable, the internal structure of its forming basis states does not manifest itself in measurements. However, if a composite system is unstable and decays onto its forming subsystems, then the measurables are the quantum numbers, associated with these subsystems. In such a case, the entangled state has a dynamical origin, determined by the Hamiltonian of the corresponding decay process. Possible correlations between the quantum numbers of resulting subsystems are determined by the symmetries-conservation laws of corresponding dynamical variables, and not by the quantum entanglement feature.
Quantum dynamics of vibrational excitations and vibrational charge ...
Indian Academy of Sciences (India)
Administrator
Present address: The Fritz Haber Research Centre and The Department of Physical Chemisry,. Hebrew University of Jerusalem, ... state of the diatom. Good amount of state-selected experimental data obtained from the molecular beam and the H+/H energy-loss spectroscopy also exists at. Ec.m. = 23 eV for both the IVE ...
Solid-state quantum metamaterials
Wilson, Richard; Everitt, Mark; Saveliev, Sergey; Zagoskin, Alexandre
2013-03-01
Quantum metamaterials provide a promising potential test bed for probing the quantum-classical transition. We propose a scalable and feasible architecture for a solid-state quantum metamaterial. This consists of an ensemble of superconducting flux qubits inductively coupled to a superconducting transmission line. We make use of fully quantum mechanical models which account for decoherence, input and readout to study the behaviour of prototypical 1D and 2D quantum metamaterials. In addition to demonstrating some of the novel phenomena that arise in these systems, such as ``quantum birefringence,'' we will also discuss potential applications.
Preparation of quantum state (review)
Ali, N.; Yusof, N. R.; Soekardjo, S.; Saharudin, S.; Endut, R.
2017-11-01
We reviewed experimental results and publications prepared by the Quantum Laboratory, Mimos Berhad. The complexity of the setups lies mainly in preparing the quantum states. Optics is chosen as the medium of this quantum system. The two methods - fiber based and free space systems are different from each other in terms of experimental setups, components configuration, and selections.
Peters, William K.; Tiwari, Vivek; Jonas, David M.
2017-11-01
The nonadiabatic states and dynamics are investigated for a linear vibronic coupling Hamiltonian with a static electronic splitting and weak off-diagonal Jahn-Teller coupling through a single vibration with a vibrational-electronic resonance. With a transformation of the electronic basis, this Hamiltonian is also applicable to the anti-correlated vibration in a symmetric homodimer with marginally strong constant off-diagonal coupling, where the non-adiabatic states and dynamics model electronic excitation energy transfer or self-exchange electron transfer. For parameters modeling a free-base naphthalocyanine, the nonadiabatic couplings are deeply quantum mechanical and depend on wavepacket width; scalar couplings are as important as the derivative couplings that are usually interpreted to depend on vibrational velocity in semiclassical curve crossing or surface hopping theories. A colored visualization scheme that fully characterizes the non-adiabatic states using the exact factorization is developed. The nonadiabatic states in this nested funnel have nodeless vibrational factors with strongly avoided zeroes in their vibrational probability densities. Vibronic dynamics are visualized through the vibrational coordinate dependent density of the time-dependent dipole moment in free induction decay. Vibrational motion is amplified by the nonadiabatic couplings, with asymmetric and anisotropic motions that depend upon the excitation polarization in the molecular frame and can be reversed by a change in polarization. This generates a vibrational quantum beat anisotropy in excess of 2/5. The amplitude of vibrational motion can be larger than that on the uncoupled potentials, and the electronic population transfer is maximized within one vibrational period. Most of these dynamics are missed by the adiabatic approximation, and some electronic and vibrational motions are completely suppressed by the Condon approximation of a coordinate-independent transition dipole between
Vibrating soap films An analog for quantum chaos on billiards
Arcos, E; Cuatlayol, P A; Prian, M L H; Méndez-Sánchez, R A; Hernández-Saldaña, H
1998-01-01
We present an experimental setup based on the normal modes of vibrating soap films which shows quantum features of integrable and chaotic billiards. In particular, we obtain the so-called scars -narrow linear regions with high probability along classical periodic orbits- for the classically chaotic billiards. We show that these scars are also visible at low frequencies. Finally, we suggest some applications of our experimental setup in other related two-dimensional wave phenomena.
Quantum-polarization state tomography
Bayraktar, Ömer; Swillo, Marcin; Canalias, Carlota; Björk, Gunnar
2016-01-01
We propose and demonstrate a method for quantum-state tomography of qudits encoded in the quantum polarization of $N$-photon states. This is achieved by distributing $N$ photons nondeterministically into three paths and their subsequent projection, which for $N=1$ is equivalent to measuring the Stokes (or Pauli) operators. The statistics of the recorded $N$-fold coincidences determines the unknown $N$-photon polarization state uniquely. The proposed, fixed setup manifestly rules out any syste...
Quantum States as Ordinary Information
Directory of Open Access Journals (Sweden)
Ken Wharton
2014-03-01
Full Text Available Despite various parallels between quantum states and ordinary information, quantum no-go-theorems have convinced many that there is no realistic framework that might underly quantum theory, no reality that quantum states can represent knowledge about. This paper develops the case that there is a plausible underlying reality: one actual spacetime-based history, although with behavior that appears strange when analyzed dynamically (one time-slice at a time. By using a simple model with no dynamical laws, it becomes evident that this behavior is actually quite natural when analyzed “all-at-once” (as in classical action principles. From this perspective, traditional quantum states would represent incomplete information about possible spacetime histories, conditional on the future measurement geometry. Without dynamical laws imposing additional restrictions, those histories can have a classical probability distribution, where exactly one history can be said to represent an underlying reality.
Vibrational Scattering Anisotropy Generated by Multichannel Quantum Interference
Miron, Catalin; Kimberg, Victor; Morin, Paul; Nicolas, Christophe; Kosugi, Nobuhiro; Gavrilyuk, Sergey; Gel'Mukhanov, Faris
2010-08-01
Based on angularly and vibrationally resolved electron spectroscopy measurements in acetylene, we report the first observation of anomalously strong vibrational anisotropy of resonant Auger scattering through the C 1s→π* excited state. We provide a theoretical model explaining the new phenomenon by three coexisting interference effects: (i) interference between resonant and direct photoionization channels, (ii) interference of the scattering channels through the core-excited bending states with orthogonal orientation of the molecular orbitals, (iii) scattering through two wells of the double-well bending mode potential. The interplay of nuclear and electronic motions offers in this case a new type of nuclear wave packet interferometry sensitive to the anisotropy of nuclear dynamics: whether which-path information is available or not depends on the final vibrational state serving for path selection.
Inelastic Kondo-Andreev tunneling in a vibrating quantum dot
Cao, Zhan; Fang, Tie-Feng; Sun, Qing-Feng; Luo, Hong-Gang
2017-03-01
Phonon-assisted electronic tunneling through a vibrating quantum dot embedded between normal and superconducting leads is studied in the Kondo regime. In such a hybrid device, with the bias applied to the normal lead, we find a series of Kondo sidebands separated by half a phonon energy in the differential conductance, which are distinct from the phonon-assisted sidebands previously observed in conventional Andreev tunneling and in systems with only normal leads. These Kondo sidebands originate from the Kondo-Andreev cooperative cotunneling mediated by phonons, which exhibit an interesting Kondo transport behavior due to the interplay of the Kondo effect, the Andreev tunneling, and the mechanical vibrations. Our result could be observed in a recent experiment setup [J. Gramich et al., Phys. Rev. Lett. 115, 216801 (2015), 10.1103/PhysRevLett.115.216801], provided that their carbon nanotube device reaches the Kondo regime at low temperatures.
Optical properties of a vibrationally modulated solid state Mott insulator.
Kaiser, S; Clark, S R; Nicoletti, D; Cotugno, G; Tobey, R I; Dean, N; Lupi, S; Okamoto, H; Hasegawa, T; Jaksch, D; Cavalleri, A
2014-01-22
Optical pulses at THz and mid-infrared frequencies tuned to specific vibrational resonances modulate the lattice along chosen normal mode coordinates. In this way, solids can be switched between competing electronic phases and new states are created. Here, we use vibrational modulation to make electronic interactions (Hubbard-U) in Mott-insulator time dependent. Mid-infrared optical pulses excite localized molecular vibrations in ET-F2TCNQ, a prototypical one-dimensional Mott-insulator. A broadband ultrafast probe interrogates the resulting optical spectrum between THz and visible frequencies. A red-shifted charge-transfer resonance is observed, consistent with a time-averaged reduction of the electronic correlation strength U. Secondly, a sideband manifold inside of the Mott-gap appears, resulting from a periodically modulated U. The response is compared to computations based on a quantum-modulated dynamic Hubbard model. Heuristic fitting suggests asymmetric holon-doublon coupling to the molecules and that electron double-occupancies strongly squeeze the vibrational mode.
Quantum state revivals in quantum walks on cycles
Directory of Open Access Journals (Sweden)
Phillip R. Dukes
2014-01-01
Full Text Available Recurrence in the classical random walk is well known and described by the Pólya number. For quantum walks, recurrence is similarly understood in terms of the probability of a localized quantum walker to return to its origin. Under certain circumstances the quantum walker may also return to an arbitrary initial quantum state in a finite number of steps. Quantum state revivals in quantum walks on cycles using coin operators which are constant in time and uniform across the path have been described before but only incompletely. In this paper we find the general conditions for which full-quantum state revival will occur.
Cluster State Quantum Computation
2014-02-01
important result is called the threshold theorem of quantum computation [Aliferis06]. Fault-tolerant schemes for OWQC using photons have recently...defined in terms of the standard Fubini -Study distance Approved for Public Release; Distribution Unlimited. 25 ( ) ( ) 1
Cluster State Quantum Computing
2012-12-01
discuss the potential advantages of such a system and the difficulties of the design. When an incident photon strikes a Niobium nitride ( NbN ...counted. Present superconducting nanowire systems, such as NbN , have reasonably good counting efficiency [Dauler10], [Marsili11], by which we mean...L. O’Brein, A. Furusawa, J. Vuchovic, “Photonic quantum technologies ,” Nat. Photonics 3 Dec. (2009) doi:10.1038/nphoton.2009.229. [Pawlowski09
Quantum state transfer via Bloch oscillations
Tamascelli, Dario; Olivares, Stefano; Rossotti, Stefano; Osellame, Roberto; Paris, Matteo G. A.
2016-01-01
The realization of reliable quantum channels, able to transfer a quantum state with high fidelity, is a fundamental step in the construction of scalable quantum devices. In this paper we describe a transmission scheme based on the genuinely quantum effect known as Bloch oscillations. The proposed protocol makes it possible to carry a quantum state over different distances with a minimal engineering of the transmission medium and can be implemented and verified on current quantum technology hardware. PMID:27189630
Killoran, N; Huelga, S F; Plenio, M B
2015-10-21
Recent evidence suggests that quantum effects may have functional importance in biological light-harvesting systems. Along with delocalized electronic excitations, it is now suspected that quantum coherent interactions with certain near-resonant vibrations may contribute to light-harvesting performance. However, the actual quantum advantage offered by such coherent vibrational interactions has not yet been established. We investigate a quantum design principle, whereby coherent exchange of single energy quanta between electronic and vibrational degrees of freedom can enhance a light-harvesting system's power above what is possible by thermal mechanisms alone. We present a prototype quantum heat engine which cleanly illustrates this quantum design principle and quantifies its quantum advantage using thermodynamic measures of performance. We also demonstrate the principle's relevance in parameter regimes connected to natural light-harvesting structures.
Energy Technology Data Exchange (ETDEWEB)
Killoran, N.; Huelga, S. F.; Plenio, M. B. [Institut für Theoretische Physik, Universität Ulm, Albert-Einstein-Allee 11, D-89069 Ulm (Germany)
2015-10-21
Recent evidence suggests that quantum effects may have functional importance in biological light-harvesting systems. Along with delocalized electronic excitations, it is now suspected that quantum coherent interactions with certain near-resonant vibrations may contribute to light-harvesting performance. However, the actual quantum advantage offered by such coherent vibrational interactions has not yet been established. We investigate a quantum design principle, whereby coherent exchange of single energy quanta between electronic and vibrational degrees of freedom can enhance a light-harvesting system’s power above what is possible by thermal mechanisms alone. We present a prototype quantum heat engine which cleanly illustrates this quantum design principle and quantifies its quantum advantage using thermodynamic measures of performance. We also demonstrate the principle’s relevance in parameter regimes connected to natural light-harvesting structures.
Rectangular Parallelepiped Vibration in Plane Strain State
Hanckowiak, Jerzy
2004-01-01
In this paper we present a vibration spectrum of a homogenous parallelepiped (HP) under the action of volume and surface forces resulting from the exponent displacements entering the Fourier transforms. Vibration under the action of axial surface tractions and the free vibration are described separately. A relationship between the high frequency vibration and boundary conditions (BC) is also considered.
Dai, Peng; Jiang, Nan; Tan, Ren-Xiang
2016-01-01
Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.
Spectroscopy of Vibrational States in Diatomic Iodine Molecules
Mulholland, Mary; Harrill, Charles H.; Smith, R. Seth
2015-04-01
This project is focused on understanding the vibrational structure of iodine, which is a homonuclear diatomic molecule. A 20 mW, 532 nm cw diode laser was used to selectively excite neutral iodine molecules to a higher energy electronic state. By performing spectroscopy on the transitions from this state to a lower energy electronic state, the data only showed those vibrational bands which connect the two electronic states. Since a number of vibrational levels are populated in the higher energy electronic state, the transitions to all of the allowed vibrational levels in the lower energy electronic state provided sufficient data to determine the vibrational structures of both states. Emission spectra were collected with an Ocean Optics USB4000 Compact CCD Spectrometer. The spectrometer had a range of 500 - 770 nm with a resolution of approximately 0.5 nm and was sensitive enough to resolve the vibrational states in diatomic iodine molecules. The results were compared to a simple harmonic oscillator model.
Coherent states in the quantum multiverse
Energy Technology Data Exchange (ETDEWEB)
Robles-Perez, S., E-mail: salvarp@imaff.cfmac.csic.e [Colina de los Chopos, Centro de Fisica ' Miguel Catalan' , Instituto de Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 121, 28006 Madrid (Spain); Estacion Ecologica de Biocosmologia, Medellin (Spain); Hassouni, Y. [Laboratoire de Physique Theorique, Faculte des Sciences-Universite Sidi Med Ben Abdellah, Avenue Ibn Batouta B.P: 1014, Agdal Rabat (Morocco); Gonzalez-Diaz, P.F. [Colina de los Chopos, Centro de Fisica ' Miguel Catalan' , Instituto de Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 121, 28006 Madrid (Spain); Estacion Ecologica de Biocosmologia, Medellin (Spain)
2010-01-11
In this Letter, we study the role of coherent states in the realm of quantum cosmology, both in a second-quantized single universe and in a third-quantized quantum multiverse. In particular, most emphasis will be paid to the quantum description of multiverses made of accelerated universes. We have shown that the quantum states involved at a quantum mechanical multiverse whose single universes are accelerated are given by squeezed states having no classical analogs.
Coherent states in the quantum multiverse
Robles-Pérez, S.; Hassouni, Y.; González-Díaz, P. F.
2010-01-01
In this Letter, we study the role of coherent states in the realm of quantum cosmology, both in a second-quantized single universe and in a third-quantized quantum multiverse. In particular, most emphasis will be paid to the quantum description of multiverses made of accelerated universes. We have shown that the quantum states involved at a quantum mechanical multiverse whose single universes are accelerated are given by squeezed states having no classical analogs.
Entanglement for All Quantum States
de la Torre, A. C.; Goyeneche, D.; Leitao, L.
2010-01-01
It is shown that a state that is factorizable in the Hilbert space corresponding to some choice of degrees of freedom becomes entangled for a different choice of degrees of freedom. Therefore, entanglement is not a special case but is ubiquitous in quantum systems. Simple examples are calculated and a general proof is provided. The physical…
New solid forms of efavirenz: Synthesis, vibrational spectroscopy and quantum chemical calculations
Marques, Marcelo M.; Rezende, Carlos A.; Lima, Gabriel C.; Marques, Andressa C. S.; Prado, Lívia D.; Leal, Kátia Z.; Rocha, Helvécio V. A.; Ferreira, Gláucio B.; Resende, Jackson A. L. C.
2017-06-01
Efavirenz,(S)-6-chloro-4-(cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one, is an anti HIV agent from the class of the non-nucleoside inhibitors of the HIV-1 virus reverse transcriptase. This paper describes the synthesis of two new solvatomorphs of efavirenz (EFV). The results through XRPD and DSC/TG indicate that the new forms undergo a solvent loss over the days, and then return to the original polymorph. Structural and spectral characteristics of EFV were studied by vibrational spectroscopy and quantum chemical methods. Density functional theory (DFT) calculations for the potential energy curve, optimized geometries and vibrational spectra were carried out using 6-311 + G** basis sets and CAM-B3LYP functional, solid state calculations were also performed using DFT-XGGA (PBE-D3) exchange-correlation functional with the option of mixtures of Gaussian and plane waves method (GPW). Based on these results, the paper discussed the correlation between the vibrational modes and the crystalline structure of the most stable form of EFV. A complete analysis of the experimental infrared and Raman spectra was reported on the basis of the wavenumbers of the vibrational bands and the potential energy distribution.
Quantum Contextuality with Stabilizer States
Directory of Open Access Journals (Sweden)
Jiri Vala
2013-06-01
Full Text Available The Pauli groups are ubiquitous in quantum information theory because of their usefulness in describing quantum states and operations and their readily understood symmetry properties. In addition, the most well-understood quantum error correcting codes—stabilizer codes—are built using Pauli operators. The eigenstates of these operators—stabilizer states—display a structure (e.g., mutual orthogonality relationships that has made them useful in examples of multi-qubit non-locality and contextuality. Here, we apply the graph-theoretical contextuality formalism of Cabello, Severini and Winter to sets of stabilizer states, with particular attention to the effect of generalizing two-level qubit systems to odd prime d-level qudit systems. While state-independent contextuality using two-qubit states does not generalize to qudits, we show explicitly how state-dependent contextuality associated with a Bell inequality does generalize. Along the way we note various structural properties of stabilizer states, with respect to their orthogonality relationships, which may be of independent interest.
Vibration-induced coherence enhancement of the performance of a biological quantum heat engine.
Chen, Hong-Bin; Chiu, Pin-Yi; Chen, Yueh-Nan
2016-11-01
Photosynthesis has been a long-standing research interest due to its fundamental importance. Recently, studies on photosynthesis processes also have inspired attention from a thermodynamical aspect when considering photosynthetic apparatuses as biological quantum heat engines. Quantum coherence is shown to play a crucial role in enhancing the performance of these quantum heat engines. Based on the experimentally reported structure, we propose a quantum heat engine model with a non-Markovian vibrational mode. We show that one can obtain a performance enhancement easily for a wide range of parameters in the presence of the vibrational mode. Our results provide insights into the photosynthetic processes and a design principle mimicking natural organisms.
Vibration-induced coherence enhances the performance of a biological quantum heat engine
Chen, Hong-Bin; Chen, Yueh-Nan
2016-01-01
Photosynthesis has been the long-standing research interest due to its fundamental importance. Recently, studies on photosynthesis processes also inspire attention from thermodynamical aspect when considering photosynthetic apparatuses as biological quantum heat engines. Quantum coherence is shown to play a crucial role in enhancing the performance of these quantum heat engines. Based on the experimentally reported structure, we propose a quantum heat engine model with a non-Markovian vibrational mode. We show that one can obtain a performance enhancement easily for a wide range of parameters in the presence of the vibrational mode. Our results suggest new insights into the photosynthetic processes and a design principle mimicking natural organisms.
The Metric of Quantum States Revisited
Pandya, Aalok; Nagawat, Ashok K.
2002-01-01
A generalised definition of the metric of quantum states is proposed by using the techniques of differential geometry. The metric of quantum state space derived earlier by Anandan, is reproduced and verified here by this generalised definition. The metric of quantum states in the configuration space and its possible geometrical framework is explored. Also, invariance of the metric of quantum states under local gauge transformations, coordinate transformations, and the relativistic transformat...
Fujisaki, Hiroshi; Yagi, Kiyoshi; Kikuchi, Hiroto; Takami, Toshiya; Stock, Gerhard
2017-01-01
Performing comprehensive quantum-chemical calculations, a vibrational Hamiltonian of acetylbenzonitrile is constructed, on the basis of which a quantum-mechanical "tier model" is developed that describes the vibrational dynamics following excitation of the CN stretch mode. Taking into account 36 vibrational modes and cubic and quartic anharmonic couplings between up to three different modes, the tier model calculations are shown to qualitatively reproduce the main findings of the experiments of Rubtsov and coworkers (2011), including the energy relaxation of the initially excited CN mode and the structure-dependent vibrational transport. Moreover, the calculations suggest that the experimentally measured cross-peak among the CN and CO modes does not correspond to direct excitation of the CO normal mode but rather reflects excited low-frequency vibrations that anharmonically couple to the CO mode. Complementary quasiclassical trajectory calculations are found to be in good overall agreement with the quantum calculations.
Energy Technology Data Exchange (ETDEWEB)
Gollub, C; De Vivie-Riedle, R [LMU Department Chemie, Butenandt-Str. 11, 81377 Muenchen (Germany)], E-mail: Caroline.Gollub@cup.uni-muenchen.de, E-mail: Regina.de_Vivie@cup.uni-muenchen.de
2009-01-15
A multi-objective genetic algorithm is applied to optimize picosecond laser fields, driving vibrational quantum processes. Our examples are state-to-state transitions and unitary transformations. The approach allows features of the shaped laser fields and of the excitation mechanisms to be controlled simultaneously with the quantum yield. Within the parameter range accessible to the experiment, we focus on short pulse durations and low pulse energies to optimize preferably robust laser fields. Multidimensional Pareto fronts for these conflicting objectives could be constructed. Comparison with previous work showed that the solutions from Pareto optimizations and from optimal control theory match very well.
Gollub, C.; de Vivie-Riedle, R.
2009-01-01
A multi-objective genetic algorithm is applied to optimize picosecond laser fields, driving vibrational quantum processes. Our examples are state-to-state transitions and unitary transformations. The approach allows features of the shaped laser fields and of the excitation mechanisms to be controlled simultaneously with the quantum yield. Within the parameter range accessible to the experiment, we focus on short pulse durations and low pulse energies to optimize preferably robust laser fields. Multidimensional Pareto fronts for these conflicting objectives could be constructed. Comparison with previous work showed that the solutions from Pareto optimizations and from optimal control theory match very well.
Investigating Quantum Modulation States
2016-03-01
process incurs ambiguity in the interpretation of measurement results. When the average photon number per transmission of a message bit grows...estimates to gain the information conveyed therein. Is the message bit sent a one or zero? That eavesdropper’s minimum probability of error converges...to ½, a coin toss, when the average photon number and the number of possible states satisfy the aforementioned conditions. The eavesdropper
Quantum State Transfer on Coronas
Ackelsberg, Ethan; Brehm, Zachary; Chan, Ada; Mundinger, Joshua; Tamon, Christino
2016-01-01
We study state transfer in quantum walk on graphs relative to the adjacency matrix. Our motivation is to understand how the addition of pendant subgraphs affect state transfer. For two graphs $G$ and $H$, the Frucht-Harary corona product $G \\circ H$ is obtained by taking $|G|$ copies of the cone $K_{1} + H$ and by connecting the conical vertices according to $G$. Our work explores conditions under which the corona $G \\circ H$ exhibits state transfer. We also describe new families of graphs wi...
Quantum state atomic force microscopy
Passian, Ali; Siopsis, George
2017-01-01
New classical modalities of atomic force microscopy continue to emerge to achieve higher spatial, spectral, and temporal resolution for nanometrology of materials. Here, we introduce the concept of a quantum mechanical modality that capitalizes on squeezed states of probe displacement. We show that such squeezing is enabled nanomechanically when the probe enters the van der Waals regime of interaction with a sample. The effect is studied in the non-contact mode, where we consider the paramete...
Quantum State Engineering Via Coherent-State Superpositions
Janszky, Jozsef; Adam, P.; Szabo, S.; Domokos, P.
1996-01-01
The quantum interference between the two parts of the optical Schrodinger-cat state makes possible to construct a wide class of quantum states via discrete superpositions of coherent states. Even a small number of coherent states can approximate the given quantum states at a high accuracy when the distance between the coherent states is optimized, e. g. nearly perfect Fock state can be constructed by discrete superpositions of n + 1 coherent states lying in the vicinity of the vacuum state.
Quantum Computing in Solid State Systems
Ruggiero, B; Granata, C
2006-01-01
The aim of Quantum Computation in Solid State Systems is to report on recent theoretical and experimental results on the macroscopic quantum coherence of mesoscopic systems, as well as on solid state realization of qubits and quantum gates. Particular attention has been given to coherence effects in Josephson devices. Other solid state systems, including quantum dots, optical, ion, and spin devices which exhibit macroscopic quantum coherence are also discussed. Quantum Computation in Solid State Systems discusses experimental implementation of quantum computing and information processing devices, and in particular observations of quantum behavior in several solid state systems. On the theoretical side, the complementary expertise of the contributors provides models of the various structures in connection with the problem of minimizing decoherence.
The Roles of a Quantum Channel on a Quantum State
Wang, Lin; Yu, Chang-shui
2013-10-01
When a quantum state undergoes a quantum channel, the state will be inevitably influenced. In general, the fidelity of the state is reduced, so is the entanglement if the subsystems go through the channel. However, the influence on the coherence of the state is quite different. Here we present some state-independent quantities to describe to what degree the fidelity, the entanglement and the coherence of the state are influenced. As applications, we consider some quantum channels on a qubit and find that the infidelity ability monotonically depends on the decay rate, but in usual the decoherence ability is not the case and strongly depends on the channel.
Universal damping mechanism of quantum vibrations in deep sub-barrier fusion reactions
Ichikawa, Takatoshi
2017-11-01
I demonstrate that the coordinate dependence of the coupling strengths of colliding nuclei is important for describing the deep sub-barrier fusion hindrance. To this end, I firstly show the performance of an extended coupled-channel model by phenomenologically introducing a damping factor in the coupling potential. The damping factor stimulates the damping of quantum vibrations occurring near the touching point of colliding nuclei and introduce a coordinate dependence in the coupling strengths. Next, I directly show the coordinate dependence of the transition strengths of colliding nuclei by microscopically calculating excited states using the random phase approximation method. The obtained transition strengths of colliding nuclei as a function of the center-of-mass distance strongly correlate with the damping factor that reproduces very well the fusion hindrance. This is a direct justification for the concept of the coordinate-dependent coupling strengths. Finally, I conclude that the damping of quantum vibrations near the touching point is the universal mechanism for the deep sub-barrier fusion hindrance.
DECOY STATE QUANTUM KEY DISTRIBUTION
Directory of Open Access Journals (Sweden)
Sellami Ali
2010-03-01
Full Text Available Experimental weak + vacuum protocol has been demonstrated using commercial QKD system based on a standard bi-directional ‘Plug & Play’ set-up. By making simple modifications to a commercial quantum key distribution system, decoy state QKD allows us to achieve much better performance than QKD system without decoy state in terms of key generation rate and distance. We demonstrate an unconditionally secure key rate of 6.2931 x 10-4per pulse for a 25 km fiber length.
Distinguishability of quantum states and shannon complexity in quantum cryptography
Arbekov, I. M.; Molotkov, S. N.
2017-07-01
The proof of the security of quantum key distribution is a rather complex problem. Security is defined in terms different from the requirements imposed on keys in classical cryptography. In quantum cryptography, the security of keys is expressed in terms of the closeness of the quantum state of an eavesdropper after key distribution to an ideal quantum state that is uncorrelated to the key of legitimate users. A metric of closeness between two quantum states is given by the trace metric. In classical cryptography, the security of keys is understood in terms of, say, the complexity of key search in the presence of side information. In quantum cryptography, side information for the eavesdropper is given by the whole volume of information on keys obtained from both quantum and classical channels. The fact that the mathematical apparatuses used in the proof of key security in classical and quantum cryptography are essentially different leads to misunderstanding and emotional discussions [1]. Therefore, one should be able to answer the question of how different cryptographic robustness criteria are related to each other. In the present study, it is shown that there is a direct relationship between the security criterion in quantum cryptography, which is based on the trace distance determining the distinguishability of quantum states, and the criterion in classical cryptography, which uses guesswork on the determination of a key in the presence of side information.
Quantum State Tomography via Reduced Density Matrices.
Xin, Tao; Lu, Dawei; Klassen, Joel; Yu, Nengkun; Ji, Zhengfeng; Chen, Jianxin; Ma, Xian; Long, Guilu; Zeng, Bei; Laflamme, Raymond
2017-01-13
Quantum state tomography via local measurements is an efficient tool for characterizing quantum states. However, it requires that the original global state be uniquely determined (UD) by its local reduced density matrices (RDMs). In this work, we demonstrate for the first time a class of states that are UD by their RDMs under the assumption that the global state is pure, but fail to be UD in the absence of that assumption. This discovery allows us to classify quantum states according to their UD properties, with the requirement that each class be treated distinctly in the practice of simplifying quantum state tomography. Additionally, we experimentally test the feasibility and stability of performing quantum state tomography via the measurement of local RDMs for each class. These theoretical and experimental results demonstrate the advantages and possible pitfalls of quantum state tomography with local measurements.
Assessments of macroscopicity for quantum optical states
DEFF Research Database (Denmark)
Laghaout, Amine; Neergaard-Nielsen, Jonas Schou; Andersen, Ulrik Lund
2015-01-01
With the slow but constant progress in the coherent control of quantum systems, it is now possible to create large quantum superpositions. There has therefore been an increased interest in quantifying any claims of macroscopicity. We attempt here to motivate three criteria which we believe should...... enter in the assessment of macroscopic quantumness: The number of quantum fluctuation photons, the purity of the states, and the ease with which the branches making up the state can be distinguished. © 2014....
Past Quantum States of a Monitored System
DEFF Research Database (Denmark)
Gammelmark, Søren; Julsgaard, Brian; Mølmer, Klaus
2013-01-01
A density matrix ρ(t) yields probabilistic information about the outcome of measurements on a quantum system. We introduce here the past quantum state, which, at time T, accounts for the state of a quantum system at earlier times t
Sunlight-Initiated Photochemistry: Excited Vibrational States of Atmospheric Chromophores
Veronica Vaida; Karl J. Feierabend; Nabilah Rontu; Kaito Takahashi
2008-01-01
Atmospheric chemical reactions are often initiated by ultraviolet (UV) solar radiation since absorption in that wavelength range coincides to typical chemical bond energies. In this review, we present an alternative process by which chemical reactions occur with the excitation of vibrational levels in the ground electronic state by red solar photons. We focus on the O–H vibrational manifold which can be an atmospheric chromophore for driving vibrationally mediated overtone-induced chemical re...
Quantum entanglement between electronic and vibrational degrees of freedom in molecules.
McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S; Reimers, Jeffrey R
2011-12-28
We consider the quantum entanglement of the electronic and vibrational degrees of freedom in molecules with tendencies towards double welled potentials. In these bipartite systems, the von Neumann entropy of the reduced density matrix is used to quantify the electron-vibration entanglement for the lowest two vibronic wavefunctions obtained from a model Hamiltonian based on coupled harmonic diabatic potential-energy surfaces. Significant entanglement is found only in the region in which the ground vibronic state contains a density profile that is bimodal (i.e., contains two separate local maxima). However, in this region two distinct types of density and entanglement profiles are found: one type arises purely from the degeneracy of energy levels in the two potential wells and is destroyed by slight asymmetry, while the other arises through strong interactions between the diabatic levels of each well and is relatively insensitive to asymmetry. These two distinct types are termed fragile degeneracy-induced entanglement and persistent entanglement, respectively. Six classic molecular systems describable by two diabatic states are considered: ammonia, benzene, BNB, pyridine excited triplet states, the Creutz-Taube ion, and the radical cation of the "special pair" of chlorophylls involved in photosynthesis. These chemically diverse systems are all treated using the same general formalism and the nature of the entanglement that they embody is elucidated.
An Approach to Quantum State Pooling from Quantum Conditional Independence
Leifer, Matthew
2008-03-01
In approaches to quantum theory in which the quantum state is taken to represent an agent's belief, knowledge or information about a physical system, it is legitimate for different agents to assign different states to one and the same physical system. The question then arises of what state they should assign if they get together and share their information about the system. This is the problem of quantum state pooling. The classical counterpart of this problem for probability distributions only has a unique solution under additional assumptions about how the data are collected, such as conditional independence constraints. Recently, Spekkens and Wiseman found a quantum pooling rule analogous to the classical one, which is valid if the differing state assignments arise from making indirect measurements on special classes of tripartite quantum state. We show that this pooling rule applies to a much wider class of tripartite states, and that its validity rests on quantum analogs of conditional independence recently studied by one of the authors, as well as a generalization of the notion of a sufficient statistic to the quantum case. Work done in collaboration with Robert Spekkens, University of Cambridge.
Tuned Transition from Quantum to Classical for Macroscopic Quantum States
Fedorov, A.; Macha, P.; Feofanov, A.K.; Harmans, C.J.P.M.; Mooij, J.E.
2011-01-01
The boundary between the classical and quantum worlds has been intensely studied. It remains fascinating to explore how far the quantum concept can reach with use of specially fabricated elements. Here we employ a tunable flux qubit with basis states having persistent currents of 1???A carried by a
PT-symmetric quantum state discrimination.
Bender, Carl M; Brody, Dorje C; Caldeira, João; Günther, Uwe; Meister, Bernhard K; Samsonov, Boris F
2013-04-28
The objective of this paper is to explain and elucidate the formalism of PT quantum mechanics by applying it to a well-known problem in conventional Hermitian quantum mechanics, namely the problem of state discrimination. Suppose that a system is known to be in one of two quantum states, |ψ(1)> or |ψ(2)>. If these states are not orthogonal, then the requirement of unitarity forbids the possibility of discriminating between these two states with one measurement; that is, determining with one measurement what state the system is in. In conventional quantum mechanics, there is a strategy in which successful state discrimination can be achieved with a single measurement but only with a success probability p that is less than unity. In this paper, the state-discrimination problem is examined in the context of PT quantum mechanics and the approach is based on the fact that a non-Hermitian PT-symmetric Hamiltonian determines the inner product that is appropriate for the Hilbert space of physical states. It is shown that it is always possible to choose this inner product so that the two states |ψ(1)> and |ψ(2)> are orthogonal. Using PT quantum mechanics, one cannot achieve a better state discrimination than in ordinary quantum mechanics, but one can instead perform a simulated quantum state discrimination, in which with a single measurement a perfect state discrimination is realized with probability p.
Quantum cryptography with 3-state systems.
Bechmann-Pasquinucci, H; Peres, A
2000-10-09
We consider quantum cryptographic schemes where the carriers of information are 3-state particles. One protocol uses four mutually unbiased bases and appears to provide better security than obtainable with 2-state carriers. Another possible method allows quantum states to belong to more than one basis. Security is not better, but many curious features arise.
Mapping quantum state dynamics in spontaneous emission
Naghiloo, M.; Foroozani, N.; Tan, D.; Jadbabaie, A.; Murch, K. W.
2016-01-01
The evolution of a quantum state undergoing radiative decay depends on how its emission is detected. If the emission is detected in the form of energy quanta, the evolution is characterized by a quantum jump to a lower energy state. In contrast, detection of the wave nature of the emitted radiation leads to different dynamics. Here, we investigate the diffusive dynamics of a superconducting artificial atom under continuous homodyne detection of its spontaneous emission. Using quantum state tomography, we characterize the correlation between the detected homodyne signal and the emitter's state, and map out the conditional back-action of homodyne measurement. By tracking the diffusive quantum trajectories of the state as it decays, we characterize selective stochastic excitation induced by the choice of measurement basis. Our results demonstrate dramatic differences from the quantum jump evolution associated with photodetection and highlight how continuous field detection can be harnessed to control quantum evolution. PMID:27167893
Coherent states in quantum physics
Gazeau, Jean-Pierre
2009-01-01
This self-contained introduction discusses the evolution of the notion of coherent states, from the early works of Schrödinger to the most recent advances, including signal analysis. An integrated and modern approach to the utility of coherent states in many different branches of physics, it strikes a balance between mathematical and physical descriptions.Split into two parts, the first introduces readers to the most familiar coherent states, their origin, their construction, and their application and relevance to various selected domains of physics. Part II, mostly based on recent original results, is devoted to the question of quantization of various sets through coherent states, and shows the link to procedures in signal analysis. Title: Coherent States in Quantum Physics Print ISBN: 9783527407095 Author(s): Gazeau, Jean-Pierre eISBN: 9783527628292 Publisher: Wiley-VCH Dewey: 530.12 Publication Date: 23 Sep, 2009 Pages: 360 Category: Science, Science: Physics LCCN: Language: English Edition: N/A LCSH:
Vasilyuk, G. T.; Askirka, V. F.; Lavysh, A. V.; Kurguzenkov, S. A.; Yasinskii, V. M.; Kobeleva, O. I.; Valova, T. M.; Ayt, A. O.; Barachevsky, V. A.; Yarovenko, V. N.; Krayushkin, M. M.; Maskevich, S. A.
2017-11-01
The structure and photochromic transformations of nanostructured organometallic composites consisting of Ag nanoparticles with shells of photochromic diarylethenes (DAEs) deposited from various solutions onto the nanoparticles were studied using infrared absorption and surface enhanced Raman scattering (SERS) vibrational spectroscopy and quantum chemistry. The studied nanostructures exhibited photochromic properties manifested as reversible photoinduced changes of the relative intensities of SERS bands related to vibrations of bonds participating in the reversible photoisomerization. Spectral manifestations of chemical interaction between metal nanoparticles and DAE molecules were detected.
Quantum pump in quantum spin Hall edge states
Cheng, Fang
2016-09-01
We present a theory for quantum pump in a quantum spin Hall bar with two quantum point contacts (QPCs). The pump currents can be generated by applying harmonically modulating gate voltages at QPCs. The phase difference between the gate voltages introduces an effective gauge field, which breaks the time-reversal symmetry and generates pump currents. The pump currents display very different pump frequency dependence for weak and strong e-e interaction. These unique properties are induced by the helical feature of the edge states, and therefore can be used to detect and control edge state transport.
Vibrational Energy Relaxation: A Benchmark for Mixed Quantum-Classical Methods.
Jain, Amber; Subotnik, Joseph E
2018-01-11
We investigate the ability of mixed quantum-classical methods to capture the dynamics of vibrational energy relaxation. Several methods, including surface hopping, and Ehrenfest and symmetrical quasiclassical (SQC) dynamics, are benchmarked for the exactly solvable model problem of a harmonic oscillator bilinearly coupled to a bath of harmonic oscillators. Results show that, very often, one can recover accurate vibrational relaxation rates and detailed balance using simple mixed quantum-classical approaches. A few anomalous results do appear, however, especially regarding Ehrenfest and SQC dynamics.
Vibrational effects in charge transport through a molecular double quantum dot
Sowa, Jakub K.; Mol, Jan A.; Briggs, G. Andrew D.; Gauger, Erik M.
2017-02-01
Recent progress in the field of molecular electronics has revealed the fundamental importance of the coupling between the electronic degrees of freedom and specific vibrational modes. Considering the examples of a molecular dimer and a carbon nanotube double quantum dot, we here theoretically investigate transport through a two-site system that is strongly coupled to a single vibrational mode. Using a quantum master equation approach, we demonstrate that, depending on the relative positions of the two dots, electron-phonon interactions can lead to negative differential conductance and suppression of the current through the system. We also discuss the experimental relevance of the presented results and possible implementations of the studied system.
Vibrational kinetics of electronically excited states in H2 discharges
Colonna, Gianpiero; Pietanza, Lucia D.; D'Ammando, Giuliano; Celiberto, Roberto; Capitelli, Mario; Laricchiuta, Annarita
2017-11-01
The evolution of atmospheric pressure hydrogen plasma under the action of repetitively ns electrical pulse has been investigated using a 0D state-to-state kinetic model that self-consistently couples the master equation of heavy particles and the Boltzmann equation for free electrons. The kinetic model includes, together with atomic hydrogen states and the vibrational kinetics of H2 ground state, vibrational levels of singlet states, accounting for the collisional quenching, having a relevant role because of the high pressure. The mechanisms of excitations, radiative decay and collisional quenching involving the excited H2 states and the corresponding cross sections, integrated over the non-equilibrium electron energy distribution function (EEDF) to obtain kinetic rates, are discussed in the light of the kinetic simulation results, i.e. the time evolution during the pulse of the plasma composition, of the EEDF and of the vibrational distributions of ground and singlet excited states.
Introduction to quantum-state estimation
Teo, Yong Siah
2016-01-01
Quantum-state estimation is an important field in quantum information theory that deals with the characterization of states of affairs for quantum sources. This book begins with background formalism in estimation theory to establish the necessary prerequisites. This basic understanding allows us to explore popular likelihood- and entropy-related estimation schemes that are suitable for an introductory survey on the subject. Discussions on practical aspects of quantum-state estimation ensue, with emphasis on the evaluation of tomographic performances for estimation schemes, experimental realizations of quantum measurements and detection of single-mode multi-photon sources. Finally, the concepts of phase-space distribution functions, which compatibly describe these multi-photon sources, are introduced to bridge the gap between discrete and continuous quantum degrees of freedom. This book is intended to serve as an instructive and self-contained medium for advanced undergraduate and postgraduate students to gra...
pH titration monitored by quantum cascade laser-based vibrational circular dichroism.
Rüther, Anja; Pfeifer, Marcel; Lórenz-Fonfría, Víctor A; Lüdeke, Steffen
2014-04-10
Vibrational circular dichroism (VCD) spectra of aqueous solutions of proline were recorded in the course of titrations from basic to acidic pH using a spectrometer equipped with a quantum cascade laser (QCL) as an infrared light source in the spectral range from 1320 to 1220 cm(-1). The pH-dependent spectra were analyzed by singular value decomposition and global fitting of a two-pK Henderson-Hasselbalch model. The analysis delivered relative fractions of the three different protonation species. Their agreement with the relative fractions obtained from performing the same analysis on pH-dependent Fourier transform infrared (FT-IR) and QCL-IR spectra validates the quantitative results from QCL-VCD. Global fitting of the pH-dependent VCD spectra of L-proline allowed for extraction of pure spectra corresponding to anionic, zwitterionic, and cationic L-proline. From a static experiment, only pure spectra of the zwitterion would be accessible in a straightforward way. A comparison to VCD spectra calculated for all three species led to assignment of vibrational modes that are characteristic for the respective protonation states. The study demonstrates the applicability of QCL-VCD both for quantitative evaluation and for qualitative interpretation of dynamic processes in aqueous solutions.
Quantum Conditional Mutual Information, Reconstructed States, and State Redistribution.
Brandão, Fernando G S L; Harrow, Aram W; Oppenheim, Jonathan; Strelchuk, Sergii
2015-07-31
We give two strengthenings of an inequality for the quantum conditional mutual information of a tripartite quantum state recently proved by Fawzi and Renner, connecting it with the ability to reconstruct the state from its bipartite reductions. Namely, we show that the conditional mutual information is an upper bound on the regularized relative entropy distance between the quantum state and its reconstructed version. It is also an upper bound for the measured relative entropy distance of the state to its reconstructed version. The main ingredient of the proof is the fact that the conditional mutual information is the optimal quantum communication rate in the task of state redistribution.
Entanglement and Coherence in Quantum State Merging.
Streltsov, A; Chitambar, E; Rana, S; Bera, M N; Winter, A; Lewenstein, M
2016-06-17
Understanding the resource consumption in distributed scenarios is one of the main goals of quantum information theory. A prominent example for such a scenario is the task of quantum state merging, where two parties aim to merge their tripartite quantum state parts. In standard quantum state merging, entanglement is considered to be an expensive resource, while local quantum operations can be performed at no additional cost. However, recent developments show that some local operations could be more expensive than others: it is reasonable to distinguish between local incoherent operations and local operations which can create coherence. This idea leads us to the task of incoherent quantum state merging, where one of the parties has free access to local incoherent operations only. In this case the resources of the process are quantified by pairs of entanglement and coherence. Here, we develop tools for studying this process and apply them to several relevant scenarios. While quantum state merging can lead to a gain of entanglement, our results imply that no merging procedure can gain entanglement and coherence at the same time. We also provide a general lower bound on the entanglement-coherence sum and show that the bound is tight for all pure states. Our results also lead to an incoherent version of Schumacher compression: in this case the compression rate is equal to the von Neumann entropy of the diagonal elements of the corresponding quantum state.
Quantum state transfer and network engineering
Nikolopoulos, Georgios M
2013-01-01
Faithful communication is a necessary precondition for large-scale quantum information processing and networking, irrespective of the physical platform. Thus, the problems of quantum-state transfer and quantum-network engineering have attracted enormous interest over the last years, and constitute one of the most active areas of research in quantum information processing. The present volume introduces the reader to fundamental concepts and various aspects of this exciting research area, including links to other related areas and problems. The implementation of state-transfer schemes and the en
Quantum cobwebs: Universal entangling of quantum states
Indian Academy of Sciences (India)
ZSA) multipartite, pure entangled states for qubits and study their salient features. ... Institute of Physics, Bhubaneswar 751 005, India; Center for Philosophy and Foundation of Science, New Delhi, India; School of Informatics, University of Wales, ...
Quantum information processing with mesoscopic photonic states
DEFF Research Database (Denmark)
Madsen, Lars Skovgaard
2012-01-01
The thesis is built up around a versatile optical experimental setup based on a laser, two optical parametric ampliers, a few sets of modulators and two sets of homodyne detectors, which together with passive linear optics generate, process and characterize various types of Gaussian quantum states....... Using this setup we have experimentally and theoretically investigated Gaussian quantum discord, continuous variable quantum key distribution and quantum polarization. The Gaussian discord broadens the definition of non-classical correlations from entanglement, to all types of correlations which cannot...... in the mixture of coherent states. Further we investigate the robustness of the discord of a broader range of states and suggest a toolbox of states which can be used to test if a protocol is discord based, before performing a rigid proof. Gaussian quantum key distribution can be implemented with current...
Quantum information. Unconditional quantum teleportation between distant solid-state quantum bits.
Pfaff, W; Hensen, B J; Bernien, H; van Dam, S B; Blok, M S; Taminiau, T H; Tiggelman, M J; Schouten, R N; Markham, M; Twitchen, D J; Hanson, R
2014-08-01
Realizing robust quantum information transfer between long-lived qubit registers is a key challenge for quantum information science and technology. Here we demonstrate unconditional teleportation of arbitrary quantum states between diamond spin qubits separated by 3 meters. We prepare the teleporter through photon-mediated heralded entanglement between two distant electron spins and subsequently encode the source qubit in a single nuclear spin. By realizing a fully deterministic Bell-state measurement combined with real-time feed-forward, quantum teleportation is achieved upon each attempt with an average state fidelity exceeding the classical limit. These results establish diamond spin qubits as a prime candidate for the realization of quantum networks for quantum communication and network-based quantum computing. Copyright © 2014, American Association for the Advancement of Science.
Classical topology and quantum states
Indian Academy of Sciences (India)
Classical topology is in this manner incorporated in conventional quantum physics by formulating it using ... touches both on issues of relevance to quantum gravity such as the meaning of 'quantized topology' and the ..... thus is equivalent to a classical probability measure for an instantaneous measurement. (which any way ...
Quantum key distribution using three basis states
Indian Academy of Sciences (India)
This note presents a method of public key distribution using quantum communication of photons that simultaneously provides a high probability that the bits have not been tampered. It is a variant of the quantum method of Bennett and Brassard (BB84) where the transmission states have been decreased from 4 to 3 and ...
Sending Quantum Information with Gaussian States
Holevo, Alexander S.
Quantum information characteristics, such as quantum mutual information, loss, noise and coherent information are explicitly calculated for Bosonic attenuation/amplification channel with input Gaussian state. The coherent information is shown to be negative for the values of the attenuation coefficient k < 1sqrt 2.
Sending Quantum Information with Gaussian States
Holevo, Alexander S.
1998-01-01
Quantum information characteristics, such as quantum mutual information, loss, noise and coherent information are explicitly calculated for Bosonic attenuation/amplification channel with input Gaussian state. The coherent information is shown to be negative for the values of the attenuation coefficient $k
Invariant measures on multimode quantum Gaussian states
Energy Technology Data Exchange (ETDEWEB)
Lupo, C. [School of Science and Technology, Universita di Camerino, I-62032 Camerino (Italy); Mancini, S. [School of Science and Technology, Universita di Camerino, I-62032 Camerino (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy); De Pasquale, A. [NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, I-56126 Pisa (Italy); Facchi, P. [Dipartimento di Matematica and MECENAS, Universita di Bari, I-70125 Bari (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Florio, G. [Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Piazza del Viminale 1, I-00184 Roma (Italy); Dipartimento di Fisica and MECENAS, Universita di Bari, I-70126 Bari (Italy); Pascazio, S. [Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Dipartimento di Fisica and MECENAS, Universita di Bari, I-70126 Bari (Italy)
2012-12-15
We derive the invariant measure on the manifold of multimode quantum Gaussian states, induced by the Haar measure on the group of Gaussian unitary transformations. To this end, by introducing a bipartition of the system in two disjoint subsystems, we use a parameterization highlighting the role of nonlocal degrees of freedom-the symplectic eigenvalues-which characterize quantum entanglement across the given bipartition. A finite measure is then obtained by imposing a physically motivated energy constraint. By averaging over the local degrees of freedom we finally derive the invariant distribution of the symplectic eigenvalues in some cases of particular interest for applications in quantum optics and quantum information.
Structural, vibrational, NMR, quantum chemical, DNA binding and ...
Indian Academy of Sciences (India)
Smith B C 1996 In Infrared Spectral Interpretation. (Boca Raton, FL: CRC Press). 31. Green J H S, Harrison D J and Kynaston W 1971. Spectrochim. Acta A 27 2199. 32. Varsanyi G 1974 In Assignments for Vibrational Spectra of Seven Hundred Benzene Derivatives. Vols. 1 and 2. (Budapest: Adam Hilger). 33. Lutz E T G ...
Quantum control of vibrational excitations in a heteronuclear ...
Indian Academy of Sciences (India)
Optimal control theory is applied to obtain infrared laser pulses for selective vibrational excitation in a heteronuclear diatomic molecule. The problem of finding the optimized field is phrased as a maximization of a cost functional which depends on the laser field. A time dependent Gaussian factor is introduced in the field ...
Quantum fidelity and quantum phase transitions in matrix product states
Cozzini, Marco; Ionicioiu, Radu; Zanardi, Paolo
2007-09-01
Matrix product states, a key ingredient of numerical algorithms widely employed in the simulation of quantum spin chains, provide an intriguing tool for quantum phase transition engineering. At critical values of the control parameters on which their constituent matrices depend, singularities in the expectation values of certain observables can appear, in spite of the analyticity of the ground state energy. For this class of generalized quantum phase transitions, we test the validity of the recently introduced fidelity approach, where the overlap modulus of ground states corresponding to slightly different parameters is considered. We discuss several examples, successfully identifying all the present transitions. We also study the finite size scaling of fidelity derivatives, pointing out its relevance in extracting critical exponents.
Energy Technology Data Exchange (ETDEWEB)
Uranga-Piña, L. [Facultad de Física, Universidad de la Habana, San Lázaro y L, Vedado, 10400 Havana (Cuba); Institute for Chemistry and Biochemistry, Freie Universität Berlin, Takustr. 3, D-14195 Berlin (Germany); Tremblay, J. C., E-mail: jean.c.tremblay@gmail.com [Institute for Chemistry and Biochemistry, Freie Universität Berlin, Takustr. 3, D-14195 Berlin (Germany)
2014-08-21
We investigate the effect of inter-mode coupling on the vibrational relaxation dynamics of molecules in weak dissipative environments. The simulations are performed within the reduced density matrix formalism in the Markovian regime, assuming a Lindblad form for the system-bath interaction. The prototypical two-dimensional model system representing two CO molecules approaching a Cu(100) surface is adapted from an ab initio potential, while the diatom-diatom vibrational coupling strength is systematically varied. In the weak system-bath coupling limit and at low temperatures, only first order non-adiabatic uni-modal coupling terms contribute to surface-mediated vibrational relaxation. Since dissipative dynamics is non-unitary, the choice of representation will affect the evolution of the reduced density matrix. Two alternative representations for computing the relaxation rates and the associated operators are thus compared: the fully coupled spectral basis, and a factorizable ansatz. The former is well-established and serves as a benchmark for the solution of Liouville-von Neumann equation. In the latter, a contracted grid basis of potential-optimized discrete variable representation is tailored to incorporate most of the inter-mode coupling, while the Lindblad operators are represented as tensor products of one-dimensional operators, for consistency. This procedure results in a marked reduction of the grid size and in a much more advantageous scaling of the computational cost with respect to the increase of the dimensionality of the system. The factorizable method is found to provide an accurate description of the dissipative quantum dynamics of the model system, specifically of the time evolution of the state populations and of the probability density distribution of the molecular wave packet. The influence of intra-molecular vibrational energy redistribution appears to be properly taken into account by the new model on the whole range of coupling strengths. It
Effect of Moisture Sorption State on Vibrational Properties of Wood
Jianxiong Lu; Jiali Jiang; Yiqiang Wu; Xianjun Li; Zhiyong Cai
2012-01-01
The purpose of this study was to investigate the vibrational properties and corresponding anisotropicity in wood during different states of moisture sorption. Samples of maple (Acer spp.) and red oak (Quercus rubra Michx.f.) were moisture conditioned by the adsorption process from an ovendried state and by the desorption process...
Vibrationally excited state stectroscopy of radicals in a supersonic plasma
G. Bazalgette Courreges-Lacoste, J. Bulthuis, S. Stolte, T. Motylewski; Linnartz, H.V.J.
2001-01-01
A plasma source based on a multilayer discharge geometry in combination with a time-of-flight REMPI experiment is used to study rotationally cold spectra of highly excited vibrational states of mass selected radicals. The rovibrational state distributions upon discharge excitation are characterised
Solid-State Quantum Refrigeration
2013-03-01
are generated. It has been shown that in strained quantum wells grown on (111B) substrates, the direction of the piezoelectric field is toward...compressively strained quantum well . So that the heavy hole band are pushed upwards in the band diagram and consequently the interband transition with...fifth layer 6 InP 2.5 undoped Quantum well sixth layer In this structure (VE1889) we put the InAlAs layer inside the InGaAs layer to see if
Rukhlenko, Ivan D; Fedorov, Anatoly V; Baymuratov, Anvar S; Premaratne, Malin
2011-08-01
We develop a low-temperature theory of quasi-elastic secondary emission from a semiconductor quantum dot, the electronic subsystem of which is resonant with the confined longitudinal-optical (LO) phonon modes. Our theory employs a generalized model for renormalization of the quantum dot's energy spectrum, which is induced by the polar electron-phonon interaction. The model takes into account the degeneration of electronic states and allows for several LO-phonon modes to be involved in the vibrational resonance. We give solutions to three fundamental problems of energy-spectrum renormalization--arising if one, two, or three LO-phonon modes resonantly couple a pair of electronic states--and discuss the most general problem of this kind that admits an analytical solution. With these results, we solve the generalized master equation for the reduced density matrix, in order to derive an expression for the differential cross section of secondary emission from a single quantum dot. The obtained expression is then analyzed to establish the basics of optical spectroscopy for measuring fundamental parameters of the quantum dot's polaron-like states.
Quantum state transfer and network engineering
Energy Technology Data Exchange (ETDEWEB)
Nikolopoulos, Georgios M. [Institute of Electronic Structure and Laser Foundation for Research and Technology, Hellas (Greece); Jex, Igor (ed.) [Czech Technical Univ., Prague (Czech Republic). Faculty of Nuclear Sciences and Physical Engineering
2014-03-01
Presents the basics of large-scale quantum information processing and networking. Covers most aspects of the problems of state transfer and quantum network engineering. Reflects the interdisciplinary nature of the field. Presents various theoretical approaches as well as possible implementations and related experiments. Faithful communication is a necessary precondition for large-scale quantum information processing and networking, irrespective of the physical platform. Thus, the problems of quantum-state transfer and quantum-network engineering have attracted enormous interest over the last years, and constitute one of the most active areas of research in quantum information processing. The present volume introduces the reader to fundamental concepts and various aspects of this exciting research area, including links to other related areas and problems. The implementation of state-transfer schemes and the engineering of quantum networks are discussed in the framework of various quantum optical and condensed matter systems, emphasizing the interdisciplinary character of the research area. Each chapter is a review of theoretical or experimental achievements on a particular topic, written by leading scientists in the field. The volume aims at both newcomers as well as experienced researchers.
Quantum Interference in the Vibrational Relaxation of the O-H Stretch Overtone of Liquid H2O.
van der Post, Sietse T; Woutersen, Sander; Bakker, Huib J
2016-05-26
Using femtosecond two-color infrared pump-probe spectroscopy, we study the vibrational relaxation of the O-H stretch vibrations of liquid H2O after excitation of the overtone transition. The overtone transition has its maximum at 6900 cm(-1) (1.45 μm), which is a relatively high frequency in view of the central frequency of 3400 cm(-1) of the fundamental transition. The excitation of the overtone leads to a transient induced absorption of two-exciton states of the O-H stretch vibrations. When the overtone excitation frequency is tuned from 6600 to 7200 cm(-1), the vibrational relaxation time constant of the two-exciton states increases from 400 ± 50 fs to 540 ± 40 fs. These values define a limited range of relatively long relaxation time constants compared to the range of relaxation time constants of 250-550 fs that we recently observed for the one-exciton O-H stretch vibrational state of liquid H2O ( S. T. van der Post et al., Nature Comm. 2015 , 6 , 8384 ). We explain the high central frequency and the limited range of relatively long relaxation time constants of the overtone transition from the destructive quantum interference of the mechanical and electrical anharmonic contributions to the overtone transition probability. As a result of this destructive interference, the overtone transition of liquid H2O is dominated by molecules of which the O-H groups donate relatively weak hydrogen bonds to other H2O molecules.
Energy Technology Data Exchange (ETDEWEB)
Vazhappilly, Tijo Joseph
2008-04-15
This thesis investigates the femtosecond laser induced associative photodesorption of hydrogen, H{sub 2}, and deuterium, D{sub 2}, from a ruthenium metal surface. One of the goals of the present thesis is to suggest, on the basis of theoretical simulations, strategies to control/enhance the photodesorption yield from Ru(0001). For this purpose, we suggest a hybrid scheme to control the reaction, where the adsorbate vibrations are initially excited by an infrared (IR) pulse, prior to the vis pulse. Both adiabatic and non-adiabatic representations for photoinduced desorption problems are employed here. The adiabatic representation is realized within the classical picture using Molecular Dynamics (MD) with electronic frictions. In a quantum mechanical description, non-adiabatic representations are employed within open-system density matrix theory. The time evolution of the desorption process is studied using a two-mode reduced dimensionality model with one vibrational coordinate and one translational coordinate of the adsorbate. The ground and excited electronic state potentials, and dipole function for the IR excitation are taken from first principles. The IR driven vibrational excitation of adsorbate modes with moderate efficiency is achieved by (modified) {pi}-pulses or/and optimal control theory. The fluence dependence of the desorption reaction is computed by including the electronic temperature of the metal calculated from the two-temperature model. We then employed the IR+vis strategy in both models. Here, we found that vibrational excitation indeed promotes the desorption of hydrogen and deuterium. (orig.)
Quantum filtering of optical coherent states
DEFF Research Database (Denmark)
Wittmann, C.; Elser, D.; Andersen, Ulrik Lund
2008-01-01
We propose and experimentally demonstrate nondestructive and noiseless removal (filtering) of vacuum states from an arbitrary set of coherent states of continuous variable systems. Errors, i.e., vacuum states in the quantum information are diagnosed through a weak measurement, and on that basis...
Classical and Quantum-Mechanical State Reconstruction
Khanna, F. C.; Mello, P. A.; Revzen, M.
2012-01-01
The aim of this paper is to present the subject of state reconstruction in classical and in quantum physics, a subject that deals with the experimentally acquired information that allows the determination of the physical state of a system. Our first purpose is to explain a method for retrieving a classical state in phase space, similar to that…
The Lowest Vibrational States of Urea from the Rotational Spectrum
Kisiel, Zbigniew; Thomas, Jessica; Medvedev, Ivan
2014-06-01
The urea molecule, (NH_2)_2CO, has a complex potential energy surface resulting from a combination of the NH_2 torsion and NH_2 inversion motions. This leads to a distribution of lowest vibrational states that is expected to be significantly different from the more familiar picture from simple inversion or normal mode models. The broadband 207-500 GHz spectrum of urea recorded in Dayton has signal to noise sufficient for assignment of rotational transitions in excited vibrational states up to at least 500 cm-1. In addition to the previously reported analysis of the ground and the lowest excited state we have been able to assign transitions in at least five other excited vibrational states. Strongly perturbed transitions in a close doublet of such states have been fitted to within experimental accuracy with a coupled fit and a splitting in the region of 1 cm-1. These assignments combined with vibrational energy estimates from relative intensity measurements allow for empirical discrimination between different models for the energy level manifestation of the large amplitude motions in urea.^b P.D.Godfrey, R.D.Brown, A.N.Hunter J. Mol. Struct., 413-414, 405-414 (1997). N.Inostroza, M.L.Senent, Chem. Phys. Lett., 524, 25 (2012).
Signature of nonadiabatic coupling in excited-state vibrational modes.
Soler, Miguel A; Nelson, Tammie; Roitberg, Adrian E; Tretiak, Sergei; Fernandez-Alberti, Sebastian
2014-11-13
Using analytical excited-state gradients, vibrational normal modes have been calculated at the minimum of the electronic excited-state potential energy surfaces for a set of extended conjugated molecules with different coupling between them. Molecular model systems composed of units of polyphenylene ethynylene (PPE), polyphenylenevinylene (PPV), and naphthacene/pentacene (NP) have been considered. In all cases except the NP model, the influence of the nonadiabatic coupling on the excited-state equilibrium normal modes is revealed as a unique highest frequency adiabatic vibrational mode that overlaps with the coupling vector. This feature is removed by using a locally diabatic representation in which the effect of NA interaction is removed. Comparison of the original adiabatic modes with a set of vibrational modes computed in the locally diabatic representation demonstrates that the effect of nonadiabaticity is confined to only a few modes. This suggests that the nonadiabatic character of a molecular system may be detected spectroscopically by identifying these unique state-specific high frequency vibrational modes.
Numerical analysis using state space method for vibration control of ...
African Journals Online (AJOL)
ATHARVA
Numerical analysis using state space method for vibration control of car seat by employing passive and semi active dampers. Udit S. Kotagi1, G.U. Raju1, V.B. Patil2, Krishnaraja G. Kodancha1*. 1Department of Mechanical Engineering, B.V. Bhoomaraddi College of Engineering & Technology, Hubli, Karnataka, INDIA.
Electronic and Vibrational Spectra of InP Quantum Dots Formed by Sequential Ion Implantation
Hall, C.; Mu, R.; Tung, Y. S.; Ueda, A.; Henderson, D. O.; White, C. W.
1997-01-01
We have performed sequential ion implantation of indium and phosphorus into silica combined with controlled thermal annealing to fabricate InP quantum dots in a dielectric host. Electronic and vibrational spectra were measured for the as-implanted and annealed samples. The annealed samples show a peak in the infrared spectra near 320/cm which is attributed to a surface phonon mode and is in good agreement with the value calculated from Frolich's theory of surface phonon polaritons. The electronic spectra show the development of a band near 390 nm that is attributed to quantum confined InP.
Stretching vibrational overtone and combination states in silicon tetrafluoride
Halonen, Lauri
1986-11-01
A simple three-parameter model is shown to account for the observed SiF stretching vibrational states of silicon tetrafluoride. A symmetrized anharmonic bond oscillator basis set is used to calculate stretching overtone and combination eigen values, all of which are given up to v1 + v3 = 5. The results show that the highest levels of the nν3 manifold move gradually out of resonances with n quanta of ν3 as n increases, which indicates that anharmonic resonances between the ν3 ladder and some other vibrational ladders and (or) multiphoton resonances are needed to explain the observed multiphoton processes.
Sunlight-Initiated Photochemistry: Excited Vibrational States of Atmospheric Chromophores
Directory of Open Access Journals (Sweden)
Veronica Vaida
2008-01-01
Full Text Available Atmospheric chemical reactions are often initiated by ultraviolet (UV solar radiation since absorption in that wavelength range coincides to typical chemical bond energies. In this review, we present an alternative process by which chemical reactions occur with the excitation of vibrational levels in the ground electronic state by red solar photons. We focus on the O–H vibrational manifold which can be an atmospheric chromophore for driving vibrationally mediated overtone-induced chemical reactions. Experimental and theoretical O–H intensities of several carboxylic acids, alcohols, and peroxides are presented. The importance of combination bands in spectra at chemically relevant energies is examined in the context of atmospheric photochemistry. Candidate systems for overtone-initiated chemistry are provided, and their lowest energy barrier for reaction and the minimum quanta of O–H stretch required for reaction are calculated. We conclude with a discussion of the major pathways available for overtone-induced reactions in the atmosphere.
Graph state-based quantum authentication scheme
Liao, Longxia; Peng, Xiaoqi; Shi, Jinjing; Guo, Ying
2017-04-01
Inspired by the special properties of the graph state, a quantum authentication scheme is proposed in this paper, which is implemented with the utilization of the graph state. Two entities, a reliable party, Trent, as a verifier and Alice as prover are included. Trent is responsible for registering Alice in the beginning and confirming Alice in the end. The proposed scheme is simple in structure and convenient to realize in the realistic physical system due to the use of the graph state in a one-way quantum channel. In addition, the security of the scheme is extensively analyzed and accordingly can resist the general individual attack strategies.
Classical codes in quantum state space
Howard, Mark
2015-12-01
We present a construction of Hermitian operators and quantum states labelled by strings from a finite field. The distance between these operators or states is then simply related (typically, proportional) to the Hamming distance between their corresponding strings. This allows a straightforward application of classical coding theory to find arrangements of operators or states with a given distance distribution. Using the simplex or extended Reed-Solomon code in our construction recovers the discrete Wigner function, which has important applications in quantum information theory.
Song, Yi; Ni, Jiang-Li; Wang, Zhang-Yin; Lu, Yan; Han, Lian-Fang
2017-10-01
We present a new scheme for deterministically realizing the mutual interchange of quantum information between two distant parties via selected quantum states as the shared entangled resource. We first show the symmetric bidirectional remote state preparation (BRSP), where two single-qubit quantum states will be simultaneously exchanged in a deterministic manner provided that each of the users performs single-qubit von Neumann measurements with proper measurement bases as well as appropriate unitary operations, depending essentially on the outcomes of the prior measurements. Then we consider to extend the symmetric protocol to an asymmetric case, in which BRSP of a general single-qubit state and an arbitrary two-qubit state is investigated successfully. The necessary quantum operations and the employed quantum resources are feasible according to the present technology, resulting in that this protocol may be realizable in the realm of current physical experiment.
Phonon induced pure dephasing process of excitonic state in colloidal semiconductor quantum dots
Huang, Tongyun; Han, Peng; Wang, Xinke; Feng, Shengfei; Sun, Wenfeng; Ye, Jiasheng; Zhang, Yan
2016-04-01
We present a theoretical study on the pure dephasing process of colloidal semiconductor quantum dots induced by lattice vibrations using continuum model calculations. By solving the time dependent Liouville-von Neumann equation, we present the ultrafast Rabi oscillations between excitonic state and virtual state via exciton-phonon interaction and obtain the pure dephasing time from the fast decayed envelope of the Rabi oscillations. The interaction between exciton and longitudinal optical phonon vibration is found to dominate the pure dephasing process and the dephasing time increases nonlinearly with the reduction of exciton-phonon coupling strength. We further find that the pure dephasing time of large quantum dots is more sensitive to temperature than small quantum dots.
Quantum communication with coherent states of light
Khan, Imran; Elser, Dominique; Dirmeier, Thomas; Marquardt, Christoph; Leuchs, Gerd
2017-06-01
Quantum communication offers long-term security especially, but not only, relevant to government and industrial users. It is worth noting that, for the first time in the history of cryptographic encoding, we are currently in the situation that secure communication can be based on the fundamental laws of physics (information theoretical security) rather than on algorithmic security relying on the complexity of algorithms, which is periodically endangered as standard computer technology advances. On a fundamental level, the security of quantum key distribution (QKD) relies on the non-orthogonality of the quantum states used. So even coherent states are well suited for this task, the quantum states that largely describe the light generated by laser systems. Depending on whether one uses detectors resolving single or multiple photon states or detectors measuring the field quadratures, one speaks of, respectively, a discrete- or a continuous-variable description. Continuous-variable QKD with coherent states uses a technology that is very similar to the one employed in classical coherent communication systems, the backbone of today's Internet connections. Here, we review recent developments in this field in two connected regimes: (i) improving QKD equipment by implementing front-end telecom devices and (ii) research into satellite QKD for bridging long distances by building upon existing optical satellite links. This article is part of the themed issue 'Quantum technology for the 21st century'.
Quantum communication with coherent states of light.
Khan, Imran; Elser, Dominique; Dirmeier, Thomas; Marquardt, Christoph; Leuchs, Gerd
2017-08-06
Quantum communication offers long-term security especially, but not only, relevant to government and industrial users. It is worth noting that, for the first time in the history of cryptographic encoding, we are currently in the situation that secure communication can be based on the fundamental laws of physics (information theoretical security) rather than on algorithmic security relying on the complexity of algorithms, which is periodically endangered as standard computer technology advances. On a fundamental level, the security of quantum key distribution (QKD) relies on the non-orthogonality of the quantum states used. So even coherent states are well suited for this task, the quantum states that largely describe the light generated by laser systems. Depending on whether one uses detectors resolving single or multiple photon states or detectors measuring the field quadratures, one speaks of, respectively, a discrete- or a continuous-variable description. Continuous-variable QKD with coherent states uses a technology that is very similar to the one employed in classical coherent communication systems, the backbone of today's Internet connections. Here, we review recent developments in this field in two connected regimes: (i) improving QKD equipment by implementing front-end telecom devices and (ii) research into satellite QKD for bridging long distances by building upon existing optical satellite links.This article is part of the themed issue 'Quantum technology for the 21st century'. © 2017 The Author(s).
Quantum state engineering with single atom laser
Stefanov, V. P.
2017-11-01
On the basis of quantum stochastic trajectories approach it is shown that a single atom laser with coherent pumping can generate not only coherent states, but squeezed and Fock states, when different schemes of detection are followed by coherent feedback pulses or feedforward actions.
Quantum state sharing against the controller's cheating
Shi, Run-hua; Zhong, Hong; Huang, Liu-sheng
2013-08-01
Most existing QSTS schemes are equivalent to the controlled teleportation, in which a designated agent (i.e., the recoverer) can recover the teleported state with the help of the controllers. However, the controller may attempt to cheat the recoverer during the phase of recovering the secret state. How can we detect this cheating? In this paper, we considered the problem of detecting the controller's cheating in Quantum State Sharing, and further proposed an effective Quantum State Sharing scheme against the controller's cheating. We cleverly use Quantum Secret Sharing, Multiple Quantum States Sharing and decoy-particle techniques. In our scheme, via a previously shared entanglement state Alice can teleport multiple arbitrary multi-qubit states to Bob with the help of Charlie. Furthermore, by the classical information shared previously, Alice and Bob can check whether there is any cheating of Charlie. In addition, our scheme only needs to perform Bell-state and single-particle measurements, and to apply C-NOT gate and other single-particle unitary operations. With the present techniques, it is feasible to implement these necessary measurements and operations.
Local Unitary Invariants of Quantum States
Cui, Meiyu; Chang, Jingmei; Zhao, Ming-Jing; Huang, Xiaofen; Zhang, Tinggui
2017-11-01
We study the equivalence of mixed states under local unitary transformations. First we express quantum states in Bloch representation. Then based on the coefficient matrices, some invariants are constructed. This method and results can be extended to multipartite high dimensional system.
Engineering quantum hyperentangled states in atomic systems
Nawaz, Mehwish; -Islam, Rameez-ul; Abbas, Tasawar; Ikram, Manzoor
2017-11-01
Hyperentangled states have boosted many quantum informatics tasks tremendously due to their high information content per quantum entity. Until now, however, the engineering and manipulation of such states were limited to photonic systems only. In present article, we propose generating atomic hyperentanglement involving atomic internal states as well as atomic external momenta states. Hypersuperposition, hyperentangled cluster, Bell and Greenberger–Horne–Zeilinger states are engineered deterministically through resonant and off-resonant Bragg diffraction of neutral two-level atoms. Based on the characteristic parameters of the atomic Bragg diffraction, such as comparatively large interaction times and spatially well-separated outputs, such decoherence resistant states are expected to exhibit good overall fidelities and offer the evident benefits of full controllability, along with extremely high detection efficiency, over the counterpart photonic states comprised entirely of flying qubits.
Extracting Entanglement Geometry from Quantum States
Hyatt, Katharine; Garrison, James R.; Bauer, Bela
2017-10-01
Tensor networks impose a notion of geometry on the entanglement of a quantum system. In some cases, this geometry is found to reproduce key properties of holographic dualities, and subsequently much work has focused on using tensor networks as tractable models for holographic dualities. Conventionally, the structure of the network—and hence the geometry—is largely fixed a priori by the choice of the tensor network ansatz. Here, we evade this restriction and describe an unbiased approach that allows us to extract the appropriate geometry from a given quantum state. We develop an algorithm that iteratively finds a unitary circuit that transforms a given quantum state into an unentangled product state. We then analyze the structure of the resulting unitary circuits. In the case of noninteracting, critical systems in one dimension, we recover signatures of scale invariance in the unitary network, and we show that appropriately defined geodesic paths between physical degrees of freedom exhibit known properties of a hyperbolic geometry.
Quantum Correlations in Mixed-State Metrology
Directory of Open Access Journals (Sweden)
Kavan Modi
2011-12-01
Full Text Available We analyze the effects of quantum correlations, such as entanglement and discord, on the efficiency of phase estimation by studying four quantum circuits that can be readily implemented using NMR techniques. These circuits define a standard strategy of repeated single-qubit measurements, a classical strategy where only classical correlations are allowed, and two quantum strategies where nonclassical correlations are allowed. In addition to counting space (number of qubits and time (number of gates requirements, we introduce mixedness as a key constraint of the experiment. We compare the efficiency of the four strategies as a function of the mixedness parameter. We find that the quantum strategy gives sqrt[N] enhancement over the standard strategy for the same amount of mixedness. This result applies even for highly mixed states that have nonclassical correlations but no entanglement.
Current noise in a vibrating quantum dot array
DEFF Research Database (Denmark)
Flindt, Christian; Novotny, Tomas; Jauho, Antti-Pekka
2004-01-01
different formulations are presented: (i) quantum regression theorem and (ii) the counting variable approach. It is demonstrated, both analytically and numerically, that the two formulations yield identical results, when the conditions of their respective applicability are fulfilled. We describe the results...... of extensive numerical calculations for current and current noise (Fano factor), based on a solution of a Markovian generalized master equation. The results for the current and noise are further analyzed in terms of Wigner functions, which help to distinguish different transport regimes (in particular......, shuttling versus cotunneling). In the case of weak interdot coupling, the electron transport proceeds via sequential tunneling between neighboring dots. A simple rate equation with the rates calculated analytically from the P(E) theory is developed and shown to agree with the full numerics....
Yamada, Yuji; Mikami, Naohiko; Ebata, Takayuki
2004-01-01
A picosecond time-resolved IR-UV pump-probe spectroscopic study was carried out for the intramolecular vibrational energy redistribution of the OH/OD stretching vibration of isolated phenol and its isotopomers in supersonic beams. The time evolution due to IVR showed a significant isotope effect; the OH stretch vibration showed a single exponential decay and its lifetime is greatly lengthened upon the deuterium substitution of the CH group. The OD stretch vibration exhibited prominent quantum...
Storing quantum states in bosonic dissipative networks
Energy Technology Data Exchange (ETDEWEB)
De Ponte, M A; Mizrahi, S S [Departamento de Fisica, Universidade Federal de Sao Carlos, Caixa Postal 676, Sao Carlos, 13565-905, Sao Paulo (Brazil); Moussa, M H Y [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, 13560-590 Sao Carlos, SP (Brazil)
2008-11-14
By considering a network of dissipative quantum harmonic oscillators, we deduce and analyse the optimum topologies which are able to store quantum superposition states, protecting them from decoherence, for the longest period of time. The storage is made dynamically, in that the states to be protected evolve through the network before being retrieved back in the oscillator where they were prepared. The decoherence time during the dynamic storage process is computed and we demonstrate that it is proportional to the number of oscillators in the network for a particular regime of parameters.
Exotic states in quantum nanostructures
2002-01-01
Mesoscopic physics has made great strides in the last few years It is an area of research that is attractive to many graduate students of theoretical condensed matter physics The techniques that are needed to understand it go beyond the conventional perturbative approaches that still form the bulk of the graduate lectures that are given to students Even when the non-perturbative techniques are presented, they often are presented within an abstract context It is important to have lectures given by experts in the field, which present both theory and experiment in an illuminating and inspiring way, so that the impact of new methodology on novel physics is clear It is an apt time to have such a volume since the field has reached a level of maturity The pedagogical nature of the articles and the variety of topics makes it an important resource for newcomers to the field The topics range from the newly emerging area of quantum computers and quantum information using Josephson junctions to the formal mathematical me...
Optimal convex approximations of quantum states
Sacchi, Massimiliano F.
2017-10-01
We consider the problem of optimally approximating an unavailable quantum state ρ by the convex mixing of states drawn from a set of available states {νi} . The problem is recast to look for the least distinguishable state from ρ among the convex set ∑ipiνi , and the corresponding optimal weights {pi} provide the optimal convex mixing. We present the complete solution for the optimal convex approximation of a qubit mixed state when the set of available states comprises the three bases of the Pauli matrices.
Statistical tests for quantum state reconstruction II: Experiment
Energy Technology Data Exchange (ETDEWEB)
Schindler, Philipp; Monz, Thomas [Innsbruck Univ. (Austria). Inst. fuer Experimentalphysik; Kleinmann, Matthias; Guehne, Otfried [Naturwissenschaftlich-Technische Fakultaet, Universitaet Siegen (Germany); Moroder, Tobias [Institut fuer Quantenoptik und Quanteninformation, Innsbruck (Austria); Blatt, Rainer [Innsbruck Univ. (Austria). Inst. fuer Experimentalphysik; Institut fuer Quantenoptik und Quanteninformation, Innsbruck (Austria)
2012-07-01
Quantum state tomography is nowadays routinely used in many experiments, for instance to characterize entangled quantum states or to determine input and output states of a quantum processor. Tomography reconstruction algorithms are designed to restrict the results onto physical states. These methods will always return a valid quantum state for any data and therefore it seems necessary to test the recorded data prior to reconstructing the quantum state. We directly apply statistical tests on our experimental data taken in an ion trap quantum computer. In particular, we analyze the sensitivity of these tests to various experimental imperfections like crosstalk and rotated bases.
Quantum Entanglement in Neural Network States
Deng, Dong-Ling; Li, Xiaopeng; Das Sarma, S.
2017-04-01
Machine learning, one of today's most rapidly growing interdisciplinary fields, promises an unprecedented perspective for solving intricate quantum many-body problems. Understanding the physical aspects of the representative artificial neural-network states has recently become highly desirable in the applications of machine-learning techniques to quantum many-body physics. In this paper, we explore the data structures that encode the physical features in the network states by studying the quantum entanglement properties, with a focus on the restricted-Boltzmann-machine (RBM) architecture. We prove that the entanglement entropy of all short-range RBM states satisfies an area law for arbitrary dimensions and bipartition geometry. For long-range RBM states, we show by using an exact construction that such states could exhibit volume-law entanglement, implying a notable capability of RBM in representing quantum states with massive entanglement. Strikingly, the neural-network representation for these states is remarkably efficient, in the sense that the number of nonzero parameters scales only linearly with the system size. We further examine the entanglement properties of generic RBM states by randomly sampling the weight parameters of the RBM. We find that their averaged entanglement entropy obeys volume-law scaling, and the meantime strongly deviates from the Page entropy of the completely random pure states. We show that their entanglement spectrum has no universal part associated with random matrix theory and bears a Poisson-type level statistics. Using reinforcement learning, we demonstrate that RBM is capable of finding the ground state (with power-law entanglement) of a model Hamiltonian with a long-range interaction. In addition, we show, through a concrete example of the one-dimensional symmetry-protected topological cluster states, that the RBM representation may also be used as a tool to analytically compute the entanglement spectrum. Our results uncover the
Quantum Entanglement in Neural Network States
Directory of Open Access Journals (Sweden)
Dong-Ling Deng
2017-05-01
Full Text Available Machine learning, one of today’s most rapidly growing interdisciplinary fields, promises an unprecedented perspective for solving intricate quantum many-body problems. Understanding the physical aspects of the representative artificial neural-network states has recently become highly desirable in the applications of machine-learning techniques to quantum many-body physics. In this paper, we explore the data structures that encode the physical features in the network states by studying the quantum entanglement properties, with a focus on the restricted-Boltzmann-machine (RBM architecture. We prove that the entanglement entropy of all short-range RBM states satisfies an area law for arbitrary dimensions and bipartition geometry. For long-range RBM states, we show by using an exact construction that such states could exhibit volume-law entanglement, implying a notable capability of RBM in representing quantum states with massive entanglement. Strikingly, the neural-network representation for these states is remarkably efficient, in the sense that the number of nonzero parameters scales only linearly with the system size. We further examine the entanglement properties of generic RBM states by randomly sampling the weight parameters of the RBM. We find that their averaged entanglement entropy obeys volume-law scaling, and the meantime strongly deviates from the Page entropy of the completely random pure states. We show that their entanglement spectrum has no universal part associated with random matrix theory and bears a Poisson-type level statistics. Using reinforcement learning, we demonstrate that RBM is capable of finding the ground state (with power-law entanglement of a model Hamiltonian with a long-range interaction. In addition, we show, through a concrete example of the one-dimensional symmetry-protected topological cluster states, that the RBM representation may also be used as a tool to analytically compute the entanglement spectrum. Our
Collective and single particle states in medium mass vibrational nuclei
Suliman, G
2001-01-01
The particle-core coupling model has been employed to describe the low lying nuclear excitations in the vibrational odd-A nuclei. In the frame of this model the following observables were calculated: excitation energies, spin and parity quantum numbers, electric quadrupole moments, magnetic dipole moments and reduced transition probabilities. Two computer codes were employed. The first one, PCOREC, diagonalized the Hamiltonian providing the eigenvectors and eigenvalues. The second one, PCORECTR, starts from the eigenvector computer by the first program and computes the observables which are compared we results of experiments. A good description of the experimental data has been obtained for the sup 1 sup 3 sup 3 Sb, sup 1 sup 2 sup 3 Sb and sup 1 sup 2 sup 5 Sb nuclei. (authors)
Controlled teleportation of a 3-dimensional bipartite quantum state
Energy Technology Data Exchange (ETDEWEB)
Cao Haijing; Chen Zhonghua [Physics Department, Shanghai University of Electric Power, Shanghai 201300 (China); Song Heshan [Physics Department, Dalian University of Technology, Dalian 116024 (China)], E-mail: 2007000084@shiep.edu.cn
2008-07-15
A controlled teleportation scheme of an unknown 3-dimensional (3D) two-particle quantum state is proposed, where a 3D Bell state and 3D GHZ state function as the quantum channel. This teleportation scheme can be directly generalized to teleport an unknown d-dimensional bipartite quantum state.
Criteria for reachability of quantum states
Energy Technology Data Exchange (ETDEWEB)
Schirmer, S.G.; Solomon, A.I. [Quantum Processes Group and Department of Applied Maths, Open University, Milton Keynes (United Kingdom)]. E-mails: S.G.Schirmer@open.ac.uk; A.I.Solomon@open.ac.uk; Leahy, J.V. [Department of Mathematics and Institute of Theoretical Science, University of Oregon, Eugene, OR (United States)]. E-mail: leahy@math.uoregon.edu
2002-10-11
We address the question of which quantum states can be inter-converted under the action of a time-dependent Hamiltonian. In particular, we consider the problem as applied to mixed states, and investigate the difference between pure- and mixed-state controllabilities introduced in previous work. We provide a complete characterization of the eigenvalue spectrum for which the state is controllable under the action of the symplectic group. We also address the problem of which states can be prepared if the dynamical Lie group is not sufficiently large to allow the system to be controllable. (author)
Linear Quantum Systems: Non-Classical States and Robust Stability
2016-06-29
quantum mechanics . Non-classical quantum states. Gaussian distributions play a fundamental role in classical (non-quantum) linear systems theory, and...quantum systems, we will consider perturbed quantum linear systems described by coupling and Hamiltonian operators with components that depend on a... Hamiltonian . The case of a nominal linear quantum system is considered with quadratic perturbations to the system Hamiltonian . A robust stability
Fermionic topological quantum states as tensor networks
Wille, C.; Buerschaper, O.; Eisert, J.
2017-06-01
Tensor network states, and in particular projected entangled pair states, play an important role in the description of strongly correlated quantum lattice systems. They do not only serve as variational states in numerical simulation methods, but also provide a framework for classifying phases of quantum matter and capture notions of topological order in a stringent and rigorous language. The rapid development in this field for spin models and bosonic systems has not yet been mirrored by an analogous development for fermionic models. In this work, we introduce a tensor network formalism capable of capturing notions of topological order for quantum systems with fermionic components. At the heart of the formalism are axioms of fermionic matrix-product operator injectivity, stable under concatenation. Building upon that, we formulate a Grassmann number tensor network ansatz for the ground state of fermionic twisted quantum double models. A specific focus is put on the paradigmatic example of the fermionic toric code. This work shows that the program of describing topologically ordered systems using tensor networks carries over to fermionic models.
Mixed quantum states with variable Planck constant
de Gosson, Maurice A.
2017-09-01
Recent cosmological measurements tend to confirm that the fine structure constant α is not immutable and has undergone a tiny variation since the Big Bang. Choosing adequate units, this could also reflect a variation of Planck's constant h. The aim of this Letter is to explore some consequences of such a possible change of h for the pure and mixed states of quantum mechanics. Surprisingly enough it is found that not only is the purity of a state extremely sensitive to such changes, but that quantum states can evolve into classical states, and vice versa. A complete classification of such transitions is however not possible for the moment being because of yet unsolved mathematical difficulties related to the study of positivity properties of trace class operators.
Efficient quantum optical state engineering and applications
McCusker, Kevin T.
Over a century after the modern prediction of the existence of individual particles of light by Albert Einstein, a reliable source of this simple quantum state of one photon does not exist. While common light sources such as a light bulb, LED, or laser can produce a pulse of light with an average of one photon, there is (currently) no way of knowing the number of photons in that pulse without first absorbing (and thereby destroying) them. Spontaneous parametric down-conversion, a process in which one high-energy photon splits into two lower-energy photons, allows us to prepare a single-photon state by detecting one of the photons, which then heralds the existence of its twin. This process has been the workhorse of quantum optics, allowing demonstrations of a myriad of quantum processes and protocols, such as entanglement, cryptography, superdense coding, teleportation, and simple quantum computing demonstrations. All of these processes would benefit from better engineering of the underlying down-conversion process, but despite significant effort (both theoretical and experimental), optimization of this process is ongoing. The focus of this work is to optimize certain aspects of a down-conversion source, and then use this tool in novel experiments not otherwise feasible. Specifically, the goal is to optimize the heralding efficiency of the down-conversion photons, i.e., the probability that if one photon is detected, the other photon is also detected. This source is then applied to two experiments (a single-photon source, and a quantum cryptography implementation), and the detailed theory of an additional application (a source of Fock states and path-entangled states, called N00N states) is discussed, along with some other possible applications.
Continuous variable quantum cryptography using coherent states.
Grosshans, Frédéric; Grangier, Philippe
2002-02-04
We propose several methods for quantum key distribution (QKD) based on the generation and transmission of random distributions of coherent or squeezed states, and we show that they are secure against individual eavesdropping attacks. These protocols require that the transmission of the optical line between Alice and Bob is larger than 50%, but they do not rely on "sub-shot-noise" features such as squeezing. Their security is a direct consequence of the no-cloning theorem, which limits the signal-to-noise ratio of possible quantum measurements on the transmission line. Our approach can also be used for evaluating various QKD protocols using light with Gaussian statistics.
Adaptive Quantum State Tomography Improves Accuracy Quadratically
Mahler, D. H.; Rozema, Lee A.; Darabi, Ardavan; Ferrie, Christopher; Blume-Kohout, Robin; Steinberg, A. M.
2013-11-01
We introduce a simple protocol for adaptive quantum state tomography, which reduces the worst-case infidelity [1-F(ρ^,ρ)] between the estimate and the true state from O(1/N) to O(1/N). It uses a single adaptation step and just one extra measurement setting. In a linear optical qubit experiment, we demonstrate a full order of magnitude reduction in infidelity (from 0.1% to 0.01%) for a modest number of samples (N≈3×104).
Hahn, Seungsoo
2016-10-28
The Hamiltonian matrix for the first excited vibrational states of a protein can be effectively represented by local vibrational modes constituting amide III, II, I, and A modes to simulate various vibrational spectra. Methods for obtaining the Hamiltonian matrix from ab initio quantum calculation results are discussed, where the methods consist of three steps: selection of local vibrational mode coordinates, calculation of a reduced Hessian matrix, and extraction of the Hamiltonian matrix from the Hessian matrix. We introduce several methods for each step. The methods were assessed based on the density functional theory calculation results of 24 oligopeptides with four different peptide lengths and six different secondary structures. The completeness of a Hamiltonian matrix represented in the reduced local mode space is improved by adopting a specific atom group for each amide mode and reducing the effect of ignored local modes. The calculation results are also compared to previous models using C=O stretching vibration and transition dipole couplings. We found that local electric transition dipole moments of the amide modes are mainly bound on the local peptide planes. Their direction and magnitude are well conserved except amide A modes, which show large variation. Contrary to amide I modes, the vibrational coupling constants of amide III, II, and A modes obtained by analysis of a dipeptide are not transferable to oligopeptides with the same secondary conformation because coupling constants are affected by the surrounding atomic environment.
Quantum marginals from pure doubly excited states
Maciążek, Tomasz; Tsanov, Valdemar
2017-11-01
The possible spectra of one-particle reduced density matrices that are compatible with a pure multipartite quantum system of finite dimension form a convex polytope. We introduce a new construction of inner- and outer-bounding polytopes that constrain the polytope for the entire quantum system. The outer bound is sharp. The inner polytope stems only from doubly excited states. We find all quantum systems, where the bounds coincide giving the entire polytope. We show, that those systems are: (i) any system of two particles (ii) L qubits, (iii) three fermions on N≤slant 7 levels, (iv) any number of bosons on any number of levels and (v) fermionic Fock space on N≤slant 5 levels. The methods we use come from symplectic geometry and representation theory of compact Lie groups. In particular, we study the images of proper momentum maps, where our method describes momentum images for all representations that are spherical.
Rotational Spectra in 29 Vibrationally Excited States of Interstellar Aminoacetonitrile
Energy Technology Data Exchange (ETDEWEB)
Kolesniková, L.; Alonso, E. R.; Mata, S.; Alonso, J. L. [Grupo de Espectroscopia Molecular (GEM), Edificio Quifima, Área de Química-Física, Laboratorios de Espectroscopia y Bioespectroscopia, Parque Científico UVa, Unidad Asociada CSIC, Universidad de Valladolid, E-47011 Valladolid (Spain)
2017-04-01
We report a detailed spectroscopic investigation of the interstellar aminoacetonitrile, a possible precursor molecule of glycine. Using a combination of Stark and frequency-modulation microwave and millimeter wave spectroscopies, we observed and analyzed the room-temperature rotational spectra of 29 excited states with energies up to 1000 cm{sup −1}. We also observed the {sup 13}C isotopologues in the ground vibrational state in natural abundance (1.1%). The extensive data set of more than 2000 new rotational transitions will support further identifications of aminoacetonitrile in the interstellar medium.
Siegert State Approach to Quantum Defect Theory
Hategan, C.; Ionescu, R. A.; Wolter, H. H.
2016-01-01
The Siegert states are approached in framework of Bloch-Lane-Robson formalism for quantum collisions. The Siegert state is not described by a pole of Wigner R- matrix but rather by the equation $1- R_{nn}L_n = 0$, relating R- matrix element $R_{nn}$ to decay channel logarithmic derivative $L_n$. Extension of Siegert state equation to multichannel system results into replacement of channel R- matrix element $R_{nn}$ by its reduced counterpart ${\\cal R}_{nn}$. One proves the Siegert state is a ...
Control aspects of quantum computing using pure and mixed states.
Schulte-Herbrüggen, Thomas; Marx, Raimund; Fahmy, Amr; Kauffman, Louis; Lomonaco, Samuel; Khaneja, Navin; Glaser, Steffen J
2012-10-13
Steering quantum dynamics such that the target states solve classically hard problems is paramount to quantum simulation and computation. And beyond, quantum control is also essential to pave the way to quantum technologies. Here, important control techniques are reviewed and presented in a unified frame covering quantum computational gate synthesis and spectroscopic state transfer alike. We emphasize that it does not matter whether the quantum states of interest are pure or not. While pure states underly the design of quantum circuits, ensemble mixtures of quantum states can be exploited in a more recent class of algorithms: it is illustrated by characterizing the Jones polynomial in order to distinguish between different (classes of) knots. Further applications include Josephson elements, cavity grids, ion traps and nitrogen vacancy centres in scenarios of closed as well as open quantum systems.
Charge asymmetry and relativistic corrections in pure vibrational states of the HD+ ion
Stanke, Monika; Adamowicz, Ludwik
2014-03-01
In this work we present very accurate quantum-mechanical calculations of all bound pure vibrational states of the HD+ ion performed without the Born-Oppenheimer (BO) approximation. All three particles forming the system are treated on equal footing. The approach involves separating the center-of-mass motion from the laboratory-frame nonrelativistic Hamiltonian and expending the wave function of each considered state in terms of all-particle explicitly correlated Gaussian functions. The Gaussian exponential parameters are variationally optimized with the aid of the analytical energy gradient calculated with respect to these parameters. For each state the leading relativistic corrections are calculated as expectation values of the corresponding operators with the non-BO wave function of the state. The non-BO approach allows us to directly describe the charge asymmetry in HD+ which is due to the nuclear-mass asymmetry. The effect increases with the vibrational excitation and affects the values of the relativistic corrections. This phenomenon is the focus of the present study.
Delgado, Francisco
2017-12-01
Quantum information processing should be generated through control of quantum evolution for physical systems being used as resources, such as superconducting circuits, spinspin couplings in ions and artificial anyons in electronic gases. They have a quantum dynamics which should be translated into more natural languages for quantum information processing. On this terrain, this language should let to establish manipulation operations on the associated quantum information states as classical information processing does. This work shows how a kind of processing operations can be settled and implemented for quantum states design and quantum processing for systems fulfilling a SU(2) reduction in their dynamics.
Hybrid quantum processors: molecular ensembles as quantum memory for solid state circuits.
Rabl, P; DeMille, D; Doyle, J M; Lukin, M D; Schoelkopf, R J; Zoller, P
2006-07-21
We investigate a hybrid quantum circuit where ensembles of cold polar molecules serve as long-lived quantum memories and optical interfaces for solid state quantum processors. The quantum memory realized by collective spin states (ensemble qubit) is coupled to a high-Q stripline cavity via microwave Raman processes. We show that, for convenient trap-surface distances of a few microm, strong coupling between the cavity and ensemble qubit can be achieved. We discuss basic quantum information protocols, including a swap from the cavity photon bus to the molecular quantum memory, and a deterministic two qubit gate. Finally, we investigate coherence properties of molecular ensemble quantum bits.
Quantum Nonadiabatic Cloning of Entangled Coherent States.
Izmaylov, Artur F; Joubert-Doriol, Loïc
2017-04-20
We propose a systematic approach to the basis set extension for nonadiabatic dynamics of entangled combination of nuclear coherent states (CSs) evolving according to the time-dependent variational principle (TDVP). The TDVP provides a rigorous framework for fully quantum nonadiabatic dynamics of closed systems; however, the quality of results strongly depends on available basis functions. Starting with a single nuclear CS replicated vertically on all electronic states, our approach clones this function when replicas of the CS on different electronic states experience increasingly different forces. Created clones move away from each other (decohere), extending the basis set. To determine a moment for cloning, we introduce generalized forces based on derivatives that maximally contribute to a variation of the total quantum action and thus account for entanglement of all basis functions.
Lapierre, David; Kochanov, Roman; Kokoouline, Viatcheslav; Tyuterev, Vladimir
2016-01-01
Energies and lifetimes (widths) of vibrational states above the lowest dissociation limit of $^{16}$O$_3$ were determined using a previously-developed efficient approach, which combines hyperspherical coordinates and a complex absorbing potential. The calculations are based on a recently-computed potential energy surface of ozone determined with a spectroscopic accuracy [J. Chem. Phys. {\\bf 139}, 134307 (2013)]. The effect of permutational symmetry on rovibrational dynamics and the density of resonance states in O$_3$ is discussed in detail. Correspondence between quantum numbers appropriate for short- and long-range parts of wave functions of the rovibrational continuum is established. It is shown, by symmetry arguments, that the allowed purely vibrational ($J=0$) levels of $^{16}$O$_3$ and $^{18}$O$_3$, both made of bosons with zero nuclear spin, cannot dissociate on the ground state potential energy surface. Energies and wave functions of bound states of the ozone isotopologue $^{16}$O$_3$ with rotational ...
Quantum coherence generated by interference-induced state selectiveness
Garreau, Jean Claude
2001-01-01
The relations between quantum coherence and quantum interference are discussed. A general method for generation of quantum coherence through interference-induced state selection is introduced and then applied to `simple' atomic systems under two-photon transitions, with applications in quantum optics and laser cooling.
Cooling a Single Atom in an Optical Tweezer to Its Quantum Ground State
Directory of Open Access Journals (Sweden)
A. M. Kaufman
2012-11-01
Full Text Available We report cooling of a single neutral atom to its three-dimensional vibrational ground state in an optical tweezer. After employing Raman sideband cooling for tens of milliseconds, we measure via sideband spectroscopy a three-dimensional ground-state occupation of about 90%. We further observe coherent control of the spin and motional state of the trapped atom. Our demonstration shows that an optical tweezer, formed simply by a tightly focused beam of light, creates sufficient confinement for efficient sideband cooling. This source of ground-state neutral atoms will be instrumental in numerous quantum simulation and logic applications that require a versatile platform for storing and manipulating ultracold single neutral atoms. For example, these results will improve current optical-tweezer experiments studying atom-photon coupling and Rydberg quantum logic gates, and could provide new opportunities such as rapid production of single dipolar molecules or quantum simulation in tweezer arrays.
Fourth-Order Vibrational Transition State Theory and Chemical Kinetics
Stanton, John F.; Matthews, Devin A.; Gong, Justin Z.
2015-06-01
Second-order vibrational perturbation theory (VPT2) is an enormously successful and well-established theory for treating anharmonic effects on the vibrational levels of semi-rigid molecules. Partially as a consequence of the fact that the theory is exact for the Morse potential (which provides an appropriate qualitative model for stretching anharmonicity), VPT2 calculations for such systems with appropriate ab initio potential functions tend to give fundamental and overtone levels that fall within a handful of wavenumbers of experimentally measured positions. As a consequence, the next non-vanishing level of perturbation theory -- VPT4 -- offers only slight improvements over VPT2 and is not practical for most calculations since it requires information about force constants up through sextic. However, VPT4 (as well as VPT2) can be used for other applications such as the next vibrational correction to rotational constants (the ``gammas'') and other spectroscopic parameters. In addition, the marriage of VPT with the semi-classical transition state theory of Miller (SCTST) has recently proven to be a powerful and accurate treatment for chemical kinetics. In this talk, VPT4-based SCTST tunneling probabilities and cumulative reaction probabilities are give for the first time for selected low-dimensional model systems. The prospects for VPT4, both practical and intrinsic, will also be discussed.
Extreme Violation of Local Realism in Quantum Hypergraph States.
Gachechiladze, Mariami; Budroni, Costantino; Gühne, Otfried
2016-02-19
Hypergraph states form a family of multiparticle quantum states that generalizes the well-known concept of Greenberger-Horne-Zeilinger states, cluster states, and more broadly graph states. We study the nonlocal properties of quantum hypergraph states. We demonstrate that the correlations in hypergraph states can be used to derive various types of nonlocality proofs, including Hardy-type arguments and Bell inequalities for genuine multiparticle nonlocality. Moreover, we show that hypergraph states allow for an exponentially increasing violation of local realism which is robust against loss of particles. Our results suggest that certain classes of hypergraph states are novel resources for quantum metrology and measurement-based quantum computation.
Quantum correlations support probabilistic pure state cloning
Energy Technology Data Exchange (ETDEWEB)
Roa, Luis, E-mail: lroa@udec.cl [Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Alid-Vaccarezza, M.; Jara-Figueroa, C. [Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Klimov, A.B. [Departamento de Física, Universidad de Guadalajara, Avenida Revolución 1500, 44420 Guadalajara, Jalisco (Mexico)
2014-02-01
The probabilistic scheme for making two copies of two nonorthogonal pure states requires two auxiliary systems, one for copying and one for attempting to project onto the suitable subspace. The process is performed by means of a unitary-reduction scheme which allows having a success probability of cloning different from zero. The scheme becomes optimal when the probability of success is maximized. In this case, a bipartite state remains as a free degree which does not affect the probability. We find bipartite states for which the unitarity does not introduce entanglement, but does introduce quantum discord between some involved subsystems.
The Ã1Au state of acetylene: ungerade vibrational levels in the region 45,800-46,550 cm-1
Baraban, Joshua H.; Changala, P. Bryan; Merer, Anthony J.; Steeves, Adam H.; Bechtel, Hans A.; Field, Robert W.
2012-11-01
The ungerade vibrational levels of the ? 1Au (S1-trans) state of C2H2 lying in the region 45,800-46,550 cm-1 have been assigned from IR-UV double resonance spectra. The aim has been to classify the complete manifold of S1-trans levels in this region, so as to facilitate the assignment of the bands of S1-cis C2H2. The rotational structure is complicated because of the overlapping of vibrational polyads with different Coriolis and Darling-Dennison parameters, but assignments have been possible with the help of predictions based on the properties of polyads at lower energy. An important result is that the analysis of the (1141, 1161) polyad determines the anharmonicity constants x 14 and x 16, which will be needed to proceed to higher energies. Some regions of impressive complexity occur. Among these is the band given by the 3361, K = 1 state at 45,945 cm-1, where a three-level interaction within the S1 state is confused by triplet perturbations. Several probable S1-cis states have been observed, including cis-62, K = 1; this vibrational level appears to show a K-staggering, of the type that arises when quantum mechanical tunnelling through the barrier to cis-trans isomerization is possible. The total number of identified cis vibrational states is now 6 out of an expected 10 up to the energies discussed in this paper.
Extremal quantum correlations: Experimental study with two-qubit states
Energy Technology Data Exchange (ETDEWEB)
Chiuri, A.; Mataloni, P. [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Istituto Nazionale di Ottica (INO-CNR), L.go E. Fermi 6, I-50125 Firenze (Italy); Vallone, G. [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Via Panisperna 89/A, Compendio del Viminale, I-00184 Roma (Italy); Paternostro, M. [Centre for Theoretical Atomic, Molecular, and Optical Physics, School of Mathematics and Physics, Queen' s University, Belfast BT7 1NN (United Kingdom)
2011-08-15
We explore experimentally the space of two-qubit quantum-correlated mixed states, including frontier states as defined by the use of quantum discord and von Neumann entropy. Our experimental setup is flexible enough to allow for high-quality generation of a vast variety of states. We address quantitatively the relation between quantum discord and a recently suggested alternative measure of quantum correlations.
Heralded amplification of path entangled quantum states
Monteiro, F.; Verbanis, E.; Caprara Vivoli, V.; Martin, A.; Gisin, N.; Zbinden, H.; Thew, R. T.
2017-06-01
Device-independent quantum key distribution (DI-QKD) represents one of the most fascinating challenges in quantum communication, exploiting concepts of fundamental physics, namely Bell tests of nonlocality, to ensure the security of a communication link. This requires the loophole-free violation of a Bell inequality, which is intrinsically difficult due to losses in fibre optic transmission channels. Heralded photon amplification (HPA) is a teleportation-based protocol that has been proposed as a means to overcome transmission loss for DI-QKD. Here we demonstrate HPA for path entangled states and characterise the entanglement before and after loss by exploiting a recently developed displacement-based detection scheme. We demonstrate that by exploiting HPA we are able to reliably maintain high fidelity entangled states over loss-equivalent distances of more than 50 km.
Quantum Darwinism for mixed-state environment
Quan, Haitao; Zwolak, Michael; Zurek, Wojciech
2009-03-01
We exam quantum darwinism when a system is in the presence of a mixed environment, and we find a general relation between the mutual information for the mixed-state environment and the change of the entropy of the fraction of the environment. We then look at a particular solvable model, and we numerically exam the time evolution of the ``mutual information" for large environment. Finally we discuss about the exact expressions for all entropies and the mutual information at special time.
Solid State Quantum Computer in Silicon
2008-09-30
focused microprobe of 2 MeV alpha particles, produced by the 5U Pelletron accelerator at the University of Melbourne and the MP2 nuclear microprobe...Kotthaus and S. Ludwig, “ Electrostatically defined serial triple quantum dot charged with few electrons”, Physical Review B 76, 075306 (2007). M.Y...ESR line to induce Rabi oscillation of the spin state. In addition, the electrostatic potential on the ESR line is used to shift the Zeeman-split
Spectral coherent-state quantum cryptography.
Cincotti, Gabriella; Spiekman, Leo; Wada, Naoya; Kitayama, Ken-ichi
2008-11-01
A novel implementation of quantum-noise optical cryptography is proposed, which is based on a simplified architecture that allows long-haul, high-speed transmission in a fiber optical network. By using a single multiport encoder/decoder and 16 phase shifters, this new approach can provide the same confidentiality as other implementations of Yuen's encryption protocol, which use a larger number of phase or polarization coherent states. Data confidentiality and error probability for authorized and unauthorized receivers are carefully analyzed.
Possible splitting of the isovector vibrational state due to triaxiality
Energy Technology Data Exchange (ETDEWEB)
Faessler, A.; Nojarov, R.; Zubik, S.
1986-06-01
A microscopic calculation of the restoring force for isovector scissor vibrations using the wave functions of a triaxial Woods-Saxon potential shows that the experimentally observed splitting of the isovector M1 state in /sup 164/Dy(50 keV), /sup 168/Er(70 keV) and /sup 174/Yb(200 keV) could be attributed to the presence of a possible small non-axially symmetric deformation (..gamma..=0.8/sup 0/, 1/sup 0/ and 3/sup 0/ respectively).
Extracting Entanglement Geometry from Quantum States.
Hyatt, Katharine; Garrison, James R; Bauer, Bela
2017-10-06
Tensor networks impose a notion of geometry on the entanglement of a quantum system. In some cases, this geometry is found to reproduce key properties of holographic dualities, and subsequently much work has focused on using tensor networks as tractable models for holographic dualities. Conventionally, the structure of the network-and hence the geometry-is largely fixed a priori by the choice of the tensor network ansatz. Here, we evade this restriction and describe an unbiased approach that allows us to extract the appropriate geometry from a given quantum state. We develop an algorithm that iteratively finds a unitary circuit that transforms a given quantum state into an unentangled product state. We then analyze the structure of the resulting unitary circuits. In the case of noninteracting, critical systems in one dimension, we recover signatures of scale invariance in the unitary network, and we show that appropriately defined geodesic paths between physical degrees of freedom exhibit known properties of a hyperbolic geometry.
Statistical constraints on state preparation for a quantum computer
Indian Academy of Sciences (India)
Quantum computing algorithms require that the quantum register be initially present in a superposition state. To achieve this, we consider the practical problem of creating a coherent superposition state of several qubits. We show that the constraints of quantum statistics require that the entropy of the system be brought ...
A Quantum Version of Wigner’s Transition State Theory
Schubert, R.; Waalkens, H.; Wiggins, S.
2009-01-01
A quantum version of a recent realization of Wigner’s transition state theory in phase space is presented. The theory developed builds on a quantum normal form which locally decouples the quantum dynamics near the transition state to any desired order in ħ. This leads to an explicit algorithm to
A Quantum Version of Wigner's Transition State Theory
Schubert, R.; Waalkens, H.; Wiggins, S.
A quantum version of a recent realization of Wigner's transition state theory in phase space is presented. The theory developed builds on a quantum normal form which locally decouples the quantum dynamics near the transition state to any desired order in (h) over bar. This leads to an explicit
Vibrational studies of Thyroxine hormone: Comparative study with quantum chemical calculations
Borah, Mukunda Madhab; Devi, Th. Gomti
2017-11-01
The FTIR and Raman techniques have been used to record spectra of Thyroxine. The stable geometrical parameters and vibrational wave numbers were calculated based on potential energy distribution (PED) using vibrational energy distribution analysis (VEDA) program. The vibrational energies are assigned to monomer, chain dimer and cyclic dimers of this molecule using the basis set B3LYP/LANL2DZ. The computational scaled frequencies are in good agreements with the experimental results. The study is extended to calculate the HOMO-LUMO energy gap, Molecular Electrostatic Potential (MEP) surface, hardness (η), chemical potential (μ), Global electrophilicity index (ω) and different thermo dynamical properties of Thyroxine in different states. The calculated HOMO-LUMO energies show the charge transfer occurs within the molecule. The calculated Natural bond orbital (NBO) analysis confirms the presence of intra-molecular charge transfer as well as the hydrogen bonding interaction.
Neural-Network Quantum States, String-Bond States, and Chiral Topological States
Glasser, Ivan; Pancotti, Nicola; August, Moritz; Rodriguez, Ivan D.; Cirac, J. Ignacio
2018-01-01
Neural-network quantum states have recently been introduced as an Ansatz for describing the wave function of quantum many-body systems. We show that there are strong connections between neural-network quantum states in the form of restricted Boltzmann machines and some classes of tensor-network states in arbitrary dimensions. In particular, we demonstrate that short-range restricted Boltzmann machines are entangled plaquette states, while fully connected restricted Boltzmann machines are string-bond states with a nonlocal geometry and low bond dimension. These results shed light on the underlying architecture of restricted Boltzmann machines and their efficiency at representing many-body quantum states. String-bond states also provide a generic way of enhancing the power of neural-network quantum states and a natural generalization to systems with larger local Hilbert space. We compare the advantages and drawbacks of these different classes of states and present a method to combine them together. This allows us to benefit from both the entanglement structure of tensor networks and the efficiency of neural-network quantum states into a single Ansatz capable of targeting the wave function of strongly correlated systems. While it remains a challenge to describe states with chiral topological order using traditional tensor networks, we show that, because of their nonlocal geometry, neural-network quantum states and their string-bond-state extension can describe a lattice fractional quantum Hall state exactly. In addition, we provide numerical evidence that neural-network quantum states can approximate a chiral spin liquid with better accuracy than entangled plaquette states and local string-bond states. Our results demonstrate the efficiency of neural networks to describe complex quantum wave functions and pave the way towards the use of string-bond states as a tool in more traditional machine-learning applications.
Neural-Network Quantum States, String-Bond States, and Chiral Topological States
Directory of Open Access Journals (Sweden)
Ivan Glasser
2018-01-01
Full Text Available Neural-network quantum states have recently been introduced as an Ansatz for describing the wave function of quantum many-body systems. We show that there are strong connections between neural-network quantum states in the form of restricted Boltzmann machines and some classes of tensor-network states in arbitrary dimensions. In particular, we demonstrate that short-range restricted Boltzmann machines are entangled plaquette states, while fully connected restricted Boltzmann machines are string-bond states with a nonlocal geometry and low bond dimension. These results shed light on the underlying architecture of restricted Boltzmann machines and their efficiency at representing many-body quantum states. String-bond states also provide a generic way of enhancing the power of neural-network quantum states and a natural generalization to systems with larger local Hilbert space. We compare the advantages and drawbacks of these different classes of states and present a method to combine them together. This allows us to benefit from both the entanglement structure of tensor networks and the efficiency of neural-network quantum states into a single Ansatz capable of targeting the wave function of strongly correlated systems. While it remains a challenge to describe states with chiral topological order using traditional tensor networks, we show that, because of their nonlocal geometry, neural-network quantum states and their string-bond-state extension can describe a lattice fractional quantum Hall state exactly. In addition, we provide numerical evidence that neural-network quantum states can approximate a chiral spin liquid with better accuracy than entangled plaquette states and local string-bond states. Our results demonstrate the efficiency of neural networks to describe complex quantum wave functions and pave the way towards the use of string-bond states as a tool in more traditional machine-learning applications.
Coherent states in quantum mechanics; Estados coerentes em mecanica quantica
Energy Technology Data Exchange (ETDEWEB)
Rodrigues, R. de Lima [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)]. E-mail: rafaelr@cbpf.br; Fernandes Junior, Damasio; Batista, Sheyla Marques [Paraiba Univ., Campina Grande, PB (Brazil). Dept. de Engenharia Eletrica
2001-12-01
We present a review work on the coherent states is non-relativistic quantum mechanics analysing the quantum oscillators in the coherent states. The coherent states obtained via a displacement operator that act on the wave function of ground state of the oscillator and the connection with Quantum Optics which were implemented by Glauber have also been considered. A possible generalization to the construction of new coherent states it is point out. (author)
Generating quantum states through spin chain dynamics
Kay, Alastair
2017-04-01
The spin chain is a theoretical work-horse of the physicist, providing a convenient, tractable model that yields insight into a host of physical phenomena including conduction, frustration, superconductivity, topological phases, localisation, phase transitions, quantum chaos and even string theory. Our ultimate aim, however, is not just to understand the properties of a physical system, but to harness it for our own ends. We therefore study the possibilities for engineering a special class of spin chain, envisaging the potential for this to feedback into the original physical systems. We pay particular attention to the generation of multipartite entangled states such as the W (Dicke) state, superposed over multiple sites of the chain.
Quantum state transfer between light and matter via teleportation
DEFF Research Database (Denmark)
Krauter, Hanna; Sherson, Jacob; Polzik, Eugene Simon
2010-01-01
Quantum teleportation is an interesting feature of quantum mechanics. Entanglement is used as a link between two remote locations to transfer a quantum state without physically sending it - a process that cannot be realized utilizing merely classical tools. Furthermore it has become evident...... that teleportation is also an important element of future quantum networks and it can be an ingredient for quantum computation. This article reports for the first time the teleportation from light to atoms. In the experiment discussed, the quantum state of a light beam is transferred to an atomic ensemble. The key...
The Astrophysical Weeds: Rotational Transitions in Excited Vibrational States
Alonso, José L.; Kolesniková, Lucie; Alonso, Elena R.; Mata, Santiago
2017-06-01
The number of unidentified lines in the millimeter and submillimeter wave surveys of the interstellar medium has grown rapidly. The major contributions are due to rotational transitions in excited vibrational states of a relatively few molecules that are called the astrophysical weeds. necessary data to deal with spectral lines from astrophysical weeds species can be obtained from detailed laboratory rotational measurements in the microwave and millimeter wave region. A general procedure is being used at Valladolid combining different time and/or frequency domain spectroscopic tools of varying importance for providing the precise set of spectroscopic constants that could be used to search for this species in the ISM. This is illustrated in the present contribution through its application to several significant examples. Fortman, S. M., Medvedev, I. R., Neese, C.F., & De Lucia, F.C. 2010, ApJ,725, 1682 Rotational Spectra in 29 Vibrationally Excited States of Interstellar Aminoacetonitrile, L. Kolesniková, E. R. Alonso, S. Mata, and J. L. Alonso, The Astrophysical Journal Supplement Series 2017, (in press).
Mixed state dynamical quantum phase transitions
Bhattacharya, Utso; Bandyopadhyay, Souvik; Dutta, Amit
2017-11-01
Preparing an integrable system in a mixed state described by a thermal density matrix, we subject it to a sudden quench and explore the subsequent unitary dynamics. To address the question of whether the nonanalyticities, namely, the dynamical quantum phase transitions (DQPTs), persist when the initial state is mixed, we consider two versions of the generalized Loschmidt overlap amplitude (GLOA). Our study shows that the GLOA constructed using the Uhlmann approach does not show any signature of DQPTs at any nonzero initial temperature. On the other hand, a GLOA defined in the interferometric phase approach through the purifications of the time-evolved density matrix, indeed shows that nonanalyiticies in the corresponding "dynamical free-energy density" persist, thereby establishing the existence of mixed state dynamical quantum phase transitions (MSDQPTs). Our work provides a framework that perfectly reproduces both the nonanalyticities and also the emergent topological structure in the pure state limit. These claims are corroborated by analyzing the nonequilibrium dynamics of a transverse Ising chain initially prepared in a thermal state and subjected to a sudden quench of the transverse field.
Controlling the quantum state of trapped ions
Roos, C
2000-01-01
brace quadrupole transition enables the transfer of the ion's motional state into the ground state with up to 99.9 % probability. Different aspects of the cooling process are investigated. In particular, a measurement of the length of time that the ion spends on average in the final state after switching off the cooling lasers (heating time) is made. In contrast to prior experiments, this time is found to be orders of magnitude longer than the time required to manipulate the ion's quantum state. By coherently exciting the ion after preparing it in Fock states of motion, the coherence time is probed and found to be on the order of a millisecond, thus allowing the realization of a few quantum gates. Coherence-limiting processes have been investigated, as well as first steps towards extending the experiments to the case of two trapped ions. In addition to the experiments mentioned above, the possibility of performing cavity-QED experiments with trapped ions is explored. How to efficiently couple the quadrupole t...
Cis-trans isomerization in the S1 state of acetylene: identification of cis-well vibrational levels.
Merer, Anthony J; Steeves, Adam H; Baraban, Joshua H; Bechtel, Hans A; Field, Robert W
2011-06-28
A systematic analysis of the S(1)-trans (Ã(1)A(u)) state of acetylene, using IR-UV double resonance along with one-photon fluorescence excitation spectra, has allowed assignment of at least part of every single vibrational state or polyad up to a vibrational energy of 4200 cm(-1). Four observed vibrational levels remain unassigned, for which no place can be found in the level structure of the trans-well. The most prominent of these lies at 46 175 cm(-1). Its (13)C isotope shift, exceptionally long radiative lifetime, unexpected rotational selection rules, and lack of significant Zeeman effect, combined with the fact that no other singlet electronic states are expected at this energy, indicate that it is a vibrational level of the S(1)-cis isomer (Ã(1)A(2)). Guided by ab initio calculations [J. H. Baraban, A. R. Beck, A. H. Steeves, J. F. Stanton, and R. W. Field, J. Chem. Phys. 134, 244311 (2011)] of the cis-well vibrational frequencies, the vibrational assignments of these four levels can be established from their vibrational symmetries together with the (13)C isotope shift of the 46 175 cm(-1) level (assigned here as cis-3(1)6(1)). The S(1)-cis zero-point level is deduced to lie near 44 900 cm(-1), and the ν(6) vibrational frequency of the S(1)-cis well is found to be roughly 565 cm(-1); these values are in remarkably good agreement with the results of recent ab initio calculations. The 46 175 cm(-1) vibrational level is found to have a 3.9 cm(-1) staggering of its K-rotational structure as a result of quantum mechanical tunneling through the isomerization barrier. Such tunneling does not give rise to ammonia-type inversion doubling, because the cis and trans isomers are not equivalent; instead the odd-K rotational levels of a given vibrational level are systematically shifted relative to the even-K rotational levels, leading to a staggering of the K-structure. These various observations represent the first definite assignment of an isomer of acetylene
Cis-trans isomerization in the S1 state of acetylene: Identification of cis-well vibrational levels
Merer, Anthony J.; Steeves, Adam H.; Baraban, Joshua H.; Bechtel, Hans A.; Field, Robert W.
2011-06-01
A systematic analysis of the S1-trans ({tilde A}1Au) state of acetylene, using IR-UV double resonance along with one-photon fluorescence excitation spectra, has allowed assignment of at least part of every single vibrational state or polyad up to a vibrational energy of 4200 cm-1. Four observed vibrational levels remain unassigned, for which no place can be found in the level structure of the trans-well. The most prominent of these lies at 46 175 cm-1. Its 13C isotope shift, exceptionally long radiative lifetime, unexpected rotational selection rules, and lack of significant Zeeman effect, combined with the fact that no other singlet electronic states are expected at this energy, indicate that it is a vibrational level of the S1-cis isomer ({tilde A}1A2). Guided by ab initio calculations [J. H. Baraban, A. R. Beck, A. H. Steeves, J. F. Stanton, and R. W. Field, J. Chem. Phys. 134, 244311 (2011)], 10.1063/1.3570823 of the cis-well vibrational frequencies, the vibrational assignments of these four levels can be established from their vibrational symmetries together with the 13C isotope shift of the 46 175 cm-1 level (assigned here as cis-3161). The S1-cis zero-point level is deduced to lie near 44 900 cm-1, and the ν6 vibrational frequency of the S1-cis well is found to be roughly 565 cm-1; these values are in remarkably good agreement with the results of recent ab initio calculations. The 46 175 cm-1 vibrational level is found to have a 3.9 cm-1 staggering of its K-rotational structure as a result of quantum mechanical tunneling through the isomerization barrier. Such tunneling does not give rise to ammonia-type inversion doubling, because the cis and trans isomers are not equivalent; instead the odd-K rotational levels of a given vibrational level are systematically shifted relative to the even-K rotational levels, leading to a staggering of the K-structure. These various observations represent the first definite assignment of an isomer of acetylene that was
Bipartite quantum states and random complex networks
Garnerone, Silvano; Giorda, Paolo; Zanardi, Paolo
2012-01-01
We introduce a mapping between graphs and pure quantum bipartite states and show that the associated entanglement entropy conveys non-trivial information about the structure of the graph. Our primary goal is to investigate the family of random graphs known as complex networks. In the case of classical random graphs, we derive an analytic expression for the averaged entanglement entropy \\bar S while for general complex networks we rely on numerics. For a large number of nodes n we find a scaling \\bar {S} \\sim c log n +g_{ {e}} where both the prefactor c and the sub-leading O(1) term ge are characteristic of the different classes of complex networks. In particular, ge encodes topological features of the graphs and is named network topological entropy. Our results suggest that quantum entanglement may provide a powerful tool for the analysis of large complex networks with non-trivial topological properties.
Quantum Information Protocols with Gaussian States of Light
DEFF Research Database (Denmark)
Jacobsen, Christian Scheffmann
Quantum cryptography is widely regarded as the most mature field within the context of quantum information in the sense that its application and development has produced companies that base their products on genuine quantum mechanical principles. Examples include quantum random number generators...... and hardware for secure quantum key distribution. These technologies directly exploit quantum effects, and indeed this is where they offer advantages to classical products. This thesis deals with the development and implementation of quantum information protocols that utilize the rather inexpensive resource...... of Gaussian states. A quantum information protocol is essentially a sequence of state exchanges between some number of parties and a certain ordering of quantum mechanical unitary operators performed by these parties. An example of this is the famous BB84 protocol for secret key generation, where photons...
Optimal estimation of parameters of an entangled quantum state
Virzì, S.; Avella, A.; Piacentini, F.; Gramegna, M.; Brida, G.; Degiovanni, I. P.; Genovese, M.
2017-05-01
Two-photon entangled quantum states are a fundamental tool for quantum information and quantum cryptography. A complete description of a generic quantum state is provided by its density matrix: the technique allowing experimental reconstruction of the density matrix is called quantum state tomography. Entangled states density matrix reconstruction requires a large number of measurements on many identical copies of the quantum state. An alternative way of certifying the amount of entanglement in two-photon states is represented by the estimation of specific parameters, e.g., negativity and concurrence. If we have a priori partial knowledge of our state, it’s possible to develop several estimators for these parameters that require lower amount of measurements with respect to full density matrix reconstruction. The aim of this work is to introduce and test different estimators for negativity and concurrence for a specific class of two-photon states.
Self-calibrating quantum state tomography
Brańczyk, A. M.; Mahler, D. H.; Rozema, L. A.; Darabi, A.; Steinberg, A. M.; James, D. F. V.
2012-08-01
We introduce and experimentally demonstrate a technique for performing quantum state tomography (QST) on multiple-qubit states despite incomplete knowledge about the unitary operations used to change the measurement basis. Given unitary operations with unknown rotation angles, our method can be used to reconstruct the density matrix of the state up to local \\hat \\sigma _z rotations as well as recover the magnitude of the unknown rotation angle. We demonstrate high-fidelity self-calibrating tomography on polarization-encoded one- and two-photon states. The unknown unitary operations are realized in two ways: using a birefringent polymer sheet—an inexpensive smartphone screen protector—or alternatively a liquid crystal wave plate with a tuneable retardance. We explore how our technique may be adapted for QST of systems such as biological molecules where the magnitude and orientation of the transition dipole moment is not known with high accuracy.
Advantages of Unfair Quantum Ground-State Sampling.
Zhang, Brian Hu; Wagenbreth, Gene; Martin-Mayor, Victor; Hen, Itay
2017-04-21
The debate around the potential superiority of quantum annealers over their classical counterparts has been ongoing since the inception of the field. Recent technological breakthroughs, which have led to the manufacture of experimental prototypes of quantum annealing optimizers with sizes approaching the practical regime, have reignited this discussion. However, the demonstration of quantum annealing speedups remains to this day an elusive albeit coveted goal. We examine the power of quantum annealers to provide a different type of quantum enhancement of practical relevance, namely, their ability to serve as useful samplers from the ground-state manifolds of combinatorial optimization problems. We study, both numerically by simulating stoquastic and non-stoquastic quantum annealing processes, and experimentally, using a prototypical quantum annealing processor, the ability of quantum annealers to sample the ground-states of spin glasses differently than thermal samplers. We demonstrate that (i) quantum annealers sample the ground-state manifolds of spin glasses very differently than thermal optimizers (ii) the nature of the quantum fluctuations driving the annealing process has a decisive effect on the final distribution, and (iii) the experimental quantum annealer samples ground-state manifolds significantly differently than thermal and ideal quantum annealers. We illustrate how quantum annealers may serve as powerful tools when complementing standard sampling algorithms.
Effective quantum state reconstruction using compressed sensing in NMR quantum computing
Yang, J.; Cong, S.; Liu, X.; Li, Z.; Li, K.
2017-11-01
Compressed sensing (CS) has been verified as an effective technique in the reconstruction of quantum state; however, it is still unknown if CS can reconstruct quantum states given the incomplete data measured by nuclear magnetic resonance (NMR). In this paper, we propose an effective NMR quantum state reconstruction method based on CS. Different from the conventional CS-based quantum state reconstruction, our method uses the actual observation data from NMR experiments rather than the data measured by the Pauli operators. We implement measurements on quantum states in practical NMR computing experiments and reconstruct states of two, three, and four qubits using fewer number of measurement settings, respectively. The proposed method is easy to implement and performs more efficiently with the increase of the system dimension size. The performance reveals both efficiency and accuracy, which provides an alternative for the quantum state reconstruction in practical NMR.
How to spell out the epistemic conception of quantum states
Friederich, Simon
The paper investigates the epistemic conception of quantum states-the view that quantum states are not descriptions of quantum systems but rather reflect the assigning agents' epistemic relations to the systems. This idea, which can be found already in the works of Copenhagen adherents Heisenberg and Peierls, has received increasing attention in recent years because it promises an understanding of quantum theory in which neither the measurement problem nor a conflict between quantum non-locality and relativity theory arises. Here it is argued that the main challenge for proponents of this idea is to make sense of the notion of a state assignment being performed correctly without thereby acknowledging the notion of a true state of a quantum system-a state it is in. An account based on the epistemic conception of states is proposed that fulfills this requirement by interpreting the rules governing state assignment as constitutive rules in the sense of John Searle.
Directory of Open Access Journals (Sweden)
Vita Solomko
2016-01-01
Full Text Available The energetic structures and conformations of trimethine cyanine dye molecules were investigated. For research, group theoretical and quantum chemical calculation methods were used. The theoretical group analysis of electronic and vibrational structure of molecules was carried out. Also, the energetic structures and conformations of the molecule of this dye were studied. Research shows that the investigated molecule may reside in three different conformational states, one of which is highly symmetric (symmetry C2v and the other two with low symmetry. The third conformer is characterized by lowering of binding energy of the electronic system by 0.23 eV, and the long-wavelength absorption band is shifted to lower energies. Also the group theoretical analysis of the trimethine cyanine molecule had allowed systematizing the vibrational and electronic quantum transitions and identifying the bands in the absorption spectra. It is shown that the excitation of the molecule in S1-state causes trans-cis-isomerization. The presence of the barrier of ~0.1 eV allows the fluorescence process to compete with isomerization process, but isomerization causes a decrease in the fluorescence quantum yield of the dye.
Hundt, P Morten; van Reijzen, Maarten E; Beck, Rainer D; Guo, Han; Jackson, Bret
2017-02-07
Quantum state resolved reactivity measurements probe the role of vibrational symmetry on the vibrational activation of the dissociative chemisorption of CH4 on Ni(111). IR-IR double resonance excitation in a molecular beam was used to prepare CH4 in three different vibrational symmetry components, A1, E, and F2, of the 2ν3 antisymmetric stretch overtone vibration as well as in the ν1+ν3 symmetric plus antisymmetric C-H stretch combination band of F2 symmetry. The quantum state specific dissociation probability S0 (sticking coefficient) was measured for each of the four vibrational states by detecting chemisorbed carbon on Ni(111) as the product of CH4 dissociation by Auger electron spectroscopy. We observe strong mode specificity, where S0 for the most reactive state ν1+ν3 is an order of magnitude higher than for the least reactive, more energetic 2ν3-E state. Our first principles quantum scattering calculations show that as molecules in the ν1 state approach the surface, the vibrational amplitude becomes localized on the reacting C-H bond, making them very reactive. This behavior results from the weakening of the reacting C-H bond as the molecule approaches the surface, decoupling its motion from the three non-reacting C-H stretches. Similarly, we find that overtone normal mode states with more ν1 character are more reactive: S0(2ν1) > S0(ν1 + ν3) > S0(2ν3). The 2ν3 eigenstates excited in the experiment can be written as linear combinations of these normal mode states. The highly reactive 2ν1 and ν1 + ν3 normal modes, being of A1 and F2 symmetry, can contribute to the 2ν3-A1 and 2ν3-F2 eigenstates, respectively, boosting their reactivity over the E component, which contains no ν1 character due to symmetry.
Directory of Open Access Journals (Sweden)
K. S. Kalogerakis
2018-01-01
Full Text Available The question of whether mesospheric OH(v rotational population distributions are in equilibrium with the local kinetic temperature has been debated over several decades. Despite several indications for the existence of non-equilibrium effects, the general consensus has been that emissions originating from low rotational levels are thermalized. Sky spectra simultaneously observing several vibrational levels demonstrated reproducible trends in the extracted OH(v rotational temperatures as a function of vibrational excitation. Laboratory experiments provided information on rotational energy transfer and direct evidence for fast multi-quantum OH(high-v vibrational relaxation by O atoms. We examine the relationship of the new relaxation pathways with the behavior exhibited by OH(v rotational population distributions. Rapid OH(high-v + O multi-quantum vibrational relaxation connects high and low vibrational levels and enhances the hot tail of the OH(low-v rotational distributions. The effective rotational temperatures of mesospheric OH(v are found to deviate from local thermodynamic equilibrium for all observed vibrational levels. Dedicated to Tom G. Slanger in celebration of his 5 decades of research in aeronomy.
Quantum Ground States as Equilibrium Particle-Vacuum Interaction States
Puthoff, Harold E
2012-01-01
A remarkable feature of atomic ground states is that they are observed to be radiationless in nature, despite (from a classical viewpoint) typically involving charged particles in accelerated motions. The simple hydrogen atom is a case in point. This universal groundstate characteristic is shown to derive from particle-vacuum interactions in which a dynamic equilibrium is established between radiation emission due to particle acceleration, and compensatory absorption from the zero-point fluctuations of the vacuum electromagnetic field. The result is a net radiationless ground state. This principle constitutes an overarching constraint that delineates an important feature of quantum ground states.
Generating nonclassical quantum input field states with modulating filters
Energy Technology Data Exchange (ETDEWEB)
Gough, John E. [Aberystwyth University, Department of Physics, Aberystwyth, Wales (United Kingdom); Zhang, Guofeng [The Hong Kong Polytechnic University, Department of Applied Mathematics, Hong Kong (China)
2015-12-15
We give explicit constructions of quantum dynamical filters which generate nonclassical states (coherent states, cat states, shaped single and multi-photon states) of quantum optical fields as inputs to general quantum Markov systems. The filters will be quantum harmonic oscillators damped by the input fields, and we exploit the fact that the cascaded filter and system will have a Lindbladian that is naturally Wick-ordered in the filter modes. In particular the initialization of the modulating filter will determine the signal state generated. (orig.)
Spatial evolution of quantum mechanical states
Christensen, N. D.; Unger, J. E.; Pinto, S.; Su, Q.; Grobe, R.
2018-02-01
The time-dependent Schrödinger equation is solved traditionally as an initial-time value problem, where its solution is obtained by the action of the unitary time-evolution propagator on the quantum state that is known at all spatial locations but only at t = 0. We generalize this approach by examining the spatial evolution from a state that is, by contrast, known at all times t, but only at one specific location. The corresponding spatial-evolution propagator turns out to be pseudo-unitary. In contrast to the real energies that govern the usual (unitary) time evolution, the spatial evolution can therefore require complex phases associated with dynamically relevant solutions that grow exponentially. By introducing a generalized scalar product, for which the spatial generator is Hermitian, one can show that the temporal integral over the probability current density is spatially conserved, in full analogy to the usual norm of the state, which is temporally conserved. As an application of the spatial propagation formalism, we introduce a spatial backtracking technique that permits us to reconstruct any quantum information about an atom from the ionization data measured at a detector outside the interaction region.
Quantum hydrodynamic description of collective nuclear states
Energy Technology Data Exchange (ETDEWEB)
Sapershtein, E.E.; Fayans, S.A.; Khodel' , V.A.
1978-03-01
The nature of low-lying collective nuclear states is analyzed in the framework of the Fermi-liquid approach. It is shown that in a drop of Fermi liquid one has not only the ordinary zero-sound branch but also a new collective mode resulting from the spontaneous breaking of the translational invariance. These are quantum capillary waves that have much in common with ordinary surface excitations of a classical drop. Numerical calculations show that the first collective levels of nuclei belong to this branch.
Semiconductor Nanostructures Quantum States and Electronic Transport
Ihn, Thomas
2009-01-01
This textbook describes the physics of semiconductor nanostructures with emphasis on their electronic transport properties. At its heart are five fundamental transport phenomena: quantized conductance, tunnelling transport, the Aharonov-Bohm effect, the quantum Hall effect, and the Coulomb blockade effect. The book starts out with the basics of solid state and semiconductor physics, such as crystal structure, band structure, and effective mass approximation, including spin-orbit interaction effects important for research in semiconductor spintronics. It contains material aspects such as band e
Han, Jiande; Freel, Keith; Heaven, Michael C.
2011-06-01
We have examined state-to-state rotational and vibrational energy transfers for the vibrational levels (1010000) and (0112000) of C2H2 in the ground electronic state at ambient temperature. Measurements were made using a pulsed IR - UV double resonance technique. Total removal rate constants and state-to-state rotational energy transfer rate constants have been characterized for certain even-numbered rotational levels from J = 0 to 12 within the two vibrational modes. The measured state-to-state rotational energy transfer rate constants were fit to some energy-based empirical scaling and fitting laws, and the rate constants were found to be best reproduced by the statistical power-exponential gap law (PEGL). The measured rate constants were then further evaluated by a kinetic model which simulated the experimental spectra by solving simultaneous first order differential rate equations. Some rotationally-resolved vibrational energy transfer channels were also observed following excitation of (1010000). The vibrational relaxation channels were found to contribute less than 30% to the total removal rate constants of the measured rotational levels for both of the studied vibrational states.
Experimental magic state distillation for fault-tolerant quantum computing.
Souza, Alexandre M; Zhang, Jingfu; Ryan, Colm A; Laflamme, Raymond
2011-01-25
Any physical quantum device for quantum information processing (QIP) is subject to errors in implementation. In order to be reliable and efficient, quantum computers will need error-correcting or error-avoiding methods. Fault-tolerance achieved through quantum error correction will be an integral part of quantum computers. Of the many methods that have been discovered to implement it, a highly successful approach has been to use transversal gates and specific initial states. A critical element for its implementation is the availability of high-fidelity initial states, such as |0〉 and the 'magic state'. Here, we report an experiment, performed in a nuclear magnetic resonance (NMR) quantum processor, showing sufficient quantum control to improve the fidelity of imperfect initial magic states by distilling five of them into one with higher fidelity.
Can a quantum state over time resemble a quantum state at a single time?
Horsman, Dominic; Heunen, Chris; Pusey, Matthew F; Barrett, Jonathan; Spekkens, Robert W
2017-09-01
The standard formalism of quantum theory treats space and time in fundamentally different ways. In particular, a composite system at a given time is represented by a joint state, but the formalism does not prescribe a joint state for a composite of systems at different times. If there were a way of defining such a joint state, this would potentially permit a more even-handed treatment of space and time, and would strengthen the existing analogy between quantum states and classical probability distributions. Under the assumption that the joint state over time is an operator on the tensor product of single-time Hilbert spaces, we analyse various proposals for such a joint state, including one due to Leifer and Spekkens, one due to Fitzsimons, Jones and Vedral, and another based on discrete Wigner functions. Finding various problems with each, we identify five criteria for a quantum joint state over time to satisfy if it is to play a role similar to the standard joint state for a composite system: that it is a Hermitian operator on the tensor product of the single-time Hilbert spaces; that it represents probabilistic mixing appropriately; that it has the appropriate classical limit; that it has the appropriate single-time marginals; that composing over multiple time steps is associative. We show that no construction satisfies all these requirements. If Hermiticity is dropped, then there is an essentially unique construction that satisfies the remaining four criteria.
Moorthi, P. P.; Gunasekaran, S.; Swaminathan, S.; Ramkumaar, G. R.
2015-02-01
A collective experimental and theoretical study was conducted on the molecular structure and vibrational spectra of mannitol. The FT-IR and FT-Raman spectra of mannitol were recorded in the solid phase. The molecular geometry, vibrational frequencies, thermodynamic functions and atomic charges of mannitol in the ground state have been calculated by using the ab initio HF (Hartree-Fock) and density functional methods (B3LYP) invoking cc-pVDZ basis set. The complete vibrational assignments were performed on the basis of Total Energy Distribution (TED) of the vibrational modes. The UV absorption spectra of the title compound dissolved in water. Natural bond orbital analysis has been carried out to explain the charge transfer or delocalization of charge due to the intra-molecular interactions. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO methods. The first order hyperpolarizability (β0) of this novel molecular system and related properties (β, α0 and Δα) of mannitol are calculated using B3LYP/cc-pVDZ and HF/cc-pVDZ methods on the finite-field approach. By using TD-DFT calculation, electronic absorption spectra of the title compound have been predicted and a good agreement with experimental one is established. In addition, the molecular electrostatic potential (MEP) have been investigated using theoretical calculations, the calculated HOMO and LUMO energies shows that the charge transfer within the molecule.
Quantum logic gates using coherent population trapping states
Indian Academy of Sciences (India)
Coherent population trap; quantum computation; controlled phase gate. PACS Nos 42.50.Ex; 32.80.Qk; 32.90+a; 03.67.Lx. Conventional computers handle information in the form of bits – which take up values 0 or. 1. Quantum computers on the other hand, use quantum bits (qubits), which can be prepared in states 0, 1 or ...
Protected State Transfer via an Approximate Quantum Adder.
Gatti, G; Barberena, D; Sanz, M; Solano, E
2017-07-31
We propose a decoherence protected protocol for sending single photon quantum states through depolarizing channels. This protocol is implemented via an approximate quantum adder engineered through spontaneous parametric down converters, and shows higher success probability than distilled quantum teleportation protocols for distances below a threshold depending on the properties of the channel.
Erratum to "Quantum Limits of Eisenstein Series and Scattering States''
DEFF Research Database (Denmark)
Petridis, Y.N.; Raulf, N.; Risager, Morten S.
2013-01-01
We identify the quantum limits of scattering states for the modular surface. This is obtained through the study of quantum measures of non-holomorphic Eisenstein series away from the critical line. We provide a range of stability for the quantum unique ergodicity theorem of Luo and Sarnak. © Cana....... © Canadian Mathematical Society 2012....
Quantum limits of Eisenstein series and scattering states
DEFF Research Database (Denmark)
Petridis, Y.N.; Raulf, N.; Risager, Morten S.
2013-01-01
We identify the quantum limits of scattering states for the modular surface. This is obtained through the study of quantum measures of non-holomorphic Eisenstein series away from the critical line. We provide a range of stability for the quantum unique ergodicity theorem of Luo and Sarnak....
Finding resource states of measurement-based quantum computing is harder than quantum computing
Morimae, Tomoyuki
2017-11-01
Measurement-based quantum computing enables universal quantum computing with only adaptive single-qubit measurements on certain many-qubit states, such as the graph state, the Affleck-Kennedy-Lieb-Tasaki (AKLT) state, and several tensor-network states. Finding new resource states of measurement-based quantum computing is a hard task, since for a given state there are exponentially many possible measurement patterns on the state. In this paper, we consider the problem of deciding, for a given state and a set of unitary operators, whether there exists a way of measurement-based quantum computing on the state that can realize all unitaries in the set, or not. We show that the decision problem is QCMA-hard (where QCMA stands for quantum classical Merlin Arthur), which means that finding new resource states of measurement-based quantum computing is harder than quantum computing itself [unless BQP (bounded-error quantum polynomial time) is equal to QCMA]. We also derive an upper bound of the decision problem: the problem is in a quantum version of the second level of the polynomial hierarchy.
Quantum Entanglement in Random Physical States
Hamma, Alioscia; Santra, Siddhartha; Zanardi, Paolo
2012-07-01
Most states in the Hilbert space are maximally entangled. This fact has proven useful to investigate—among other things—the foundations of statistical mechanics. Unfortunately, most states in the Hilbert space of a quantum many-body system are not physically accessible. We define physical ensembles of states acting on random factorized states by a circuit of length k of random and independent unitaries with local support. We study the typicality of entanglement by means of the purity of the reduced state. We find that for a time k=O(1), the typical purity obeys the area law. Thus, the upper bounds for area law are actually saturated, on average, with a variance that goes to zero for large systems. Similarly, we prove that by means of local evolution a subsystem of linear dimensions L is typically entangled with a volume law when the time scales with the size of the subsystem. Moreover, we show that for large values of k the reduced state becomes very close to the completely mixed state.
Equivalence of Quantum Resource Measures for X States
Huang, Zhiming; Zhang, Cai; Zhang, Wei; Zhao, Lianghui
2017-11-01
In this paper, we investigate some X states, quantum resource measures of which are equivalent. We find that for a class of X states, trace norm geometric quantum discord (TGQD), trace norm measurement-induced nonlocality (TMIN) and l 1 norm quantum coherence (L1QC) are all equal, and for some special states, therein two measures are equal. We also exemplify relative application of the equivalent relations.
Multiple-state quantum Otto engine, 1D box system
Latifah, E.; Purwanto, A.
2014-03-01
Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes.
Multiple-state quantum Otto engine, 1D box system
Energy Technology Data Exchange (ETDEWEB)
Latifah, E., E-mail: enylatifah@um.ac.id [Laboratory of Theoretical Physics and Natural Philosophy, Physics Department, Institut Teknologi Sepuluh Nopember, ITS, Surabaya, Indonesia and Physics Department, Malang State University (Indonesia); Purwanto, A. [Laboratory of Theoretical Physics and Natural Philosophy, Physics Department, Institut Teknologi Sepuluh Nopember, ITS, Surabaya (Indonesia)
2014-03-24
Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes.
Information Divergence and Distance Measures for Quantum States
Jiang, Nan; Zhang, Zhaozhi
2015-02-01
Both information divergence and distance are measures of closeness of two quantum states which are widely used in the theory of information processing and quantum cryptography. For example, the quantum relative entropy and trace distance are well known. Here we introduce a number of new quantum information divergence and distance measures into the literature and discuss their relations and properties. We also propose a method to analyze the properties and relations of various distance and pseudo-distance measures.
Photo-vibrational spectroscopy using quantum cascade laser and laser Doppler vibrometer
Liu, Huan; Hu, Qi; Xie, Jiecheng; Fu, Yu
2017-06-01
Photoacoustic/photothermal spectroscopy is an established technique for detection of chemicals and explosives. However, prior sample preparation is required and the analysis is conducted in a sealed space with a high-sensitivity sensor coupled with a lock-in amplifier, limiting the technique to applications in a controllable laboratory environment. Hence, this technique may not be suitable for defense and security applications where the detection of explosives or hazardous chemicals is required in an open environment at a safe standoff distance. In this study, chemicals in various forms were excited by an intensity-modulated quantum cascade laser (QCL), while a laser Doppler vibrometer (LDV) was applied to detect the vibration signal resulting from the photocoustic/photothermal effect. The photo-vibrational spectrum obtained by scanning the QCL's wavelength in MIR range, coincides well with the corresponding spectrum obtained using typical FTIR equipment. The experiment in short and long standoff distances demonstrated that the LDV is a capable sensor for chemical detection in an open environment.
Srivastava, Anubha; Joshi, B. D.; Tandon, Poonam; Ayala, A. P.; Bansal, A. K.; Grillo, Damián
2013-02-01
Imatinib mesylate, 4-(4-methyl-piperazin-1-ylmethyl)-N-u[4-methyl-3-(4-pyridin-3-yl)pyrimidine-2-ylamino)phenyl]benzamide methanesulfonate is a therapeutic drug that is approved for the treatment of chronic myelogeneous leukemia (CML) and gastrointestinal stromal tumors (GIST). It is known that imatinib mesylate exists in two polymorphic forms α and β. However, β-form is more stable than the α-form. In this work, we present a detailed vibrational spectroscopic investigation of β-form by using FT-IR and FT-Raman spectra. These data are supported by quantum mechanical calculations using DFT employing 6-311G(d,p) basis set, which allow us to characterize completely the vibrational spectra of this compound. The FT-IR spectrum of α-form has also been discussed. The importance of hydrogen-bond formation in the molecular packing arrangements of both forms has been examined with the vibrational shifts observed due to polymorphic changes. The red shift of the NH stretching bands in the infrared spectrum from the computed wavenumber indicates the weakening of the NH bond. The UV-vis spectroscopic studies along with the HOMO-LUMO analysis of both polymorphs (α and β) were performed and their chemical activity has been discussed. The TD-DFT method was used to calculate the electronic absorption spectra in the gas phase as well as in the solvent environment using IEF-PCM model and 6-31G basis set. Finally, the results obtained complements to the experimental findings.
Non-classical state engineering for quantum networks
Energy Technology Data Exchange (ETDEWEB)
Vollmer, Christina E.
2014-01-24
The wide field of quantum information processing and quantum networks has developed very fast in the last two decades. Besides the regime of discrete variables, which was developed first, the regime of continuous variables represents an alternative approach to realize many quantum applications. Non-classical states of light, like squeezed or entangled states, are a fundamental resource for quantum applications like quantum repeaters, quantum memories, quantum key distribution, quantum spectroscopy, and quantum metrology. These states can be generated successfully in the infrared wavelength regime. However, for some tasks other wavelengths, especially in the visible wavelength regime, are desirable. To generate non-classical states of light in this wavelength regime frequency up-conversion can be used, since all quantum properties are maintained in this process. The first part of this thesis deals with the experimental frequency up-conversion of quantum states. Squeezed vacuum states of light at 1550 nm were up-converted to 532 nm and a noise reduction of -1.5 dB at 532 nm was achieved. These states can be used for increasing the sensitivity of gravitational wave detectors or spectroscopic measurements. Furthermore, one part of an entangled state at 1550 nm was up-converted to 532 nm and, thus, entanglement between these two wavelengths was generated and characterized to -1.4 dB following Duan et al. With such a quantum link it is possible to establish a quantum network, which takes advantage of the low optical loss at 1550 nm for information transmission and of atomic transitions around 532 nm for a quantum memory in a quantum repeater. For quantum networks the distribution of entanglement and especially of a quantum key is essential. In the second part of this thesis the experimental distribution of entanglement by separable states is demonstrated. The underlying protocol requires a special three-mode state, which is separable in two of the three splittings. With
Random Bosonic States for Robust Quantum Metrology
Directory of Open Access Journals (Sweden)
M. Oszmaniec
2016-12-01
Full Text Available We study how useful random states are for quantum metrology, i.e., whether they surpass the classical limits imposed on precision in the canonical phase sensing scenario. First, we prove that random pure states drawn from the Hilbert space of distinguishable particles typically do not lead to superclassical scaling of precision even when allowing for local unitary optimization. Conversely, we show that random pure states from the symmetric subspace typically achieve the optimal Heisenberg scaling without the need for local unitary optimization. Surprisingly, the Heisenberg scaling is observed for random isospectral states of arbitrarily low purity and preserved under loss of a fixed number of particles. Moreover, we prove that for pure states, a standard photon-counting interferometric measurement suffices to typically achieve resolution following the Heisenberg scaling for all values of the phase at the same time. Finally, we demonstrate that metrologically useful states can be prepared with short random optical circuits generated from three types of beam splitters and a single nonlinear (Kerr-like transformation.
Preparation and coherent manipulation of pure quantum states of a single molecular ion
Chou, Chin-Wen; Kurz, Christoph; Hume, David B.; Plessow, Philipp N.; Leibrandt, David R.; Leibfried, Dietrich
2017-05-01
Laser cooling and trapping of atoms and atomic ions has led to advances including the observation of exotic phases of matter, the development of precision sensors and state-of-the-art atomic clocks. The same level of control in molecules could also lead to important developments such as controlled chemical reactions and sensitive probes of fundamental theories, but the vibrational and rotational degrees of freedom in molecules pose a challenge for controlling their quantum mechanical states. Here we use quantum-logic spectroscopy, which maps quantum information between two ion species, to prepare and non-destructively detect quantum mechanical states in molecular ions. We develop a general technique for optical pumping and preparation of the molecule into a pure initial state. This enables us to observe high-resolution spectra in a single ion (CaH+) and coherent phenomena such as Rabi flopping and Ramsey fringes. The protocol requires a single, far-off-resonant laser that is not specific to the molecule, so many other molecular ions, including polyatomic species, could be treated using the same methods in the same apparatus by changing the molecular source. Combined with the long interrogation times afforded by ion traps, a broad range of molecular ions could be studied with unprecedented control and precision. Our technique thus represents a critical step towards applications such as precision molecular spectroscopy, stringent tests of fundamental physics, quantum computing and precision control of molecular dynamics.
Preparation and coherent manipulation of pure quantum states of a single molecular ion.
Chou, Chin-Wen; Kurz, Christoph; Hume, David B; Plessow, Philipp N; Leibrandt, David R; Leibfried, Dietrich
2017-05-10
Laser cooling and trapping of atoms and atomic ions has led to advances including the observation of exotic phases of matter, the development of precision sensors and state-of-the-art atomic clocks. The same level of control in molecules could also lead to important developments such as controlled chemical reactions and sensitive probes of fundamental theories, but the vibrational and rotational degrees of freedom in molecules pose a challenge for controlling their quantum mechanical states. Here we use quantum-logic spectroscopy, which maps quantum information between two ion species, to prepare and non-destructively detect quantum mechanical states in molecular ions. We develop a general technique for optical pumping and preparation of the molecule into a pure initial state. This enables us to observe high-resolution spectra in a single ion (CaH+) and coherent phenomena such as Rabi flopping and Ramsey fringes. The protocol requires a single, far-off-resonant laser that is not specific to the molecule, so many other molecular ions, including polyatomic species, could be treated using the same methods in the same apparatus by changing the molecular source. Combined with the long interrogation times afforded by ion traps, a broad range of molecular ions could be studied with unprecedented control and precision. Our technique thus represents a critical step towards applications such as precision molecular spectroscopy, stringent tests of fundamental physics, quantum computing and precision control of molecular dynamics.
Security enhanced memory for quantum state.
Mukai, Tetsuya
2017-07-27
Security enhancement is important in terms of both classical and quantum information. The recent development of a quantum storage device is noteworthy, and a coherence time of one second or longer has been demonstrated. On the other hand, although the encryption of a quantum bit or quantum memory has been proposed theoretically, no experiment has yet been carried out. Here we report the demonstration of a quantum memory with an encryption function that is realized by scrambling and retrieving the recorded quantum phase. We developed two independent Ramsey interferometers on an atomic ensemble trapped below a persistent supercurrent atom chip. By operating the two interferometers with random phases, the quantum phase recorded by a pulse of the first interferometer was modulated by the second interferometer pulse. The scrambled quantum phase was restored by employing another pulse of the second interferometer with a specific time delay. This technique paves way for improving the security of quantum information technology.
Khater, Brahim; Guillemin, Jean-Claude; Benidar, Abdessamad; Bégué, Didier; Pouchan, Claude
2008-12-14
Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH(2)=CHPH(2) x BH(3)), a donor-acceptor complex. The gas phase infrared spectra (3500-600 cm(-1)) have been recorded at 0.5 cm(-1) resolution. This first primary alpha,beta-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH(2)=CHPH(2) and the monoborane BH(3) which dimerizes to form the more stable diborane B(2)H(6). Spectra of free CH(2)=CHPH(2) and B(2)H(6) compounds were also recorded to assign some vibration modes of the complex in very dense spectral regions. The analysis was completed by carrying out quantum mechanical calculations by density functional theory method at the B3LYP/6-31+G(**) level. Anharmonic frequencies and infrared intensities of the two predicted gauche and syn conformers of the vinylphosphine-borane complex were calculated in the 3500-100 cm(-1) region with the use of a variational approach, implemented in the P_ANHAR_V1.2 code. Because of the relatively weak interaction between the vinylphosphine and the monoborane, the vibrations of the complex can easily be subdivided into modes localized in the CH(2)=CHPH(2) and BH(3) moieties and into "intermolecular" modes. Localized modes are unambiguously correlated with the modes of the isolated monomers. Therefore, they are described in terms of the monomer vibrations, and the complexation shifts are defined as Delta nu = nu(complex) - nu(monomer) to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH(3) monomer and the stable gauche and syn conformers of the free vinylphosphine were obtained at the same level of theory. In the gas phase, only the syn form of the complex was observed and assigned. All theoretically predicted frequencies and complexation shifts in magnitude and
El-Mansy, M. A. M.
2017-08-01
Structural and vibrational spectroscopic studies were performed on indigo carmine (IC) isomers using FT-IR spectral analysis along with DFT/B3LYP method utilizing Gaussian 09 software. GaussView 5 program has been employed to perform a detailed interpretation of vibrational spectra. Simulation of infrared spectra has led to an excellent overall agreement with the observed spectral patterns. Mulliken population analyses on atomic charges, MEP, HOMO-LUMO, NLO, first order hyperpolarizability and thermodynamic properties have been examined by (DFT/B3LYP) method with the SDD basis set level. Density of state spectra (DOS) were calculated using GaussSum 3 at the same level of theory. Molecular modeling approved that DOS Spectra are the most significant tools for differentiating between two IC isomers so far. Moreover, The IC isomers (cis-isomer) have shown an extended applicability for manufacturing both NLO and photovoltaic devices such as solar cells.
Quantum Entanglement Swapping between Two Multipartite Entangled States.
Su, Xiaolong; Tian, Caixing; Deng, Xiaowei; Li, Qiang; Xie, Changde; Peng, Kunchi
2016-12-09
Quantum entanglement swapping is one of the most promising ways to realize the quantum connection among local quantum nodes. In this Letter, we present an experimental demonstration of the entanglement swapping between two independent multipartite entangled states, each of which involves a tripartite Greenberger-Horne-Zeilinger (GHZ) entangled state of an optical field. The entanglement swapping is implemented deterministically by means of a joint measurement on two optical modes coming from the two multipartite entangled states respectively and the classical feedforward of the measurement results. After entanglement swapping the two independent multipartite entangled states are merged into a large entangled state in which all unmeasured quantum modes are entangled. The entanglement swapping between a tripartite GHZ state and an Einstein-Podolsky-Rosen entangled state is also demonstrated and the dependence of the resultant entanglement on transmission loss is investigated. The presented experiment provides a feasible technical reference for constructing more complicated quantum networks.
Operating Quantum States in Single Magnetic Molecules: Implementation of Grover's Quantum Algorithm.
Godfrin, C; Ferhat, A; Ballou, R; Klyatskaya, S; Ruben, M; Wernsdorfer, W; Balestro, F
2017-11-03
Quantum algorithms use the principles of quantum mechanics, such as, for example, quantum superposition, in order to solve particular problems outperforming standard computation. They are developed for cryptography, searching, optimization, simulation, and solving large systems of linear equations. Here, we implement Grover's quantum algorithm, proposed to find an element in an unsorted list, using a single nuclear 3/2 spin carried by a Tb ion sitting in a single molecular magnet transistor. The coherent manipulation of this multilevel quantum system (qudit) is achieved by means of electric fields only. Grover's search algorithm is implemented by constructing a quantum database via a multilevel Hadamard gate. The Grover sequence then allows us to select each state. The presented method is of universal character and can be implemented in any multilevel quantum system with nonequal spaced energy levels, opening the way to novel quantum search algorithms.
Operating Quantum States in Single Magnetic Molecules: Implementation of Grover's Quantum Algorithm
Godfrin, C.; Ferhat, A.; Ballou, R.; Klyatskaya, S.; Ruben, M.; Wernsdorfer, W.; Balestro, F.
2017-11-01
Quantum algorithms use the principles of quantum mechanics, such as, for example, quantum superposition, in order to solve particular problems outperforming standard computation. They are developed for cryptography, searching, optimization, simulation, and solving large systems of linear equations. Here, we implement Grover's quantum algorithm, proposed to find an element in an unsorted list, using a single nuclear 3 /2 spin carried by a Tb ion sitting in a single molecular magnet transistor. The coherent manipulation of this multilevel quantum system (qudit) is achieved by means of electric fields only. Grover's search algorithm is implemented by constructing a quantum database via a multilevel Hadamard gate. The Grover sequence then allows us to select each state. The presented method is of universal character and can be implemented in any multilevel quantum system with nonequal spaced energy levels, opening the way to novel quantum search algorithms.
Large electron transfer rate effects from the Duschinsky mixing of vibrations
DEFF Research Database (Denmark)
Sando, Gerald M.; Spears, Kenneth G; Hupp, Joseph T
2001-01-01
vibrations are very important. The Duschinsky effect arises when two electronic states have vibrational normal mode coordinate systems that are rotated and translated relative to each other. We use a conventional quantum rate model for ET, and the examples include 6-8 vibrations, where two vibrational modes...
Nuclear quantum state engineering in ion channeling regime
Directory of Open Access Journals (Sweden)
Berec Vesna
2015-01-01
Full Text Available A key challenge in quantum state engineering is to identify coherent quantum mechanical systems that can be precisely manipulated and scaled, but at the same time to allow decoupling from unwanted interactions. Such systems, once realized, would represent an efficient tool for characterization of quantum behavior reflected in the properties of matter with prerequisites for meeting dissipation constraints imposed in the nuclear physics as well in the quantum information theory. Using the pure29Si nanocrystal system we present a novel high resolution method for initialization of single electron polarized spin interaction and control of nuclear spin qubits. The presented study fuses field of particle channeling in MeV energy regime with quantum state engineering utilized via entanglement as an essential quantum property. Its aim is to bring focus on new theoretical proposals testing the quantum mechanical models for systems producible at particle accelerator facilities.
Error Free Quantum Reading by Quasi Bell State of Entangled Coherent States
Hirota, Osamu
2017-12-01
Nonclassical states of light field have been exploited to provide marvellous results in quantum information science. Usefulness of nonclassical states in quantum information science depends on whether a physical parameter as a signal is continuous or discrete. Here we present an investigation of the potential of quasi Bell states of entangled coherent states in quantum reading of the classical digital memory which was pioneered by Pirandola (Phys.Rev.Lett.,106,090504,2011). This is a typical example of discrimination for discrete quantum parameters. We show that the quasi Bell state gives the error free performance in the quantum reading that cannot be obtained by any classical state.
Bound Electron States in Skew-symmetric Quantum Wire Intersections
2014-01-01
for electronic transport studies was to confine resonant- tunneling heterostructures laterally with a fabrication-imposed po- tential. This approach...Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 Quantum Wires, Crossed Nanowires , Trapped Electron States, Quantum Dots REPORT...realistic systems such as semiconductor nanowire films and carbon nanotube bundles. Bound electron states in skew-symmetric quantum wire intersections by
Relativistic quantum correlations in bipartite fermionic states
Indian Academy of Sciences (India)
2016-09-21
Sep 21, 2016 ... quantum information brought to fore the relative beha- viour of entanglement. It is an observer-dependent quantity which degrades with acceleration from the perspective of accelerated observer. On the other hand, correlations other than entanglement exist in quantum system whose benefits in quantum ...
Quantum nonlinear lattices and coherent state vectors
DEFF Research Database (Denmark)
Ellinas, Demosthenes; Johansson, M.; Christiansen, Peter Leth
1999-01-01
for the CSV parameters. The so obtained evolution equations are intimately related to the respective evolution equations for the classical lattices, provided we account for the ordering rules (normal, symmetric) adopted for their quantization. Analysing the geometrical content of the factorization ansatz made......Quantized nonlinear lattice models are considered for two different classes, boson and fermionic ones. The quantum discrete nonlinear Schrodinger model (DNLS) is our main objective, but its so called modified discrete nonlinear (MDNLS) version is also included, together with the fermionic polaron...... (FP) model. Based on the respective dynamical symmetries of the models, a method is put forward which by use of the associated boson and spin coherent state vectors (CSV) and a factorization ansatz for the solution of the Schrodinger equation, leads to quasiclassical Hamiltonian equations of motion...
Kremer, Gilberto M.; Kunova, Olga V.; Kustova, Elena V.; Oblapenko, George P.
2018-01-01
A detailed kinetic-theory model for the vibrationally state-resolved transport coefficients is developed taking into account the dependence of the collision cross section on the size of vibrationally excited molecule. Algorithms for the calculation of shear and bulk viscosity, thermal conductivity, thermal diffusion and diffusion coefficients for vibrational states are proposed. The transport coefficients are evaluated for single-component diatomic gases N2, O2, NO, H2, Cl2 in the wide range of temperature, and the effects of molecular diameters and the number of accounted states are discussed. The developed model is applied to study wave propagation in diatomic gases. For the case of initial Boltzmann distribution, the influence of vibrational excitation on the phase velocity and attenuation coefficient is found to be weak. We expect more significant effect in the case of initial thermal non-equilibrium, for instance in gases with optically pumped selected vibrational states.
The structure of states and maps in quantum theory
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 73; Issue 3. The structure of states and maps in quantum theory ... Quantum state spaces and maps on them have rich convex structures arising from the superposition principle and consequent entanglement. Communication channels (physical processes) in the ...
Quantum State Generation and Entanglement Manipulation Using Linear Optics
ÖZDEMİR, Şahin Kaya; Yamamoto, Takashi; Koashi, Masato
2014-01-01
Quantum information processing (QIP) requires unitary operations, measurements and synthesis, manipulation and characterization of arbitrary quantum states. Linear optics provides efficient tools for these purposes. In this review paper, we introduce the elements of linear optics toolbox, and briefly discuss some experimental and theoretical investigations using this toolbox. Our main focus will be the qubit state generation and entanglement extraction using linear optics toolbox.
From Shannon to Quantum Information Science-Mixed States
Indian Academy of Sciences (India)
... Journals; Resonance – Journal of Science Education; Volume 7; Issue 5. From Shannon to Quantum Information Science - Mixed States. Rajiah Simon. General Article Volume 7 Issue 5 May 2002 pp 16-33 ... Keywords. Mixed states; entanglement witnesses; partial transpose; quantum computers; von Neumann entropy ...
Moorthi, P P; Gunasekaran, S; Swaminathan, S; Ramkumaar, G R
2015-02-25
A collective experimental and theoretical study was conducted on the molecular structure and vibrational spectra of mannitol. The FT-IR and FT-Raman spectra of mannitol were recorded in the solid phase. The molecular geometry, vibrational frequencies, thermodynamic functions and atomic charges of mannitol in the ground state have been calculated by using the ab initio HF (Hartree-Fock) and density functional methods (B3LYP) invoking cc-pVDZ basis set. The complete vibrational assignments were performed on the basis of Total Energy Distribution (TED) of the vibrational modes. The UV absorption spectra of the title compound dissolved in water. Natural bond orbital analysis has been carried out to explain the charge transfer or delocalization of charge due to the intra-molecular interactions. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO methods. The first order hyperpolarizability (β0) of this novel molecular system and related properties (β, α0 and Δα) of mannitol are calculated using B3LYP/cc-pVDZ and HF/cc-pVDZ methods on the finite-field approach. By using TD-DFT calculation, electronic absorption spectra of the title compound have been predicted and a good agreement with experimental one is established. In addition, the molecular electrostatic potential (MEP) have been investigated using theoretical calculations, the calculated HOMO and LUMO energies shows that the charge transfer within the molecule. Copyright © 2014 Elsevier B.V. All rights reserved.
Mukuta, Tatsuhiko; Fukazawa, Naoto; Murata, Kei; Inagaki, Akiko; Akita, Munetaka; Tanaka, Sei'ichi; Koshihara, Shin-ya; Onda, Ken
2014-03-03
This work involved a detailed investigation into the infrared vibrational spectra of ruthenium polypyridyl complexes, specifically heteroleptic [Ru(bpy)2(bpm)](2+) (bpy = 2,2'-bipyridine and bpm = 2,2'-bipyrimidine) and homoleptic [Ru(bpy)3](2+), in the excited triplet state. Transient spectra were acquired 500 ps after photoexcitation, corresponding to the vibrational ground state of the excited triplet state, using time-resolved infrared spectroscopy. We assigned the observed bands to specific ligands in [Ru(bpy)2(bpm)](2+) based on the results of deuterium substitution and identified the corresponding normal vibrational modes using quantum-chemical calculations. Through this process, the more complex vibrational bands of [Ru(bpy)3](2+) were assigned to normal vibrational modes. The results are in good agreement with the model in which excited electrons are localized on a single ligand. We also found that the vibrational bands of both complexes associated with the ligands on which electrons are little localized appear at approximately 1317 and 1608 cm(-1). These assignments should allow the study of the reaction dynamics of various photofunctional systems including ruthenium polypyridyl complexes.
Quantum State Transfer via Noisy Photonic and Phononic Waveguides.
Vermersch, B; Guimond, P-O; Pichler, H; Zoller, P
2017-03-31
We describe a quantum state transfer protocol, where a quantum state of photons stored in a first cavity can be faithfully transferred to a second distant cavity via an infinite 1D waveguide, while being immune to arbitrary noise (e.g., thermal noise) injected into the waveguide. We extend the model and protocol to a cavity QED setup, where atomic ensembles, or single atoms representing quantum memory, are coupled to a cavity mode. We present a detailed study of sensitivity to imperfections, and apply a quantum error correction protocol to account for random losses (or additions) of photons in the waveguide. Our numerical analysis is enabled by matrix product state techniques to simulate the complete quantum circuit, which we generalize to include thermal input fields. Our discussion applies both to photonic and phononic quantum networks.
Quantum State Transfer via Noisy Photonic and Phononic Waveguides
Vermersch, B.; Guimond, P.-O.; Pichler, H.; Zoller, P.
2017-03-01
We describe a quantum state transfer protocol, where a quantum state of photons stored in a first cavity can be faithfully transferred to a second distant cavity via an infinite 1D waveguide, while being immune to arbitrary noise (e.g., thermal noise) injected into the waveguide. We extend the model and protocol to a cavity QED setup, where atomic ensembles, or single atoms representing quantum memory, are coupled to a cavity mode. We present a detailed study of sensitivity to imperfections, and apply a quantum error correction protocol to account for random losses (or additions) of photons in the waveguide. Our numerical analysis is enabled by matrix product state techniques to simulate the complete quantum circuit, which we generalize to include thermal input fields. Our discussion applies both to photonic and phononic quantum networks.
Multi-bit dark state memory: Double quantum dot as an electronic quantum memory
Aharon, Eran; Pozner, Roni; Lifshitz, Efrat; Peskin, Uri
2016-12-01
Quantum dot clusters enable the creation of dark states which preserve electrons or holes in a coherent superposition of dot states for a long time. Various quantum logic devices can be envisioned to arise from the possibility of storing such trapped particles for future release on demand. In this work, we consider a double quantum dot memory device, which enables the preservation of a coherent state to be released as multiple classical bits. Our unique device architecture uses an external gating for storing (writing) the coherent state and for retrieving (reading) the classical bits, in addition to exploiting an internal gating effect for the preservation of the coherent state.
DEFF Research Database (Denmark)
Johansen, Jeppe; Stobbe, Søren; Nikolaev, I.S.
2007-01-01
We have measured time-resolved spontaneous emission from quantum dots near a dielectric interface with known photonic local density of states. We thus experimentally determine the quantum efficiency and the dipole moment, important for quantum optics.......We have measured time-resolved spontaneous emission from quantum dots near a dielectric interface with known photonic local density of states. We thus experimentally determine the quantum efficiency and the dipole moment, important for quantum optics....
Quantum broadcast scheme and multi-output quantum teleportation via four-qubit cluster state
Yu, Yan; Zha, Xin Wei; Li, Wei
2017-02-01
In this paper, two theoretical schemes of the arbitrary single-qubit states via four-qubit cluster state are proposed. One is three-party quantum broadcast scheme, which realizes the broadcast among three participants. The other is multi-output quantum teleportation. Both allow two distant receivers to simultaneously and deterministically obtain the arbitrary single-qubit states, respectively. Compared with former schemes of an arbitrary single-qubit state, the proposed schemes realize quantum multi-cast communication efficiently, which enables Bob and Charlie to obtain the states simultaneously in the case of just knowing Alice's measurement results. The proposed schemes play an important role in quantum information, specially in secret sharing and quantum teleportation.
Generation of Exotic Quantum States of a Cold Atomic Ensemble
DEFF Research Database (Denmark)
Christensen, Stefan Lund
Over the last decades quantum effects have become more and more controllable, leading to the implementations of various quantum information protocols. These protocols are all based on utilizing quantum correlation. In this thesis we consider how states of an atomic ensemble with such correlations...... can be created and characterized. First we consider a spin-squeezed state. This state is generated by performing quantum non-demolition measurements of the atomic population difference. We show a spectroscopically relevant noise reduction of -1.7dB, the ensemble is in a many-body entangled state...... — a nanofiber based light-atom interface. Using a dual-frequency probing method we measure and prepare an ensemble with a sub-Poissonian atom number distribution. This is a first step towards the implementation of more exotic quantum states....
Fractional quantum Hall states of bosons on cones
Wu, Ying-Hai; Tu, Hong-Hao; Sreejith, G. J.
2017-09-01
Motivated by a recent experiment, which synthesizes Landau levels for photons on cones [Schine et al., Nature (London) 534, 671 (2016), 10.1038/nature17943], and more generally the interest in understanding gravitational responses of quantum Hall states, we study fractional quantum Hall states of bosons on cones. A variety of trial wave functions for conical systems are constructed and compared with exact diagonalization results. The tip of a cone is a localized geometrical defect with singular curvature, which can modify the density profiles of quantum Hall states. The density profiles on cones can be used to extract some universal information about quantum Hall states. The values of certain quantities are computed numerically using the density profiles of some quantum Hall states and they agree with analytical predictions.
Bimetric Theory of Fractional Quantum Hall States
Gromov, Andrey; Son, Dam Thanh
2017-10-01
We present a bimetric low-energy effective theory of fractional quantum Hall (FQH) states that describes the topological properties and a gapped collective excitation, known as the Girvin-Macdonald-Platzman (GMP) mode. The theory consists of a topological Chern-Simons action, coupled to a symmetric rank-2 tensor, and an action à la bimetric gravity, describing the gapped dynamics of a spin-2 mode. The theory is formulated in curved ambient space and is spatially covariant, which allows us to restrict the form of the effective action and the values of phenomenological coefficients. Using bimetric theory, we calculate the projected static structure factor up to the k6 order in the momentum expansion. To provide further support for the theory, we derive the long-wave limit of the GMP algebra, the dispersion relation of the GMP mode, and the Hall viscosity of FQH states. The particle-hole (PH) transformation of the theory takes a very simple form, making the duality between FQH states and their PH conjugates manifest. We also comment on the possible applications to fractional Chern insulators, where closely related structures arise. It is shown that the familiar FQH observables acquire a curious geometric interpretation within the bimetric formalism.
Bimetric Theory of Fractional Quantum Hall States
Directory of Open Access Journals (Sweden)
Andrey Gromov
2017-11-01
Full Text Available We present a bimetric low-energy effective theory of fractional quantum Hall (FQH states that describes the topological properties and a gapped collective excitation, known as the Girvin-Macdonald-Platzman (GMP mode. The theory consists of a topological Chern-Simons action, coupled to a symmetric rank-2 tensor, and an action à la bimetric gravity, describing the gapped dynamics of a spin-2 mode. The theory is formulated in curved ambient space and is spatially covariant, which allows us to restrict the form of the effective action and the values of phenomenological coefficients. Using bimetric theory, we calculate the projected static structure factor up to the k^{6} order in the momentum expansion. To provide further support for the theory, we derive the long-wave limit of the GMP algebra, the dispersion relation of the GMP mode, and the Hall viscosity of FQH states. The particle-hole (PH transformation of the theory takes a very simple form, making the duality between FQH states and their PH conjugates manifest. We also comment on the possible applications to fractional Chern insulators, where closely related structures arise. It is shown that the familiar FQH observables acquire a curious geometric interpretation within the bimetric formalism.
Energy Technology Data Exchange (ETDEWEB)
Ramírez-Porras, A., E-mail: aramirez@fisica.ucr.ac.cr [Centro de Investigación en Ciencia e Ingeniería de Materiales (CICIMA), Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); García, O. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Química, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Vargas, C. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Corrales, A. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Escuela de Química, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica); Solís, J.D. [Escuela de Física, Universidad de Costa Rica, San Pedro de Montes de Oca 11501 (Costa Rica)
2015-08-30
Highlights: • PL spectra of porous silicon samples have been studied using a stochastic model. • This model can deconvolute PL spectra into three components. • Quantum dots, quantum wires and localized states have been identified. • Nanostructure diameters are in the range from 2.2 nm to 4.0 nm. • Contributions from quantum wires are small compared to the others. - Abstract: Nanocrystallites of Silicon have been produced by electrochemical etching of crystal wafers. The obtained samples show photoluminescence in the red band of the visible spectrum when illuminated by ultraviolet light. The photoluminescence spectra can be deconvolved into three components according to a stochastic quantum confinement model: one band coming from Nanocrystalline dots, or quantum dots, one from Nanocrystalline wires, or quantum wires, and one from the presence of localized surface states related to silicon oxide. The results fit well within other published models.
Generation and storage of quantum states using cold atoms
DEFF Research Database (Denmark)
Dantan, Aurelien Romain; Josse, Vincent; Cviklinski, Jean
2006-01-01
Cold cesium or rubidium atomic samples have a good potential both for generation and storage of nonclassical states of light. Generation of nonclassical states of light is possible through the high non-linearity of cold atomic samples excited close to a resonance line. Quadrature squeezing......, polarization squeezing and entanglement have been demonstrated. Quantum state storage is made possible by the presence of long-lived angular momentum in the ground state. Cold atoms are thus a promising resource in quantum information....
Concrete Quantum Logics and Δ -Logics, States and Δ -States
Hroch, Michal; Pták, Pavel
2017-12-01
By a concrete quantum logic (in short, by a logic) we mean the orthomodular poset that is set-representable. If L=({Ω },L) is a logic and L is closed under the formation of symmetric difference, Δ , we call L a Δ -logic. In the first part we situate the known results on logics and states to the context of Δ -logics and Δ -states (the Δ -states are the states that are subadditive with respect to the symmetric difference). Moreover, we observe that the rather prominent logic E^{ {even}}_{Ω } of all even-coeven subsets of the countable set Ω possesses only Δ -states. Then we show when a state on the logics given by the divisibility relation allows for an extension as a state. In the next paragraph we consider the so called density logic and its Δ -closure. We find that the Δ -closure coincides with the power set. Then we investigate other properties of the density logic and its factor.
Energy Technology Data Exchange (ETDEWEB)
Jeon, Jonggu; Cho, Minhaeng, E-mail: mcho@korea.ac.k [Department of Chemistry, Korea University, Seoul 136-701 (Korea, Republic of)
2010-06-15
Multidimensional infrared (IR) spectroscopy has emerged as a viable tool to study molecular structure and dynamics in condensed phases, and the third-order vibrational response function is the central quantity underlying various nonlinear IR spectroscopic techniques, such as pump-probe, photon echo and two-dimensional (2D) IR spectroscopy. In this paper, a new computational method is presented that calculates this nonlinear response function in the classical limit from a series of classical molecular dynamics (MD) simulations, employing a quantum mechanical/molecular mechanical (QM/MM) force field. The method relies on the stability matrix formalism where the dipole-dipole quantum mechanical commutators appearing in the exact quantum response function are replaced by the corresponding Poisson brackets. We present the formulation and computational algorithm of the method for both the classical and the QM/MM force fields and apply it to the 2D IR spectroscopy of carbon monoxide (CO) and N-methylacetamide (NMA), each solvated in a water cluster. The conventional classical force field with harmonic bond potentials is shown to be incapable of producing a reliable 2D IR signal because intramolecular vibrational anharmonicity, essential to the production of the nonlinear signal, is absent in such a model. The QM/MM force field, on the other hand, produces distinct 2D spectra for the NMA and CO systems with clear vertical splitting and cross peaks, reflecting the vibrational anharmonicities and the vibrational couplings between the underlying vibrational modes, respectively. In the NMA spectrum, the coupling between the amide I and II modes is also well reproduced. While attaining the converged spectrum is found to be challenging with this method, with an adequate amount of computing it can be straightforwardly applied to new systems containing multiple chromophores with little modeling effort, and therefore it would be useful in understanding the multimode 2D IR spectrum
Energy Technology Data Exchange (ETDEWEB)
Gornyi, I. V. [Karlsruhe Institute of Technology, Institut für Nanotechnologie (Germany); Dmitriev, A. P., E-mail: apd1812@hotmail.com [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Mirlin, A. D.; Protopopov, I. V. [Karlsruhe Institute of Technology, Institut für Nanotechnologie (Germany)
2016-08-15
We have studied the motion of an electron in a membrane under the influence of flexural vibrations with a correlator that decreases upon an increase in the distance in accordance with the law r–{sup 2η}. We have conducted a detailed consideration of the case with η < 1/2, in which the perturbation theory is inapplicable, even for an arbitrarily weak interaction. It is shown that, in this case, reciprocal quantum time 1/τ{sub q} is proportional to g{sup 1/(1–η)}T{sup (2–η)/(2–2η)}, where g is the electron–phonon interaction constant and T is the temperature. The method developed here is applied for calculating the electron density of states in a magnetic field perpendicular to the membrane. In particular, it is shown that the Landau levels in the regime with ω{sub c}τ{sub q} » 1 have a Gaussian shape with a width that depends on the magnetic field as B{sup η}. In addition, we calculate the time τ{sub φ} of dephasing of the electron wave function that emerges due to the interaction with flexural phonons for η < 1/2. It has been shown that, in several temperature intervals, quantity 1/τ{sub φ} can be expressed by various power functions of the electron–phonon interaction constant, temperature, and electron energy.
Karhu, J.; Nauta, J.; Vainio, M.; Metsala, M.; Hoekstra, S.; Halonen, L.
2016-01-01
A novel mid-infrared/near-infrared double resonant absorption setup for studying infrared-inactive vibrational states is presented. A strong vibrational transition in the mid-infrared region is excited using an idler beam from a singly resonant continuous-wave optical parametric oscillator, to
Karhu, J; Vainio, M; Metsälä, M; Hoekstra, S; Halonen, L
2016-01-01
A novel mid-infrared/near-infrared double resonant absorption setup for studying infrared-inactive vibrational states is presented. A strong vibrational transition in the mid-infrared region is excited using an idler beam from a singly resonant continuous-wave optical parametric oscillator, to populate an intermediate vibrational state. High output power of the optical parametric oscillator and the strength of the mid-infrared transition result in efficient population transfer to the intermediate state, which allows measuring secondary transitions from this state with a high signal-to-noise ratio. A secondary, near-infrared transition from the intermediate state is probed using cavity ring down spectroscopy, which provides high sensitivity in this wavelength region. Due to the narrow linewidths of the excitation sources, the rovibrational lines of the secondary transition are measured with sub-Doppler resolution. The setup is used to access a previously unreported symmetric vibrational state of acetylene, $\
Quantum state engineering using one-dimensional discrete-time quantum walks
Innocenti, Luca; Majury, Helena; Giordani, Taira; Spagnolo, Nicolò; Sciarrino, Fabio; Paternostro, Mauro; Ferraro, Alessandro
2017-12-01
Quantum state preparation in high-dimensional systems is an essential requirement for many quantum-technology applications. The engineering of an arbitrary quantum state is, however, typically strongly dependent on the experimental platform chosen for implementation, and a general framework is still missing. Here we show that coined quantum walks on a line, which represent a framework general enough to encompass a variety of different platforms, can be used for quantum state engineering of arbitrary superpositions of the walker's sites. We achieve this goal by identifying a set of conditions that fully characterize the reachable states in the space comprising walker and coin and providing a method to efficiently compute the corresponding set of coin parameters. We assess the feasibility of our proposal by identifying a linear optics experiment based on photonic orbital angular momentum technology.
Quantum state majorization at the output of bosonic Gaussian channels
Mari, A.; Giovannetti, V.; Holevo, A. S.
2014-05-01
Quantum communication theory explores the implications of quantum mechanics to the tasks of information transmission. Many physical channels can be formally described as quantum Gaussian operations acting on bosonic quantum states. Depending on the input state and on the quality of the channel, the output suffers certain amount of noise. For a long time it has been conjectured, but never proved, that output states of Gaussian channels corresponding to coherent input signals are the less noisy ones (in the sense of a majorization criterion). Here we prove this conjecture. Specifically we show that every output state of a phase-insensitive Gaussian channel is majorized by the output state corresponding to a coherent input. The proof is based on the optimality of coherent states for the minimization of strictly concave output functionals. Moreover we show that coherent states are the unique optimizers.
Quantum synchronization and quantum state sharing in an irregular complex network.
Li, Wenlin; Li, Chong; Song, Heshan
2017-02-01
We investigate the quantum synchronization phenomenon of the complex network constituted by coupled optomechanical systems and prove that the unknown identical quantum states can be shared or distributed in the quantum network even though the topology is varying. Considering a channel constructed by quantum correlation, we show that quantum synchronization can sustain and maintain high levels in Markovian dissipation for a long time. We also analyze the state-sharing process between two typical complex networks, and the results predict that linked nodes can be directly synchronized, but the whole network will be synchronized only if some specific synchronization conditions are satisfied. Furthermore, we give the synchronization conditions analytically through analyzing network dynamics. This proposal paves the way for studying multi-interaction synchronization and achieving effective quantum information processing in a complex network.
Quantum key distribution based on orthogonal states allows secure quantum bit commitment
He, Guang Ping
2011-11-01
For more than a decade, it was believed that unconditionally secure quantum bit commitment (QBC) is impossible. But based on a previously proposed quantum key distribution scheme using orthogonal states, here we build a QBC protocol in which the density matrices of the quantum states encoding the commitment do not satisfy a crucial condition on which the no-go proofs of QBC are based. Thus, the no-go proofs could be evaded. Our protocol is fault-tolerant and very feasible with currently available technology. It reopens the venue for other ‘post-cold-war’ multi-party cryptographic protocols, e.g. quantum bit string commitment and quantum strong coin tossing with an arbitrarily small bias. This result also has a strong influence on the Clifton-Bub-Halvorson theorem which suggests that quantum theory could be characterized in terms of information-theoretic constraints.
Efficient state initialization by a quantum spectral filtering algorithm
Fillion-Gourdeau, François; MacLean, Steve; Laflamme, Raymond
2017-04-01
An algorithm that initializes a quantum register to a state with a specified energy range is given, corresponding to a quantum implementation of the celebrated Feit-Fleck method. This is performed by introducing a nondeterministic quantum implementation of a standard spectral filtering procedure combined with an apodization technique, allowing for accurate state initialization. It is shown that the implementation requires only two ancilla qubits. A lower bound for the total probability of success of this algorithm is derived, showing that this scheme can be realized using a finite, relatively low number of trials. Assuming the time evolution can be performed efficiently and using a trial state polynomially close to the desired states, it is demonstrated that the number of operations required scales polynomially with the number of qubits. Tradeoffs between accuracy and performance are demonstrated in a simple example: the harmonic oscillator. This algorithm would be useful for the initialization phase of the simulation of quantum systems on digital quantum computers.
Open quantum dots in graphene: Scaling relativistic pointer states
Energy Technology Data Exchange (ETDEWEB)
Ferry, D K; Huang, L; Yang, R; Lai, Y-C; Akis, R, E-mail: ferry@asu.ed [School of Electrical, Computer, and Energy Engineering and Center for Solid State Electronics Research, Arizona State University, Tempe, AZ 85287-5706 (United States)
2010-04-01
Open quantum dots provide a window into the connection between quantum and classical physics, particularly through the decoherence theory, in which an important set of quantum states are not 'ashed out' through interaction with the environment-the pointer states provide connection to trapped classical orbits which remain stable in the dots. Graphene is a recently discovered material with highly unusual properties. This single layer, one atom thick, sheet of carbon has a unique bandstructure, governed by the Dirac equation, in which charge carriers imitate relativistic particles with zero rest mass. Here, an atomic orbital-based recursive Green's function method is used for studying the quantum transport. We study quantum fluctuations in graphene and bilayer graphene quantum dots with this recursive Green's function method. Finally, we examine the scaling of the domiant fluctuation frequency with dot size.
Quantum light and topological surface states
Dai, C. M.; Wang, W.; Yi, X. X.
2017-12-01
We demonstrate theoretically that, when quantum light interacts with massless Dirac fermions on the surface of a three-dimensional topological insulator, the elementary excitation spectrum depends on the polarizations of quantum light. Linear-polarized light cannot open a gap and leads to an anisotropic Dirac cone, but circular-polarized light can induce a mass term and the sign of mass is determined by the helicity of light. The effects due to quantum fluctuations are also discussed.
DEFF Research Database (Denmark)
Abdali, Salim; Jensen, Morten Østergaard; Bohr, Henrik
2003-01-01
This paper describes a theoretical and experimental study of [Leu]enkephalin conformations with respect to the quantum estates of the atomic structure of the peptide. Results from vibrational absorption measurements and quantum calculations are used to outline a quantum picture and to assign vibr...
Statistical constraints on state preparation for a quantum computer ∑
Indian Academy of Sciences (India)
tation on a quantum computer. How do we load information on the quantum register if the information-carrying particles in the cells of the register are indistinguishable? Quantum computing algorithms as visualized now [1,2] proceed with the register of n cells in a pure state. Each cell is seen to store a qubit αeiθ1 0 +βeiθ2 1 ...
Steady state quantum discord for circularly accelerated atoms
Energy Technology Data Exchange (ETDEWEB)
Hu, Jiawei, E-mail: hujiawei@nbu.edu.cn [Center for Nonlinear Science and Department of Physics, Ningbo University, Ningbo, Zhejiang 315211 (China); Yu, Hongwei, E-mail: hwyu@hunnu.edu.cn [Center for Nonlinear Science and Department of Physics, Ningbo University, Ningbo, Zhejiang 315211 (China); Synergetic Innovation Center for Quantum Effects and Applications, Hunan Normal University, Changsha, Hunan 410081 (China)
2015-12-15
We study, in the framework of open quantum systems, the dynamics of quantum entanglement and quantum discord of two mutually independent circularly accelerated two-level atoms in interaction with a bath of fluctuating massless scalar fields in the Minkowski vacuum. We assume that the two atoms rotate synchronically with their separation perpendicular to the rotating plane. The time evolution of the quantum entanglement and quantum discord of the two-atom system is investigated. For a maximally entangled initial state, the entanglement measured by concurrence diminishes to zero within a finite time, while the quantum discord can either decrease monotonically to an asymptotic value or diminish to zero at first and then followed by a revival depending on whether the initial state is antisymmetric or symmetric. When both of the two atoms are initially excited, the generation of quantum entanglement shows a delayed feature, while quantum discord is created immediately. Remarkably, the quantum discord for such a circularly accelerated two-atom system takes a nonvanishing value in the steady state, and this is distinct from what happens in both the linear acceleration case and the case of static atoms immersed in a thermal bath.
Quantum metrology with spin cat states under dissipation
Huang, Jiahao; Qin, Xizhou; Zhong, Honghua; Ke, Yongguan; Lee, Chaohong
2015-12-01
Quantum metrology aims to yield higher measurement precisions via quantum techniques such as entanglement. It is of great importance for both fundamental sciences and practical technologies, from testing equivalence principle to designing high-precision atomic clocks. However, due to environment effects, highly entangled states become fragile and the achieved precisions may even be worse than the standard quantum limit (SQL). Here we present a high-precision measurement scheme via spin cat states (a kind of non-Gaussian entangled states in superposition of two quasi-orthogonal spin coherent states) under dissipation. In comparison to maximally entangled states, spin cat states with modest entanglement are more robust against losses and their achievable precisions may still beat the SQL. Even if the detector is imperfect, the achieved precisions of the parity measurement are higher than the ones of the population measurement. Our scheme provides a realizable way to achieve high-precision measurements via dissipative quantum systems of Bose atoms.
Mishra, Rashmi; Joshi, Bhawani Datt; Srivastava, Anubha; Tandon, Poonam; Jain, Sudha
2014-01-01
The study concentrates on an important natural product, phthalide isoquinoline alkaloid Corlumine (COR) [(6R)-6-[(1S)-1,2,3,4-Tetrahydro-6,7-dimethoxy-2-methylisoquinolin-1-yl] furo [3,4-e]-1,3-benzodioxol-8(6H)-one] well known to exhibit spasmolytic and GABA antagonist activity. It was fully characterized by a variety of experimental methods including vibrational spectroscopy (IR and Raman), thermal analysis (DSC), UV and SEM. For a better interpretation and analysis of the results quantum chemical calculations employing DFT were also performed. TD-DFT was employed to elucidate electronic properties for both gaseous and solvent environment using IEF-PCM model. Graphical representation of HOMO and LUMO would provide a valuable insight into the nature of reactivity and some of the structural and physical properties of the title molecule. The structure-activity relationship have been interpreted by mapping electrostatic potential surface (MEP), which is valuable information for the quality control of medicines and drug-receptor interactions. Stability of the molecule arising from hyper conjugative interactions, charge delocalisation has been analyzed using natural bond orbital (NBO) analysis. Computation of thermodynamical properties would help to have a deep insight into the molecule for further applications.
Rectifying the output of vibrational piezoelectric energy harvester using quantum dots.
Li, Lijie
2017-03-20
Piezoelectric energy harvester scavenges mechanical vibrations and generates electricity. Researchers have strived to optimize the electromechanical structures and to design necessary external power management circuits, aiming to deliver high power and rectified outputs ready for serving as batteries. Complex deformation of the mechanical structure results in charges with opposite polarities appearing on same surface, leading to current loss in the attached metal electrode. External power management circuits such as rectifiers comprise diodes that consume power and have undesirable forward bias. To address the above issues, we devise a novel integrated piezoelectric energy harvesting device that is structured by stacking a layer of quantum dots (QDs) and a layer of piezoelectric material. We find that the QD can rectify electrical charges generated from the piezoelectric material because of its adaptable conductance to the electrochemical potentials of both sides of the QDs layer, so that electrical current causing energy loss on the same surface of the piezoelectric material can be minimized. The QDs layer has the potential to replace external rectification circuits providing a much more compact and less power-consumption solution.
Comment on "Observer dependence of quantum states in relativistic quantum field theories"
Bloch, I.
1984-04-01
In response to Malin's recent paper it is suggested that the important aspect of timing in relativistic descriptions of position determinations is the timing with which a pure state is converted to a mixture, rather than the timing of the mixture's reduction to a new pure state; this suggestion removes some of the subjectivism that Malin finds in quantum states. It is suggested also that viewing quantum mechanics as a branch of psychology raises more questions than it answers.
Xiao, Hailin; Zhang, Zhongshan
2017-01-01
Quantum key distribution (QKD) system is presently being developed for providing high-security transmission in future free-space optical communication links. However, current QKD technique restricts quantum secure communication to a low bit rate. To improve the QKD bit rate, we propose a subcarrier multiplexing multiple-input multiple-output quantum key distribution (SCM-MQKD) scheme with orthogonal quantum states. Specifically, we firstly present SCM-MQKD system model and drive symmetrical SCM-MQKD system into decoherence-free subspaces. We then utilize bipartite Werner and isotropic states to construct multiple parallel single photon with orthogonal quantum states that are invariant for unitary operations. Finally, we derive the density matrix and the capacity of SCM-MQKD system, respectively. Theoretical analysis and numerical results show that the capacity of SCM-MQKD system will increase {log _2}(N^2+1) times than that of single-photon QKD system.
Quantum state transfer between hybrid qubits in a circuit QED
Feng, Zhi-Bo
2012-01-01
In this Brief Report, we propose a theoretical scheme to transfer quantum states between superconducting charge qubits and semiconductor spin qubits in a circuit QED device. Under dispersive conditions, resonator-assisted state transfer between qubits can be performed controllably only by addressing the flux bias applied to the charge qubits. The low infidelity and existing advantages show that the proposal may provide an effective route toward scalable quantum-information transfer with solid-state hybrid qubits.
Dynamics of quantum observables in entangled states
Sudheesh, C.; Lakshmibala, S.; Balakrishnan, V.
2009-08-01
We examine the dynamics of a radiation field propagating through a nonlinear medium. A time series analysis of the mean photon number illustrates how an open quantum system interacting with a quantum environment can exhibit remarkably diverse ergodicity properties, both nonlinearity and departure from coherence playing a crucial role.
Imperfect state preparation in continuous-variable quantum key distribution
Liu, Wenyuan; Wang, Xuyang; Wang, Ning; Du, Shanna; Li, Yongmin
2017-10-01
In continuous-variable quantum key distribution, the loss and excess noise of the quantum channel are key parameters that determine the secure key rate and the maximal distribution distance. We investigate the imperfect quantum state preparation in Gaussian modulation coherent-state protocol both theoretically and experimentally. We show that the Gaussian distribution characteristic of the prepared states in phase space is broken due to the incorrect calibration of the working parameters for the amplitude modulator and phase modulator. This further causes a significant increase of the excess noise and misestimate of the channel loss. To ensure an accurate estimate of the quantum channel parameters and achieve a reliable quantum key distribution, we propose and demonstrate two effective schemes to calibrate the working parameters of the modulators.
Entanglement distillation between solid-state quantum network nodes.
Kalb, N; Reiserer, A A; Humphreys, P C; Bakermans, J J W; Kamerling, S J; Nickerson, N H; Benjamin, S C; Twitchen, D J; Markham, M; Hanson, R
2017-06-02
The impact of future quantum networks hinges on high-quality quantum entanglement shared between network nodes. Unavoidable imperfections necessitate a means to improve remote entanglement by local quantum operations. We realize entanglement distillation on a quantum network primitive of distant electron-nuclear two-qubit nodes. The heralded generation of two copies of a remote entangled state is demonstrated through single-photon-mediated entangling of the electrons and robust storage in the nuclear spins. After applying local two-qubit gates, single-shot measurements herald the distillation of an entangled state with increased fidelity that is available for further use. The key combination of generating, storing, and processing entangled states should enable the exploration of multiparticle entanglement on an extended quantum network. Copyright © 2017, American Association for the Advancement of Science.
Entanglement distillation between solid-state quantum network nodes
Kalb, N.; Reiserer, A. A.; Humphreys, P. C.; Bakermans, J. J. W.; Kamerling, S. J.; Nickerson, N. H.; Benjamin, S. C.; Twitchen, D. J.; Markham, M.; Hanson, R.
2017-06-01
The impact of future quantum networks hinges on high-quality quantum entanglement shared between network nodes. Unavoidable imperfections necessitate a means to improve remote entanglement by local quantum operations. We realize entanglement distillation on a quantum network primitive of distant electron-nuclear two-qubit nodes. The heralded generation of two copies of a remote entangled state is demonstrated through single-photon-mediated entangling of the electrons and robust storage in the nuclear spins. After applying local two-qubit gates, single-shot measurements herald the distillation of an entangled state with increased fidelity that is available for further use. The key combination of generating, storing, and processing entangled states should enable the exploration of multiparticle entanglement on an extended quantum network.
Blind Quantum Signature with Controlled Four-Particle Cluster States
Li, Wei; Shi, Jinjing; Shi, Ronghua; Guo, Ying
2017-08-01
A novel blind quantum signature scheme based on cluster states is introduced. Cluster states are a type of multi-qubit entangled states and it is more immune to decoherence than other entangled states. The controlled four-particle cluster states are created by acting controlled-Z gate on particles of four-particle cluster states. The presented scheme utilizes the above entangled states and simplifies the measurement basis to generate and verify the signature. Security analysis demonstrates that the scheme is unconditional secure. It can be employed to E-commerce systems in quantum scenario.
Photodissociation of ultracold diatomic strontium molecules with quantum state control.
McDonald, M; McGuyer, B H; Apfelbeck, F; Lee, C-H; Majewska, I; Moszynski, R; Zelevinsky, T
2016-07-07
Chemical reactions at ultracold temperatures are expected to be dominated by quantum mechanical effects. Although progress towards ultracold chemistry has been made through atomic photoassociation, Feshbach resonances and bimolecular collisions, these approaches have been limited by imperfect quantum state selectivity. In particular, attaining complete control of the ground or excited continuum quantum states has remained a challenge. Here we achieve this control using photodissociation, an approach that encodes a wealth of information in the angular distribution of outgoing fragments. By photodissociating ultracold (88)Sr2 molecules with full control of the low-energy continuum, we access the quantum regime of ultracold chemistry, observing resonant and nonresonant barrier tunnelling, matter-wave interference of reaction products and forbidden reaction pathways. Our results illustrate the failure of the traditional quasiclassical model of photodissociation and instead are accurately described by a quantum mechanical model. The experimental ability to produce well-defined quantum continuum states at low energies will enable high-precision studies of long-range molecular potentials for which accurate quantum chemistry models are unavailable, and may serve as a source of entangled states and coherent matter waves for a wide range of experiments in quantum optics.
Optimal eavesdropping in cryptography with three-dimensional quantum states.
Bruss, D; Macchiavello, C
2002-03-25
We study optimal eavesdropping in quantum cryptography with three-dimensional systems, and show that this scheme is more secure against symmetric attacks than protocols using two-dimensional states. We generalize the according eavesdropping transformation to arbitrary dimensions, and discuss the connection with optimal quantum cloning.
Experimental Study of Optimal Measurements for Quantum State Tomography
Sosa-Martinez, H.; Lysne, N. K.; Baldwin, C. H.; Kalev, A.; Deutsch, I. H.; Jessen, P. S.
2017-10-01
Quantum tomography is a critically important tool to evaluate quantum hardware, making it essential to develop optimized measurement strategies that are both accurate and efficient. We compare a variety of strategies using nearly pure test states. Those that are informationally complete for all states are found to be accurate and reliable even in the presence of errors in the measurements themselves, while those designed to be complete only for pure states are far more efficient but highly sensitive to such errors. Our results highlight the unavoidable trade-offs inherent in quantum tomography.
Extending SDL and LMC complexity measures to quantum states
Piqueira, José Roberto C.; Campbell-Borges, Yuri Cássio
2013-10-01
An extension of SDL (Shiner, Davison, Landsberg) and LMC (López-Ruiz, Mancini, Calbet) complexity measures is proposed for the quantum information context, considering that Von Neumann entropy is a natural disorder quantifier for quantum states. As a first example of application, the simple qubit was studied, presenting results similar to that obtained by applying SDL and LMC measures to a classical probability distribution. Then, for the Werner state, a mixture of Bell states, SDL and LMC measures were calculated, depending on the mixing factor γ, providing some conjectures concerning quantum systems.
Topological quantum computing with Read-Rezayi states.
Hormozi, L; Bonesteel, N E; Simon, S H
2009-10-16
Read-Rezayi fractional quantum Hall states are among the prime candidates for realizing non-Abelian anyons which, in principle, can be used for topological quantum computation. We present a prescription for efficiently finding braids which can be used to carry out a universal set of quantum gates on encoded qubits based on anyons of the Read-Rezayi states with k>2, k not equal 4. This work extends previous results which only applied to the case k=3 (Fibonacci) and clarifies why, in that case, gate constructions are simpler than for a generic Read-Rezayi state.
Bound states in Galilean-invariant quantum field theory
Energy Technology Data Exchange (ETDEWEB)
Corley, S.R.; Greenberg, O.W. [Center for Theoretical Physics, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States)
1997-02-01
We consider the nonrelativistic quantum mechanics of a model of two spinless fermions interacting via a two-body potential. We introduce quantum fields associated with the two particles as well as the expansion of these fields in asymptotic {open_quotes}in{close_quotes} and {open_quotes}out{close_quotes} fields, including such fields for bound states, in principle. We limit our explicit discussion to a two-body bound state. In this context we discuss the implications of the Galilean invariance of the model and, in particular, show how to include bound states in a strictly Galilean-invariant quantum field theory. {copyright} {ital 1997 American Institute of Physics.}
Quantum reciprocity conjecture for the non-equilibrium steady state
Energy Technology Data Exchange (ETDEWEB)
Coleman, P; Mao, W [Center for Materials Theory, Rutgers University, Piscataway, NJ 08854 (United States)
2004-05-26
A consideration of the lack of history dependence in the non-equilibrium steady state of a quantum system leads us to conjecture that in such a system there is a set of quantum mechanical observables whose retarded response functions are insensitive to the arrow of time, and which consequently satisfy a quantum analogue of the Onsager reciprocity relations. Systems which satisfy this conjecture can be described by an effective free energy functional. We demonstrate that the conjecture holds in a resonant level model of a multi-lead quantum dot. (letter to the editor)
A secure quantum group signature scheme based on Bell states
Zhang, Kejia; Song, Tingting; Zuo, Huijuan; Zhang, Weiwei
2013-04-01
In this paper, we propose a new secure quantum group signature with Bell states, which may have applications in e-payment system, e-government, e-business, etc. Compared with the recent quantum group signature protocols, our scheme is focused on the most general situation in practice, i.e. only the arbitrator is trusted and no intermediate information needs to be stored in the signing phase to ensure the security. Furthermore, our scheme has achieved all the characteristics of group signature—anonymity, verifiability, traceability, unforgetability and undeniability, by using some current developed quantum and classical technologies. Finally, a feasible security analysis model for quantum group signature is presented.
Quantum-classical correspondence in steady states of nonadiabatic systems
Energy Technology Data Exchange (ETDEWEB)
Fujii, Mikiya; Yamashita, Koichi [Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Tokyo 113-8656 (Japan); CREST, JST, Tokyo 113-8656 (Japan)
2015-12-31
We first present nonadiabatic path integral which is exact formulation of quantum dynamics in nonadiabatic systems. Then, by applying the stationary phase approximations to the nonadiabatic path integral, a semiclassical quantization condition, i.e., quantum-classical correspondence, for steady states of nonadiabatic systems is presented as a nonadiabatic trace formula. The present quantum-classical correspondence indicates that a set of primitive hopping periodic orbits, which are invariant under time evolution in the phase space of the slow degree of freedom, should be quantized. The semiclassical quantization is then applied to a simple nonadiabatic model and accurately reproduces exact quantum energy levels.
Zounia, M.; Shamirzaie, M.; Ashouri, A.
2017-09-01
In this paper quantum teleportation of an unknown quantum state via noisy maximally bipartite (Bell) and maximally tripartite (Greenberger-Horne-Zeilinger (GHZ)) entangled states are investigated. We suppose that one of the observers who would receive the sent state accelerates uniformly with respect to the sender. The interactions of the quantum system with its environment during the teleportation process impose noises. These (unital and nonunital) noises are: phase damping, phase flip, amplitude damping and bit flip. In expressing the modes of the Dirac field used as qubits, in the accelerating frame, the so-called single mode approximation is not imposed. We calculate the fidelities of teleportation, and discuss their behaviors using suitable plots. The effects of noise, acceleration and going beyond the single mode approximation are discussed. Although the Bell states bring higher fidelities than GHZ states, the global behaviors of the two quantum systems with respect to some noise types, and therefore their fidelities, are different.
Kobayashi, Masaki; Yoshimatsu, Kohei; Mitsuhashi, Taichi; Kitamura, Miho; Sakai, Enju; Yukawa, Ryu; Minohara, Makoto; Fujimori, Atsushi; Horiba, Koji; Kumigashira, Hiroshi
2017-11-30
Controlling quantum critical phenomena in strongly correlated electron systems, which emerge in the neighborhood of a quantum phase transition, is a major challenge in modern condensed matter physics. Quantum critical phenomena are generated from the delicate balance between long-range order and its quantum fluctuation. So far, the nature of quantum phase transitions has been investigated by changing a limited number of external parameters such as pressure and magnetic field. We propose a new approach for investigating quantum criticality by changing the strength of quantum fluctuation that is controlled by the dimensional crossover in metallic quantum well (QW) structures of strongly correlated oxides. With reducing layer thickness to the critical thickness of metal-insulator transition, crossover from a Fermi liquid to a non-Fermi liquid has clearly been observed in the metallic QW of SrVO3 by in situ angle-resolved photoemission spectroscopy. Non-Fermi liquid behavior with the critical exponent α = 1 is found to emerge in the two-dimensional limit of the metallic QW states, indicating that a quantum critical point exists in the neighborhood of the thickness-dependent Mott transition. These results suggest that artificial QW structures provide a unique platform for investigating novel quantum phenomena in strongly correlated oxides in a controllable fashion.
Structural characterization of carbon nanotubes via the vibrational density of states
Pool, Albert J.; Jain, Sandeep K.; Barkema, Gerard T.
2017-01-01
The electrical and chemical properties of carbon nanotubes vary significantly with different chirality and diameter, making the experimental determination of these structural properties important. Here, we show that the vibrational density of states (VDOS) contains information on the structure of
Quantum state resolved gas-surface reaction dynamics experiments: a tutorial review.
Chadwick, Helen; Beck, Rainer D
2016-07-07
We present a tutorial review of our quantum state resolved experiments designed to study gas-surface reaction dynamics. The combination of a molecular beam, state specific reactant preparation by infrared laser pumping, and ultrahigh vacuum surface analysis techniques make it possible to study chemical reactivity at the gas-surface interface in unprecedented detail. We describe the experimental techniques used for state specific reactant preparation and for detection of surface bound reaction products developed in our laboratory. Using the example of the reaction of methane on Ni and Pt surfaces, we show how state resolved experiments uncovered clear evidence for vibrational mode specificity and bond selectivity, as well as steric effects in chemisorption reactions. The state resolved experimental data provides valuable benchmarks for comparison with theoretical models for gas-surface reactivity aiding in the development of a detailed microscopic understanding of chemical reactivity at the gas-surface interface.
Experimental demonstration of efficient quantum state tomography of matrix product states.
Zhao, Yuan-Yuan; Hou, Zhibo; Xiang, Guo-Yong; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can
2017-04-17
Quantum state tomography is a key technology for fully determining a quantum state. Unfortunately, standard quantum state tomography is intractable for general many-body quantum states, because the number of measurements and the post-processing time increase exponentially with the size of the system. However, for the matrix product states (MPSs), there exists an efficient method using linearly scaled local measurements and polynomially scaled post-processing times. In this study, we demonstrate the validity of the method in practice by reconstructing a four-photon MPS from its local two- or three-photon reduced-density matrices with the presence of statistical errors and systematical errors in experiment.
Observing Quantum State Diffusion by Heterodyne Detection of Fluorescence
Directory of Open Access Journals (Sweden)
P. Campagne-Ibarcq
2016-01-01
Full Text Available A qubit can relax by fluorescence, which prompts the release of a photon into its electromagnetic environment. By counting the emitted photons, discrete quantum jumps of the qubit state can be observed. The succession of states occupied by the qubit in a single experiment, its quantum trajectory, depends in fact on the kind of detector. How are the quantum trajectories modified if one measures continuously the amplitude of the fluorescence field instead? Using a superconducting parametric amplifier, we perform heterodyne detection of the fluorescence of a superconducting qubit. For each realization of the measurement record, we can reconstruct a different quantum trajectory for the qubit. The observed evolution obeys quantum state diffusion, which is characteristic of quantum measurements subject to zero-point fluctuations. Independent projective measurements of the qubit at various times provide a quantitative verification of the reconstructed trajectories. By exploring the statistics of quantum trajectories, we demonstrate that the qubit states span a deterministic surface in the Bloch sphere at each time in the evolution. Additionally, we show that when monitoring fluorescence field quadratures, coherent superpositions are generated during the decay from excited to ground state. Counterintuitively, measuring light emitted during relaxation can give rise to trajectories with increased excitation probability.
Fluctuation Theorem for Many-Body Pure Quantum States
Iyoda, Eiki; Kaneko, Kazuya; Sagawa, Takahiro
2017-09-01
We prove the second law of thermodynamics and the nonequilibrium fluctuation theorem for pure quantum states. The entire system obeys reversible unitary dynamics, where the initial state of the heat bath is not the canonical distribution but is a single energy eigenstate that satisfies the eigenstate-thermalization hypothesis. Our result is mathematically rigorous and based on the Lieb-Robinson bound, which gives the upper bound of the velocity of information propagation in many-body quantum systems. The entanglement entropy of a subsystem is shown connected to thermodynamic heat, highlighting the foundation of the information-thermodynamics link. We confirmed our theory by numerical simulation of hard-core bosons, and observed dynamical crossover from thermal fluctuations to bare quantum fluctuations. Our result reveals a universal scenario that the second law emerges from quantum mechanics, and can be experimentally tested by artificial isolated quantum systems such as ultracold atoms.
Fluctuation Theorem for Many-Body Pure Quantum States.
Iyoda, Eiki; Kaneko, Kazuya; Sagawa, Takahiro
2017-09-08
We prove the second law of thermodynamics and the nonequilibrium fluctuation theorem for pure quantum states. The entire system obeys reversible unitary dynamics, where the initial state of the heat bath is not the canonical distribution but is a single energy eigenstate that satisfies the eigenstate-thermalization hypothesis. Our result is mathematically rigorous and based on the Lieb-Robinson bound, which gives the upper bound of the velocity of information propagation in many-body quantum systems. The entanglement entropy of a subsystem is shown connected to thermodynamic heat, highlighting the foundation of the information-thermodynamics link. We confirmed our theory by numerical simulation of hard-core bosons, and observed dynamical crossover from thermal fluctuations to bare quantum fluctuations. Our result reveals a universal scenario that the second law emerges from quantum mechanics, and can be experimentally tested by artificial isolated quantum systems such as ultracold atoms.
Quantum State-Resolved Studies of Chemisorption Reactions.
Chadwick, Helen; Beck, Rainer D
2017-05-05
Chemical reactions at the gas-surface interface are ubiquitous in the chemical industry as well as in nature. Investigating these processes at a microscopic, quantum state-resolved level helps develop a predictive understanding of this important class of reactions. In this review, we present an overview of the field of quantum state-resolved gas-surface reactivity measurements that explore the role of the initial quantum state on the dissociative chemisorption of a gas-phase reactant incident on a solid surface. Using molecular beams and either quantum state-specific reactant preparation or product detection by laser excitation, these studies have observed mode specificity and bond selectivity as well as steric effects in chemisorption reactions, highlighting the nonstatistical and complex nature of gas-surface reaction dynamics.
Data processing inequality and open quantum systems: Beyond Markov states
Türkmen, A.; Verçin, A.; Yılmaz, S.
2017-10-01
Using a tripartite framework consisting of an open quantum system, its environment, and a passive reference system, in this study we discuss quantum mutual information (QMI) and data processing inequality (DPI). Without any restriction on the initial correlations, the necessary and sufficient conditions for the decrease or increase as well as for the conservation of QMI are obtained for any joint unitary evolution of the open quantum system and its environment. In the special case of the input Markov states, it has been shown that as long as the tripartite input state is a Markov state then DPI holds for every joint unitary evolution even in the presence of initial correlations encoded in the input. We also point out that the converse of the last statement, that is, sufficiency of the existence of a local quantum channel or of the fulfillment of DPI for the input Markov state does not hold in general and this fact is exhibited by counterexamples.
Theoretically extensible quantum digital signature with starlike cluster states
Yang, Yu-Guang; Liu, Zhi-Chao; Li, Jian; Chen, Xiu-Bo; Zuo, Hui-Juan; Zhou, Yi-Hua; Shi, Wei-Min
2017-01-01
Chen et al. (Phys Rev A 73:012303, 2006) constructed this "starlike cluster" state, which involves one qubit located at the center and n neighboring two-qubit arms. This genuine entangled state has been used for the construction of 2D and 3D cluster states, topological one-way computation, and dynamical quantum secret sharing. In this paper, we investigate the usefulness of this starlike cluster state and propose a theoretically extensible quantum digital signature scheme. The proposed scheme can be theoretically generalized to more than three participants. Moreover, it retains the merits of no requirements such as authenticated quantum channels and long-term quantum memory. We also give a security proof for the proposed scheme against repudiation and forgery.
Photon-echo-based quantum memory for optical squeezed states
Wu, Miao-Xin; Wang, Ming-Feng; Zheng, Yi-Zhuang
2015-08-01
The ability to efficiently realize storage and readout of optical squeezed states plays a key roll in continuous-variables quantum information processing. Here we study the quantum memory for squeezed state of propagating light in atoms based on the hybrid photon echo re-phasing. The optical quantum state is recorded in two sublevels of the ground state of an atomic ensemble to realize long-lived quantum memory. Taking into account the noise effect due to atomic decay, our estimation indicates that high fidelities larger than the classical fidelity threshold 81.5% are obtainable even with currently available techniques. Moreover, our result shows that the decay rate of atoms restricts the maximal fidelity. Our work provides some practical guidance for the realization of efficient and faithful photon-echo-based memory for squeezed light.
Absence of quantum states corresponding to unstable classical channels
DEFF Research Database (Denmark)
Herbst, Ira; Skibsted, Erik
2008-01-01
We develop a general theory of absence of quantum states corresponding to unstable classical scattering channels. We treat in detail Hamiltonians arising from symbols of degree zero in x and outline a generalization in an Appendix.......We develop a general theory of absence of quantum states corresponding to unstable classical scattering channels. We treat in detail Hamiltonians arising from symbols of degree zero in x and outline a generalization in an Appendix....
Measuring the effective phonon density of states of a quantum dot in cavity quantum electrodynamics
DEFF Research Database (Denmark)
Madsen, Kristian Høeg; Nielsen, Per Kær; Kreiner-Møller, Asger
2013-01-01
We employ detuning-dependent decay-rate measurements of a quantum dot in a photonic-crystal cavity to study the influence of phonon dephasing in a solid-state quantum-electrodynamics experiment. The experimental data agree with a microscopic non-Markovian model accounting for dephasing from...... longitudinal acoustic phonons, and the analysis explains the difference between nonresonant cavity feeding in different nanocavities. From the comparison between experiment and theory we extract the effective phonon density of states experienced by the quantum dot in the nanocavity. This quantity determines...
Heralded atomic-ensemble quantum memory for photon polarization states
Energy Technology Data Exchange (ETDEWEB)
Tanji, Haruka; Simon, Jonathan [Department of Physics, Harvard University, Cambridge, MA 02138 (United States); Ghosh, Saikat; Bloom, Benjamin; Vuletic, Vladan [Department of Physics, MIT-Harvard Center for Ultracold Atoms, and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)], E-mail: vuletic@mit.edu
2009-07-15
We describe the mapping of quantum states between single photons and an atomic ensemble. In particular, we demonstrate a heralded quantum memory based on the mapping of a photon polarization state onto a single collective-spin excitation (magnon) shared between two atomic ensembles. The polarization fidelity above 90(2)% for any input polarization far exceeds the classical limit of 2/3. The process also constitutes a quantum non-destructive probe that detects and regenerates a photon without measuring its polarization.
Experimental demonstration of macroscopic quantum coherence in Gaussian states
DEFF Research Database (Denmark)
Marquardt, C.; Andersen, Ulrik Lund; Leuchs, G.
2007-01-01
We witness experimentally the presence of macroscopic coherence in Gaussian quantum states using a recently proposed criterion [E. G. Cavalcanti and M. D. Reid, Phys. Rev. Lett. 97 170405 (2006)]. The macroscopic coherence stems from interference between macroscopically distinct states in phase...... space, and we prove experimentally that a coherent state contains these features with a distance in phase space of 0.51 +/- 0.02 shot noise units. This is surprising because coherent states are generally considered being at the border between classical and quantum states, not yet displaying any...
Xie, Changjian; Jiang, Bin; Kłos, Jacek; Kumar, Praveen; Alexander, Millard H; Poirier, Bill; Guo, Hua
2017-07-06
The fragmentation dynamics of predissociative SO2(C̃1B2) is investigated on an accurate adiabatic potential energy surface (PES) determined from high level ab initio data. This singlet PES features non-C2v equilibrium geometries for SO2, which are separated from the SO(X̃3Σ-) + O(3P) dissociation limit by a barrier resulting from a conical intersection with a repulsive singlet state. The ro-vibrational state distribution of the SO fragment is determined quantum mechanically for many predissociative states of several sulfur isotopomers of SO2. Significant rotational and vibrational excitations are found in the SO fragment. It is shown that these fragment internal state distributions are strongly dependent on the predissociative vibronic states, and the excitation typically increases with the photon energy.
Singly and Doubly Occupied Higher Quantum States in Nanocrystals.
Jeong, Juyeon; Yoon, Bitna; Kwon, Young-Wan; Choi, Dongsun; Jeong, Kwang Seob
2017-02-08
Filling the lowest quantum state of the conduction band of colloidal nanocrystals with a single electron, which is analogous to the filling the lowest unoccupied molecular orbital in a molecule with a single electron, has attracted much attention due to the possibility of harnessing the electron spin for potential spin-based applications. The quantized energy levels of the artificial atom, in principle, make it possible for a nanocrystal to be filled with an electron if the Fermi-energy level is optimally tuned during the nanocrystal growth. Here, we report the singly occupied quantum state (SOQS) and doubly occupied quantum state (DOQS) of a colloidal nanocrystal in steady state under ambient conditions. The number of electrons occupying the lowest quantum state can be controlled to be zero, one (unpaired), and two (paired) depending on the nanocrystal growth time via changing the stoichiometry of the nanocrystal. Electron paramagnetic resonance spectroscopy proved the nanocrystals with single electron to show superparamagnetic behavior, which is a direct evidence of the SOQS, whereas the DOQS of the two- or zero-electron occupied nanocrystals in the 1Se exhibit diamagnetic behavior. In combination with the superconducting quantum interference device measurement, it turns out that the SOQS of the HgSe colloidal quantum dots has superparamagnetic property. The appearance and change of the steady-state mid-IR intraband absorption spectrum reflect the sequential occupation of the 1Se state with electrons. The magnetic property of the colloidal quantum dot, initially determined by the chemical synthesis, can be tuned from diamagnetic to superparamagnetic and vice versa by varying the number of electrons through postchemical treatment. The switchable magnetic property will be very useful for further applications such as colloidal nanocrystal based spintronics, nonvolatile memory, infrared optoelectronics, catalyst, imaging, and quantum computing.
Extreme quantum nonequilibrium, nodes, vorticity, drift and relaxation retarding states
Underwood, Nicolas G.
2018-02-01
Consideration is given to the behaviour of de Broglie trajectories that are separated from the bulk of the Born distribution with a view to describing the quantum relaxation properties of more ‘extreme’ forms of quantum nonequilibrium. For the 2D isotropic harmonic oscillator, through the construction of what is termed the ‘drift field’, a description is given of a general mechanism that causes the relaxation of ‘extreme’ quantum nonequilibrium. Quantum states are found which do not feature this mechanism, so that relaxation may be severely delayed or possibly may not take place at all. A method by which these states may be identified, classified and calculated is given in terms of the properties of the nodes of the state. Properties of the nodes that enable this classification are described for the first time.
Quantum Public Key Cryptosystem Based on Bell States
Wu, WanQing; Cai, QingYu; Zhang, HuanGuo; Liang, XiaoYan
2017-11-01
Classical public key cryptosystems ( P K C), such as R S A, E I G a m a l, E C C, are no longer secure in quantum algorithms, and quantum cryptography has become a novel research topic. In this paper we present a quantum asymmetrical cryptosystem i.e. quantum public key cryptosystem ( Q P K C) based on the Bell states. In particular, in the proposed QPKC the public key are given by the first n particles of Bell states and generalized Pauli operations. The corresponding secret key are the last n particles of Bell states and the inverse of generalized Pauli operations. The proposed QPKC encrypts the message using a public key and decrypts the ciphertext using a private key. By H o l e v o ' s theorem, we proved the security of the secret key and messages during the QPKC.
Controlling the Quantum State with a time varying potential.
Carrasco, Sebastián; Rogan, José; Valdivia, Juan Alejandro
2017-10-16
The problem of controlling the quantum state of a system is investigated using a time varying potential. As a concrete example we study the problem of a particle in a box with a periodically oscillating infinite square-well potential, from which we obtain results that can be applied to systems with periodically oscillating boundary conditions. We derive an analytic expression for the frequencies of resonance between states, and against standard intuition, we show how to use this behavior to control the quantum state of the system at will. In particular, we offer as an example the transition from the ground state to the first excited state of the square well potential. At first sight, it may be counter intuitive that we can control the state of such a quantum Hamiltonian, as the Schrödinger equation conserves the norm of the wave function. In this manuscript, we show how that can be achieved.
Trivikram, T Madhu; Wcisło, P; Ubachs, W; Salumbides, E J
2016-01-01
Accurate $EF{}^1\\Sigma^+_g-X{}^1\\Sigma^+_g$ transition energies in molecular hydrogen were determined for transitions originating from levels with highly-excited vibrational quantum number, $v=11$, in the ground electronic state. Doppler-free two-photon spectroscopy was applied on vibrationally excited H$_2^*$, produced via the photodissociation of H$_2$S, yielding transition frequencies with accuracies of $45$ MHz or $0.0015$ cm$^{-1}$. An important improvement is the enhanced detection efficiency by resonant excitation to autoionizing $7p\\pi$ electronic Rydberg states, resulting in narrow transitions due to reduced ac-Stark effects. Using known $EF$ level energies, the level energies of $X(v=11, J=1,3-5)$ states are derived with accuracies of typically 0.002 cm$^{-1}$. These experimental values are in excellent agreement with, and are more accurate than the results obtained from the most advanced ab initio molecular theory calculations including relativistic and QED contributions.
Decomposition of fractional quantum Hall states: New symmetries and approximations
Thomale, R.; Estienne, B.; Regnault, N.; Bernevig, B.A.
2010-01-01
Abstract: We provide a detailed description of a new symmetry structure of the monomial (Slater) expansion coefficients of bosonic (fermionic) fractional quantum Hall states first obtained in Ref. 1, which we now extend to spin-singlet states. We show that the Haldane-Rezayi spin-singlet state can
Coherent states of non-Hermitian quantum systems
Roy, B.; Roy, P.
2006-01-01
We use the Gazeau-Klauder formalism to construct coherent states of non-Hermitian quantum systems. In particular we use this formalism to construct coherent state of a PT symmetric system. We also discuss construction of coherent states following Klauder's minimal prescription.
Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin.
He, Yu; He, Yu-Ming; Wei, Yu-Jia; Jiang, Xiao; Chen, Kai; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Höfling, Sven
2017-08-11
Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of 0.796±0.020. Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path, and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 m. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axes on the Bloch sphere, with an average fidelity of 78.5%.
Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin
He, Yu; He, Yu-Ming; Wei, Yu-Jia; Jiang, Xiao; Chen, Kai; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Höfling, Sven
2017-08-01
Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of 0.796 ±0.020 . Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path, and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 m. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axes on the Bloch sphere, with an average fidelity of 78.5%.
Translational vibrations between chains of hydrogen-bonded molecules in solid-state aspirin form I
Takahashi, Masae; Ishikawa, Yoichi
2013-06-01
We perform dispersion-corrected first-principles calculations, and far-infrared (terahertz) spectroscopic experiments at 4 K, to examine translational vibrations between chains of hydrogen-bonded molecules in solid-state aspirin form I. The calculated frequencies and relative intensities reproduce the observed spectrum to accuracy of 11 cm-1 or less. The stronger one of the two peaks assigned to the translational mode includes the stretching vibration of the weak hydrogen bond between the acetyl groups of a neighboring one-dimensional chain. The calculation of aspirin form II performed for comparison gives the stretching vibration of the weak hydrogen bond in one-dimensional chain.
Directory of Open Access Journals (Sweden)
Ze Zhang
2014-01-01
Full Text Available A feedback control method based on an extended state observer (ESO method is implemented to vibration reduction in a typical semiactive suspension (SAS system using a magnetorheological (MR damper as actuator. By considering the dynamic equations of the SAS system and the MR damper model, an active disturbance rejection control (ADRC is designed based on the ESO. Numerical simulation and real-time experiments are carried out with similar vibration disturbances. Both the simulation and experimental results illustrate the effectiveness of the proposed controller in vibration suppression for a SAS system.
STABILITY AND NATURAL VIBRATIONS OF INHOMOGENEOUS SHELLS TAKING INTO ACCOUNT THE STRESS STATE
Directory of Open Access Journals (Sweden)
Bazhenov V.A.
2015-12-01
Full Text Available The work is devoted to the problem of developing a unified methodology based on the efficient numerical analysis of problems of stability and natural vibrations of a wide class of inhomogeneous shells, thin and medium thickness. In problems of its natural vibrations takes into account the presence of a pre-stressed state of the structure from the action of static loads, which significantly affect the spectrum of natural vibrations and allows determining the bifurcation point and the value of the critical force of buckling by dynamic criteria.
Methane dissociation on the steps and terraces of Pt(211) resolved by quantum state and impact site.
Chadwick, Helen; Guo, Han; Gutiérrez-González, Ana; Menzel, Jan Paul; Jackson, Bret; Beck, Rainer D
2018-01-07
Methane dissociation on the step and terrace sites of a Pt(211) single crystal was studied by reflection absorption infrared spectroscopy (RAIRS) at a surface temperature of 120 K. The C-H stretch RAIRS signal of the chemisorbed methyl product species was used to distinguish between adsorption on step and terrace sites allowing methyl uptake to be monitored as a function of incident kinetic energy for both sites. Our results indicate a direct dissociation mechanism on both sites with higher reactivity on steps than on terraces consistent with a difference in an activation barrier height of at least 30 kJ/mol. State-specific preparation of incident CH4 with one quantum of antisymmetric (ν3) stretch vibration further increases the CH4 reactivity enabling comparison between translational and vibrational activation on both steps and terraces. The reaction is modeled with first principles quantum theory that accurately describes dissociative chemisorption at different sites on the surface.
Methane dissociation on the steps and terraces of Pt(211) resolved by quantum state and impact site
Chadwick, Helen; Guo, Han; Gutiérrez-González, Ana; Menzel, Jan Paul; Jackson, Bret; Beck, Rainer D.
2018-01-01
Methane dissociation on the step and terrace sites of a Pt(211) single crystal was studied by reflection absorption infrared spectroscopy (RAIRS) at a surface temperature of 120 K. The C—H stretch RAIRS signal of the chemisorbed methyl product species was used to distinguish between adsorption on step and terrace sites allowing methyl uptake to be monitored as a function of incident kinetic energy for both sites. Our results indicate a direct dissociation mechanism on both sites with higher reactivity on steps than on terraces consistent with a difference in an activation barrier height of at least 30 kJ/mol. State-specific preparation of incident CH4 with one quantum of antisymmetric (ν3) stretch vibration further increases the CH4 reactivity enabling comparison between translational and vibrational activation on both steps and terraces. The reaction is modeled with first principles quantum theory that accurately describes dissociative chemisorption at different sites on the surface.
Delocalized Quantum States Enhance Photocell Efficiency
Zhang, Yiteng; Alharbi, Fahhad H; Engel, Greg; Kais, Sabre
2014-01-01
The high quantum efficiency of photosynthetic complexes has inspired researchers to explore new routes to utilize this process for photovoltaic devices. Quantum coherence has been demonstrated to play a crucial role within this process. Herein, we propose a three-dipole system as a model of a new photocell type which exploits the coherence among its three dipoles. We have proved that the efficiency of such a photocell is greatly enhanced by quantum coherence. We have also predicted that the photocurrents can be enhanced by about 49.5 % in such a coherent coupled dipole system compared with the uncoupled dipoles. These results suggest a promising novel design aspect of photosynthesis-mimicking photovoltaic devices.
Relaxation of vibrationally excited states in solid "nitrate-nitrite" binary systems
Aliev, A. R.; Akhmedov, I. R.; Kakagasanov, M. G.; Aliev, Z. A.; Gafurov, M. M.; Rabadanov, K. Sh.; Amirov, A. M.
2017-10-01
The processes of molecular relaxation in the solid NaNO3-NaNO2 and KNO3-KNO2 "nitrate-nitrite" binary systems have been investigated by Raman spectroscopy. The relaxation time of the vibration ν1(A) of an NO- 3 anion in the binary system is found to be shorter than that in individual nitrate. The increase in the relaxation rate is explained by the existence of an additional mechanism of relaxation of vibrationally excited states of the nitrate ion in the system. This mechanism is related to the excitation of vibration of another anion (NO- 2) and generation of a lattice phonon. It has been established that this relaxation mechanism is implemented provided that the difference between the frequencies of the aforementioned vibrations correspond to the range of sufficiently high density of states in the phonon spectrum.
Chen, Ye-Hong; Shi, Zhi-Cheng; Song, Jie; Xia, Yan; Zheng, Shi-Biao
2017-10-01
In this paper, we propose an approach to accelerate the dissipation dynamics for quantum state generation with Lyapunov control. The strategy is to add target-state-related coherent control fields into the dissipation process to intuitively improve the evolution speed. By applying the current approach, without losing the advantages of dissipation dynamics, the target stationary states can be generated in a much shorter time as compared to that via traditional dissipation dynamics. As a result, the current approach containing the advantages of coherent unitary dynamics and dissipation dynamics allows for a significant improvement in quantum state generation.
High-NOON states by mixing quantum and classical light.
Afek, Itai; Ambar, Oron; Silberberg, Yaron
2010-05-14
Precision measurements can be brought to their ultimate limit by harnessing the principles of quantum mechanics. In optics, multiphoton entangled states, known as NOON states, can be used to obtain high-precision phase measurements, becoming more and more advantageous as the number of photons grows. We generated "high-NOON" states (N = 5) by multiphoton interference of quantum down-converted light with a classical coherent state in an approach that is inherently scalable. Super-resolving phase measurements with up to five entangled photons were produced with a visibility higher than that obtainable using classical light only.
Weak measurements, quantum-state collapse, and the Born rule
Patel, Apoorva; Kumar, Parveen
2017-08-01
Projective measurement is used as a fundamental axiom in quantum mechanics, even though it is discontinuous and cannot predict which measured operator eigenstate will be observed in which experimental run. The probabilistic Born rule gives it an ensemble interpretation, predicting proportions of various outcomes over many experimental runs. Understanding gradual weak measurements requires replacing this scenario with a dynamical evolution equation for the collapse of the quantum state in individual experimental runs. We revisit the quantum trajectory framework that models quantum measurement as a continuous nonlinear stochastic process. We describe the ensemble of quantum trajectories as noise fluctuations on top of geodesics that attract the quantum state towards the measured operator eigenstates. In this effective theory framework for the ensemble of quantum trajectories, the measurement interaction can be specific to each system-apparatus pair, a context necessary for understanding weak measurements. Also in this framework, the constraint to reproduce projective measurement as per the Born rule in the appropriate limit requires that the magnitudes of the noise and the attraction are precisely related, in a manner reminiscent of the fluctuation-dissipation relation. This relation implies that both the noise and the attraction have a common origin in the underlying measurement interaction between the system and the apparatus. We analyze the quantum trajectory ensemble for the scenarios of quantum diffusion and binary quantum jump, and show that the ensemble distribution is completely determined in terms of a single evolution parameter. This trajectory ensemble distribution can be tested in weak measurement experiments. We also comment on how the required noise may arise in the measuring apparatus.
Gaussian private quantum channel with squeezed coherent states
Jeong, Kabgyun; Kim, Jaewan; Lee, Su-Yong
2015-01-01
While the objective of conventional quantum key distribution (QKD) is to secretly generate and share the classical bits concealed in the form of maximally mixed quantum states, that of private quantum channel (PQC) is to secretly transmit individual quantum states concealed in the form of maximally mixed states using shared one-time pad and it is called Gaussian private quantum channel (GPQC) when the scheme is in the regime of continuous variables. We propose a GPQC enhanced with squeezed coherent states (GPQCwSC), which is a generalization of GPQC with coherent states only (GPQCo) [Phys. Rev. A 72, 042313 (2005)]. We show that GPQCwSC beats the GPQCo for the upper bound on accessible information. As a subsidiary example, it is shown that the squeezed states take an advantage over the coherent states against a beam splitting attack in a continuous variable QKD. It is also shown that a squeezing operation can be approximated as a superposition of two different displacement operations in the small squeezing regime. PMID:26364893
Single-Atom Gating of Quantum State Superpositions
Energy Technology Data Exchange (ETDEWEB)
Moon, Christopher
2010-04-28
The ultimate miniaturization of electronic devices will likely require local and coherent control of single electronic wavefunctions. Wavefunctions exist within both physical real space and an abstract state space with a simple geometric interpretation: this state space - or Hilbert space - is spanned by mutually orthogonal state vectors corresponding to the quantized degrees of freedom of the real-space system. Measurement of superpositions is akin to accessing the direction of a vector in Hilbert space, determining an angle of rotation equivalent to quantum phase. Here we show that an individual atom inside a designed quantum corral1 can control this angle, producing arbitrary coherent superpositions of spatial quantum states. Using scanning tunnelling microscopy and nanostructures assembled atom-by-atom we demonstrate how single spins and quantum mirages can be harnessed to image the superposition of two electronic states. We also present a straightforward method to determine the atom path enacting phase rotations between any desired state vectors. A single atom thus becomes a real-space handle for an abstract Hilbert space, providing a simple technique for coherent quantum state manipulation at the spatial limit of condensed matter.
Gaussian private quantum channel with squeezed coherent states
Jeong, Kabgyun; Kim, Jaewan; Lee, Su-Yong
2015-09-01
While the objective of conventional quantum key distribution (QKD) is to secretly generate and share the classical bits concealed in the form of maximally mixed quantum states, that of private quantum channel (PQC) is to secretly transmit individual quantum states concealed in the form of maximally mixed states using shared one-time pad and it is called Gaussian private quantum channel (GPQC) when the scheme is in the regime of continuous variables. We propose a GPQC enhanced with squeezed coherent states (GPQCwSC), which is a generalization of GPQC with coherent states only (GPQCo) [Phys. Rev. A 72, 042313 (2005)]. We show that GPQCwSC beats the GPQCo for the upper bound on accessible information. As a subsidiary example, it is shown that the squeezed states take an advantage over the coherent states against a beam splitting attack in a continuous variable QKD. It is also shown that a squeezing operation can be approximated as a superposition of two different displacement operations in the small squeezing regime.
Gaussian private quantum channel with squeezed coherent states.
Jeong, Kabgyun; Kim, Jaewan; Lee, Su-Yong
2015-09-14
While the objective of conventional quantum key distribution (QKD) is to secretly generate and share the classical bits concealed in the form of maximally mixed quantum states, that of private quantum channel (PQC) is to secretly transmit individual quantum states concealed in the form of maximally mixed states using shared one-time pad and it is called Gaussian private quantum channel (GPQC) when the scheme is in the regime of continuous variables. We propose a GPQC enhanced with squeezed coherent states (GPQCwSC), which is a generalization of GPQC with coherent states only (GPQCo) [Phys. Rev. A 72, 042313 (2005)]. We show that GPQCwSC beats the GPQCo for the upper bound on accessible information. As a subsidiary example, it is shown that the squeezed states take an advantage over the coherent states against a beam splitting attack in a continuous variable QKD. It is also shown that a squeezing operation can be approximated as a superposition of two different displacement operations in the small squeezing regime.
Disentanglement of source and target and the laser quantum state.
Noh, Changsuk; Carmichael, H J
2008-03-28
Disentanglement of a laser source from its target qubit is proposed as a criterion establishing the laser quantum state as a coherent state. It is shown that the source-target density operator has a unique factorization in coherent states when the environmental record monitoring laser pump quanta is ignored. The source-target state conditioned upon the complete environmental record is entangled, though, as a state of known total quanta number (source plus target).
Energy Technology Data Exchange (ETDEWEB)
Levy, James E; Carroll, Malcolm S; Ganti, Anand; Phillips, Cynthia A; Landahl, Andrew J; Gurrieri, Thomas M; Carr, Robert D; Stalford, Harold L; Nielsen, Erik, E-mail: jelevy@sandia.gov [Sandia National Laboratories, Albuquerque, NM 87185 (United States)
2011-08-15
In this paper we present the impact of classical electronics constraints on a solid-state quantum dot logical qubit architecture. Constraints due to routing density, bandwidth allocation, signal timing and thermally aware placement of classical supporting electronics significantly affect the quantum error correction circuit's error rate (by a factor of {approx}3-4 in our specific analysis). We analyze one level of a quantum error correction circuit using nine data qubits in a Bacon-Shor code configured as a quantum memory. A hypothetical silicon double quantum dot quantum bit (qubit) is used as the fundamental element. A pessimistic estimate of the error probability of the quantum circuit is calculated using the total number of gates and idle time using a provably optimal schedule for the circuit operations obtained with an integer program methodology. The micro-architecture analysis provides insight about the different ways the electronics impact the circuit performance (e.g. extra idle time in the schedule), which can significantly limit the ultimate performance of any quantum circuit and therefore is a critical foundation for any future larger scale architecture analysis.
Reducing collective quantum state rotation errors with reversible dephasing
Energy Technology Data Exchange (ETDEWEB)
Cox, Kevin C.; Norcia, Matthew A.; Weiner, Joshua M.; Bohnet, Justin G.; Thompson, James K. [JILA, NIST, and Department of Physics, University of Colorado, 440 UCB, Boulder, Colorado 80309 (United States)
2014-12-29
We demonstrate that reversible dephasing via inhomogeneous broadening can greatly reduce collective quantum state rotation errors, and observe the suppression of rotation errors by more than 21 dB in the context of collective population measurements of the spin states of an ensemble of 2.1×10{sup 5} laser cooled and trapped {sup 87}Rb atoms. The large reduction in rotation noise enables direct resolution of spin state populations 13(1) dB below the fundamental quantum projection noise limit. Further, the spin state measurement projects the system into an entangled state with 9.5(5) dB of directly observed spectroscopic enhancement (squeezing) relative to the standard quantum limit, whereas no enhancement would have been obtained without the suppression of rotation errors.
On the nature of highly vibrationally excited states of thiophosgene
Indian Academy of Sciences (India)
to understand, and hence assign, the eigenstates. Since the approximate quantum numbers arise out of the local dynamics due to specific resonances, relevant at the energies of interest, the assignment is inherently dynamical in nature. In a nutshell, several decades of work have shown that dynamical assignments can be.
Quantum Communication Using Macroscopic Phase Entangled States
2015-12-10
realistic requirement. vi. List of patents • Patent application # 14/508,741, “Quantum key distribution over large distances using amplifiers...and unitary transformations”, James Franson, Todd Pittman, Brian Kirby, and Garrett Hickman 8 vii. List of publications • G. Jaeger, D. S
Quantum Averaging of Squeezed States of Light
DEFF Research Database (Denmark)
Squeezing has been recognized as the main resource for quantum information processing and an important resource for beating classical detection strategies. It is therefore of high importance to reliably generate stable squeezing over longer periods of time. The averaging procedure for a single...
Quenched dynamics of entangled states in correlated quantum dots
Maslova, N. S.; Arseyev, P. I.; Mantsevich, V. N.
2017-10-01
The time evolution of an initially prepared entangled state in the system of coupled quantum dots has been analyzed by means of two different theoretical approaches: equations of motion for all orders localized electron correlation functions, considering interference effects, and kinetic equations for the pseudoparticle occupation numbers with constraint on the possible physical states. Results obtained by means of different approaches were carefully analyzed and compared to each other. Revealing a direct link between concurrence (degree of entanglement) and quantum dots pair correlation functions allowed us to follow the changes of entanglement during the time evolution of the coupled quantum dots system. It was demonstrated that the degree of entanglement can be controllably tuned during the time evolution of quantum dots system.
Wigner function and the probability representation of quantum states
Directory of Open Access Journals (Sweden)
Man’ko Margarita A.
2014-01-01
Full Text Available The relation of theWigner function with the fair probability distribution called tomographic distribution or quantum tomogram associated with the quantum state is reviewed. The connection of the tomographic picture of quantum mechanics with the integral Radon transform of the Wigner quasidistribution is discussed. The Wigner–Moyal equation for the Wigner function is presented in the form of kinetic equation for the tomographic probability distribution both in quantum mechanics and in the classical limit of the Liouville equation. The calculation of moments of physical observables in terms of integrals with the state tomographic probability distributions is constructed having a standard form of averaging in the probability theory. New uncertainty relations for the position and momentum are written in terms of optical tomograms suitable for directexperimental check. Some recent experiments on checking the uncertainty relations including the entropic uncertainty relations are discussed.
Can a quantum critical state represent a blackbody?
Chakravarty, Sudip; Kraus, Per
2018-01-01
The blackbody theory of Planck played a seminal role in the development of quantum theory at the turn of the past century. A blackbody cavity is generally thought to be a collection of photons in thermal equilibrium; the radiation emitted is at all wavelengths, and the intensity follows a scaling law, which is Planck's characteristic distribution law. These photons arise from non-interacting normal modes. Here we suggest that certain quantum critical states when heated emit ;radiation; at all wavelengths and satisfy all the criteria of a blackbody. An important difference is that the ;radiation; does not necessarily consist of non-interacting photons, but also emergent relativistic bosons or fermions. The examples we provide include emergent relativistic fermions at a topological quantum critical point. This perspective on a quantum critical state may be illuminating in many unforeseen ways.
Can a quantum critical state represent a blackbody?
Chakravarty, Sudip
2016-01-01
The blackbody theory of Planck played a seminal role in the development of quantum theory at the turn of the past century. A blackbody cavity is generally thought to be a collection of photons in thermal equilibrium; the radiation emitted is at all wavelengths, and the intensity follows a scaling law, which is Planck's characteristic distribution law. These photons arise from non-interacting normal modes. Here we suggest that certain quantum critical states when heated emit "radiation" at all wavelengths and satisfy all the criteria of a blackbody. An important difference is that the "radiation" does not necessarily consist of non-interacting photons, but also emergent relativistic bosons or fermions. The examples we provide include emergent relativistic fermions at a topological quantum critical point. This perspective on a quantum critical state may be illuminating in many unforeseen ways.
Directory of Open Access Journals (Sweden)
Daniel Tirelli
2014-01-01
Full Text Available A new passive device for mitigating cable vibrations is proposed and its efficiency is assessed on 45-meter long taut cables through a series of free and forced vibration tests. It consists of a unilateral spring attached perpendicularly to the cable near the anchorage. Because of its ability to change the cable dynamic behaviour through intermittent activation, the device has been called state switched inducer (SSI. The cable behaviour is shown to be deeply modified by the SSI: the forced vibration response is anharmonicc and substantially reduced in amplitude whereas the free vibration decay is largely sped up through a beating phenomenon. The vibration mitigation effect is mainly due to the activation and coupling of various vibration modes, as evidenced in the response spectra of the equipped cable. This first large-scale experimental campaign shows that the SSI outperforms classical passive devices, thus paving the way to a new kind of low-cost vibration mitigation systems which do not rely on dissipation.
Lattice Gauge Quantum Simulation via State-Dependent Hopping
DEFF Research Database (Denmark)
Salami Dehkharghani, Amin
2017-01-01
We develop a quantum simulator architecture that is suitable for the simulation of U(1) Abelian gauge theories such as quantum electrodynamics. Our approach relies on the ability to control the hopping of a particle through a barrier by means of the internal quantum states of a neutral or charged...... impurity-particle sitting at the barrier. This scheme is highly experimentally feasible, as the correlated hopping does not require fine-tuning of the intra- and inter-species interactions. We investigate the applicability of the scheme in a double well potential, which is the basic building block...
Karhu, J.; Nauta, J.; Vainio, M.; Metsälä, M.; Hoekstra, S.; Halonen, L.
2016-06-01
A novel mid-infrared/near-infrared double resonant absorption setup for studying infrared-inactive vibrational states is presented. A strong vibrational transition in the mid-infrared region is excited using an idler beam from a singly resonant continuous-wave optical parametric oscillator, to populate an intermediate vibrational state. High output power of the optical parametric oscillator and the strength of the mid-infrared transition result in efficient population transfer to the intermediate state, which allows measuring secondary transitions from this state with a high signal-to-noise ratio. A secondary, near-infrared transition from the intermediate state is probed using cavity ring-down spectroscopy, which provides high sensitivity in this wavelength region. Due to the narrow linewidths of the excitation sources, the rovibrational lines of the secondary transition are measured with sub-Doppler resolution. The setup is used to access a previously unreported symmetric vibrational state of acetylene, ν 1 + ν 2 + ν 3 + ν4 1 + ν5 - 1 in the normal mode notation. Single-photon transitions to this state from the vibrational ground state are forbidden. Ten lines of the newly measured state are observed and fitted with the linear least-squares method to extract the band parameters. The vibrational term value was measured to be at 9775.0018(45) cm-1, the rotational parameter B was 1.162 222(37) cm-1, and the quartic centrifugal distortion parameter D was 3.998(62) × 10-6 cm-1, where the numbers in the parenthesis are one-standard errors in the least significant digits.
Karhu, J; Nauta, J; Vainio, M; Metsälä, M; Hoekstra, S; Halonen, L
2016-06-28
A novel mid-infrared/near-infrared double resonant absorption setup for studying infrared-inactive vibrational states is presented. A strong vibrational transition in the mid-infrared region is excited using an idler beam from a singly resonant continuous-wave optical parametric oscillator, to populate an intermediate vibrational state. High output power of the optical parametric oscillator and the strength of the mid-infrared transition result in efficient population transfer to the intermediate state, which allows measuring secondary transitions from this state with a high signal-to-noise ratio. A secondary, near-infrared transition from the intermediate state is probed using cavity ring-down spectroscopy, which provides high sensitivity in this wavelength region. Due to the narrow linewidths of the excitation sources, the rovibrational lines of the secondary transition are measured with sub-Doppler resolution. The setup is used to access a previously unreported symmetric vibrational state of acetylene, ν1+ν2+ν3+ν4 (1)+ν5 (-1) in the normal mode notation. Single-photon transitions to this state from the vibrational ground state are forbidden. Ten lines of the newly measured state are observed and fitted with the linear least-squares method to extract the band parameters. The vibrational term value was measured to be at 9775.0018(45) cm(-1), the rotational parameter B was 1.162 222(37) cm(-1), and the quartic centrifugal distortion parameter D was 3.998(62) × 10(-6) cm(-1), where the numbers in the parenthesis are one-standard errors in the least significant digits.
Quantum localized states in photonic flat-band lattices
Rojas-Rojas, S.; Morales-Inostroza, L.; Vicencio, R. A.; Delgado, A.
2017-10-01
The localization of light in flat-band lattices has been recently proposed and experimentally demonstrated in several configurations, assuming a classical description of light. Here we study the problem of light localization in the quantum regime. We focus on quasi-one-dimensional and two-dimensional lattices which exhibit a perfect flat band inside their linear spectrum. Localized quantum states are constructed as eigenstates of the interaction Hamiltonian with a vanishing eigenvalue and a well defined total photon number. These are superpositions of Fock states with probability amplitudes given by positive as well as negative square roots of multinomial coefficients. The classical picture can be recovered by considering Poissonian superpositions of localized quantum states with different total photon number. We also study the separability properties of flat-band quantum states and apply them to the transmission of information via multicore fibers, where these states allow for the total passive suppression of photon crosstalk and exhibit robustness against photon losses. At the end, we propose an on-chip setup for the experimental preparation of localized quantum states of light for any number of photons.
Macroscopic superposition states and decoherence by quantum telegraph noise
Energy Technology Data Exchange (ETDEWEB)
Abel, Benjamin Simon
2008-12-19
In the first part of the present thesis we address the question about the size of superpositions of macroscopically distinct quantum states. We propose a measure for the ''size'' of a Schroedinger cat state, i.e. a quantum superposition of two many-body states with (supposedly) macroscopically distinct properties, by counting how many single-particle operations are needed to map one state onto the other. We apply our measure to a superconducting three-junction flux qubit put into a superposition of clockwise and counterclockwise circulating supercurrent states and find this Schroedinger cat to be surprisingly small. The unavoidable coupling of any quantum system to many environmental degrees of freedom leads to an irreversible loss of information about an initially prepared superposition of quantum states. This phenomenon, commonly referred to as decoherence or dephasing, is the subject of the second part of the thesis. We have studied the time evolution of the reduced density matrix of a two-level system (qubit) subject to quantum telegraph noise which is the major source of decoherence in Josephson charge qubits. We are able to derive an exact expression for the time evolution of the reduced density matrix. (orig.)
Komnik, A; Saleur, H
2011-09-02
We verify the validity of the Cohen-Gallavotti fluctuation theorem for the strongly correlated problem of charge transfer through an impurity in a chiral Luttinger liquid, which is realizable experimentally as a quantum point contact in a fractional quantum Hall edge state device. This is accomplished via the development of an analytical method to calculate the full counting statistics of the problem in all the parameter regimes involving the temperature, the Hall voltage, and the gate voltage.
Vibrational dynamics of aniline (N2)1 clusters in their first excited singlet state
Hineman, M. F.; Kim, S. K.; Bernstein, E. R.; Kelley, D. F.
1992-04-01
The first excited singlet state S1 vibrational dynamics of aniline(N2)1 clusters are studied and compared to previous results on aniline(CH4)1 and aniline(Ar)1. Intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP) rates fall between the two extremes of the CH4 (fast IVR, slow VP) and Ar (slow IVR, fast VP) cluster results as is predicted by a serial IVR/VP model using Fermi's golden rule to describe IVR processes and a restricted Rice-Ramsperger-Kassel-Marcus (RRKM) theory to describe unimolecular VP rates. The density of states is the most important factor determining the rates. Two product states, 00 and 10b1, of bare aniline and one intermediate state ˜(00) in the overall IVR/VP process are observed and time resolved measurements are obtained for the 000 and ˜(000) transitions. The results are modeled with the serial mechanism described above.
Continuous variables triple-photon states quantum entanglement
Gonzalez, E. A. Rojas; Borne, A.; Boulanger, B.; Levenson, J.A.; Bencheikh, K
2017-01-01
We investigate the quantum entanglement of the three modes associated with the three-photon states obtained by triple-photon generation in a phase-matched third-order nonlinear optical interaction. Although the second order processes have been extensively dealt with, there is no direct analogy between the second and third-order mechanisms. We show for example the absence of quantum entanglement between the quadratures of the three modes in the case of spontaneous parametric triple-photon gene...
On the density of states of circular graphene quantum dots
Chau Nguyen, H.; Nguyen, Nhung T. T.; Nguyen, V. Lien
2017-10-01
We suggest a simple approach to calculate the local density of states that effectively applies to any structure created by an axially symmetric potential on a continuous graphene sheet such as circular graphene quantum dots or rings. Calculations performed for the graphene quantum dot studied in a recent scanning tunneling microscopy measurement (Gutierrez et al 2016 Nat. Phys. 12 1069-75) show an excellent experimental-theoretical agreement.
High-dimensional quantum state transfer through a quantum spin chain
Qin, Wei; Wang, Chuan; Long, Gui Lu
2013-01-01
In this paper, we investigate a high-dimensional quantum state transfer protocol. An arbitrary unknown high-dimensional state can be transferred with high fidelity between two remote registers through an XX coupling spin chain of arbitrary length. The evolution of the state transfer is determined by the natural dynamics of the chain without external modulation and coupling strength engineering. As a consequence, entanglement distribution with a high efficiency can be achieved. Also the strong field and high spin quantum number can partly counteract the effect of finite temperature to ensure the high fidelity of the protocol when the quantum data bus is in the thermal equilibrium state under an external magnetic field.
Network-based Arbitrated Quantum Signature Scheme with Graph State
Ma, Hongling; Li, Fei; Mao, Ningyi; Wang, Yijun; Guo, Ying
2017-08-01
Implementing an arbitrated quantum signature(QAS) through complex networks is an interesting cryptography technology in the literature. In this paper, we propose an arbitrated quantum signature for the multi-user-involved networks, whose topological structures are established by the encoded graph state. The determinative transmission of the shared keys, is enabled by the appropriate stabilizers performed on the graph state. The implementation of this scheme depends on the deterministic distribution of the multi-user-shared graph state on which the encoded message can be processed in signing and verifying phases. There are four parties involved, the signatory Alice, the verifier Bob, the arbitrator Trent and Dealer who assists the legal participants in the signature generation and verification. The security is guaranteed by the entanglement of the encoded graph state which is cooperatively prepared by legal participants in complex quantum networks.
State hybridization shapes the photocurrent in triple quantum dot nanojunctions
Energy Technology Data Exchange (ETDEWEB)
Beltako, Katawoura; Cavassilas, Nicolas; Michelini, Fabienne [Universités Aix Marseille et Toulon, CNRS, IM2NP, UMR 7334, 13288 Marseille (France)
2016-08-15
We investigated a prototype of a quantum dot based photodetector made of a dot absorber interconnected with two lateral dot filters in contact with semiconducting leads. Using the nonequilibrium Green's function technique, we found that there are two opposite evolutions of the photocurrent in the vicinity of the tunnel resonance for such a kind of nanodevice. This evolution depends on where the strongest hybridization of states happens, and hence still reveals a quantum effect. If the filter states hybridize more with the absorber states than the ones of the leads, the photocurrent shows a maximum at the tunnel resonance, while it is minimized in the opposite case.
Manipulating collective quantum states of ultracold atoms by probing
DEFF Research Database (Denmark)
Wade, Andrew Christopher James
2015-01-01
nature of the measurement interaction and backaction is yet to be realised. This dissertation is concerned with ultracold atoms and their control via fully quantum mechanical probes. Nonclassical, squeezed and entangled states of matter and single photon sources are important for fundamental studies...... and quantum technologies. By probing, the production of squeezed and entangled states of collective variables in a Bose-Einstein condensate is investigated. Thereafter, an atomic probe using the strong interactions between highly excited atomic states, manipulates the light-matter dynamics of an ultracold gas...
Continuous variable quantum key distribution with modulated entangled states
DEFF Research Database (Denmark)
Madsen, Lars S; Usenko, Vladyslav C.; Lassen, Mikael
2012-01-01
based on coherent states and continuous variable measurements are resilient to high loss in the channel, but are strongly affected by small amounts of channel excess noise. Here we propose and experimentally address a continuous variable quantum key distribution protocol that uses modulated fragile...... entangled states of light to greatly enhance the robustness to channel noise. We experimentally demonstrate that the resulting quantum key distribution protocol can tolerate more noise than the benchmark set by the ideal continuous variable coherent state protocol. Our scheme represents a very promising...
Average subentropy, coherence and entanglement of random mixed quantum states
Energy Technology Data Exchange (ETDEWEB)
Zhang, Lin, E-mail: godyalin@163.com [Institute of Mathematics, Hangzhou Dianzi University, Hangzhou 310018 (China); Singh, Uttam, E-mail: uttamsingh@hri.res.in [Harish-Chandra Research Institute, Allahabad, 211019 (India); Pati, Arun K., E-mail: akpati@hri.res.in [Harish-Chandra Research Institute, Allahabad, 211019 (India)
2017-02-15
Compact expressions for the average subentropy and coherence are obtained for random mixed states that are generated via various probability measures. Surprisingly, our results show that the average subentropy of random mixed states approaches the maximum value of the subentropy which is attained for the maximally mixed state as we increase the dimension. In the special case of the random mixed states sampled from the induced measure via partial tracing of random bipartite pure states, we establish the typicality of the relative entropy of coherence for random mixed states invoking the concentration of measure phenomenon. Our results also indicate that mixed quantum states are less useful compared to pure quantum states in higher dimension when we extract quantum coherence as a resource. This is because of the fact that average coherence of random mixed states is bounded uniformly, however, the average coherence of random pure states increases with the increasing dimension. As an important application, we establish the typicality of relative entropy of entanglement and distillable entanglement for a specific class of random bipartite mixed states. In particular, most of the random states in this specific class have relative entropy of entanglement and distillable entanglement equal to some fixed number (to within an arbitrary small error), thereby hugely reducing the complexity of computation of these entanglement measures for this specific class of mixed states.
Electron states in semiconductor quantum dots.
Dhayal, Suman S; Ramaniah, Lavanya M; Ruda, Harry E; Nair, Selvakumar V
2014-11-28
In this work, the electronic structures of quantum dots (QDs) of nine direct band gap semiconductor materials belonging to the group II-VI and III-V families are investigated, within the empirical tight-binding framework, in the effective bond orbital model. This methodology is shown to accurately describe these systems, yielding, at the same time, qualitative insights into their electronic properties. Various features of the bulk band structure such as band-gaps, band curvature, and band widths around symmetry points affect the quantum confinement of electrons and holes. These effects are identified and quantified. A comparison with experimental data yields good agreement with the calculations. These theoretical results would help quantify the optical response of QDs of these materials and provide useful input for applications.
Ghazaryan, E M; Sarkisyan, H A
2002-01-01
Electron states in spherical quantum dots are studied, taking into account boundary conditions. The threshold habit of level appearance inside the quantum dots is revealed. The electron energy dependences on the quantum dots radius and confinement potential height
Projected gradient descent algorithms for quantum state tomography
Bolduc, Eliot; Knee, George C.; Gauger, Erik M.; Leach, Jonathan
2017-10-01
Accurate quantum tomography is a vital tool in both fundamental and applied quantum science. It is a task that involves processing a noisy measurement record in order to construct a reliable estimate of an unknown quantum state, and is central to quantum computing, metrology and communication. To date, many different approaches to quantum state estimation have been developed, yet no one method fits all applications, and all fail relatively quickly as the dimensionality of the unknown state grows. In this work, we suggest that projected gradient descent is a method that can evade some of these shortcomings. We present three tomography algorithms that use projected gradient descent and compare their performance with state-of-the-art alternatives, i.e., the diluted iterative algorithm and convex programming. Our results find in favour of the general class of projected gradient descent methods due to their speed, applicability to large states, and the range of conditions in which they perform as well as providing insight into which variant of projected gradient descent ought to be used in various measurement scenarios.
On the initial state of the Universe in quantum cosmology
Directory of Open Access Journals (Sweden)
N.N. Gorobey
2015-06-01
Full Text Available The paper discusses the problem of the initial state of a quantum inflationary Universe. Considering the dynamics of the inflation scalar field at the beginning of the inflation stage in the context of semi-classical approximation, we have identified this field with a cosmic time parameter. The early Universe state was defined as an initial value of the inflation field. Other degrees of the Universe freedom, including the scale factor, are treated within the framework of the quantum theory. The initial state of quantum degrees of freedom at the beginning of the inflation must be defined as well. A principle of the least excitation of physical degrees of freedom for the Universe has been proposed to determine the initial state of the quantum Universe. A uniform anisotropic model of the Universe was considered where its size and the anisotropic parameters were quantum dynamical variables. Assuming that the Universe size is a radial variable in the configuration space of the theory, the definition of the Hamiltonian of the Universe is rendered more precise. A simple exponential form of the initial state of the Universe is suggested and the Universe initial size is estimated for this form.
Li, Ao; Chen, Tian; Zhou, Yiheng; Wang, Xiangbin
2016-05-01
Quantum blockades as a nonlinear quantum optical process have been well studied in recent years. Using the quantum trajectory method, we calculate and discuss the output photon number distributions of a single-photon blockade process in a Kerr nonlinear dissipative resonator, revealing that the probability of the single-photon state can be optimized. Then we show through numerical simulations that such a quasi-single-photon source can drastically raise the key rate in the decoy-state quantum key distribution.
ierarchies of non-classical states in quantum optics
Indian Academy of Sciences (India)
states of the quantised electromagnetic ﬁeld, and drawing out the experimental implica- tions of such classiﬁcation. In particular it is interesting to see how one can bring out as sharply as possible those features that show the nonclassical properties of radiation. Given a quantum mechanical state of radiation produced in ...
The Capacity of Quantum Channel with General Signal States
Holevo, A. S.
1996-01-01
It is shown that the capacity of a classical-quantum channel with arbitrary (possibly mixed) states equals to the maximum of the entropy bound with respect to all apriori distributions. This completes the recent result of Hausladen, Jozsa, Schumacher, Westmoreland and Wooters, who proved the equality for the pure state channel.
Greca, Ileana Maria; Freire, Olival
Teaching physics implies making choices. In the case of teaching quantum physics, besides an educational choice - the didactic strategy - another choice must be made, an epistemological one, concerning the interpretation of quantum theory itself. These two choices are closely connected. We have chosen a didactic strategy that privileges the phenomenological-conceptual approach, with emphasis upon quantum features of the systems, instead of searching for classical analogies. This choice has led us to present quantum theory associated with an orthodox, yet realistic, interpretation of the concept of quantum state, considered as the key concept of quantum theory, representing the physical reality of a system, independent of measurement processes. The results of the mplementation of this strategy, with three groups of engineering students, showed that more than a half of them attained a reasonable understanding of the basics of quantum mechanics (QM) for this level. In addition, a high degree of satisfaction was attained with the classes as 80% of the students of the experimental groups claimed to have liked it and to be interested in learning more about QM.
Van der Waals potential and vibrational energy levels of the ground state radon dimer
Sheng, Xiaowei; Qian, Shifeng; Hu, Fengfei
2017-08-01
In the present paper, the ground state van der Waals potential of the Radon dimer is described by the Tang-Toennies potential model, which requires five essential parameters. Among them, the two dispersion coefficients C6 and C8 are estimated from the well determined dispersion coefficients C6 and C8 of Xe2. C10 is estimated by using the approximation equation that C6C10/C82 has an average value of 1.221 for all the rare gas dimers. With these estimated dispersion coefficients and the well determined well depth De and Re the Born-Mayer parameters A and b are derived. Then the vibrational energy levels of the ground state radon dimer are calculated. 40 vibrational energy levels are observed in the ground state of Rn2 dimer. The last vibrational energy level is bound by only 0.0012 cm-1.
Quantum Harmonic Oscillator State Control in a Squeezed Fock Basis.
Kienzler, D; Lo, H-Y; Negnevitsky, V; Flühmann, C; Marinelli, M; Home, J P
2017-07-21
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 sqrt[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.
Kaposi, A D; Vanderkooi, J. M.
1992-01-01
The vibrational frequencies of the singlet excited state of Mg-substituted myoglobin and relative absorption probabilities were determined by fluorescence line-narrowing spectroscopy. These spectra contain information on the structure of the excited state species, and the availability of vibrationally resolved spectra from excited state biomolecules should aid in elucidating their structure and reactivity.
Optimal secure quantum teleportation of coherent states of light
Liuzzo-Scorpo, Pietro; Adesso, Gerardo
2017-08-01
We investigate quantum teleportation of ensembles of coherent states of light with a Gaussian distributed displacement in phase space. Recently, the following general question has been addressed in [P. Liuzzo-Scorpo et al., arXiv:1705.03017]: Given a limited amount of entanglement and mean energy available as resources, what is the maximal fidelity that can be achieved on average in the teleportation of such an alphabet of states? Here, we consider a variation of this question, where Einstein-Podolsky-Rosen steering is used as a resource rather than plain entanglement. We provide a solution by means of an optimisation within the space of Gaussian quantum channels, which allows for an intuitive visualisation of the problem. We first show that not all channels are accessible with a finite degree of steering, and then prove that practical schemes relying on asymmetric two-mode Gaussian states enable one to reach the maximal fidelity at the border with the inaccessible region. Our results provide a rigorous quantitative assessment of steering as a resource for secure quantum teleportation beyond the so-called no-cloning threshold. The schemes we propose can be readily implemented experimentally by a conventional Braunstein-Kimble continuous variable teleportation protocol involving homodyne detections and corrective displacements with an optimally tuned gain. These protocols can be integrated as elementary building blocks in quantum networks, for reliable storage and transmission of quantum optical states.
Optimal quantum error correcting codes from absolutely maximally entangled states
Raissi, Zahra; Gogolin, Christian; Riera, Arnau; Acín, Antonio
2018-02-01
Absolutely maximally entangled (AME) states are pure multi-partite generalizations of the bipartite maximally entangled states with the property that all reduced states of at most half the system size are in the maximally mixed state. AME states are of interest for multipartite teleportation and quantum secret sharing and have recently found new applications in the context of high-energy physics in toy models realizing the AdS/CFT-correspondence. We work out in detail the connection between AME states of minimal support and classical maximum distance separable (MDS) error correcting codes and, in particular, provide explicit closed form expressions for AME states of n parties with local dimension \
Faizan, Mohd; Alam, Mohammad Jane; Ahmad, Shabbir
2017-11-01
In the present investigation, spectroscopic techniques (FTIR, FT-Raman and UV-Vis) and quantum chemical calculations are employed for exploring vibrational and electronic spectra of sulindac compound. The calculations are performed on most stable conformer of the sulindac molecule using density functional theory (DFT). Anharmonic corrections are made to frequencies using vibrational second-order perturbation theory (VPT2). The effect of intermolecular interactions on the vibrational dynamics has been analyzed using dimeric structure of sulindac molecule. Hirshfeld surface analysis and 2D fingerprint plots are utilized to investigate the nature of interaction present in the crystal system. To account for electronic spectra in different solvents, an integral equation formalism of polarizable continuum model (IEFPCM) at TD-DFT/B3LYP/6-31G(d,p) level of theory has been employed. An excellent agreement between the theoretical and experimental data over the entire spectral region is observed. In addition, natural bond orbital (NBO) analysis, frontier molecular orbitals, nonlinear optical properties (NLO) and molecular electrostatic potential (MEP) analysis are also reported.
Dynamical topological quantum phase transitions for mixed states
Heyl, M.; Budich, J. C.
2017-11-01
We introduce and study the dynamical probes of band-structure topology in the postquench time evolution of quantum many-body systems initialized in mixed states. Our construction generalizes the notion of dynamical quantum phase transitions (DQPTs), a real-time counterpart of conventional equilibrium phase transitions in quantum dynamics, to finite temperatures and generalized Gibbs ensembles. The nonanalytical signatures hallmarking these mixed-state DQPTs are found to be characterized by observable phase singularities manifesting in the dynamical formation of vortex-antivortex pairs in the interferometric phase of the density matrix. Studying quenches in Chern insulators, we find that changes in the topological properties of the Hamiltonian can be identified in this scenario, without ever preparing a topologically nontrivial or low-temperature initial state. Our observations are of immediate relevance for current experiments aimed at realizing topological phases in ultracold atomic gases.
Influence of scattering processes on electron quantum states in nanowires
Directory of Open Access Journals (Sweden)
Pozdnyakov Dmitry
2007-01-01
Full Text Available AbstractIn the framework of quantum perturbation theory the self-consistent method of calculation of electron scattering rates in nanowires with the one-dimensional electron gas in the quantum limit is worked out. The developed method allows both the collisional broadening and the quantum correlations between scattering events to be taken into account. It is an alternativeper seto the Fock approximation for the self-energy approach based on Green’s function formalism. However this approach is free of mathematical difficulties typical to the Fock approximation. Moreover, the developed method is simpler than the Fock approximation from the computational point of view. Using the approximation of stable one-particle quantum states it is proved that the electron scattering processes determine the dependence of electron energy versus its wave vector.
Radtke, T.; Fritzsche, S.
2008-11-01
Entanglement is known today as a key resource in many protocols from quantum computation and quantum information theory. However, despite the successful demonstration of several protocols, such as teleportation or quantum key distribution, there are still many open questions of how entanglement affects the efficiency of quantum algorithms or how it can be protected against noisy environments. The investigation of these and related questions often requires a search or optimization over the set of quantum states and, hence, a parametrization of them and various other objects. To facilitate this kind of studies in quantum information theory, here we present an extension of the FEYNMAN program that was developed during recent years as a toolbox for the simulation and analysis of quantum registers. In particular, we implement parameterizations of hermitian and unitary matrices (of arbitrary order), pure and mixed quantum states as well as separable states. In addition to being a prerequisite for the study of many optimization problems, these parameterizations also provide the necessary basis for heuristic studies which make use of random states, unitary matrices and other objects. Program summaryProgram title: FEYNMAN Catalogue identifier: ADWE_v4_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v4_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 24 231 No. of bytes in distributed program, including test data, etc.: 1 416 085 Distribution format: tar.gz Programming language: Maple 11 Computer: Any computer with Maple software installed Operating system: Any system that supports Maple; program has been tested under Microsoft Windows XP, Linux Classification: 4.15 Does the new version supersede the previous version?: Yes Nature of problem: During the last decades
Quantum theory of the solid state
Callaway, Joseph
1991-01-01
This new edition presents a comprehensive, up-to-date survey of the concepts and methods in contemporary condensed matter physics, emphasizing topics that can be treated by quantum mechanical methods. The book features tutorial discussions of a number of current research topics.Also included are updated treatments of topics that have developed significantly within the past several years, such as superconductivity, magnetic impurities in metals, methods for electronic structure calculations, magnetic ordering in insulators and metals, and linear response theory. Advanced level graduate students
STOCHASTIC PARAMETRIC VIBRATIONS OF ELASTIC SYSTEMS WITH REGARD TO THEIR PREVIOUS STATES
Directory of Open Access Journals (Sweden)
Vorona Y.V.
2014-06-01
Full Text Available Reduced models of stochastic parametric vibrations of elastic systems with regard to their previous states were constructed on the base of the finite element method, generalized coordinates method, asymptotic method and functional approach. Stochastic stability problem was formulated in the average for the moment functions of the first order phase coordinates. The stability of stochastic parametric vibrations of the single degree of freedom system with regard to its previous states was investigated by the 7-stages 5-order continuous Runge-Kutta method and nested formulas Dormand-Prince.
Local decoherence-resistant quantum states of large systems
Energy Technology Data Exchange (ETDEWEB)
Mishra, Utkarsh; Sen, Aditi; Sen, Ujjwal, E-mail: ujjwal@hri.res.in
2015-02-06
We identify an effectively decoherence-free class of quantum states, each of which consists of a “minuscule” and a “large” sector, against local noise. In particular, the content of entanglement and other quantum correlations in the minuscule to large partition is independent of the number of particles in their large sectors, when all the particles suffer passage through local amplitude and phase damping channels. The states of the large sectors are distinct in terms of markedly different amounts of violation of Bell inequality. In case the large sector is macroscopic, such states are akin to the Schrödinger cat. - Highlights: • We identify an effectively decoherence-free class of quantum states of large systems. • We work with local noise models. • Decay of entanglement as well as information-theoretic quantum correlations considered. • The states are of the form of the Schrödinger cats, with minuscule and large sectors. • The states of the large sector are distinguishable by their violation of Bell inequality.
Quantum non-Gaussian Depth of Single-Photon States.
Straka, Ivo; Predojević, Ana; Huber, Tobias; Lachman, Lukáš; Butschek, Lorenz; Miková, Martina; Mičuda, Michal; Solomon, Glenn S; Weihs, Gregor; Ježek, Miroslav; Filip, Radim
2014-11-28
We introduce and experimentally explore the concept of the non-Gaussian depth of single-photon states with a positive Wigner function. The depth measures the robustness of a single-photon state against optical losses. The directly witnessed quantum non-Gaussianity withstands significant attenuation, exhibiting a depth of 18 dB, while the nonclassicality remains unchanged. Quantum non-Gaussian depth is an experimentally approachable quantity that is much more robust than the negativity of the Wigner function. Furthermore, we use it to reveal significant differences between otherwise strongly nonclassical single-photon sources.
Quantum state transfer in a q-deformed chain
Energy Technology Data Exchange (ETDEWEB)
L' Innocente, Sonia [Dipartimento di Matematica ed Informatica, Universita di Camerino, 62032 Camerino (Italy); Lupo, Cosmo; Mancini, Stefano [Dipartimento di Fisica, Universita di Camerino, 62032 Camerino (Italy)], E-mail: sonia.linnocente@unicam.it, E-mail: cosmo.lupo@unicam.it, E-mail: stefano.mancini@unicam.it
2009-11-27
We investigate the quantum state transfer in a chain of particles satisfying the q-deformed oscillators algebra. This general algebraic setting includes the spin chain and the bosonic chain as limiting cases. We study conditions for perfect state transfer depending on the number of sites and excitations on the chain. They are formulated by means of irreducible representations of a quantum algebra realized through Jordan-Schwinger maps. Playing with deformation parameters, we can study the effects of nonlinear perturbations or interpolate between the spin and bosonic chains.
Exotic quantum states for charmed baryons at finite temperature
Directory of Open Access Journals (Sweden)
Jiaxing Zhao
2017-12-01
Full Text Available The significantly screened heavy-quark potential in hot medium provides the possibility to study exotic quantum states of three-heavy-quark systems. By solving the Schrödinger equation for a three-charm-quark system at finite temperature, we found that, there exist Borromean states which might be realized in high energy nuclear collisions, and the binding energies of the system satisfy precisely the scaling law for Efimov states in the resonance limit.
Exotic quantum states for charmed baryons at finite temperature
Zhao, Jiaxing; Zhuang, Pengfei
2017-12-01
The significantly screened heavy-quark potential in hot medium provides the possibility to study exotic quantum states of three-heavy-quark systems. By solving the Schrödinger equation for a three-charm-quark system at finite temperature, we found that, there exist Borromean states which might be realized in high energy nuclear collisions, and the binding energies of the system satisfy precisely the scaling law for Efimov states in the resonance limit.
Quantum state generation via integrated frequency combs (Conference Presentation)
Roztocki, Piotr; Kues, Michael; Reimer, Christian; Wetzel, Benjamin; Grazioso, Fabio; Little, Brent E.; Chu, Sai T.; Johnston, Tudor W.; Bromberg, Yaron; Caspani, Lucia; Moss, David J.; Morandotti, Roberto
2017-02-01
The on-chip generation of optical quantum states will enable accessible advances for quantum technologies. We demonstrate that integrated quantum frequency combs (based on high-Q microring resonators made from a CMOS-compatible, high refractive-index doped-glass platform) can enable the generation of pure heralded single photons, cross-polarized photon pairs, as well as bi- and multi-photon entangled qubit states over a broad frequency comb covering the S, C, L telecommunications band, with photon frequencies corresponding to standard telecommunication channels spaced by 200 GHz. Exploiting a self-locked, intra-cavity excitation configuration, a highly-stable source of multiplexed heralded single photons is demonstrated, operating continuously for several weeks with less than 5% fluctuations. The photon bandwidth of 110 MHz is compatible with quantum memories, and high photon purity was confirmed through single-photon auto-correlation measurements. In turn, by simultaneously exciting two orthogonal polarization mode resonances, we demonstrate the first realization of type-II spontaneous FWM (in analogy to type-II spontaneous parametric down-conversion), allowing the direct generation of orthogonally-polarized photon pairs on a chip. By using a double-pulse excitation, we demonstrate the generation of time-bin entangled photon pairs. We measure qubit entanglement with visibilities above 90%, enabling the implementation of quantum information processing protocols. Finally, the excitation field and the generated photons are intrinsically bandwidth-matched due to the resonant characteristics of the ring cavity, enabling the multiplication of Bell states and the generation of a four-photon time-bin entangled state. We confirm the generation of this four-photon entangled state through four-photon quantum interference.
Quantum teleportation and information splitting via four-qubit cluster state and a Bell state
Ramírez, Marlon David González; Falaye, Babatunde James; Sun, Guo-Hua; Cruz-Irisson, M.; Dong, Shi-Hai
2017-10-01
Quantum teleportation provides a "bodiless" way of transmitting the quantum state from one object to another, at a distant location, using a classical communication channel and a previously shared entangled state. In this paper, we present a tripartite scheme for probabilistic teleportation of an arbitrary single qubit state, without losing the information of the state being teleported, via a fourqubit cluster state of the form | ϕ>1234 = α|0000>+ β|1010>+ γ|0101>- η|1111>, as the quantum channel, where the nonzero real numbers α, β, γ, and η satisfy the relation j αj2 + | β|2 + | γ|2 + | η|2 = 1. With the introduction of an auxiliary qubit with state |0>, using a suitable unitary transformation and a positive-operator valued measure (POVM), the receiver can recreate the state of the original qubit. An important advantage of the teleportation scheme demonstrated here is that, if the teleportation fails, it can be repeated without teleporting copies of the unknown quantum state, if the concerned parties share another pair of entangled qubit. We also present a protocol for quantum information splitting of an arbitrary two-particle system via the aforementioned cluster state and a Bell-state as the quantum channel. Problems related to security attacks were examined for both the cases and it was found that this protocol is secure. This protocol is highly efficient and easy to implement.
High-resolution infrared spectrum of triacetylene: The ν5 state revisited and new vibrational states
Doney, K. D.; Zhao, D.; Linnartz, H.
2015-10-01
New data are presented that follow from a high-resolution survey, from 3302 to 3352 cm-1, through expanding acetylene plasma, and covering the Csbnd H asymmetric (ν5) fundamental band of triacetylene (HC6H). Absorption signals are recorded using continuous wave cavity ring-down spectroscopy (cw-CRDS). A detailed analysis of the resulting spectra allows revisiting the molecular parameters of the ν5 fundamental band in terms of interactions with a perturbing state, which is observed for the first time. Moreover, four fully resolved hot bands (501 1011, 501 1111, 501 1311, and 101 801 1110), with band origins at 3328.5829(2), 3328.9994(2), 3328.2137(2) and 3310.8104(2) cm-1, respectively, are reported for the first time. These involve low lying bending vibrations that have been studied previously, which guarantees unambiguous identifications. Combining available data allows to derive accurate molecular parameters, both for the ground state as well as the excited states involved in the bands.
Qu, Zhiguo; Wu, Shengyao; Wang, Mingming; Sun, Le; Wang, Xiaojun
2017-12-01
As one of important research branches of quantum communication, deterministic remote state preparation (DRSP) plays a significant role in quantum network. Quantum noises are prevalent in quantum communication, and it can seriously affect the safety and reliability of quantum communication system. In this paper, we study the effect of quantum noise on deterministic remote state preparation of an arbitrary two-particle state via different quantum channels including the χ state, Brown state and GHZ state. Firstly, the output states and fidelities of three DRSP algorithms via different quantum entangled channels in four noisy environments, including amplitude-damping, phase-damping, bit-flip and depolarizing noise, are presented, respectively. And then, the effects of noises on three kinds of preparation algorithms in the same noisy environment are discussed. In final, the theoretical analysis proves that the effect of noise in the process of quantum state preparation is only related to the noise type and the size of noise factor and independent of the different entangled quantum channels. Furthermore, another important conclusion is given that the effect of noise is also independent of how to distribute intermediate particles for implementing DRSP through quantum measurement during the concrete preparation process. These conclusions will be very helpful for improving the efficiency and safety of quantum communication in a noisy environment.
Lee, Gyeongjin; Kim, Junwoo; Kim, So Young; Kim, Dong Eon; Joo, Taiha
2017-03-17
Coherent nuclear wave packet motions in an electronic excited state of a molecule are measured directly by time-resolved spontaneous fluorescence spectroscopy with an unprecedented time resolution by using two-photon absorption excitation and fluorescence upconversion by noncollinear sum frequency generation. With an estimated time resolution of approximately 25 fs, wave packet motions of vibrational modes up to 1600 cm(-1) are recorded for coumarin 153 in ethanol. Two-color transient absorption at 13 fs time resolution are measured to confirm the result. Vibrational displacements between the ground and excited states and Huang-Rhys factors (HRFs) are calculated by quantum mechanical methods and are compared with the experimental results. HRFs calculated by density functional theory (DFT) and time-dependent DFT reproduce the experiment adequately. This fluorescence-based method provides a unique and direct way to obtain the vibrational spectrum of a molecule in an electronic excited state and the HRFs, as well as the dynamics of excited states, and it might provide information on the structure of an excited state through the HRFs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Wang, Qian; Quan, H. T.
2017-09-01
By analyzing the probability distributions of the Loschmidt echo (LE) and quantum work, we examine the nonequilibrium effects of a quantum many-body system, which exhibits an excited-state quantum phase transition (ESQPT). We find that depending on the value of the controlling parameter the distribution of the LE displays different patterns. At the critical point of the ESQPT, both the averaged LE and the averaged work show a cusplike shape. Furthermore, by employing the finite-size scaling analysis of the averaged work, we obtain the critical exponent of the ESQPT. Finally, we show that at the critical point of ESQPT the eigenstate is a highly localized state, further highlighting the influence of the ESQPT on the properties of the many-body system.
Nonadiabatic quantum state engineering driven by fast quench dynamics
Herrera, Marcela; Sarandy, Marcelo S.; Duzzioni, Eduardo I.; Serra, Roberto M.
2014-02-01
There are a number of tasks in quantum information science that exploit nontransitional adiabatic dynamics. Such a dynamics is bounded by the adiabatic theorem, which naturally imposes a speed limit in the evolution of quantum systems. Here, we investigate an approach for quantum state engineering exploiting a shortcut to the adiabatic evolution, which is based on rapid quenches in a continuous-time Hamiltonian evolution. In particular, this procedure is able to provide state preparation faster than the adiabatic brachistochrone. Remarkably, the evolution time in this approach is shown to be ultimately limited by its "thermodynamical cost," provided in terms of the average work rate (average power) of the quench process. We illustrate this result in a scenario that can be experimentally implemented in a nuclear magnetic resonance setup.
On the Quantum Mechanical State of the Δ++ Baryon
Directory of Open Access Journals (Sweden)
Comay E.
2011-01-01
Full Text Available The ++ and the baryons have been used as the original reason for the construction of the Quantum Chromodynamics theory of Strong Interactions. The present analy- sis relies on the multiconfiguration structure of states which are made of several Dirac particles. It is shown that this property, together with the very strong spin-dependent interactions of quarks provide an acceptable explanation for the states of these baryons and remove the classical reason for the invention of color within Quantum Chromody- namics. This explanation is supported by several examples that show a Quantum Chro- modynamics’ inconsistency with experimental results. The same arguments provide an explanation for the problem called the proton spin crisis.
On the Quantum Mechanical State of the Delta++ Baryon
Directory of Open Access Journals (Sweden)
Comay E.
2011-01-01
Full Text Available The Delta++ and the Omega- baryons have been used as the original reason for the construction of the Quantum Chromodynamics theory of Strong Interactions. The present analysis relies on the multiconfiguration structure of states which are made of several Dirac particles. It is shown that this property, together with the very strong spin-dependent interactions of quarks provide an acceptable explanation for the states of these baryons and remove the classical reason for the invention of color within Quantum Chromodynamics. This explanation is supported by several examples that show a Quantum Chromodynamics' inconsistency with experimental results. The same arguments provide an explanation for the problem called the proton spin crisis.
Quantum phase fluctuations and density of states in superconducting nanowires
Radkevich, Alexey; Semenov, Andrew G.; Zaikin, Andrei D.
2017-08-01
We argue that quantum fluctuations of the phase of the order parameter may strongly affect the electron density of states (DOS) in ultrathin superconducting wires. We demonstrate that the effect of such fluctuations is equivalent to that of a quantum dissipative environment formed by soundlike plasma modes propagating along the wire. We derive a nonperturbative expression for the local electron DOS in superconducting nanowires which fully accounts for quantum phase fluctuations. At any nonzero temperature these fluctuations smear out the square-root singularity in DOS near the superconducting gap and generate quasiparticle states at subgap energies. Furthermore, at sufficiently large values of the wire impedance this singularity is suppressed down to T =0 in which case DOS tends to zero at subgap energies and exhibits the power-law behavior above the gap. Our predictions can be directly tested in tunneling experiments with superconducting nanowires.
Nemausat, Ruidy; Gervais, Christel; Brouder, Christian; Trcera, Nicolas; Bordage, Amélie; Coelho-Diogo, Cristina; Florian, Pierre; Rakhmatullin, Aydar; Errea, Ion; Paulatto, Lorenzo; Lazzeri, Michele; Cabaret, Delphine
2017-02-22
A combined experimental-theoretical study on the temperature dependence of the X-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectra of periclase (MgO), spinel (MgAl2O4), corundum (α-Al2O3), berlinite (α-AlPO4), stishovite and α-quartz (SiO2) is reported. Predictive calculations are presented when experimental data are not available. For these light-element oxides, both experimental techniques detect systematic effects related to quantum thermal vibrations which are well reproduced by density-functional theory simulations. In calculations, thermal fluctuations of the nuclei are included by considering nonequilibrium configurations according to finite-temperature quantum statistics at the quasiharmonic level. The influence of nuclear quantum fluctuations on XANES and NMR spectroscopies is particularly sensitive to the coordination number of the probed cation. Furthermore, the relative importance of nuclear dynamics and thermal expansion is quantified over a large range of temperatures.
Creating a bosonic fractional quantum Hall state by pairing fermions
Repellin, Cécile; Yefsah, Tarik; Sterdyniak, Antoine
2017-10-01
We numerically study the behavior of spin-1 /2 fermions on a two-dimensional square lattice subject to a uniform magnetic field, where opposite spins interact via an on-site attractive interaction. Starting from the noninteracting case where each spin population is prepared in a quantum Hall state with unity filling, we follow the evolution of the system as the interaction strength is increased. Above a critical value and for sufficiently low flux density, we observe the emergence of a twofold quasidegeneracy accompanied by the opening of an energy gap to the third level. Analysis of the entanglement spectra shows that the gapped ground state is the bosonic 1 /2 Laughlin state. Our work therefore provides compelling evidence of a topological phase transition from the fermionic quantum Hall state at unity filling to the bosonic Laughlin state at a critical attraction strength of the order of the one-body spectrum linewidth.
Quantifying non-Gaussianity of quantum-state correlation
Park, Jiyong; Lee, Jaehak; Ji, Se-Wan; Nha, Hyunchul
2017-11-01
We consider how to quantify non-Gaussianity for the correlation of a bipartite quantum state by using various measures such as relative entropy and geometric distances. We first show that an intuitive approach, i.e., subtracting the correlation of a reference Gaussian state from that of a target non-Gaussian state, fails to yield a non-negative measure with monotonicity under local Gaussian channels. Our finding clearly manifests that quantum-state correlations generally have no Gaussian extremality. We therefore propose a different approach by introducing relevantly averaged states to address correlation. This enables us to define a non-Gaussianity measure based on, e.g., the trace-distance and the fidelity, fulfilling all requirements as a measure of non-Gaussian correlation. For the case of the fidelity-based measure, we also present readily computable lower bounds of non-Gaussian correlation.
Bound on local unambiguous discrimination between multipartite quantum states
Yang, Ying-Hui; Gao, Fei; Tian, Guo-Jing; Cao, Tian-Qing; Zuo, Hui-Juan; Wen, Qiao-Yan
2015-02-01
We investigate the upper bound on unambiguous discrimination by local operations and classical communication. We demonstrate that any set of linearly independent multipartite pure quantum states can be locally unambiguously discriminated if the number of states in the set is no more than , where the space spanned by the set can be expressed in the irreducible form and is the optimal local dimension of the party. That is, is an upper bound. We also show that it is tight, namely there exists a set of states, in which at least one of the states cannot be locally unambiguously discriminated. Our result gives the reason why the multiqubit system is the only exception when any three quantum states are locally unambiguously distinguished.
Memory-built-in quantum cloning in a hybrid solid-state spin register.
Wang, W-B; Zu, C; He, L; Zhang, W-G; Duan, L-M
2015-07-16
As a way to circumvent the quantum no-cloning theorem, approximate quantum cloning protocols have received wide attention with remarkable applications. Copying of quantum states to memory qubits provides an important strategy for eavesdropping in quantum cryptography. We report an experiment that realizes cloning of quantum states from an electron spin to a nuclear spin in a hybrid solid-state spin register with near-optimal fidelity. The nuclear spin provides an ideal memory qubit at room temperature, which stores the cloned quantum states for a millisecond under ambient conditions, exceeding the lifetime of the original quantum state carried by the electron spin by orders of magnitude. The realization of a cloning machine with built-in quantum memory provides a key step for application of quantum cloning in quantum information science.
Solid-State Source of Nonclassical Photon Pairs with Embedded Multimode Quantum Memory.
Kutluer, Kutlu; Mazzera, Margherita; de Riedmatten, Hugues
2017-05-26
The generation and distribution of quantum correlations between photonic qubits is a key resource in quantum information science. For applications in quantum networks and quantum repeaters, it is required that these quantum correlations be stored in a quantum memory. In 2001, Duan, Lukin, Cirac, and Zoller (DLCZ) proposed a scheme combining a correlated photon-pair source and a quantum memory in atomic gases, which has enabled fast progress towards elementary quantum networks. In this Letter, we demonstrate a solid-state source of correlated photon pairs with embedded spin-wave quantum memory, using a rare-earth-ion-doped crystal. We show strong quantum correlations between the photons, high enough for performing quantum communication. Unlike the original DLCZ proposal, our scheme is inherently multimode thanks to a built-in rephasing mechanism, allowing us to demonstrate storage of 11 temporal modes. These results represent an important step towards the realization of complex quantum networks architectures using solid-state resources.
State preparation for quantum information science and metrology
Energy Technology Data Exchange (ETDEWEB)
Samblowski, Aiko
2012-06-08
The precise preparation of non-classical states of light is a basic requirement for performing quantum information tasks and quantum metrology. Depending on the assignment, the range of required states varies from preparing and modifying squeezed states to generating bipartite entanglement and establishing multimode entanglement networks. Every state needs special preparation techniques and hence it is important to develop the experimental expertise to generate all states with the desired degree of accuracy. In this thesis, the experimental preparation of different kinds of non-classical states of light is demonstrated. Starting with a multimode entangled state, the preparation of an unconditionally generated bound entangled state of light of unprecedented accuracy is shown. Its existence is of fundamental interest, since it certifies an intrinsic irreversibility of entanglement and suggests a connection with thermodynamics. The state is created in a network of linear optics, utilizing optical parametric amplifiers, operated below threshold, beam splitters and phase gates. The experimental platform developed here afforded the precise and stable control of all experimental parameters. Focusing on the aspect of quantum information networks, the generation of suitable bipartite entangled states of light is desirable. The optical connection between atomic transitions and light that can be transmitted via telecommunications fibers opens the possibility to employ quantum memories within fiber networks. For this purpose, a non-degenerate optical parametric oscillator is operated above threshold and the generation of bright bipartite entanglement between its twin beams at the wavelengths of 810 nm and 1550 nm is demonstrated. In the field of metrology, quantum states are used to enhance the measurement precision of interferometric gravitational wave (GW) detectors. Recently, the sensitivity of a GW detector operated at a wavelength of 1064 nm was increased using squeezed
Unified quantum no-go theorems and transforming of quantum pure states in a restricted set
Luo, Ming-Xing; Li, Hui-Ran; Lai, Hong; Wang, Xiaojun
2017-12-01
The linear superposition principle in quantum mechanics is essential for several no-go theorems such as the no-cloning theorem, the no-deleting theorem and the no-superposing theorem. In this paper, we investigate general quantum transformations forbidden or permitted by the superposition principle for various goals. First, we prove a no-encoding theorem that forbids linearly superposing of an unknown pure state and a fixed pure state in Hilbert space of a finite dimension. The new theorem is further extended for multiple copies of an unknown state as input states. These generalized results of the no-encoding theorem include the no-cloning theorem, the no-deleting theorem and the no-superposing theorem as special cases. Second, we provide a unified scheme for presenting perfect and imperfect quantum tasks (cloning and deleting) in a one-shot manner. This scheme may lead to fruitful results that are completely characterized with the linear independence of the representative vectors of input pure states. The upper bounds of the efficiency are also proved. Third, we generalize a recent superposing scheme of unknown states with a fixed overlap into new schemes when multiple copies of an unknown state are as input states.
Speedup of quantum evolution of multiqubit entanglement states.
Zhang, Ying-Jie; Han, Wei; Xia, Yun-Jie; Tian, Jian-Xiang; Fan, Heng
2016-06-10
As is well known, quantum speed limit time (QSLT) can be used to characterize the maximal speed of evolution of quantum systems. We mainly investigate the QSLT of generalized N-qubit GHZ-type states and W-type states in the amplitude-damping channels. It is shown that, in the case N qubits coupled with independent noise channels, the QSLT of the entangled GHZ-type state is closely related to the number of qubits in the small-scale system. And the larger entanglement of GHZ-type states can lead to the shorter QSLT of the evolution process. However, the QSLT of the W-type states are independent of the number of qubits and the initial entanglement. Furthermore, by considering only M qubits among the N-qubit system respectively interacting with their own noise channels, QSLTs for these two types states are shorter than in the case N qubits coupled with independent noise channels. We therefore reach the interesting result that the potential speedup of quantum evolution of a given N-qubit GHZ-type state or W-type state can be realized in the case the number of the applied noise channels satisfying M < N.
Semenov, Alexander; Babikov, Dmitri
2013-11-07
We formulated the mixed quantum/classical theory for rotationally and vibrationally inelastic scattering process in the diatomic molecule + atom system. Two versions of theory are presented, first in the space-fixed and second in the body-fixed reference frame. First version is easy to derive and the resultant equations of motion are transparent, but the state-to-state transition matrix is complex-valued and dense. Such calculations may be computationally demanding for heavier molecules and/or higher temperatures, when the number of accessible channels becomes large. In contrast, the second version of theory requires some tedious derivations and the final equations of motion are rather complicated (not particularly intuitive). However, the state-to-state transitions are driven by real-valued sparse matrixes of much smaller size. Thus, this formulation is the method of choice from the computational point of view, while the space-fixed formulation can serve as a test of the body-fixed equations of motion, and the code. Rigorous numerical tests were carried out for a model system to ensure that all equations, matrixes, and computer codes in both formulations are correct.
Entanglement concentration of continuous variable quantum states
Fiurasek, Jaromir; Mista, Jr., Ladislav; Filip, Radim
2002-01-01
We propose two probabilistic entanglement concentration schemes for a single copy of two-mode squeezed vacuum state. The first scheme is based on the off-resonant interaction of a Rydberg atom with the cavity field while the second setup involves the cross Kerr interaction, auxiliary mode prepared in a strong coherent state and a homodyne detection. We show that the continuous-variable entanglement concentration allows us to improve the fidelity of teleportation of coherent states.
Single photon response in GaAs quantum transport devices for photon-spin quantum state transfer
Energy Technology Data Exchange (ETDEWEB)
Kutsuwa, T. [CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, 332-0012 (Japan); Arai, K. [CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, 332-0012 (Japan); ERATO-JST, Semiconductor Spintronics, Project, JST (Japan); Shigyo, H.; Kinjo, H.; Edamatsu, K. [Research Institute of Electrical Communication, Tohoku University, Sendai (Japan); Ono, K. [CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, 332-0012 (Japan); Low Temperature Physics Laboratory, RIKEN, Saitama (Japan); Mitsumori, Y.; Kosaka, H. [CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama, 332-0012 (Japan); Research Institute of Electrical Communication, Tohoku University, Sendai (Japan)
2006-07-01
Quantum information can be stored and manipulated by an electron spin if its state was faithfully transferred from messenger photon qubit. Such a quantum state transfer needs to have a function of conversion from photon polarization to electron spin state and flagging the safe conversion without destroying the spin state. We have achieved single photon response by using a quantum dot as an electron trap and a quantum point contact as a charge sensor on GaAs/AlGaAs-based modulation doped structure. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Finite temperature quantum correlations in su(2)(c) quark states and quantum spin models
Hamieh, S; Tawfik, A
The entanglement at finite temperatures is analyzed by using thermal models for colored quarks making tip the hadron physical states. We have found that these quantum correlations entirely vanish at T-c >= m(q)/ln(1.5). For temperatures larger than T-c the correlations are classical. We have also
Density of low-energy vibrational states in a protein solution
Brill, A. S.; Fiamingo, F. G.; Hampton, D. A.; Levin, P. D.; Thorkildsen, R.
1985-04-01
Electron paramagnetic resonance measurements on the aquo complex of sperm whale skeletal myoglobin in solution at T<4 K show that, at phonon energies around 20 cm-1, the density of vibrational states is that of a three-dimensional system.
Quantum Separability Criteria for Arbitrary Dimensional Multipartite States
Li,Ming; Wang,Jing; Fei, Shao-Ming; Li-Jost, Xianqing
2014-01-01
We present separability criteria for both bipartite and multipartite quantum states. These criteria include the criteria based on the correlation matrix and its generalized form as special cases. We show by detailed examples that our criteria are more powerful than the positive partial transposition criterion, the realignment criterion and the criteria based on the correlation matrices.
Generation of optical coherent state superpositions for quantum information processing
DEFF Research Database (Denmark)
Tipsmark, Anders
2012-01-01
I dette projektarbejde med titlen “Generation of optical coherent state superpositions for quantum information processing” har målet været at generere optiske kat-tilstande. Dette er en kvantemekanisk superpositions tilstand af to koherente tilstande med stor amplitude. Sådan en tilstand er...
A quantum bound-state description of black holes
Energy Technology Data Exchange (ETDEWEB)
Hofmann, Stefan [Arnold Sommerfeld Center for Theoretical Physics, LMU-München, Theresienstrasse 37, 80333 München (Germany); Rug, Tehseen, E-mail: Tehseen.Rug@physik.uni-muenchen.de [Arnold Sommerfeld Center for Theoretical Physics, LMU-München, Theresienstrasse 37, 80333 München (Germany); Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München (Germany)
2016-01-15
A relativistic framework for the description of bound states consisting of a large number of quantum constituents is presented, and applied to black-hole interiors. At the parton level, the constituent distribution, number and energy density inside black holes are calculated, and gauge corrections are discussed. A simple scaling relation between the black-hole mass and constituent number is established.
Quantum states with continuous spectrum for a general time ...
Indian Academy of Sciences (India)
The time-dependent oscillators whose spectra of the wave function are continuous are not oscillatory. The wave function for ω2 < 0 is expressed in terms of the parabolic cylinder function. We applied our theory to the driven harmonic oscillator with strongly pulsating mass. Keywords. Quantum states with continuous ...
Test-state approach to the quantum search problem
Sehrawat, Arun; Nguyen, Le Huy; Englert, Berthold-Georg
2011-05-01
The search for “a quantum needle in a quantum haystack” is a metaphor for the problem of finding out which one of a permissible set of unitary mappings—the oracles—is implemented by a given black box. Grover’s algorithm solves this problem with quadratic speedup as compared with the analogous search for “a classical needle in a classical haystack.” Since the outcome of Grover’s algorithm is probabilistic—it gives the correct answer with high probability, not with certainty—the answer requires verification. For this purpose we introduce specific test states, one for each oracle. These test states can also be used to realize “a classical search for the quantum needle” which is deterministic—it always gives a definite answer after a finite number of steps—and 3.41 times as fast as the purely classical search. Since the test-state search and Grover’s algorithm look for the same quantum needle, the average number of oracle queries of the test-state search is the classical benchmark for Grover’s algorithm.
Experimental determination of the degree of polarization of quantum states
DEFF Research Database (Denmark)
Kothe-Termén, Christian; Madsen, Lars Skovgaard; Andersen, Ulrik Lund
2013-01-01
We demonstrate experimental excitation-manifold-resolved polarization characterization of quantum states of light ranging from the few-photon to the many-photon level. In contrast to the traditional characterization of polarization that is based on the Stokes parameters, we experimentally determi...
Quantum information processing using designed defect states in
DEFF Research Database (Denmark)
Pedersen, Jesper; Flindt, Christian; Mortensen, Niels Asger
2007-01-01
We propose a new physical implementation of spin qubits for quantum information processing, namely defect states in antidot lattices de¯ned in the two-dimensional electron gas at a semiconductor heterostructure. Calculations of the band structure of the periodic antidot lattice are presented. A p...
Commensurate and incommensurate states of topological quantum matter
DEFF Research Database (Denmark)
Milsted, Ashley; Cobanera, Emilio; Burrello, Michele
2014-01-01
We prove numerically and by dualities the existence of modulated, commensurate and incommensurate states of topological quantum matter in systems of parafermions, motivated by recent proposals for the realization of such systems in mesoscopic arrays. In two space dimensions, we obtain the simplest...
Catalytic synthesis of ammonia using vibrationally excited nitrogen molecules
DEFF Research Database (Denmark)
Hansen, Flemming Yssing; Henriksen, Niels Engholm; Billing, Gert D.
1992-01-01
are vibrationally excited to states with quantum numbers 3-10. The rate and equilibrium constants for the process using vibrationally excited nitrogen molecules are calculated and expressions for the reaction rates are derived. A comparison with the ordinary process, where the nitrogen molecules...
Paulat, Florian; Praneeth, V K K; Näther, Christian; Lehnert, Nicolai
2006-04-03
Vibrational properties of the five-coordinate porphyrin complexes [M(TPP)(Cl)] (M = Fe, Mn, Co) are analyzed in detail. For [Fe(TPP)(Cl)] (1), a complete vibrational data set is obtained, including nonresonance (NR) Raman, and resonance Raman (RR) spectra at multiple excitation wavelengths as well as IR spectra. These data are completely assigned using density functional (DFT) calculations and polarization measurements. Compared to earlier works, a number of bands are reassigned in this one. These include the important, structure-sensitive band at 390 cm(-1), which is reassigned here to the totally symmetric nu(breathing)(Fe-N) vibration for complex 1. This is in agreement with the assignments for [Ni(TPP)]. In general, the assignments are on the basis of an idealized [M(TPP)]+ core with D(4h) symmetry. In this Work, small deviations from D(4h) are observed in the vibrational spectra and analyzed in detail. On the basis of the assignments of the vibrational spectra of 1, [Mn(TPP)(Cl)] (2), and diamagnetic [Co(TPP)(Cl)] (3), eight metal-sensitive bands are identified. Two of them correspond to the nu(M-N) stretching modes with B(1g) and Eu symmetries and are assigned here for the first time. The shifts of the metal sensitive modes are interpreted on the basis of differences in the porphyrin C-C, C-N, and M-N distances. Besides the porphyrin core vibrations, the M-Cl stretching modes also show strong metal sensitivity. The strength of the M-Cl bond in 1-3 is further investigated. From normal coordinate analysis (NCA), force constants of 1.796 (Fe), 0.932 (Mn), and 1.717 (Co) mdyn/A are obtained for 1-3, respectively. The weakness of the Mn-Cl bond is attributed to the fact that it only corresponds to half a sigma bond. Finally, RR spectroscopy is used to gain detailed insight into the nature of the electronically excited states. This relates to the mechanism of resonance enhancement and the actual nature of the enhanced vibrations. It is of importance that anomalous
Multilevel distillation of magic states for quantum computing
Jones, Cody
2013-04-01
We develop a procedure for distilling magic states used in universal quantum computing that requires substantially fewer initial resources than prior schemes. Our distillation circuit is based on a family of concatenated quantum codes that possess a transversal Hadamard operation, enabling each of these codes to distill the eigenstate of the Hadamard operator. A crucial result of this design is that low-fidelity magic states can be consumed to purify other high-fidelity magic states to even higher fidelity, which we call multilevel distillation. When distilling in the asymptotic regime of infidelity ɛ→0 for each input magic state, the number of input magic states consumed on average to yield an output state with infidelity O(ɛ2r) approaches 2r+1, which comes close to saturating the conjectured bound in another investigation [Bravyi and Haah, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.86.052329 86, 052329 (2012)]. We show numerically that there exist multilevel protocols such that the average number of magic states consumed to distill from error rate ɛin=0.01 to ɛout in the range 10-5-10-40 is about 14log10(1/ɛout)-40; the efficiency of multilevel distillation dominates all other reported protocols when distilling Hadamard magic states from initial infidelity 0.01 to any final infidelity below 10-7. These methods are an important advance for magic-state distillation circuits in high-performance quantum computing and provide insight into the limitations of nearly resource-optimal quantum error correction.
Quantum state tomography on long-coherent superconducting transmon qubit
Energy Technology Data Exchange (ETDEWEB)
Schneider, Andre; Braumueller, Jochen; Schloer, Steffen; Weides, Martin; Ustinov, Alexey [Physikalisches Institut, Karlsruher Institut fuer Technologie, 76131 Karlsruhe (Germany)
2016-07-01
The state of a qubit is commonly measured by probing a readout resonator coupled to it with a readout tone and detecting the dispersive shift of the resonator. This measurement only gives access to the z-component of the qubit state. Quantum state tomography provides a measurement for all components of the Bloch vector by rotating the qubit state prior to the readout. We present a method of measuring the Bloch vector components. This method is demonstrated by measuring the time evolution for long-''living'' transmon qubits with T{sub 1} and T{sub 2} times in excess of 10 μs. By recording the decay trace of the qubit state after a slightly detuned ((π)/(2)){sup x} pulse, we detect decay and dephasing as well as Larmor precession of the qubit. Furthermore, we introduce a benchmark for measuring the qubit manipulation fidelity and optimize the envelopes of the qubit manipulation pulses. Quantum state tomography is a powerful tool to observe changes in the qubit quantum state under interactions with magnonic systems.
Superconducting Analogue of the Parafermion Fractional Quantum Hall States
Directory of Open Access Journals (Sweden)
Abolhassan Vaezi
2014-07-01
Full Text Available Read-Rezayi Z_{k} parafermion wave functions describe ν=2+(k/kM+2 fractional quantum Hall (FQH states. These states support non-Abelian excitations from which protected quantum gates can be designed. However, there is no experimental evidence for these non-Abelian anyons to date. In this paper, we study the ν=2/k FQH-superconductor heterostructure and find the superconducting analogue of the Z_{k} parafermion FQH state. Our main tool is the mapping of the FQH into coupled one-dimensional chains, each with a pair of counterpropagating modes. We show that by inducing intrachain pairing and charge preserving backscattering with identical couplings, the one-dimensional chains flow into gapless Z_{k} parafermions when k<4. By studying the effect of interchain coupling, we show that every parafermion mode becomes massive except for the two outermost ones. Thus, we achieve a fractional topological superconductor whose chiral edge state is described by a Z_{k} parafermion conformal field theory. For instance, we find that a ν=2/3 FQH in proximity to a superconductor produces a Z_{3} parafermion superconducting state. This state is topologically indistinguishable from the non-Abelian part of the ν=12/5 Read-Rezayi state. Both of these systems can host Fibonacci anyons capable of performing universal quantum computation through braiding operations.
Extremal properties of conditional entropy and quantum discord for XXZ, symmetric quantum states
Yurischev, M. A.
2017-10-01
For the XXZ subclass of symmetric two-qubit X states, we study the behavior of quantum conditional entropy S_{cond} as a function of measurement angle θ \\in [0,π /2]. Numerical calculations show that the function S_{cond}(θ ) for X states can have at most one local extremum in the open interval from zero to π /2 (unimodality property). If the extremum is a minimum, the quantum discord displays region with variable (state-dependent) optimal measurement angle θ ^*. Such θ -regions (phases, fractions) are very tiny in the space of X-state parameters. We also discover the cases when the conditional entropy has a local maximum inside the interval (0,π /2). It is remarkable that the maxima exist in surprisingly wide regions, and the boundaries for such regions are defined by the same bifurcation conditions as for those with a minimum.
Quantum-disordered state of magnetic and electric dipoles in an organic Mott system.
Shimozawa, M; Hashimoto, K; Ueda, A; Suzuki, Y; Sugii, K; Yamada, S; Imai, Y; Kobayashi, R; Itoh, K; Iguchi, S; Naka, M; Ishihara, S; Mori, H; Sasaki, T; Yamashita, M
2017-11-28
Strongly enhanced quantum fluctuations often lead to a rich variety of quantum-disordered states. Developing approaches to enhance quantum fluctuations may open paths to realize even more fascinating quantum states. Here, we demonstrate that a coupling of localized spins with the zero-point motion of hydrogen atoms, that is, proton fluctuations in a hydrogen-bonded organic Mott insulator provides a different class of quantum spin liquids (QSLs). We find that divergent dielectric behavior associated with the approach to hydrogen-bond order is suppressed by the quantum proton fluctuations, resulting in a quantum paraelectric (QPE) state. Furthermore, our thermal-transport measurements reveal that a QSL state with gapless spin excitations rapidly emerges upon entering the QPE state. These findings indicate that the quantum proton fluctuations give rise to a QSL-a quantum-disordered state of magnetic and electric dipoles-through the coupling between the electron and proton degrees of freedom.
Entanglement entropy in excited states of the quantum Lifshitz model
Parker, Daniel E.; Vasseur, Romain; Moore, Joel E.
2017-06-01
We investigate the entanglement properties of an infinite class of excited states in the quantum Lifshitz model (QLM). The presence of a conformal quantum critical point in the QLM makes it unusually tractable for a model above one spatial dimension, enabling the ground state entanglement entropy for an arbitrary domain to be expressed in terms of geometrical and topological quantities. Here we extend this result to excited states and find that the entanglement can be naturally written in terms of quantities which we dub ‘entanglement propagator amplitudes’ (EPAs). EPAs are geometrical probabilities that we explicitly calculate and interpret. A comparison of lattice and continuum results demonstrates that EPAs are universal. This work shows that the QLM is an example of a 2 + 1d field theory where the universal behavior of excited-state entanglement may be computed analytically.
Photoinduced blinking in a solid-state quantum system
Berhane, Amanuel M.; Bradac, Carlo; Aharonovich, Igor
2017-07-01
Solid-state single-photon emitters (SPEs) are one of the prime components of many quantum nanophotonics devices. In this work, we report on an unusual, photoinduced blinking phenomenon of SPEs in gallium nitride. This is shown to be due to the modification in the transition kinetics of the emitter, via the introduction of additional laser-activated states. We investigate and characterize the blinking effect on the brightness of the source and the statistics of the emitted photons. Combining second-order correlation and fluorescence trajectory measurements, we determine the photodynamics of the trap states and characterize power-dependent decay rates and characteristic "off"-time blinking. Our work sheds light into understanding solid-state quantum system dynamics and, specifically, power-induced blinking phenomena in SPEs.
Quantum measurements without Schroedinger cat states
Energy Technology Data Exchange (ETDEWEB)
Spehner, D [Institut Fourier, 100 rue des Maths, 38402 Saint-Martin d' Heres (France); Haake, F [Fachbereich Physik, Universitaet Duisburg-Essen, Lotharstrasse 1, 47048 Duisburg (Germany)
2007-10-15
We report and give an alternative derivation of some results on a model for a quantum measurement studied in [1]. The measured microscopic system is coupled to the position of a macroscopic pointer, which itself interacts with its environment via its momentum. The entanglement between the system and the pointer produced by their mutual interaction is simultaneous with the decoherence of distinct pointer readings resulting from leakage of information to the environment. After a discussion on the various time scales in the model we calculate the matrix elements of the system-pointer density operator between eigenstates of the measured observable with distinct eigenvalues. In general, the decay with time of these coherences is neither exponential nor gaussian. We determine the decoherence (decay) time in terms of the strength of the system-pointer and pointer-environment couplings. This decoherence time does not depend upon the details of the pointer-bath coupling as soon as it is smaller than the bath correlation time (non-Markov regime). In contrast, in the Markov regime it depends strongly on whether this coupling is Ohmic or super-Ohmic.
Experimental demonstration of squeezed-state quantum averaging
DEFF Research Database (Denmark)
Lassen, Mikael Østergaard; Madsen, Lars Skovgaard; Sabuncu, Metin
2010-01-01
We propose and experimentally demonstrate a universal quantum averaging process implementing the harmonic mean of quadrature variances. The averaged variances are prepared probabilistically by means of linear optical interference and measurement-induced conditioning. We verify that the implemented...... harmonic mean yields a lower value than the corresponding value obtained for the standard arithmetic-mean strategy. The effect of quantum averaging is experimentally tested for squeezed and thermal states as well as for uncorrelated and partially correlated noise sources. The harmonic-mean protocol can...
Quantum Private Comparison Based on χ-Type Entangled States
Hong-Ming, Pan
2017-10-01
A two-party quantum private comparison (QPC) protocol is constructed with χ-type entangled states in this paper. The proposed protocol employs a semi-honest third party (TP) that is allowed to misbehave on his own but cannot conspire with the adversary. The proposed protocol need perform Bell basis measurements and single-particle measurements but neither unitary operations nor quantum entanglement swapping technology. The proposed protocol possesses good security toward both the outside attack and the participant attack. TP only knows the comparison result of the private information from two parties in the proposed protocol.
On the reduction criterion for random quantum states
Energy Technology Data Exchange (ETDEWEB)
Jivulescu, Maria Anastasia, E-mail: maria.jivulescu@upt.ro; Lupa, Nicolae, E-mail: nicolae.lupa@upt.ro [Department of Mathematics, Politehnica University of Timişoara, Victoriei Square 2, 300006 Timişoara (Romania); Nechita, Ion, E-mail: nechita@irsamc.ups-tlse.fr [CNRS, Laboratoire de Physique Théorique, IRSAMC, Université de Toulouse, UPS, F-31062 Toulouse (France)
2014-11-15
In this paper, we study the reduction criterion for detecting entanglement of large dimensional bipartite quantum systems. We first obtain an explicit formula for the moments of a random quantum state to which the reduction criterion has been applied. We show that the empirical eigenvalue distribution of this random matrix converges strongly to a limit that we compute, in three different asymptotic regimes. We then employ tools from free probability theory to study the asymptotic positivity of the reduction operators. Finally, we compare the reduction criterion with other entanglement criteria, via thresholds.
Spectrum of localized states in graphene quantum dots and wires
Energy Technology Data Exchange (ETDEWEB)
Zalipaev, V.V. [Department of Mathematical Sciences, Loughborough University, Leicestershire, LE11 3TU (United Kingdom); Maksimov, D.N. [LV Kirensky Institute of Physics, Krasnoyarsk 660036 (Russian Federation); Linton, C.M. [Department of Mathematical Sciences, Loughborough University, Leicestershire, LE11 3TU (United Kingdom); Kusmartsev, F.V., E-mail: F.Kusmartsev@lboro.ac.uk [Department of Physics, Loughborough University, Leicestershire, LE11 3TU (United Kingdom)
2013-01-03
We developed semiclassical method and show that any smooth potential in graphene describing elongated a quantum dot or wire may behave as a barrier or as a trapping well or as a double barrier potential, Fabry–Perot structure, for 1D Schrödinger equation. The energy spectrum of quantum wires has been found and compared with numerical simulations. We found that there are two types of localized states, stable and metastable, having finite life time. These life times are calculated, as is the form of the localized wave functions which are exponentially decaying away from the wire in the perpendicular direction.
Energy Technology Data Exchange (ETDEWEB)
Plenio, M. B.; Almeida, J.; Huelga, S. F. [Institute for Theoretical Physics, Albert-Einstein-Allee 11, University Ulm, D-89069 Ulm (Germany)
2013-12-21
We demonstrate that the coupling of excitonic and vibrational motion in biological complexes can provide mechanisms to explain the long-lived oscillations that have been obtained in nonlinear spectroscopic signals of different photosynthetic pigment protein complexes and we discuss the contributions of excitonic versus purely vibrational components to these oscillatory features. Considering a dimer model coupled to a structured spectral density we exemplify the fundamental aspects of the electron-phonon dynamics, and by analyzing separately the different contributions to the nonlinear signal, we show that for realistic parameter regimes purely electronic coherence is of the same order as purely vibrational coherence in the electronic ground state. Moreover, we demonstrate how the latter relies upon the excitonic interaction to manifest. These results link recently proposed microscopic, non-equilibrium mechanisms to support long lived coherence at ambient temperatures with actual experimental observations of oscillatory behaviour using 2D photon echo techniques to corroborate the fundamental importance of the interplay of electronic and vibrational degrees of freedom in the dynamics of light harvesting aggregates.
Plenio, M B; Almeida, J; Huelga, S F
2013-12-21
We demonstrate that the coupling of excitonic and vibrational motion in biological complexes can provide mechanisms to explain the long-lived oscillations that have been obtained in nonlinear spectroscopic signals of different photosynthetic pigment protein complexes and we discuss the contributions of excitonic versus purely vibrational components to these oscillatory features. Considering a dimer model coupled to a structured spectral density we exemplify the fundamental aspects of the electron-phonon dynamics, and by analyzing separately the different contributions to the nonlinear signal, we show that for realistic parameter regimes purely electronic coherence is of the same order as purely vibrational coherence in the electronic ground state. Moreover, we demonstrate how the latter relies upon the excitonic interaction to manifest. These results link recently proposed microscopic, non-equilibrium mechanisms to support long lived coherence at ambient temperatures with actual experimental observations of oscillatory behaviour using 2D photon echo techniques to corroborate the fundamental importance of the interplay of electronic and vibrational degrees of freedom in the dynamics of light harvesting aggregates.
Experimental entanglement distillation of mesoscopic quantum states
DEFF Research Database (Denmark)
Dong, Ruifang; Lassen, Mikael Østergaard; Heersink, Joel
2008-01-01
channel, the distribution of loss-intolerant entangled states is inevitably afflicted by decoherence, which causes a degradation of the transmitted entanglement. To combat the decoherence, entanglement distillation, a process of extracting a small set of highly entangled states from a large set of less...... entangled states, can be used(4-14). Here we report on the distillation of deterministically prepared light pulses entangled in continuous variables that have undergone non-Gaussian noise. The entangled light pulses(15-17) are sent through a lossy channel, where the transmission is varying in time similarly...
Use of dynamical coupling for improved quantum state transfer
Lyakhov, A. O.; Bruder, C.
2006-12-01
We propose a method to improve quantum state transfer in transmission lines. The idea is to localize the information on the last qubit of a transmission line by dynamically varying the coupling constants between the first and the last pair of qubits. The fidelity of state transfer is higher then in a chain with fixed coupling constants. The effect is stable against small fluctuations in the system parameters.
Use of dynamical coupling for improved quantum state transfer
Lyakhov, A. O.; Bruder, C.
2006-01-01
We propose a method to improve quantum state transfer in transmission lines. The idea is to localize the information on the last qubit of a transmission line, by dynamically varying the coupling constants between the first and the last pair of qubits. The fidelity of state transfer is higher then in a chain with fixed coupling constants. The effect is stable against small fluctuations in the system parameters.
Theory of ground state factorization in quantum cooperative systems.
Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio
2008-05-16
We introduce a general analytic approach to the study of factorization points and factorized ground states in quantum cooperative systems. The method allows us to determine rigorously the existence, location, and exact form of separable ground states in a large variety of, generally nonexactly solvable, spin models belonging to different universality classes. The theory applies to translationally invariant systems, irrespective of spatial dimensionality, and for spin-spin interactions of arbitrary range.
The Study of Dynamical Potentials of Highly Excited Vibrational States of HOBr
Directory of Open Access Journals (Sweden)
Chao Fang
2013-03-01
Full Text Available The vibrational nonlinear dynamics of HOBr in the bending and O–Br stretching coordinates with anharmonicity and Fermi 2:1 coupling are studied with dynamical potentials in this article. The result shows that the H–O stretching vibration mode has significantly different effects on the coupling between the O–Br stretching mode and the H–O–Br bending mode under different Polyad numbers. The dynamical potentials and the corresponding phase space trajectories are obtained when the Polyad number is 27, for instance, and the fixed points in the dynamical potentials of HOBr are shown to govern the various quantal environments in which the vibrational states lie. Furthermore, it is also found that the quantal environments could be identified by the numerical values of action integrals, which is consistent with former research.
Ritschel, Gerhard; Möbius, Sebastian; Strunz, Walter T; Eisfeld, Alexander
2014-01-01
Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an effective method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the strong coupling of electronic transitions to vibrational modes of the chromophores. In this paper we show how to calculate linear optical spectra at finite temperatures in an efficient way. To this end we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The zero temperature case equations can then be solved efficiently by standard integrators. As an example we calculate absorption and circular dichroism spectra of a linear aggregate. The formalism developed can be applied to calculate arbitrary correlation functions.
Discrimination of mixed quantum states. Reversible maps and unambiguous strategies
Energy Technology Data Exchange (ETDEWEB)
Kleinmann, Matthias
2008-06-30
The discrimination of two mixed quantum states is a fundamental task in quantum state estimation and quantum information theory. In quantum state discrimination a quantum system is assumed to be in one of two possible - in general mixed - non-orthogonal quantum states. The discrimination then consists of a measurement strategy that allows to decide in which state the system was before the measurement. In unambiguous state discrimination the aim is to make this decision without errors, but it is allowed to give an inconclusive answer. Especially interesting are measurement strategies that minimize the probability of an inconclusive answer. A starting point for the analysis of this optimization problem was a result by Eldar et al. [Phys. Rev. A 69, 062318 (2004)], which provides non-operational necessary and sufficient conditions for a given measurement strategy to be optimal. These conditions are reconsidered and simplified in such a way that they become operational. The simplified conditions are the basis for further central results: It is shown that the optimal measurement strategy is unique, a statement that is e.g. of importance for the complexity analysis of optimal measurement devices. The optimal measurement strategy is derived for the case, where one of the possible input states has at most rank two, which was an open problem for many years. Furthermore, using the optimality criterion it is shown that there always exists a threshold probability for each state, such that below this probability it is optimal to exclude this state from the discrimination strategy. If the two states subject to discrimination can be brought to a diagonal structure with (2 x 2)-dimensional blocks, then the unambiguous discrimination of these states can be reduced to the unambiguous discrimination of pure states. A criterion is presented that allows to identify the presence of such a structure for two self-adjoint operators. This criterion consists of the evaluation of three
Hamiltonian approach to Ehrenfest expectation values and Gaussian quantum states.
Bonet-Luz, Esther; Tronci, Cesare
2016-05-01
The dynamics of quantum expectation values is considered in a geometric setting. First, expectation values of the canonical observables are shown to be equivariant momentum maps for the action of the Heisenberg group on quantum states. Then, the Hamiltonian structure of Ehrenfest's theorem is shown to be Lie-Poisson for a semidirect-product Lie group, named the Ehrenfest group. The underlying Poisson structure produces classical and quantum mechanics as special limit cases. In addition, quantum dynamics is expressed in the frame of the expectation values, in which the latter undergo canonical Hamiltonian motion. In the case of Gaussian states, expectation values dynamics couples to second-order moments, which also enjoy a momentum map structure. Eventually, Gaussian states are shown to possess a Lie-Poisson structure associated with another semidirect-product group, which is called the Jacobi group. This structure produces the energy-conserving variant of a class of Gaussian moment models that have previously appeared in the chemical physics literature.
Campelo, M. J. M.; Freire, P. T. C.; Mendes Filho, J.; de Toledo, T. A.; Teixeira, A. M. R.; da Silva, L. E.; Bento, R. R. F.; Faria, J. L. B.; Pizani, P. S.; Gusmão, G. O. M.; Coutinho, H. D. M.; Oliveira, M. T. A.
2017-10-01
A new derivative of Meldrum's acid 5-((5-chloropyridin-2-ylamino)methylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (CYMM) of molecular formula C12H11ClN2O4 was synthesized and structurally characterized using single crystal X-ray diffraction technique. The vibrational properties of the crystal were studied by Fourier Transform infrared (FT-IR), Fourier Transform Raman (FT-Raman) techniques and theoretical calculations of quantum chemistry using Density functional theory (DFT) and Density functional perturbation theory (DFPT). A comparison with experimental spectra allowed the assignment of all the normal modes. The descriptions of the normal modes were carried by means of potential energy distribution (PED). Additionally, analysis of the antimicrobial activity and antibiotic resistance modulatory activity was carried out to evaluate the antibacterial potential of the CYMM.
Niu, X. Y.; Huang, X. L.; Shang, Y. F.; Wang, X. Y.
2015-04-01
Superposition principle plays a crucial role in quantum mechanics, thus its effects on thermodynamics is an interesting topic. Here, the effects of superpositions of quantum states on isoenergetic cycle are studied. We find superposition can improve the heat engine efficiency and release the positive work condition in general case. In the finite time process, we find the efficiency at maximum power output in superposition case is lower than the nonsuperposition case. This efficiency depends on one index of the energy spectrum of the working substance. This result does not mean the superposition discourages the heat engine performance. For fixed efficiency or fixed power, the superposition improves the power or efficiency respectively. These results show how quantum mechanical properties affect the thermodynamical cycle.
State-to-State Internal Energy Relaxation Following the Quantum-Kinetic Model in DSMC
Liechty, Derek S.
2014-01-01
A new model for chemical reactions, the Quantum-Kinetic (Q-K) model of Bird, has recently been introduced that does not depend on macroscopic rate equations or values of local flow field data. Subsequently, the Q-K model has been extended to include reactions involving charged species and electronic energy level transitions. Although this is a phenomenological model, it has been shown to accurately reproduce both equilibrium and non-equilibrium reaction rates. The usefulness of this model becomes clear as local flow conditions either exceed the conditions used to build previous models or when they depart from an equilibrium distribution. Presently, the applicability of the relaxation technique is investigated for the vibrational internal energy mode. The Forced Harmonic Oscillator (FHO) theory for vibrational energy level transitions is combined with the Q-K energy level transition model to accurately reproduce energy level transitions at a reduced computational cost compared to the older FHO models.
Quenching vibrations by collisions in cold traps: A quantum study for ...
Indian Academy of Sciences (India)
cold traps, interacting with 4He(1S) as a buffer gas at relative temperatures down to millikelvins, is discussed using an ab initio computed potential energy surface. The relative efficiency of collisional cooling with respect to collisional quenching of the internal vibrations is examined from the results of the relative sizes of the.
Directory of Open Access Journals (Sweden)
Alessandro Seri
2017-05-01
Full Text Available Quantum correlations between long-lived quantum memories and telecom photons that can propagate with low loss in optical fibers are an essential resource for the realization of large-scale quantum information networks. Significant progress has been realized in this direction with atomic and solid-state systems. Here, we demonstrate quantum correlations between a telecom photon and a multimode on-demand solid state quantum memory. This is achieved by mapping a correlated single photon onto a spin collective excitation in a Pr^{3+}:Y_{2}SiO_{5} crystal for a controllable time. The stored single photons are generated by cavity-enhanced spontaneous parametric down-conversion and heralded by their partner photons at telecom wavelength. These results represent the first demonstration of a multimode on-demand solid state quantum memory for external quantum states of light. They provide an important resource for quantum repeaters and pave the way for the implementation of quantum information networks with distant solid state quantum nodes.
Seri, Alessandro; Lenhard, Andreas; Rieländer, Daniel; Gündoǧan, Mustafa; Ledingham, Patrick M.; Mazzera, Margherita; de Riedmatten, Hugues
2017-04-01
Quantum correlations between long-lived quantum memories and telecom photons that can propagate with low loss in optical fibers are an essential resource for the realization of large-scale quantum information networks. Significant progress has been realized in this direction with atomic and solid-state systems. Here, we demonstrate quantum correlations between a telecom photon and a multimode on-demand solid state quantum memory. This is achieved by mapping a correlated single photon onto a spin collective excitation in a Pr3 +:Y2SiO5 crystal for a controllable time. The stored single photons are generated by cavity-enhanced spontaneous parametric down-conversion and heralded by their partner photons at telecom wavelength. These results represent the first demonstration of a multimode on-demand solid state quantum memory for external quantum states of light. They provide an important resource for quantum repeaters and pave the way for the implementation of quantum information networks with distant solid state quantum nodes.
Metal-to-insulator switching in quantum anomalous Hall states
Pan, Lei; Kou, Xufeng; Wang, Jing; Fan, Yabin; Choi, Eun Sang; Shao, Qiming; Zhang, Shou Cheng; Wang, Kang Lung
Quantum anomalous Hall effect (QAHE) was recently achieved in magnetic topological insulator films as a form of dissipationless transport without external magnetic field. However, the universal phase diagram of QAHE and its relation with quantum Hall effect (QHE) remain to be investigated. Here, we report the experimental observation of the giant longitudinal resistance peak and zero Hall conductance plateau at the coercive field in the six quintuple-layer (Cr0.12Bi0.26Sb0.62)2 Te3 film, and demonstrate the metal-to-insulator switching between two opposite QAHE plateau states up to 0.3 K. The universal QAHE phase diagram is further confirmed through the angle-dependent measurements. Our results address that the quantum phase transitions in both QAHE and QHE regimes are in the same universality class, yet the microscopic details are different.
Reconstructing quantum states from single-party information
Schilling, Christian; Benavides-Riveros, Carlos L.; Vrana, Péter
2017-11-01
The possible compatibility of density matrices for single-party subsystems is described by linear constraints on their respective spectra. Whenever some of those quantum marginal constraints are saturated, the total quantum state has a specific, simplified structure. We prove that these remarkable global implications of extremal local information are stable; i.e., they hold approximately for spectra close to the boundary of the allowed region. Application of this general result to fermionic quantum systems allows us to characterize natural extensions of the Hartree-Fock ansatz and to quantify their accuracy by resorting to one-particle information, only: The fraction of the correlation energy not recovered by such an ansatz can be estimated from above by a simple geometric quantity in the occupation number picture.
Quantum secret sharing based on Smolin states alone
Energy Technology Data Exchange (ETDEWEB)
He Guangping [School of Physics and Engineering and Advanced Research Center, Sun Yat-sen University, Guangzhou 510275 (China); Wang, Z D; Bai, Yankui [Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China)], E-mail: hegp@mail.sysu.edu.cn, E-mail: zwang@hkucc.hku.hk, E-mail: ykbai@semi.ac.cn
2008-10-17
It was indicated (Yu 2007 Phys. Rev. A 75 066301) that a previously proposed quantum secret sharing (QSS) protocol based on Smolin states (Augusiak 2006 Phys. Rev. A 73 012318) is insecure against an internal cheater. Here we build a different QSS protocol with Smolin states alone, and prove it to be secure against known cheating strategies. Thus we open a promising venue for building secure QSS using merely Smolin states, which is a typical kind of bound entangled states. We also propose a feasible scheme to implement the protocol experimentally.
Multiconfigurational quantum propagation with trajectory-guided generalized coherent states.
Grigolo, Adriano; Viscondi, Thiago F; de Aguiar, Marcus A M
2016-03-07
A generalized version of the coupled coherent states method for coherent states of arbitrary Lie groups is developed. In contrast to the original formulation, which is restricted to frozen-Gaussian basis sets, the extended method is suitable for propagating quantum states of systems featuring diversified physical properties, such as spin degrees of freedom or particle indistinguishability. The approach is illustrated with simple models for interacting bosons trapped in double- and triple-well potentials, most adequately described in terms of SU(2) and SU(3) bosonic coherent states, respectively.
Quantum state readout of individual quantum dots by electrostatic force detection.
Miyahara, Yoichi; Roy-Gobeil, Antoine; Grutter, Peter
2017-02-10
Electric charge detection by atomic force microscopy (AFM) with single-electron resolution (e-EFM) is a promising way to investigate the electronic level structure of individual quantum dots (QDs). The oscillating AFM tip modulates the energy of the QDs, causing single electrons to tunnel between QDs and an electrode. The resulting oscillating electrostatic force changes the resonant frequency and damping of the AFM cantilever, enabling electrometry with a single-electron sensitivity. Quantitative electronic level spectroscopy is possible by sweeping the bias voltage. Charge stability diagram can be obtained by scanning the AFM tip around the QD. e-EFM technique enables to investigate individual colloidal nanoparticles and self-assembled QDs without nanoscale electrodes. e-EFM is a quantum electromechanical system where the back-action of a tunneling electron is detected by AFM; it can also be considered as a mechanical analog of admittance spectroscopy with a radio frequency resonator, which is emerging as a promising tool for quantum state readout for quantum computing. In combination with the topography imaging capability of the AFM, e-EFM is a powerful tool for investigating new nanoscale material systems which can be used as quantum bits.
CSIR Research Space (South Africa)
de Clercq, L
2010-09-01
Full Text Available Coherent control of the upper vibrational level populations in the electronic ground state of a polyatomic molecule was simulated. Results indicate that selective excitation of a specific upper state level is possible...
CSIR Research Space (South Africa)
De Clercq, L
2010-09-01
Full Text Available Coherent control of the upper vibrational level populations in the electronic ground state of a polyatomic molecule was simulated. Results indicate that selective excitation of a specific upper state level is possible....
Small-scale quantum computers: current state of the art and applications
Lloyd, Seth
This talk discusses the various applications of small scale quantum computers consisting of a few hundred qubits and capable of performing a few thousand quantum logic operations reliably without error corrections. Such small scale quantum computers could perform useful quantum simulations of many-body quantum systems, including processes of many body localization and scrambling. I will show that such small scale quantum computers could also be useful for quantum machine learning, revealing patterns in quantum states and in classical data that could not be revealed by even the most powerful classical supercomputer.
Minimal-excitation states for electron quantum optics using levitons.
Dubois, J; Jullien, T; Portier, F; Roche, P; Cavanna, A; Jin, Y; Wegscheider, W; Roulleau, P; Glattli, D C
2013-10-31
The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong-Ou-Mandel noise correlations. The latter, obtained by colliding synchronized levitons on a beam splitter, exemplifies the potential use of levitons for quantum information: using linear electron quantum optics in ballistic conductors, it is possible to imagine flying-qubit operation in which the Fermi statistics are exploited to entangle synchronized electrons emitted by distinct sources. Compared with electron sources based on quantum dots, the generation of levitons does not require delicate nanolithography, considerably simplifying the circuitry for scalability. Levitons are not limited to carrying a single charge, and so in a broader context n-particle levitons could find application in the study of full electron counting statistics. But they can also carry a fraction of charge if they are implemented in Luttinger liquids or in fractional quantum Hall edge channels; this allows the study of Abelian and non-Abelian quasiparticles in the
Energy Technology Data Exchange (ETDEWEB)
Xie, Min; Sen, Zhitao; Pratt, S. T.; Lee, Yuan-Pern
2017-11-21
Vibrational autoionization of Rydberg states provides key information about nonadiabatic processes above an ionization threshold. We employed time-of-flight mass detection of CH_{3}SH+ to record vibrational-state selective photo-ionization efficiency (PIE) spectra of jet-cooled methanethiol (CH_{3}SH) on exciting CH_{3}SH to a specific vibrationally excited state with an infrared (IR) laser, followed by excitation with a tunable laser in the vacuum-ultraviolet (VUV) region for ionization. Autoionizing Rydberg states assigned to the ns, np, nd and nf series are identified. When IR light at 2601 (ν_{3}, SH stretching mode) and 2948 cm^{-1} (ν_{2}, CH_{3} symmetric stretching mode) was employed, the Rydberg series converged to the respective vibrationally excited (ν_{3} and ν_{2}) states of CH_{3}SH+. When IR light at 3014 cm^{-1} (overlapped ν_{1}/ν_{9}, CH_{3} antisymmetric stretching and CH_{2} antisymmetric stretching modes) was employed, two converging limits towards vibrationally excited states (ν_{1} and ν_{9}) of CH_{3}SH+ were observed. In contrast, when IR light at 2867 cm^{-1} (2ν_{10}, overtone of CH_{3} deformation mode) and 2892 cm^{-1} (2ν_{4}, overtone of CH_{2} scissoring mode) was employed, both Δν = -1 and Δν = -2 ionization transitions were observed; there is evidence for direct ionization from the initial state into the CH_{3}SH+ (v_{4}+ = 1) continuum. In all observed IR-VUV-PIE spectra, the ns and nd series show intensity greater than the other Rydberg series, which is consistent with the fact that the highest-occupied molecular orbital of CH_{3}SH is a p-like lone pair orbital on the S atom. The quantum yields for autoionization of various vibrational excited states are discussed.
Numerical analysis using state space method for vibration control of ...
African Journals Online (AJOL)
... on sagged bridges and car moving on road humps. The paper also presents the comparison of performance of both the dampers for the two cases. State space method has been employed for the numerical analysis of the study. It is found that the amplitude of displacements is reduced considerably by the employment of ...
Investigating Anisotropic Quantum Hall States with Bimetric Geometry
Gromov, Andrey; Geraedts, Scott D.; Bradlyn, Barry
2017-10-01
We construct a low energy effective theory of anisotropic fractional quantum Hall (FQH) states. We develop a formalism similar to that used in the bimetric approach to massive gravity, and apply it to describe Abelian anisotropic FQH states in the presence of external electromagnetic and geometric backgrounds. We derive a relationship between the shift, the Hall viscosity, and a new quantized coupling to anisotropy, which we term anisospin. We verify this relationship by numerically computing the Hall viscosity for a variety of anisotropic quantum Hall states using the density matrix renormalization group. Finally, we apply these techniques to the problem of nematic order and clarify certain disagreements that exist in the literature about the meaning of the coefficient of the Berry phase term in the nematic effective action.
Efficient steady-state solver for hierarchical quantum master equations.
Zhang, Hou-Dao; Qiao, Qin; Xu, Rui-Xue; Zheng, Xiao; Yan, YiJing
2017-07-28
Steady states play pivotal roles in many equilibrium and non-equilibrium open system studies. Their accurate evaluations call for exact theories with rigorous treatment of system-bath interactions. Therein, the hierarchical equations-of-motion (HEOM) formalism is a nonperturbative and non-Markovian quantum dissipation theory, which can faithfully describe the dissipative dynamics and nonlinear response of open systems. Nevertheless, solving the steady states of open quantum systems via HEOM is often a challenging task, due to the vast number of dynamical quantities involved. In this work, we propose a self-consistent iteration approach that quickly solves the HEOM steady states. We demonstrate its high efficiency with accurate and fast evaluations of low-temperature thermal equilibrium of a model Fenna-Matthews-Olson pigment-protein complex. Numerically exact evaluation of thermal equilibrium Rényi entropies and stationary emission line shapes is presented with detailed discussion.
Simulating quantum systems on classical computers with matrix product states
Energy Technology Data Exchange (ETDEWEB)
Kleine, Adrian
2010-11-08
In this thesis, the numerical simulation of strongly-interacting many-body quantum-mechanical systems using matrix product states (MPS) is considered. Matrix-Product-States are a novel representation of arbitrary quantum many-body states. Using quantum information theory, it is possible to show that Matrix-Product-States provide a polynomial-sized representation of one-dimensional quantum systems, thus allowing an efficient simulation of one-dimensional quantum system on classical computers. Matrix-Product-States form the conceptual framework of the density-matrix renormalization group (DMRG). After a general introduction in the first chapter of this thesis, the second chapter deals with Matrix-Product-States, focusing on the development of fast and stable algorithms. To obtain algorithms to efficiently calculate ground states, the density-matrix renormalization group is reformulated using the Matrix-Product-States framework. Further, time-dependent problems are considered. Two different algorithms are presented, one based on a Trotter decomposition of the time-evolution operator, the other one on Krylov subspaces. Finally, the evaluation of dynamical spectral functions is discussed, and a correction vector-based method is presented. In the following chapters, the methods presented in the second chapter, are applied to a number of different physical problems. The third chapter deals with the existence of chiral phases in isotropic one-dimensional quantum spin systems. A preceding analytical study based on a mean-field approach indicated the possible existence of those phases in an isotropic Heisenberg model with a frustrating zig-zag interaction and a magnetic field. In this thesis, the existence of the chiral phases is shown numerically by using Matrix-Product-States-based algorithms. In the fourth chapter, we propose an experiment using ultracold atomic gases in optical lattices, which allows a well controlled observation of the spin-charge separation (of
Statistical tests for quantum state reconstruction I: Theory
Energy Technology Data Exchange (ETDEWEB)
Kleinmann, Matthias; Guehne, Otfried [Naturwissenschaftlich-Technische Fakultaet, Universitaet Siegen (Germany); Moroder, Tobias [Naturwissenschaftlich-Technische Fakultaet, Universitaet Siegen (Germany); Institut fuer Quantenoptik und Quanteninformation, Innsbruck (Austria); Monz, Thomas; Schindler, Philipp [Innsbruck Univ. (Austria). Inst. fuer Experimentalphysik; Blatt, Rainer [Institut fuer Quantenoptik und Quanteninformation, Innsbruck (Austria); Innsbruck Univ. (Austria). Inst. fuer Experimentalphysik
2012-07-01
In quantum state tomography and similar schemes, the measured data is usually not used directly but rather becomes subject of a sophisticated reconstruction procedure that squeezes the data into a quantum state. In general such techniques are only admissible if the statistical error - as due to low sampling - dominates over the systematical errors, such as misaligned measurement bases. We here present tests that allow to detect situations in which a state reconstruction will become statistically inadmissible. In particular, the positivity of the density operator and the linear dependencies that occur in overcomplete tomography lead to strong conditions on the measured data. Furthermore, we argue, that certain unphysical properties of naive reconstruction schemes are merely statistical effects and hence can be safely ignored in many situations.
Yuen, H. P.; Shapiro, J. H.
1978-01-01
To determine the ultimate performance limitations imposed by quantum effects, it is also essential to consider optimum quantum-state generation. Certain 'generalized' coherent states of the radiation field possess novel quantum noise characteristics that offer the potential for greatly improved optical communications. These states have been called two-photon coherent states because they can be generated, in principle, by stimulated two-photon processes. The use of two-photon coherent state (TCS) radiation in free-space optical communications is considered. A simple theory of quantum state propagation is developed. The theory provides the basis for representing the free-space channel in a quantum-mechanical form convenient for communication analysis. The new theory is applied to TCS radiation.
Quantum entanglement between an optical photon and a solid-state spin qubit.
Togan, E; Chu, Y; Trifonov, A S; Jiang, L; Maze, J; Childress, L; Dutt, M V G; Sørensen, A S; Hemmer, P R; Zibrov, A S; Lukin, M D
2010-08-05
Quantum entanglement is among the most fascinating aspects of quantum theory. Entangled optical photons are now widely used for fundamental tests of quantum mechanics and applications such as quantum cryptography. Several recent experiments demonstrated entanglement of optical photons with trapped ions, atoms and atomic ensembles, which are then used to connect remote long-term memory nodes in distributed quantum networks. Here we realize quantum entanglement between the polarization of a single optical photon and a solid-state qubit associated with the single electronic spin of a nitrogen vacancy centre in diamond. Our experimental entanglement verification uses the quantum eraser technique, and demonstrates that a high degree of control over interactions between a solid-state qubit and the quantum light field can be achieved. The reported entanglement source can be used in studies of fundamental quantum phenomena and provides a key building block for the solid-state realization of quantum optical networks.
Unitary equilibration after a quantum quench of a thermal state
Jacobson, N. Tobias; Venuti, Lorenzo Campos; Zanardi, Paolo
2011-08-01
In this work we investigate the equilibration dynamics after a sudden Hamiltonian quench of a quantum spin system initially prepared in a thermal state. To characterize the equilibration we evaluate the Loschmidt echo, a global measure for the degree of distinguishability between the initial and time-evolved quenched states. We present general results valid for small quenches and detailed analysis of the quantum XY chain. The result is that quantum criticality manifests, even at small but finite temperatures, in a universal double-peaked form of the echo statistics and poor equilibration for sufficiently relevant perturbations. In addition, for this model we find a tight lower bound on the Loschmidt echo in terms of the purity of the initial state and the more easily evaluated Hilbert-Schmidt inner product between initial and time-evolved quenched states. This bound allows us to relate the time-averaged Loschmidt echo with the purity of the time-averaged state, a quantity that has been shown to provide an upper bound on the variance of observables.
Unitary equilibration after a quantum quench of a thermal state
Energy Technology Data Exchange (ETDEWEB)
Jacobson, N. Tobias [Department of Physics and Astronomy and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089-0484 (United States); Venuti, Lorenzo Campos [Institute for Scientific Interchange (ISI), Viale Settimio Severo 65, I-10133 Torino (Italy); Zanardi, Paolo [Department of Physics and Astronomy and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089-0484 (United States); Institute for Scientific Interchange (ISI), Viale Settimio Severo 65, I-10133 Torino (Italy)
2011-08-15
In this work we investigate the equilibration dynamics after a sudden Hamiltonian quench of a quantum spin system initially prepared in a thermal state. To characterize the equilibration we evaluate the Loschmidt echo, a global measure for the degree of distinguishability between the initial and time-evolved quenched states. We present general results valid for small quenches and detailed analysis of the quantum XY chain. The result is that quantum criticality manifests, even at small but finite temperatures, in a universal double-peaked form of the echo statistics and poor equilibration for sufficiently relevant perturbations. In addition, for this model we find a tight lower bound on the Loschmidt echo in terms of the purity of the initial state and the more easily evaluated Hilbert-Schmidt inner product between initial and time-evolved quenched states. This bound allows us to relate the time-averaged Loschmidt echo with the purity of the time-averaged state, a quantity that has been shown to provide an upper bound on the variance of observables.
DEFF Research Database (Denmark)
Filsinger, Frank; Küpper, Jochen; Meijer, Gerard
2009-01-01
Supersonic beams of polar molecules are deflected using inhomogeneous electric fields. The quantum-state selectivity of the deflection is used to spatially separate molecules according to their quantum state. A detailed analysis of the deflection and the obtained quantum-state selection...
Quantum tele-amplification with a continuous-variable superposition state
DEFF Research Database (Denmark)
Neergaard-Nielsen, Jonas S.; Eto, Yujiro; Lee, Chang-Woo
2013-01-01
Optical coherent states are classical light fields with high purity, and are essential carriers of information in optical networks. If these states could be controlled in the quantum regime, allowing for their quantum superposition (referred to as a Schrödinger-cat state), then novel quantum...
Deterministic quantum state transfer between remote qubits in cavities
Vogell, B.; Vermersch, B.; Northup, T. E.; Lanyon, B. P.; Muschik, C. A.
2017-12-01
Performing a faithful transfer of an unknown quantum state is a key challenge for enabling quantum networks. The realization of networks with a small number of quantum links is now actively pursued, which calls for an assessment of different state transfer methods to guide future design decisions. Here, we theoretically investigate quantum state transfer between two distant qubits, each in a cavity, connected by a waveguide, e.g., an optical fiber. We evaluate the achievable success probabilities of state transfer for two different protocols: standard wave packet shaping and adiabatic passage. The main loss sources are transmission losses in the waveguide and absorption losses in the cavities. While special cases studied in the literature indicate that adiabatic passages may be beneficial in this context, it remained an open question under which conditions this is the case and whether their use will be advantageous in practice. We answer these questions by providing a full analysis, showing that state transfer by adiabatic passage—in contrast to wave packet shaping—can mitigate the effects of undesired cavity losses, far beyond the regime of coupling to a single waveguide mode and the regime of lossless waveguides, as was proposed so far. Furthermore, we show that the photon arrival probability is in fact bounded in a trade-off between losses due to non-adiabaticity and due to coupling to off-resonant waveguide modes. We clarify that neither protocol can avoid transmission losses and discuss how the cavity parameters should be chosen to achieve an optimal state transfer.
Zakharenko, Olena; Motiyenko, R. A.; Aviles Moreno, Juan-Ramon; Huet, T. R.
2016-06-01
Methacrolein and methyl vinyl ketone are the two major oxidation products of isoprene emitted in the troposphere. New spectroscopic information is provided with the aim to allow unambiguous identification of these molecules, characterized by a large amplitude motion associated with the methyl top. State-of-the-art millimeter-wave spectroscopy experiments coupled to quantum chemical calculations have been performed. Comprehensive sets of molecular parameters have been obtained. The torsion-rotation-vibration effects will be discussed in detail. From the atmospheric application point of view the results provide precise ground state molecular constants essential as a foundation (by using the Ground State Combination Differences method) for the analysis of high resolution spectrum, recorded from 600 to 1600 wn. The infrared range can be then refitted using appropriate Hamiltonian parameters. The present work is funded by the French ANR through the PIA under contract ANR-11-LABX-0005-01 (Labex CaPPA), by the Regional Council Nord-Pas de Calais and by the European Funds for Regional Economic Development (FEDER).
Matrix product state calculations for one-dimensional quantum chains and quantum impurity models
Energy Technology Data Exchange (ETDEWEB)
Muender, Wolfgang
2011-09-28
This thesis contributes to the field of strongly correlated electron systems with studies in two distinct fields thereof: the specific nature of correlations between electrons in one dimension and quantum quenches in quantum impurity problems. In general, strongly correlated systems are characterized in that their physical behaviour needs to be described in terms of a many-body description, i.e. interactions correlate all particles in a complex way. The challenge is that the Hilbert space in a many-body theory is exponentially large in the number of particles. Thus, when no analytic solution is available - which is typically the case - it is necessary to find a way to somehow circumvent the problem of such huge Hilbert spaces. Therefore, the connection between the two studies comes from our numerical treatment: they are tackled by the density matrix renormalization group (DMRG) and the numerical renormalization group (NRG), respectively, both based on matrix product states. The first project presented in this thesis addresses the problem of numerically finding the dominant correlations in quantum lattice models in an unbiased way, i.e. without using prior knowledge of the model at hand. A useful concept for this task is the correlation density matrix (CDM) which contains all correlations between two clusters of lattice sites. We show how to extract from the CDM, a survey of the relative strengths of the system's correlations in different symmetry sectors as well as detailed information on the operators carrying long-range correlations and the spatial dependence of their correlation functions. We demonstrate this by a DMRG study of a one-dimensional spinless extended Hubbard model, while emphasizing that the proposed analysis of the CDM is not restricted to one dimension. The second project presented in this thesis is motivated by two phenomena under ongoing experimental and theoretical investigation in the context of quantum impurity models: optical absorption
Quantum states for quantum processes: A toy model for ammonia inversion spectra
Energy Technology Data Exchange (ETDEWEB)
Arteca, Gustavo A. [Departement de Chimie et Biochimie and Biomolecular Sciences Programme, Laurentian University, Ramsey Lake Road, Sudbury, Ontario, Canada P3E 2C6 (Canada); Department of Physical Chemistry, Uppsala University, A ring ngstroemlaboratoriet, Box 259, S-751 05 Uppsala (Sweden); Tapia, O. [Department of Physical Chemistry, Uppsala University, A ring ngstroemlaboratoriet, Box 259, S-751 05 Uppsala (Sweden)
2011-07-15
Chemical transformations are viewed here as quantum processes modulated by external fields, that is, as shifts in reactant to product amplitudes within a quantum state represented by a linear (coherent) superposition of electronuclear basis functions; their electronic quantum numbers identify the ''chemical species.'' This basis set can be mapped from attractors built from a unique electronic configurational space that is invariant with respect to the nuclear geometry. In turn, the quantum numbers that label these basis functions and the semiclassical potentials for the electronic attractors may be used to derive reaction coordinates to monitor progress as a function of the applied field. A generalization of Feynman's three-state model for the ammonia inversion process illustrates the scheme; to enforce symmetry for the entire inversion process model and ensure invariance with respect to nuclear configurations, the three attractors and their basis functions are computed with a grid of fixed floating Gaussian functions. The external-field modulation of the effective inversion barrier is discussed within this conceptual approach. This analysis brings the descriptions of chemical processes near modern technologies that employ molecules to encode information by means of confinement and external fields.
Cao, Fangfei; Liu, Jinkun
2017-10-01
Considering full state constraints, this paper designs a boundary controller for a two-link rigid-flexible manipulator via Barrier Lyapunov Function. The dynamic model of the two-link rigid-flexible manipulator is described by coupled ordinary differential equations- partial differential equations (ODEs-PDEs). Based on the original model without neglecting the high-frequency modes, boundary controller is proposed to regulate the joint positions and eliminate the elastic vibration simultaneously. To ensure that the full state constraints which include position, speed and vibration constraints are not transgressed, a Barrier Lyapunov Function is employed in the proposed controller. The asymptotic stability of the closed-loop system is rigorously proved by the LaSalle's Invariance Principle. Simulations are given to verify the effectiveness of the proposed controller with state constraints.
Entanglement in valence-bond-solid states and quantum search
Xu, Ying
The present dissertation covers two independent subjects: (i) The quantum entanglement in Valence-Bond-Solid states, and (ii) quantum database search algorithms. Both subjects are presented in a self-contained and pedagogical way. (i) The first chapter is a through introduction to the subject of quantum entanglement in Valence-Bond-Solid (VBS) states defined on a lattice or graph. The VBS state was first introduced as the ground state of the celebrated Affleck-Kennedy-Lieb-Tasaki (AKLT) spin chain model in statistical mechanics. Then it became essential in condensed matter physics, quantum information and measurement-based quantum computation. Recent studies elucidated important entanglement properties of the VBS state. We start with the definition of a general AKLT model and the construction of VBS ground states. A subsystem is introduced and described by the density matrix. Exact spectrum properties of the density matrix are proved and discussed. Density matrices of 1-dimensional models are diagonalized and the entanglement entropies (the von Neumann entropy and Renyi entropy) are calculated. The entropies take saturated value and the density matrix is proportional to a projector in the large subsystem limit. (ii) The second chapter is a detailed introduction to the subject of quantum database search algorithms. The problem of searching a large database (a Hilbert space) for a target item is performed by the famous Grover algorithm which locates the target item with probability 1 and a quadratic speed up compared with the corresponding classical algorithm. If the database is partitioned into blocks and one is searching for the block containing the target item instead of the target item itself, then the problem is referred to as partial search. Partial search trades accuracy for speed and the most efficient version is the Grover-Radhakrishnan-Korepin (GRK) algorithm. The target block can be further partitioned into subblocks so that GRK can be performed in a
Hierarchy of graph-diagonal states based on quantum discord and entanglement classification
Jafarizadeh, Mohammad Ali; Karimi, Naser; Sahlan, Davood Amidi; Heshmati, Ahmad; Yahyavi, Marziyeh
2017-10-01
For the relative entropy-based measure of quantum discord the key idea is to find the closest classical state (CCS) for a given state ρ, which is in general a more complicated problem. In this work, we study three and four qubit graph-diagonal states and give the explicit expressions of CCS for these states. Using the CCS, we compute the quantum discord of graph-diagonal states of three and four qubit systems and show that there is a hierarchy for the quantum discord of graph-diagonal states of any three and four qubit systems. Then we classify the entanglement of graph-diagonal states of three and four qubit systems and draw the hierarchy of entanglement of these graph-diagonal states. Finally, we compare the hierarchy of quantum discord and quantum entanglement of the these graph-diagonal states and show that the hierarchy of quantum entanglement is at least in equivalence of quantum discord.
Multi-state analysis of the OCS ultraviolet absorption including vibrational structure
DEFF Research Database (Denmark)
Schmidt, Johan Albrecht; Johnson, Matthew Stanley; McBane, G.C.
2012-01-01
The first absorption band of OCS (carbonyl sulfide) is analyzed using potential energy surfaces and transition dipole moment functions of the lowest four singlet and the lowest four triplet states. Excitation of the 2 (1)A' state is predominant except at very low photon energies. It is shown that...... that the vibrational structures in the center of the band are due to excitation of the 2 (3)A'' triplet state, whereas the structures at very low energies are caused by bending excitation in the potential wells of states 2 (1)A' and 1 (1)A''....
Spin-vibrational 1+ states in 140Ce
Guliyev, E.; Yavas, O.; Kuliev, A. A.
2001-01-01
The properties of collective I^$\\Pi$=1+ states in double even semimagic nucleus 140Ce are investigated in random phase approximation(RPA). The calculation of the B(M1) strength, elastic gamma-scattering cross section $\\sigma_(gamma)(\\omega)$ and gamma-decay width $\\Sigma_(gamma)(\\omega_i)$ show that in 140Ce the isovector spin-spin interactions concenrate the main strength of M1 transition at energy 7.89 MeV where the isovector spin-flip magnetic resonance may appear. The predisctions are con...
Inducing superconducting correlation in quantum Hall edge states
Lee, Gil-Ho; Huang, Ko-Fan; Efetov, Dmitri K.; Wei, Di S.; Hart, Sean; Taniguchi, Takashi; Watanabe, Kenji; Yacoby, Amir; Kim, Philip
2017-07-01
The quantum Hall (QH) effect supports a set of chiral edge states at the boundary of a two-dimensional system. A superconductor (SC) contacting these states can provide correlations of the quasiparticles in the dissipationless edge states. Here we fabricated highly transparent and nanometre-scale SC junctions to graphene. We demonstrate that the QH edge states can couple via superconducting correlations through the SC electrode narrower than the superconducting coherence length. We observe that the chemical potential of the edge state exhibits a sign reversal across the SC electrode. This provides direct evidence of conversion of the incoming electron to the outgoing hole along the chiral edge state, termed crossed Andreev conversion (CAC). We show that CAC can successfully describe the temperature, bias and SC electrode width dependences. This hybrid SC/QH system could provide a novel route to create isolated non-Abelian anyonic zero modes, in resonance with the chiral edge states.
Quantum Probability Cancellation Due to a Single-Photon State
Ou, Z. Y.
1996-01-01
When an N-photon state enters a lossless symmetric beamsplitter from one input port, the photon distribution for the two output ports has the form of Bernouli Binormial, with highest probability at equal partition (N/2 at one outport and N/2 at the other). However, injection of a single photon state at the other input port can dramatically change the photon distribution at the outputs, resulting in zero probability at equal partition. Such a strong deviation from classical particle theory stems from quantum probability amplitude cancellation. The effect persists even if the N-photon state is replaced by an arbitrary state of light. A special case is the coherent state which corresponds to homodyne detection of a single photon state and can lead to the measurement of the wave function of a single photon state.
Sun, Wen-Yang; Wang, Dong; Ding, Zhi-Yong; Ye, Liu
2017-12-01
In this letter, we mainly investigate the dynamic behavior of quantum steering and how to effectively recover the lost steerability of quantum states within non-Markovian environments. We consider two different cases (one-subsystem or all-subsystem interaction with dissipative environments), and find that the dynamical interaction between a system initialized by a Werner state and a non-Markovian environment can induce quasi-periodic quantum entanglement (concurrence) resurgence, however, quantum steering cannot be retrieved in such a condition. We also find that the resurgent quantum entanglement cannot be utilized to achieve quantum steering. Subsequently, we put forward a feasible physical scheme for recovering the steerability of quantum states within non-Markovian noises by prior weak measurement on each subsystem before interaction with dissipative environments, followed by post weak measurement reversal. It is shown that the steerability of quantum states and fidelity can be effectively restored. Furthermore, the results show that the larger the weak measurement strength, the better the effectiveness of the scheme. Consequently, our investigations might be beneficial to recover the lost steerability of quantum states within non-Markovian regimes.
Quantum cryptography using coherent states: Randomized encryption and key generation
Corndorf, Eric
With the advent of the global optical-telecommunications infrastructure, an increasing number of individuals, companies, and agencies communicate information with one another over public networks or physically-insecure private networks. While the majority of the traffic flowing through these networks requires little or no assurance of secrecy, the same cannot be said for certain communications between banks, between government agencies, within the military, and between corporations. In these arenas, the need to specify some level of secrecy in communications is a high priority. While the current approaches to securing sensitive information (namely the public-key-cryptography infrastructure and deterministic private-key ciphers like AES and 3DES) seem to be cryptographically strong based on empirical evidence, there exist no mathematical proofs of secrecy for any widely deployed cryptosystem. As an example, the ubiquitous public-key cryptosystems infer all of their secrecy from the assumption that factoring of the product of two large primes is necessarily time consuming---something which has not, and perhaps cannot, be proven. Since the 1980s, the possibility of using quantum-mechanical features of light as a physical mechanism for satisfying particular cryptographic objectives has been explored. This research has been fueled by the hopes that cryptosystems based on quantum systems may provide provable levels of secrecy which are at least as valid as quantum mechanics itself. Unfortunately, the most widely considered quantum-cryptographic protocols (BB84 and the Ekert protocol) have serious implementation problems. Specifically, they require quantum-mechanical states which are not readily available, and they rely on unproven relations between intrusion-level detection and the information available to an attacker. As a result, the secrecy level provided by these experimental implementations is entirely unspecified. In an effort to provably satisfy the cryptographic
DEFF Research Database (Denmark)
Wu, Shengjun; Poulsen, Uffe Vestergaard; Mølmer, Klaus
2009-01-01
We consider the classical correlations that two observers can extract by measurements on a bipartite quantum state and we discuss how they are related to the quantum mutual information of the state. We show with several examples how complementarity gives rise to a gap between the quantum...... and the classical correlations and we relate our quantitative finding to the so-called classical correlation locked in a quantum state. We derive upper bounds for the sum of classical correlation obtained by measurements in different mutually unbiased bases and we show that the complementarity gap is also present...... in the deterministic quantum computation with one quantum bit....
Jacobs, M.H.G.; van den Berg, A.P.; Schmid-Fetzer, R.
2013-01-01
We use Kieffer's model to represent the vibrational density of states (VDoS) and thermodynamic properties of pure substances in pressure-temperature space. We show that this model can be simplified to a vibrational model in which the VDoS is represented by multiple Einstein frequencies without
Knowledge-Concealing Evidencing of Knowledge About a Quantum State
Adlam, Emily; Kent, Adrian
2018-01-01
Bob has a black box that emits a single pure state qudit which is, from his perspective, uniformly distributed. Alice wishes to give Bob evidence that she has knowledge about the emitted state while giving him little or no information about it. We show that zero-knowledge evidencing of such knowledge is impossible in quantum relativistic protocols, extending a previous result of Horodecki, Horodecki, and Horodecki. We also show that no such protocol can be both sound and complete. We present a new quantum relativistic protocol which we conjecture to be close to optimal in security against Alice and which reveals little knowledge to Bob, for large dimension d . We analyze its security against general attacks by Bob and restricted attacks by Alice.
Quantum Decoherence Timescales for Ionic Superposition States in Ion Channels
Salari, V; Fazileh, F; Shahbazi, F
2014-01-01
There are many controversial and challenging discussions about quantum effects in microscopic structures in neurons of the human brain. The challenge is mainly because of quick decoherence of quantum states due to hot, wet and noisy environment of the brain which forbids long life coherence for brain processing. Despite these critical discussions, there are only a few number of published papers about numerical aspects of decoherence in neurons. Perhaps the most important issue is offered by Max Tegmark who has calculated decoherence times for the systems of "ions" and "microtubules" in neurons of the brain. In fact, Tegmark did not consider ion channels which are responsible for ions displacement through the membrane and are the building blocks of electrical membrane signals in the nervous system. Here, we would like to re-investigate decoherence times for ionic superposition states by using the data obtained via molecular dynamics simulations. Our main approach is according to what Tegmark has used before. I...
Construction of state-independent proofs for quantum contextuality
Tang, Weidong; Yu, Sixia
2017-12-01
Since the enlightening proofs of quantum contextuality first established by Kochen and Specker, and also by Bell, various simplified proofs have been constructed to exclude the noncontextual hidden variable theory of our nature at the microscopic scale. The conflict between the noncontextual hidden variable theory and quantum mechanics is commonly revealed by Kochen-Specker sets of yes-no tests, represented by projectors (or rays), via either logical contradictions or noncontextuality inequalities in a state-(in)dependent manner. Here we propose a systematic and programmable construction of a state-independent proof from a given set of nonspecific rays in C3 according to their Gram matrix. This approach brings us a greater convenience in the experimental arrangements. Besides, our proofs in C3 can also be generalized to any higher-dimensional systems by a recursive method.
Cornering Gapless Quantum States via Their Torus Entanglement.
Witczak-Krempa, William; Hayward Sierens, Lauren E; Melko, Roger G
2017-02-17
The entanglement entropy (EE) has emerged as an important window into the structure of complex quantum states of matter. We analyze the universal part of the EE for gapless systems on tori in 2D and 3D, denoted by χ. Focusing on scale-invariant systems, we derive general nonperturbative properties for the shape dependence of χ and reveal surprising relations to the EE associated with corners in the entangling surface. We obtain closed-form expressions for χ in 2D and 3D within a model that arises in the study of conformal field theories (CFTs), and we use them to obtain Ansätze without fitting parameters for the 2D and 3D free boson CFTs. Our numerical lattice calculations show that the Ansätze are highly accurate. Finally, we discuss how the torus EE can act as a fingerprint of exotic states such as gapless quantum spin liquids, e.g., Kitaev's honeycomb model.
Cornering Gapless Quantum States via Their Torus Entanglement
Witczak-Krempa, William; Hayward Sierens, Lauren E.; Melko, Roger G.
2017-02-01
The entanglement entropy (EE) has emerged as an important window into the structure of complex quantum states of matter. We analyze the universal part of the EE for gapless systems on tori in 2D and 3D, denoted by χ . Focusing on scale-invariant systems, we derive general nonperturbative properties for the shape dependence of χ and reveal surprising relations to the EE associated with corners in the entangling surface. We obtain closed-form expressions for χ in 2D and 3D within a model that arises in the study of conformal field theories (CFTs), and we use them to obtain Ansätze without fitting parameters for the 2D and 3D free boson CFTs. Our numerical lattice calculations show that the Ansätze are highly accurate. Finally, we discuss how the torus EE can act as a fingerprint of exotic states such as gapless quantum spin liquids, e.g., Kitaev's honeycomb model.
Quantum secret sharing using orthogonal multiqudit entangled states
Bai, Chen-Ming; Li, Zhi-Hui; Liu, Cheng-Ji; Li, Yong-Ming
2017-12-01
In this work, we investigate the distinguishability of orthogonal multiqudit entangled states under restricted local operations and classical communication. According to these properties, we propose a quantum secret sharing scheme to realize three types of access structures, i.e., the ( n, n)-threshold, the restricted (3, n)-threshold and restricted (4, n)-threshold schemes (called LOCC-QSS scheme). All cooperating players in the restricted threshold schemes are from two disjoint groups. In the proposed protocol, the participants use the computational basis measurement and classical communication to distinguish between those orthogonal states and reconstruct the original secret. Furthermore, we also analyze the security of our scheme in four primary quantum attacks and give a simple encoding method in order to better prevent the participant conspiracy attack.
Quantum memory receiver for superadditive communication using binary coherent states.
Klimek, Aleksandra; Jachura, Michał; Wasilewski, Wojciech; Banaszek, Konrad
2016-11-12
We propose a simple architecture based on multimode quantum memories for collective readout of classical information keyed using a pair coherent states, exemplified by the well-known binary phase shift keying format. Such a configuration enables demonstration of the superadditivity effect in classical communication over quantum channels, where the transmission rate becomes enhanced through joint detection applied to multiple channel uses. The proposed scheme relies on the recently introduced idea to prepare Hadamard sequences of input symbols that are mapped by a linear optical transformation onto the pulse position modulation format [Guha, S. Phys. Rev. Lett.2011, 106, 240502]. We analyze two versions of readout based on direct detection and an optional Dolinar receiver which implements the minimum-error measurement for individual detection of a binary coherent state alphabet.
Simple variational ground state and pure-cat-state generation in the quantum Rabi model
Leroux, C.; Govia, L. C. G.; Clerk, A. A.
2017-10-01
We introduce a simple, physically motivated variational ground state for the quantum Rabi model and demonstrate that it provides a high-fidelity approximation of the true ground state in all parameter regimes (including intermediate- and strong-coupling regimes). Our variational state is constructed using Gaussian cavity states and nonorthogonal qubit pointer states and contains only three variational parameters. We use our state to develop a heuristic understanding of how the ground state evolves with increasing coupling and find a parameter regime where the ground state corresponds to the cavity being in a nearly pure Schrödinger cat state.
Quantum Theory of Conditional Phonon States in a Dual-Pumped Raman Optical Frequency Comb
Mondloch, Erin
In this work, we theoretically and numerically investigate nonclassical phonon states created in the collective vibration of a Raman medium by the generation of a dual-pumped Raman optical frequency comb in an optical cavity. This frequency comb is generated by cascaded Raman scattering driven by two phase-locked pump lasers that are separated in frequency by three times the Raman phonon frequency. We characterize the variety of conditioned phonon states that are created when the number of photons in all optical frequency modes except the pump modes are measured. Almost all of these conditioned phonon states are extremely well approximated as three-phonon-squeezed states or Schrodinger-cat states, depending on the outcomes of the photon number measurements. We show how the combinations of first-, second-, and third-order Raman scattering that correspond to each set of measured photon numbers determine the fidelity of the conditioned phonon state with model three-phonon-squeezed states and Schrodinger-cat states. All of the conditioned phonon states demonstrate preferential growth of the phonon mode along three directions in phase space. That is, there are three preferred phase values that the phonon state takes on as a result of Raman scattering. We show that the combination of Raman processes that produces a given set of measured photon numbers always produces phonons in multiples of three. In the quantum number-state representation, these multiples of three are responsible for the threefold phase-space symmetry seen in the conditioned phonon states. With a semiclassical model, we show how this three-phase preference can also be understood in light of phase correlations that are known to spontaneously arise in single-pumped Raman frequency combs. Additionally, our semiclassical model predicts that the optical modes also grow preferentially along three phases, suggesting that the dual-pumped Raman optical frequency comb is partially phase-stabilized.
Initial-State Graviton Radiation in Quantum Black Hole Production
AUTHOR|(CDS)2262067
2017-01-01
Monte Carlo simulation of quantum black hole production in the ATLAS experiment that allows for graviton radiation in the initial state is discussed and studied. It is concluded that, using trapped surface calculations and graviton emission, a black hole signal would be significant for Planck scales up to 4.5 TeV given a proton-proton luminosity of 37 fb$^{-1}$ in the 13 TeV LHC configuration.
A quantum bound-state description of black holes
Directory of Open Access Journals (Sweden)
Stefan Hofmann
2016-01-01
Full Text Available A relativistic framework for the description of bound states consisting of a large number of quantum constituents is presented, and applied to black-hole interiors. At the parton level, the constituent distribution, number and energy density inside black holes are calculated, and gauge corrections are discussed. A simple scaling relation between the black-hole mass and constituent number is established.
On the convergence of quantum resonant-state expansion
Energy Technology Data Exchange (ETDEWEB)
Brown, J. M.; Bahl, A. [College of Optical Sciences, University of Arizona, 1630 East University Boulevard, Tucson, Arizona 85721 (United States); Jakobsen, P. [Department of Mathematics and Statistics, University of Tromsø, Tromsø (Norway); Moloney, J. V.; Kolesik, M. [College of Optical Sciences, University of Arizona, 1630 East University Boulevard, Tucson, Arizona 85721 (United States); Arizona Center for Mathematical Sciences, University of Arizona, Tucson, Arizona 85721 (United States)
2016-03-15
Completeness of the system of Stark resonant states is investigated for a one-dimensional quantum particle with the Dirac-delta potential exposed to an external homogeneous field. It is shown that the resonant series representation of a given wavefunction converges on the negative real axis while the series diverges on the positive axis. Despite the divergent nature of the resonant expansion, good approximations can be obtained in a compact spatial domain.
Theoretical Study of Solid State Quantum Information Processing
2013-08-28
Implementing a topological quantum model using a cavity lattice , Science China Physics, Mechanics and Astronomy, (07 2012): 0. doi: 10.1007/s11433... Rabi frequency as a function of the magnetic field for sufficiently large Zeeman energies, which can alternatively be interpreted as the magnetic...DQD), where coherent Rabi oscillations between the singlet and triplet states are induced by jittering the inter-dot distance at the resonance
Quasi-Superradiant Soliton State of Matter in Quantum Metamaterials
Asai, H.; Kawabata, S.; Zagoskin, A. M.; Savel'ev, S. E.
2016-01-01
Strong interaction of a system of quantum emitters (e.g., two-level atoms) with electromagnetic field induces specific correlations in the system accompanied by a drastic insrease of emitted radiation (superradiation or superfluorescence). Despite the fact that since its prediction this phenomenon was subject to a vigorous experimental and theoretical research, there remain open question, in particular, concerning the possibility of a first order phase transition to the superradiant state fro...
Asymptotic estimation of shift parameter of a quantum state
Holevo, A. S.
2003-01-01
We develop an asymptotic theory of estimation of a shift parameter in a pure quantum state to study the relation between entangled and unentangled covariant estimates in the analytically most transparent way. After recollecting basics of estimation of shift parameter in Sec. 2, we study the structure of the optimal covariant estimate in Sec. 3, showing how entanglement comes into play for several independent trials. In Secs. 4,5 we give the asymptotics of the performance of the optimal covari...
The separation of vibrational coherence from ground- and excited-electronic states in P3HT film
Song, Yin
2015-06-07
© 2015 AIP Publishing LLC. Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S (λ 1, T∼ 2, λ 3)) along the population time (T∼ 2) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S (λ 1, ν∼ 2, λ 3)). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+ ν∼ 2) in the rephasing beating map and at negative frequency (- ν∼ 2) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems.
Energy Technology Data Exchange (ETDEWEB)
Harper, Warren W.(BATTELLE (PACIFIC NW LAB)); Nizkorodov, Sergey A.(California Institute of Technology); Nesbitt, David (Colorado, University Of)
2001-12-01
Single collision reactive scattering dynamics of F+ HDHF(v,J)+ D have been investigated exploiting high-resolution (0.0001 cm?1) infrared laser absorption for quantum state resolved detection of nascent HF(v,J) product states. State resolved Doppler profiles are recorded for a series of HF rovibrational transitions and converted into state resolved fluxes via density-to-flux analysis, yielding cross-section data for relative formation of HF(v,J) at Ecom0.6(2), 1.0(3), 1.5(3), and 1.9(4) kcal/mol. State resolved HF(v,J) products at all but the lowest collision energy exhibit Boltzmann-type populations, characteristic of direct reactive scattering dynamics. At the lowest collision energy[Ecom0.6(2) kcal/mol], however, the HF(v= 2,J) populations behave quite anomalously, exhibiting a nearly''flat'' distribution out to J11 before dropping rapidly to zero at the energetic limit. These results provide strong experimental support for quantum transition state resonance dynamics near Ecom0.6 kcal /mol corresponding classically to H atom chattering between the F and D atoms, and prove to be in remarkably quantitative agreement with theoretical wave packet predictions by Skodje et al.[J. Chem. Phys. 112, 4536 (2000)]. These fully quantum state resolved studies therefore nicely complement the recent crossed beam studies of Dong et al.[J. Chem. Phys. 113, 3633 (2000)], which confirm the presence of this resonance via angle resolved differential cross-section measurements. The observed quantum state distributions near threshold also indicate several rotational states in the HF(v= 3) vibrational manifold energetically inaccessible to F(2P3/2) reagent, but which are consistent with a minor (5%) nonadiabatic contribution from spin?orbit excited F*(2P1/2).?2002 American Institute of Physics.
Evaluation of the vehicle state with vibration-based diagnostics methods
Gai, V. E.; Polyakov, I. V.; Krasheninnikov, M. S.; Koshurina, A. A.; Dorofeev, R. A.
2017-02-01
Timely detection of a trouble in the mechanisms work is a guarantee of the stable operation of the entire machine complex. It allows minimizing unexpected losses, and avoiding any injuries inflicted on working people. The solution of the problem is the most important for vehicles and machines, working in remote areas of the infrastructure. All-terrain vehicles can be referred to such type of transport. The potential object of application of the described methodology is the multipurpose rotary-screw amphibious vehicle for rescue; reconnaissance; transport and technological operations. At the present time, there is no information on the use of these kinds of systems in ground-based vehicles. The present paper is devoted to the state estimation of a mechanism based on the analysis of vibration signals produced by the mechanism, in particular, the vibration signals of rolling bearings. The theory of active perception was used for the solution of the problem of the state estimation.
Resource theory of quantum states out of thermal equilibrium.
Brandão, Fernando G S L; Horodecki, Michał; Oppenheim, Jonathan; Renes, Joseph M; Spekkens, Robert W
2013-12-20
The ideas of thermodynamics have proved fruitful in the setting of quantum information theory, in particular the notion that when the allowed transformations of a system are restricted, certain states of the system become useful resources with which one can prepare previously inaccessible states. The theory of entanglement is perhaps the best-known and most well-understood resource theory in this sense. Here, we return to the basic questions of thermodynamics using the formalism of resource theories developed in quantum information theory and show that the free energy of thermodynamics emerges naturally from the resource theory of energy-preserving transformations. Specifically, the free energy quantifies the amount of useful work which can be extracted from asymptotically many copies of a quantum system when using only reversible energy-preserving transformations and a thermal bath at fixed temperature. The free energy also quantifies the rate at which resource states can be reversibly interconverted asymptotically, provided that a sublinear amount of coherent superposition over energy levels is available, a situation analogous to the sublinear amount of classical communication required for entanglement dilution.
Coherent states and parasupersymmetric quantum mechanics
Debergh, Nathalie
1992-01-01
It is well known that Parafermi and Parabose statistics are natural extensions of the usual Fermi and Bose ones, enhancing trilinear (anti)commutation relations instead of bilinear ones. Due to this generalization, positive parameters appear: the so-called orders of paraquantization p (= 1, 2, 3, ...) and h sub 0 (= 1/2, 1, 3/2, ...), respectively, the first value leading in each case to the usual statistics. The superpostion of the parabosonic and parafermionic operators gives rise to parasupermultiplets for which mixed trilinear relations have already been studied leading to two (nonequivalent) sets: the relative Parabose and the relative Parafermi ones. For the specific values p = 1 = 2h sub 0, these sets reduce to the well known supersymmetry. Coherent states associated with this last model have been recently put in evidence through the annihilation operator point of view and the group theoretical approach or displacement operator context. We propose to realize the corresponding studies within the new context p = 2 = 2h sub 0, being then directly extended to any order of paraquantization.
Many Worlds, the Cluster-state Quantum Computer, and the Problem of the Preferred Basis
Cuffaro, Michael
2011-01-01
I argue that the many worlds explanation of quantum computation is not licensed by, and in fact is conceptually inferior to, the many worlds interpretation of quantum mechanics from which it is derived. I argue that the many worlds explanation of quantum computation is incompatible with the recently developed cluster state model of quantum computation. Based on these considerations I conclude that we should reject the many worlds explanation of quantum computation.
A New Quantum Proxy Multi-signature Scheme Using Maximally Entangled Seven-Qubit States
Cao, Hai-Jing; Zhang, Jia-Fu; Liu, Jian; Li, Zeng-You
2016-02-01
In this paper, we propose a new secure quantum proxy multi-signature scheme using seven-qubit entangled quantum state as quantum channels, which may have applications in e-payment system, e-government, e-business, etc. This scheme is based on controlled quantum teleportation. The scheme uses the physical characteristics of quantum mechanics to guarantee its anonymity, verifiability, traceability, unforgetability and undeniability.
Tunable refraction in a two-dimensional quantum-state metamaterial
Everitt, M. J.; Samson, J. H.; Savel'ev, S. E.; Wilson, R.; Zagoskin, A. M.; Spiller, T. P.
2014-08-01
In this paper we consider a two-dimensional quantum-state metamaterial comprising an array of qubits (two-level quantum objects). Here we propose that it should be possible to manipulate the propagation of quantum information. We show that a quantum metamaterial such as the one considered here exhibits several different modes of operation, which we have termed Aharonov-Bohm, intermediate, and quantum-Zeno. We also see interesting behavior which could be thought of as either quantum birefringence (where the material acts like a beam splitter) as well as the emergence of quantum correlations in the circuit's measurement statistics. Quantum-state metamaterials as proposed here may be fabricated from a variety of technologies from superconducting qubits to quantum dots and would be readily testable in existing state-of-the-art laboratories.