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Non-Markovian fermionic stochastic Schrödinger equation for open system dynamics

Physical Review A 2013年第5期87卷 052127-052127页

作者： Wufu Shi Xinyu Zhao Ting Yu []Center for Controlled Quantum Systems and the Department of Physics and Engineering Physics Stevens Institute of Technology Hoboken New Jersey 07030 USA

This paper presents an exact Grassmann stochastic Schrödinger equation for the dynamics of an open fermionic quantum system coupled to a reservoir consisting of a finite or infinite number of fermions. We use this stochastic Schrödinger equation as a generic open system tool to derive the exact master equation for an electronic system strongly coupled to fermionic reservoirs. The generality and applicability of this Grassmann stochastic approach are justified and exemplified by several quantum fermionic system problems concerning quantum coherence coupled to vacuum or finite-temperature fermionic reservoirs. Our studies show that the quantum coherence property of a quantum dot system can be profoundly modified by the environmental memory.

关键词： quantum dots FERMIONS STOCHASTIC processes SCHRODINGER equation quantum coherence ELECTRONIC structure MARKOV processes

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Dynamic and energetic stabilization of persistent currents in Bose-Einstein condensates

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Physical Review A 2014年第5期89卷 053606-053606页

作者： K. J. H. Law T. W. Neely P. G. Kevrekidis B. P. Anderson A. S. Bradley R. Carretero-González Computer Electrical and Mathematical Sciences & Engineering King Abdullah University of Science and Technology Thuwal 23955-6900 KSA College of Optical Sciences University of Arizona Tucson Arizona 85721 USA Department of Mathematics and Statistics University of Massachusetts Amherst Massachusetts 01003-4515 USA College of Optical Sciences and Department of Physics University of Arizona Tucson Arizona 85721 USA Jack Dodd Centre for Quantum Technology Department of Physics University of Otago P.O. Box 56 Dunedin New Zealand Nonlinear Dynamical Systems Group† Department of Mathematics and Statistics and Computational Science Research Center San Diego State University San Diego California 92182-7720 USA

We study conditions under which vortices in a highly oblate harmonically trapped Bose-Einstein condensate (BEC) can be stabilized due to pinning by a blue-detuned Gaussian laser beam, with particular emphasis on the potentially destabilizing effects of laser beam positioning within the BEC. Our approach involves theoretical and numerical exploration of dynamically and energetically stable pinning of vortices with winding number up to S=6, in correspondence with experimental observations. Stable pinning is quantified theoretically via Bogoliubov-de Gennes excitation spectrum computations and confirmed via direct numerical simulations for a range of conditions similar to those of experimental observations. The theoretical and numerical results indicate that the pinned winding number, or equivalently the winding number of the superfluid current about the laser beam, decays as a laser beam of fixed intensity moves away from the BEC center. Our theoretical analysis helps explain previous experimental observations and helps define limits of stable vortex pinning for future experiments involving vortex manipulation by laser beams.

关键词： PERSISTENT currents BOSE-Einstein condensation GAUSSIAN beams EXCITATION spectrum FLUX pinning

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Many-body quantum trajectories of non-Markovian open systems

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Physical Review A 2013年第5期88卷 052122-052122页

作者： Jun Jing Xinyu Zhao J. Q. You Walter T. Strunz Ting Yu Center for Controlled Quantum Systems and Department of Physics and Engineering Physics Stevens Institute of Technology Hoboken New Jersey 07030 USA Department of Physics Shanghai University 200444 China Laboratory for Quantum Optics and Quantum Information Beijing Computational Science Research Center Beijing 100084 China Institut für Theoretische Physik Technische Universität Dresden D-01062 Dresden Germany

A long-standing open problem in the non-Markovian quantum state diffusion (QSD) approach to open quantum systems is to establish the non-Markovian QSD equations for multiple-qubit systems. In this paper, we settle this important question by explicitly constructing a set of exact time-local QSD equations for N-qubit systems. Our exact time-local (convolutionless) QSD equations have paved the way towards simulating quantum dynamics of many-body open systems interacting with a common bosonic environment. The applicability of this multiple-qubit stochastic equation is exemplified by numerically solving several quantum open many-body systems concerning quantum coherence dynamics and dynamical control.

关键词： MANY-body problem quantum trajectories MARKOV spectrum OPEN systems (physics) quantum states DIFFUSION PROBLEM solving

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Boosting optical magnetism with symmetry breaking in a subwavelength plasmonic metamolecule

Boosting optical magnetism with symmetry breaking in a subwa...

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Frontiers in Optics, FIO 2013

作者： Monticone, Francesco Li, Xiaoqin Alù, Andrea The University of Texas at Austin Department of Electrical and Computer Engineering Austin TX 78712 United States The University of Texas at Austin Department of Physics Center for Complex Quantum Systems Austin TX 78712 United States

We theoretically and experimentally show that, by introducing controlled structural asymmetries in a subwavelength plasmonic metamolecule, we may trigger a near-field interference between plasmon modes that can effici... 详细信息

ISBN: (纸本)9781557529879

关键词： Plasmonic metamaterials

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Nonperturbative quantum dynamical decoupling

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Physical Review A 2013年第2期88卷 022333-022333页

作者： Jun Jing Lian-Ao Wu J. Q. You Ting Yu Center for Controlled Quantum Systems and Department of Physics and Engineering Physics Stevens Institute of Technology Hoboken New Jersey 07030 USA Department of Physics Shanghai University Shanghai 200444 China Ikerbasque Basque Foundation for Science 48011 Bilbao and Department of Theoretical Physics and History of Science The Basque Country University (EHU/UPV) P.O. Box 644 48080 Bilbao Spain Department of Physics and State Key Laboratory of Surface Physics Fudan University Shanghai 200433 China

Current dynamical control based on the bang-bang control mechanism involving various types of pulse sequences is essentially a perturbative theory. This paper presents a nonperturbative dynamical control approach based on the exact stochastic Schrödinger equation. We report our findings on the pulse parameter regions in which the effective dynamical control can be exercised. The onset of the effective control zones reflects the nonperturbative feature of our approach. The nonperturbative methods offer possible new implementations when several different parameter regions are available.

关键词： PERTURBATION (quantum dynamics) quantum theory DECOUPLING (Mathematics) FEEDBACK control systems PARAMETER estimation SCHRODINGER equation

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Generation and stabilization of a three-qubit entangled W state in circuit QED via quantum feedback control

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Physical Review A 2013年第6期88卷 062311-062311页

作者： Shang-Yu Huang Hsi-Sheng Goan Xin-Qi Li G. J. Milburn Department of Physics and Center for Theoretical Sciences National Taiwan University Taipei 10617 Taiwan Center for Quantum Science and Engineering and National Center for Theoretical Sciences National Taiwan University Taipei 10617 Taiwan Department of Physics Beijing Normal University Beijing 100875 China Centre for Engineered Quantum Systems School of Mathematics and Physics The University of Queensland St Lucia QLD 4072 Australia

Circuit cavity quantum electrodynamics (QED) is proving to be a powerful platform to implement quantum feedback control schemes due to the ability to control superconducting qubits and microwaves in a circuit. Here, we present a simple and promising quantum feedback control scheme for deterministic generation and stabilization of a three-qubit W state in the superconducting circuit QED system. The control scheme is based on continuous joint Zeno measurements of multiple qubits in a dispersive regime, which enables us not only to infer the state of the qubits for further information processing but also to create and stabilize the target W state through adaptive quantum feedback control. We simulate the dynamics of the proposed quantum feedback control scheme using the quantum trajectory approach with an effective stochastic maser equation obtained by a polaron-type transformation method and demonstrate that in the presence of moderate environmental decoherence, the average state fidelity higher than 0.9 can be achieved and maintained for a considerably long time (much longer than the single-qubit decoherence time). This control scheme is also shown to be robust against measurement inefficiency and individual qubit decay rate differences. Finally, the comparison of the polaron-type transformation method to the commonly used adiabatic elimination method to eliminate the cavity mode is presented.

关键词： quantum electrodynamics FEEDBACK control systems quantum field theory quantum entanglement SUPERCONDUCTING circuits

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Proposed Rabi-Kondo Correlated State in a Laser-Driven Semiconductor quantum Dot

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Physical Review Letters 2013年第15期111卷 157402-157402页

作者： B. Sbierski M. Hanl A. Weichselbaum H. E. Türeci M. Goldstein L. I. Glazman J. von Delft A. İmamoğlu Institute for Quantum Electronics ETH Zürich CH-8093 Zürich Switzerland Dahlem Center for Complex Quantum Systems and Institut für Theoretische Physik FU Berlin D-14195 Berlin Germany Arnold Sommerfeld Center for Theoretical Physics and Center for NanoScience LMU München D-80333 München Germany Department of Electrical Engineering Princeton University Princeton New Jersey 08544 USA Department of Physics Yale University 217 Prospect Street New Haven Connecticut 06520 USA

Spin exchange between a single-electron charged quantum dot and itinerant electrons leads to an emergence of Kondo correlations. When the quantum dot is driven resonantly by weak laser light, the resulting emission spectrum allows for a direct probe of these correlations. In the opposite limit of vanishing exchange interaction and strong laser drive, the quantum dot exhibits coherent oscillations between the single-spin and optically excited states. Here, we show that the interplay between strong exchange and nonperturbative laser coupling leads to the formation of a new nonequilibrium quantum-correlated state, characterized by the emergence of a laser-induced secondary spin screening cloud, and examine the implications for the emission spectrum.

关键词： SPIN exchange quantum dots KONDO effect LASER beams quantum correlations

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Non-Abelian fractional Chern insulators from long-range interactions

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Physical Review B 2013年第20期88卷 205101-205101页

作者： Zhao Liu Emil J. Bergholtz Eliot Kapit Department of Electrical Engineering Princeton University Princeton New Jersey 08544 USA Beijing Computational Science Research Center Beijing 100084 China Dahlem Center for Complex Quantum Systems and Institut für Theoretische Physik Freie Universität Berlin Arnimallee 14 14195 Berlin Germany Rudolf Peierls Center for Theoretical Physics Oxford University 1 Keble Road Oxford OX1 3NP United Kingdom

The recent theoretical discovery of fractional Chern insulators (FCIs) has provided an important new way to realize topologically ordered states in lattice models. In earlier works, on-site and nearest-neighbor Hubbard-like interactions have been used extensively to stabilize Abelian FCIs in systems with nearly flat, topologically nontrivial bands. However, attempts to use two-body interactions to stabilize non-Abelian FCIs, where the ground state in the presence of impurities can be massively degenerate and manipulated through anyon braiding, have proven very difficult in uniform lattice systems. Here, we study the remarkable effect of long-range interactions in a lattice model that possesses an exactly flat lowest band with a unit Chern number. When spinless bosons with two-body long-range interactions partially fill the lowest Chern band, we find convincing evidence of gapped, bosonic Read-Rezayi (RR) phases with non-Abelian anyon statistics. We characterize these states through studying topological degeneracies, the overlap between the ground states of two-body interactions and the exact RR ground states of three- and four-body interactions, and state counting in the particle-cut entanglement spectrum. Moreover, we demonstrate how an approximate lattice form of Haldane's pseudopotentials, analogous to that in the continuum, can be used as an efficient guiding principle in the search for lattice models with stable non-Abelian phases.

关键词： ELECTRIC insulators & insulation LATTICE models (Statistical physics) GROUND state (quantum mechanics) ANYONS PSEUDOPOTENTIAL method HUBBARD model

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Time-local quantum-state-diffusion equation for multilevel quantum systems

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Physical Review A 2012年第4期85卷 042106-042106页

作者： Jun Jing Xinyu Zhao J. Q. You Ting Yu Center for Controlled Quantum Systems and Department of Physics and Engineering Physics Stevens Institute of Technology Hoboken New Jersey 07030 USA Department of Physics Shanghai University Shanghai CN-200444 China Department of Physics and State Key Laboratory of Surface Physics Fudan University Shanghai CN-200433 China

An open quantum system with multiple levels coupled to a bosonic environment at zero temperature is investigated systematically using the non-Markovian quantum-state-diffusion (QSD) method [W. T. Strunz, L. Diósi, and N. Gisin, Phys. Rev. Lett. 82, 1801 (1999)]. We have established exact time-local QSD equations for a set of interesting multilevel open systems, including high-spin systems, multiple-transition atomic models, and multilevel atomic models driven by time-dependent external fields. These exact QSD equations have paved the way to evaluate the dynamics of open multilevel atomic systems in the general non-Markovian regimes without any approximation.

关键词： Atoms

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Fermionic stochastic Schrödinger equation and master equation: An open-system model

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Physical Review A 2012年第3期86卷 032116-032116页

作者： Xinyu Zhao Wufu Shi Lian-Ao Wu Ting Yu Center for Controlled Quantum Systems and Department of Physics and Engineering Physics Stevens Institute of Technology Hoboken New Jersey 07030 USA Department of Theoretical Physics and History of Science Basque Country University (EHU/UPV) Post Office Box 644 48080 Bilbao Spain

This paper considers the extension of the non-Markovian stochastic approach for quantum open systems strongly coupled to a fermionic bath to the models in which the system operators commute with the fermionic bath. This technique can also be a useful tool for studying open quantum systems coupled to a spin-chain environment, which can be further transformed into an effective fermionic bath. We derive an exact stochastic Schrödinger equation (SSE), called the fermionic quantum state diffusion (QSD) equation, from the first principle by using the fermionic coherent state representation. The reduced density operator for the open system can be recovered from the stochastic average of the solutions to the QSD equation over the Grassmann-type noise. By employing the exact fermionic QSD equation, we can derive the corresponding exact master equation. The power of our approach is illustrated by the applications of our stochastic approach to several models of interest including the one-qubit dissipative model, the coupled two-qubit dissipative model, the quantum Brownian motion model, and the N-fermion model coupled to a fermionic bath. Different effects caused by the fermionic and bosonic baths on the dynamics of open systems are also discussed.

关键词： STOCHASTIC processes FERMIONS SCHRODINGER equation MATHEMATICAL models quantum theory ROTATIONAL motion BROWNIAN motion

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