ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 16 Jul 2024 12:46:16 GMT2024-07-16T12:46:16Z501131- All-optical imprinting of geometric phases onto matter waveshttps://scholarbank.nus.edu.sg/handle/10635/116921Title: All-optical imprinting of geometric phases onto matter waves
Authors: Zhang, Q.; Gong, J.; Oh, C.H.
Abstract: Traditional optical phase imprinting of matter waves is of a dynamical nature. Here we show that both Abelian and non-Abelian geometric phases can be optically imprinted onto matter waves, yielding a number of interesting phenomena such as wave-packet redirecting and wave-packet splitting. In addition to their fundamental interest, our results open up opportunities for robust optical control of matter waves. © 2009 The American Physical Society.
Wed, 01 Apr 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1169212009-04-01T00:00:00Z
- Two-mode Bose-Einstein condensate in a high-frequency driving field that directly couples the two modeshttps://scholarbank.nus.edu.sg/handle/10635/116013Title: Two-mode Bose-Einstein condensate in a high-frequency driving field that directly couples the two modes
Authors: Zhang, Q.; Hänggi, P.; Gong, J.
Abstract: A two-mode Bose-Einstein condensate coupled by a high-frequency modulation field is found to display rich features. An effective stationary Hamiltonian approach reveals the emergence of additional degenerate eigenstates as well as additional topological structures of the spectrum. Possible applications, such as the suppression of nonlinear Landau-Zener tunneling, are discussed. An interesting phenomenon, which we call "deterministic symmetry-breaking trapping" associated with separatrix crossing, is also found in an adiabatic process. © 2008 The American Physical Society.
Tue, 13 May 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1160132008-05-13T00:00:00Z
- Quantum diffusion dynamics in nonlinear systems: A modified kicked-rotor modelhttps://scholarbank.nus.edu.sg/handle/10635/115250Title: Quantum diffusion dynamics in nonlinear systems: A modified kicked-rotor model
Authors: Gong, J.; Wang, J.
Abstract: Using a simple method analogous to a quantum rephasing technique, a simple modification to a paradigm of classical and quantum chaos is proposed. The interesting quantum maps thus obtained display remarkably rich quantum dynamics. Emphasis is placed on the destruction of dynamical localization without breaking periodicity, unbounded quantum anomalous diffusion in integrable systems, and transient dynamical localization. Experimental realizations of this work are also discussed. © 2007 The American Physical Society.
Thu, 27 Sep 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1152502007-09-27T00:00:00Z
- Emergent PT -symmetry breaking of collective modes with topological critical phenomenahttps://scholarbank.nus.edu.sg/handle/10635/231893Title: Emergent PT -symmetry breaking of collective modes with topological critical phenomena
Authors: Pan, Jian-Song; Yi, Wei; Gong, Jiangbin
Abstract: The spontaneous breaking of parity-time (PT) symmetry yields rich critical behavior in non-Hermitian systems, and has stimulated much interest, albeit most previous studies were performed within the single-particle or mean-field framework. Here, by studying the collective excitations of a Fermi superfluid with PT-symmetric spin-orbit coupling, we uncover an emergent PT-symmetry breaking in the Anderson-Bogoliubov (AB) collective modes, even as the superfluid ground state retains an unbroken PT symmetry. The critical point of the transition is marked by a non-analytic kink in the speed of sound, which derives from the coalescence and annihilation of the AB mode and its hole partner, reminiscent of the particle-antiparticle annihilation. The system consequently becomes immune to low-frequency external perturbations at the critical point, a phenomenon associated with the spectral topology of the complex quasiparticle dispersion. This critical phenomenon offers a fascinating route toward perturbation-free quantum states. © 2021, The Author(s).
Wed, 01 Dec 2021 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2318932021-12-01T00:00:00Z
- Deformed Jarzynski equalityhttps://scholarbank.nus.edu.sg/handle/10635/175155Title: Deformed Jarzynski equality
Authors: Deng J.; Jaramillo J.D.; Hänggi P.; Gong J.
Abstract: The well-known Jarzynski equality, often written in the form e-??F = ?e-?W?, provides a non-equilibrium means to measure the free energy difference DF of a system at the same inverse temperature ? based on an ensemble average of non-equilibrium workW. The accuracy of Jarzynski's measurement scheme was known to be determined by the variance of exponential work, denoted as var (e-?W) . However, it was recently found that var (e-?W) can systematically diverge in both classical and quantum cases. Such divergence will necessarily pose a challenge in the applications of Jarzynski equality because it may dramatically reduce the efficiency in determining ?F. In this work, we present a deformed Jarzynski equality for both classical and quantum non-equilibrium statistics, in efforts to reuse experimental data that already suffers from a diverging var (e-?W) . The main feature of our deformed Jarzynski equality is that it connects free energies at different temperatures and it may still work efficiently subject to a diverging var (e-?W) . The conditions for applying our deformed Jarzynski equality may be met in experimental and computational situations. If so, then there is no need to redesign experimental or simulation methods. Furthermore, using the deformed Jarzynski equality, we exemplify the distinct behaviors of classical and quantum work fluctuations for the case of a time-dependent driven harmonic oscillator dynamics and provide insights into the essential performance differences between classical and quantum Jarzynski equalities. © 2017 by the authors.
Sun, 01 Jan 2017 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1751552017-01-01T00:00:00Z
- Interband coherence induced correction to Thouless pumping: possible observation in cold-atom systemshttps://scholarbank.nus.edu.sg/handle/10635/167774Title: Interband coherence induced correction to Thouless pumping: possible observation in cold-atom systems
Authors: Raghava, Gudapati Naresh; Zhou, Longwen; Gong, Jiangbin
Abstract: © 2017, EDP Sciences, SIF, Springer-Verlag GmbH Germany. In Thouless pump, the charge transport in a one-dimensional insulator over an adiabatic cycle is topologically quantized. For nonequilibrium initial states, however, interband coherence will induce a previously unknown contribution to Thouless pumping. Though not geometric in nature, this contribution is independent of the time scale of the pumping protocol. In this work, we perform a detailed analysis of our previous finding [H.L. Wang et al., Phys. Rev. B 91, 085420 (2015)] in an already available cold-atom setup. We show that initial states with interband coherence can be obtained via a quench of the system’s Hamiltonian. Adiabatic pumping in the post-quench system are then examined both theoretically and numerically, in which the interband coherence is shown to play an important role and can hence be observed experimentally. By choosing adiabatic protocols with different switching-on rates, we also show that the contribution of interband coherence to adiabatic pumping can be tuned. It is further proposed that the interband coherence induced correction to Thouless pumping may be useful in capturing a topological phase transition point. All our results have direct experimental interests.
Tue, 08 Aug 2017 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1677742017-08-08T00:00:00Z
- Geometry of time-dependent PT -symmetric quantum mechanicshttps://scholarbank.nus.edu.sg/handle/10635/226615Title: Geometry of time-dependent PT -symmetric quantum mechanics
Authors: Zhang, DJ; Wang, QH; Gong, J
Abstract: A new type of quantum theory known as time-dependent PT -symmetric quantum mechanics has received much attention recently. It has a conceptually intriguing feature of equipping the Hilbert space of a PT -symmetric system with a time-varying inner product. In this work, we explore the geometry of time-dependent PT -symmetric quantum mechanics. We find that a geometric phase can emerge naturally from the cyclic evolution of a PT -symmetric system, and further formulate a series of related differential-geometry concepts, including connection, curvature, parallel transport, metric tensor, and quantum geometric tensor. These findings constitute a useful, perhaps indispensible, tool to investigate geometric properties of PT -symmetric systems with time-varying system's parameters. To exemplify the application of our findings, we show that the unconventional geometric phase [Phys. Rev. Lett. 91 187902 (2003)], which is the sum of a geometric phase and a dynamical phase proportional to the geometric phase, can be expressed as a single geometric phase unveiled in this work.
Fri, 01 Oct 2021 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2266152021-10-01T00:00:00Z
- Geometric characterization of non-Hermitian topological systems through the singularity ring in pseudospin vector spacehttps://scholarbank.nus.edu.sg/handle/10635/168525Title: Geometric characterization of non-Hermitian topological systems through the singularity ring in pseudospin vector space
Authors: Li, Linhu; Lee, Ching Hua; Gong, Jiangbin
Abstract: © 2019 American Physical Society. This work unveils how geometric features of two-band non-Hermitian Hamiltonians can classify the topology of their eigenstates and energy manifolds. Our approach generalizes the Bloch sphere visualization of Hermitian systems to a "Bloch torus" picture for non-Hermitian systems, by extending the origin of the Bloch sphere to a singularity ring (SR) in the vector space of the real pseudospin. The SR captures the structure of generic spectral exceptional degeneracies, which emerge only if the real pseudospin vector actually falls on the SR. Applicable to non-Hermitian systems that may or may not have exceptional degeneracies, this SR picture affords convenient visualization of various symmetry constraints and reduces their topological characterization to the classification of simple intersection or winding behavior, as detailed by our explicit study of chiral, sublattice, particle-hole, and conjugated particle-hole symmetries. In 1D, the winding number about the SR corresponds to the band vorticity measurable through the Berry phase. In 2D, more complicated winding behavior leads to a variety of phases that illustrates the richness of the interplay between SR topology and geometry beyond mere Chern number classification. Through a normalization procedure that puts generic two-band non-Hermitian Hamiltonians on equal footing, our SR approach also allows for vivid visualization of the non-Hermitian skin effect.
Thu, 01 Aug 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685252019-08-01T00:00:00Z
- Coupled-wire construction of static and Floquet second-order topological insulatorshttps://scholarbank.nus.edu.sg/handle/10635/168534Title: Coupled-wire construction of static and Floquet second-order topological insulators
Authors: Bomantara, Raditya Weda; Zhou, Longwen; Pan, Jiaxin; Gong, Jiangbin
Abstract: © 2019 American Physical Society. Second-order topological insulators (SOTI) exhibit protected gapless boundary states at their hinges or corners. In this paper, we propose a generic means to construct SOTIs in static and Floquet systems by coupling one-dimensional topological insulator wires along a second dimension through dimerized hopping amplitudes. The Hamiltonian of such SOTIs admits a Kronecker sum structure, making it possible for obtaining its features by analyzing two constituent one-dimensional lattice Hamiltonians defined separately in two orthogonal dimensions. The resulting topological corner states do not rely on any delicate spatial symmetries, but are solely protected by the chiral symmetry of the system. We further utilize our idea to construct Floquet SOTIs, whose number of topological corner states is arbitrarily tunable via changing the hopping amplitudes of the system. Finally, we propose to detect the topological invariants of static and Floquet SOTIs constructed with our approach in experiments by measuring the mean chiral displacements of wavepackets.
Tue, 29 Jan 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685342019-01-29T00:00:00Z
- Hybrid Higher-Order Skin-Topological Modes in Nonreciprocal Systemshttps://scholarbank.nus.edu.sg/handle/10635/168528Title: Hybrid Higher-Order Skin-Topological Modes in Nonreciprocal Systems
Authors: Lee, Ching Hua; Li, Linhu; Gong, Jiangbin
Abstract: © 2019 American Physical Society. Higher-order phases are characterized by corner or hinge modes that arise due to the interesting interplay of localization mechanisms along two or more dimensions. In this work, we introduce and construct a novel class of "hybrid" higher-order skin-topological boundary modes in nonreciprocal systems with two or more open boundaries. Their existence crucially relies on nonreciprocal pumping in addition to topological localization. Unlike usual non-Hermitian "skin" modes, they can exist in lattices with vanishing net reciprocity due to the selective nature of nonreciprocal pumping: While the bulk modes remain extended due to the cancellation of nonreciprocity within each unit cell, boundary modes experience a curious spontaneous breaking of reciprocity in the presence of topological localization, thereby experiencing the non-Hermitian skin effect. The number of possible hybridization channels increases rapidly with dimensionality, leading to a proliferation of distinct phases. In addition, skin modes or hybrid skin-topological modes can restore unitarity and are hence stable, allowing for experimental observations and manipulations in non-Hermitian photonic and electrical metamaterials.
Tue, 02 Jul 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685282019-07-02T00:00:00Z
- Piecewise adiabatic following: General analysis and exactly solvable modelshttps://scholarbank.nus.edu.sg/handle/10635/168540Title: Piecewise adiabatic following: General analysis and exactly solvable models
Authors: Gong, Jiangbin; Wang, Qing-hai
Abstract: © 2019 American Physical Society. The dynamics of a periodically driven system whose time evolution is governed by the Schrödinger equation with non-Hermitian Hamiltonians can be perfectly stable. This finding was only obtained very recently and will be enhanced by many exact solutions discovered in this work. The main concern of this study is to investigate the adiabatic following dynamics in such non-Hermitian systems stabilized by periodic driving. We focus on the peculiar behavior of stable cyclic (Floquet) states in the slow-driving limit. It is found that the stable cyclic states can either behave as intuitively expected by following instantaneous eigenstates, or exhibit piecewise adiabatic following by sudden switching between instantaneous eigenstates. We aim to cover broad categories of non-Hermitian systems under a variety of different driving scenarios. We systematically analyze the sudden-switch behavior by a universal route. That is, the sign change of the critical exponent in our asymptotic analysis of the solutions is always found to be the underlying mechanism to determine if the adiabatic following dynamics is trivial or piecewise. This work thus considerably extends our early study on the same topic [Gong and Wang, Phys. Rev. A 97, 052126 (2018)2469-992610.1103/PhysRevA.97.052126] and shall motivate more interest in non-Hermitian systems.
Tue, 08 Jan 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685402019-01-08T00:00:00Z
- Discrete time crystals in many-body quantum chaoshttps://scholarbank.nus.edu.sg/handle/10635/168531Title: Discrete time crystals in many-body quantum chaos
Authors: Nurwantoro, P; Bomantara, RW; Gong, J
Abstract: © 2019 American Physical Society. Discrete time crystals (DTCs) are phases of matter characterized by the presence of an observable evolving with nT periodicity under a T-periodic Hamiltonian, where n>1 is an integer insensitive to small parameter variations. In particular, DTCs with n=2 have been extensively studied in periodically quenched and kicked spin systems in recent years. In this paper, we study the emergence of DTCs in a many-body system whose semiclassical mean-field dynamics is nonintegrable, using a rather simple model depicting a harmonically driven spin chain. We advocate to first employ a semiclassical approximation to arrive at a mean-field Hamiltonian and then identify the parameter regime at which DTCs exist, with standard tools borrowed from studies of classical chaos. Specifically, we seek symmetric-breaking solutions by examining the stable islands on the Poincaré surface of section of the mean-field Hamiltonian. We then turn to the actual many-body quantum system, evaluate the stroboscopic dynamics of the total magnetization in the full quantum limit, and verify the existence of DTCs. Our effective and straightforward approach indicates that in general DTCs are one natural aspect of many-body quantum chaos with mixed classical phase space structure. Our approach can also be applied to general time-periodic systems, which is thus promising for finding DTCs with n>2 and opening possibilities for exploring DTCs properties beyond their time-translational breaking features.
Mon, 23 Dec 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685312019-12-23T00:00:00Z
- Floquet dynamical quantum phase transitionshttps://scholarbank.nus.edu.sg/handle/10635/168524Title: Floquet dynamical quantum phase transitions
Authors: Yang, Kai; Zhou, Longwen; Ma, Wenchao; Kong, Xi; Wang, Pengfei; Qin, Xi; Rong, Xing; Wang, Ya; Shi, Fazhan; Gong, Jiangbin; Du, Jiangfeng
Abstract: © 2019 American Physical Society. Dynamical quantum phase transitions (DQPTs) are manifested by time-domain nonanalytic behaviors of many-body systems. Introducing a quench is so far understood as a typical scenario to induce DQPTs. In this work, we discover a type of DQPTs, termed Floquet DQPTs, as intrinsic features of time-periodic systems. Floquet DQPTs occur within each period of continuous driving, without the need for any quenches. In particular, in a harmonically driven spin chain model, we find analytically the existence of Floquet DQPTs in and only in a parameter regime hosting a certain nontrivial Floquet topological phase. The Floquet DQPTs are further characterized by a dynamical topological invariant defined as the winding number of the Pancharatnam geometric phase versus quasimomentum. These findings are experimentally demonstrated with a single spin in diamond. This work thus opens a door for future studies of DQPTs in connection with topological matter.
Wed, 28 Aug 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685242019-08-28T00:00:00Z
- Non-Hermitian Floquet topological phases: Exceptional points, coalescent edge modes, and the skin effecthttps://scholarbank.nus.edu.sg/handle/10635/168515Title: Non-Hermitian Floquet topological phases: Exceptional points, coalescent edge modes, and the skin effect
Authors: Zhang, Xizheng; Gong, Jiangbin
Abstract: © 2020 American Physical Society. Periodically driven non-Hermitian systems can exhibit rich topological band structure and non-Hermitian skin effect, without analogs in their static or Hermitian counterparts. In this work we investigate the exceptional band-touching points in the Floquet quasienergy bands, the topological characterization of such exceptional points and the Floquet non-Hermitian skin effect (FNHSE). Specifically, we exploit the simplicity of periodically quenched two-band systems in one dimension or two dimensions to analytically obtain the Floquet effective Hamiltonian as well as locations of the many exceptional points possessed by the Floquet bulk bands. Two different types of topological winding numbers are used to characterize the topological features. Bulk-boundary correspondence (BBC) is naturally found to break down due to FNHSE, which can be drastically different among different bulk states. Remarkably, given the simple nature of our model systems, recovering the BBC is doable in practice only for certain parameter regime where a low-order truncation of the characteristic polynomial (which determines the Floquet band structure) becomes feasible. Furthermore, irrespective of which parameter regime we work with, we find a number of intriguing aspects of Floquet topological zero modes and π modes. For example, under the open boundary condition, zero edge modes and π edge modes can individually coalesce and localize at two different boundaries. These anomalous edge states can also switch their accumulation boundaries when a certain system parameter is tuned. These results indicate that non-Hermitian Floquet topological phases, though more challenging to understand than their Hermitian counterparts, can be extremely rich in the presence of FNHSE.
Mon, 13 Jan 2020 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685152020-01-13T00:00:00Z
- Revealing many-body effects on interband coherence through adiabatic charge pumpinghttps://scholarbank.nus.edu.sg/handle/10635/168513Title: Revealing many-body effects on interband coherence through adiabatic charge pumping
Authors: Mu, Sen; Zhang, Da-Jian; Zhou, Longwen; Gong, Jiangbin
Abstract: © 2019 American Physical Society. The adiabatic charge pumping of a nonequilibrium state of spinless fermions in a one-dimensional lattice is investigated, with an emphasis placed on its usefulness in revealing many-body interaction effects on interband coherence. For a noninteracting system, the pumped charge per adiabatic cycle depends not only on the topology of the occupied bands but also on the interband coherence in the initial state. This insight leads to an interesting opportunity for quantitatively observing how quantum coherence is affected by many-body interaction that is switched on for a varying duration prior to adiabatic pumping. In particular, interband coherence effects can be clearly observed by adjusting the switch-on rates with different adiabatic pumping protocols and by scanning the duration of many-body interaction prior to adiabatic pumping. The time dependence of single-particle interband coherence in the presence of many-body interaction can then be examined in detail. As an interesting side result, for relatively weak interaction strength, it is found that the difference in the pumped charges between different pumping protocols vanishes if a coherence measure defined by the single-particle density matrix in the sublattice representation reaches its local minima. Our results hence provide an interesting means to quantitatively probe the dynamics of quantum coherence in the presence of many-body interaction (e.g., in a thermalization process).
Fri, 04 Oct 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685132019-10-04T00:00:00Z
- Measurement-only quantum computation with Floquet Majorana corner modeshttps://scholarbank.nus.edu.sg/handle/10635/168517Title: Measurement-only quantum computation with Floquet Majorana corner modes
Authors: Bomantara, RW; Gong, J
Abstract: © 2020 American Physical Society. Majorana modes, typically arising at the edges of one-dimensional topological superconductors, are considered to be a promising candidate for encoding nonlocal qubits in fault-tolerant quantum computing. Here we exploit the two-dimensional geometry of Majorana corner modes in second-order topological superconductors to establish measurement-only quantum computation. It is shown that eight Majorana corner modes emerge when such systems are periodically driven, through which two nonlocal logical qubits and one nonlocal ancilla qubit can be constructed. Quantum gate operations can then be implemented by a designed series of parity measurements of topologically protected Majorana corner modes, accomplished via Mach-Zehnder type interference in the conductance between different corners of a second-order topological superconductor. Our theoretical proposal represents a scenario in which topologically protected single- A nd two-qubit gate operations can be carried out in a minimal setup, thus potentially establishing an efficient and low-cost building block for Majorana-based qubit architectures.
Sat, 15 Feb 2020 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685172020-02-15T00:00:00Z
- Floquet engineering with particle swarm optimization: Maximizing topological invariantshttps://scholarbank.nus.edu.sg/handle/10635/168518Title: Floquet engineering with particle swarm optimization: Maximizing topological invariants
Authors: Zhang, S; Gong, J
Abstract: © 2019 American Physical Society. It is of theoretical and experimental interest to engineer topological phases with very large topological invariants via periodic driving. As advocated by this paper, such Floquet engineering can be elegantly achieved by the particle swarm optimization (PSO) technique from the swarm intelligence family. With the recognition that conventional gradient-based optimization approaches are not suitable for directly optimizing topological invariants as integers, the highly effective PSO route yields new promises in the search for exotic topological phases, requiring limited physical resources. Our results are especially timely in view of two important insights from literature: Low-frequency driving may be beneficial in creating large topological invariants, but an open-ended low-frequency driving often leads to drastic fluctuations in the obtained topological invariants. Indeed, using a simple continuously driven Harper model with three quasienergy bands, we show that the Floquet-band Chern numbers can enjoy a many-fold increase compared with that using a simple harmonic driving of the same period, without demanding more energy cost of the driving field. It is also found that the resulting Floquet insulator bands are still well gapped with the maximized topological invariants in agreement with physical observations from Thouless pumping. The emergence of many edge modes under the open boundary condition is also consistent with the bulk-edge correspondence. Our results are expected to be highly useful towards the optimization of many different types of topological invariants in Floquet topological matter.
Thu, 26 Dec 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685182019-12-26T00:00:00Z
- Time-dependent PT-symmetric quantum mechanics in generic non-Hermitian systemshttps://scholarbank.nus.edu.sg/handle/10635/168523Title: Time-dependent PT-symmetric quantum mechanics in generic non-Hermitian systems
Authors: Zhang, DJ; Wang, QH; Gong, J
Abstract: © 2019 American Physical Society. A conceptual framework extending (time-independent) PT-symmetric quantum mechanics into the time-dependent domain is presented. It is built upon a nontrivial time-dependent metric operator identified here and works for generic finite-dimensional non-Hermitian systems. All the ingredients of our framework, such as the time-dependent Hilbert space, the observable, and the measurement postulate, can be "realized" by means of dilating and reinterpreting the non-Hermitian system in question as a part of a larger Hermitian system. Aided by our metric operator, we formulate the concepts of stable and unstable phases for generic non-Hermitian systems and argue that they, respectively, generalize the notions of unbroken and broken phases in time-independent PT-symmetric systems. Possible applications of our framework are illustrated with well-known examples in quantum thermodynamics.
Fri, 20 Dec 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1685232019-12-20T00:00:00Z
- Single-atom energy-conversion device with a quantum loadhttps://scholarbank.nus.edu.sg/handle/10635/168823Title: Single-atom energy-conversion device with a quantum load
Authors: Van Horne, N; Yum, D; Dutta, T; HANGGI,PETER; Gong, J; Poletti, D; Mukherjee, M
Abstract: © 2020, The Author(s). We report on a single-atom energy-conversion quantum device operating as an engine, or a refrigerator, coupled to a quantum load. The ‘working fluid’ consists of the two optical levels of an ion, while the load is one of its vibrational modes, cooled down to the quantum regime. We explore two important differences with classical engines: (1) the presence of a strong generic coupling interaction between engine and load, which can induce correlations between them and (2) the use of nonthermal baths. We examine the ergotropy of the load, which indicates the maximum amount of energy of the load extractable using solely unitary operations. We show that ergotropy rises with the number of engine cycles despite an increase in the information entropy of the load. The increase of ergotropy of the load points to the possibility of using the phonon distribution of a single atom as a form of quantum battery.
Tue, 01 Dec 2020 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1688232020-12-01T00:00:00Z
- Graph-theory treatment of one-dimensional strongly repulsive fermionshttps://scholarbank.nus.edu.sg/handle/10635/168818Title: Graph-theory treatment of one-dimensional strongly repulsive fermions
Authors: Decamp, Jean; Gong, Jiangbin; Loh, Huanqian; Miniatura Christian Pierre-Marie
Mon, 20 Apr 2020 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1688182020-04-20T00:00:00Z
- Statistical properties of power-law random banded unitary matrices in the delocalization-localization transition regimehttps://scholarbank.nus.edu.sg/handle/10635/53190Title: Statistical properties of power-law random banded unitary matrices in the delocalization-localization transition regime
Authors: Bandyopadhyay, J.N.; Gong, J.
Abstract: Power-law random banded unitary matrices (PRBUM), whose matrix elements decay in a powerlaw fashion, were recently proposed to model the critical statistics of the Floquet eigenstates of periodically driven quantum systems. In this work, we numerically study in detail the statistical properties of PRBUM ensembles in the delocalization-localization transition regime. In particular, implications of the delocalization-localization transition for the fractal dimension of the eigenvectors, for the distribution function of the eigenvector components, and for the nearest neighbor spacing statistics of the eigenphases are examined. On the one hand, our results further indicate that a PRBUM ensemble can serve as a unitary analog of the power-law random Hermitian matrix model for Anderson transition. On the other hand, some statistical features unseen before are found from PRBUM. For example, the dependence of the fractal dimension of the eigenvectors of PRBUM upon one ensemble parameter displays features that are quite different from that for the power-law random Hermitian matrix model. Furthermore, in the timereversal symmetric case the nearest neighbor spacing distribution of PRBUM eigenphases is found to obey a semi-Poisson distribution for a broad range, but display an anomalous level repulsion in the absence of time-reversal symmetry. © 2012 EDP Sciences, Società Italiana di Fisica, Springer-Verlag.
Mon, 01 Oct 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/531902012-10-01T00:00:00Z
- Spectral relationships between kicked Harper and on-resonance double kicked rotor operatorshttps://scholarbank.nus.edu.sg/handle/10635/53186Title: Spectral relationships between kicked Harper and on-resonance double kicked rotor operators
Authors: Lawton, W.; Mouritzen, A.S.; Wang, J.; Gong, J.
Abstract: Kicked Harper operators and on-resonance double kicked rotor operators model quantum systems whose semiclassical limits exhibit chaotic dynamics. Recent computational studies indicate a striking resemblance between the spectra of these operators. In this paper we apply C -algebra methods to explain this resemblance. We show that each pair of corresponding operators belongs to a common rotation C -algebra Bα, prove that their spectra are equal if α is irrational, and prove that the Hausdorff distance between their spectra converges to zero as q increases if α=p/q with p and q coprime integers. Moreover, we show that corresponding operators in Bα are homomorphic images of mother operators in the universal rotation C -algebra Aα that are unitarily equivalent and hence have identical spectra. These results extend analogous results for almost Mathieu operators. We also utilize the C -algebraic framework to develop efficient algorithms to compute the spectra of these mother operators for rational α and present preliminary numerical results that support the conjecture that their spectra are Cantor sets if α is irrational. This conjecture for almost Mathieu operators, called the ten Martini problem, was recently proven after intensive efforts over several decades. This proof for the almost Mathieu operators utilized transfer matrix methods, which do not exist for the kicked operators. We outline a strategy, based on a special property of loop groups of semisimple Lie groups, to prove this conjecture for the kicked operators. © 2009 American Institute of Physics.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/531862009-01-01T00:00:00Z
- Phase-space characterization of complexity in quantum many-body dynamicshttps://scholarbank.nus.edu.sg/handle/10635/112484Title: Phase-space characterization of complexity in quantum many-body dynamics
Authors: Balachandran, V.; Benenti, G.; Casati, G.; Gong, J.
Abstract: We propose a phase-space Wigner harmonics entropy measure for many-body quantum dynamical complexity. This measure, which reduces to the well-known measure of complexity in classical systems and which is valid for both pure and mixed states in single-particle and many-body systems, takes into account the combined role of chaos and entanglement in the realm of quantum mechanics. The effectiveness of the measure is illustrated in the example of the Ising chain in a homogeneous tilted magnetic field. We provide numerical evidence that the multipartite entanglement generation leads to a linear increase in entropy until saturation in both integrable and chaotic regimes, so that in both cases the number of harmonics of the Wigner function grows exponentially with time. The entropy growth rate can be used to detect quantum phase transitions. The proposed entropy measure can also distinguish between integrable and chaotic many-body dynamics by means of the size of long-term fluctuations which become smaller when quantum chaos sets in. © 2010 The American Physical Society.
Wed, 20 Oct 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124842010-10-20T00:00:00Z
- Intrinsic dynamical fluctuation assisted symmetry breaking in adiabatic followinghttps://scholarbank.nus.edu.sg/handle/10635/112456Title: Intrinsic dynamical fluctuation assisted symmetry breaking in adiabatic following
Authors: Zhang, Q.; Gong, J.; Oh, C.H.
Abstract: Classical adiabatic invariants in actual adiabatic processes possess intrinsic dynamical fluctuations. The magnitude of such intrinsic fluctuations is often thought to be negligible. This widely believed physical picture is contested here. For adiabatic following of a moving stable fixed-point solution facing a pitchfork bifurcation, we show that intrinsic dynamical fluctuations in an adiabatic process can assist in a deterministic selection between two symmetry-connected fixed-point solutions, with the outcome independent of the duration of the adiabatic process. Using a classical model Hamiltonian also relevant to a two-mode quantum system, we further demonstrate the formation of an adiabatic hysteresis loop in purely Hamiltonian mechanics and the generation of a Berry phase via changing one single-valued parameter only. © 2013 American Physical Society.
Mon, 25 Mar 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124562013-03-25T00:00:00Z
- Symmetry breaking and self-trapping of a dipolar Bose-Einstein condensate in a double-well potentialhttps://scholarbank.nus.edu.sg/handle/10635/53203Title: Symmetry breaking and self-trapping of a dipolar Bose-Einstein condensate in a double-well potential
Authors: Xiong, B.; Gong, J.; Pu, H.; Bao, W.; Li, B.
Abstract: The quantum self-trapping phenomenon of a Bose-Einstein condensate (BEC) represents a remarkable nonlinear effect of wide interest. By considering a purely dipolar BEC in a double-well potential, we study how the dipole orientation affects the ground-state structure and the transition between self-trapping and Josephson oscillations in dynamics. Three-dimensional numerical results and an effective two-mode model demonstrate that the onset of self-trapping of a dipolar BEC can be radically modified by the dipole orientation. We also analyze the failure of the two-mode model in predicting the rate of Josephson oscillations. We hope that our results can motivate experimental work as well as future studies of self-trapping of ultracold dipolar gases in optical lattices. © 2009 The American Physical Society.
Mon, 05 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/532032009-01-05T00:00:00Z
- Dynamical fluctuations in classical adiabatic processes: General description and their implicationshttps://scholarbank.nus.edu.sg/handle/10635/112421Title: Dynamical fluctuations in classical adiabatic processes: General description and their implications
Authors: Zhang, Q.; Gong, J.; Oh, C.H.
Abstract: Dynamical fluctuations in classical adiabatic processes are not considered by the conventional classical adiabatic theorem. In this work a general result is derived to describe the intrinsic dynamical fluctuations in classical adiabatic processes. Interesting implications of our general result are discussed via two subtopics, namely, an intriguing adiabatic geometric phase in a dynamical model with an adiabatically moving fixed-point solution, and the possible "pollution" to Hannay's angle or to other adiabatic phase objects for adiabatic processes involving non-fixed-point solutions. © 2011 Elsevier Inc..
Sun, 01 Apr 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124212012-04-01T00:00:00Z
- Converting Zitterbewegung oscillation to directed motionhttps://scholarbank.nus.edu.sg/handle/10635/112403Title: Converting Zitterbewegung oscillation to directed motion
Authors: Zhang, Q.; Gong, J.B.; Oh, C.H.
Abstract: Zitterbewegung (ZB) oscillation, namely, the jittering center-of-mass motion predicted by free-space Dirac (or Dirac-like) equations, has been studied in several different contexts. It is shown here that ZB can be converted to directed center-of-mass motion by a modulation of the Dirac-like equation, if the modulation is on resonance with the ZB frequency. Tailored modulation may also stop, re-launch or even reverse the directed motion of a wavepacket with negligible distortion. The predictions may be examined by current ZB experiments using trapped-ion systems. © 2011 Europhysics Letters Association.
Sat, 01 Oct 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124032011-10-01T00:00:00Z
- Optimization of the environment for generating entanglement and spin squeezinghttps://scholarbank.nus.edu.sg/handle/10635/127563Title: Optimization of the environment for generating entanglement and spin squeezing
Authors: Tan Da Yang; Chaudhry Adam Z.; Gong Jiangbin
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1275632015-01-01T00:00:00Z
- Generating a fractal butterfly Floquet spectrum in a class of driven SU(2) systems: Eigenstate statisticshttps://scholarbank.nus.edu.sg/handle/10635/52954Title: Generating a fractal butterfly Floquet spectrum in a class of driven SU(2) systems: Eigenstate statistics
Authors: Bandyopadhyay, J.N.; Wang, J.; Gong, J.
Abstract: The Floquet spectra of a class of driven SU(2) systems have been shown to display butterfly patterns with multifractal properties. The implication of such critical spectral behavior for the Floquet eigenstate statistics is studied in this work. Following the methodologies for understanding the fractal behavior of energy eigenstates of time-independent systems on the Anderson transition point, we analyze the distribution profile, the mean value, and the variance of the logarithm of the inverse participation ratio of the Floquet eigenstates associated with multifractal Floquet spectra. The results show that the Floquet eigenstates also display fractal behavior but with features markedly different from those in time-independent Anderson-transition models. This motivated us to propose random unitary matrix ensemble, called "power-law random banded unitary matrix" ensemble, to illuminate the Floquet eigenstate statistics of critical driven systems. The results based on the proposed random matrix model are consistent with those obtained from our dynamical examples with or without time-reversal symmetry. © 2010 The American Physical Society.
Fri, 18 Jun 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529542010-06-18T00:00:00Z
- Fokker-Planck equation with arbitrary dc and ac fields: Continued fraction methodhttps://scholarbank.nus.edu.sg/handle/10635/52944Title: Fokker-Planck equation with arbitrary dc and ac fields: Continued fraction method
Authors: Lee, C.K.; Gong, J.
Abstract: The continued fraction method (CFM) is used to solve the Fokker-Planck equation with arbitrary dc and ac fields. With an appropriate choice of basis functions, the Fokker-Planck equation is converted into a set of linear algebraic equations with short-ranged coupling and then CFM is implemented to obtain numerical solutions with high efficiency. Both a proposed perturbative CFM and the numerically exact matrix CFM are used to study the nonlinear response of driven systems, with their results compared to assess the validity regime of the perturbative approach. The proposed perturbative CFM approach needs scalar quantities only and hence is more efficient within its validity regime. Two nonlinear systems of different nature are used as examples: molecular dipole (rotational Brownian motion) and particle in a periodic potential (translational Brownian motion). The associated full dynamics is presented in the compact form of hysteresis loops. It is observed that as the strength of an AC driving field increases, pronounced nonlinear effects are manifested in the deformation of the hysteresis loops. © 2011 American Physical Society.
Wed, 06 Jul 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529442011-07-06T00:00:00Z
- Interband coherence induced correction to adiabatic pumping in periodically driven systemshttps://scholarbank.nus.edu.sg/handle/10635/127996Title: Interband coherence induced correction to adiabatic pumping in periodically driven systems
Authors: Wang H.; Zhou L.; Gong J.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1279962015-01-01T00:00:00Z
- Critical non-Hermitian skin effecthttps://scholarbank.nus.edu.sg/handle/10635/198117Title: Critical non-Hermitian skin effect
Authors: Li, L.; Lee, C.H.; Mu, S.; Gong, J.
Abstract: Critical systems represent physical boundaries between different phases of matter and have been intensely studied for their universality and rich physics. Yet, with the rise of non-Hermitian studies, fundamental concepts underpinning critical systems - like band gaps and locality - are increasingly called into question. This work uncovers a new class of criticality where eigenenergies and eigenstates of non-Hermitian lattice systems jump discontinuously across a critical point in the thermodynamic limit, unlike established critical scenarios with spectrum remaining continuous across a transition. Such critical behavior, dubbed the “critical non-Hermitian skin effect”, arises whenever subsystems with dissimilar non-reciprocal accumulations are coupled, however weakly. This indicates, as elaborated with the generalized Brillouin zone approach, that the thermodynamic and zero-coupling limits are not exchangeable, and that even a large system can be qualitatively different from its thermodynamic limit. Examples with anomalous scaling behavior are presented as manifestations of the critical non-Hermitian skin effect in finite-size systems. More spectacularly, topological in-gap modes can even be induced by changing the system size. We provide an explicit proposal for detecting the critical non-Hermitian skin effect in an RLC circuit setup, which also directly carries over to established setups in non-Hermitian optics and mechanics. © 2020, The Author(s).
Wed, 01 Jan 2020 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1981172020-01-01T00:00:00Z
- The effect of state preparation in a many-body systemhttps://scholarbank.nus.edu.sg/handle/10635/98261Title: The effect of state preparation in a many-body system
Authors: Chaudhry, A.Z.; Gong, J.
Abstract: For a quantum system interacting with its environment, the role of state preparation is nontrivial. The reason is that before the state preparation procedure, the system and the environment are correlated. Consequently, the state preparation procedure (which acts on the system) indirectly influences the state of the environment depending on the state preparation. In this paper, we use an experimentally realizable model describing a collection of N two-level atoms coupled to a common environment to investigate the influence of the state preparation procedure. We show that the dynamical map describing the evolution of the open quantum system can depend appreciably on the state preparation procedure. Moreover, this effect can be enhanced by increasing N. Our results should be useful for quantum control and quantum tomography. © 2013 Published by NRC Research Press.
Sat, 01 Feb 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/982612014-02-01T00:00:00Z
- Topological characterization of one-dimensional open fermionic systemshttps://scholarbank.nus.edu.sg/handle/10635/155026Title: Topological characterization of one-dimensional open fermionic systems
Authors: Zhang, Da-Jian; Gong, Jiangbin
Abstract: © 2018 American Physical Society. A topological measure characterizing symmetry-protected topological phases in one-dimensional open fermionic systems is proposed. It is built upon the kinematic approach to the geometric phase of mixed states and facilitates the extension of the notion of topological phases from zeroerature to nonzeroerature cases. In contrast to a previous finding that topological properties may not survive above a certain critical temperature, we find that topological properties of open systems, in the sense of the measure suggested here, can persist at any finite temperature and disappear only in the mathematical limit of infinite temperature. Our result is illustrated with two paradigmatic models of topological matter. The bulk topology at nonzero temperatures manifested as robust mixed edge state populations is examined via two figures of merit.
Thu, 01 Nov 2018 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1550262018-11-01T00:00:00Z
- Adiabatic quantum transport in a spin chain with a moving potentialhttps://scholarbank.nus.edu.sg/handle/10635/95730Title: Adiabatic quantum transport in a spin chain with a moving potential
Authors: Balachandran, V.; Gong, J.
Abstract: Many schemes to realize quantum state transfer in spin chains are not robust to random fluctuations in the spin-spin coupling strength. In efforts to achieve robust quantum state transfer, an adiabatic quantum population transfer scheme is proposed in this study. The proposed scheme makes use of a slowly moving external parabolic potential and is qualitatively explained in terms of the adiabatic following of a quantum state with a moving separatrix structure in the classical phase space of a pendulum analogy. Detailed aspects of our adiabatic population transfer scheme, including its robustness, is studied computationally. Applications of our adiabatic scheme in quantum information transfer are also discussed, with emphasis placed on the usage of a dual spin chain to encode quantum phases. The results should also be useful for the control of electron tunneling in an array of quantum dots. © 2008 The American Physical Society.
Fri, 04 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/957302008-01-04T00:00:00Z
- Time-dependent PT -symmetric quantum mechanicshttps://scholarbank.nus.edu.sg/handle/10635/98412Title: Time-dependent PT -symmetric quantum mechanics
Authors: Gong, J.; Wang, Q.-H.
Abstract: The parity-time-reversal (PT )-symmetric quantum mechanics (QM) (PTQM) has developed into a noteworthy area of research. However, to date, most known studies of PTQM focused on the spectral properties of non-Hermitian Hamiltonian operators. In this work, we propose an axiom in PTQM in order to study general time-dependent problems in PTQM, e.g., those with a timedependent PT -symmetric Hamiltonian and with a time-dependent metric. We illuminate our proposal by examining a proper mapping from a timedependent Schrodinger-like equation of motion for TQM to the familiar timedependent Schrodinger equation in conventional QM. The rich structure of the proper mapping hints that time-dependent PTQM can be a fruitful extension of conventional QM. Under our proposed framework, we further study in detail the Berry-phase generation in a class of PT -symmetric two-level systems. It is found that a closed path in the parameter space of PTQM is often associated with an open path in a properly mapped problem in conventional QM. In one interesting case, we further interpret the Berry phase as the flux of a continuously tunable fictitious magnetic monopole, thus highlighting the difference between PTQM and conventional QM despite he existence of a proper mapping between them. © 2013 IOP Publishing Ltd Printed in the UK and the USA.
Fri, 06 Dec 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984122013-12-06T00:00:00Z
- Universal dynamical decoupling: Two-qubit states and beyondhttps://scholarbank.nus.edu.sg/handle/10635/98525Title: Universal dynamical decoupling: Two-qubit states and beyond
Authors: Mukhtar, M.; Saw, T.B.; Soh, W.T.; Gong, J.
Abstract: Uhrig's dynamical decoupling pulse sequence has emerged as a universal and highly promising approach to decoherence suppression. So far, both the theoretical and experimental studies have examined single-qubit decoherence only. This work extends Uhrig's universal dynamical decoupling from one-qubit to two-qubit systems and even to general multilevel quantum systems. In particular, we show that by designing appropriate control Hamiltonians for a two-qubit or a multilevel system, Uhrig's pulse sequence can also preserve a generalized quantum coherence measure to the order of 1+O(TN+1) with only N pulses. Our results lead to a very useful scheme for efficiently locking two-qubit entangled states. Future important applications of Uhrig's pulse sequence in preserving the quantum coherence of multilevel quantum systems can also be anticipated. © 2010 The American Physical Society.
Fri, 29 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985252010-01-29T00:00:00Z
- Wave-scattering formalism for thermal conductance in thin wires with surface disorderhttps://scholarbank.nus.edu.sg/handle/10635/98576Title: Wave-scattering formalism for thermal conductance in thin wires with surface disorder
Authors: Akguc, G.B.; Gong, J.
Abstract: Elastic wave characteristics of the heat conduction in low-temperature thin wires can be studied via a wave scattering formalism. A reaction matrix formulation of heat conductance modeled by elastic wave scattering is advocated. This formulation allows us to treat thin wires with arbitrary surface disorder. It is found that the correlation in the surface disorder may significantly affect the temperature dependence of the heat conductance. © 2009 The American Physical Society.
Fri, 06 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985762009-11-06T00:00:00Z
- Wave packet dynamics in one-dimensional linear and nonlinear generalized Fibonacci latticeshttps://scholarbank.nus.edu.sg/handle/10635/98573Title: Wave packet dynamics in one-dimensional linear and nonlinear generalized Fibonacci lattices
Authors: Zhang, Z.; Tong, P.; Gong, J.; Li, B.
Abstract: The spreading of an initially localized wave packet in one-dimensional linear and nonlinear generalized Fibonacci (GF) lattices is studied numerically. The GF lattices can be classified into two classes depending on whether or not the lattice possesses the Pisot-Vijayaraghavan property. For linear GF lattices of the first class, both the second moment and the participation number grow with time. For linear GF lattices of the second class, in the regime of a weak on-site potential, wave packet spreading is close to ballistic diffusion, whereas in the regime of a strong on-site potential, it displays stairlike growth in both the second moment and the participation number. Nonlinear GF lattices are then investigated in parallel. For the first class of nonlinear GF lattices, the second moment of the wave packet still grows with time, but the corresponding participation number does not grow simultaneously. For the second class of nonlinear GF lattices, an analogous phenomenon is observed for the weak on-site potential only. For a strong on-site potential that leads to an enhanced nonlinear self-trapping effect, neither the second moment nor the participation number grows with time. The results can be useful in guiding experiments on the expansion of noninteracting or interacting cold atoms in quasiperiodic optical lattices. © 2011 American Physical Society.
Fri, 06 May 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985732011-05-06T00:00:00Z
- Amplification and suppression of system-bath-correlation effects in an open many-body systemhttps://scholarbank.nus.edu.sg/handle/10635/95750Title: Amplification and suppression of system-bath-correlation effects in an open many-body system
Authors: Chaudhry, A.Z.; Gong, J.
Abstract: Understanding the rich dynamics of open quantum systems is of fundamental interest to quantum control and quantum information processing. By considering an open system of many identical two-level atoms interacting with a common bath, we show that the effects of system-bath correlations are amplified in a many-body system via the generation of a bath-dependent short time scale (inversely proportional to the number of atoms) in the system dynamics. The effects of system-bath correlations are therefore considerable even when each individual atom interacts with the bath weakly. We further show that the correlation-induced dynamical effects may still be suppressed via the dynamical decoupling approach, but they present a challenge for quantum state protection as the number of atom increases. © 2013 American Physical Society.
Wed, 30 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/957502013-01-30T00:00:00Z
- Quantum geometric tensor in PT -symmetric quantum mechanicshttps://scholarbank.nus.edu.sg/handle/10635/155024Title: Quantum geometric tensor in PT -symmetric quantum mechanics
Authors: Zhang, DJ; Wang, QH; Gong, J
Abstract: © 2019 American Physical Society. A series of geometric concepts are formulated for PT-symmetric quantum mechanics and they are further unified into one entity, i.e., an extended quantum geometric tensor (QGT). The imaginary part of the extended QGT gives a Berry curvature whereas the real part induces a metric tensor on the system's parameter manifold. This results in a unified conceptual framework to understand and explore physical properties of PT-symmetric systems from a geometric perspective. To illustrate the usefulness of the extended QGT, we show how its real part, the metric tensor, can be exploited as a tool to detect quantum phase transitions as well as spontaneous PT symmetry breaking in PT-symmetric systems.
Thu, 04 Apr 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1550242019-04-04T00:00:00Z
- Spin-dependent electron transport in two-dimensional waveguides of arbitrary geometryhttps://scholarbank.nus.edu.sg/handle/10635/97994Title: Spin-dependent electron transport in two-dimensional waveguides of arbitrary geometry
Authors: Akguc, G.B.; Gong, J.
Abstract: An efficient computational approach to spin-dependent electron transport in two-dimensional waveguides with rather arbitrary geometry is presented, with necessary details about how to include the spin-orbit Rashba coupling and the so-called evanescent modes. The spin conductance properties are then examined for various waveguide geometries, with an emphasis placed on those waveguides for which the classical scattering is associated with chaotic and mixed phase space structures. Quantum conductance fluctuations, which is first observed in microwave waveguide experiments, are also studied, yielding an interesting observation called "spin conductance echo." The results should be of general interest to studies in spintronics and to studies of quantum chaos in scattering problems. © 2008 The American Physical Society.
Thu, 01 May 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979942008-05-01T00:00:00Z
- Simulation of chemical isomerization reaction dynamics on a NMR quantum simulatorhttps://scholarbank.nus.edu.sg/handle/10635/97929Title: Simulation of chemical isomerization reaction dynamics on a NMR quantum simulator
Authors: Lu, D.; Xu, N.; Xu, R.; Chen, H.; Gong, J.; Peng, X.; Du, J.
Abstract: Quantum simulation can beat current classical computers with minimally a few tens of qubits. Here we report an experimental demonstration that a small nuclear-magnetic-resonance quantum simulator is already able to simulate the dynamics of a prototype laser-driven isomerization reaction using engineered quantum control pulses. The experimental results agree well with classical simulations. We conclude that the quantum simulation of chemical reaction dynamics not computable on current classical computers is feasible in the near future. © 2011 American Physical Society.
Tue, 05 Jul 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979292011-07-05T00:00:00Z
- Boosting work characteristics and overall heat-engine performance via shortcuts to adiabaticity: Quantum and classical systemshttps://scholarbank.nus.edu.sg/handle/10635/95880Title: Boosting work characteristics and overall heat-engine performance via shortcuts to adiabaticity: Quantum and classical systems
Authors: Deng, J.; Wang, Q.-H.; Liu, Z.; Hänggi, P.; Gong, J.
Abstract: Under a general framework, shortcuts to adiabatic processes are shown to be possible in classical systems. We study the distribution function of the work done on a small system initially prepared at thermal equilibrium. We find that the work fluctuations can be significantly reduced via shortcuts to adiabatic processes. For example, in the classical case, probabilities of having very large or almost zero work values are suppressed. In the quantum case, negative work may be totally removed from the otherwise non-positive-definite work values. We also apply our findings to a micro Otto-cycle-based heat engine. It is shown that the use of shortcuts, which directly enhances the engine output power, can also increase the heat-engine efficiency substantially, in both quantum and classical regimes. © 2013 American Physical Society.
Thu, 12 Dec 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958802013-12-12T00:00:00Z
- Hierarchical theory of quantum adiabatic evolutionhttps://scholarbank.nus.edu.sg/handle/10635/180130Title: Hierarchical theory of quantum adiabatic evolution
Authors: Zhang, Q; Gong, J; Wu, B
Abstract: Quantum adiabatic evolution is a dynamical evolution of a quantum system under slow external driving. According to the quantum adiabatic theorem, no transitions occur between nondegenerate instantaneous energy eigenstates in such a dynamical evolution. However, this is true only when the driving rate is infinitesimally small. For a small nonzero driving rate, there are generally small transition probabilities between the energy eigenstates. We develop a classical mechanics framework to address the small deviations from the quantum adiabatic theorem order by order. A hierarchy of Hamiltonians is constructed iteratively with the zeroth-order Hamiltonian being determined by the original system Hamiltonian. The kth-order deviations are governed by a kth-order Hamiltonian, which depends on the time derivatives of the adiabatic parameters up to the kth-order. Two simple examples, the Landau-Zener model and a spin-1/2 particle in a rotating magnetic field, are used to illustrate our hierarchical theory. Our analysis also exposes a deep, previously unknown connection between classical adiabatic theory and quantum adiabatic theory. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Wed, 01 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1801302014-01-01T00:00:00Z
- Conductance properties of rough quantum wires with colored surface disorderhttps://scholarbank.nus.edu.sg/handle/10635/96061Title: Conductance properties of rough quantum wires with colored surface disorder
Authors: Akguc, G.B.; Gong, J.
Abstract: Effects of correlated disorder on wave localization have attracted considerable interest. Motivated by the importance of studies of quantum transport in rough nanowires, here we examine how colored surface roughness impacts the conductance of two-dimensional quantum waveguides, using direct-scattering calculations based on the reaction matrix approach. The computational results are analyzed in connection with a theoretical relation between the localization length and the structure factor of correlated disorder. We also examine and discuss several cases that have not been treated theoretically or are beyond the validity regime of available theories. Results indicate that conductance properties of quantum wires are controllable via colored surface disorder. ©2008 The American Physical Society.
Mon, 22 Sep 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/960612008-09-22T00:00:00Z
- Stabilizing non-Hermitian systems by periodic drivinghttps://scholarbank.nus.edu.sg/handle/10635/127981Title: Stabilizing non-Hermitian systems by periodic driving
Authors: Gong J.; Wang Q.-H.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1279812015-01-01T00:00:00Z
- Delocalization of topological edge stateshttps://scholarbank.nus.edu.sg/handle/10635/202786Title: Delocalization of topological edge states
Authors: Zhu, Weiwei; Teo, Wei Xin; Li, Linhu; Gong, Jiangbin
Abstract: The non-Hermitian skin effect (NHSE) in non-Hermitian lattice systems depicts the exponential localization of eigenstates at the system's boundaries. It has led to a number of counterintuitive phenomena and challenged our understanding of bulk-boundary correspondence in topological systems. This work aims to investigate how the NHSE localization and topological localization of in-gap edge states compete with each other, with several representative static and periodically driven 1D models, whose topological properties are protected by different symmetries. The emerging insight is that at critical system parameters, even topologically protected edge states can be perfectly delocalized. In particular, it is discovered that this intriguing delocalization occurs if the real spectrum of the system's edge states falls on the same system's complex spectral loop obtained under the periodic boundary condition. We have also performed sample numerical simulation to show that such delocalized topological edge states can be safely reconstructed from time-evolving states. One particular application of delocalized topological edge states in assisting adiabatic edge state pumping is also computationally demonstrated.
Wed, 12 May 2021 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2027862021-05-12T00:00:00Z
- Impurity induced scale-free localizationhttps://scholarbank.nus.edu.sg/handle/10635/200713Title: Impurity induced scale-free localization
Authors: Li, Linhu; Lee, Ching Hua; Gong, Jiangbin
Abstract: Non-Hermitian systems have been shown to have a dramatic sensitivity to their boundary conditions. In particular, the non-Hermitian skin effect induces collective boundary localization upon turning off boundary coupling, a feature very distinct from that under periodic boundary conditions. Here we develop a full framework for non-Hermitian impurity physics in a non-reciprocal lattice, with periodic/open boundary conditions and even their interpolations being special cases across a whole range of boundary impurity strengths. We uncover steady states with scale-free localization along or even against the direction of non-reciprocity in various impurity strength regimes. Also present are Bloch-like states that survive albeit broken translational invariance. We further explore the co-existence of non-Hermitian skin effect and scale-free localization, where even qualitative aspects of the system’s spectrum can be extremely sensitive to impurity strength. Specific circuit setups are also proposed for experimentally detecting the scale-free accumulation, with simulation results confirming our main findings.
Wed, 03 Mar 2021 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2007132021-03-03T00:00:00Z
- Point-gap topology with complete bulk-boundary correspondence and anomalous amplification in the Fock space of dissipative quantum systemshttps://scholarbank.nus.edu.sg/handle/10635/202785Title: Point-gap topology with complete bulk-boundary correspondence and anomalous amplification in the Fock space of dissipative quantum systems
Authors: Pan, Jian-Song; Li, Linhu; Gong, Jiangbin
Abstract: The spectral and dynamical properties of dissipative quantum systems, as modeled by a damped oscillator in the Fock space, are investigated from a topological point of view. Unlike a physical lattice system that is naturally under the open boundary condition, the bounded-from-below nature of the Fock space offers a unique setting for understanding and verifying non-Hermitian skin modes under semi-infinity boundary conditions that are elusive in actual physical lattices. A topological characterization based on the complex spectra of the Liouvillian superoperator is proposed and the associated complete set of topologically protected skin modes can be identified, thus reflecting the complete bulk-boundary correspondence of point-gap topology generally absent in realistic materials. Moreover, we discover anomalous skin modes with exponential amplification even though the quantum system is purely dissipative, a counterintuitive dynamical phenomenon that can be accessed in actual experiments. Our results indicate that current studies of non-Hermitian topological matter can greatly benefit research on quantum open systems and vice versa.
Mon, 24 May 2021 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2027852021-05-24T00:00:00Z