arXiv subjects

Jiangbin Gong

Publications and source records attributed to Jiangbin Gong.

At least 199 records · Page 11Linked to original sources

arXiv2009

Conductance properties of rough quantum wires with colored surface disorder

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.

cond-mat.dis-nn↗

arXiv2009

Many-Body Coherent Destruction of Tunneling

A new route to coherent destruction of tunneling is established by considering a monochromatic fast modulation of the self-interaction strength of a many-boson system. The modulation can be tuned such that only an arbitrarily, a priori prescribed number of particles are allowed to tunnel. The associated tunneling dynamics is sensitive to the odd or even nature of the number of bosons.

quant-ph↗

arXiv2009

Generating a Fractal Butterfly Floquet Spectrum in a Class of Driven SU(2) Systems

A scheme for generating a fractal butterfly Floquet spectrum, first proposed by Wang and Gong [Phys. Rev. A {\bf 77}, 031405(R) (2008)], is extended to driven SU(2) systems such as a driven two-mode Bose-Einstein condensate. A new class of driven systems without a link with the Harper model context is shown to have an intriguing butterfly Floquet spectrum. The found butterfly spectrum shows remarkable deviations from the known Hosftadter's butterfly. In addition, the level crossings between Floquet states of the same parity and between Floquet states of different parities are studied and highlighted. The results are relevant to studies of fractal statistics, quantum chaos, coherent destruction of tunneling, as well as the validity of mean-field descriptions of Bose-Einstein condensates.

quant-ph↗

arXiv2009

Butterfly Floquet Spectrum in Driven SU(2) Systems

The Floquet spectrum of a class of driven SU(2) systems is shown to display a butterfly pattern with multi-fractal properties. The level crossing between Floquet states of the same parity or different parities is studied. The results are relevant to studies of fractal statistics, quantum chaos, coherent destruction of tunneling, and the validity of mean-field descriptions of Bose-Einstein condensates.

quant-ph↗

arXiv2009

Chaos and Correspondence in Classical and Quantum Hamiltonian Ratchets: A Heisenberg Approach

Previous work [Gong and Brumer, Phys. Rev. Lett., 97, 240602 (2006)] motivates this study as to how asymmetry-driven quantum ratchet effects can persist despite a corresponding fully chaotic classical phase space. A simple perspective of ratchet dynamics, based on the Heisenberg picture, is introduced. We show that ratchet effects are in principle of common origin in classical and quantum mechanics, though full chaos suppresses these effects in the former but not necessarily the latter. The relationship between ratchet effects and coherent dynamical control is noted.

nlin.CD↗

arXiv2009

All-optical Imprinting of Geometric Phases onto Matter Waves

Traditional optical phase imprinting of matter waves is of a dynamical nature. In this paper 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 wavepacket re-directing and wavepacket splitting. In addition to their fundamental interest, our results open up new opportunities for robust optical control of matter waves.

quant-ph↗

arXiv2009

Symmetry Breaking and Self-trapping of a Dipolar Bose-Einstein Condensate in a Double-well Potential

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 oscillation 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.

cond-mat.other↗

arXiv2008

Formation and Transformation of Vector-Solitons in Two-Species Bose-Einstein Condensates with Tunable Interaction

Under a unified theory we investigate the formation of various types of vector-solitons in two-species Bose-Einstein condensates with arbitrary scattering lengths. We then show that by tuning the interaction parameter via Feshbach resonance, transformation between different types of vector solitons is possible. Our results open up new ways in the quantum control of multi-species Bose-Einstein condensates.

cond-mat.other↗

arXiv2008

Spectral Relationships Between Kicked Harper and On-Resonance Double Kicked Rotor Operators

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 spectrums of these operators. In this paper we apply C*-algebra methods to explain this resemblance. We show that each pair of corresponding operators belong to a common rotation C*-algebra B_α, prove that their spectrums are equal if αis irrational, and prove that the Hausdorff distance between their spectrums converges to zero as q increases if α= p/q with p and q coprime integers. Moreover, we show that corresponding operators in B_αare homomorphic images of mother operators in the universal rotation C*-algebra A_αthat are unitarily equivalent and hence have identical spectrums. These results extend analogous results for almost Mathieu operators. We also utilize the C*-algebraic framework to develop efficient algorithms to compute the spectrums of these mother operators for rational αand present preliminary numerical results that support the conjecture that their spectrums are Cantor sets if αis irrational. This conjecture for almost Mathieu operators, called the Ten Martini Problem, was recently proved 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.

math-ph↗

arXiv2008

Nonlinear Landau-Zener Processes in a Periodic Driving Field

Effects of a periodic driving field on Landau-Zener processes are studied using a nonlinear two-mode model that describes the mean-field dynamics of a many-body system. A variety of different dynamical phenomena in different parameter regimes of the driving field are discussed and analyzed. These include shifted, weakened, or enhanced phase dependence of nonlinear Landau-Zener processes, nonlinearity-enhanced population transfer in the adiabatic limit, and Hamiltonian chaos on the mean field level. The emphasis of this work is placed on how the impact of a periodic driving field on Landau-Zener processes with self-interaction differs from those without self-interaction. Aside from gaining understandings of driven nonlinear Landau-Zener processes, our findings can be used to gauge the strength of nonlinearity and for efficient manipulation of the mean-field dynamics of many-body systems.

cond-mat.other↗

arXiv2008

Controlling the Population Imbalance of a Bose-Einstein Condensate by a Symmetry-Breaking Driving Field

Nonlinear Floquet states associated with a symmetry-breaking driving field are exploited to control the dynamics of a Bose-Einstein condensate in a double-well potential. The population imbalance between the two wells is shown to be controllable by slowly tuning system parameters along a closed path. The results extend symmetry-breaking-based quantum control to many-body systems and extend navigation of linear Floquet states to navigation of nonlinear Floquet states.

cond-mat.other↗

arXiv2008

Quantum Ratchet Accelerator without a Bichromatic Lattice Potential

In a quantum ratchet accelerator system, a linearly increasing directed current can be dynamically generated without using a biased field. Generic quantum ratchet acceleration with full classical chaos [Gong and Brumer, Phys. Rev. Lett. 97, 240602 (2006)] constitutes a new element of quantum chaos and an interesting violation of a sum rule of classical ratchet transport. Here we propose a simple quantum ratchet accelerator model that can also generate linearly increasing quantum current with full classical chaos. This new model does not require a bichromatic lattice potential. It is based on a variant of an on-resonance kicked-rotor system, periodically kicked by two optical lattice potentials of the same lattice constant, but with unequal amplitudes and a fixed phase shift between them. The dependence of the ratchet current acceleration rate on the system parameters is studied in detail. The cold-atom version of our new quantum ratchet accelerator model should be realizable by introducing slight modifications to current cold-atom experiments.

quant-ph↗

arXiv2008

Two-mode Bose-Einstein condensate in a high-frequency driving field that directly couples the two modes

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 new 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.

quant-ph↗

arXiv2008

Quantum Control of Ultra-cold Atoms: Uncovering a Novel Connection between Two Paradigms of Quantum Nonlinear Dynamics

Controlling the translational motion of cold atoms using optical lattice potentials is of both theoretical and experimental interest. By designing two on-resonance time sequences of kicking optical lattice potentials, a novel connection between two paradigms of nonlinear mapping systems, i.e., the kicked rotor model and the kicked Harper model, is established. In particular, it is shown that Hofstadter's butterfly quasi-energy spectrum in periodically driven quantum systems may soon be realized experimentally, with the effective Planck constant tunable by varying the time delay between two sequences of control fields. Extensions of this study are also discussed. The results are intended to open up a new generation of cold-atom experiments of quantum nonlinear dynamics

quant-ph↗

arXiv2008

Proposal of a Cold-atom Realization of Quantum Maps with Hofstadter's Butterfly Spectrum

Quantum systems with Hofstadter's butterfly spectrum are of fundamental interest to many research areas. Based upon slight modifications of existing cold-atom experiments, a cold-atom realization of quantum maps with Hofstadter's butterfly spectrum is proposed. Connections and differences between our realization and the kicked Harper model are identified. This work also exposes, for the first time, a simple connection between the kicked Harper model and the kicked rotor model, the two paradigms of classical and quantum chaos.

quant-ph↗

arXiv2008

Entanglement-induced Decoherence and Energy Eigenstates

Using recent results in the field of quantum chaos we derive explicit expressions for the time scale of decoherence induced by the system-environment entanglement. For a generic system-environment interaction and for a generic quantum chaotic system as environment, conditions are derived for energy eigenstates to be preferred states in the weak coupling regime. A simple model is introduced to numerically confirm our predictions. The results presented here may also help understanding the dynamics of quantum entanglement generation in chaotic quantum systems.

quant-ph↗

arXiv2007

Adiabatic Quantum Transport in a Spin Chain with a Moving Potential

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.

quant-ph↗

arXiv2007

Controlling the Ratchet Effect for Cold Atoms

Low-order quantum resonances manifested by directed currents have been realized with cold atoms. Here we show that by increasing the strength of an experimentally achievable delta-kicking ratchet potential, quantum resonances of a very high order may naturally emerge and can induce larger ratchet currents than low-order resonances, with the underlying classical limit being fully chaotic. The results offer a means of controlling quantum transport of cold atoms.

quant-ph↗