Coherent Backscattering in Fock Space: a Signature of Quantum Many-Body Interference in Interacting Bosonic Systems

Quantum catastrophes and ergodicity in the dynamics of bosonic Josephson junctions

We study rainbow (fold) and cusp catastrophes that form in Fock space following a quench in a Bose Josephson junction. In the Gross-Pitaevskii mean-field theory the rainbows are singular caustics, but in the second-quantized theory a Poisson resummation of the wave function shows that they are described by well behaved Airy functions. The structural stability of these Fock space caustics against variations in the initial conditions and Hamiltonian evolution is guaranteed by catastrophe theory. We also show that the long-time dynamics are ergodic. Our results are relevant to the question posed …

从玻色子和费米子到自旋：Jordan-Schwinger 映射的多模推广

From bosons and fermions to spins: A multi-mode extension of the Jordan-Schwinger map

该工作将 Jordan-Schwinger 映射推广到多模情形，通过算法构造完备自旋态集合，实现任意多模玻色子或费米子系统的自旋描述，并揭示与高斯多项式的联系，为三模 GHZ 和 W 纠缠态提供新解释。

Decoherence and entanglement in a bosonic Josephson junction: Bose-enhanced quantum-Zeno control of phase-diffusion

We study the effect of decoherence on dynamical phase diffusion in the two-site Bose-Hubbard model. Starting with an odd parity excited coherent state, the initial loss of single particle coherence varies from small bound oscillations in the Rabi regime, through hyperbolic depletion in the Josephson regime, to a Gaussian decay in the Fock regime. The inclusion of local-site noise, measuring the relative number difference between the modes, is shown to enhance phase-diffusion. In comparison, site-indiscriminate noise measuring the population imbalance between the two quasi-momentum modes, slows…

$\mathbb{Z}_2$ topological insulator analog for vortices in an interacting bosonic quantum fluid

$\mathbb{Z}_2$ topological insulators for photons and in general bosons cannot be strictly implemented because of the lack of symmetry-protected pseudospins. We show that the required protection can be provided by the real-space topological excitation of an interacting quantum fluid: quantum vortex. We consider a Bose-Einstein Condensate at the $Γ$ point of the Brillouin zone of a quantum valley Hall system based on two staggered honeycomb lattices. We demonstrate the existence of a coupling between the winding number of a vortex and the valley of the bulk Bloch band. This leads to chiral vort…

Self-consistent determination of the many-body state of ultracold bosonic atoms in a one-dimensional harmonic trap

We study zero-temperature quantum fluctuations in harmonically trapped one-dimensional interacting Bose gases, using the self-consistent multiconfigurational time-dependent Hartree method. We define $phase$ $fluctuations$ from the full single-particle density matrix by the spatial decay exponent of off-diagonal long-range order. In a regime of mesoscopic particle numbers and moderate contact couplings, we derive the spatial dependence of the amplitude of phase fluctuations, determined from the {\em self-consistently} derived shape of the field operator orbitals and Fock space orbital occupatio…

Hartree-Fock近似用于具有对称性适配变分波函数的玻色子

Hartree-Fock approximation for bosons with symmetry-adapted variational wave functions

本研究提出一种对称性适配的变分后投影方案，用于玻色子Hartree-Fock近似，在多个对称群模型上准确估计能量和关联函数，并应用于束缚态、超流分数及Yrast线研究。

多体动力学局域化在Fock空间中

Many-body dynamical localization in Fock space

研究了相互作用双模玻色子系统在周期驱动下Fock空间中多体动力学局域化现象，揭示了经典混沌扩散与量子干涉效应的相互作用，发现量子动力学在Fock空间中表现出强抑制传输，类比于无序晶格中的安德森局域化。

Non-equilibrium Dynamics of Renyi Entropy for Bosonic Many-Particle Systems

We propose a new field theoretic method for calculating Renyi entropy of a sub-system of many interacting Bosons without using replica methods. This method is applicable to dynamics of both open and closed quantum systems starting from arbitrary initial conditions. Our method identifies the Wigner characteristic of a reduced density matrix with the partition function of the whole system with a set of linear sources turned on only in the subsystem and uses this to calculate the subsystem's Renyi entropy. We use this method to study evolution of Renyi entropy in a non-interacting open quantum sy…

For high-precision bosonic Josephson junctions, many-body effects matter

Typical treatments of superconducting or superfluid Josephson junctions rely on mean-field or two-mode models; we explore many-body dynamics of an isolated, ultracold, Bose-gas long Josephson junction using time-evolving block decimation simulations. We demonstrate that with increasing repulsive interaction strength, localized dynamics emerge that influence macroscopic condensate behavior and can lead to formation of solitons that directly oppose the symmetry of the junction. Initial state population and phase yield insight into dynamic tunneling regimes of a quasi one-dimensional double well …

通过层分辨的局域化-离局域化转变探究交错玻色子Kitaev链中的量子相变

Probing quantum phase transition in a staggered Bosonic Kitaev chain via layer-resolved localization-delocalization transition

本研究通过Nambu框架分析交错玻色子Kitaev链的非厄米Bloch核心矩阵，推导出例外点（EPs）的解析条件，并证明这些EP精确对应集体本征态的局域化-离局域化转变，从而为相互作用玻色子晶格的量子相变提供了基于EP的解析判据。

Non-equilibrium scalar field dynamics starting from Fock states: Absence of thermalization in one dimensional phonons coupled to fermions

We propose a new method to study non-equilibrium dynamics of scalar fields starting from non-Gaussian initial conditions using Keldysh field theory. We use it to study dynamics of phonons coupled to non-interacting bosonic and fermionic baths, starting from initial Fock states. We find that in one dimension long wavelength phonons coupled to fermionic baths do not thermalize both at low and high bath-temperatures. At low temperature, constraints from energy-momentum conservation lead to a narrow bandwidth of particle-hole excitations and the phonons effectively do not see this bath. On the oth…