arXiv subjects

H. D. Liu

Publications and source records attributed to H. D. Liu.

12 recordsLinked to original sources

arXiv2026

Giant-Atom-Induced High-Order Output Zeros in a Coupled-Cavity Array

Coherent perfect absorption, zero transmission and zero reflection are several scattering phenomena governed by interference engineering in Hermitian and non-Hermitian systems. Higher-order coherent perfect absorption can significantly broaden the absorption bandwidth, while existing implementations rely on scattering zero degeneracy induced by exceptional points or additional momentum-dependent phase delays introduced in incident waves. We propose a scheme where a giant atom couples to a one-dimensional coupled-cavity array at two spatially separated sites. The spatially separated coupling configuration of the giant atom generates tunable nonlocal interference phases that dominate the scattering interference process. We further investigate the zero-reflection and zero-transmission behaviors under single-sided incidence. Remarkably, we find that for certain parameter choices, zero transmission can persist over the entire propagating band, rather than being restricted to a single momentum. Our results reveal that the giant-atom interference mechanism enables bandwidth-enhanced coherent perfect absorption and bandwidth-enhanced zero transmission in the absence of exceptional points and incident momentum-dependent phase delays. Our work provides a physical route for coherent wave manipulation in coupled-cavity quantum networks.

quant-ph↗

arXiv2025

Non-Hermitian effects on the quantum parameter estimation in pseudo-Hermitian systems

Quantum Fisher Information (QFI) is a fundamental quantity in quantum parameter estimation theory, characterizing the ultimate precision bound of parameter estimation. In this work, we investigate QFI for quantum states in non-Hermitian systems. By employing the projected Hilbert space method and spectral decomposition, we derive an explicit expression for the QFI in terms of the density matrix and parameter generators. This formulation not only recovers the well-known results in the Hermitian case but also captures the non-Hermitian effects induced by the time-dependent norm of the state. To validate our theoretical framework, we analyze a single-qubit pseudo-Hermitian system and apply Naimark dilation theory to embed it into an equivalent Hermitian system. The comparison between the original and dilated systems demonstrates the consistency and applicability of the proposed QFI formula in non-Hermitian settings. In addition, we investigate a $\mathcal{PT}$-symmetric system to further explore the influence of non-Hermiticity on QFI. Our findings offer a new perspective for analyzing and enhancing QFI in non-Hermitian systems, paving the way for promising applications in non-Hermitian quantum metrology and sensing.

quant-ph↗

arXiv2023

Nonlinear Non-Hermitian Landau-Zener-Stückelberg-Majorana interferometry

In this work, we have studied the non-Hermitian nonlinear LZSM interferometry in a non-Hermitian N-body interacting boson system in which the non-Hermicity is from the nonreciprocal tunnelings between the bosons. By using the mean-field approximation and projective Hilbert space, the effect of nonreciprocity and nonlinearity on the energy spectrum, the dynamics, and the formation of the interference fringes have been studied. The different symmetries and the impact of the two different types of reciprocity, i.e. the in-phase tunneling and anti-phase tunneling, on the energy spectrum and the phase transition between the Josephson oscillation and the self-trapping have been investigated. For the LZSM interferometry, the strength of the nonreciprocity is found to take an essential role in the population of the projective state and the strengths of the interference patterns in the projective space. While the conditions of destructive and constructive interference under the weak-coupling approximation still only depend on the strength of nonlinearity. Our result provides an application of the nonlinear non-Hermitian LZSM interferometry in studying the parameters of a non-Hermitian nonlinear two-level system which related to the nonlinearity and the non-Hermicity.

quant-ph↗

arXiv2022

Counterdiabatic driving for pseudo- and antipseudo- Hermitian systems

In this work, we study the counterdiabatic driving scheme in pseudo- and antipseudo- Hermitian systems. By discussing the adiabatic condition for non-Hermitian system, we show that the adiabatic evolution of state can only be realized in the non-Hermitian system which possesses real energy spectrum. Therefore, the counterdiabatic driving scheme to reproduce an exact evolution of an energy eigenstate needs either real energy spectrum or dropping its parts of dynamic phase and Berry phase. In this sense, we derive the adiabatic conditions and counterdiabatic driving Hamiltonians for the pseudo-Hermitian Hamiltonian which possesses either real or complex energy spectrum and the antipseudo-Hermitian Hamiltonian which possesses either imaginary or complex energy spectrum. We also find the condition to get self-normalized energy eigenstates in pseudo- and antipseudo- Hermitian system and derive the well-defined population of bare states on this energy eigenstate. Our results are illustrated by studying the counterdiabatic driving for a non-Hermitian three level system, and a perfect population transfer with loss or gain is realized.

quant-ph↗

arXiv2020

Quantum $φ$-synchronization in coupled optomechanical system with periodic modulation

Based on the concepts of quantum synchronization and quantum phase synchronization proposed by A. Mari \textit{et al.} in Phys. Rev. Lett. 111, 103605 (2013), we introduce and characterize the measure of a more generalized quantum synchronization called quantum $φ$-synchronization under which the pairs of variables have the same amplitude and possess the same $φ$ phase shift. Naturally, quantum synchronization and quantum anti-synchronization become special cases of quantum $φ$-synchronization. Their relations and differences are also discussed. To illustrate these theories, we investigate the quantum $φ$-synchronization and quantum phase synchronization phenomena of two coupled optomechanical systems with periodic modulation and show that quantum $φ$-synchronization is more general as a measure of synchronization. We also show the phenomenon of quantum anti-synchronization when $φ=π$.

quant-ph↗

arXiv2018

Effect of spin relaxations on the spin mixing conductances for a bilayer structure

The spin current can result in a spin-transfer torque in the normal-metal(NM)|ferromagnetic-insulator(FMI) or normal-metal(NM)|ferromagnetic-metal(FMM) bilayer. In the earlier study on this issue, the spin relaxations were ignored or introduced phenomenologically. In this paper, considering the FMM or FMI with spin relaxations described by a non-Hermitian Hamiltonian, we derive an effective spin-transfer torque and an effective spin mixing conductance in the non-Hermitian bilayer. The dependence of the effective spin mixing conductance on the system parameters (such as insulating gap, \textit{s-d} coupling, and layer thickness) as well as the relations between the real part and the imaginary part of the effective spin mixing conductance are given and discussed. We find that the effective spin mixing conductance can be enhanced in the non-Hermitian system. This provides us with the possibility to enhance the spin mixing conductance.

cond-mat.mes-hall↗

arXiv2016

Dissipative preparation of tripartite singlet state in coupled arrays of cavities via quantum feedback control

We propose an experimentally feasible scheme for dissipative preparation of tripartite entangled state with atoms separately trapped in an array of three coupled cavities. The combination of coherent driving fields and quantum-jump-based feedback control will drive the system into a non-equilibrium steady state, which has a nearly perfect overlap with the genuine three-atom singlet state. Different control strategies are investigated and the corresponding optimal parameters are confirmed. Moreover, the fidelity of target state is insensitive to detection inefficiencies, and it oversteps 90\% for a wide range of decoherence parameters as long as the single-atom cooperativity parameter $C\equiv g^2/(γκ)>350$.

quant-ph↗

arXiv2016

Coherent-State Approach for Majorana representation

By representing a quantum state and its evolution with the majorana stars on the Bloch sphere, the Majorana representation (MR) provide us an intuitive way to study a physical system with SU(2) symmetry. In this work, based on coherent states, we propose a method to establish generalization of MR for a general symmetry. By choosing a generalized coherent state as a reference state, we give a more general MR for both finite and infinite systems and the corresponding star equations are given. Using this method, we study the squeezed vacuum states for three different symmetries, Heisenberg-Weyl, SU(2) and SU(1,1), and express the effect of squeezing parameter on the distribution of stars. Furthermore, we also study the dynamical evolution of stars for an initial coherent state driven by a nonlinear Hamiltonian, and find that at a special time point, the stars are distributed on two orthogonal large circles.

quant-ph↗

arXiv2014

Representation of Berry phase by the trajectories of Majorana stars

The Majorana's stellar representation, which represents the evolution of a quantum state with the trajectories of the Majorana stars on a Bloch sphere, provides an intuitive way to study a physical system with high dimensional projective Hilbert space. In this Letter, we study the Berry phase by these stars and their loops on the Bloch sphere. It is shown that the Berry phase of a general spin state can be expressed by an elegant formula with the solid angles of Majorana star loops. Furthermore, these results can be naturally used to a general state with arbitrary dimensions. To demonstrate our theory, we study a two mode interacting boson system. Finally, the relation between stars' correlations and quantum entanglement is discussed.

quant-ph↗

arXiv2011

Berry Phase and Hannay's Angle in a Quantum-Classical Hybrid System

Berry phase, which had been discovered for more than two decades, provides us a very deep insight on the geometric structure of quantum mechanics. Its classical counterpart--Hannay's angle is defined if closed curves of action variables return to the same curves in phase space after a time evolution. In this paper, we study the Berry phase and Hannay's angle in a quantum-classical hybrid system under the Born-Oppenheimer approximation. By quantum-classical hybrid system, we denote a composite system consists of a quantum subsystem and a classical subsystem. The effects of subsystem-subsystem couplings on the Berry phase and Hannay's angle are explored. The results show that the Berry phase has been changed sharply by the couplings, whereas the couplings have small effect on the Hannay's angle.

quant-ph↗

arXiv2011

Geometric phases in a scattering process

The study of geometric phase in quantum mechanics has so far be confined to discrete (or continuous) spectra and trace preserving evolutions. Consider only the transmission channel, a scattering process with internal degrees of freedom is neither a discrete spectrum problem nor a trace preserving process. We explore the geometric phase in a scattering process taking only the transmission process into account. We find that the geometric phase can be calculated by the some method as in an unitary evolution. The interference visibility depends on the transmission amplitude. The dependence of the geometric phase on the barrier strength and the spin-spin coupling constant is also presented and discussed.

quant-ph↗

arXiv2009

Nonlinear effect on the transmission of light in a cavity array

Taking nonlinear effect into account, we study theoretically the transmission properties of photons in a one-dimensional coupled cavities, the cavity located at the center of the cavity array is coupled to a two-level system. By the traditional scattering theory, we calculate the transmission rate of photons along the cavities, and discuss the effect of nonlinearity on the photon transport. The results show that the controllable two-level system can act as a quantum switch in the coherent transport of photons. The dynamics of such a system is also studied by numerical simulations, the effect of the atom-field detuning and nonlinearity on the dynamics is shown and discussed.

quant-ph↗