arXiv subjects

X. L. Huang

Publications and source records attributed to X. L. Huang.

At least 37 records · Page 2Linked to original sources

arXiv2022

Shortcuts to adiabaticity for open quantum systems and a mixed-state inverse engineering scheme

We propose a fast mixed-state control scheme to transfer the quantum state along designable trajectories in Hilbert space, which is robust to multiple decoherence noises. Starting with the dynamical invariants of open quantum systems, we present the shortcuts to adiabaticity (STAs) of open quantum systems at first, then apply the STAs to speed up the adiabatic steady process. Our scheme drives open systems from a initial steady state to a target steady state by a controlled Liouvillian that possesses the same form as the reference (original) one which is accessible in present-day experiments. The experimental observation with current available parameters for the nitrogen-vacancy (NV) center in diamond is suggested and discussed.

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arXiv2018

Multilevel quantum Otto heat engines with identical particles

A quantum Otto heat engine is studied with multilevel identical particles trapped in one-dimensional box potential as working substance. The symmetrical wave function for Bosons and the anti-symmetrical wave function for Fermions are considered. In two-particle case, we focus on the ratios of $W^i$ ($i=B,F$) to $W_s$, where $W^B$ and $W^F$ are the work done by two Bosons and Fermions respectively, and $W_s$ is the work output of a single particle under the same conditions. Due to the symmetric of the wave functions, the ratios are not equal to $2$. Three different regimes, low temperature regime, high temperature regime, and intermediate temperature regime, are analyzed, and the effects of energy level number and the differences between the two baths are calculated. In the multiparticle case, we calculate the ratios of $W^i_M/M$ to $W_s$, where $W^i_M/M$ can be seen as the average work done by a single particle in multiparticle heat engine. For other working substances whose energy spectrum have the form of $E_n\sim n^2$, the results are similar. For the case $E_n\sim n$, two different conclusions are obtained.

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arXiv2017

Adiabatic Decoherence-Free Subspaces and its Shortcuts

The adiabatic theorem and "shortcuts to adiabaticity" for the adiabatic dynamics of time-dependent decoherence-free subspaces are explored in this paper. Starting from the definition of the dynamical stable decoherence-free subspaces, we show that, under a compact adiabatic condition, the quantum state follows time-dependent decoherence-free subspaces (the adiabatic decoherence free subspaces) into the target subspace with extremely high purity, even though the dynamics of the quantum system may be non-adiabatic. The adiabatic condition mentioned in the adiabatic theorem is very similar with the adiabatic condition for closed quantum systems, except that the operators required to be "slowness" is on the Lindblad operators. We also show that the adiabatic decoherence-free subspaces program depends on the existence of instantaneous decoherence-free subspaces, which requires that the Hamiltonian of open quantum systems has to be engineered according to the incoherent control program. Besides, "the shortcuts to adiabaticity" for the adiabatic decoherence-free subspaces program is also presented based on the transitionless quantum driving method. Finally, we provide an example of physical systems that support our programs. Our approach employs Markovian master equations and applies primarily to finite-dimensional quantum systems.

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arXiv2013

Evaluation of the 1077keV gamma-ray emission probability from 68Ga decay

68Ga decays to the excited states of 68Zn through the electron capture decay mode. New recommended values for the emission probability of 1077keV gamma-ray given by the ENSDF and DDEP databases all use data from absolute measurements. In 2011 Jiang Liyang deduced a new value for 1077keV gamma-ray emission probability by measuring the 69Ga(n,2n)68Ga reaction cross section. The new value is about 20% lower than values obtained from previous absolute measurements and evaluations. In this paper, the discrepancies among the measurements and evaluations are analyzed carefully and the new values are re-recommended. Our recommended value for the emission probability of 1077keV gamma-ray is 2.72+-0.16 %.

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arXiv2013

Quantum Brayton cycle with coupled systems as working substance

We explore the quantum version of Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process, one corresponds to the external magnetic field (characterized by $F_x$) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by $F_y$). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by $F_x$), whereas the subsystem's cycle is of quantum Otto in another Brayton cycle (characterized by $F_y$). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system are usually larger than the sum of work done by the two subsystems. The other interesting finding is that for the cycle characterized by $F_y$, the subsystem can be a refrigerator while the total system is a heat engine. The result in the paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance.

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arXiv2010

Information Flow, Non-Markovianity and Geometric Phases

Geometric phases and information flows of a two-level system coupled to its environment are calculated and analyzed. The information flow is defined as a cumulant of changes in trace distance between two quantum states, which is similar to the measure for non-Markovianity given by Breuer. We obtain an analytic relation between the geometric phase and the information flow for pure initial states, and a numerical result for mixed initial states. The geometric phase behaves differently depending on whether there are information flows back to the two-level system from its environment.

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arXiv2010

Suppressing decoherence and improving entanglement by quantum-jump-based feedback control in two-level systems

We study the quantum-jump-based feedback control on the entanglement shared between two qubits with one of them subject to decoherence, while the other qubit is under the control. This situation is very relevant to a quantum system consisting of nuclear and electron spins in solid states. The possibility to prolong the coherence time of the dissipative qubit is also explored. Numerical simulations show that the quantum-jump-based feedback control can improve the entanglement between the qubits and prolong the coherence time for the qubit subject directly to decoherence.

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arXiv2010

Born-Oppenheimer approximation for open quantum systems within the quantum trajectory approach

Based on the quantum trajectory approach, we extend the Born-Oppenheimer (BO) approximation from closed quantum system to open quantum system, where the open quantum system is described by a master equation in Lindblad form. The BO approximation is defined and the validity condition is derived. We find that the dissipation in fast variables benefits the BO approximation that is different from the dissipation in slow variables. A detailed comparison between this extension and our previous approximation (that is based on the effective Hamiltonian approach, see X. L. Huang and X. X. Yi, Phys. Rev. A 80, 032108 (2009)) is presented. Several new features and advantages are analyzed, which show that the two approximations are complementary to each other. Two examples are taken to illustrate our method.

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arXiv2010

Entropy and specific heat for open systems in steady states

The fundamental assumption of statistical mechanics is that the system is equally likely in any of the accessible microstates. Based on this assumption, the Boltzmann distribution is derived and the full theory of statistical thermodynamics can be built. In this paper, we show that the Boltzmann distribution in general can not describe the steady state of open system. Based on the effective Hamiltonian approach, we calculate the specific heat, the free energy and the entropy for an open system in steady states. Examples are illustrated and discussed.

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arXiv2009

Nonequilibrium thermal entanglement in three-qubit $XX$ model

Making use of the master equation and effective Hamiltonian approach, we investigate the steady state entanglement in a three-qubit $XX$ model. Both symmetric and nonsymmetric qubit-qubit couplings are considered. The system (the three qubits) is coupled to two bosonic baths at different temperatures. We calculate the steady state by the effective Hamiltonian approach and discuss the dependence of the steady state entanglement on the temperatures and couplings. The results show that for symmetric qubit-qubit couplings, the entanglements between the nearest neighbor are equal, independent of the temperatures of the two baths. The maximum of the entanglement arrives at $T_L=T_R$. For nonsymmetric qubit-qubit couplings, however, the situation is totally different. The baths at different temperatures would benefit the entanglement and the entanglements between the nearest neighbors are no longer equal. By examining the probability distribution of each eigenstate in the steady state, we present an explanation for these observations. These results suggest that the steady entanglement can be controlled by the temperature of the two baths.

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arXiv2009

Dynamics of quantum-classical hybrid system: effect of matter-wave pressure

Radiation pressure affects the kinetics of a system exposed to the radiation and it constitutes the basis of laser cooling. In this paper, we study {\it matter-wave pressure} through examining the dynamics of a quantum-classical hybrid system. The quantum and classical subsystem have no explicit coupling to each other, but affect mutually via a changing boundary condition. Two systems, i.e., an atom and a Bose-Einstein condensate(BEC), are considered as the quantum subsystems, while an oscillating wall is taken as the classical subsystem. We show that the classical subsystem would experience a force proportional to $Q^{-3}$ from the quantum atom, whereas it acquires an additional force proportional to $Q^{-2}$ from the BEC due to the atom-atom interaction in the BEC. These forces can be understood as the {\it matter-wave pressure}.

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arXiv2009

Born-Oppenheimer approximation in open systems

We generalize the standard Born-Oppenheimer approximation to the case of open quantum systems. We define the zeroth order Born-Oppenheimer approximation of an open quantum system as the regime in which its effective Hamiltonian can be diagonalized with fixed slowly changing variables. We then establish validity and invalidity conditions for this approximation for two kinds of dissipations--the spin relaxation and the dissipation of center-of-mass motion. As an example, the Born-Oppenheimer approximation of a two-level open system is analyzed.

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arXiv2009

Driving Quantum System into Decoherence-free Subspaces by Lyapunov Control

We present a scheme to drive a finite-dimensional quantum system into the decoherence-free subspaces(DFS) by Lyapunov control. Control fields are established by Lyapunov function. This proposal works well for both closed and open quantum systems, with replacing the DFS by desired subspaces for closed systems. An example which consists of a four-level system with three degenerate states driven by three lasers is presented to gain further insight of the scheme, numerical simulations for the dynamics of the system are performed and the results are good.

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arXiv2008

Non-Markovian Effects on the Geometric Phase

The geometric phases of a two-level atom interacting with non-Markovian environments are calculated and the non-Markovian effects on the geometric phases are discussed in this paper. Three kinds of methods that describe the non-Markovian process, projection superoperator technique, memory kernel master equation and post-Markovian master equation, are used in the discussions. The results show that when the dissipation rate is large, the non-Markovian effects change the geometric phase more strikingly than the small one.

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arXiv2008

Effective Hamiltonian Approach to Open Systems and Its Applications

By using the effective Hamiltonian approach, we present a self-consistent framework for the analysis of geometric phases and dynamically stable decoherence-free subspaces in open systems. Comparisons to the earlier works are made. This effective Hamiltonian approach is then extended to a non-Markovian case with the generalized Lindblad master equation. Based on this extended effective Hamiltonian approach, the non-Markovian master equation describing a dissipative two-level system is solved, an adiabatic evolution is defined and the corresponding adiabatic condition is given.

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arXiv2008

Non-Markovian Quantum Jump with Generalized Lindblad Master Equation

The Monte Carlo wave function method or the quantum trajectory/jump approach is a powerful tool to study dissipative dynamics governed by the Markovian master equation, in particular for high-dimensional systems and when it is difficult to simulate directly. In this paper, we extend this method to the non-Markovian case described by the generalized Lindblad master equation. Two examples to illustrate the method are presented and discussed. The results show that the method can correctly reproduce the dissipative dynamics for the system. The difference between this method and the traditional Markovian jump approach and the computational efficiency of this method are also discussed.

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arXiv2008

Effect of feedback on the control of a two-level dissipative quantum system

We show that it is possible to modify the stationary state by a feedback control in a two-level dissipative quantum system. Based on the geometric control theory, we also analyze the effect of the feedback on the time-optimal control in the dissipative system governed by the Lindblad master equation. These effects are reflected in the function $Δ_A(\vec{x})$ and $Δ_B(\vec{x})$ that characterize the optimal trajectories, as well as the switching function $Φ(t)$ and $θ(t),$ which characterize the switching point in time for the time-optimal trajectory.

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arXiv2008

Loschmidt echo and Berry phase around degeneracies in nonlinear systems

We study the Loschmidt echo and Berry phase in a nonlinear system transported around a double and triple degeneracy. The nonlinearity of the system makes the Berry phase different from that in linear systems. We propose a witness of nonlinearity for the nonlinear system and show its dependence on the parameters of the system, taking the standard Landau-Zener model as an example. We calculate the Loschmidt echo(LE) or quantum fidelity in the quantum dynamics under perturbations around the degeneracy, and establish a connection between the LE and the witness of nonlinearity. These phases and Loschmidt echo can be observed with current experimental technology in a nonlinear resonator.

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