arXiv subjects

Jun Jing

Publications and source records attributed to Jun Jing.

100 records · Page 6Linked to original sources

arXiv2010

Qubit Entanglement Dephasing Dynamics Driven by a Bath of Spins

We study the entanglement dynamics for a two-spin system coupled to a spin environment of different configurations by z-x type interaction. The models considered in this paper are solved both analytically and numerically giving rise to some concise analytical expressions when certain approximations are properly made. Our purpose is to find how the initial states of the environment with different numbers of spins affect the decay or revival of the entanglement between central qubits. In Particular, it is found that the block-entangled environment could speed up the decay and revival of the qubit entanglement. Our results exhibit some interesting features that have not been found for a boson bath.

quant-ph↗

arXiv2009

Breakdown of the rotating-wave approximation in entanglement description of spin anti-correlated states

It is well established that an entanglement encoded in the Bell states of a two-qubit system with correlated spins exhibits completely different evolution properties than that encoded in states with the anti-correlated spins. A complete and abrupt loss of the entanglement, called the entanglement sudden death, can be found to occur for the spin correlated states, but the entanglement evolves without any discontinuity or decays asymptotically for the spin anti-correlated states. We consider the evolution of an initial entanglement encoded in the spin anti-correlated states and demonstrate that the asymptotic behavior predicted before occurs only in the weak coupling limit or equivalently when the rotating-wave approximation (RWA) is made on the interaction Hamiltonian of the qubits with the field. If we do not restrict ourselves to the RWA, we find that the entanglement undergoes a discontinuity, the sudden death phenomenon. We illustrate this behavior by employing an efficient scheme for entanglement evolution between two cold-trapped atoms located inside a single-mode cavity. Although only a single excitation is initially present in the system, we find that the two-photon excited state, which plays the key role for the discontinuity in the behavior of the entanglement, gains a population over a short time of the evolution. When the RWA is made on the interaction, the two-photon excited state remains unpopulated for all times and the discontinuity is absent. We attribute this phenomenon to the principle of complementarity between the evolution time and energy, and the presence of the counter-rotating terms in the interaction Hamiltonian.

quant-ph↗

arXiv2007

Non-local dynamics of Bell states in separate cavities

We present non-local dynamics of Bell states in separate cavities. It is demonstrated that (i) the entanglement damping speed will saturate when the cavity leakage rate $γ\geq 0.4$; (ii) the synchronism relationship between the fidelity and the concurrence depends on the initial state; (iii) if the initial state is $1/\sqrt{2}(|01>+|10>)$, the dynamics of entropy is opposite to that of fidelity.

quant-ph↗

arXiv2007

Dynamics of two qubits in a spin-bath of Quantum anisotropic Heisenberg XY coupling type

The dynamics of two 1/2-spin qubits under the influence of a quantum Heisenberg XY type spin-bath is studied. After the Holstein-Primakoff transformation, a novel numerical polynomial scheme is used to give the time-evolution calculation of the center qubits initially prepared in a product state or a Bell state. Then the concurrence of the two qubits, the $z$-component moment of either of the subsystem spins and the fidelity of the subsystem are shown, which exhibit sensitive dependence on the anisotropic parameter, the temperature, the coupling strength and the initial state. It is found that (i) the larger the anisotropic parameter $γ$, the bigger the probability of maintaining the initial state of the two qubits; (ii) with increasing temperature $T$, the bath plays a more strong destroy effect on the dynamics of the subsystem, so does the interaction $g_0$ between the subsystem and the bath; (iii) the time evolution of the subsystem is dependent on the initial state. The revival of the concurrence does not always means the restore of the state. Further, the dynamical properties of the subsystem should be judged by the combination of concurrence and fidelity.

cond-mat.stat-mech↗

arXiv2007

Quantum dynamics of double-qubits in a spin star lattice with an XY interaction

The dynamics of two coupled spins-1/2 interacting with a spin-bath via the quantum Heisenberg XY coupling is studied. The pair of central spins served as a quantum open subsystem are initially prepared in two types of states: the product states and the Bell states. The bath, which consists of $N$ (in the thermodynamic limit $N\to\infty$) mutually coupled spins-1/2, is in a thermal state at the beginning. By the Holstein-Primakoff transformation, the model can be treated effectively as two spin qubits embedded in a single mode cavity. The time-evolution of the purity, z-component summation and the concurrence of the central spins can be determined by a Laguerre polynomial scheme. It is found that (i) at a low temperature, the uncoupled subsystem in a product state can be entangled due to the interaction with bath, which is tested by the Peres-Horodecki separability; however, at a high temperature, the bath produces a stronger destroy effect on the purity and entanglement of the subsystem; (ii) when the coupling strength between the two central spins is large, they are protected strongly against the bath; (iii) when the interaction between the subsystem and the bath is strong, the collapse of the two spin qubits from their initial entangled state is fast.

quant-ph↗

arXiv2007

Controllable dynamics of two separate qubits in Bell states

The dynamics of entanglement and fidelity for a subsystem of two separate spin-1/2 qubits prepared in Bell states is investigated. One of the subsystem qubit labelled $A$ is under the influence of a Heisenberg XY spin-bath, while another one labelled $B$ is uncoupled with that. We discuss two cases: (i) the number of bath spins $N\to\infty$; (ii) $N$ is finite: N=40. In both cases, the bath is initially prepared in a thermal equilibrium state. It is shown that the time dependence of the concurrence and the fidelity of the two subsystem qubits can be controlled by tuning the parameters of the spin-bath, such as the anisotropic parameter, the temperature and the coupling strength with qubit $A$. It is interesting to find the dynamics of the concurrence is independent of four different initial Bell states and that of the fidelity is divided into two groups.

quant-ph↗

arXiv2006

Polynomial scheme for time evolution of open and closed quantum systems

Based on the generation function of Laguerre polynomials, We proposed a new Laguerre polynomial expansion scheme in the calculation of evolution of time dependent Schrödinger equation. Theoretical analysis and numerical test show that the method is equally as good as Chebyshev polynomial expansion method in efficiency and accuracy, with extra merits that no scaling to Hamiltonian is needed and wider suitability.

quant-ph↗

arXiv2006

Entanglement evolution for excitons of two separate quantum dots in a cavity driven by magnetic field

The time evolution of entanglement for excitons in two quantum dots embedded in a single mode cavity is studied in a ``spin-boson'' regime. It is found that although with the dissipation from the boson mode, the excitons in the two quantum dots can be entangled by only modulating their energy bias $ε$ under the influence of external driving magnetic field. Initially, the two excitons are prepared in a pure separate state. When the time-dependent magnetic field is switched on, a highly entangled state is produced and maintained even in a very long time interval. The mechanism may be used to control the quantum devices in practical applications.

quant-ph↗

arXiv2006

Level crossing and quantum phase transition of the XY model

The ground state of a one-dimensional spin-1/2 chain with periodical boundary condition in the Heisenberg XY model is investigated. We consider the spatial correlation and concurrence between any nearest-neighbor pair of spins under the conditions of different coupling strength, anisotropic parameter and magnitude of a transverse field. Quantum phase transitions due to the competition between coupling and alignment which cause the abrupt changes of the correlation and concurrence are observed. The transition are direct results of the level crossing.

quant-ph↗

arXiv2006

Suppression of decoherence by bath ordering

The dynamics of two coupled spins-1/2 coupled to a spin-bath is studied as an extended model of the Tessieri-Wilkie Hamiltonian \cite{TWmodel}. The pair of spins served as an open subsystem were prepared in one of the Bell states and the bath consisted of some spins-1/2 is in a thermal equilibrium state from the very beginning. It is found that with the increasing the coupling strength of the bath spins, the bath forms a resonant antiferromagnetic order. The polarization correlation between the two spins of the subsystem and the concurrence are recovered in some extent to the isolated subsystem. This suppression of the subsystem decoherence may be used to control the quantum devices in practical applications.

quant-ph↗