Zhiguo Lü

Breakdown of the rotating-wave approximation in the description of entanglement of spin-anticorrelated 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 from that encoded in states with the anticorrelated 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-anticorrelated states. We consider the evolution of an initial entanglement encoded in the spin-anticorrelated 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.

Non-Markovian dynamical effects and time evolution of the entanglement entropy of a dissipative two-state system

We investigate the dynamical information exchange between a two-state system and its environment which is measured by the von Neumann entropy. It is found that in the underdamping regime, the entropy dynamics exhibits an extremely non-Markovian oscillation-hump feature, in which oscillations manifest quantum coherence and a hump of envelop demonstrates temporal memory of bath. It indicates that the process of entropy exchange is bidirectional. When the coupling strength increases up to a certain threshold, the hump along with ripple disappears, which is indicative of the coherent-incoherent dynamical crossover. The long-time limit of entropy evolution reaches the ground-state value which agrees with that of the numerical renormalization group.

Dynamics of two qubits in a spin bath with anisotropic X Y coupling

The dynamics of two

Sub-Ohmic spin-boson model with off-diagonal coupling: Ground state properties

1∕2

Influence of temperature on coherent dynamics of a two-level system immersed in a dissipative spin bath

-spin qubits under the influence of a quantum Heisenberg

Position-dependent dynamics of two qubits in a leakage cavity

XY

Quantum Zeno and anti-Zeno effects in open quantum systems

-type spin-bath is studied. After the Holstein-Primakoff transformation, 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

Quantum critical point of spin-boson model and infrared catastrophe in bosonic bath.

z

Role of the counter-rotating terms in the creation of entanglement between two atoms

-component moment of either of the subsystem spins, and the fidelity of the subsystem are shown; they 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

Bias-modulated dynamics of a strongly driven two-level system

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