First-order quantum phase transition and entanglement in the Jaynes-Cummings model with a squeezed light

We study the quantum phase transition and entanglement in the Jaynes-Cummings model with squeezed light,utilize a special transformation method to obtain the analytical ground state of the model within the near-resonance regime,and numerically verify the validity of the analytical ground state.It is found that the ground state exhibits a first-order quantum phase transition at the critical point linearly induced by squeezed light,and the ground state entanglement reaches its maximum when the qubit-field coupling strength is large enough at the critical point.

Engineering steady-state entanglement for two atoms held in separate cavities through laser cooling

We propose a scheme to prepare the steady-state entanglement for two atoms, which are held in separate cavities that are coupled through a short optical fiber or optical resonator. The entangled steady-state with a high fidelity can be achieved even with a low cooperativity parameter, by making use of the driving laser fields. Such a cooling mechanism is based on a resonant laser pump of the unwanted ground states to the excited states, which finally decay to the desired steady-state.

宏观场与环境作用过程中的纠缠突然死亡与突然产生

研究了两个初始处于纠缠相干态上的宏观场各自独立地与一个环境相互作用的系统,环境对腔场的影响只体现在腔场光子数的泄漏上.采用共生纠缠(concurrence)度量两个宏观场间的纠缠,并给出宏观场纠缠的解析解,以分析这种系统中宏观场纠缠的动力学特性.研究表明当场的初始平均光子数较大时,即使很小的光子泄漏率也会导致腔场间出现纠缠突然死亡现象.同时研究结果也表明光子从腔场泄漏到环境后会导致两环境间的纠缠突然产生,而这种纠缠产生的时机直接与腔场的初始光子数相关.本文还进一步发现在大光子数的情况下,在任何时刻任意一个腔场与任意一个环境间都不会产生纠缠.

Non-Geometric Conditional Phase Gate by Quantum Zeno Dynamics in Laser-Excited Nitrogen-Vacancy Centers

Based on the quantum Zeno dynamics,we propose a two-qubit non-geometric conditional phase gate between two nitrogen-vacancy centers coupled to a whispering-gallery mode cavity.The varying phases design of periodic laser can be used for realizing non-geometric conditional phase gate,and the cavity mode is virtually excited during the gate operation.Thus,the fidelity of the gate operation is insensitive to cavity decay and the fluctuation of the preset laser intensity.The numerical simulation with a realistic set of experimental parameters shows that the gate fidelity 0.987 can be within reached in the near future.

基于离散与连续变量系统的混合纠缠态的非局域关联性

研究离散变量与连续变量系统在纠缠态下的非局域关联性是量子信息处理中的基本理论与应用课题。对于局域隐变量理论的Bell不等式的违背可以很好地体现这些关联。在本文中,我们对量子比特自旋操作与谐振子旋转宇称操作进行联合测量,研究了量子比特与谐振子相干态的纠缠对Bell不等式的影响,并且证明,当量子比特与谐振子之间的纠缠接近最大值时,二者的非局域关联几乎最大限度地违背了Bell不等式。之后通过对Mermin-Klyshko不等式的违背,进一步研究了一个或多个比特与两个谐振子相干态纠缠的系统的非局域关联性。结果表明随着谐振子相干态的振幅增大,非局域性也会快速增强,同时,相干态振幅取值适中,就能使Mermin-Klyshko不等式接近最大违背。