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arXiv 1302.2771quant-ph
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强耦合量子比特振子系统中的准Bell态及其在相空间中的离域

Quasi-Bell states in a strongly coupled qubit-oscillator system and their delocalization in the phase space

R. Chakrabarti, B. Virgin Jenisha

摘要:

研究了强耦合量子比特-振子系统中两体纠缠准Bell态在静态偏置下的演化,并将其推广到了超强耦合情形。利用绝热近似,得到了包含Jacobi θ函数线性组合的封闭形式的强耦合域的量子比特约化密度矩阵.振子的约化密度矩阵产生相空间Husimi Q分布。在强耦合制度的$Q$ -功能演变成均匀分离的宏观不同的高斯峰表示“小猫”状态在某些特定的时间,取决于多个时间尺度存在于相互作用的系统。对于超强耦合区域,利用Wehrl熵和量子态的复杂性研究了振子在相空间中的离域。对于小的相空间振幅,纠缠准Bell态在时间演化过程中呈现出压缩特性和光子统计的非经典性,分别用正交方差和Mandel参数来度量。

英文摘要:

We study the evolution of bipartite entangled quasi-Bell states in a strongly coupled qubit-oscillator system in the presence of a static bias, and extend it to the ultra-strong coupling regime. Using the adiabatic approximation the reduced density matrix of the qubit is obtained for the strong coupling domain in closed form that involves linear combinations of the Jacobi theta functions. The reduced density matrix of the oscillator yields the phase space Husimi Q-distribution. In the strong coupling regime the $Q$-function evolves to uniformly separated macroscopically distinct Gaussian peaks representing `kitten' states at certain specified times that depend on multiple time scales present in the interacting system. For the ultra-strong coupling realm the delocalization in the phase space of the oscillator is studied by using the Wehrl entropy and the complexity of the quantum state. For a small phase space amplitude the entangled quasi-Bell state develops, during its time evolution, squeezing property and nonclassicality of the photon statistics which are measured by the quadrature variance and the Mandel parameter, respectively.

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