Nonclassicality of open circuit QED systems in the deep-strong coupling regime
Nonclassicality of open circuit QED systems in the deep-strong coupling regime
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DOI：
10.1088/1367-2630/ac2850
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发表时间：
2020-06
影响因子：
3.3
通讯作者：
Tomohiro Shitara;M. Bamba;F. Yoshihara;T. Fuse;S. Ashhab;K. Semba;K. Koshino
中科院分区：
文献类型：
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作者：
Tomohiro Shitara;M. Bamba;F. Yoshihara;T. Fuse;S. Ashhab;K. Semba;K. Koshino
我们从理论上研究了量子比特-谐振腔（Q-R）系统在深强耦合（DSC）机制下的基态如何受到与环境耦合的影响。我们采用量子比特-态相关方向位移的相干态叠加作为Q-R环境系统基态的变分近似。我们表明，约化密度矩阵的Q-R系统强烈地依赖于系统是如何耦合到环境中，即电容或电感，因为破缺的旋转对称性的DSC系统的本征态在谐振器相空间。当谐振器以不同的方式耦合到量子比特和环境时（例如，一个是电感的，另一个是电容的），系统几乎不受谐振器-波导（R-W）耦合的影响。相反，当两个耦合是相同类型的（例如，都是电感），通过增加R-W耦合强度，虚光子的平均数量增加，在Q-R纠缠基态实现的量子叠加部分退化。由于叠加态随着Q-R耦合的增加而变得更加脆弱，因此存在一个最佳耦合强度，使得Q-R系统的非经典性最大化。
We investigate theoretically how the ground state of a qubit–resonator (Q–R) system in the deep-strong coupling (DSC) regime is affected by the coupling to an environment. We employ as a variational ansatz for the ground state of the Q–R–environment system a superposition of coherent states displaced in qubit-state-dependent directions. We show that the reduced density matrix of the Q–R system strongly depends on how the system is coupled to the environment, i.e. capacitive or inductive, because of the broken rotational symmetry of the eigenstates of the DSC system in the resonator phase space. When the resonator couples to the qubit and the environment in different ways (for instance, one is inductive and the other is capacitive), the system is almost unaffected by the resonator–waveguide (R–W) coupling. In contrast, when the two couplings are of the same type (for instance, both are inductive), by increasing the R–W coupling strength, the average number of virtual photons increases and the quantum superposition realized in the Q–R entangled ground state is partially degraded. Since the superposition becomes more fragile with increasing the Q–R coupling, there exists an optimal coupling strength to maximize the nonclassicality of the Q–R system.