采用纵向和横向耦合超导电路的多输出微波单光子源
Multi-output microwave single-photon source using superconducting circuits with longitudinal and transverse couplings
摘要：
微波频率下的单光子器件对于微波区域中的量子信息处理和通信的应用是重要的。在这项工作中，我们描述了一个多输出单光子器件的建议。我们考虑两个超导谐振器耦合到一个间隙可调量子比特通过其纵向和横向的自由度。因此，这种量子位-谐振器耦合不同于Jaynes-Cummings模型描述的标准电路量子电动力学系统中的耦合。我们证明了一个有效的二次耦合之间的正常模式和量子比特可以诱导，这种诱导的二阶非线性比传统的克尔型系统表现出光子封锁大得多。假设耦合简正模是共振驱动的，我们观察到从谐振腔的输出场表现出很强的亚泊松光子数统计和光子反聚束。与以前对共振光子封锁的研究相反，我们的器件的第一激发态是纯单光子Fock态而不是极化激元态，即，一种高度杂化的量子比特光子态此外，还发现强量子比特非线性效应引起的光态截断会导致两个谐振腔之间的纠缠，即使在马尔可夫近似下处于稳态时也是如此.
英文摘要：
Single-photon devices at microwave frequencies are important for applications in quantum information processing and communication in the microwave regime. In this work, we describe a proposal of a multi-output single-photon device. We consider two superconducting resonators coupled to a gap-tunable qubit via both its longitudinal and transverse degrees of freedom. Thus, this qubit-resonator coupling differs from the coupling in standard circuit quantum-electrodynamic systems described by the Jaynes-Cummings model. We demonstrate that an effective quadratic coupling between one of the normal modes and the qubit can be induced, and this induced second-order nonlinearity is much larger than that for conventional Kerr-type systems exhibiting photon blockade. Assuming that a coupled normal mode is resonantly driven, we observe that the output fields from the resonators exhibit strong sub-Poissonian photon-number statistics and photon antibunching. Contrary to previous studies on resonant photon blockade, the first-excited state of our device is a pure single-photon Fock state rather than a polariton state, i.e., a highly hybridized qubit-photon state. In addition, it is found that the optical state truncation caused by the strong qubit-induced nonlinearity can lead to an entanglement between the two resonators, even in their steady state under the Markov approximation.
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