标题： 一种快速且大带宽的超导可变耦合器 显示英文标题

标题： A fast and large bandwidth superconducting variable coupler

摘要： 可变微波频率耦合器是经典通信系统中非常有用的组件，并且很可能在量子通信应用中发挥重要作用。传统的基于半导体的微波耦合器已被用于超导量子电路，例如通过公共读出链实现多个器件的原位测量。然而，半导体元件具有损耗，并且在切换时会耗散能量，这使得它们不适合需要快速、重复切换的低温应用。基于超导约瑟夫森结的耦合器可以设计为无耗散操作，具有快速切换能力，并且易于与超导量子电路集成。这些特性实现了芯片上的量子相干微波光子路由，为半导体开关提供了一种有吸引力的替代方案。在这里，我们提出并表征了一种基于芯片的宽带可变微波耦合器，其工作频率范围为4-8 GHz，瞬时带宽超过1.5 GHz，该耦合器基于具有两个并联约瑟夫森结的超导量子干涉装置（SQUID）。该耦合器无耗散，具有超过40 dB的大的开-关比，耦合可以在约10 ns内改变。这里提出的简单设计可以轻松集成到超导量子比特电路中，并且可以很容易地推广以实现四端口或更多端口的器件。 显示英文摘要

摘要： Variable microwave-frequency couplers are highly useful components in classical communication systems, and likely will play an important role in quantum communication applications. Conventional semiconductor-based microwave couplers have been used with superconducting quantum circuits, enabling for example the in situ measurements of multiple devices via a common readout chain. However, the semiconducting elements are lossy, and furthermore dissipate energy when switched, making them unsuitable for cryogenic applications requiring rapid, repeated switching. Superconducting Josephson junction-based couplers can be designed for dissipation-free operation with fast switching and are easily integrated with superconducting quantum circuits. These enable on-chip, quantum-coherent routing of microwave photons, providing an appealing alternative to semiconductor switches. Here, we present and characterize a chip-based broadband microwave variable coupler, tunable over 4-8 GHz with over 1.5 GHz instantaneous bandwidth, based on the superconducting quantum interference device (SQUID) with two parallel Josephson junctions. The coupler is dissipation-free, features large on-off ratios in excess of 40 dB, and the coupling can be changed in about 10 ns. The simple design presented here can be readily integrated with superconducting qubit circuits, and can be easily generalized to realize a four- or more port device.