Abdo Baleegh, Bronn Nicholas T, Jinka Oblesh, Olivadese Salvatore, Córcoles Antonio D, Adiga Vivekananda P, Brink Markus, Lake Russell E, Wu Xian, Pappas David P, Chow Jerry M
IBM T. J. Watson Research Center, Yorktown Heights, New York, NY, 10598, USA.
National Institute of Standards and Technology, Boulder, CO, 80305, USA.
Nat Commun. 2019 Jul 17;10(1):3154. doi: 10.1038/s41467-019-11101-3.
Nonreciprocal microwave devices play critical roles in high-fidelity, quantum-nondemolition (QND) measurement schemes. They impose unidirectional routing of readout signals and protect the quantum systems from unwanted noise originated by the output chain. However, cryogenic circulators and isolators are disadvantageous in scalable superconducting architectures because they use magnetic materials and strong magnetic fields. Here, we realize an active isolator formed by coupling two nondegenerate Josephson mixers in an interferometric scheme and driving them with phase-shifted, same-frequency pumps. By incorporating our Josephson-based isolator into a superconducting qubit setup, we demonstrate fast, high-fidelity, QND measurements of the qubit while providing 20 dB of protection within a bandwidth of 10 MHz against amplified noise reflected off the Josephson amplifier in the output chain. A moderate reduction of 35% is observed in T when the Josephson-based isolator is turned on. Such a moderate degradation can be mitigated by minimizing heat dissipation in the pump lines.
非互易微波器件在高保真量子非破坏（QND）测量方案中起着关键作用。它们实现读出信号的单向路由，并保护量子系统免受输出链产生的有害噪声影响。然而，低温循环器和隔离器在可扩展超导架构中存在劣势，因为它们使用磁性材料和强磁场。在此，我们通过在干涉测量方案中耦合两个非简并约瑟夫森混频器并用相移、同频泵浦驱动它们，实现了一种有源隔离器。通过将基于约瑟夫森的隔离器集成到超导量子比特装置中，我们展示了对量子比特的快速、高保真QND测量，同时在10 MHz带宽内提供20 dB的保护，以抵御输出链中约瑟夫森放大器反射的放大噪声。当基于约瑟夫森的隔离器开启时，观察到T有35%的适度降低。通过最小化泵浦线路中的热耗散，可以减轻这种适度的性能下降。
