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Active protection of a superconducting qubit with an interferometric Josephson isolator



Baleegh Abdo, Nicholas T. Bronn, Oblesh Jinka, Salvatore B. Olivadese, Antonio D. Corcoles, Vivekananda P. Adiga, Markus Brink, Russell Lake, Xian Wu, David P. Pappas, Jerry M. Chow


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 T2E when the Josephson-based isolator is turned on. Such a moderate degradation can be mitigated by minimizing heat dissipation in the pump lines.
Nature Communications


quantum information, amplifiers, circulators, isolators, non-reciprocal devices, microwave, high-fidelity, signals, cryogenic, magnetic materials, fields, nondegenerate Josephson mixers, interferometric scheme, superconducting qubit setup


Abdo, B. , Bronn, N. , Jinka, O. , Olivadese, S. , Corcoles, A. , Adiga, V. , Brink, M. , Lake, R. , Wu, X. , Pappas, D. and Chow, J. (2019), Active protection of a superconducting qubit with an interferometric Josephson isolator, Nature Communications, [online],, (Accessed April 14, 2024)
Created July 16, 2019, Updated October 12, 2021