2020/06/30 by Baleegh Abdo, Oblesh Jinka, Nicholas T. Bronn +2
Engineering · Physics and Astronomy · #Amplifier #CMOS #Electrical engineering #Electronic engineering #Engineering #Magneto-Optical Properties and Applications #Optoelectronics #Phase qubit #Physics #Physics of Superconductivity and Magnetism #Quantum #Quantum and electron transport phenomena #Qubit #cond-mat.supr-con #quant-ph
paper · pdf · doi:10.1103/prxquantum.2.040360
published as PRX Quantum 2, 040360 (2021) · Revised and enhanced manuscript that includes new experimental results
arxiv created 2021/09/29 · openalex publication_date 2021/12/28 · arxiv updated 2021/12/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Nonreciprocal microwave devices, such as circulators and isolators, are needed in high-fidelity qubit readout schemes to unidirectionally route the readout signals and protect the qubits against noise coming from the output chain. However, cryogenic circulators and isolators are prohibitive in scalable superconducting architectures because they rely on magnetic materials. Here we report a fast (750 ns) high-fidelity (95%) quantum nondemolition readout of a coherent superconducting qubit (T 1 = 52 s, T 2E = 35 s) without any nonreciprocal magnetic devices. We use in our readout chain a microwave-controlled qubit readout multichip module (QRMCM) that integrates interferometric directional Josephson devices consisting of an isolator and a reconfigurable isolator or amplifier device, and an off-chip low-pass filter. Using the QRMCM, we demonstrate isolation up to 45 dB within 13 MHz, when both directional devices are operated as isolators, and low-noise amplification in excess of 10 dB within a dynamical bandwidth of 10 MHz, when the reconfigurable device is operated as an amplifier. We also investigate the dependence of the qubit coherence times T and T 2E on the isolation response of the QRMCM, which we control in situ using the microwave drives feeding the isolators. Furthermore, by directly comparing the QRMCM performance with that of a state-of-art configuration (with T 2E 2T 1 ) that uses a pair of wideband magnetic isolators, we find that the excess pure dephasing measured with the QRMCM (for which T 2E T 1 ) is likely limited by the residual thermal photon population in the readout resonator. Improved versions of the QRMCM could replace magnetic circulators and isolators in large superconducting quantum processors.