2020/06/30 by Jeffrey A. Grover, James I. Basham, Alexander Marakov +24
Computer Science · Physics and Astronomy · #Coherence (philosophical gambling strategy) #Computer science #Physics #Quantum #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum and electron transport phenomena #Quantum mechanics #quant-ph
paper · pdf · doi:10.1103/prxquantum.1.020314
published as PRX Quantum 1, 020314 (2020) · 14 pages, 11 figures; version accepted for publication in PRX Quantum
arxiv created 2020/11/19 · openalex publication_date 2020/11/19 · arxiv updated 2022/02/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We demonstrate, for the first time, that a quantum flux parametron (QFP) is capable of acting as both isolator and amplifier in the readout circuit of a capacitively shunted flux qubit (CSFQ). By treating the QFP like a tunable coupler and biasing it such that the coupling is off, we show that T 1 of the CSFQ is not impacted by Purcell loss from its low-Q readout resonator (Q e = 760) despite being detuned by only 40 MHz. When annealed, the QFP amplifies the qubit's persistent current signal such that it generates a flux qubit-state-dependent frequency shift of 85 MHz in the readout resonator, which is over 9 times its linewidth. The device is shown to read out a flux qubit in the persistent current basis with fidelities surpassing 98.6% with only 80 ns integration, and reaches fidelities of 99.6% when integrated for 1 s. This combination of speed and isolation is critical to the readout of high-coherence quantum annealers.