Fast, Lifetime-Preserving Readout for High-Coherence Quantum Annealers
Jeffrey A. Grover, James I. Basham, Alexander Marakov +15 more
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 μs.This combination of speed and isolation is critical to the readout of high-coherence quantum annealers.
arXiv:2006.10817•PRX Quantum•Nov 19, 2020•15 citations