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arXiv · 2006.10817

Fast, Lifetime-Preserving Readout for High-Coherence Quantum Annealers

Jeffrey A. Grover·James I. Basham·Alexander Marakov·Steven M. Disseler·Robert T. Hinkey·Moe Khalil·Zachary A. Stegen·Thomas Chamberlin·Wade DeGottardi·David J. Clarke·James R. Medford·Joel D. Strand·Micah J. A. Stoutimore·Sergey Novikov·David G. Ferguson·Daniel Lidar·Kenneth M. Zick·Anthony J. Przybysz
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Abstract

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 $1$ $\mu$s. This combination of speed and isolation is critical to the readout of high-coherence quantum annealers.

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Jeffrey A. Grover, James I. Basham, Alexander Marakov, Steven M. Disseler, Robert T. Hinkey, Moe Khalil, Zachary A. Stegen, Thomas Chamberlin, Wade DeGottardi, David J. Clarke, James R. Medford, Joel D. Strand, Micah J. A. Stoutimore, Sergey Novikov, David G. Ferguson, Daniel Lidar, Kenneth M. Zick, Anthony J. Przybysz. 2020-06-18. Fast, Lifetime-Preserving Readout for High-Coherence Quantum Annealers. https://doi.org/10.1103/prxquantum.1.020314

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