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Resonant Readout of a Persistent Current Qubit

Janice C. Lee·William D. Oliver·Terry P. Orlando·Karl K. Berggren
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Abstract

We have implemented a resonant circuit that uses a SQUID as a flux-sensitive Josephson inductor for qubit readout. In contrast to the conventional switching current measurement that generates undesired quasi-particles when the SQUID switches to the voltage state, our approach keeps the readout SQUID biased along the supercurrent branch during the measurement. By incorporating the SQUID inductor in a high-Q resonant circuit, we can distinguish the two flux states of a niobium persistent-current (PC) qubit by observing a shift in the resonant frequency of both the magnitude and the phase spectra. The readout circuit was also characterized in the nonlinear regime to investigate its potential use as a nonlinear amplifier.

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Janice C. Lee, William D. Oliver, Terry P. Orlando, Karl K. Berggren. 2005-01-12. Resonant Readout of a Persistent Current Qubit. https://doi.org/10.1109/tasc.2005.850077

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