Fast high-fidelity charge readout by operating the cavity-embedded Cooper pair transistor in the Kerr bistable regime

TL;DR

This paper demonstrates a fast, high-fidelity charge readout method using a cavity-embedded Cooper pair transistor in the Kerr bistable regime, achieving single-shot resolution with low photon numbers and analyzing switching dynamics.

Contribution

It introduces a novel charge readout technique leveraging Kerr bistability in the cCPT, with detailed empirical analysis of switching behavior and low photon operation.

Findings

Achieved 94% fidelity in 3 microseconds for charge state discrimination.

Operated with only 20 intracavity photons, much fewer than traditional rf-SETs.

Identified spontaneous fluctuation-induced switching as the main limiting factor.

Abstract

Operating the cavity-embedded Cooper pair transistor (cCPT) in the Kerr bistable regime, we demonstrate single-shot resolution between two charge states that are $0.09e$ apart. The measurement is performed with 94$\%$ fidelity in a duration of 3 $\mu$s. The drive power at which the measurement is performed corresponds to only 20 intracavity photons on average in the high oscillation amplitude state of the cCPT, which is orders-of-magnitude smaller than that in rf-SETs. We find that the limiting factor for this mode of operation of the cCPT is the spontaneous fluctuation-induced switching between the two metastable oscillation amplitude states. We present empirical data on the variation of the switching dynamics with drive parameters and cCPT DC bias.