Active resonator reset in the nonlinear dispersive regime of circuit QED

TL;DR

This paper introduces two optimized pulse schemes for actively removing measurement photons in the nonlinear dispersive regime of circuit QED, significantly reducing depletion time and improving quantum error detection fidelity.

Contribution

It develops and compares digital feedback and unconditional pulse schemes for photon depletion, optimized via numerical methods in a nonlinear regime where analytic solutions are unavailable.

Findings

Depletion time reduced by over six inverse resonator linewidths.

Increased mean cycles before spurious error detection from 1 to 75.

Enhanced quantum parity check performance in a repetition code.

Abstract

We present two pulse schemes for actively depleting measurement photons from a readout resonator in the nonlinear dispersive regime of circuit QED. One method uses digital feedback conditioned on the measurement outcome while the other is unconditional. In the absence of analytic forms and symmetries to exploit in this nonlinear regime, the depletion pulses are numerically optimized using the Powell method. We shorten the photon depletion time by more than six inverse resonator linewidths compared to passive depletion by waiting. We quantify the benefit by emulating an ancilla qubit performing repeated quantum parity checks in a repetition code. Fast depletion increases the mean number of cycles to a spurious error detection event from order 1 to 75 at a 1 microsecond cycle time.