High-contrast dispersive readout of a superconducting flux qubit using a nonlinear resonator

TL;DR

This paper presents a method for high-contrast, high-sensitivity detection of a superconducting flux qubit using a nonlinear resonator, achieving 87% contrast and demonstrating effective state measurement with minimal loss.

Contribution

The work introduces a nonlinear resonator-based detection technique that enables high-contrast, sensitive qubit readout with bistable operation and intrinsic latching capabilities.

Findings

Achieved 87% contrast in Rabi oscillation detection.

Demonstrated bistable operation for enhanced sensitivity.

Confirmed qubit state preparation through consecutive measurements.

Abstract

We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realized by probing the microwave transmission of a nonlinear resonator, based on a SQUID. Depending on the driving strength of the resonator, the detector can be operated in the monostable or the bistable mode. The bistable operation combines high-sensitivity with intrinsic latching. The measured contrast of Rabi oscillations is as high as 87 %; of the missing 13 %, only 3 % is unaccounted for. Experiments involving two consecutive detection pulses are consistent with preparation of the qubit state by the first measurement.