Improved Superconducting Qubit Readout by Qubit-Induced Nonlinearities

TL;DR

This paper proposes leveraging qubit-induced nonlinearities in dispersive readout to enhance signal-to-noise ratio, especially in systems with many energy levels, improving measurement fidelity.

Contribution

It introduces a regime where qubit nonlinearity boosts SNR and explains recent high-fidelity measurements using this physics.

Findings

Existence of a regime where nonlinearity increases SNR

Analytical model accounting for high-fidelity avalanche measurements

Reconciliation of nonlinearity effects with improved readout fidelity

Abstract

In dispersive readout schemes, qubit-induced nonlinearity typically limits the measurement fidelity by reducing the signal-to-noise ratio (SNR) when the measurement power is increased. Contrary to seeing the nonlinearity as a problem, here we propose to use it to our advantage in a regime where it can increase the SNR. We show analytically that such a regime exists if the qubit has a many-level structure. We also show how this physics can account for the high-fidelity avalanchelike measurement recently reported by Reed {\it et al.} [arXiv:1004.4323v1].