Undoing measurement-induced dephasing in circuit QED

TL;DR

This paper demonstrates that measurement-induced dephasing in circuit QED can be completely reversed if the measurement signal is fully considered, enabling perfect quantum measurements and improved qubit control.

Contribution

It shows that backaction from homodyne and photodetection can be perfectly undone, enabling high-fidelity quantum measurements in circuit QED.

Findings

Backaction causes stochastic phase rotations leading to dephasing.

Complete reversal of measurement backaction is theoretically achievable.

Experimental parameters are within current technological capabilities.

Abstract

We analyze the backaction of homodyne detection and photodetection on superconducting qubits in circuit quantum electrodynamics. Although both measurement schemes give rise to backaction in the form of stochastic phase rotations, which leads to dephasing, we show that this can be perfectly undone provided that the measurement signal is fully accounted for. This result improves upon that of Phys. Rev. A, 82, 012329 (2010), showing that the method suggested can be made to realize a perfect two-qubit parity measurement. We propose a benchmarking experiment on a single qubit to demonstrate the method using homodyne detection. By analyzing the limited measurement efficiency of the detector and bandwidth of the amplifier, we show that the parameter values necessary to see the effect are within the limits of existing technology.