Quantum Nondemolition Measurement of a Kicked Qubit

TL;DR

This paper introduces a quantum nondemolition measurement method for a kicked qubit system, enabling reduced back-action and improved measurement fidelity by tuning the waiting time to the qubit's oscillation period.

Contribution

It presents a novel measurement scheme using a kicked two-state system that enhances measurement quality and minimizes back-action compared to traditional methods.

Findings

Nondemolition measurement can slow relaxation of diagonal density matrix elements.

The scheme avoids detector back-action, improving measurement fidelity.

Large signal-to-noise ratio is achievable with the proposed method.

Abstract

We propose a quantum nondemolition measurement using a kicked two-state system (qubit). By tuning the waiting time between kicks to be the qubit oscillation period, the kicking apparatus performs a nondemolition measurement. While dephasing is unavoidable, the nondemolition measurement can (1) slow relaxation of diagonal density matrix elements, (2) avoid detector back-action, and (3) allow for a large signal-to-noise ratio. Deviations from the ideal behavior are studied by allowing for detuning of the waiting time, as well as finite-time, noisy pulses. The scheme is illustrated with a double-dot qubit measured by a gate-pulsed quantum point contact.