Robust Adaptive measurement for qubit state preparation

TL;DR

This paper introduces a robust adaptive measurement scheme for qubit state preparation that maintains effectiveness under unknown unitary evolution by adaptively adjusting measurements to ensure convergence to the target state.

Contribution

It proposes an alternative adaptive measurement method that remains robust despite uncertainties in the qubit's unitary evolution, with constant measurement strength.

Findings

The scheme converges reliably to the target state.

It maintains robustness against unknown unitary dynamics.

Constant measurement strength simplifies implementation.

Abstract

This paper reconsiders the method of adaptive measurement for qubit state preparation developed by Jacobs and shows an alternative scheme that works even under unknown unitary evolution of the state. The key idea is that the measurement is adaptively changed so that one of the eigenstates of the measured observable is always set between the current and the target states at while that eigenstate converges to the target. The most significant feature of this scheme is that the measurement strength can be taken constant unlike Jacobs' one, which eventually provides fine robustness property of the controlled state against the uncertainty of the unitary evolution.