Maximizing information on the environment by dynamically controlled qubit probes

TL;DR

This paper develops a method to optimize dynamical control of qubit probes for precise environmental parameter estimation, achieving fundamental accuracy bounds with minimal measurements, demonstrated on nitrogen-vacancy centers in diamond.

Contribution

It analytically derives the ultimate precision bounds for estimating environmental parameters using controlled qubit probes, integrating quantum estimation theory with dynamical control strategies.

Findings

Optimal control protocols reach the fundamental precision bounds.

Minimal measurements suffice for maximal estimation accuracy.

Application demonstrated on nitrogen-vacancy centers in diamond.

Abstract

We explore the ability of a qubit probe to characterize unknown parameters of its environment. By resorting to quantum estimation theory, we analytically find the ultimate bound on the precision of estimating key parameters of a broad class of ubiquitous environmental noises ("baths") which the qubit may probe. These include the probe-bath coupling strength, the correlation time of generic bath spectra, the power laws governing these spectra, as well as their dephasing times T2. Our central result is that by optimizing the dynamical control on the probe under realistic constraints one may attain the maximal accuracy bound on the estimation of these parameters by the least number of measurements possible. Applications of this protocol that combines dynamical control and estimation theory tools to quantum sensing are illustrated for a nitrogen-vacancy center in diamond used as a probe.