Spin bath narrowing with adaptive parameter estimation

TL;DR

This paper introduces an adaptive measurement scheme that reaches quantum-limited parameter estimation, robust against errors, and applicable to solid-state spin systems to enhance sensor coherence by narrowing the spin bath.

Contribution

The paper proposes a robust adaptive measurement protocol for quantum parameter estimation that can be applied to solid-state spins, improving sensor performance.

Findings

Achieves quantum-limited estimation with adaptive strategy.

Robust against readout errors in solid-state systems.

Reduces spin bath entropy, extending sensor coherence.

Abstract

We present a measurement scheme capable of achieving the quantum limit of parameter estimation using an adaptive strategy that minimizes the parameter's variance at each step. The adaptive rule we propose makes the scheme robust against errors, in particular imperfect readouts, a critical requirement to extend adaptive schemes from quantum optics to solid-state sensors. Thanks to recent advances in single-shot readout capabilities for electronic spins in the solid state (such as Nitrogen Vacancy centers in diamond), this scheme can be as well applied to estimate the polarization of a spin bath coupled to the sensor spin. In turns, the measurement process decreases the entropy of the spin bath resulting in longer coherence times of the sensor spin.