Thermal quantum metrology in memoryless and correlated environments

TL;DR

This paper demonstrates that correlated thermal sources can be engineered to achieve or surpass the precision of pure quantum states in loss parameter estimation, even under Gaussian decoherence, enabling practical quantum metrology with thermal sources.

Contribution

It introduces a method to use correlated thermal sources for quantum metrology, challenging the notion that pure states are necessary for optimal precision.

Findings

Correlated thermal sources can approach or surpass coherent state performance.

Thermal sources with correlations are effective under Gaussian decoherence.

Practical quantum metrology can be achieved without complex quantum features.

Abstract

In bosonic quantum metrology, the estimate of a loss parameter is typically performed by means of pure states, such as coherent, squeezed or entangled states, while mixed thermal probes are discarded for their inferior performance. Here we show that thermal sources with suitable correlations can be engineered in such a way to approach, or even surpass, the error scaling of coherent states in the presence of general Gaussian decoherence. Our findings pave the way for practical quantum metrology with thermal sources in optical instruments (e.g., photometers) or at different wavelengths (e.g., far infrared, microwave or X-ray) where the generation of quantum features, such as coherence, squeezing or entanglement, may be extremely challenging.