Quantum phase sensing with states out of thermal equilibrium

TL;DR

This paper explores how non-thermal quantum states can enhance phase sensing precision in interferometry, establishing fundamental limits and applying to various quantum systems.

Contribution

It introduces a framework linking athermality of quantum states to phase sensitivity and derives fundamental sensing limits under energy conservation.

Findings

Athermality improves phase sensitivity in quantum interferometry.

Established fundamental precision bounds for energy-conserving interactions.

Applied techniques to both finite-dimensional and linear quantum optical systems.

Abstract

Interferometry can be viewed generally as the measurement of a relative phase between two subsystems. I consider the problem of interfering a quantum resource state with a thermal bath, drawing a precise connection between the athermality of the resource and the resulting phase sensitivity. This is done by finding the fundamental sensing precision limit under the minimal conditions of global unitarity and energy conservation. The results here apply both to general finite-dimensional systems and to linear quantum optics. The same techniques further upper-bound the speed at which a system and bath can jointly evolve under an energy-conserving interaction.