Length scale estimation of excited quantum oscillators

TL;DR

This paper investigates quantum estimation of the length scale parameter in massive quantum oscillators, demonstrating Heisenberg scaling with excitation number and entanglement, and proposing optimal measurement strategies for high-precision sensing.

Contribution

It introduces quantum estimation methods for the length scale parameter, showing Heisenberg scaling and entanglement-enhanced sensitivity in massive quantum oscillators.

Findings

Displaced squeezed states achieve Heisenberg scaling for length scale estimation.

Entangled states of two oscillators boost sensitivity similarly to adding a third oscillator.

N-oscillator states exhibit Heisenberg scaling with total energy.

Abstract

Massive quantum oscillators are finding increasing applications in proposals for high-precision quantum sensors and interferometric detection of weak forces. Although optimal estimation of certain properties of massive quantum oscillators such as phase shifts and displacements have strict counterparts in the theory of quantum estimation of the electromagnetic field, the phase space anisotropy of the massive oscillator is characterized by a length scale parameter that is an independent target for quantum estimation methods. We show that displaced squeezed states and excited eigenstates of a massive oscillator exhibit Heisenberg scaling of the quantum Fisher information for the length scale with respect to excitation number, and discuss asymptotically unbiased and efficient estimation allowing to achieve the predicted sensitivity. We construct a sequence of entangled states of two massive oscillators that provides a boost in length scale sensitivity equivalent to appending a third massive oscillator to a non-entangled system, and a state of $N$ oscillators exhibiting Heisenberg scaling with respect to the total energy.