Weakly invasive metrology: quantum advantage and physical implementations

TL;DR

This paper explores quantum-enhanced methods for estimating Hamiltonian parameters in highly photosensitive samples, demonstrating how quantum states can outperform classical strategies under damage constraints, with practical implementation in cavity QED systems.

Contribution

It introduces a quantum metrology approach that surpasses classical limits for damaged samples, including an analysis of robustness and a cavity QED implementation using superradiance.

Findings

Quantum states outperform classical coherent states in information gain.

Superradiance enhances measurement speed and efficiency.

Quantum advantage persists under realistic imperfections.

Abstract

We consider the estimation of a Hamiltonian parameter of a set of highly photosensitive samples, which are damaged after a few photons $N_{\rm abs}$ are absorbed, for a total time $T$. The samples are modelled as a two mode photonic system, where photons simultaneously acquire information on the unknown parameter and are absorbed at a fixed rate. We show that arbitrarily intense coherent states can obtain information at a rate that scales at most linearly with $N_{\rm abs}$ and $T$, whereas quantum states with finite intensity can overcome this bound. We characterise the quantum advantage as a function of $N_{\rm abs}$ and $T$, as well as its robustness to imperfections (non-ideal detectors, finite preparation and measurement rates for quantum photonic states). We discuss an implementation in cavity QED, where Fock states are both prepared and measured by coupling atomic ensembles to the cavities. We show that superradiance, arising due to a collective coupling between the cavities and the atoms, can be exploited for improving the speed and efficiency of the measurement.