Quantum enhanced estimation of optical detector efficiencies

TL;DR

This paper investigates the fundamental limits of estimating detector efficiencies in quantum photonics, revealing a transition in optimal probe states depending on loss levels, with practical implications for quantum measurement precision.

Contribution

It demonstrates that optimal probe states for detector efficiency estimation differ from those for quantum channel loss, identifying a crossover based on loss parameter and providing explicit results for common detectors.

Findings

Fock states are optimal for quantum channel loss estimation.

Optimal probe states for detector efficiency vary with loss levels.

Explicit results for on-off and homodyne detectors are provided.

Abstract

Quantum mechanics establishes the ultimate limit to the scaling of the precision on any parameter, by iden- tifying optimal probe states and measurements. While this paradigm is, at least in principle, adequate for the metrology of quantum channels involving the estimation of phase and loss parameters, we show that estimat- ing the loss parameters associated with a quantum channel and a realistic quantum detector are fundamentally different. While Fock states are provably optimal for the former, we identify a crossover in the nature of the optimal probe state for estimating detector imperfections as a function of the loss parameter. We provide explicit results for on-off and homodyne detectors, the most widely used detectors in quantum photonics technologies.