Entanglement Requirements for Coherent Enhancement in Detectors

TL;DR

This paper establishes fundamental bounds linking entanglement entropy to the achievable coherent enhancement in detector sensitivity, impacting quantum metrology and scattering experiments.

Contribution

It provides general bounds on how coherent effects scale with system size based on entanglement, unifying metrology and scattering perspectives.

Findings

Bounds on quantum Fisher information limits parameter sensitivity.

Limits on scattering cross sections based on entanglement.

Scaling laws for detectable interaction strengths with system size.

Abstract

Coherent enhancement is a powerful mechanism for improving the sensitivity of a wide range of detectors, but its practical use is often limited by the difficulty of preparing the required quantum states. We show that this difficulty has a fundamental origin: coherent enhancement of a signal interacting with a detector is quantitatively constrained by entanglement. We prove general bounds on how the strength of coherent effects can scale with system size, as a function of the single-mode entanglement entropy of the detector. These bounds smoothly interpolate between the incoherent and fully coherent regimes, and apply both to parameter-estimation problems and to scattering processes. We discuss these results from two complementary perspectives: First, they appear as bounds on the quantum Fisher information of many-body states, which translate directly into limits on parameter sensitivity via the quantum Cram\'er-Rao bound. Second, they can be interpreted as limits on a class of scattering cross sections, leading to predictions for how minimum detectable interaction strengths scale with target size. Together, these results provide a unified view of coherent enhancement in metrology and scattering experiments, and motivate the development of new techniques for generating entangled detector states.