Fundamental quantum interferometry bound for the squeezed-light-enhanced gravitational-wave detector GEO600

TL;DR

This paper establishes a fundamental quantum interferometry bound for gravitational-wave detectors and shows GEO600's current sensitivity is near this limit, confirming the optimality of its quantum state strategy.

Contribution

Theoretical demonstration of the quantum interferometry bound for gravitational-wave detectors and validation that GEO600's current approach is near optimal.

Findings

GEO600's sensitivity is close to the fundamental quantum limit.

The combination of a bright coherent state and squeezed vacuum is optimal.

More complex quantum states would not significantly improve sensitivity.

Abstract

The fundamental quantum interferometry bound limits the sensitivity of an interferometer for a given total rate of photons and for a given decoherence rate inside the measurement device.We theoretically show that the recently reported quantum-noise limited sensitivity of the squeezed-light-enhanced gravitational-wave detector GEO600 is exceedingly close to this bound, given the present amount of optical loss. Furthermore, our result proves that the employed combination of a bright coherent state and a squeezed vacuum state is generally the optimum practical approach for phase estimation with high precision on absolute scales. Based on our analysis we conclude that neither the application of Fock states nor N00N states or any other sophisticated nonclassical quantum states would have yielded an appreciably higher quantum-noise limited sensitivity.