Quantum improvement of time transfer between remote clocks

TL;DR

This paper introduces a quantum-enhanced scheme for time transfer between remote clocks, surpassing the Standard Quantum Limit by using multimode squeezed light, with potential applications in ultra-precise space-time positioning.

Contribution

It proposes a novel measurement scheme combining homodyne detection and mode-locked lasers to beat the SQL, and demonstrates the use of multimode squeezing to further improve sensitivity.

Findings

Achieved a new SQL in time transfer potentially reaching yoctosecond precision.

Proved that no other shot noise limited measurement strategy can outperform the proposed method.

Showed that multimode squeezing can overcome the SQL, enabling significant improvements in space-time positioning.

Abstract

Exchanging light pulses to perform accurate space-time positioning is a paradigmatic issue of physics. It is ultimately limited by the quantum nature of light, which introduces fluctuations in the optical measurements and leads to the so-called Standard Quantum Limit (SQL). We propose a new scheme combining homodyne detection and mode-locked femtosecond lasers that lead to a new SQL in time transfer, potentially reaching the yoctosecond range (10^-21-10^-24 s). We prove that no other measurement strategy can lead to better sensitivity with shot noise limited light. We then demonstrate that this already very low SQL can be overcome using appropriately multimode squeezed light. Benefitting from the large number of photons used in the experiment and from the optimal choice of both the detection strategy and of the quantum resource, the proposed scheme represents a significant potential improvement in space-time positioning.