Improving the Q factor of an optical atomic clock using quantum non-demolition measurement

TL;DR

This paper demonstrates that quantum non-demolition measurements can significantly enhance the quality factor of an optical atomic clock by preserving quantum coherence and extending interrogation times, leading to improved clock stability.

Contribution

The authors apply cavity-based QND measurement to an optical lattice clock, achieving an 80% fidelity in preserving quantum coherence and a seven-fold increase in the clock's Q factor.

Findings

QND measurement preserves quantum coherence with 80% fidelity.

Extended Ramsey interrogation time from 300 ms to 2 s.

Achieved a seven-fold increase in the clock's Q factor to 1.7×10^{15}.

Abstract

Quantum non-demolition (QND) measurement is a remarkable tool for the manipulation of quantum systems. It allows specific information to be extracted while still preserving fragile quantum observables of the system. Here we apply cavity-based QND measurement to an optical lattice clock---a type of atomic clock with unrivalled frequency precision---preserving the quantum coherence of the atoms after readout with 80\% fidelity. We apply this technique to stabilise the phase of an ultrastable laser to a coherent atomic state via a series of repeated QND measurements. We exploit the improved phase-coherence of the ultrastable laser to interrogate a separate optical lattice clock, using a Ramsey spectroscopy time extended from 300~ms to 2~s. With this technique we maintain 95\% contrast and observe a seven-fold increase in the clock's \emph{Q} factor to $1.7\times10^{15}$.