Progress in quantum metrology and applications for optical atomic clocks

TL;DR

This paper reviews how quantum entanglement enhances optical atomic clock precision, discussing theoretical frameworks, entangled states, decoherence challenges, and practical applications in timekeeping.

Contribution

It provides a comprehensive overview of entanglement-based quantum metrology principles and their application to improving optical atomic clock performance, including recent theoretical and experimental insights.

Findings

Entanglement can surpass classical measurement limits in atomic clocks.

Decoherence significantly limits practical quantum metrology gains.

Emerging quantum techniques are advancing clock precision.

Abstract

Quantum entanglement offers powerful opportunities for enhancing measurement sensitivity beyond classical limits, with optical atomic clocks serving as a leading platform for such advances. This chapter introduces the principles of entanglement-enhanced quantum metrology and explores their applications to timekeeping. We review the theoretical framework of quantum phase estimation, comparing frequentist and Bayesian approaches, and discuss paradigmatic entangled states such as spin-squeezed and GHZ states. Particular emphasis is placed on the challenges posed by decoherence, which constrain the practical advantages that can be realized in large-scale devices. The discussion then turns to frequency estimation in atomic clocks, highlighting how experimental constraints shape the translation of abstract quantum limits into real performance gains. Finally, we outline emerging directions of contemporary quantum metrology. Together, these developments underscore the increasingly close interplay between quantum information processing and precision metrology.