Abstract
We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. Importantly the protocol is designed to work under realistic conditions where the drift of the phase of the laser interrogating the atoms is the main source of decoherence. The simultaneous interrogation of the laser phase with a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the coherent interrogation time beyond the laser noise limit. We compare and merge the new protocol with existing state of the art interrogation schemes, and identify the precise conditions under which entanglement provides an advantage for clock stabilization: it allows a significant gain in the stability for short averaging time.
Highlights
High precision atomic frequency standards form a cornerstone of precision metrology, and are of great importance for science and technology in modern society
We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states, that achieves the best clock stability allowed by quantum theory up to a logarithmic correction
The simultaneous interrogation of the laser phase with such a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the Ramsey interrogation time beyond the laser noise limit
Summary
Single ensemble Ramsey spectroscopy is limited to estimating either the real or the imaginary part of eiΦLO. Performing the same Ramsey measurement on them, we can get estimates on both the real and imaginary parts of eiΦLO and deduce the value of ΦLO up to 2π shifts, instead of π. After performing the measurement with N total qubits, we obtain ΦeLsOt from the estimates of px and py. Since both provide information on ΦeLsOt equivalent of N/2 measurement bits, this results in a total information of N measurement bits, which gives an uncertainty of. Up to 2π phase shifts, that are fundamentally undetectable. This method is identical to the one described in [17]
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