Abstract
Spin squeezing is a form of entanglement that can improve the stability of quantum sensors operating with multiple particles, by inducing inter-particle correlations that redistribute the quantum projection noise. Previous analyses of potential metrological gain when using spin squeezing were performed on theoretically ideal states, without incorporating experimental imperfections or inherent limitations which result in non-unitary quantum state evolution. Here, we show that potential gains in clock stability are substantially reduced when the spin squeezing is non-unitary, and derive analytic formulas for the clock performance as a function of squeezing, excess spin noise, and interferometer contrast. Our results highlight the importance of creating and employing nearly pure entangled states for improving atomic clocks.
Highlights
Spin squeezed states (SSSs) [1] offer a path toward entanglement-enhanced quantum sensors by reducing the variance of one spin quadrature
We have analyzed the effect of non-unitary squeezing and derived simple expressions for potential improvements in clock stability in the presence of local oscillator (LO) noise, as a function of the squeezing and antisqueezing
We find that for a state with N atoms, the squeezed state offers no metrological gain over a coherent spin state (CSS) if the excess antisqueezing variance exceeds N−1/2, and that highly squeezed states with large excess antisqueezing can lead to worse clock performance than moderately squeezed states with less antisqueezing
Summary
Templeton Street, Ottawa, Ontario K1N 6N5, Canada. 3 Author to whom any correspondence should be addressed. Hansen Experimental Physics Laboratory and Department of Physics, Stanford University, Stanford, CA 94305, United States of America. Original content from this Keywords: atomic clocks, precision sensors, quantum entanglement, spin squeezing, antisqueezing work may be used under the terms of the Creative
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