Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit

TLDR

Squeezing of quantum fluctuations via entanglement is a well-recognized goal in quantum information science and precision measurements, and entanglement between two-level atoms can enhance the precision of sensing, clocks, metrology, and spectroscopy. A two-color quantum nondemolition scheme is employed, offering advantages over single-color QND for generating entanglement. The experiment achieves 3.4 dB of metrologically relevant squeezing and entanglement in ≳10⁵ cold cesium atoms, and identifies an optimal decoherence level induced by the measurement that maximizes entanglement.

Abstract

Squeezing of quantum fluctuations by means of entanglement is a well-recognized goal in the field of quantum information science and precision measurements. In particular, squeezing the fluctuations via entanglement between 2-level atoms can improve the precision of sensing, clocks, metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically relevant squeezing and entanglement for ≳ 10 5 cold caesium atoms via a quantum nondemolition (QND) measurement on the atom clock levels. We show that there is an optimal degree of decoherence induced by the quantum measurement which maximizes the generated entanglement. A 2-color QND scheme used in this paper is shown to have a number of advantages for entanglement generation as compared with a single-color QND measurement.