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Dr. Yanhong Xiao (Fudan Univ.), Title of talk: "Concurrent spin squeezing and magnetic field tracking with machine learning"

Abstract: Squeezing and entanglement play crucial roles in proposals for quantum metrology. Yet, demonstrating quantum enhancement in continuous signal tracking remains a challenging endeavor, because entanglement generation and signal perturbations are often incompatible. We show that concurrent steady-state spin-squeezing and sensing are possible using continuous quantum nondemolition measurements under constant optical pumping. We achieve a sustained spin squeezed state containing 4 × 10^10 hot atoms with a metrologically relevant steady state squeezing of 3.23±0.24dB, by using both predictive and retrodictive measurement records. We further employ the system to track different types of continuous time-fluctuating magnetic fields, where we demonstrate the use of deep learning models to infer the time varying fields from the optical measurement record, at or below the quantum level. The quantum enhancement due to spin squeezing is verified by a degraded performance in test experiments where spin squeezing is deliberately prevented. In the end of the talk, I will describe my group’s effort towards further reduction of quantum fluctuations in quantum metrology, including simultaneous squeezing of the atomic spin and the light, and hybrid squeezing of internal atomic spin and the collective spin. 

Sponsored by: Physics

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