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Long-lived spin squeezing in a metrologically relevant regime

Friday June 12, 2020
1:00 pm

 Presenter:  Jakob Reichel, Sorbonne University / Laboratoire Kastler Brossel de l'ENS
 Series:  CQuIC Seminars
 Abstract:  A VIRTUAL AMO SEMINAR presented in a Zoom meeting vetted by CQuIC. See https://sites.google.com/stanford.edu/virtual-amo-seminar/schedule for the meeting link. Spin squeezing is a fascinating manifestation of many-particle entanglement as well as one of the most promising quantum technologies. By using quantum correlations to reduce the quantum projection noise in a collection of atomic spin-1/2's, spin squeezing removes a limitation that has already been reached in atomic fountain clocks and is expected to limit state-of-the-art lattice clocks and atomic sensors in the near future. Ground-breaking experiments have demonstrated methods to create spin-squeezed states and have even demonstrated squeezing enhancement in proof-of-principle clock and magnetometer measurements, though not yet at a metrologically relevant level. in all experiments so far, however, the coherence time of the atomic superpositions was short (typically below 10ms), while interrogation times in real clocks and sensors are often ten or hundred times longer. How squeezed states evolve on these timescales is a question that experiments have not yet been able to address. Besides its practical importance, the physics of this time evolution is an interesting question in itself. Long coherent evolution acts like a magnifying glass for atomic interactions, often leading to surprising effects. How do these interactions evolve when the initial state is no longer a product state of N independent atoms, but an entangled state with quantum correlations between all the atomic spins?

In a collaboration with the French time and frequency laboratory SYRTE (Observatoire de Paris), we have built an experiment combining a trapped-atom clock on an atom chip with a fiber Fabry-Perot microcavity to generate spin squeezing. This has enabled us to produce spin-squeezed states with with a lifetime on the order of a second. Observing the time evolution of the squeezed state over these long times reveals a surprising quantum phase magnification effect in the final measurement of the spin state. This effect results from a subtle interplay of the spin dynamics of interacting indistinguishable particles and the physics of cavity-based quantum non-demolition measurement of the collective spin.

 Host:  Ivan Deutsch
 Location:  Zoom, Physics & Astronomy

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