Nuclear spin-squeezing by continuous measurement

Alice Sinatra
ENS Paris, France

The nuclear spin of helium-3 is very well isolated from the environment and has coherence times measured to be hundreds of hours. We propose a method to manipulate at the quantum level the collective nuclear spin of a helium gas in a cell at room temperature, by means of a continuous quantum non demolition measurement. A discharge is temporarily switched-on in the gas which populates the metastable state of helium. The nuclear collectivespin then slightly hybridizes with the collective spin of metastable atoms thanks to metastability exchange collisions. The metastable atoms interact with light in an optical cavity, and the eld leaking out from the cavity is continuously measured. Nuclear spin squeezing provides a metrological gain for nuclear-spin based sensors such as miniaturized magnetometers and gyrometers whose sensitivity will ultimately reach the limits imposed by quantum mechanics. It also opens up fascinating perspectives on the possibility of creating and maintaining a macroscopic quantum state over very long periods of time.

[1] Nuclear spin squeezing in Helium-3 by continuous quantum nondemolition measurement, A. Sera n, M. Fadel, P. Treutlein, A. Sinatra, Phys. Rev. Lett 127, 013601 (2021).
[2] Etude theorique de la compression de spin nucleaire par mesure quantique non destructive en continu A. Sera n, Y. Castin, M. Fadel, P. Treutlein, A. Sinatra, Comptes Redus Physique Tome 22, pp. 1-35 (2021).