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arXiv:2012.07216 · Physical Review Letters

Nuclear Spin Squeezing in Helium-3 by Continuous Quantum Nondemolition Measurement

Alan Serafin, Matteo Fadel, Philipp Treutlein, Alice Sinatra

Published Jun 29, 2021• 28 citations
arXivHTMLPDF

Abstract

We propose a technique to control the macroscopic collective nuclear spin of a helium-3 gas in the quantum regime using light. The scheme relies on metastability exchange collisions to mediate interactions between optically accessible metastable states and the ground-state nuclear spin, giving rise to an effective nuclear spin-light quantum nondemolition interaction of the Faraday form. Our technique enables measurement-based quantum control of nuclear spins, such as the preparation of spin-squeezed states. This, combined with the day-long coherence time of nuclear spin states in helium-3, opens the possibility for a number of applications in quantum technology.

DOI
10.1103/physrevlett.127.013601

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We propose a technique to control the macroscopic collective nuclear spin of a helium-3 gas in the quantum regime using light. The scheme relies on metastability exchange collisions to mediate interactions between optically accessible metastable states and the ground-state nuclear spin, giving rise to an effective nuclear spin-light quantum nondemolition interaction of the Faraday form. Our technique enables measurement-based quantum control of nuclear spins, such as the preparation of spin-squeezed states. This, combined with the day-long coherence time of nuclear spin states in helium-3, opens the possibility for a number of applications in quantum technology.
Helium-3 nuclear spins form an exceptionally stable quantum system with extremely long coherence time, offering exciting opportunities for quantum technologies. In particular, nuclear spin-squeezed states promise enhanced precision for sensing tasks and tests of new physics. A central challenge for all these applications is the realization of a controllable light-nuclear spin interface. Here we experimentally demonstrate such an interface by exploiting metastability-exchange collisions in a low-pressure helium-3 gas cell at room temperature. A radio-frequency discharge produces a small population of metastable atoms that both enables efficient optical pumping and mediates an effective Faraday interaction between the collective nuclear spin and an optical probe. We quantitatively characterize the strength of this interaction as a function of the nuclear polarization, applied magnetic field, and probe-beam parameters. Moreover, we show that using a multi-pass cell enhances this interaction by effectively increasing the optical depth. Extrapolating to a tenfold increase of the probe power used in the present experiment, we project a measurement-induced squeezing rate of 0.52 s−1^{-1}−1. Our results provide a practical pathway for optical access to helium-3 nuclear spins and open prospects for generating long-lived, macroscopic nuclear spin-squeezed states for quantum metrology.
Isolation from environment leads to the days-long lifetime of noble-gas nuclear spins, but also brings great challenges to the preparation, manipulation, and measurement of nuclear-spin quantum states. Here we find that nuclear spin squeezing, with ultra-long lifetime and huge atomic number, can be efficiently obtained and manipulated based on the coherent spin-exchange interaction between alkali-metal and noble-gas ensembles. Thanks to the considerable advantage of our proposal in preparing the spin squeezing of the macroscopic atomic ensemble with a huge atomic number, even the nuclear spin-squeezed state containing 10^20 atoms or more is obtainable with preexisting techniques. Further, the days-long storage and measurement of nuclear spin squeezing can be performed by the coherent manipulation of a magnetic field. This proposal can be implemented in hot atomic ensembles, whose ease of access and high adaptability to various environments will significantly facilitate the research and application of nuclear-spin nonclassical states in precision measurement, quantum information, and fundamental physics.
We study the joint effects of vector and tensor light shifts in a set of large spin atoms, prepared in a polarized state and interacting with light. Depending on the ratio \epsilon ϵ between tensor and vector coupling and a measurement rate \Gamma Γ , we identify a regime of quantum non-demolition measurement squeezing for times shorter than (\sqrt{\epsilon}\Gamma)^{-1} ( ϵ Γ ) − 1 , and a deterministic squeezing regime for times longer than (\epsilon \Gamma)^{-1} ( ϵ Γ ) − 1 . We apply our results to fermionic isotopes of strontium, ytterbium, and helium, which are atoms with purely nuclear spin in their ground state, benefiting from very low decoherence. For ytterbium 173, with a cavity such as that of [J. A. Muniz et al., Phys. Rev. Res. 3, 023152 (2021)], it would be possible to achieve an atomic spin variance reduction of 0.03 0.03 in \simeq 50 \rm ms .
Abstract We derive the semiclassical evolution equations for a system consisting of helium-3 atoms in the 2 3 S metastable state interacting with a light field far-detuned from the 2 3 S − 2 3 P transition, in the presence of metastability exchange collisions with ground state helium atoms and a static magnetic field. For two configurations, each corresponding to a particular choice of atom–light detuning in which the contribution of either the metastable level F = 1 / 2 or F = 3 / 2 is dominant, we derive a simple model of three coupled collective spins from which we can analytically extract an effective coupling constant between the collective nuclear spin and light. In these two configurations, we compare the predictions of our simplified model with the full model.