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arXiv:2509.05717 · SciPost Physics

Deterministic nuclear spin squeezing and squeezing by continuous measurement using vector and tensor light shifts

Ali Moshiri, Alice Sinatra

Published Mar 5, 2026• 1 citation

Abstract

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 .

DOI: 10.21468/scipostphys.20.3.069

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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.

In order to establish an applicable system for advanced quantum information processing based on the interaction between light and atoms, we have demonstrated a quantum nondemolition measurement with a collective spin of cold ytterbium atoms (171Yb), and have observed 1.8(-1.5)+2.4 dB spin squeezing. Since 171Yb atoms have only a nuclear spin of one-half in the ground state, the system constitutes the simplest spin ensemble and is thus robust against decoherence. We used very short pulses with a width of 100 ns, and as a result the interaction time became much shorter than the decoherence time, which is important for multistep quantum information processing.

We consider an ensemble of trapped atoms interacting with a continuous-wave laser field. For sufficiently polarized atoms and for a polarized light field, we may approximate the nonclassical components of the collective spin angular momentum operator for the atoms and the Stokes vectors of the field by effective position and momentum variables for which we assume a Gaussian state. Within this approximation, we present a theory for the squeezing of the atomic spin by polarization rotation measurements on the probe light. We derive analytical expressions for the squeezing with and without inclusion of the noise effects introduced by atomic decay and by photon absorption. The theory is readily adapted to the case of inhomogeneous light-atom coupling [A. Kuzmich and T.A.B. Kennedy, Phys. Rev. Lett. 92, 030407 (2004)]. As a special case, we show how to formulate the theory for an optically thick sample by slicing the gas into pieces, each having only small photon absorption probability. Our analysis of a realistic probing and measurement scheme shows that it is the maximally squeezed component of the atomic gas that determines the accuracy of the measurement.

We have demonstrated a quantum non‐demolition (QND) measurement with a collective spin of cold ytterbium atoms (171Yb) via Faraday rotation interaction, and have observed 1.8−1.5+2.4 dB spin squeezing. Since 171Yb atoms have only a nuclear spin of one‐half in the ground state, the system constitutes the simplest spin ensemble and is thus robust against decoherence. Furthermore, we have considered the atomic quantum swapping gate as a quantum information device using multiple Faraday rotation interactions, and have found that we can realize the quantum‐domain performance for a realistic experimental condition.