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arxiv: 2606.20328 · v1 · pith:FKYBWQODnew · submitted 2026-06-18 · 🪐 quant-ph · physics.atom-ph

Effective Faraday interaction between light and Helium-3 nuclear spins in a multi-pass cell

Kaiwen Yi , Yida Sha , Zejia Lin , Matteo Fadel , Xiang Peng This is my paper

Pith reviewed 2026-06-26 17:23 UTC · model grok-4.3

classification 🪐 quant-ph physics.atom-ph
keywords helium-3nuclear spinsFaraday interactionmetastability-exchangespin squeezingmulti-pass celloptical pumpingquantum metrology
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The pith

Metastability-exchange collisions in a multi-pass helium-3 cell mediate an effective Faraday interaction between light and nuclear spins.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that a controllable optical interface to helium-3 nuclear spins is possible at room temperature through metastability-exchange collisions inside a low-pressure gas cell. Metastable atoms generated by radio-frequency discharge both enable optical pumping and transmit the effective Faraday coupling to a probe beam. A multi-pass geometry raises the optical depth and thereby strengthens the interaction, which the authors characterize against nuclear polarization, magnetic field, and beam settings. Extrapolation from these measurements yields a projected measurement-induced squeezing rate of 0.52 s^{-1} once probe power is increased tenfold, supplying a route to long-lived squeezed nuclear states.

Core claim

By exploiting metastability-exchange collisions in a low-pressure helium-3 gas cell at room temperature, an effective Faraday interaction is established between the collective nuclear spin and an optical probe. The interaction is enhanced using a multi-pass cell, and extrapolation to increased probe power yields a projected measurement-induced squeezing rate of 0.52 s^{-1}.

What carries the argument

The effective Faraday interaction mediated by metastability-exchange collisions between metastable and ground-state helium-3 atoms in a radio-frequency discharge.

Load-bearing premise

The interaction strength scales linearly with a tenfold increase in probe power without added decoherence, technical noise, or saturation effects.

What would settle it

A measurement at ten times the present probe power that shows either a sub-linear rise in interaction strength or a rise in decoherence that prevents reaching the projected 0.52 s^{-1} squeezing rate.

Figures

Figures reproduced from arXiv: 2606.20328 by Kaiwen Yi, Matteo Fadel, Xiang Peng, Yida Sha, Zejia Lin.

Figure 1
Figure 1. Figure 1: 3He transitions and experimental setup. (a) Fine struc￾ture and hyperfine structure of states 23S1 and 23P in 3He (not to scale). The two probe-frequency operating points employed in this work are marked as “Config.1” and “Config.2”. (b) Schematic of the experimental setup. PBS: polarization beam splitter; M: mirrors; PD: photodiodes; WP: half-wave plate for S y measurement. (c) Coupling constants χ, η, µ … view at source ↗
Figure 2
Figure 2. Figure 2: Effective coupling measurement sequence and magnetic field dependence. (a) Timing diagram for the pump beam, rf Rabi pulse Brf, probe readout, and bias magnetic field Bx. High (low) level denotes on (off) state. (b) Typical S y FID signal measured for the single-pass 3He cell at a Bx = 600 nT, M = 0.38, and θ = 28.4 ◦ under Config.2. Dependence of the FID signal amplitude (c) and of the corresponding effec… view at source ↗
Figure 3
Figure 3. Figure 3: Coupling dependence on the nuclear polarization and on the probe power. (a,b) Comparison of the scaling function f (i) (M) obtained in the single- and multi-pass experiments (dots) with the analytical/full models (lines, see Eqs. (4) and Sec. IV C of [35], including a factor 1/2 to correct for a typo in Ref. [34]). Error bars mostly come from uncertainty in the value of M. (c) Dependence of the effective c… view at source ↗
read the original abstract

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$^{-1}$. 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.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript experimentally demonstrates an effective Faraday interaction between an optical probe and helium-3 nuclear spins in a low-pressure room-temperature gas cell, mediated by metastability-exchange collisions with a small metastable-atom population produced by RF discharge. The interaction strength is quantitatively characterized versus nuclear polarization, applied magnetic field, and probe-beam parameters; multi-pass geometry is shown to enhance the effective optical depth. The authors extrapolate the measured interaction to tenfold higher probe power and project a measurement-induced squeezing rate of 0.52 s^{-1}.

Significance. If the demonstrated interface and its scaling hold, the work supplies a practical optical route to long-coherence-time helium-3 nuclear spins at room temperature, opening a path to long-lived macroscopic spin-squeezed states for quantum metrology and fundamental-physics tests. The quantitative, multi-parameter characterization and the explicit multi-pass enhancement constitute clear experimental strengths; the projection, while labeled as extrapolation, directly links the measured interface to a concrete metrological figure of merit.

major comments (1)
  1. [Abstract and extrapolation paragraph] Abstract and the extrapolation paragraph (likely §5 or Discussion): the projected squeezing rate of 0.52 s^{-1} is obtained by linear extrapolation of the measured Faraday interaction strength to a tenfold increase in probe power. No data, model, or bound is supplied for possible deviations from linearity arising from changes in metastable-atom density, optical-pumping efficiency, absorption saturation, or additional technical/spin-relaxation noise at the higher power; this assumption is load-bearing for the headline metrological claim.
minor comments (2)
  1. [Figure captions] Figure captions (e.g., Fig. 3 or 4): the procedure used to extract the effective Faraday rotation angle or coupling rate from the raw time traces is not stated, making it difficult to assess systematic uncertainties in the reported interaction strengths.
  2. [§2] §2 (Experimental setup): the precise value of the metastable-atom fraction and its uncertainty are not given, although this parameter directly enters the effective interaction strength.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive review and for recognizing the experimental characterization and multi-pass enhancement. We address the single major comment below.

read point-by-point responses

  1. Referee: [Abstract and extrapolation paragraph] Abstract and the extrapolation paragraph (likely §5 or Discussion): the projected squeezing rate of 0.52 s^{-1} is obtained by linear extrapolation of the measured Faraday interaction strength to a tenfold increase in probe power. No data, model, or bound is supplied for possible deviations from linearity arising from changes in metastable-atom density, optical-pumping efficiency, absorption saturation, or additional technical/spin-relaxation noise at the higher power; this assumption is load-bearing for the headline metrological claim.

    Authors: We agree that the projection assumes linear scaling of the Faraday interaction with probe power and that the manuscript provides no explicit model or quantitative bounds on deviations at 10 imes power. In the revised version we will expand the extrapolation paragraph (and adjust the abstract wording) to state the operating regime explicitly: the metastable fraction is set by the RF discharge and remains ≪1 % even at the projected power; optical-pumping efficiency and absorption are measured to be linear in the present data set; and saturation of the probe transition would require intensities well above the extrapolated value. We will add a short paragraph noting that additional technical or relaxation noise cannot be ruled out a priori and therefore qualify the 0.52 s^{-1} figure as an estimate under the stated assumptions rather than a guaranteed rate. A full quantitative model or new data at higher power lies outside the scope of the present experiment. revision: yes

Circularity Check

0 steps flagged

No significant circularity; experimental characterization with explicit linear extrapolation

full rationale

The paper reports quantitative experimental measurements of the effective Faraday interaction strength versus nuclear polarization, magnetic field, and probe parameters, plus multi-pass optical depth enhancement. The 0.52 s^{-1} projection is stated as an extrapolation of the measured interaction to 10x probe power; no equations or derivations in the provided text reduce this projection to a fitted quantity by construction, nor invoke self-citations as load-bearing uniqueness theorems. The work is self-contained against external benchmarks as a characterization study.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The central claim rests on experimental observation of the mediated interaction and the scaling assumption for power extrapolation; no new theoretical entities or axioms are introduced beyond standard atomic-physics background.

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Reference graph

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