A synchronized pulsed-readout method was associated with lower reported probe disturbance and more reliable detection of spin noise—fluctuations in the spins—in a high-density potassium-vapor radio-frequency optical quantum sensor, according to an arXiv preprint. The same processing was associated with nearly two orders of magnitude suppression of coherent technical noise while preserving sensitivity to appropriately phase-cycled external radio-frequency signals.
The study estimated the fundamental spin-noise level at 6.4–8.6 fT/√Hz and independently measured probe-background noise at 17 fT/√Hz. It did not establish a quantitative degree of spin squeezing because an independent spin-squeezing parameter was not determined.
A timed readout
The experiment used orthogonal pump and probe beams, a static magnetic field defining the sensing frequency, and probe pulses synchronized with spin precession. Its protocol combined periodic probing, phase cycling and window-shifted acquisition; temporally correlated signals acquired within the spin-relaxation time were subtracted during processing.
The reported measurements used a potassium cell measuring 2 × 2 × 2 centimetres and held at 168°C. The probe wavelength was 769.60 nanometres, its blue detuning was +257 gigahertz, and the beam was approximately 0.5 millimetres in diameter. The probe used a 20% duty cycle, meaning pulses were present during 20% of the measurement cycle; the radio-frequency resonance was approximately 35 kilohertz.
In a comparison with the initial 50% duty-cycle condition, the approximately 20% setting was associated with disturbance about one order of magnitude lower. Spin noise was also more reliably detected at approximately 20% duty cycle.
The probe’s relaxation rates
At 20% duty cycle, the reported pulse-induced relaxation rate was approximately 193 s−1, the time-averaged rate was approximately 39 s−1, and the effective transverse relaxation rate was approximately 103 s−1. The estimated optimum range was 30–50 s−1.
The three figures refer to pulse-induced, time-averaged and effective transverse rates, respectively; together they describe the reported 20% probe condition from different angles rather than reducing it to a single relaxation number.
Noise changed with the delay
When the delay between preparation and the readout probe-pulse sequence was varied, measured noise rose toward an asymptotic, or long-delay, level. An exponential fit gave N∞ = 19.20 ± 0.17 fT/√Hz, A = −3.25 ± 0.18, and T2, the transverse spin-relaxation time, = 0.62 ms with a reported +0.10 ms uncertainty.
At short delays, the measured noise was below the asymptotic level, then rose as the delay increased. The authors say this pattern is consistent with correlated spin dynamics, but it does not uniquely distinguish those dynamics from residual probe-induced correlations, diffusion or other technical noise.
Building the noise budget
On the reported noise budget, the fundamental spin-noise contribution was estimated at 6.4–8.6 fT/√Hz, while independently measured probe-background noise was 17 fT/√Hz. Assuming those contributions were statistically independent, the expected long-delay noise was 18.16–19.05 fT/√Hz.
That expected range was reported to agree with the fitted asymptotic value of 19.20 ± 0.17 fT/√Hz. The agreement describes the long-delay noise accounting; it does not by itself identify the source of the lower short-delay noise.
The combined phase-cycling and window-shifted-subtraction processing was associated with nearly two orders of magnitude suppression of coherent technical noise. Sensitivity to appropriately phase-cycled external radio-frequency signals was preserved in the reported processing.
What the result does not show
The reported result is a protocol and noise-characterization finding, not a numerical measurement of spin squeezing. The study did not establish a quantitative degree of spin squeezing because it did not determine an independent spin-squeezing parameter.
The observed delay dependence is consistent with correlated spin dynamics, as the authors report, but the measurements do not uniquely separate those dynamics from residual probe-induced correlations, diffusion or other technical noise.
The document is an arXiv preprint, version 1, dated 25 August 2026. The work was supported by Quantum Information Science Enabled Discovery 2.0 for the United States Department of Energy, Office of Science, Office of High Energy Physics, under DE-FOA-0003354.
The authors declared no competing financial interests. The datasets generated and analyzed during the study are available from the corresponding author upon reasonable request.
Paper data and sources
Original title: High-density Optical Quantum Sensors with Pulsed Probe Read-out for Correlated Spin-Noise Reduction
Authors: Igor Savukov, Young Jin Kim
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-25
DOI: Not available
Original paper · Full text