Spin Squeezing of Macroscopic Nuclear Spin Ensembles

TL;DR

This paper demonstrates that macroscopic nuclear spin ensembles can be spin-squeezed via circuit coupling, significantly enhancing quantum sensing capabilities and expanding the potential for fundamental physics experiments.

Contribution

It introduces a method to achieve spin squeezing in macroscopic nuclear spin ensembles using resonant circuit coupling, accounting for decoherence effects.

Findings

Achieving 7 dB spin squeezing is feasible in nuclear spin systems.

Squeezing reduces technical noise, improving measurement sensitivity.

Enhanced bandwidth for detecting signals of unknown frequency.

Abstract

Spin squeezing has been explored in atomic systems as a tool for quantum sensing, improving experimental sensitivity beyond the spin standard quantum limit for certain measurements. To optimize absolute metrological sensitivity, it is beneficial to consider macroscopic spin ensembles, such as nuclear spins in solids and liquids. Coupling a macroscopic spin ensemble to a parametrically-modulated resonant circuit can create collective spin squeezing by generating spin correlations mediated by the circuit. We analyze the squeezing dynamics in the presence of decoherence and finite spin polarization, showing that achieving 7 dB spin squeezing is feasible in several nuclear spin systems. The metrological benefit of squeezing a macroscopic spin ensemble lies in the suppression of technical noise sources in the spin detection system relative to the spin projection noise. This expands the experimental sensitivity bandwidth when searching for signals of unknown frequency and can improve the resonant signal-to-noise ratio. Squeezing macroscopic spin ensembles may prove to be a useful technique for fundamental physics experiments aimed at detecting spin interactions with oscillating background fields, such as ultralight dark matter.