Enhancing NMR Sensitivity through Quantum Spin Squeezing

Spin squeezing, a novel quantum sensing technique used to obtain uncertainties below the Heisenberg limit, originated in atomic, molecular, and optical (AMO) systems and has been demonstrated in liquid-state nuclear magnetic resonance (NMR) experiments [1]. Solid-state NMR systems are a natural next step for spin squeezing, as samples with a spin $I > \frac{1}{2}$ have a quadrupolar Hamiltonian term that naturally gives rise to the quadratic spin operator required to generate squeezing. Experimental demonstration of spin squeezing in solid-state NMR requires the creation of an optimal coherent spin state and the implementation of quantum state tomography, using techniques that differ from AMO and liquid state NMR systems. Simulation results of a solid state system indicate that significant squeezing can be achieved under realistic experimental conditions, with predicted squeezing parameters approaching those observed in AMO systems [2]. Using PULSEE to simulate the creation of a coherent spin state in an NMR system, we demonstrate how the NMR Hamiltonian can squeeze the uncertainty below the Heisenberg limit. Standard NMR spectra are limited by factors such as too much noise or spectral broadening, and we hope to use spin squeezing to probe for orders previously undetectable, such as local structural distortions or multipolar orders.

[1] R. Auccaise, A. G. Araujo-Ferreira, R. S. Sarthour, I. S. Oliveira, T. J. Bonagamba, and I. Roditi, Phys. Rev. Lett. 114, 043604 (2015).

[2] I. K. Nikolov, S. Carr, A. G. Del Maestro, C. Ramanathan, and V. F. Mitrović, JPS Conf. Proc. 38, 011149 (2023).