Super-universality of spin squeezing [Rabi Prize: Norman Yao]

Quantum metrology makes use of structured entanglement to perform measurements with greater precision than would be possible with only classically correlated particles. A paradigmatic example of such entanglement is spin squeezing, which is known to be dynamically generated by the celebrated one-axis-twisting model, corresponding to an all-to-all coupled Ising Hamiltonian. Motivated by recent advances in a variety of quantum simulation platforms, there has been tremendous interest in the possibility of generating spin squeezing via Hamiltonians which do not require all-to-all interactions. In my talk, I will present evidence for the following conjecture, namely, that scalable spin squeezing can be realized in any model exhibiting finite-temperature, easy-plane ferromagnetism. This greatly expands upon the landscape of Hamiltonians that can be utilized to dynamically generate metrologically-useful entanglement.

I will show that this conjecture leads to a remarkable intellectual unification, both experimentally, where spin squeezing has recently been demonstrated in dipolar Rydberg arrays, magnetic atoms in optical lattices, and nearest neighbor spin-exchange Hamiltonians, as well as theoretically, where the emerging picture is that any spin model exhibiting finite-temperature, continuous symmetry breaking can be used to generate scalable spin squeezing. Finally, I will describe recent efforts in my group aimed at observing spin squeezing using strongly-interacting, atom-like impurity ensembles in the solid-state; particular emphasis will be placed on the tools borrowed from nuclear magnetic resonance and the lasting legacy of I. I. Rabi.