2020/03/31 by Emily J. Davis, Avikar Periwal, Eric S. Cooper +4 · 2 citations
Physics and Astronomy · #quant-ph #cond-mat.quant-gas
paper · pdf · doi:10.1103/physrevlett.125.060402
published as Phys. Rev. Lett. 125, 060402 (2020)
arxiv created 2020/08/30 · arxiv updated 2020/09/01
Using an ensemble of atoms in an optical cavity, we engineer a family of nonlocal Heisenberg Hamiltonians with continuously tunable anisotropy of the spin-spin couplings. We thus gain access to a rich phase diagram, including a paramagnetic-to-ferromagnetic Ising phase transition that manifests as a diverging magnetic susceptibility at the critical point. The susceptibility displays a symmetry between Ising interactions and XY (spin-exchange) interactions of the opposite sign, which is indicative of the spatially extended atomic system behaving as a single collective spin. Images of the magnetization dynamics show that spin-exchange interactions protect the coherence of the collective spin, even against inhomogeneous fields that completely dephase the non-interacting and Ising systems. Our results underscore prospects for harnessing spin-exchange interactions to enhance the robustness of spin squeezing protocols.