Squeezed Ground States in a Spin-1 Bose-Einstein Condensate*

In this work, we generate spin squeezed ground states in an atomic spin-1 Bose-Einstein condensate tuned near the quantum critical point between the polar and ferromagnetic quantum phases of the interacting spin ensemble. In contrast to typical non-equilibrium methods for preparing atomic squeezed states by quenching through a quantum phase transition, squeezed ground states are time-stationary and remain squeezed for the lifetime of the condensate.

We use a nonadiabatic shortcut protocol consisting of a pair of controlled quenches of an external magnetic field to approach the quantum phase transition, significantly shortening the state preparation time compared to adiabatic methods. A squeezed ground state with a metrological improvement of up to 6-8 dB and a constant squeezing angle maintained over 2s is both simulated and experimentally demonstrated.