Spin-nematic squeezed vacuum in a quantum gas

The standard quantum limit of measurement uncertainty can be surpassed using squeezed states, which minimize the uncertainty product in Heisenberg's relation by reducing the uncertainty of one property at the expense of another(1). Collisions in ultracold atomic gases have been used to induce quadrature spin squeezing in two-component Bose condensates(2,3), for which the complementary properties are the components of the total spin vector. Here, we generalize this finding to a higher-dimensional spin space by measuring squeezing in a spin-1 Bose condensate. Following a quench through a quantum phase transition, we demonstrate that spin-nematic quadrature squeezing improves on the standard quantum limit by up to 8-10 dB-a significant increase on previous measurements. This squeezing is associated with negligible occupation of the squeezed modes, and is analogous to optical two-mode vacuum squeezing. The observation has implications for continuous variable quantum information and quantum-enhanced magnetometry.