Spin-Nematic Squeezed Vacuum in a Quantum Gas

TL;DR

This paper reports the observation of spin-nematic squeezing in a spin-1 Bose condensate, surpassing the standard quantum limit and demonstrating potential for quantum information and magnetometry applications.

Contribution

First measurement of spin-nematic squeezing in a spin-1 Bose condensate, expanding quantum squeezing studies beyond pseudo spin-1/2 systems.

Findings

Achieved up to -8.3 dB squeezing below SQL

Squeezing observed after a quench through a quantum phase transition

Potential applications in quantum information and magnetometry

Abstract

Using squeezed states it is possible to surpass the standard quantum limit of measurement uncertainty by reducing the measurement uncertainty of one property at the expense of another complementary property. Squeezed states were first demonstrated in optical fields and later with ensembles of pseudo spin-1/2 atoms using non-linear atom-light interactions. Recently, collisional interactions in ultracold atomic gases have been used to generate a large degree of quadrature spin squeezing in two-component Bose condensates. For pseudo spin-1/2 systems, the complementary properties are the different components of the total spin vector <S>, which fully characterize the state on an SU(2) Bloch sphere. Here, we measure squeezing in a spin-1 Bose condensate, an SU(3) system, which requires measurement of the rank-2 nematic or quadrupole tensor <Q_ij> as well to fully characterize the state. Following a quench through a nematic to ferromagnetic quantum phase transition, squeezing is observed in the variance of the quadratures up to -8.3(-0.7 +0.6) dB (-10.3(-0.9 +0.7) dB corrected for detection noise) below the standard quantum limit. This spin-nematic squeezing is observed for negligible occupation of the squeezed modes and is analogous to optical two-mode vacuum squeezing. This work has potential applications to continuous variable quantum information and quantum-enhanced magnetometry.