Active SU(1,1) atom interferometry

TL;DR

This paper demonstrates an active SU(1,1) atom interferometer using spin exchange in a Bose-Einstein condensate, which amplifies and detects phase shifts through nonlinear processes, generating nonclassical states.

Contribution

It experimentally implements an active SU(1,1) interferometer with spin exchange, showcasing nonlinear amplification and phase measurement in a quantum atomic system.

Findings

Successfully demonstrated nonlinear amplification of atomic states.

Showed phase-dependent deamplification and entanglement generation.

Compared SU(1,1) dynamics with traditional SU(2) interferometers.

Abstract

Active interferometers use amplifying elements for beam splitting and recombination. We experimentally implement such a device by using spin exchange in a Bose-Einstein condensate. The two interferometry modes are initially empty spin states that get spontaneously populated in the process of parametric amplification. This nonlinear mechanism scatters atoms into both modes in a pairwise fashion and generates a nonclassical state. Finally, a matched second period of spin exchange is performed that nonlinearly amplifies the output signal and maps the phase onto readily detectable first moments. Depending on the accumulated phase this nonlinear readout can reverse the initial dynamics and deamplify the entangled state back to empty spin states. This sequence is described in the framework of SU(1,1) mode transformations and compared to the SU(2) angular momentum description of passive interferometers.