"Photonic" cat states from strongly interacting matter waves

TL;DR

This paper demonstrates that strongly interacting ultracold bosonic gases can form matter wave cat states, which are quantum superpositions analogous to optical photon cat states, and can be experimentally observed via density correlations.

Contribution

It reveals the existence of matter wave cat states in ultracold gases and links their properties to many-body correlations, extending quantum optics concepts to matter waves.

Findings

Matter wave cat states are identical to photon cat states in Fock space.

Their nonclassical quadratures can be measured through density-density correlations.

The states depend critically on many-body correlations of the particles.

Abstract

We consider ultracold quantum gases of scalar bosons, residing in a coupling strength--density regime in which they constitute a twofold fragmented condensate trapped in a single well. It is shown that the corresponding quantum states are, in the appropriate Fock space basis, identical to the photon cat states familiar in quantum optics, which correspond to superpositions of coherent states of the light field with a phase difference of $\pi$. In marked distinction to photon cat states, the very existence of matter wave cat states however crucially depends on the many-body correlations of the constituent particles. We consequently establish that the quadratures of the effective "photons," expressing the highly nonclassical nature of the macroscopic matter wave superposition state, can be experimentally accessed by measuring the density-density correlations of the interacting quantum gas.