Relationship between spin squeezing and single-particle coherence in two-component Bose-Einstein condensates with Josephson coupling

TL;DR

This paper explores the relationship between spin squeezing and single-particle coherence in two-component Bose-Einstein condensates with Josephson coupling, revealing a direct measurement method and characterizing optimal squeezing conditions.

Contribution

It establishes an exact relation between spin squeezing and coherence, and derives power laws for maximum squeezing and optimal coupling as functions of particle number.

Findings

Exact relation between squeezing and coherence at maximal squeezing.

Maximum squeezing occurs along the $J_z$ axis, indicating atom number squeezing.

Power laws for strongest squeezing and optimal coupling with particle number $N$.

Abstract

We investigate spin squeezing of a two-mode boson system with a Josephson coupling. An exact relation between the squeezing and the single-particle coherence at the maximal-squeezing time is discovered, which provides a more direct way to measure the squeezing by readout the coherence in atomic interference experiments. We prove explicitly that the strongest squeezing is along the $J_z$ axis, indicating the appearance of atom number-squeezed state. Power laws of the strongest squeezing and the optimal coupling with particle number $N$ are obtained based upon a wide range of numerical simulations.