Production and characterization of a fragmented spinor Bose-Einstein condensate

TL;DR

This paper reports the creation and detailed analysis of a fragile, multi-component spinor Bose-Einstein condensate with three fragments, revealing complex quantum entanglement and symmetry effects in a small atomic system.

Contribution

It demonstrates the first production of a three-fragment condensate in a spin-1 gas with anti-ferromagnetic interactions and provides high-resolution detection of its many-body quantum state.

Findings

Successfully produced a 3-fragment condensate with ~100 atoms

Reconstructed the many-body state as quasi-pure despite mixed one-body observables

Showed the role of symmetry and interactions in entanglement development

Abstract

Understanding the ground state of many-body fluids is a central question of statistical physics. Usually for weakly interacting Bose gases, most particles occupy the same state, corresponding to a Bose--Einstein condensate. However, another scenario may occur with the emergence of several, macroscopically populated single-particle states. The observation of such fragmented states remained elusive so far, due to their fragility to external perturbations. Here we produce a 3-fragment condensate for a spin 1 gas of $\sim 100$ atoms, with anti-ferromagnetic interactions and vanishing collective spin. Using a spin-resolved detection approaching single-atom resolution, we show that the reconstructed many-body state is quasi-pure, while one-body observables correspond to a mixed state. Our results highlight the interplay between symmetry and interaction to develop entanglement in a quantum system.