Beyond mean-field physics using multi-mode quantum gases

Quantum gases have been shown to be an ideal platform for exploring fundamental aspects of magnetism and symmetry breaking. Here, we engineer a multi-component quantum gas by using Bragg laser fields to controllably couple momentum orders of a rubidium Bose-Einstein condensate. Using this synthetic momentum-state spinor gas, we present evidence for mean-field magnetic phenomena as well as beyond-mean-field effects such as symmetry breaking. In extending to three-site rings of momentum states, we further explore the influence of artificial gauge fields on phase transitions in this system. These results demonstrate the versatility of synthetic spinor gases for the exploration of fundamental mean-field and many-body physics.