Observation of Bose-Einstein Condensation in a Strong Synthetic Magnetic Field

TL;DR

This paper reports the first observation of Bose-Einstein condensation in a system described by the Harper-Hofstadter model with a synthetic magnetic field, demonstrating a new quantum state of matter with topological properties.

Contribution

It experimentally realizes and observes the ground state of the Harper-Hofstadter Hamiltonian with strong synthetic magnetic fields in ultracold atoms, a significant step forward in quantum simulation.

Findings

Observation of Bose-Einstein condensation in a synthetic magnetic field

Direct measurement of momentum distribution showing gauge dependence

Successful adiabatic preparation of the superfluid ground state

Abstract

Extensions of Berry's phase and the quantum Hall effect have led to the discovery of new states of matter with topological properties. Traditionally, this has been achieved using gauge fields created by magnetic fields or spin orbit interactions which couple only to charged particles. For neutral ultracold atoms, synthetic magnetic fields have been created which are strong enough to realize the Harper-Hofstadter model. Despite many proposals and major experimental efforts, so far it has not been possible to prepare the ground state of this system. Here we report the observation of Bose-Einstein condensation for the Harper-Hofstadter Hamiltonian with one-half flux quantum per lattice unit cell. The diffraction pattern of the superfluid state directly shows the momentum distribution on the wavefuction, which is gauge-dependent. It reveals both the reduced symmetry of the vector potential and the twofold degeneracy of the ground state. We explore an adiabatic many-body state preparation protocol via the Mott insulating phase and observe the superfluid ground state in a three-dimensional lattice with strong interactions.