A two-particle, four-mode interferometer for atoms

Understand

We present a free-space interferometer to observe two-particle interference of a pair of atoms with entangled momenta.

• The source of atom pairs is a Bose--Einstein condensate subject to a dynamical instability, and the interferometer is realized using Bragg diffraction on optical lattices, in the spirit of our recent Hong--Ou--Mandel experiment.
• We report an observation consistent with an entangled state at the input of the interferometer.
• We explain how our current setup can be extended to enable a test of a Bell inequality on momentum observables.