High-contrast spatial interference of BECs

We use magnetic levitation [1-3] and a variable-separation dual optical plug [4] to obtain clear spatial interference between two BECs axially separated by up to 0.25mm. Fringes are observed using standard (i.e. non-tomographic) resonant absorption imaging. The `magnifying' effect of a weak inverted parabola potential on fringe separation is observed and agrees well with theory [4]. With 160ms levitation we recently observed single-shot interference contrasts of 95% (see 1.5×0.75mm absorption image below), close to the theoretical limit due to pixellation of the sinusoidal fringes on our CCD camera. Interference patterns with fringe periods of 85microns (individual de Broglie wavelengths of 170microns) are possible with 200ms levitation.