Collisional deexcitation in a quasi-two-dimensional degenerate bosonic gas

We separate a Bose-Einstein condensate into an array of two-dimensional (2D) sheets and excite quantized vibrational motion in the direction normal to the sheets. The measured collisional decay rates are suppressed due to the reduced dimensionality, a matter wave analog to inhibited spontaneous emission. After decay, the large excitation energy is transferred to back-to-back outgoing atoms, imaged as rings in the 2D plane. The ring diameters correspond to vibrational energy level differences, and edge-on imaging allows identification of the final vibrational states.