title: Planck distribution of phonons in a Bose-Einstein condensate.
abstract: The Planck distribution of photons emitted by a blackbody led to the development of quantum theory. An analogous distribution of phonons should exist in a Bose-Einstein condensate. We observe this Planck distribution of thermal phonons in a 3D condensate. This observation provides an important confirmation of the basic nature of the condensate's quantized excitations. In contrast to the bunching effect, the density fluctuations are seen to increase with increasing temperature. This is due to the nonconservation of the number of phonons. In the case of rapid cooling, the phonon temperature is out of equilibrium with the surrounding thermal cloud. In this case, a Bose-Einstein condensate is not as cold as previously thought. These measurements are enabled by our in situ k-space technique.
authors: Department of Physics, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel.
authors: R
authors: R
authors: Schley
authors: A
authors: A
authors: Berkovitz
authors: S
authors: S
authors: Rinott
authors: I
authors: I
authors: Shammass
authors: A
authors: A
authors: Blumkin
authors: J
authors: J
authors: Steinhauer