Quantum expulsion of impurities from a Bose-Einstein condensate

When a sizable, hard-sphere-like impurity is placed in a confined Bose-Einstein condensate, it will force a hole in the condensate wave function. Since it costs more energy to drill a hole at the wave function's maximum (near the trap center) than at its minimum (near the trap edge), the impurity will be expelled from the condensate. In sharp contrast to the classical case, the Bose condensed atoms can collectively expel impurities much more massive than themselves with essentially no individual collision with the impurity. For C-60 molecules freely falling through a condensate of atomic hydrogens, we estimate that they will be deflected with a radial acceleration comparable to g. At the extremely low density of the hydrogen condensate, only one out of two hundred C-60 will likely to encounter a single hydrogen atom during its fall. The scattered fullerenes would then form a detectable, banded density pattern outside of the trap. (C) 2000 Published by Elsevier Science B.V. PACS: 03.75.Fi; 05.30.Jp; 32.80.Pj.