Impurity Expulsion From a Bose-Einstein Condensate

TL;DR

This paper explores how impurities are expelled from a Bose-Einstein condensate due to energy considerations, proposing a method to detect condensation onset via impurity deflection patterns.

Contribution

It introduces a novel mechanism for impurity expulsion in BECs and suggests a practical detection method using impurity deflection patterns.

Findings

Impurities are expelled from the condensate center due to energy costs.

Deflected impurities form characteristic density patterns outside the trap.

Detection of impurity deflection indicates the onset of Bose-Einstein condensation.

Abstract

When a sizable, hard-sphere-like impurity is placed in a trapped Bose-Einstein condensate, it will create 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. This suggests that C-60 molecules freely falling through a condensate of atomic hydrogen may be deflected by a radial acceleration comparable to g. The scattered fullerenes would then form a characteristic banded density pattern outside of the trap. The detection of these deflected molecules can be used to identify the onset of Bose-Einstein condensation.