Exploding electron bubbles The first observations of excited electron bubbles in superfluid helium reveal some puzzling features From

The “particle in a box'' is a standard second year quantum mechanics problem, much beloved by lecturers and mastered by successive generations of undergraduates. An electron bubble in liquid helium provides a strikingly simple example of this kind of system, and theory predicts that it should exhibit a series of excited states. But these states have never been demonstrated experimentally. Now Denis Konstantinov and Humphrey Maris of Brown University in the US have observed one of the excited states for the first time by exploding electrons bubbles with sound waves (D Konstantinov and H Maris 2003 Phys. Rev. Lett. 90 025302).