Macroscopic Quantum Physics of a Superfluid ³He Weak Link
or
"Whistle While You Work"

An applied chemical potential difference between two weakly coupled macroscopic quantum systems should generate mass current oscillations between them. In superconductors, where the weak coupling is usually achieved by using a Josephson tunnel junction, this oscillating current is sometimes called the AC Josepson Effect.

I will describe recent experiments, with an array of 100 nm diameter apertures, which have confirmed the existence of these quantum oscillations in superfluid ³He-B. I will also report on the first direct measurement of the current phase-difference relation, I(phi), for a superfluid ³He weak link, along with a number of other phenomena associated with the Josephson effect which have now been observed in ³He. In addition, a newly discovered metastable macroscopic quantum state will be discussed.

This experiment reveals several remarkable phenomena heretofore inaccessible to superconducting Josephson junctions, such as direct observation of quantum oscillations and continuous knowledge of the dynamics of the quantum phase difference. I will also describe how the observation of a sine-like I(phi) relation lays the foundation for the future creation of a superfluid analog of a dc-SQUID.