The development of superfluid weak links has led both to the discovery of new physical phenomena and also to the development of superfluid helium quantum interference devices (SHeQUIDs). We describe the physics underlying the SHeQUID and present a brief overview of the current state of this promising technology.
Josephson weak links between samples of macroscopic quantum systems such as superconductors, superfluids, and Bose-Einstein condensates provide a unique tool with which to explore quantum mechanics and an opportunity to create applications based on macroscopic quantum physics. In this review we describe the development of the field of weak links in superfluid 3He. We review the basic techniques used to study this system and then describe the experimental and theoretical milestones that have led to our present understanding.
This book reports on the latest developments in the field of Superfluidity. The phenomenon has had a tremendous impact on the fundamental sciences as well as a host of technologies. It began with the discovery of superconductivity in mercury in 1911, which was ultimately described theoretically by the theory of Bardeen Cooper and Schriever (BCS) in 1957. The analogous phenomena, superfluidity, was discovered in helium in 1938 and tentatively explained shortly thereafter as arising from a Bose-Einstein Condensation (BEC) by London. But the importance of superfluidity, and the range of systems in which it occurs, has grown enormously. In addition to metals and the helium liquids the phenomena has now been observed for photons in cavities, excitons in semiconductors, magnons in certain materials, and cold gasses trapped in high vacuum. It very likely exist for neutrons in a neutron star and, possibly, in a conjectured quark state at their center. Even the Universe itself can be regarded as being in a kind of superfluid state. All these topics are discussed by experts in the respective subfields.
We report the first observation of quantum interference from a grating structure consisting of four weak link junctions in superfluid 4He. We find that an interference grating can be implemented successfully in a superfluid matter wave interferometer to enhance its sensitivity while trading away some of its dynamic range. We also show that this type of device can be used to measure absolute quantum mechanical phase differences. The results demonstrate the robust nature of superfluid phase coherence arising from quantum mechanics on a macroscopic scale.
The aims of this dissertation are twofold. Firstly, the study of superfluidity, presented in the first part, has more a fundational character, since we investigate some well known problems, already raised in the context of superfluid helium, in order to gain a deeper understanding, by exploiting the cleannes of dilute BECs systems, as well as analyzing the new features emerging from the unique dilute BECs properties. We study the BEC flow through weak-links, first analyzing the various regimes of transport by the current-phase relation and the Josephson plasma oscillations, and then turning to the superfluid instability, determining critical velocities and examining the dissipation dynamics in different geometries and dimensionalities. Secondly, the analysis of quantum interferometry, given in the second part, has instead a more technological character, since we propose two possible implementation of interferometric protocols in double-well traps, with application to the measurement of weak-forces, and study their sensitivity in detail, especially in relation to its possible quantum enhancement.