Experiments using helium-4 weak links

This dissertation presents results from experiments involving two reservoirs of superfluid 4He coupled through an array of nanosize apertures. Following the introductory chapter, we present our measurement showing the smooth evolution of current-phase relation as the system leaves the strongly coupled phase slip regime and enters the weakly coupled Josephson regime.;In the low temperature strongly coupled regime, we have discovered a transition from synchronous to asynchronous superfluid phase slippage in an array of apertures. We have investigated the underlying mechanism with three different experiments and same numerical simulations.;We have developed a superfluid 4He interferometer using two weak link junctions configured as in a dc-SQUID. The first observation of quantum interference in superfluid 4He is presented.;Using this new class of matter wave interferometer, we have investigated the connection between the classical two fluid model and the quantum mechanical wavefunction picture of superfluid helium. We have quantitatively verified the relation between the superfluid velocity and the phase gradient of the condensate macroscopic wavefunction. We have also discovered a new method to probe the initial onset of the motion of a single vortex line driven by axial flow in a macroscopic channel. The results presented should lead to an enhanced understanding of vortex instability processes in superfluid helium flow.;Finally, we have demonstrated a flux locking technique using injected heat current to linearize the output of a superfluid 4He interferometer. This is the first time any matter wave interferometer has been linearized. We present its principle and demonstrate its operation.;The results reported in this dissertation reveal some fascinating nature of superfluid 4H weak link physics and represent a breakthrough in superfluid matter wave interferometry.