Interferometric Measurement of Quantized Currents in Bose-Einstein Condensates

Weak connections between superconductors or superfluids can differ from classical links due to quantum coherence, which allows for flow without resistance. The weak connections are known as “weak links” and they are a useful element in a number of superconducting circuits.  In recent experiments with a ring-shaped Bose Einstein condensate, we have developed a technique to directly characterize the properties of a superfluid weak link.  To accomplish this, we use two Bose Einstein condensates and take advantage of their unique matter-wave behavior to interfere them together.  The interference patterns allow us to visualize the flow, and in addition, they allow us to characterize the weak link in our system by measuring its current-phase relationship.   This relationship is analogous to the current-voltage relationship in a classical circuit, except that we measure the current that flows through the weak link as a function of the difference in the phase of the matter wave on either side.  These measurements will allow for better characterization of superfluid weak links in atom circuits and may open new avenues of research in quantum transport.