Colloquium: Dr. Stephen Eckel, NIST/JQI
Location
Physics : 401
Date & Time
February 4, 2015, 3:30 pm – 4:30 pm
Description
TITLE: Superfluid atom circuits
ABSTRACT: Persistent currents are a hallmark of both superfluidity and superconductivity. Just as a current in a superconducting circuit will flow forever, if a current is created in a superfluid Bose-Einstein condensate, the flow will not decay as long as the current is below a critical value. Using a ring-shaped Bose-Einstein Condensate we have created a superfluid “atom circuit” that supports long-lived persistent currents. A laser beam is used as a barrier across one side of the torus to create a tunable “weak link” in the condensate circuit and can be used to control the current around the loop. Weak connections between superconductors or superfluids can differ from classical links due to quantum coherence. The properties of a weak link are characterized by a single function, the current-phase relationship. In recent experiments, we have developed a technique to directly measure the current-phase relationship of a weak link. When the weak link is rotated at low rotation rates, we have observed phase slips between well-defined, quantized, current states, and have demonstrated that the system exhibits hysteresis. In electronic circuits, hysteresis plays in important role, particularly in applications like memory and digital noise filters, it's possible in future "atomtronic" circuits, our device could possibly play a similar role.
ABSTRACT: Persistent currents are a hallmark of both superfluidity and superconductivity. Just as a current in a superconducting circuit will flow forever, if a current is created in a superfluid Bose-Einstein condensate, the flow will not decay as long as the current is below a critical value. Using a ring-shaped Bose-Einstein Condensate we have created a superfluid “atom circuit” that supports long-lived persistent currents. A laser beam is used as a barrier across one side of the torus to create a tunable “weak link” in the condensate circuit and can be used to control the current around the loop. Weak connections between superconductors or superfluids can differ from classical links due to quantum coherence. The properties of a weak link are characterized by a single function, the current-phase relationship. In recent experiments, we have developed a technique to directly measure the current-phase relationship of a weak link. When the weak link is rotated at low rotation rates, we have observed phase slips between well-defined, quantized, current states, and have demonstrated that the system exhibits hysteresis. In electronic circuits, hysteresis plays in important role, particularly in applications like memory and digital noise filters, it's possible in future "atomtronic" circuits, our device could possibly play a similar role.