Disque Hall 919
Physics Colloquium: "Quantum Tunneling Between Macroscopically Distinct States in Superconducting"
Thursday, October 3, 2013
3:30 PM-4:30 PM
Speaker: Dr. Alexey Bezryadin, University of Illinois, Urbana-Champaign
Abstract: The quantum tunneling effect is known to take place in the microscopic world, i.e., in the world of the electrons and atoms. Tunneling usually happens out of a metastable energy trap defined by a local energy minimum. The topic of my talk is about the applicability of the rules of quantum tunneling to larger objects, made of many atoms or many electrons. In particular, we will consider a loop made of a superconducting wire. (Remember that superconductors are such metals, which exhibit zero resistance to the electric current at low temperatures.) The metastable state for this loop is the state with a large supercurrent circling around the loop. The stable state is the state with the lowest possible energy, which is the state with zero current. It is well known, that if a supercurrent is set up in a superconducting solenoid such current can run forever without any noticeable decay. Yet we and other groups find that if the loop is made of a very thin wire, just a few nanometers in diameter, then the current can decay with time. We will discuss two different mechanisms of the current decay, namely the thermal activation of Little’s phase slips  as well as quantum tunneling of such phase slips [2,3]. We also find that under certain conditions, namely under the condition of rather weak supercurrent values, the phase slips prefer to tunnel in pairs.
Host: Dr. Goran Karapetrov
Dr. Goran Karapetrov