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Nonequilibrium Phenomena in Mesoscopic Physics Norman Birge, Michigan State University, DMR 0405238 & 0705213.  I s  + d I s. I b. sample. V s. I b +  I s  + d I s. JJ.

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  1. Nonequilibrium Phenomena in Mesoscopic PhysicsNorman Birge, Michigan State University, DMR 0405238 & 0705213 Is+dIs Ib sample Vs Ib+Is+dIs JJ Figure: Simplified schematic of FCS experiment. A constant voltage Vs is applied to the sample. The total current Is (average plus fluctuations) passes through a Josephson junction. A separate bias current, Ib, offsets the average current so that it is just below the switching current of the junction. A large enough fluctuation in the sample current will then cause the junction to switch into the normal state. When one applies a constant voltage across a resistor, one expects the electrical current that flows to be constant in time. But that is not quite what happens. The current always fluctuates a little bit – the fluctuations are called “noise.” A century ago Schottky showed that measuring the current noise in a vacuum tube provides a measurement of the charge of the electron. In the past decade researchers have shown that noise measurements can reveal a number of other properties of the system being measured. Nowadays there is interest in measuring higher moments of the noise, a subject called “Full Counting Statistics” or FCS. In collaboration with Daniel Esteve and Hugues Pothier at the CEA Saclay in France, we are looking into using Josephson junctions as detectors of FCS. The basic idea, due to Tobiska and Nazarov, is to use the Josephson junction as a “current threshold detector,” which goes off every time the sample current exceeds a threshold set by the experimenter. Initial results: B. Huard, H. Pothier, N.O. Birge, D. Esteve, X. Waintal, and J. Ankerhold, Ann. der Physik 16, 736 (2007).

  2. Nonequilibrium Phenomena in Mesoscopic PhysicsNorman Birge, Michigan State University, DMR-0405238 & 0705213 Broad scientific impact:The field of quantum optics was born when physicists recognized that photons have statistical properties dictated by quantum mechanics. The field of “quantum electronics” is only in its infancy, but an important element in its development is the full recognition of the statistical properties of electrons moving through electrical circuits. Analogies between different fields of science, even between an old subject like quantum optics and a new one like quantum electronics, often lead to in advances in both areas. Education:Graduate students working in experimental condensed matter physics learn the concepts and experimental tools that are crucial to the future development and applications of nanosciences. Former graduate students from this NSF-sponsored research program have gone on to careers in academia, industry, and government labs. Undergraduate students working in the lab gain valuable research experience that helps them choose an appropriate career path. Current graduate students:Yixing Wang, Eric Gingrich, & Curtis Walkons Recent undergrads:Hamood Arham, William Martinez, Kathy Walsh & Kyle DeGrave

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