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UID:UW-Physics-Event-1150
DTSTART:20080515T150000Z
DURATION:PT1H0M0S
DTSTAMP:20260506T200130Z
LAST-MODIFIED:20080423T154151Z
LOCATION:5310 Chamberlin
SUMMARY:Mach-Zehnder Interferometry and Microwave-Induced Cooling in P
 ersistent-Current Qubits\, R. G. Herb Condensed Matter Seminar\, Will 
 Oliver\, MIT/Lincoln Labs
DESCRIPTION:Superconducting persistent-current qubits are quantum-cohe
 rent artificial atoms with multiple energy levels. In the presence of 
 large-amplitude harmonic excitation\, the qubit state can be driven th
 rough one or more of the energy-level avoided crossings. The resulting
  Landau-Zener transitions mediate a rich array of quantum-coherent phe
 nomena as a function of the driving amplitude and frequency. <br>
\n<b
 r>
\nIn this talk\, we present three such demonstrations of quantum co
 herence in a strongly-driven niobium persistent-current qubit. The fir
 st is Mach-Zehnder-type interferometry [1]\, for which we observe quan
 tum interference fringes for 1-50 photon transitions. The second is a 
 new operating regime exhibiting coherent quasi-classical dynamics [2]\
 , for which the MZ quantum interference persists even for driving freq
 uencies smaller than the resonance linewidth. The third is microwave-i
 nduced cooling [3]\, for which we achieve effective qubit temperatures
  < 3 mK\, a factor 10x-100x lower than the dilution refrigerator ambie
 nt temperature.<br>
\n<br>
\nThese experiments exhibit a remarkable ag
 reement with theory\, and are extensible to other solid-state qubit mo
 dalities. In addition to our interest in these techniques for fundamen
 tal studies of quantum coherence in strongly-driven solid-state system
 s\, we anticipate they will find application to nonadiabatic qubit con
 trol and state-preparation methods for quantum information science and
  technology.<br>
\n<br>
\n[1] W.D. Oliver\, Y. Yu\, J.C. Lee\, et al.\
 , Science 310\, 1653 (2005).<br>
\n<br>
\n[2] D.M. Berns\, W.D. Oliver
 \, S.O. Valenzuela et al.\, PRL 97\, 150502 (2006).<br>
\n<br>
\n[3] S
 .O. Valenzuela\, W.D. Oliver\, D.M. Berns\, et al.\, Science (2006).<b
 r>
\n<br>
\nThe work at Lincoln Laboratory was sponsored by the Air Fo
 rce under Air Force Contract FA8721-05-C-0002. Opinions\, interpretati
 ons\, conclusions\, and recommendations are those of the author(s) and
  are not necessarily endorsed by the United States Government.<br>
\n
URL:https://www.physics.wisc.edu/events/?id=1150
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