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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-3500
DTSTART:20141113T160000Z
DURATION:PT1H0M0S
DTSTAMP:20260316T052027Z
LAST-MODIFIED:20141106T194023Z
LOCATION:5310 Chamberlin Hall
SUMMARY:Generalized Tunneling Model (GTM) for Two Level System (TLS) i
 n amorphous materials and its predictions for their dephasing and the 
 noise in superconducting microresonators\, R. G. Herb Condensed Matter
  Seminar\, Lara Faoro\, Universites Paris 6 et 7 and Rutgers Universit
 y
DESCRIPTION:Thin film high quality superconductor microresonators are 
 important for a number of diverse applications that range from quantum
  computation to submillimeter and far-infrared astronomy. The performa
 nce of these devices has improved dramatically over the past decades a
 nd resonator quality factors above 10^6 are now routinely achieved usi
 ng single-layer structures deposited on high-quality low-loss crystall
 ine substrate. Achieving high-quality factors requires minimizing all 
 potential sources of dissipation and noise. One prominent source of di
 ssipation in microresonators has been found to be Two Level Systems (T
 LSs) in thin amorphous dielectric surface layers of the microresonator
 s. These TLS are also responsible for an excess frequency noise (jitte
 r) in the resonators. TLS in amorphous materials are usually described
  by the Standard Tunneling Model (STM). In this theory\, TLS are repre
 sented as independent quantum two level systems with constant distribu
 tion of low energy states. Unfortunately\, STM fails to explain the da
 ta of noise in the superconducting microresonators so a consistent mod
 el for the noise due to TLS in superconducting resonators remains an o
 pen issue.<br>
\nIn this talk we shall first review data of recent exp
 eriments performed on high quality superconducting microresonator wher
 e low frequency noise spectra have been studied in varying temperature
  and different applied power and argue that the data are inconsistent 
 with the STM. We shall then propose a new model\, the Generalized Tunn
 eling Model (GTM) which includes strong interactions between TLS and a
  slow power law dependence of their density of states. We show that th
 e predictions of this model are in a perfect agreement with the recent
  studies of the noise in high quality superconducting resonators. The 
 predictions also agree with the temperature dependence of the TLS deph
 asing rates observed in phase qubits.  Finally\, we discuss the origin
  of the universal dimensionless parameter that controls the interactio
 n between TLS in glasses and show that it is consistent with the assum
 ptions of the GTM.
URL:https://www.physics.wisc.edu/events/?id=3500
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