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SEQUENCE:0
UID:UW-Physics-Event-3521
DTSTART:20150114T160000Z
DURATION:PT1H0M0S
DTSTAMP:20260419T142550Z
LAST-MODIFIED:20141107T144859Z
LOCATION:5310 Chamberlin Hall
SUMMARY:The pumpistor: understanding the parametrically flux-pumped SQ
 UID by its electrical impedance\, R. G. Herb Condensed Matter Seminar\
 , Kyle Sundqvist \, Texas A&M
DESCRIPTION:Parametric amplifiers based on superconducting circuits ha
 ve experienced recent popularity. It is possible to produce supercondu
 cting circuits which may sustain and amplify coherent states of microw
 aves close to the quantum limit. To this end\, we describe a circuit u
 nderstanding of the flux-pumped Superconducting QUantum Interference D
 evice (SQUID).  An unpumped SQUID acts as an inductance\, the Josephso
 n inductance\, whereas a flux-pumped SQUID develops an additional\, pa
 rallel element which we have coined the "pumpistor.'' Parametric gain 
 can be understood as a result of a negative resistance of the pumpisto
 r. In the degenerate case\, the gain is sensitive to the relative phas
 e between the pump and signal. In this case\, a phase-sensitive impeda
 nce provides a classical analogy to quantum squeezing found in our exp
 eriments.<br>
\n         Conversely\, in the nondegenerate case\, gain
  is independent of phase. Here the pump frequency is not a multiple of
  the signal frequency\, and it becomes necessary to consider idler ton
 es. For the nondegenerate three-wave case\, we present an intuitive pi
 cture for a parametric amplifier containing a flux-pumped SQUID where 
 current at the signal frequency depends upon the load impedance at an 
 idler frequency.  This understanding has recently lead to the experime
 ntal realization of a SQUID parametric amplifier with strong environme
 ntal coupling\, allowing for substantially increased bandwidth and dyn
 amic range.<br>
\n        The use of equivalent impedances offers insi
 ghts not always apparent from the Hamiltonian equations of motion.  In
  particular\, our "pumpistor" impedance models immediately provide rea
 dily testable predictions for many other circuits containing flux-pump
 ed SQUIDs. 
URL:https://www.physics.wisc.edu/events/?id=3521
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