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DTSTART:20180325T030000
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DTSTART:20171029T020000
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DTSTAMP:20260424T062901Z
UID:5a61e2fc61b70028312416@ist.ac.at
DTSTART:20180215T110000
DTEND:20180215T111500
DESCRIPTION:Speaker: Amin Hosseinkhani\nhosted by Maksym Serbyn\nAbstract: 
 Superconducting qubits are among the most promising candidates for quantum
  information processing. An important decoherence mechanism for these qubi
 ts originates from interaction between phase degree of freedom with quasip
 article excitations that are tunneling through the Josephson junction. In 
 this talk\, I will review qubit relaxation induced by quasiparticle tunnel
 ing and discuss some experiments showing that quasiparticles are limiting 
 the qubit coherence. I then explain how a normal-metal island in tunnel co
 ntact with the superconducting electrode of a qubit can act as a sink for 
 quasiparticles\, thus improving the qubit's coherence time. We develop the
 oretically and validate experimentally a model for the effect of a single 
 small trap on the dynamics of excess quasiparticles injected in a transmon
 -type qubit. We find that the slow energy relaxation inside the normal-met
 al trap is the bottleneck for quasiparticle trapping [1].  Optimizing quas
 iparticle traps is possible so long as the trap size is larger than a cert
 ain characteristic length. Such optimized traps lead to quick evacuation o
 f the excess quasiparticle density and at the same time suppression of the
  steady-state density and its fluctuations- this can render the qubit more
  stable in time [2]. We then study how the superconducting proximity effec
 t due to normal metal-superconductor contact can influence the qubit perfo
 rmance. The competition between proximity effect and quasiparticle density
  suppression leads to an optimum trap-junction distance at which the qubit
  relaxation rate is minimized. For a transmon qubit\, we find this optimum
  distance to be of the order of 4 to 20 coherence lengths\; the harmful in
 fluence of the proximity effect can be avoided so long as the trap is fart
 her away from the junction than this optimum [3].  [1] R.-P. Riwar\, A. Ho
 sseinkhani\, L. D. Burkhart\, Y. Y. Gao\, R. J. Schoelkopf\, L. I. Glazman
  and G. Catelani\, Phys. Rev. B 94\, 104516 (2016) [2] A. Hosseinkhani\, R
 .-P. Riwar\, R. J. Schoelkopf\, L. I. Glazman\, and G. Catelani Phys. Rev.
  Applied 8\, 064028 (2017) [3] A. Hosseinkhani and G. Catelani\, arXiv:171
 2.05235
LOCATION:Big Seminar room Ground floor / Office Bldg West (I21.EG.101)\, IS
 TA
ORGANIZER:sdanzing@ist.ac.at
SUMMARY:Amin Hosseinkhani: Suppressing quasiparticle-induced relaxation in 
 superconducting qubits
URL:https://talks-calendar.ista.ac.at/events/1055
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