BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-9218
DTSTART:20250516T150000Z
DTEND:20250516T170000Z
DTSTAMP:20260413T135756Z
LAST-MODIFIED:20250429T153029Z
LOCATION:5280 CH
SUMMARY:Noise characterization for Spin and Charge qubits\, Thesis Def
 ense\, Deepak Mallubhotla\, Physics PhD student
DESCRIPTION:Quantum computing offers substantial advantages over class
 ical computers for certain problems\, but a fundamental challenge pers
 ists: qubits suffer from environmental noise causing decoherence.    T
 o achieve scales required for practical applications\, error correctio
 n techniques must overcome these noise limitations.    Studying variou
 s noise types is essential for developing effective mitigation strateg
 ies.<br>\n<br>\nThis dissertation first analyzes evanescent-wave Johns
 on noise (EWJN) near small metallic devices.    Caused by thermal and 
 quantum charge motion in conductors\, this noise creates field fluctua
 tions beyond the conductor's surface.    Noise correlations B(x\, t) B
 (x'\, t') are calculated when device size is smaller than material ski
 n depth\, yielding closed-form solutions via multipole expansion.<br>\
 n<br>\nNext\, EWJN is examined near BCS superconductors using a half-s
 pace geometry where superconductor dimensions exceed qubit distance.  
   Superconductors generate less noise than normal conductors at temper
 atures well below critical temperature\, for both magnetic and electri
 c fields.    A Hebel-Slichter peak with enhanced noise appears just be
 low critical temperature\, dependent on qubit orientation.<br>\n<br>\n
 Finally\, this dissertation discusses 1/f charge noise.<br>\nIt has be
 en hypothesized that this noise is caused by fluctuating two-level sys
 tems (TLSs).    We show that measurements of noise power spectral dens
 ity do not fully determine TLS parameters exactly\, and present a Baye
 sian technique of assigning likelihoods to different parameter ranges 
 instead.    This allows for partial\, statistical information to be ex
 tracted\, giving predictions of TLS size and density.    Two recent me
 asurements are analyzed\, giving predictions consistent with both each
  other and with measurements in the literature obtained through other 
 techniques.
URL:https://www.physics.wisc.edu/events/?id=9218
END:VEVENT
END:VCALENDAR