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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:2
UID:UW-Physics-Event-6542
DTSTART:20211029T203000Z
DTEND:20211029T213000Z
DTSTAMP:20260414T192236Z
LAST-MODIFIED:20211029T211726Z
LOCATION:2103 Chamberlin Hall
SUMMARY:Correlating materials analysis with qubit measurements to syst
 ematically eliminate sources of noise\, Physics Department Colloquium\
 , Nathalie de Leon\, Princeton
DESCRIPTION:The nitrogen vacancy (NV) center in diamond exhibits spin-
 dependent fluorescence and long spin coherence times under ambient con
 ditions\, enabling applications in quantum information processing and 
 sensing. NV centers near the surface can have strong interactions with
  external materials and spins\, enabling new forms of nanoscale spectr
 oscopy. However\, NV spin coherence degrades within 100 nanometers of 
 the surface\, suggesting that diamond surfaces are plagued with ubiqui
 tous defects. I will describe our recent efforts to correlate direct m
 aterials characterization with single spin measurements to devise meth
 ods to stabilize highly coherent NV centers within nanometers of the s
 urface. We also deploy these shallow NV centers as a probe to study th
 e dynamics of a disordered spin ensemble at the diamond surface. 
\n
\
 nOur approach for correlating surface spectroscopy techniques with sin
 gle qubit measurements to realize directed improvements is generally a
 pplicable to many systems. Separately\, I will describe our recent eff
 orts to tackle noise and microwave losses in superconducting qubits. B
 uilding large\, useful quantum systems based on transmon qubits will r
 equire significant improvements in qubit relaxation and coherence time
 s\, which are orders of magnitude shorter than limits imposed by bulk 
 properties of the constituent materials. This indicates that relaxatio
 n likely originates from uncontrolled surfaces\, interfaces\, and cont
 aminants. Previous efforts to improve qubit lifetimes have focused pri
 marily on designs that minimize contributions from surfaces. However\,
  significant improvements in the lifetime of planar transmon qubits ha
 ve remained elusive for several years. We have fabricated planar trans
 mon qubits that have both lifetimes and coherence times exceeding 0.3 
 milliseconds by replacing niobium with tantalum in the device. Followi
 ng this discovery\, we have parametrized the remaining sources of loss
  in state-of-the-art devices using systematic measurements of the depe
 ndence of loss on temperature\, power\, and geometry. This parametriza
 tion\, complemented by direct materials characterization\, allows for 
 rational\, directed improvement of superconducting qubits.
\n
URL:https://www.physics.wisc.edu/events/?id=6542
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