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PRODID:UW-Madison-Physics-Events
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SEQUENCE:0
UID:UW-Physics-Event-1152
DTSTART:20080417T150000Z
DURATION:PT1H0M0S
DTSTAMP:20260422T233426Z
LAST-MODIFIED:20080411T170247Z
LOCATION:5310 Chamberlin
SUMMARY:Dynamic Nuclear Polarization in Double Quantum Dots\, R. G. He
 rb Condensed Matter Seminar\, Jason Petta\, Princeton University
DESCRIPTION:Trapped electrons in GaAs quantum dots are coupled to appr
 oximately one million lattice nuclei through the contact hyperfine int
 eraction. Random hyperfine fields drive rotations from the singlet sta
 te (S) to the triplet state (T_O )\, leading to an ensemble averaged s
 pin dephasing time T_2 * of 10 ns [1]. In this talk\, I will describe 
 how fast electrical control of two-electron spin states near the anti-
 crossing of the singlet (S) and triplet (T_+ ) can be used to polarize
  the nuclear spin bath. An initialized S state is cyclically brought i
 nto resonance with the T_+ state\, where hyperfine fields drive rapid 
 rotations between S and T_+ \, `flipping' an electron spin and `floppi
 ng' a nuclear spin [2]. The resulting Overhauser field approaches 80 m
 T\, in agreement with a simple rate-equation model. A self-limiting pu
 lse sequence is developed that allows the steady-state nuclear polariz
 ation to be set using a gate voltage. Lastly\, I will describe efforts
  at Princeton to fabricate semiconductor nanowire double quantum dots.
  These devices will limit nuclear spin diffusion\, resulting in increa
 sed nuclear polarization.  <br>
\n<br>
\n[1] J. R. Petta /et al./\, Sc
 ience *309*\, 2180 (2005).<br>
\n<br>
\n[2] J. R. Petta\, J. M. Taylor
  /et al./\, Phys. Rev. Lett. *100*\, 067601 (2008).
URL:https://www.physics.wisc.edu/events/?id=1152
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