Department of Physics
Research, teaching and outreach in Physics at UW–Madison

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R. G. Herb Condensed Matter Seminars
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Dynamic Nuclear Polarization in Double Quantum Dots
Date: Thursday, April 17th
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Jason Petta, Princeton University
Abstract: Trapped electrons in GaAs quantum dots are coupled to approximately one million lattice nuclei through the contact hyperfine interaction. Random hyperfine fields drive rotations from the singlet state (S) to the triplet state (T_O ), leading to an ensemble averaged spin 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 into resonance with the T_+ state, where hyperfine fields drive rapid rotations between S and T_+ , `flipping' an electron spin and `flopping' a nuclear spin [2]. The resulting Overhauser field approaches 80 mT, in agreement with a simple rate-equation model. A self-limiting pulse sequence is developed that allows the steady-state nuclear polarization 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 increased nuclear polarization.

[1] J. R. Petta /et al./, Science *309*, 2180 (2005).

[2] J. R. Petta, J. M. Taylor /et al./, Phys. Rev. Lett. *100*, 067601 (2008).
Host: Vavilov
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