Regensburg 2013 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 37: Quantum Coherence, Quantum Information Systems 1

TT 37.2: Vortrag

Mittwoch, 13. März 2013, 09:45–10:00, H19

Quantum limit of nuclear spin polarization in semiconductor quantum dots — •Julia Hildmann¹, Eleftheria Kavousanaki², Hugo Ribeiro¹, and Guido Burkard¹ — ¹Department of Physics, University of Konstanz, D-78457 Konstanz, Germany — ²Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology, Graduate University, Okinawa, 904-0412 Japan

Since the original proposal by Loss and DiVincenzo to use single electron spins confined in quantum dots (QDs) as quantum bits (qubits) [1], a lot of effort has been made to perform coherent control of electron spins in QDs. One of the challenges for using electron spins as qubits remains decoherence due to hyperfine interaction with the nuclear spin bath of the host material (III-V semiconductors). Among various proposals to extend coherence times, there is the possibility to polarize the nuclear spins to a high degree (close to 100% [2]). A recent experiment, which relies on spin-forbidden transitions between heavy holes and positive trions, shows the highest until now reported polarization of about 65% [3]. Simple rate equations describing the pumping mechanism fail to describe the observed saturation predicting a fully polarized nuclear state and not constituting an appropriate description of the nuclear spin bath dynamics. We present a full quantum mechanical approach to this particular problem and show that the pumping saturation is a consequence of the collective nuclear spin quantum dynamics. [1] D. Loss and D. P. DiVincenzo, Phys Rev. A 57, 120 (1998). [2] W. A. Coish and D. Loss, Phys. Rev. B 70, 195340 (2004). [3] E. A. Chekhovich et al, Phys. Rev. Lett. 104, 066804 (2010).