Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 24: Quantum dots and wires: Transport properties II

HL 24.5: Talk

Tuesday, March 27, 2007, 15:00–15:15, H15

Quantum Description of Nuclear Spin Cooling in a Quantum Dot — Henning Christ, Ignacio Cirac, and •Geza Giedke — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching

We study theoretically the cooling of an ensemble of nuclear spins coupled to the spin of a localized electron in a quantum dot. We obtain a master equation for the state of the nuclear spins interacting with a sequence of polarized electrons that allows to study quantitatively the cooling process including the effect of nuclear spin coherences, which can lead to ``dark states'' of the nuclear system in which further cooling is inhibited. We show that the inhomogeneous Knight field mitigates this effect strongly and that the remaining dark state limitations can be overcome by very few shifts of the electron wave function, allowing for cooling far beyond the dark state limit. Numerical integration of the master equation indicates that polarizations larger than 90% can be achieved within a millisecond timescale.