Regensburg 2010 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 6: TR: Nanoelectronics II: Spintronics and Magnetotransport

TT 6.3: Vortrag

Montag, 22. März 2010, 14:30–14:45, H19

A singlet - triplet T₊ based qubit — •Hugo Ribeiro¹, Jason Petta², and Guido Burkard¹ — ¹Department of Physics, University of Konstanz, D-78457, Konstanz, Germany — ²Department of Physics, Princeton University, Princeton, NJ 08544, USA

We theoretically model a nuclear-state preparation scheme that increases the coherence time of a two-spin qubit in a double quantum dot. The two-electron system is tuned repeatedly across a singlet-triplet level-anticrossing with alternating slow and rapid sweeps of an external bias voltage. Using a Landau-Zener-Stückelberg model, we find that in addition to a small nuclear polarization that weakly affects the electron spin coherence, the slow sweeps are only partially adiabatic and lead to a weak nuclear spin measurement and a nuclear-state narrowing which prolongs the electron spin coherence. This resolves some open problems brought up by a recent experiment [1]. We also show that the electronic two-spin states singlet and triplet T₊ are promising candidates for the implementation of a qubit in GaAs double quantum dots (DQD). A coherent superposition of the two-spin states is obtained by finite time Landau-Zener-Stückelberg interferometry and the single qubit rotations are performed by means of an external magnetic field with a typical amplitude of about 100 mT, while coherent manipulation can be done within ∼ 1 ns. We also study the nuclear induced decoherence, mainly due to hyperfine contact coupling between the electronic and nuclear spins, and compute the decoherence time T₂^* ∼ 10 ns.

[1] D. J. Reilly et al., Science 321, 817 (2008).