Dresden 2006 – wissenschaftliches Programm

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MA: Magnetismus

MA 6: Invited Talks Vandersypen / Herper

MA 6.1: Hauptvortrag

Montag, 27. März 2006, 13:45–14:15, HSZ 03

Read-out, relaxation and decoherence of electron spins in a quantum dot — •Lieven Vandersypen — Kavli Institute of NanoScience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands

We have recently demonstrated two different techniques for single-shot measurement of the state of an individual electron spin in a semiconductor quantum dot, with measurement fidelities up to ~90% [1,2]. The measurement relies on spin-to-charge conversion, combined with real-time detection of single-electron charges with a quantum point contact electrometer.

Using this readout technique, we have characterized the relaxation time, T1, for a single electron spin, as well as for two-electron spin states. In both cases, very long T1’s are observed, of order 1 ms [1,2], consistent with theoretical predictions of spin-orbit dominated spin relaxation.

Phase randomization (characterized by T2), in contrast, is expected to be dominated by the randomly fluctuating hyperfine field caused by the nuclei in the semiconductor material. We have probed the effect of the nuclei via transport measurement through two dots in series, and observe a hyperfine field of about 1 mT. When averaging over different nuclear configurations, this implies an apparent dephasing time T2* of 25 ns. We can suppress its effect by applying a small external magnetic field or by increasing the interdot tunnel coupling [3].

[1] J. Elzerman et al., Nature 430, 431-435 (2004)

[2] R. Hanson et al., Phys. Rev. Lett. 94, 196802 (2005)

[3] F. Koppens, J. Folk, et al., Science, 309, 1346 (2005)