Regensburg 2010 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 31: Poster I: Devices, Quantum Dots and Quantum Wires

HL 31.25: Poster

Tuesday, March 23, 2010, 18:30–20:30, Poster D1

Phonon-mediated vs. Coulombic Back-Action in Quantum Dot circuits — •Daniel Harbusch¹, Daniela Taubert¹, Peter Tranitz², Werner Wegscheider³, and Stefan Ludwig¹ — ¹Fakultät für Physik, Ludwig-Maximilians-Universität München, München, Germany — ²Institut für Experimentelle Physik, Universität Regensburg, Regensburg, Germany — ³Laboratory for Solid State Physics, ETH Zürich, Zürich, Switzerland

Biased quantum point contacts (QPC) are commonly employed to detect the charge states of qubits composed of coupled quantum dots (QD). Although a biased QPC can be a very sensitive charge detector, it emits energy that can be reabsorbed by the nearby QDs and thereby cause unwanted decoherence. We investigate such back-action of a QPC charge detector on coupled QDs.

Our nano-devices are defined by means of Schottky gates on the surface of a GaAs/AlGaAs heterostructure containing a two-dimensional electron system with an electron temperature of T ≈ 100 mK.

Here we observe indirect back-action of a biased QPC onto a double QD. Energy is emitted by non-equilibrium charge carriers in the leads of the biased QPC. Part of this energy is reabsorbed by the double QD where it causes charge fluctuations. The latter can be observed under certain conditions in the stability diagram of the double QD. By investigating the spectrum of the absorbed energy, we identify two different mechanisms mediating the back-action, namely acoustic phonons and Coulomb interaction. Depending on coupling constants and the geometry of the device either of the two mechanisms can be dominant.