Dresden 2003 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 49: Poster II

HL 49.36: Poster

Donnerstag, 27. März 2003, 16:30–19:00, HSZ/P2

Theory for Quantum Dot Charge Qubits - Decoherence due to Cotunneling — •Udo Hartmann and Frank K. Wilhelm — Sektion Physik und CeNS, Ludwig-Maximilians-Universität, Theresienstr. 37, 80333 München

We analyze the decoherence of a two-state system (TSS) coupled to two baths being in mutual disequilibrium: a double quantum dot in the cotunneling regime at finite voltage. This system is treated using the Bloch-Redfield generalized master equation for the Schrieffer-Wolff transformed Hamiltonian. We show that the decoherence, characterized through relaxation or dephasing time can be controlled through the external voltage and that the optimum point where these times are maximum is not necessarily in equilibrium. We furthermore study the cotunneling transport through this system. We consider the case of weak coupling to the leads and a bias point in the Coulomb blockade. We study the system for arbitrary bias voltages below the Coulomb energy. We observe a rich, non-monotonic behaviour of the stationary current depending on the internal degrees of freedom. In particular, it turns out that at fixed transport voltage, the current through the system is largest at weak-to-intermediate inter-dot coupling.