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DY: Fachverband Dynamik und Statistische Physik

DY 4: Quantum Dynamics, Decoherence, and Quantum Information

DY 4.6: Vortrag

Montag, 26. März 2012, 16:30–16:45, MA 001

Universal Quantum Computing with Spin and Valley Qubits — •Niklas Rohling and Guido Burkard — Department of Physics, University of Konstanz, D-78457 Konstanz, Germany

We study theoretically how to perform state preparation (a), universal quantum gates (b), and read-out (c) in a two-electron double quantum dot with spin and valley degrees of freedom as they are present in graphene or carbon nanotubes. In the spin-only case, task (b) can be implemented via Heisenberg-exchange coupling and local gates [1] and the tasks (a) and (c) by adiabatic transitions between (0,2)- and (1,1)-charge configurations [2]. If valley degeneracy is present, we can consider all states with symmetric charge distribution as a 16-dimensional logic space consisting of two spin and two valley qubits. We show that, although the exchange interaction couples spins as well as valleys, this exchange coupling together with local gates is sufficient to generate a unitary operation which is a universal two-qubit gate in spin space and does not change the valley qubits, or vice versa. State preparation and projective measurements on a specific state are possible by obtaining control of the spin and the valley Zeeman term in each dot.

[1] D. Loss and D. P. DiVincenzo, Phys. Rev. A 57, 120 (1998)

[2] J. R. Petta et al., Science 309, 2180 (2005)