Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 14: Symposium Superconducting Quantum Systems

TT 14.6: Fachvortrag

Samstag, 5. März 2005, 16:15–16:45, TU H104

Optimizing two-qubit quantum logic gates for superconducting systems — •Frank Wilhelm — Department Physik and CeNS, LMU, Theresienstr. 37, 80333 München

With the maturation of superconducting qubits it is now possible to implement two-qubit quantum logic operations such as the controlled-not (CNOT) gate [1]. We describe the necessary ingredients: i) An suitable interaction. I will describe a scheme for coupling flux qubits controlled by an external current [2]. ii) An appropriate pulse sequence. We will use optimum control theory, well known in nuclear magnetic resonance, to derive optimum smooth pulses. For untunable interaction [3], a substantial improvement of gate fidelity (to 0.99) and time (50 ps) compared to [1] can be achieved by pulse shaping. In the tunable case, the optimum pulse is much simpler [2]. iii) Sufficient coherence. We will discuss the sensitivity of the gate performance to decoherence and the benefit of encoding into decoherence-free subspaces (DFSs) [4].

[1] T. Yamamoto, Y.A. Pashkin, O. Astafiev, Y. Nakamura, and J.S. Tsai, Nature 425, 941 (2003).

[2] B.L.T. Plourde, J.Zhang, K.B. Whaley, F.K. Wilhelm, T.L. Robertson, T. Hime, S. Linzen, P.A. Reichardt, C.-E. Wu, and John Clarke, Phys. Rev. B(R) 70, 140501 (2004).

[3] V. Bergholm, A. Spoerl, T. Schulte-Herbrueggen, S.J. Glaser, M.J. Storcz, and F.K. Wilhelm, in preparation.

[4] M.J. Storcz, J. Vala, K.R. Brown, J. Kempe, F.K. Wilhelm, and K.B. Whaley, cond-mat/0407780.