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R. G. Herb Condensed Matter Seminar
Optimal quantum gates in imperfect qubits
Date: Thursday, September 17th
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Frank Wilhelm, University of Waterloo & ICQ
Abstract: Physical qubits are necessarily not perfect: they typically contain higher levels beyond the two-state Hilbert space of a qubit and couple to decoherence mechanisms. We show how optimal control theory helps to accommodate these imperfections and still realize fast high-fidelity quantum gates. For the case of a weakly anharmonic multilevel system containing a qubit, we introduce the derivative removal by adiabatic gate (DRAG) technique that retains adiabaticity even for fast gates. This technique allows improvement of gate fidelity in realistic superconducting setups by an order of magnitude beyond the present state of the art and to get close to the fault-tolerance threshold [1] and beyond, if multiple carrier frequencies are used. In the case of non-Markovian decoherence, optimal gates are extremely short Rabi bursts at the optimum working point, which are modulated to refocus counter-rotating terms [2].

[1] F. Motzoi, J. M. Gambetta, P. Rebentrost, and F. K. Wilhelm, Phys. Rev. Lett., in press, arXiv:0901.0534.
[2] P. Rebentrost, I. Serban, T. Schulte-Herbrueggen, and F. K. Wilhelm, Phys. Rev. Lett. 102, 090401 (2009).
Host: Robert McDermott
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