Regensburg 2002 – scientific programme

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TT: Tiefe Temperaturen

TT 23: Mesoskopische Systeme II

TT 23.1: Invited Talk

Friday, March 15, 2002, 10:15–10:45, H18

Steering the Quantum State of an Electrical Circuit — •Denis Vion, A. Aassime, A. Cottet, P. Joyez, P.F. Orfila, H. Pothier, C. Urbina, D. Esteve, and M.H. Devoret — SPEC, CEA-Saclay, F91191 Gif sur Yvette, Frankreich

We have designed, fabricated, and operated a superconducting electrical circuit that can be i) prepared in any quantum superposition of its two lowest energy eigenstates and ii) measured by projection onto one of these eigenstates. This circuit implements a quantum bit (qubit). It is based on the Cooper pair box [1], a device which combines charging and Josephson effects, and in which quantum coherence has already been demonstrated [2]. In our design [3], the qubit can be decoupled from its measuring circuitry during preparation of a quantum state. We present experimental results demonstrating quantum coherent driven and free evolutions of the qubit. The experimental coherence time of superposed states corresponds to about height thousands oscillations at the transition frequency. Such a long coherence time paves the way to multiple qubit circuits for quantum computing.

[1] V. Bouchiat et al, Physica-Scripta, 76, 165 (1998).

[2] Y. Nakamura, Y.A. Pashkin, and J.S. Tsai, Nature, 398, 786 (1999).

[3] A. Cottet et al, to be published in Physica C.