Manipulating the quantum state of an electrical circuit.
We have designed and operated a superconducting tunnel junction circuit that behaves as a two-level atom: the "quantronium." An arbitrary evolution of its quantum state can be programmed with a series of microwave pulses, and a projective measurement of the state can be performed by a pulsed readout subcircuit. The measured quality factor of quantum coherence Qphi approximately 25,000 is sufficiently high that a solid-state quantum processor based on this type of circuit can be envisioned.
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Quantronics Group, Service de Physique de l'Etat Condensé, Direction des Sciences de la Matière, Commissariat à l'Energie Atomique-Saclay, 91191 Gif-sur-Yvette, France. vion@drecam.saclay.cea.fr
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