Manipulating the Quantum State of an Electrical Circuit

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Science  03 May 2002:
Vol. 296, Issue 5569, pp. 886-889
DOI: 10.1126/science.1069372

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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 coherenceQ ϕ ≅ 25,000 is sufficiently high that a solid-state quantum processor based on this type of circuit can be envisioned.

  • * To whom correspondence should be addressed. E-mail: vion{at}

  • Member of CNRS.

  • Present address: Applied Physics Department, Yale University, New Haven, CT 06520, USA.

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