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 sub-circuit. The measured quality factor of quantum coherence Qphi=25000 is sufficiently high that a solid-state quantum processor based on this type of circuit can be envisioned.
@article{arxiv.cond-mat/0205343,
title = {Manipulating the Quantum State of an Electrical Circuit},
author = {D. Vion and A. Aassime and A. Cottet and P. Joyez and H. Pothier and C. Urbina and D. Esteve and M. H. Devoret},
journal= {arXiv preprint arXiv:cond-mat/0205343},
year = {2009}
}