Towards quantum electrical circuits

Electrical circuits can behave quantum mechanically when decoherence induced by uncontrolled degrees of freedom is sufficiently reduced. Recently, different nanofabricated superconducting circuits based on Josephson junctions have achieved a degree of quantum coherence sufficient to allow the manipulation of their quantum state with NMR-like techniques. Because of their potential scalability, these quantum circuits are presently considered for implementing quantum bits, which are the building blocks of the proposed quantum processors. We have operated such a Josephson qubit circuit in which a long coherence time is obtained by decoupling the qubit from its readout circuit during manipulation. We report pulsed microwave experiments which demonstrate the controlled manipulation of the qubit state.