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Published in:
2007 | OriginalPaper | Chapter
Decoherence of a Quantum Bit Circuit
Authors : Grégoire Ithier, François Nguyen, Eddy Collin, Nicolas Boulant, Phil J. Meeson, Philippe Joyez, Denis Vion, Daniel Estève
Published in: Quantum Decoherence
Publisher: Birkhäuser Basel
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Solid state quantum bit circuits (qubits) are candidates for the implementation of quantum processors, which can in principle perform some computational tasks beyond reach of classical sequential processors. Decoherence is there a key issue since electrical circuits are more prone to decoherence than microscopic objects such as atoms. We introduce the different families of solid state qubits, which are either based on single particle states in semiconductor nanostructures, or on global quantum states of superconducting Josephson circuits. We treat more in detail the Cooper pair box Josephson circuit, and the quantronium circuit derived from it. In this device, a decoupling strategy of the circuit from the outside circuitry allows to improve quantum coherence. We expose results obtained on the manipulation of the qubit state in the quantronium. We develop a general framework for understanding decoherence in qubit circuits, and show how coherence time measurements allow to characterize noise sources coup.