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Quantum computing


Macroscopic quantum superposition of current states in a Josephson-junction loop

 а,  а,  а,  а,  а,  а, б,  б,  в
а Delft University of Technology, Delft, The Netherlands
б Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 38-401 Cambridge, 02139-4307, Cambridge, США
в Massachusetts Institute of Technology, Cambridge, USA

Superconducting circuits with Josephson tunnel junctions are interesting systems for research on quantum-mechanical behavior of macroscopic degrees of freedom. A particular realization is a small superconducting loop containing three Josephson junctions. Close to magnetic frustration $1/2$, the physics of this system corresponds to a double well, whose minima correspond to persistent currents of opposite sign. We present DC measurements of the flux indicating a smooth transition close to the degeneracy point even at very low temperatures. Furthermore, microwave-spectroscopy experiments allow for the excitation to the next excited state. The dependence of the energy of the resonance on the applied flux clearly indicates the nature of these states as tunneling-splitted superpositions of flux states. We theoretically analyze the system using a generalized master-equation formulation of the spin-boson model. We address the nature of the measuring process by a switching DC SQUID and the possible interpretation of the spectroscopy data in terms of quantum coherence. We discuss these aspects in the context of further applications as a quantum bit.

Текст pdf (329 Кб)
English fulltext is available at DOI: 10.1070/1063-7869/44/10S/S26
PACS: 71.10.+Pm, 73.22.Dj, 85.25.−j, 73.40.Gk (все)
DOI: 10.1070/1063-7869/44/10S/S26
URL: https://ufn.ru/ru/articles/2001/13/z/
Цитата: Wilhelm F K, van der Wal C H, ter Haar A C. J, Schouten R N, Harmans C J. P. M, Mooij J E, Orlando T P, Lloyd S "Macroscopic quantum superposition of current states in a Josephson-junction loop" УФН 171 117–121 (2001)
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English citation: Wilhelm F K, van der Wal C H, ter Haar A C. J, Schouten R N, Harmans C J. P. M, Mooij J E, Orlando T P, Lloyd S “Macroscopic quantum superposition of current states in a Josephson-junction loopPhys. Usp. 44 117–121 (2001); DOI: 10.1070/1063-7869/44/10S/S26

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