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

F.K. Wilhelm^a, C.H. van der Wal^a, ter Haar A C. J^a, R.N. Schouten^a, Harmans C J. P. M^a, J.E. Mooij^a, b, T.P. Orlando^b, S. Lloyd^c
^aDelft University of Technology, Delft, The Netherlands
^bDepartment of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 38-401 Cambridge, 02139-4307, Cambridge , United States of America
^cMassachusetts 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.

PACS: 71.10.+Pm, 73.22.Dj, 85.25.−j, 73.40.Gk (all)
DOI: 10.1070/1063-7869/44/10S/S26
URL: https://ufn.ru/en/articles/2001/13/z/
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 loop" Phys. Usp. 44 117–121 (2001)

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TY JOUR
TI Macroscopic quantum superposition of current states in a Josephson-junction loop
AU Wilhelm, F. K.
AU van der Wal, C. H.
AU ter Haar A C. J
AU Schouten, R. N.
AU Harmans C J. P. M
AU Mooij, J. E.
AU Orlando, T. P.
AU Lloyd, S.
PB Physics-Uspekhi
PY 2001
JO Physics-Uspekhi
JF Physics-Uspekhi
JA Phys. Usp.
VL 44
IS 13
SP 117-121
UR https://ufn.ru/en/articles/2001/13/z/
ER https://doi.org/10.1070/1063-7869/44/10S/S26

Оригинал: 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); DOI: 10.1070/1063-7869/44/10S/S26