Macroscopic Quantum Coherence in an Rf-SQUID

Jonathan R. Friedman (), Vijay Patel, W. Chen, S. K. Tolpygo and J. E. Lukens
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Jonathan R. Friedman: The State University of New York at Stony Brook, Department of Physics and Astronomy
Vijay Patel: The State University of New York at Stony Brook, Department of Physics and Astronomy
W. Chen: The State University of New York at Stony Brook, Department of Physics and Astronomy
S. K. Tolpygo: The State University of New York at Stony Brook, Department of Physics and Astronomy
J. E. Lukens: The State University of New York at Stony Brook, Department of Physics and Astronomy

A chapter in Macroscopic Quantum Coherence and Quantum Computing, 2001, pp 7-16 from Springer

Abstract: Abstract We present experimental evidence for a coherent superposition of macroscopically distinct flux states in an rf-SQUID. When the external flux Φ x applied to the SQUID is near 1/2 of a flux quantum Φ o, the SQUID has two nearly degenerate configurations: the zero- and one-fluxoid states, corresponding to a few microamperes of current flowing clockwise or counterclockwise, respectively. The system is modeled as a particle in a double-well potential where each well represents a distinct fluxoid state (0 or 1) and the barrier between the wells can be controlled in situ. For low damping and a sufficiently high barrier, the system has a set of quantized energy levels localized in each well. The relative energies of these levels can be varied with Φ x. External microwaves are used to pump the system from the well-localized ground state of one well into one of a pair of excited states nearer the top of the barrier. We spectroscopically map out the energy of these levels in the neighborhood of their degeneracy point by varying Φ x as well as the barrier height. We find a splitting between the two states at this point, when both states are below the classical energy barrier, indicating that the system attains a coherent superposition of flux basis states that are macroscopically distinct in that their mean fluxes differ by more than 1/4 Φ o and their currents differ by several microamperes.

Keywords: Excited Level; Barium Ferrite; Coherent Superposition; Quantum Superposition; Tunnel Splitting (search for similar items in EconPapers)
Date: 2001
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DOI: 10.1007/978-1-4615-1245-5_2

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