2000/04/18 by Jonathan R. Friedman, Friedman, Jonathan R., Vijay Patel +8
Chemistry · Physics and Astronomy · #FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Quantum and electron transport phenomena #Spectroscopy and Laser Applications #Spectroscopy and Quantum Chemical Studies #Superconductivity (cond-mat.supr-con) #cond-mat.mes-hall #cond-mat.supr-con
paper · pdf · doi:10.48550/arxiv.cond-mat/0004293
3 RevTeX pages, 4 postscript figures, one in color. Submitted to Nature. Fig. 1 replaced (Postscript problem fixed)
openalex publication_date 2000/04/18 · arxiv created 2000/04/19 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We present experimental evidence for a coherent superposition of macroscopically distinct flux states in an rf-SQUID. When the external flux Phix applied to the SQUID is near 1/2 of a flux quantum Phi0, 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 Phix. 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 Phix 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 Phi0 and their currents differ by several microamperes.