Detection of a Schroedinger's Cat State in an rf-SQUID

Jonathan R. Friedman; Vijay Patel; W. Chen; S. K. Tolpygo; J. E. Lukens

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Detection of a Schroedinger's Cat State in an rf-SQUID

Jonathan R. Friedman·Vijay Patel·W. Chen·S. K. Tolpygo·J. E. Lukens

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Abstract

We present experimental evidence for a coherent superposition of macroscopically distinct flux states in an rf-SQUID. When the external flux Phi_x applied to the SQUID is near 1/2 of a flux quantum Phi_0, 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 Phi_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 Phi_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 Phi_0 and their currents differ by several microamperes.

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Jonathan R. Friedman, Vijay Patel, W. Chen, S. K. Tolpygo, J. E. Lukens. 2000-04-19. Detection of a Schroedinger's Cat State in an rf-SQUID. https://arxiv.org/abs/cond-mat/0004293

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