Quantum dynamics in a camel-back potential of a dc SQUID
  We investigate the quantum dynamics of a quadratic-quartic anharmonic oscillator formed by a potential well between two potential barriers. We realize this novel potential shape with a superconducting circuit comprised of a loop interrupted by two Josephson junctions, with near-zero current bias and flux bias near half a flux quantum. We investigate escape out of the central well, which can occur via tunneling through either of the two barriers, and find good agreement with a generalized double-path macroscopic quantum tunneling theory. We also demonstrate that this system exhibits an "optimal line" in current and flux bias space along which the oscillator, which can be operated as a phase qubit, is insensitive to decoherence due to low-frequency current fluctuations. 
E. Hoskinson, F. Lecocq, N. Didier, A. Fay, F. W. J. Hekking, W.   Guichard, R. Dolata, B. Mackrodt, A. B. Zorin, O. Buisson