Effect of an arbitrary dissipative circuit on the quantum energy levels and tunneling of a Josephson junction

The complex energy shifts of the energy levels of a macroscopic system subject to dissipation are calculated as a function of the phenomenological damping parameters describing the classical motion of the system. These results are applied to the energy levels of the zero-voltage state of a current-biased Josephson junction in parallel with an arbitrary dissipative circuit. Following the approach of Leggett, the influence of the same dissipative circuit on the tunneling rate out of the zero-voltage state is also calculated. The dependences of both phenomena, quantization of energy levels, and quantum tunneling, on the admittance of the circuit are compared.