ABSTRACT
This chapter provides an analysis of macroscopic quantum dynamics of small-size Josephson junctions. It demonstrates that nontrivial interplay between quantum coherence, dissipation, and Coulomb effects yields a rich variety of properties, which can be accessed not only by means of the phase variable but also through the canonically conjugate quantum variable of the junction charge. The chapter argues that useful and sometimes complementary information can be obtained if one considers quantum dynamics of another collective variable—the junction charge. It discusses some (quasi-) equilibrium properties of ultrasmall Josephson junctions, which can be adequately accounted for by evaluating the grand partition function Z within the imaginary-time path integral formalism. In general, however, the imaginary-time technique may be insufficient and/or inconvenient to properly describe real-time evolution of Josephson junctions in the presence of macroscopic quantum coherence and dissipation.
