Macroscopic quantum tunneling in particle-number conserved Josephson systems

The Josephson effect is one manifestation of the quantum aspect of macrosco pic objects. It has been tested in various macroscopic systems to confirm t heir quantum-mechanical nature. In some of the systems, the total number of particles in the system is fixed. In such a case, the dynamics of the syst em is restricted and hence a new dynamical state might be expected to appea r. In this paper, we discuss the Josephson effect under a particle-number r estriction, and explore the new dynamical state that emerges from the restr iction. We also discuss macroscopic quantum tunneling from the state.