Quantum coherence of double-well Bose-Einstein condensates: An SU(2) coherent-state path-integral approach

Macroscopic quantum coherence of Bose gas in a double-well potential is studied, based on an SU(2) coherent-state path-integral approach. The ground state and fluctuations around it can be obtained by this method. In this picture, one can obtain macroscopic quantum superposition states for attractive Bose gas. The coherent gap of degenerate ground states is obtained with the instanton technique. The phenomenon of macroscopic quantum self-trapping is also discussed.