Condensation of Interacting Bosons with Reduced Number Fluctuation

抄録

We analyze the condensation of interacting bosonsconfined in a finite volume V, by evaluating the time evolution of the density operator \hat{ρ}(t) in the case where the number of bosons is exactly fixed for t < 0and a small leakage occurs for t ≥q 0.We identify a “natural coordinate” \hat{b}₀ of interacting bosons, using which many physical properties can be simply described.In particular, the time evolution of \hat{ρ}(t) can be simply described as the evolution from the number state, to a phase-randomized mixture (PRM) of “number-phase squeezed states”, and finally to the PRM of coherent states, of \hat{b}₀.The order parameter, defined as the expectation value of the boson field, of each element of the PRM grows rapidly from zero to the full value.