Three-dimensional harmonic oscillator and time evolution in quantum   mechanics
  The problem of defining time (or phase) operator for three-dimensional harmonic oscillator has been analyzed. A new formula for this operator has been derived. The results have been used to demonstrate a possibility of representing quantum-mechanical time evolution in the framework of an extended Hilbert space structure. Physical interpretation of the extended structure has been discussed shortly, too. 
Pavel Kundrat, Milos V. Lokajicek