Frequency Switching of Quantum Harmonic Oscillator with Time-Dependent   Frequency
  An explicit solution of the equation for the classical harmonic oscillator with smooth switching of the frequency has been found . A detailed analysis of a quantum harmonic oscillator with such frequency has been done on the base of the method of linear invariants. It has been shown that such oscillator possesses cofluctuant states, different from widely studied Glauber's coherent and "ideal" squeezed states. 
A. Angelow (Institute of Solid State Physics, Sofia, Bulgaria)