On the path integral quantization of the damped harmonic oscillator
Christopher C. Gerry · Journal of Mathematical Physics · 1984
A time-dependent canonical transformation is performed in the path integral expression of the propagator for a damped harmonic oscillator to reduce it to a harmonic oscillator with modified frequency. The transformation is carried out in a properly time-symmetrized expression of the lattice space path integral by making expansions about the midpoint of each time interval.