Quantum fluctuations in unstable dissipative systems - art. no. 043805

We show how quantum instability is displayed in the von Neumann entropy and in the Wigner function. For this purpose, an intracavity second-harmonic g eneration close to the Hopf bifurcation range is studied. We examine die ro le of dissipation in unstable dynamics and the formation of the quantum sta res of the cavity modes, and discuss contrast ensemble behavior with that o f individual realization on the basis of a quantum-jump simulation method. Namely, it is found that the Wigner functions for fundamental and second-ha rmonic modes prepared initially in a vacuum state acquire the three-hump st ructure due to phase symmetry breaking in the bifurcation range. The time e volution of coherent states leads to long-lived swing of the system between two side humps in a phase space.