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We show that a spontaneous release of virtual photon pairs can occur in a quantum optical system in the ultrastrong coupling regime. In this regime, which is attracting interest both in semiconductor and superconducting systems, the light-matter coupling rate ΩR becomes comparable to the bare resonance frequency of photons ω0. In contrast to the dynamical Casimir effect and other pair creation mechanisms, this phenomenon does not require external forces or time dependent parameters in the Hamiltonian. [ABSTRACT FROM AUTHOR]

It is well known that spinor wave functions change their sign under 2π rotation. Several experiments have used magnetic precession of neutrons to implement rotations. Here we propose an all-optical analog of this effect based on time-resolved optical interference in coupled optical microcavities. We show that feeding the coupled-microcavity system with a pair of phase-locked probe pulses, separated by precise delay times, provides direct information on the sign change of the transmitted field after one complete Rabi-like oscillation period. [ABSTRACT FROM AUTHOR]

Superposition is the fundamental signature of quantum behavior. A quantum system can exist in a superposition of different eigenstates of an observable. Only after the measurement process, the system will collapse on one of the eigenvalues of the measured observables. We propose the realisation of the counterintuitive superposition of On and Off strong light-matter interaction using an optical resonator and a generic three-level quantum system. Leaked cavity photons can be detected and collected in order to post-select the events and to choose if we want to observe interacting or non-interacting photons. Such proposal can be readily realised within the present technology. Finally we will show that the cavity field can have a morphing behavior between On and Off interaction, by changing the area of the control pulse. [ABSTRACT FROM AUTHOR]