Investigation on the quantum-to-classical transition by optical parametric amplification: Generation and detection of multiphoton quantum superposition

We review an extended research carried out on the theoretical and experimental realization of a macroscopic quantum superposition (MQS) made up with photons. The described scheme is based on a nonlinear process, the quantum injected optical parametric amplification, that transforms the quantum coherence of a single particle state, i.e. a Micro-qubit, into a Macro-qubit, consisting in a large number M of photons in quantum superposition. Since the adopted scheme was found resilient to decoherence, the MQS demonstration was carried out experimentally at room temperature with M≥104. This result elicited an extended study on quantum cloning, quantum amplification and quantum decoherence. The MQS interference patterns for large M were revealed in the experiment and the bipartite Micro-Macro entanglement was also demonstrated for a limited number of generated particles. At last, the perspectives opened by this new method are considered in the view of further studies on quantum foundations and quantum measurement.