Quantum superposition of parametrically amplified multiphoton pure states

F. De Martini, Fabio Sciarrino

Magdalena Stobińska

Fabio Antonio Bovino, F. De Martini, Valentina Mussi

The new process of quantum-injection into an optical parametric amplifier operating in entangled configuration is adopted to amplify into a large dimensionality spin 1/2 Hilbert space the quantum entanglement and superposition properties of the photon-couples generated by parametric down-conversion. The structure of the Wigner function and of the field's correlation functions shows a decoherence-free, multiphoton Schroedinger-cat behaviour of the emitted field which is largely detectable against the squeezed-vacuum noise. Furthermore, owing to its entanglement character, the system is found to exhibit multi-particle quantum nonseparability and Bell-type nonlocality properties. These relevant quantum features are analyzed for several travelling-wave optical configurations implying different input quantum-injection schemes

Nicolò Spagnolo, Chiara Vitelli, Tiziano De Angelis +2 more

Recent experimental results demonstrated the generation of a macroscopic quantum superposition (MQS), involving a number of photons in excess of $5\ifmmode\times\else\texttimes\fi{}{10}^{4}$, which showed a high resilience to losses. In order to perform a complete analysis on the effects of decoherence on these multiphoton fields, obtained through the quantum injected optical parametric amplifier, we investigate theoretically the evolution of the Wigner functions associated to these states in lossy conditions. Recognizing the presence of negative regions in the $W$ representation as an evidence of nonclassicality, we focus our analysis on this feature. A close comparison with the MQS based on coherent $|\ensuremath{\alpha}⟩$ states allows us to identify differences and analogies.

F. De Martini, Giovanni Di Giuseppe, Sebastião Pádua

We report the creation of an entangled multiphoton quantum superposition by quantum injection of entangled 2-photon states into a parity selective parametric amplifier. The information preserving property of the state transformation suggests for these macrostates the name of large qubits. They are ideal objects for investigating the emergence of the classical world in complex quantum systems and have relevant new applications in quantum information.

Fabio Dell’Anno, Silvio De Siena, Fabrizio Illuminati