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arXiv:quant-ph/0410225 · Physical Review Letters

Realization of an Optimally Distinguishable Multiphoton Quantum Superposition

F. De Martini, Fabio Sciarrino, Veronica Secondi

Published Dec 5, 2005• 30 citations
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Abstract

We report the realization of an entangled quantum superposition of M approximately 12 photons by multiple universal cloning of a single-photon qubit via the high gain, quantum-injected optical parametric amplification. The system has been found extremely resilient to decoherence. By quantum tomography, the nonseparability and the quantum superposition are demonstrated for the mesoscopic output state of the dynamic "closed system."

DOI
10.1103/physrevlett.95.240401

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We report the realization of an entangled quantum superposition of M approximately 12 photons by multiple universal cloning of a single-photon qubit via the high gain, quantum-injected optical parametric amplification. The system has been found extremely resilient to decoherence. By quantum tomography, the nonseparability and the quantum superposition are demonstrated for the mesoscopic output state of the dynamic "closed system."
We investigate multiphoton states generated by high-gain optical parametric amplification of a single injected photon—polarization encoded as a qubit. The experimental configuration exploits the optimal phase-covariant cloning. The output state of the apparatus is found to exhibit the quantum superposition property of mesoscopic multiphoton assemblies involving about 300 photons. This work represents an experimental advance toward the test of several fundamental quantum processes in mesoscopic or macroscopic frameworks.
We investigate the multiparticle quantum superposition and the persistence of bipartite entanglement of the output field generated by the quantum injected high-gain optical parametric amplification of a single photon. The physical configuration based on the optimal universal quantum cloning has been adopted to investigate how the entanglement and the quantum coherence of the system persists for large values of the nonlinear parametric gain ggg.
We report the successful generation of an entangled multiparticle quantum superposition of pure photon states. They result from a multiple universal cloning of a single photon qubit by a high gain, quantum-injected parametric amplifier. The information preserving property of the process suggests for these states the name of ”multi-particle qubits”. They are ideal objects for investigating the emergence of the classical world in quantum systems with increasing complexity, the decoherence processes and may allow the practical implementation of the universal 2-qubit logic gates. Typeset using REVTEX 1 Since the golden years of quantum mechanics the interference of classically distinguishable quantum states, first epitomized by the famous ”Schroedinger-Cat ” apologue [1] has been the object of extensive theoretical studies and recognized as a major conceptual paradigm of Physics [2,3]. In modern times the sciences of quantum information (QI) and quantum computation deal precisely with collective processes involving a multiplicity of
We investigate the multiphoton states generated by high-gain optical parametric amplification of a single injected photon, polarization encoded as a ``qubit.'' The experiment configuration exploits the optimal phase-covariant cloning in the high gain regime. The interference fringe pattern showing the nonlocal transfer of coherence between the injected qubit and the mesoscopic amplified output field involving up to 4000 photons has been investigated. A probabilistic method to extract full information about the multiparticle output wave function has been implemented.
The new process of quantum-injection into an optical parametric amplifier operating in entangled configuration is adopted to amplify into a large dimensionality spin-½ Hilbert space the quantum entanglement and superposition properties of the photon-couples generated by parametric down-conversion. The invariance properties of the OPA interaction hamiltonian show that, under certain conditions, the device may act as a Universal Quantum Cloning Machine (UQCM) of the input qubits. Preliminary results here reported show the first experimental realization of such a device. The structure of the Wigner function and of the field's correlation functions shows a multiphoton Schrödinger-cat behaviour of the emitted field which is largely detectable against the squeezed-vacuum noise.