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Realization of a Classically Distinguishable Multi-photon Quantum Superposition

F. De Martini, Fabio Sciarrino

Published Jan 1, 2004• 0 citations
OpenAlex

Abstract

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

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F. De Martini, Fabio Sciarrino

This work reports on an extended research endeavor focused on the theoretical and experimental realization of a macroscopic quantum superposition (MQS) made up of photons. This intriguing, fundamental quantum condition is at the core of a famous argument conceived by Schr\"odinger in 1935. The main experimental challenge to the actual realization of this object resides generally in unavoidable and uncontrolled interactions with the environment, i.e., ``decoherence,'' leading to the cancellation of any evidence of the quantum features associated with the macroscopic system. The present scheme is based on a nonlinear process, ``quantum-injected optical parametric amplification,''which, by a linearized cloning process maps the quantum coherence of a single-particle state, i.e., a microqubit, onto a macroqubit consisting of a large number $M$ of photons in quantum superposition. Since the adopted scheme was found resilient to decoherence, a MQS demonstration was carried out experimentally at room temperature with $M\ensuremath{\ge}{10}^{4}$. The result led to an extended study of quantum cloning, quantum amplification, and quantum decoherence. The related theory is outlined and several experiments are reviewed, such as the test of the ``no-signaling theorem'' and the dynamical interaction of the photon MQS with a Bose-Einstein condensate. In addition, the consideration of the microqubit-macroqubit entanglement regime is extended to macroqubit-macroqubit conditions. The MQS interference patterns for large $M$ are revealed in the experiment and bipartite microqubit-macroqubit entanglement was also demonstrated for a limited number of generated particles: $M\ensuremath{\precsim}12$. Finally, the perspectives opened by this new method for further studies on quantum foundations and quantum measurement are considered.

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Multiparticle Quantum Superposition and Stimulated Entanglement by Parity Selective Amplification of Entangled States

F. De Martini, Giovanni Di Giuseppe

Abstract A multiparticle quantum superposition state has been generated by a novel phase-selective parametric amplifier of an entangled two-photon state. This realization is expected to open a new field of investigations on the persistence of the validity of the standard quantum theory for systems of increasing complexity, in a quasi decoherence-free environment. Because of its nonlocal structure the new system is expected to play a relevant role in the modem endeavor on quantum information and in the basic physics of entanglement. - Pacs: 03.65.Bz, 03.67.-a, 42.50.Ar, 89.70.+C

Zeitschrift für Naturforschung A•Feb 1, 2001•6 citations
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
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
This work reports on an extended research endeavor focused on the theoretical and experimental realization of a macroscopic quantum superposition (MQS) made up of photons. This intriguing, fundamental quantum condition is at the core of a famous argument conceived by Schr\"odinger in 1935. The main experimental challenge to the actual realization of this object resides generally in unavoidable and uncontrolled interactions with the environment, i.e., ``decoherence,'' leading to the cancellation of any evidence of the quantum features associated with the macroscopic system. The present scheme is based on a nonlinear process, ``quantum-injected optical parametric amplification,''which, by a linearized cloning process maps the quantum coherence of a single-particle state, i.e., a microqubit, onto a macroqubit consisting of a large number MMM of photons in quantum superposition. Since the adopted scheme was found resilient to decoherence, a MQS demonstration was carried out experimentally at room temperature with $M\ensuremath{\ge}{10}^{4}$. The result led to an extended study of quantum cloning, quantum amplification, and quantum decoherence. The related theory is outlined and several experiments are reviewed, such as the test of the ``no-signaling theorem'' and the dynamical interaction of the photon MQS with a Bose-Einstein condensate. In addition, the consideration of the microqubit-macroqubit entanglement regime is extended to macroqubit-macroqubit conditions. The MQS interference patterns for large MMM are revealed in the experiment and bipartite microqubit-macroqubit entanglement was also demonstrated for a limited number of generated particles: $M\ensuremath{\precsim}12$. Finally, the perspectives opened by this new method for further studies on quantum foundations and quantum measurement are considered.
Abstract A multiparticle quantum superposition state has been generated by a novel phase-selective parametric amplifier of an entangled two-photon state. This realization is expected to open a new field of investigations on the persistence of the validity of the standard quantum theory for systems of increasing complexity, in a quasi decoherence-free environment. Because of its nonlocal structure the new system is expected to play a relevant role in the modem endeavor on quantum information and in the basic physics of entanglement. - Pacs: 03.65.Bz, 03.67.-a, 42.50.Ar, 89.70.+C