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

Martini, F. De; Giuseppe, Giovanni Di; Pádua, S.

doi:10.1103/physrevlett.87.150401

Cited by 26 publications

(9 citation statements)

References 19 publications

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“…Thus, the reduction in visibility that has come to be associated with extremely brief pump pulses [11] will not be present in this scheme. Note that a symmetrization method has been developed to restore visibility for experiments using polarization-entangled photons created by such a short pulse pump [12,13].…”

Section: Figmentioning

confidence: 99%

Decoherence-Free Subspaces in Quantum Key Distribution

et al. 2003

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We demonstrate that two recent innovations in the field of practical quantum key distribution (one-way autocompensation and passive detection) are closely related to the methods developed to protect quantum computations from decoherence. We present a new scheme that combines these advantages, and propose a practical implementation of this scheme that is feasible using existing technology.PACS numbers: 03.65. Ud, 03.67.Dd, 03.67.Lx, 42.65.Ky Decoherence has been a principal impediment in quantum information processing applications. In quantum computing, decoherence-induced deviations from the desired computational trajectory at the single-qubit level will quickly accumulate if left uncorrected. Thus, techniques such as decoherence-free subspaces (DFSs, for a review, see Ref.[1]) have been developed as tools for protecting quantum computations. In quantum key distribution (QKD, for a review, see Ref.[2]), single-qubit errors are also deleterious; however, sufficiently infrequent single-qubit errors are tolerable, since the resulting errors can be corrected by classical error correction protocols. This has led many QKD experimentalists to forego the complexity of decoherence-mitigation techniques such as DFSs in favor of more conventional methods to improve the precision of single-qubit operations (periodic alignment of polarization axes, temperature stabilization of interferometers, etc.). In this letter, we consider the applicability of DFSs to QKD. This letter is organized as follows. We begin by demonstrating that a recently-proposed QKD implementation (one-way autocompensating quantum cryptography [3]) is, in fact, equivalent to a well-known DFS. We then pursue a suggestion in Ref.[2] to consider a single-qubit, phase-time coding QKD scheme in which Bob is not required to actively switch between conjugate measurement bases. We show that both one-way autocompensation (OWA) and passive detection are achieved by embedding the logical Hilbert space in a larger physical Hilbert space. Next, we describe a new scheme that combines OWA and passive detection. Finally, we propose an experimental implementation of this new scheme that is feasible using existing technology.Relating OWA and DFSs.-In Ref.[3], Klyshko's "advanced wave interpretation" [4] was used to describe OWA as a variation on round-trip autocompensation [5,6]. These schemes are called autocompensating because they allows high-visibility quantum interference without calibration or active stabilization of the receiver's (Bob's) apparatus. In the context of quantum computation theory [7], a more natural explanation of OWA is provided by DFSs. Palma et al. [8] have shown that a single logical qubit encoded in two physical qubits according to( 1) will be protected against collective dephasing. Collective dephasing describes a noise model in which each physical qubit is subject to the same transformationwhere φ is an uncontrolled degree of freedom. Under this transformation, the states |01 and |10 acquire the same phase factor (e iφ ). Thus, a qubit encode...

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Section: Figmentioning

confidence: 99%

Decoherence-Free Subspaces in Quantum Key Distribution

et al. 2003

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“…In virtue of the general information preserving property of any nonlinear (NL) transformation of parametric type, the output state is again expressed by a "massive qubit": |Ψ ≡ ( α |Ψ α + β |Ψ β ) [16]. This (pure) state is indeed a Schroedinger-Cat (S-Cat) state implying the quantum superposition of the orthonormal multiparticle states [12]:…”

Section: Quantum Injected Optical Parametric Amplifiermentioning

confidence: 99%

“…Take as input state into the QIOPA system the general qubit : [16]. This (pure) state is indeed a Schroedinger-Cat (S-Cat) state implying the quantum superposition of the orthonormal multiparticle states [12]:…”

Section: Quantum Injected Optical Parametric Amplifiermentioning

confidence: 99%

Contextual realization of the universal quantum cloning machine and of the universal-NOT gate by quantum-injected optical parametric amplification

et al. 2003

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A simultaneous, contextual experimental demonstration of the two processes of cloning an input qubit |Ψ >and of flipping it into the orthogonal qubit |Ψ ⊥ > is reported. The adopted experimental apparatus, a Quantum-Injected Optical Parametric Amplifier (QIOPA) is transformed simultaneously into a Universal Optimal Quantum Cloning Machine (UOQCM) and into a Universal NOT quantum-information gate. The two processes, indeed forbidden in their exact form for fundamental quantum limitations, will be found to be universal and optimal, i.e. the measured fidelity of both processes F < 1 will be found close to the limit values evaluated by quantum theory. A contextual theoretical and experimental investigation of these processes, which may represent the basic difference between the classical and the quantum worlds, can reveal in a unifying manner the detailed structure of quantum information. It may also enlighten the yet little explored interconnections of fundamental axiomatic properties within the deep structure of quantum mechanics. PACS numbers:03.67.-a, 03.65.Ta, 03.65.Ud

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“…Obviously for a large number of particles such entangled states are difficult to obtain. However, recently methods of achieving an amplification of entangled states, so-called massive qubits, have been demonstrated experimentally [32,33].…”

Section: 6mentioning

confidence: 99%