191 research outputs found
Experimental Bell inequality violation without the postselection loophole
We report on an experimental violation of the Bell-Clauser-Horne-Shimony-Holt
(Bell-CHSH) inequality using energy-time entangled photons. The experiment is
not free of the locality and detection loopholes, but is the first violation of
the Bell-CHSH inequality using energy-time entangled photons which is free of
the postselection loophole described by Aerts et al. [Phys. Rev. Lett. 83, 2872
(1999)].Comment: 4 pages, 3 figures, v2 minor correction
Hyperentanglement of two photons in three degrees of freedom
A 6-qubit hyperentangled state has been realized by entangling two photons in
three degrees of freedom. These correspond to the polarization, the
longitudinal momentum and the indistinguishable emission produced by a
2-crystal system operating with Type I phase matching in the spontaneous
parametric down conversion regime. The state has been characterized by a
chained interferometric apparatus and its complete entangled nature has been
tested by a novel witness criterium specifically introduced for hyperentangled
states. The experiment represents the first realization of a genuine
hyperentangled state with the maximum entanglement between the two particles
allowed in the given Hilbert space.Comment: 4 pages, 2 figures, Revtex
Hyperentangled mixed phased Dicke states: optical design and detection
We present an experimental method to produce 4-qubit phased Dicke states,
based on a source of 2-photon hyperentangled states. By introducing quantum
noise in the multipartite system in a controlled way, we have tested the
robustness of these states. To this purpose the entanglement of the resulting
multipartite entangled mixed states has been verified by using a new kind of
structural witness.Comment: 6 pages, 3 figure, supplementary information include
Complete and Deterministic discrimination of polarization Bell state assisted by momentum entanglement
A complete and deterministic Bell state measurement was realized by a simple
linear optics experimental scheme which adopts 2-photon polarization-momentum
hyperentanglement. The scheme, which is based on the discrimination among the
single photon Bell states of the hyperentangled state, requires the adoption of
standard single photon detectors. The four polarization Bell states have been
measured with average fidelity by using the linear momentum
degree of freedom as the ancilla. The feasibility of the scheme has been
characterized as a function of the purity of momentum entanglement.Comment: 4 pages, v2, comments adde
One-way quantum computation via manipulation of polarization and momentum qubits in two-photon cluster states
Four-qubit cluster states of two photons entangled in polarization and linear
momentum have been used to realize a complete set of single qubit rotations and
the C-NOT gate for equatorial qubits with high values of fidelity. By the
computational equivalence of the two degrees of freedom our result demonstrate
the suitability of two photon cluster states for rapid and efficient one-way
quantum computing.Comment: RevTex4, 4 pages, 3 figure
Polarization entangled state measurement on a chip
The emerging strategy to overcome the limitations of bulk quantum optics
consists of taking advantage of the robustness and compactness achievable by
the integrated waveguide technology. Here we report the realization of a
directional coupler, fabricated by femtosecond laser waveguide writing, acting
as an integrated beam splitter able to support polarization encoded qubits.
This maskless and single step technique allows to realize circular transverse
waveguide profiles able to support the propagation of Gaussian modes with any
polarization state. Using this device, we demonstrate the quantum interference
with polarization entangled states and singlet state projection.Comment: Revtex, 5+2 pages (with supplementary information), 4+1 figure
Experimental Realization of Optimal Noise Estimation for a General Pauli Channel
We present the experimental realization of the optimal estimation protocol
for a Pauli noisy channel. The method is based on the generation of 2-qubit
Bell states and the introduction of quantum noise in a controlled way on one of
the state subsystems. The efficiency of the optimal estimation, achieved by a
Bell measurement, is shown to outperform quantum process tomography
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