346 research outputs found
Generation of maximally entangled states of qudits using twin photons
We report an experiment to generate maximally entangled states of
D-dimensional quantum systems, qudits, by using transverse spatial correlations
of two parametric down-converted photons. Apertures with D-slits in the arms of
the twin fotons define the qudit space. By manipulating the pump beam correctly
the twin photons will pass only by symmetrically opposite slits, generating
entangled states between these differents paths. Experimental results for
qudits with D=4 and D=8 are shown. We demonstrate that the generated states are
entangled states.Comment: 04 pages, 04 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
Propagation of spatially entangled qudits through free space
We show the propagation of entangled states of high-dimensional quantum
systems. The qudits states were generated using the transverse correlation of
the twin photons produced by spontaneous parametric down-conversion. Their
free-space distribution was performed at the laboratory scale and the
propagated states maintained a high-fidelity with their original form. The use
of entangled qudits allow an increase in the quantity of information that can
be transmitted and may also guarantee more privacy for communicating parties.
Therefore, studies about propagating entangled states of qudits are important
for the effort of building quantum communication networks.Comment: 5 Pages, 4 Figures, REVTeX
Experimental Observation of Quantum Correlations in Modular Variables
We experimentally detect entanglement in modular position and momentum
variables of photon pairs which have passed through -slit apertures. We
first employ an entanglement criteria recently proposed in [Phys. Rev. Lett.
{\bf 106}, 210501 (2011)], using variances of the modular variables. We then
propose an entanglement witness for modular variables based on the Shannon
entropy, and test it experimentally. Finally, we derive criteria for
Einstein-Podolsky-Rosen-Steering correlations using variances and entropy
functions. In both cases, the entropic criteria are more successful at
identifying quantum correlations in our data.Comment: 7 pages, 4 figures, comments welcom
Decoherence in a double-slit quantum eraser
We study and experimentally implement a double-slit quantum eraser in the
presence of a controlled decoherence mechanism. A two-photon state, produced in
a spontaneous parametric down conversion process, is prepared in a maximally
entangled polarization state. A birefringent double-slit is illuminated by one
of the down-converted photons, and it acts as a single-photon two-qubits
controlled not gate that couples the polarization with the transversal momentum
of these photons. The other photon, that acts as a which-path marker, is sent
through a Mach-Zehnder-like interferometer. When the interferometer is
partially unbalanced, it behaves as a controlled source of decoherence for
polarization states of down-converted photons. We show the transition from
wave-like to particle-like behavior of the signal photons crossing the
double-slit as a function of the decoherence parameter, which depends on the
length path difference at the interferometer.Comment: Accepted in Physical Review
Multi-dimensional entanglement generation with multi-core optical fibers
Trends in photonic quantum information follow closely the technical progress
in classical optics and telecommunications. In this regard, advances in
multiplexing optical communications channels have also been pursued for the
generation of multi-dimensional quantum states (qudits), since their use is
advantageous for several quantum information tasks. One current path leading in
this direction is through the use of space-division multiplexing multi-core
optical fibers, which provides a new platform for efficiently controlling
path-encoded qudit states. Here we report on a parametric down-conversion
source of entangled qudits that is fully based on (and therefore compatible
with) state-of-the-art multi-core fiber technology. The source design uses
modern multi-core fiber beam splitters to prepare the pump laser beam as well
as measure the generated entangled state, achieving high spectral brightness
while providing a stable architecture. In addition, it can be readily used with
any core geometry, which is crucial since widespread standards for multi-core
fibers in telecommunications have yet to be established. Our source represents
an important step towards the compatibility of quantum communications with the
next-generation optical networks.Comment: 9 pages, 7 figure
Interference and complementarity for two-photon hybrid entangled states
In this work we generate two-photon hybrid entangled states (HES), where the
polarization of one photon is entangled with the transverse spatial degree of
freedom of the second photon. The photon pair is created by parametric
down-conversion in a polarization-entangled state. A birefringent double-slit
couples the polarization and spatial degrees of freedom of these photons and
finally, suitable spatial and polarization projections generate the HES. We
investigate some interesting aspects of the two-photon hybrid interference, and
present this study in the context of the complementarity relation that exists
between the visibilities of the one- and two-photon interference patterns.Comment: 10 pages, 4 figures. Accepted in Physical Review
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