434 research outputs found
Anyonic Realization of the Quantum Affine Lie Algebras
We give a realization of the quantum affine Lie algebras \uqa and \uqc in
terms of anyons defined on a one-dimensional chain (or on a two-dimensional
lattice), the deformation parameter being related to the statistical
parameter of the anyons by . In the limit of the
deformation parameter going to one we recover the Feingold-Frenkel fermionic
construction of undeformed affine Lie algebras.Comment: 8p, LaTeX, subeqn.sty. Also available at
http://lapphp0.in2p3.fr/preplapp/psth/anyon_ac.ps.g
Realization of the 1->3 optimal phase-covariant quantum cloning machine
The 1->3 quantum phase covariant cloning, which optimally clones qubits
belonging to the equatorial plane of the Bloch sphere, achieves the fidelity
Fcov(1->3)=0.833, larger than for the 1->3 universal cloning Funiv(1->3)=0.778.
We show how the 1->3 phase covariant cloning can be implemented by a smart
modification of the standard universal quantum machine by a projection of the
output states over the symmetric subspace. A complete experimental realization
of the protocol for polarization encoded qubits based on non-linear and linear
methods will be discussed.Comment: 12 pages, 2 figure
Coherent scattering of a Multiphoton Quantum Superposition by a Mirror-BEC
We present the proposition of an experiment in which the multiphoton quantum
superposition consisting of N= 10^5 particles generated by a quantum-injected
optical parametric amplifier (QI-OPA), seeded by a single-photon belonging to
an EPR entangled pair, is made to interact with a Mirror-BEC shaped as a Bragg
interference structure. The overall process will realize a Macroscopic Quantum
Superposition (MQS) involving a microscopic single-photon state of polarization
entangled with the coherent macroscopic transfer of momentum to the BEC
structure, acting in space-like separated distant places.Comment: 4 pages, 4 figure
Implementation of optimal phase-covariant cloning machines
The optimal phase covariant cloning machine (PQCM) broadcasts the information
associated to an input qubit into a multi-qubit systems, exploiting a partial
a-priori knowledge of the input state. This additional a priori information
leads to a higher fidelity than for the universal cloning. The present article
first analyzes different experimental schemes to implement the 1->3 PQCM. The
method is then generalized to any 1->M machine for odd value of M by a
theoretical approach based on the general angular momentum formalism. Finally
different experimental schemes based either on linear or non-linear methods and
valid for single photon polarization encoded qubits are discussed.Comment: 7 pages, 3 figure
Complete analysis of measurement-induced entanglement localization on a three-photon system
We discuss both theoretically and experimentally elementary two-photon
polarization entanglement localization after break of entanglement caused by
linear coupling of environmental photon with one of the system photons. The
localization of entanglement is based on simple polarization measurement of the
surrounding photon after the coupling. We demonstrate that non-zero
entanglement can be localized back irrespectively to the distinguishability of
coupled photons. Further, it can be increased by local single-copy polarization
filters up to an amount violating Bell inequalities. The present technique
allows to restore entanglement in that cases, when the entanglement
distillation does not produce any entanglement out of the coupling.Comment: 14 pages, 14 figures, submitted to Phys. Rev.
Realization of the Optimal Universal Quantum Entangler
We present the first experimental demonstration of the ''optimal'' and
''universal'' quantum entangling process involving qubits encoded in the
polarization of single photons. The structure of the ''quantum entangling
machine'' consists of the quantum injected optical parametric amplifier by
which the contextual realization of the 1->2 universal quantum cloning and of
the universal NOT (U-NOT) gate has also been achieved.Comment: 10 pages, 3 figures, to appear in Physical Review
Anyonic Realization of the Quantum Affine Lie Algebra U_q(A_N)
We give a realization of quantum affine Lie algebra in
terms of anyons defined on a two-dimensional lattice, the deformation parameter
being related to the statistical parameter of the anyons by . In the limit of the deformation parameter going to one we recover
the Feingold-Frenkel fermionic construction of undeformed affine Lie algebra.Comment: 13p LaTeX Document (should be run twice
Photonic polarization gears for ultra-sensitive angular measurements
Quantum metrology bears a great promise in enhancing measurement precision,
but is unlikely to become practical in the near future. Its concepts can
nevertheless inspire classical or hybrid methods of immediate value. Here, we
demonstrate NOON-like photonic states of m quanta of angular momentum up to
m=100, in a setup that acts as a "photonic gear", converting, for each photon,
a mechanical rotation of an angle {\theta} into an amplified rotation of the
optical polarization by m{\theta}, corresponding to a "super-resolving" Malus'
law. We show that this effect leads to single-photon angular measurements with
the same precision of polarization-only quantum strategies with m photons, but
robust to photon losses. Moreover, we combine the gear effect with the quantum
enhancement due to entanglement, thus exploiting the advantages of both
approaches. The high "gear ratio" m boosts the current state-of-the-art of
optical non-contact angular measurements by almost two orders of magnitude.Comment: 10 pages, 4 figures, + supplementary information (10 pages, 3
figures
Integrated sources of entangled photons at telecom wavelength in femtosecond-laser-written circuits
Photon entanglement is an important state of light that is at the basis of
many protocols in photonic quantum technologies, from quantum computing, to
simulation and sensing. The capability to generate entangled photons in
integrated waveguide sources is particularly advantageous due to the enhanced
stability and more efficient light-crystal interaction. Here we realize an
integrated optical source of entangled degenerate photons at telecom
wavelength, based on the hybrid interfacing of photonic circuits in different
materials, all inscribed by femtosecond laser pulses. We show that our source,
based on spontaneous parametric down-conversion, gives access to different
classes of output states, allowing to switch from path-entangled to
polarization-entangled states with net visibilities above 0.92 for all selected
combinations of integrated devices
Experimental observation of fractional topological phases with photonic qudits
Geometrical and topological phases play a fundamental role in quantum theory.
Geometric phases have been proposed as a tool for implementing unitary gates
for quantum computation. A fractional topological phase has been recently
discovered for bipartite systems. The dimension of the Hilbert space determines
the topological phase of entangled qudits under local unitary operations. Here
we investigate fractional topological phases acquired by photonic entangled
qudits. Photon pairs prepared as spatial qudits are operated inside a Sagnac
interferometer and the two-photon interference pattern reveals the topological
phase as fringes shifts when local operations are performed. Dimensions and were tested, showing the expected theoretical values.Comment: 6 pages, 4 figure
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