1,470 research outputs found
Preparation and characterisation of uranium and tungsten borides for applications in the nuclear industry
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
Measurement-induced quantum operations on multiphoton states
We investigate how multiphoton quantum states obtained through optical
parametric amplification can be manipulated by performing a measurement on a
small portion of the output light field. We study in detail how the macroqubit
features are modified by varying the amount of extracted information and the
strategy adopted at the final measurement stage. At last the obtained results
are employed to investigate the possibility of performing a
microscopic-macroscopic non-locality test free from auxiliary assumptions.Comment: 13 pages, 13 figure
Entanglement criteria for microscopic-macroscopic systems
We discuss the conclusions that can be drawn on a recent experimental
micro-macro entanglement test [F. De Martini, F. Sciarrino, and C. Vitelli,
Phys. Rev. Lett. 100, 253601 (2008). The system under investigation is
generated through optical parametric amplification of one photon belonging to
an entangled pair. The adopted entanglement criterion makes it possible to
infer the presence of entanglement before losses, that occur on the macrostate,
under a specific assumption. In particular, an a priori knowledge of the system
that generates the micro-macro pair is necessary to exclude a class of
separable states that can reproduce the obtained experimental results. Finally,
we discuss the feasibility of a micro-macro "genuine" entanglement test on the
analyzed system by considering different strategies, which show that in
principle a fraction epsilon, proportional to the number of photons that
survive the lossy process, of the original entanglement persists in any losses
regime.Comment: 11 pages, 10 figure
Non separable Werner states in spontaneous parametric down-conversion
The multiphoton states generated by high-gain spontaneous parametric
down-conversion (SPDC) in presence of large losses are investigated
theoretically and experimentally. The explicit form for the two-photon output
state has been found to exhibit a Werner structure very resilient to losses for
any value of the gain parameter, g. The theoretical results are found in
agreement with the experimental data. The last ones are obtained by quantum
tomography of the state generated by a high-gain SPDC.Comment: 16 pages, 6 figure
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