331 research outputs found
Visual assessment of multi-photon interference
Classical machine learning algorithms can provide insights on high-dimensional processes that are hardly accessible with conventional approaches. As a notable example, t-distributed Stochastic Neighbor Embedding (t-SNE) represents the state of the art for visualization of data sets of large dimensionality. An interesting question is then if this algorithm can provide useful information also in quantum experiments with very large Hilbert spaces. Leveraging these considerations, in this work we apply t-SNE to probe the spatial distribution of n-photon events in m-dimensional Hilbert spaces, showing that its findings can be beneficial for validating genuine quantum interference in boson sampling experiments. In particular, we find that nonlinear dimensionality reduction is capable to capture distinctive features in the spatial distribution of data related to multi-photon states with different evolutions. We envisage that this approach will inspire further theoretical investigations, for instance for a reliable assessment of quantum computational advantage
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
Resilience of orbital angular momentum qubits and effects on hybrid entanglement
The orbital angular momentum of light (OAM) provides a promising approach for
the implementation of multidimensional states (qudits) for quantum information
purposes. In order to characterize the degradation undergone by the information
content of qubits encoded in a bidimensional subspace of the orbital angular
momentum degree of freedom of photons, we study how the state fidelity is
affected by a transverse obstruction placed along the propagation direction of
the light beam. Emphasis is placed on the effects of planar and radial
hard-edged aperture functions on the state fidelity of Laguerre-Gaussian
transverse modes and the entanglement properties of polarization-OAM
hybrid-entangled photon pairs.Comment: 6 pages, 9 figure
Manipulation of Photonic Orbital Angular Momentum for Quantum Information Processing
Computer modelling & simulatio
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
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
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