Engineering single-photon states endowed with orbital angular momentum (OAM) is a powerful tool for quantum information photonic implementations. Indeed, due to its unbounded nature, OAM is suitable for encoding qudits, allowing a single carrier to transport a large amount of information. Most of the experimental platforms employ spontaneous parametric down-conversion processes to generate single photons, even if this approach is intrinsically probabilistic, leading to scalability issues for an increasing number of qudits. Semiconductor quantum dots (QDs) have been used to get over these limitations by producing on-demand pure and indistinguishable single-photon states, although only recently they have been exploited to create OAM modes. Our work employs a bright QD single-photon source to generate a complete set of quantum states for information processing with OAM-endowed photons. We first study hybrid intraparticle entanglement between OAM and polarization degrees of freedom of a single photon whose preparation was certified by means of Hong–Ou–Mandel visibility. Then, we investigate hybrid interparticle OAM-based entanglement by exploiting a probabilistic entangling gate. The performance of our approach is assessed by performing quantum state tomography and violating Bell inequalities. Our results pave the way for the use of deterministic sources for the on-demand generation of photonic high-dimensional quantum states.
We present a device based on liquid crystal and via Pancharatnam-Berry phase to generate Poincare beams by the coherent collinear superposition of two Free-Form Dark Hollow (FFDH) beams. We generate beams with spatially-variable polarization encoded on their cross section showing disclinations in the azimuth orientation and mappings of the Poincare sphere onto the transverse mode. We report generated beams characterized by nonuniform rotation rate of the local polarization azimuth in different polarization configurations, radial and azimuthal, lemon and star disclinations, and other richer and complex higher-order disclinations, by using tailored space-varying-axis plates based on liquid crystals.
We present newly conceived liquid-crystal-based retardation waveplates in which the optic axis distribution has a “superelliptically” symmetric azimuthal structure with a topological charge q superimposed. Such devices, named superelliptical q-plates, act as polarization-to-spatial modes converters that can be used to produce optical beams having peculiar spiral spectra. These spectra reflect the topological charge of the optic axis distribution as well as the symmetry properties of the underlying superellipse. The peculiar capability of q-plates of producing optical modes entangled with respect to spin and orbital angular momentum is here extended to superelliptical q-plates in order to create more complex optical modes structurally inseparable with respect to polarization and spatial degrees of freedom. Such superelliptical modes can play a crucial role in studying polarization singularities or to develop polarization metrology.
The orbital angular momentum carried by single photons represents a promising resource in the quantum information
field. In this paper we report the characterization in the quantum regime of a recently introduced
optical device, known as q-plate. Exploiting the spin-orbit coupling that takes place in the q-plate, it is possible
to transfer coherently the information from the polarization to the orbital angular momentum degree of freedom,
and viceversa. Hence the q-plate provides a reliable bi-directional interface between polarization and orbital
angular momentum. As a first paradigmatic demonstration of the q-plate properties, we have carried out the
first experimental Hong-Ou-mandel effect purely observed in the orbital angular momentum degree of freedom.
Intralipid is a material widely employed for the preparation of phantoms simulating optical properties of tissues in the
field of optical imaging. Two main assumptions underlie the theoretical predictions of their scattering properties: the
occurrence of single scattering for any concentrations of Intralipid, thus enabling the use of Mie theory, and a highly
anisotropic g-factor giving a forward preferential direction of photon propagation. The importance of precisely
estimating the optical properties of such phantoms requires that the accuracy of these assumptions and their range of
applicability are very well-assessed. In this paper, we report the first step of an experimental investigation on the
scattering properties of Intralipid suspensions at different concentrations. The study is carried out by the joined use of
Time-Resolved Transmittance and Dynamic and Static Light Scattering techniques. By the analysis of the angular and
temporal dependence of light scattered by Intralipid suspensions, a more reliable description of the scattering process
occurring in the samples could be obtained. The results allow us to better elucidate the dependence of scattering
properties of suspensions on Intralipid concentrations and composition. This will help in the design and realization of
tissue phantoms with more and more reliable optical properties.
Light scattering processes in unconfined nematic liquid crystals have been investigated by means of time-resolved
transmittance and static light scattering techniques. In time-resolved experiments, sample temperature has been
modulated and different modalities of propagation have been probed. The results here obtained show that a nematic
polydomain liquid crystal exhibits scattering properties strongly different from a nematic monodomain and, in a sense, it
behaves as an optically thin sample. Such a behaviour may be ascribed to the strong backscattering exhibited by the
polydomain sample, as indicated by static light scattering experiments, where the angular dependence of the scattered
intensity was measured, revealing a preferential backward direction. The two experimental techniques here adopted
have shown their complementary role to understand the actual scattering regime. The diffusion constant D has been
determined by means of time-resolved measurements and a comparison with the results obtained in monodomain
nematic liquid crystals has been attempted.
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