1,721,003 research outputs found
Engineering spin and orbital angular momentum interactions in a light beam: quantum and classical applications
No full textThe angular momentum of light is a useful resource for many applications. In specific physical architectures it can be considered as the sum of two independent terms, the spin and the orbital components, in analogy to particle systems. The spin angular momentum is related to the polarization of the optical beam, that is the direction of the oscillating electric field, whereas the orbital angular momentum is associated with the spatial distribution of the field. Being independent, spin and orbital angular momenta have been discovered and explored in separate contexts for many years, while only recently it has been considered the possibility to address both quantities on the same beam (or individual photons). The interaction between these two quantities gives rise to complex structures of the electromagnetic field, or to the so called classical entanglement in the domain of single photons.
The research presented in this work aimed to show that combining spin and orbital angular momenta in light beams or single photons may be a useful tool for a variety of applications, with particular interest to the case of architectures characterized by spin-orbit interaction. This concept was made concrete through the design and the realization of several experiments, in the framework of singular optics, foundations of quantum mechanics, quantum information theory and quantum simulation
Exploring topological phases in quantum walks of twisted light
No full textEmerged as the quantum counterpart of classical random walks, quantum walks are established precious resources in a variety of quantum sciences. Recent studies have shown that quantum walks may be characterized by topological invariants, in close analogy to condensed matter systems exhibiting topological order. Exploiting these features, quantum walks are currently used to simulate topological systems and to probe their exotic features. Here we present the implementation of a one-dimensional quantum walk protocol based on the orbital angular momentum of light, manifesting the topological phases that characterize time-periodic systems (Floquet topological insulators) showing chiral symmetry. By considering the orbital angular momentum spectrum of a light beam undergoing this quantum evolution, we show that the associated statistical moments have marked differences in distinct phases and contain information on the system topology. While varying a control parameter determining the value of the invariants, these moments in the large step-number limit exhibit a sharp variation at the phase changes. We show that these phenomena arise from the singular behavior of the dispersion relation at the transition points. The extension of our results to systems featuring different symmetries, or characterized by higher spatial dimensions, may unveil novel intriguing features associated with these complex systems
Twisting entangled photons on a chip
No full textA programmable quantum chip has been developed that generates, manipulates, and launches five-dimensional entangled photons into free-space channels, encoded as optical vortex modes, thus bridging the worlds of integrated and free-space quantum photonics
Spin–orbit photonics
No full textSpin–orbit optical phenomena involve the interaction of the photon spin with the light wave propagation and spatial distribution, mediated by suitable optical media. Here we present a short overview of the emerging photonic applications that rely on such effects
Q-plate technology: a progress review
Full text linkSince their first introduction in 2006, q-plates have found a constantly increasing number of uses in diverse contexts, ranging from fundamental research on complex structured light fields to more applicative innovations of established experimental techniques, passing through a variety of other emerging topics, such as, for instance, quantum information protocols based on the angular momentum of light. In this paper, we present a bird’s-eye view of the progress of this technology in recent years and offer some educated guesses on the most likely future developments
Tra cattedrale e cenobio: due immagini mariane del XII secolo nella diocesi di Piacenza
No full textLo studio esamina due rappresentazioni della Vergine realizzate in ambito piacentino nella seconda metà del XII secolo, il gruppo lapideo della Vergine con Bambino (Boston, Museum of Fine Arts) e la miniatura dell'Assunzione della Vergine nel Codice Magno (Biblioteca Capitolare, ms 65), sottolineando il rapporto tra la prima immagine e gli scritti di Bernardo di Chiaravalle e tra la seconda e il dibattito sull'Assunta. L'analisi rileva inoltre come le due immagini, strutturate in modo da coinvolgere emotivamente il fedele, siano indicative della trasformazione del ruolo della donna nella società del XII secolo
Large-scale 2D mode couplers via liquid-crystal metasurfaces
No full textOptical degrees of freedom, such as those associated with spatial, spectro-temporal, or polarization features of the optical field, s erve a s a c onvenient r esource f or e ncoding i nformation. T he a bundance o f t ools f or their accurate manipulation established photonics as a versatile platform for both classical and quantum information processing tasks. Optical processors based on linear circuits, performing a variety of tasks, are often referred to as photonic circuits, in analogy with canonical circuits processing electrical signals. Here we demonstrate a compact photonic circuit in free space that implements all-optical mode-coupling operations in two spatial dimensions, operating in large-scale regimes. This provides a valuable alternative to the traditional integrated waveguides approach to optical information processing. We tested it by implementing unitary transformations associated with 2D quantum walks on transverse modes of structured light
Measuring the complex orbital angular momentum spectrum and spatial mode decomposition of structured light beams
No full textLight beams carrying orbital angular momentum are key resources in modern photonics. In many applications, the ability to measure the complex spectrum of structured light beams in terms of these fundamental modes is crucial. Here we propose and experimentally validate a simple method that achieves this goal by digital analysis of the interference pattern formed by the light beam and a reference field. Our approach allows one to also characterize the beam radial distribution, hence retrieving the entire information contained in the optical field. Setup simplicity and reduced number of measurements could make this approach practical and convenient for the characterization of structured light fields
Generation and dynamics of optical beams with polarization singularities
No full textWe present a convenient method to generate vector beams
of light having polarization singularities on their axis, via partial spin-toorbital angular momentum conversion in a suitably patterned liquid crystal cell. The resulting polarization patterns exhibit a C-point on the beam axis and an L-line loop around it, and may have different geometrical structures such as “lemon”, “star”, and “spiral”. Our generation method allows us to control the radius of L-line loop around the central C-point. Moreover, we investigate the free-air propagation of these fields across a Rayleigh range
Violation of Leggett-type inequalities in the spin-orbit degrees of freedom of a single photon
No full textWe report the experimental violation of Leggett-type inequalities for a hybrid entangled state of spin and orbital angular momentum of a single photon. These inequalities give a physical criterion to verify the possible validity of a class of hidden-variable theories, originally named “crypto nonlocal,” that are not excluded by the violation of Bell-type inequalities. In our case, the tested theories assume the existence of hidden variables associated with independent degrees of freedom of the same particle, while admitting the possibility of an influence between the two measurements, i.e., the so-called contextuality of observables. We observe a violation of the Leggett inequalities for a range of experimental inputs, with a maximum violation of seven standard deviations, thus ruling out this class of hidden-variable models with a high level of confidence
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