| 1. |
- Oldoni, Matteo, et al.
(författare)
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Space-Division Demultiplexing in Orbital-Angular-Momentum-Based MIMO Radio Systems
- 2015
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 63:10, s. 4582-4587
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Tidskriftsartikel (refereegranskat)abstract
- Radio beams that carry nonzero orbital angular momentum (OAM) are analyzed from the viewpoint of a multiple-input-multiple-output (MIMO) communication system. Often, the natural OAM-beam orthogonality cannot be fully exploited because of spatial constraints on the receiving antenna size. Therefore, we investigate how far OAM-induced phase variations can be exploited in spatial demultiplexing based on conventional (linear momentum) receivers. Performances are investigated versus position and size of the transmitting and receiving devices. The use of OAM-mode coherent superpositions is also considered, in view of recent work by Edfors et al. Our final goal is to assess the merits of an OAM-based MIMO system, in comparison with a conventional one.
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| 2. |
- Tamburini, Fabrizio, et al.
(författare)
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Encoding many channels on the same frequency through radio vorticity : first experimental test
- 2012
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 14, s. 033001-
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Tidskriftsartikel (refereegranskat)abstract
- We have shown experimentally, in a real-world setting, that it is possible to use two beams of incoherent radio waves, transmitted on the same frequency but encoded in two different orbital angular momentum states, to simultaneously transmit two independent radio channels. This novel radio technique allows the implementation of, in principle, an infinite number of channels in a given, fixed bandwidth, even without using polarization, multiport or dense coding techniques. This paves the way for innovative techniques in radio science and entirely new paradigms in radio communication protocols that might offer a solution to the problem of radio-band congestion.
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| 3. |
- Tamburini, Fabrizio, et al.
(författare)
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Experimental verification of photon angular momentum and vorticity with radio techniques
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:20, s. 204102-
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Tidskriftsartikel (refereegranskat)abstract
- The experimental evidence that radio techniques can be used for synthesizing and analyzing non-integer electromagnetic (EM) orbital angular momentum (OAM) of radiation is presented. The technique used amounts to sample, in space and time, the EM field vectors and digitally processing the data to calculate the vortex structure, the spatial phase distribution, and the OAM spectrum of the radiation. The experimental verification that OAM-carrying beams can be readily generated and exploited by using radio techniques paves the way to an entirely new paradigm of radar and radio communication protocols.
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| 4. |
- Tamburini, Fabrizio, et al.
(författare)
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General relativistic electromagnetic and massive vector field effects with gamma-ray burst production
- 2017
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 96:10
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new energy extraction mechanism from the rotational energy of a Kerr-Newman black hole by a gravitating massive photon field generated by electromagnetic and gravitational field coupling effects. Numerical studies show that this mechanism that depends on the black hole rotation parameter, a, shows a clear dependence on the black hole mass, M, and charge, Q, and can extract energies up to 1054 erg for a black hole of the solar mass size. With this mechanism we can set a lower bound on the coupling ξ∼10-38 between electromagnetic and gravitational fields that might be used to explain the hypothetical extremely high energy release, >1053 erg, suggested by the observations of some gamma-ray bursts in the controversial "energy crisis" problem if and when gamma-ray bursts seem not to show evidence for collimated emission.
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| 5. |
- Tamburini, Fabrizio, et al.
(författare)
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Kerr-spacetime geometric optics for vortex beams
- 2021
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- We consider the analogy between gravitational fields and optical media within the framework of geometrical optics in curved spacetime in order to describe how light can acquire orbital angular momentum (OAM) when it traverses the gravitational field of a massive rotating compact object; in particular, we analyze the interplay between OAM and polarization. Kerr spacetimes are known not only to impose a gravitational Faraday rotation on the polarization of a light beam, but also to set a characteristic fingerprint in the orbital angular momentum distribution of the radiation passing nearby a rotating black hole (BH). Kerr spacetime behaves like an inhomogeneous and anisotropic medium, in which light can acquire orbital angular momentum and spin-to-orbital angular momentum conversion can occur, acting as a polarization and phase changing medium for the gravitationally lensed light, as confirmed by the data analysis of the M87* black hole.
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| 6. |
- Tamburini, Fabrizio, et al.
(författare)
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Majorana bosonic quasiparticles from twisted photons in free space
- 2021
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 103:3
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Tidskriftsartikel (refereegranskat)abstract
- The speed of light in vacuum, c, is a fundamental constant of nature. Photons belonging to a structured beam of finite transverse size have been observed to travel with a group velocity vg, smaller than c, also when propagating in vacuum. The paradox of slow photons in vacuum could, in a first approach, be explained as a simple projection effect that occurs when one measures the speed of light in a diverging vortex beam along the direction of the beam propagation. This effect, instead, reveals fundamental properties of structured light beams: they form a class of quasiparticle states characterized by the geometric properties of the beams such as the beam divergence, spin angular momentum, orbital angular momentum (OAM), and the group velocity. These anomalous propagation modes with group velocities different than that of c represent a class of Majorana quasiparticles with bosonic spectrum for integer OAM modes, cast in an infinite tower of quasiparticle states similar to those expected with photons propagating in a turbulent plasma.
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| 7. |
- Tamburini, Fabrizio, et al.
(författare)
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Measurement of the spin of the M87 black hole from its observed twisted light
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 492:1, s. L22-L27
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Tidskriftsartikel (refereegranskat)abstract
- We present the first observational evidence that light propagating near a rotating black hole is twisted in phase and carries orbital angular momentum (OAM). This physical observable allows a direct measurement of the rotation of the black hole. We extracted the OAM spectra from the radio intensity data collected by the Event Horizon Telescope from around the black hole M87 - by using wavefront reconstruction and phase recovery techniques and from the visibility amplitude and phase maps. This method is robust and complementary to black hole shadow circularity analyses. It shows that the M87 - rotates clockwise with an estimated rotation parameter a = 0.90 +/- 0.05 with an similar to 95 per cent confidence level (c.l.) and an inclination i = 17 degrees +/- 2 degrees, equivalent to a magnetic arrested disc with an inclination i = 163 degrees +/- 2 degrees. From our analysis, we conclude that, within a 6 sigma c.l., the M87* is rotating.
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| 8. |
- Tamburini, Fabrizio, et al.
(författare)
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Twisted Soft Photon Hair Implants on Black Holes
- 2017
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Ingår i: Entropy. - : MDPI AG. - 1099-4300. ; 19:9
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Hawking-Perry-Strominger (HPS) work states a new controversial idea about the black hole (BH) information paradox, where BHs maximally entropize and encode information in their event horizon area, with no "hair" thought to reveal information outside but angular momentum, mass, and electric charge only in a unique quantum gravity (QG) vacuum state. New conservation laws of gravitation and electromagnetism, appear to generate different QG vacua, preserving more information in soft photon/graviton hair implants. We find that BH photon hair implants can encode orbital angular momentum (OAM) and vorticity of the electromagnetic (EM) field. Methods: Numerical simulations are used to plot an EM field with OAM emitted by a set of dipolar currents together with the soft photon field they induce. The analytical results confirm that the soft photon hair implant carries OAM and vorticity. Results: a set of charges and currents generating real EM fields with precise values of OAM induce a "curly", twisted, soft-hair implant on the BH with vorticity and OAM increased by one unit with respect to the initial real field. Conclusions: Soft photon implants can be spatially shaped ad hoc, encoding structured and densely organized information on the event horizon.
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| 9. |
- Tamburini, Fabrizio, et al.
(författare)
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Twisting of light around rotating black holes
- 2011
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Ingår i: Nature Physics. - 1745-2473 .- 1745-2481. ; 7:3, s. 195-197
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Tidskriftsartikel (refereegranskat)abstract
- Kerr black holes are among the most intriguing predictions of Einstein's general relativity theory(1,2). These rotating massive astrophysical objects drag and intermix their surrounding space and time, deflecting and phase-modifying light emitted near them. We have found that this leads to a new relativistic effect that imprints orbital angular momentum on such light. Numerical experiments, based on the integration of the null geodesic equations of light from orbiting point-like sources in the Kerr black hole equatorial plane to an asymptotic observer(3), indeed identify the phase change and wavefront warping and predict the associated light-beam orbital angular momentum spectra(4). Setting up the best existing telescopes properly, it should be possible to detect and measure this twisted light, thus allowing a direct observational demonstration of the existence of rotating black holes. As non-rotating objects are more an exception than a rule in the Universe, our findings are of fundamental importance.
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| 10. |
- Thidé, Bo, et al.
(författare)
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Angular Momentum Radio Techniques
- 2015
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Ingår i: 2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC). - 9789090086286
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Konferensbidrag (refereegranskat)
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