Our research ...

Solitons evaporate as black holes!

The fact that black holes are solitons is not very well known. Abdus Salam and others outlined this issue several years ago. Stephen Hawking predicted that Black Holes evaporate, and this is a quantum effect on classical gravity governed by the highly nonlinear Einstein-Hilbert equations.

Leone Villari, Ewan Wright, Fabio Biancalana and Claudio Conti report on the possibility that all types of classical solitons may evaporate in the quantum regime. A paper in the arXiv contains the theory on the exact quantization of the nonlinear Schroedinger equation: solitons emit a blackbody radiation spectrum at a temperature given by the same formula of Hawking!

This result is intriguing. On one hand, because it represents the first theoretical prediction of the Hawking radiation in a fully nonlinear quantum field theory. The standard Hawking theory relies on the quantization of a linear field in a curved background. The theory may hence provide insights for a true quantum gravity based on the complete quantization of the Einstein-Hilbert equations.

On the other hand, the result is also important because the Hawking radiation from a quantum soliton may furnish a novel highly tunable quantum source with many possible applications.



The Math of Irreversibility

In a paper in arXiv Giulia Marcucci and Claudio Conti report on the mathematical structures of the so-called Time Asymmetric Quantum Mechanics. This theory predicts that time-travel is not possible and explain evidences as the Big Bang or the decay of unstable particles. The authors argue that possible shaping of the initial state of a system may furnish a road to validate these fascinating developments in quantum mechanics. The work also follows the experimental evidence of the quantization of the decays rates.

The picture below shows a pictorial representation of the Gelfand triplet, the phase space of the Time Asymmetric Quantum Mechanics



Quantum X waves with orbital angular momentum

Multi-level quantum protocols may potentially supersede standard quantum optical polarization-encoded protocols in terms of amount of information transmission and security. However, for free space telecomunications, we do not have tools for limiting loss due to diffraction and perturbations, as for example turbulence in air.

In a recent manuscript in arXiv, Marco Ornigotti, Leone di Mauro Villari, Alexander Szeimeit, and Claudio Conti study propagation invariant quantum X-waves with angular momentum. The adopted representation expresses the electromagnetic field as a quantum gas of weakly interacting bosons. The resulting spatio-temporal quantized light pulses are not subject to diffraction and dispersion, and are intrinsically resilient to disturbances in propagation. Spontaneous down-conversion generates squeezed X-waves useful for quantum protocols. Surprisingly the orbital angural momentum affects the squeezing angle, and a characteristic axicon aperture for maximal squeezing exists.

There results may boost the applications in free space of quantum optical transmission and multi-level quantum protocols, and may also be relevant for novel kinds of interferometers, as satellite-based gravitational wave detectors.



Cylindrically polarized X-waves paper of the week!

Journal of Optics elects the paper on cylindrically polarized X-waves, a new class of propagation invariant ultrashort light pulses with radial or azymuthal polarization as Paper of the Week.

Marco Ornigotti, Claudio Conti, and Alexander Szameit extend to the polychromatic domain the light beams with cylindrical polarization, which have widespread applications in microscopy and spectroscopy.

These light pulses represent a fully vectorial solution of Maxwell equations, can be focused at the sub-wavelength scale and may open a number of possibilities for a new generation of imaging devices, and for free space information transmission.

The paper was published in Journal of Optics (ArXiv:1602.03317)



The Quest for Quantum Gravity in Optics

Quantum gravity challenges inspire a great variety of scientists, and photonics is opening several interesting and related directions.

In a paper posted in the ArXiv, Maria Chiara Braidotti, Ziad Musslimani and Claudio Conti show the way the generalized uncertainty principle, introduced for studying physics at the Planck scale, has a role in optics, and may stimulate unexpected applications for high resolution imaging and ultrafast propagation.

The picture below shows a representation of the generalized uncertainty principle (G-UP) and the difference with the standard Heisenberg principle (H-UP), further details in our paper in the ArXiv.




Our article on curved shocks featured in Science bullettin



Designing Beauty: New Book on the Game of Life Art

A new book on the Game of Life, and specifically on the Art of the Game of Life has been published by Springer.

Edited by A. Adamatzky and Genaro J. Martinez, the book is entitled

Designing Beauty: The Art of Cellular Automata

part of the Series on Emergence, Complexity and Computation with artistic representations from simple mathematical models at the edge of physics and biology. The book contains a contribution by C. Conti on the Enlightened Game of Life.

The picture below shows the content of the book




Glauber oscillator and time travel

The standard quantum mechanics does not forbid time-travel. However, some alternative formulations (based on the so called "rigged Hilbert space") include irreversibility as a fundamental principle: a quantum particle that decays cannot travel back in time.

There are not direct evidences of the irreversibility of decay processes, but the new quantum mechanics predicts that the decay rates are quantized.

If one observes the quantization of the decay rates, one can claim to have provided experimental support to the irreversible formulation of quantum mechanics.

In simple terms, one can claim that time-travel is not possible at the quantum level (...and also at the classical level).

Silvia Gentilini, Maria Chiara Braidotti, Giulia Marcucci, Eugenio Del Re, and Claudio Conti simulated in the laboratory one of the simplest models of the irreversible quantum mechanics, that follows an original proposal of Glauber. A laser beam emulates a quantum particle in a reversed harmonic oscillator, as a result the first experimental evidence of the quantization of decay time is reported in a paper published in Scientific Reports.



How much can you twist a ultrashort pulse?

If you have a ultrashort pulse, and you want to add angular momentum, you have limitations.

This is what Andrea Ornigotti, Claudio Conti, and Alexander Szameit, discovered and published in the Physical Review Letters. An extended and generalized analysis can be found in Physical Review A.

Angular momentum of light is nowadays largely studied because you can add information to a optical beam by twisting it, or you can rotate objects by lasers with angular momentum. But if you want to transmit information, the best thing to do is using light pulses and adding to any pulse a certain amount of orbital angular momentum (OAM).  For example, by using m levels of OAM, any single pulse can encode m symbols (2 symbols correspond to one bit). The shortest the pulse you use, the higher the number of symbols you can transmit in a second (the transmission rate). This approach can be used for new classical and quantum high-bit rate transmission systems in free space or in fiber. 

But Ornigotti and others find out that the number of OAM bits you can store in a single pulse is actually limited by the duration of the pulse and by its carrier frequency.

The following picture shows the link between OAM units m and the number of optical cycles in the pulse, these two quantized observables are actually strictly related.



These findings have important outcomes in the modern multilevel transmission systems, but also reveal a novel form of spatio-temporal coupling. The latter may lead to new kinds of entanglement, which may trigger applications in Quantum Optics.





Irreversibility of Shock Waves Explained by Nonlinear Gamow Vectors

Editors of Physical Review A have retained among their suggestions a paper published by Silvia Gentilini, Maria Chiara Braidotti, Giulia Marcucci, Eugenio Del Re and Claudio Conti about a novel theoretical approach for the description of shock waves in nonlinear nonlocal media.

The novel theory is based on ideas retained from Irreversible Quantum Mechanics, a novel formulation of quantum mechanics based on the so-called Rigged Hilbert Space that include explonential decaying wavefuctions.

The theory describes the shock and wave-breaking scenario beyond the limits of the usual hydrodynamic approach, and allows to derive closed forms for the degree of irreversibility. This approach also introduces the "nonlinear Gamow Vectors," a novel kind of nonlinear waves with many possible applications in nonlinear physics.



Three-dimensional rogue waves by random media go through obstacles

Formerly considered a myth, the sudden formation of giant waves in a sea of low amplitude wavelets is nowadays an important subject of interdisciplinary research. These “rogue waves” (RW) are studied in different contexts, and their understanding is a challenge characterized by an intense discussion and a number of potential applications. 

It is commonly accepted that the physics underlying the generation of giant oceanic RW is different from that of usual waves and that the triggering mechanism of RWs is not unique: linear effects (such as the focusing of independent wave trains) as well as the nonlinear amplification of noise may produce RWs.

In a paper published in Applied Physics Letters, Marco Leonetti and Claudio Conti use a spatial light modulator (SLM) to explore the possible speckle configurations generated by a random medium  to generate and control a three-dimensional rogue wave.

They demonstrate that the SLM allows to select among all the possible realizations, the RW located at a user defined position in the shadow of the nearly totally reflecting obstacle. Moreover, by tuning the properties of the speckle pattern, the localization along the propagation axis can be controlled.

The picture below show the three-dimensional reconstruction of the observed rogue-wave.



The thinnest beam ever! In Nature Photonics

In a paper published in Nature Photonics, E. Del Re, F. Di Mei, J. Parravicini, G. Parravicini, A. J. Agranat, and C. Conti report on the observation of a sub-wavelength spatial solitons propagating in a nano-disordered ferroelectric.

The beam has transverse size of the order of 200nm with wavelength 632nm, and turns out to be the thinnest beam ever observed with a variety of applications!



Relativistic analogue in non-paraxial shock waves

Shock generation and wave-breaking are effects largely investigated in nonlinear optics. They are always occurring in extreme regimes with a variety of fundamental physical implications, and a number of applications, ranging from particle and material manipulation, to supercontinuum and X-ray generation.

In nonlinear optics, one studies shocks in space and time. Concerning the spatial case, shock waves are observed as highly irregular wave-fronts that originate upon the propagation of a smooth Gaussian beam in a strongly nonlinear medium like, for example, a thermal liquid.

So far, the analysis of spatial shock waves has been limited by the paraxial approximation. The validity of this approximation, however, is questioned by the large spatial bandwidth that is observed at the shock formation.

In a manuscript published in Optics Communications (arXiv:1412.8602) Silvia Gentilini, Eugenio Del Re and Claudio Conti study theoretically and computationally the effects of the non-paraxial regime on the shocks. The result is a predicted correction to the maximal spatial bandwidth after the shock generation, which is within experimentally measurable values, and which is also relevant for temporal shock waves.

The analysis is fascinating, as it shows that non-paraxial terms can be mapped to the relativistic corrections that occur when one considers the propagation of particles with velocity comparable with the speed of light. In other words, the mathematical treatment of the non-paraxial shock is analogue to the treatment of the relativistic particle motion. The trajectories of the particles corresponds to the so-called characteristic lines.

This problem is also relevant for mathematical investigations concerning wave-breaking in high-order nonlinear partial differential equations.

The picture below shows an example of  the calculation of the relativistic shock wave front.



Optomechanics of random media: towards Photonic Robots

The Brownian motion of photons in a random medium induces a Brownian motion of the medium.

Anderson localization of light enhances the optomechanical interaction.

These effects are considered in a manuscript, by Silvia Gentilini and Claudio Conti, based on massively parallel numerical solutions of the Maxwell equations for random media. The goal is designing micron-sized structured devices that are activated by light and perform a prescribed motion. Understanding the role of light scattering is pivotal in the realization of "Photonic Robots."

Now published in Phys. Rev. A



Light Focusing and the Anderson localization in Nature Communications

Marco Leonetti, Salman Karbasi, Arash Mafi and Claudio Conti report numerical and experimental evidence of the fact that two dimensional Anderson localization in disordered fibers enhances light focusing properties. The results have been published in Nature Communications (arXiv:1407.8062)

The picture below shows the adaptive focusing in a disordered fiber