Replica Symmetry Breaking in Random Lasers

N. Ghofraniha, I. Viola, F. Di Maria, G. Barbarella, G. Gigli, L. Leuzzi and C. Conti reported on the first evidence of Replica Symmetry Breaking in Random Lasers by the direct measurement of the Parisi overlap distribution function (arXiv:1407.5428, Nature Communications 2015)

Spin-glass theory is one of the leading paradigms of complex physics and describes condensed matter, neural networks and biological systems, ultracold atoms, random photonics, and many other research fields. According to this theory, identical systems under identical conditions may reach different states and provide different values for observable quantities. This effect is known as Replica Symmetry Breaking and is revealed by the shape of the probability distribution function of an order parameter named the Parisi overlap. However, a direct experimental evidence in any field of research is still missing. Here we investigate pulse-to-pulse fluctuations in random lasers, we introduce and measure the analogue of the Parisi overlap in independent experimental realizations of the same disordered sample, and we find that the distribution function yields evidence of atransition to a glassy light phase compatible with a replica symmetry breaking.




Last Updated (Saturday, 17 January 2015 09:04)


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


Last Updated (Monday, 11 August 2014 08:39)


Solitonized Anderson localized states move

The conventional wisdom is that transport is absent in the presence of Anderson localization. However, nonlinearity changes things.

In a paper published in Physical Review Letters (arXiv:1407.7990),  Marco Leonetti, Salman Karbasi, Arash Mafi, and Claudio Conti, report experimental evidence that disorder induced two-dimensional states in an optical fiber display collective motion and action at a distance. It is also shown that the trend of the localization length with power is compatible with that of a spatial optical soliton, giving support to the fact that two mechanicsms, disorder and nonlinearity, may cohexist.

The pictures below show the profile of one localized state versus power and the collective motion of several localizations, they exhibit a mutual attraction because of the nonlocal nonlinearity.



Last Updated (Monday, 11 August 2014 08:40)


Quantum Gravity and Nonlinear Optics: the Generalized Uncertainty Principle

Quantum gravity is one of the most intriguing fields of physics, people is working a lot for finding an experimental framework.

It is apparently impossible to reach in the laboratory the required energies, many consider the scale of the Universe, looking for high energy particles.

Perhaps we can play the quantum gravity game in the laboratory by using nonlinear optics. It is really interesting that the equations that describe some of the modifications of quantum mechanics, which are supposed to hold true at the Planck scale (as the famous KMM proposal), are also valid for the propagation of nonparaxial nonlocal optical beams. This is treated in a recent work in Phys. Rev. A (ArXiv:1406.6677)

One of the simplest and beautiful predictions of the quantum gravity literature is the possibility of a generalized uncertainty principle, which reads as

that implies that the spatial uncertainity cannot be smaller than a minimal quantity. The states that satistfy this condition are named the maximally localized states.

In Phys. Rev. A (ArXiv:1406.6677) we show that in nonlinear optics these states can be excited by an ultrafocused laser beam, this provides fascinating analogs of supposed quantum gravity effects.

quantum gravity states

Last Updated (Thursday, 26 June 2014 04:55)


Rogue waves and the landscape

Non-deterministic giant waves, denoted as rogue, killer, monster or freak waves, have been reported in many different branches of physics. Their origin is however still unknown: despite the massive numerical and experimental evidence, the ultimate reason for their spontaneous formation has not been identified yet.

In arXiv:1406.5966Andrea Armaroli, Claudio Conti, and Fabio Biancalana, show that rogue waves in optical fibres actually result from a complex dynamic process very similar to well known mechanisms such as glass transitions and protein folding. They describe the way the interaction among optical solitons produces an energy landscape in a highly-dimensional parameter space with multiple quasi-equilibrium points. These configurations have the same statistical distribution of the observed rogue events and are explored during the light dynamics due to soliton collisions, with inelastic mechanisms enhancing the process. Slightly different initial conditions lead to very different dynamics in this complex geometry; a rogue soliton turns out to stem from one particular deep quasi-equilibrium point of the energy landscape in which the system may be transiently trapped during evolution. This explanation will prove fruitful to the wide community interested in freak waves.


Last Updated (Thursday, 26 June 2014 20:09)