Topological cascade laser for frequency comb generation in PT-symmetric structures

The cascade of resonant topological structures with PT-symmetry breaking is shown to emit laser light with a frequency-comb spectrum. We consider optically active topological Aubry-Andr\’e-Harper lattices supporting edge-modes at regularly spaced frequencies. When the amplified resonances in the PT-broken regime match the edge modes of the topological gratings, we predict the emission of discrete laser lines. A proper design enables to engineer the spectral features for specific applications. The robustness of the topological protection makes the system very well suited for a novel generation of compact frequency comb emitters for spectroscopy, metrology, and quantum information.

Pilozzi and Conti, arXiv:1707.09191

The Experimental Observation of Replica Symmetry Breaking in Random Lasers

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 theoretically revealed by the change in shape of the probability distribution function of an order parameter named the Parisi overlap.

Despite the profound implications in the new physics of complexity, a direct experimental evidence of the Replica Symmetry Breaking transition, in any field of research was never reported.

C. Conti and coworkers show that pulse-to-pulse fluctuations in random lasers, and  a direct measurement of the Parisi overlap, unveil a transition to a glassy light phase in random lasers compatible with a Replica Symmetry Breaking.

This is the first evidence of Replica Symmetry Breaking and the first direct measurement of the Parisi overlap.

Reference:

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)