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 was nevere reported.
Pulse-to-pulse fluctuations in random lasers, and a measurement of the Parisi overlap in independent experimental realizations of the same disordered sample, unveil that the distribution undergoes a transition to a glassy light phase compatible with a replica symmetry breaking.
This is the first evidence of Replica Symmetry Breaking and the first direct measurment of the Parisi overlap.
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)