Phase-matching-free parametric oscillators based on two dimensional semiconductors

Optical parametric oscillators are widely-used pulsed and continuous-wave tunable sources for innumerable applications, as in quantum technologies, imaging and biophysics. A key drawback is material dispersion imposing the phase-matching condition that generally entails a complex setup design, thus hindering tunability and miniaturization. Here we show that the burden of phase-matching is surprisingly absent in parametric micro-resonators adopting monolayer transition-metal dichalcogenides as quadratic nonlinear materials. By the exact solution of nonlinear Maxwell equations and first-principle calculation of the semiconductor nonlinear response, we devise a novel kind of phase-matching-free miniaturized parametric oscillator operating at conventional pump intensities. We find that different two-dimensional semiconductors yield degenerate and non-degenerate emission at various spectral regions thanks to doubly-resonant mode excitation, which can be tuned through the incidence angle of the external pump laser. In addition we show that high-frequency electrical modulation can be achieved by doping through electrical gating that efficiently shifts the parametric oscillation threshold. Our results pave the way for new ultra-fast tunable micron-sized sources of entangled photons, a key device underpinning any quantum protocol. Highly-miniaturized optical parametric oscillators may also be employed in lab-on-chip technologies for biophysics, environmental pollution detection and security.

Ciattoni, Marini, Rizza, Conti in arXiv:1707.08843

Review In Annalen Der Physics on Time Asymmetric Quantum Mechanics

The description of irreversible phenomena is a still debated topic in quantum mechanics. Still nowadays, there is no clear procedure to distinguish the coupling with external baths from the intrinsic irreversibility in isolated systems. In 1928 Gamow introduced states with exponentially decaying observables not belonging to the conventional Hilbert space. These states are named Gamow vectors, and they belong to rigged Hilbert spaces. This review summarizes the contemporary approach using Gamow vectors and rigged Hilbert space formalism as foundations of a generalized “time asymmetric” quantum mechanics. We study the irreversible propagation of specific wave packets and show that the topic is surprisingly related to the problem of irreversibility of shock waves in classical nonlinear evolution. We specifically consider the applications in the field of nonlinear optics. We show that it is
possible to emulate irreversible quantum mechanical process by the nonlinear evolution of a laser beam and we provide experimental tests by the generation of dispersive shock waves in highly nonlocal regimes. We demonstrate experimentally the quantization of decay rates predicted by the time-asymmetric quantum mechanics. This work furnishes support to the idea of intrinsically irreversible wave propagation, and to novel tests of the foundations of quantum mechanics.

Time-Asymmetric Quantum Mechanics and Shock Waves: Exploring the Irreversibility in Nonlinear Optics, Annalen der Physik 10.1002/andp.201600349 (2017)

 

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)

 

Designing Beauty: The Art of Cellular Automata

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 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 chapter by C. Conti on the Enlightened Game of Life.

 

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.

(reprint from the former complexlight.org website)