Multipolar terahertz spectroscopy by graphene plasmons

Terahertz absorption spectroscopy plays a key role in physical, chemical and biological systems as a powerful tool to identify molecular species through their rotational spectrum fingerprint. Owing to the sub-nanometer scale of molecules, radiation-matter coupling is typically dominated by dipolar interaction. Here we show that multipolar rotational spectroscopy of molecules in proximity of localized graphene structures can be accessed through the extraordinary enhancement of their multipolar transitions provided by terahertz plasmons. In particular, specializing our calculations to homonuclear diatomic molecules, we demonstrate that a micron-sized graphene ring with a nano-hole at the core combines a strong near-field enhancement and an inherently pronounced field localization enabling the enhancement of the dipole-forbidden terahertz absorption cross-section of H+2H2+ by 8 orders of magnitude. Our results shed light on the strong potential offered by nano-structured graphene as a robust and electrically tunable platform for multipolar terahertz absorption spectroscopy at the nanoscale.

A. Ciattoni, C. Conti, and A. Marini in Communication Physics

Irreversible quantum mechanics and shock waves in highly nonlinear materials

Dispersive shock waves in thermal optical media belong to the third-order nonlinear phenomena, whose intrinsic irreversibility is described by time asymmetric quantum mechanics. Recent studies demonstrated that nonlocal wave breaking evolves in an exponentially decaying dynamics ruled by the reversed harmonic oscillator, namely, the simplest irreversible quantum system in the rigged Hilbert spaces. The generalization of this theory to more complex scenarios is still an open question. In this work, we use a thermal third-order medium with an unprecedented giant Kerr coefficient, the M-Cresol/Nylon mixed solution, to access an extremely-nonlinear highly-nonlocal regime and realize anisotropic shock waves. We prove that a superposition of the Gamow vectors in an ad hoc rigged Hilbert space describes the nonlinear beam propagation beyond the shock point. Specifically, the resulting rigged Hilbert space is a tensorial product between the reversed and the standard harmonic oscillators spaces. The anisotropy turns out from the interaction of trapping and antitrapping potentials in perpendicular directions. Our work opens the way to a complete description of novel intriguing shock phenomena, and those mediated by extreme nonlinearities.

Giulia Marcucci, Phillip Cala, Weining Man, Davide Pierangeli, Claudio Conti, Zhigang Chen in ArXiv:1909.04506

See also

Glauber oscillator

The math of irreversibility

Our Ising machine in Laser Focus World

August 2019 issue of Laser Focus World reports on our Ising machine in a featured article

Researchers have built the largest photonic Ising machine to date – an optical processor for solving difficult optimization problems by modelin interacting spins via a spatially varying light field

Other web and press release on our Ising machine

Le Scienze : la piu’ grande macchina di calcolo con la luce

Repubblica : la macchina che risolve i problemi alla velocita’ della luce

https://arstechnica.com/science/2019/06/expanding-and-focusing-beam-of-light-makes-parallel-computer/

See also

Super-Duper Ising machine

Optical Spatial Shock Waves in Nonlocal Nonlinear Media

Dispersive shock waves are fascinating phenomena occurring when nonlinearity overwhelms linear effects, such as dispersion and diffraction. Many features of shock waves are still under investigation, as the interplay with noninstantaneity in temporal pulses transmission and nonlocality in spatial beams propagation. Despite the rich and vast literature on nonlinear waves in optical Kerr media, spatial dispersive shock waves in nonlocal materials deserve further attention for their unconventional properties. Indeed, they have been investigated in colloidal matter, chemical physics and biophotonics, for sensing and control of extreme phenomena.
Here we review the last developed theoretical models and recent optical experiments on spatial dispersive shock waves in nonlocal media. Moreover, we discuss observations in novel versatile materials relevant for soft matter and biology.

Giulia Marcucci et al. in arXiv:1907.02823

See also https://giuliasnonlinearworld.wordpress.com/2019/07/08/dswreview/

Quantum Gates by TensorFlow and Reservoir Computing

Novel machine learning computational tools open new perspectives for quantum information systems. Here we adopt the open-source programming library TensorFlowTM to design multi-level quantum gates including a computing reservoir represented by a random unitary matrix. In optics, the reservoir is a disordered medium or a multimodal fiber. We show that trainable operators at the input and the readout enable to realize multi-level gates. We study single and qudit gates, including the
scaling properties of the algorithms with the size of the reservoir.

Quantum Reservoir Computing

G. Marcucci et al. in arXiv:1905.05264

See also