The race to heuristically solve non-deterministic polynomial-time (NP) problems through efficient methods is ongoing. Recently, optics was demonstrated as a promising tool to find the ground state of a spin-glass Ising Hamiltonian, which represents an archetypal NP problem. However, achieving completely programmable spin couplings in these large-scale optical Ising simulators remains an open challenge. Here, by exploiting the knowledge of the transmission matrix of a random medium, we experimentally demonstrate the possibility of controlling the couplings of a fully connected Ising spin system. By further tailoring the input wavefront we showcase the possibility of modifying the Ising Hamiltonian both by accounting for an external magnetic field and by controlling the number of degenerate ground states and their properties and probabilities. Our results represent a relevant step toward the realisation of fully-programmable Ising machines on thin optical platforms, capable of solving complex spin-glass Hamiltonians on a large scale.
There have been a number of rapid advances in the prediction of the dynamics of chaotic systems using a technique known as Reservoir Computing. These techniques are mostly not effective for large networks, as the complexity of the task increases quadratically both in time and memory. We report new advances in Optical Reservoir Computing using multiple light scattering to accelerate the recursive computation of the reservoir states. Different approaches to information encoding based on phase or amplitude spatial light modulations are compared. We demonstrate the scalability and the good prediction performance of our approach using the Kuramoto-Sivashinsky equation as an example of a spatiotemporally chaotic system.
The properties of chiral photonic crystals with a pitch gradient were investigated both experimentally and theoretically. The liquid-crystalline cell was prepared by bringing two cholesteric liquid crystals (CLCs) with different pitches into contact. There are some essential features in the dynamics of diffusion between the two CLCs. The most important feature is the fact that establishing the final equilibrium pitch (for the temperatures below 17°C) takes a long time—roughly 3 months or more—which, in turn, allows us to investigate the nonstandard change in the reflection spectra during the diffusion. The two reflection curves do not directly actually get closer and merge into one peak, as usual, but the left one gradually gets smaller and almost vanishes, and the right one expands. For this reason, a theoretical model of a pitch change was developed and it was seen that this model does not coincide with the classical ideas of the pitch change. It was also assumed that due to the “freezing” effect during the diffusion process, one could have fixed the intermediate states of the pitch gradient.
We investigate light wave propagation through a one-axis anisotropic medium layer with simultaneously non-unit
dielectric and magnetic tensors. 4x4 - Δ▵(see manuscript) matrix is built. We consider the general case when the dielectric and magnetic
permittivity tensor elements have both positive and negative sings. We obtained the dispersion equation and then built
dispersion surfaces for a homogeneous anisotropic uniaxial material when the material is negative or positive (both with
respect to the wave vector and Pointing's vector orientation of the refracted wave; the sign of the material is accordingly
defined below.) Electromagnetic plane waves propagating inside the medium can exhibit dispersion surfaces in the form
of ellipsoids of revolution, hyperboloids of one sheet, or hyperboloids of two sheets. The conditions of negative
refraction with respect to the wave vector and Pointing's vector orientation are considered. We found wave nonreciprocity
for the oblique incidence on the considered system and we showed that such a system can work as an alloptical
diode.
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