The explanation of spatial reflections—whether by light or by sound—are pretty intuitive. Electromagnetic radiation in the form of light or sound waves hit a mirror or wall, respectively, and change course. This allows our eyes to see a reflection or echo of the original input. However, for more than 50 years, scientists have theorized that there’s another kind of reflection in quantum mechanics known as time reflection.
This term might conjure up images of a nuclear-powered DeLorean or a particular police box (that’s bigger on the inside), but that’s not quite what scientists mean by the term. Instead, time reflections occur when the entire medium in which an electromagnetic wave travels suddenly changes course. This causes a portion of that wave to reverse and its frequency transforms into another one.
In the ETH experiment, self-oscillations (blue-red) cause sound waves (green, orange, violet) to travel through the circulator only in one direction. Credit: Xin Zou
Researchers at ETH Zurich have managed to make sound waves travel only in one direction. In the future, this method could also be used in technical applications with electromagnetic waves.Water, light and sound waves usually propagate in the same way forward as in a backward direction. As a consequence, when we are speaking to someone standing some distance away from us, that person can hear us as well as we can hear them. This is useful when having a conversation, but in some technical applications one would prefer the waves to be able to travel only in one direction—for instance, in order to avoid unwanted reflections of light or microwaves.Ten years ago, researchers succeeded in suppressing sound wave propagation in the backward direction; however, this also attenuated the waves traveling forwards. READ MORE...
Schematic diagram of a topological photonic alloy. The red star indicates the position of the line source, and the arrow indicates the direction of propagation of the chiral edge state. Credit: Qu et al.Photonic alloys, alloy-like materials combining two or more photonic crystals, are promising candidates for the development of structures that control the propagation of electromagnetic waves, also known as waveguides. Despite their potential, these materials typically reflect light back in the direction where it originated.This phenomenon, known as light backscattering, limits the transmission of data and energy, adversely impacting the materials' performance as waveguides. Reliably reducing or preventing light backscattering in photonic alloys will thus be a key milestone towards the practical use of these materials.Researchers at Shanxi University and the Hong Kong University of Science and Technology recently fabricated a new photonic alloy with topological properties that enables the propagation of microwaves without light backscattering. This material, introduced in Physical Review Letters, could pave the way for the development of new topological photonic crystals."Our paper introduces a new concept: the topological photonic alloy as a nonperiodic topological material," Lei Zhang, co-author of the paper, told Phys.org. "We achieved this by combining non-magnetized and magnetized rods in a nonperiodic 2D photonic crystal configuration. This created photonic alloys that sustain chiral edge states in the microwave regime." READ MORE...
