Technion researchers measure the speed of "dark points" within light waves, confirming a 50-year-old prediction
A research group from the Technion-Israel Institute of Technology reports in Nature an unprecedented achievement in electron microscopy: the direct measurement of "dark points" within light waves. By doing so, they were able to confirm a prediction from the 1970s that the speed of these points exceeds the speed of light.
The researchers who led the groundbreaking study hail from the Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering: Prof. Ido Kaminer, Ph.D. students Tomer Bucher and Alexey Gorlach, Dr. Arthur Niedermayr, and Dr. Shay Tsesses, who completed his Ph.D. in Prof. Guy Bartal's lab at the Technion and is currently a postdoctoral researcher at the Massachusetts Institute of Technology. The article is the result of an extensive international collaboration featuring researchers from the Technion, Bar-Ilan University, MIT, SIOM, Harvard, Stanford University, Milano-Bicocca, and ICFO.
The "dark points" measured by the group are essentially tiny "holes" in the wave structure. Known as vortices, the holes are a common phenomenon in nature: we encounter them in ocean waves, in air currents, and even in coffee when we stir it or pour it into the sink. As early as the 1970s, a surprising theoretical prediction was proposed: vortices may move faster than the wave in which they are formed. As strange as it sounds – imagine a vortex in a river overtaking the flow of water in which it exists – the phenomenon is real. Until now, this was based on theory. The research team's achievement has now confirmed it experimentally.
How is this possible? After all, Einstein established that the speed of light in a vacuum is the ultimate speed limit. However, relativity applies this constraint specifically to matter with mass and to signals that transmit energy or information. The vortices observed at the Technion are massless and do not carry energy or information, meaning they do not violate Einstein's principle.
So what exactly are these entities? According to the Technion researchers, these light vortices are "zero points," or "nulls," within light waves – locations where the wave's amplitude drops to zero. In simpler terms, they are points of complete darkness embedded within the light field.
As noted, this phenomenon was predicted in the 1970s as a direct result of random wave interference, and many attempts have since been made to demonstrate it experimentally. The Technion team's success is based on the construction of a unique microscopy system at the Technion's Electron Microscopy Center. By integrating a laser system with an advanced opto-mechanical setup into a specialized electron microscope, the researchers achieved record-breaking temporal and spatial resolution.
The vortices (dark points) were measured in a specific material (hBN), prepared by Prof. Hanan Herzig Sheinfux of Bar-Ilan University. In this material, light waves become special "light-sound" waves (polaritons). These can be thought of as light waves that move unusually slowly, about 100 times slower than the speed of light in a vacuum, or as sound waves that move unusually fast. It is within these "slowed" waves that light vortices can "leap" and exceed the speed of light.
Beyond the historic success of this specific experimental observation, Prof. Kaminer explained: "Our discovery reveals universal laws of nature shared by all types of waves, from sound waves and fluid flows to complex systems such as superconductors. This breakthrough provides us with a powerful technological tool: the ability to map the motion of delicate nanoscale phenomena in materials, revealed through a new method (electron interferometry) that enhances image sharpness. We believe these innovative microscopy techniques will enable the study of hidden processes in physics, chemistry, and biology, revealing for the first time how nature behaves in its fastest and most elusive moments."
Measuring the rapid "dance" of light vortices opens new scientific directions, with potential impact on the development of microscopy technologies, nanostructure-based optics, superconductivity research, and methods for encoding quantum information in materials.
The research was supported by the European Union (Horizon 2020 program), the Moore Foundation, and the Helen Diller Quantum Center at the Technion. Dr. Arthur Niedermayr, Harel Nahari, Prof. Kangfeng Wang, Dr. Yuval Adiv, and Tom Lankievitz, led by Dr. Michael Yannai, built the experimental system and conducted the experiments. Dr. Qinghui Yan and Ron Ruimy contributed to the theoretical analysis.
