For the first time, light mimics a Nobel Prize quantum effect

Science Daily · Mar 1, 2026 · Collected from RSS

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In the late 1800s, physicists discovered what is now called the Hall effect. It occurs when an electric current flows through a material while a magnetic field is applied at a right angle. Under those conditions, a voltage appears across the material in the sideways direction. In simple terms, the magnetic field pushes negatively charged electrons to one side of the conductor. This buildup of charge leaves one edge negatively charged and the opposite edge positively charged, creating a measurable voltage difference. For many years, scientists have used this effect as a reliable tool. It allows them to measure magnetic fields with high precision and determine material doping levels, that is, the addition of a tiny, controlled amount of impurity to a pure material to change how it conducts electricity. From Classical to Quantum Hall Effect During the 1980s, researchers studying ultra thin conductors at extremely low temperatures made a surprising discovery. When these sheet-like materials were exposed to very strong magnetic fields, the sideways voltage did not increase smoothly. Instead, it rose in sharply defined steps. These flat regions, known as plateaus, turned out to be universal. They do not depend on the material's composition, shape or microscopic imperfections. Their values are determined only by fundamental constants of nature: the electron charge and the Planck constant. This phenomenon became known as the quantum Hall effect. Its importance was quickly recognized, ultimately earning three Nobel Prizes in Physics: in 1985, for the discovery of the quantum Hall effect, in 1998 for the discovery of the fractional quantum Hall effect, and in 2016 for the discovery of topological phases of matter. Why Light Posed a Major Challenge Until recently, the quantum Hall effect had been observed primarily in electrons. Because electrons carry electric charge, they respond directly to electric and magnetic fields. Photons, which are particles of light, have no electric charge and therefore do not naturally react to those forces. As a result, recreating the quantum Hall effect with light seemed extraordinarily difficult. Observing a Quantized Drift of Light An international team of researchers has now achieved that goal by demonstrating a quantized transverse drift of light. Their findings were published in Physical Review X. "Light drifts in a quantized manner, following universal steps analogous to those seen with electrons under strong magnetic fields," said Philippe St-Jean, a physics professor at Université de Montréal and co author of the study. The potential impact of this result is significant. In metrology, the science of precision measurement, optical systems could one day serve as a universal reference standard, possibly working alongside or even replacing electronic systems. Implications for Measurement and Standards The quantum Hall effect already plays a central role in modern measurement science. "Today, the kilogram is defined on the basis of fundamental constants using an electromechanical device that compares electric current to mass," St-Jean explained. "For this current to be perfectly calibrated, we need a universal standard for electrical resistance. "The quantum Hall plateaus give us exactly that. Thanks to them, every country in the world shares an identical definition of mass, without relying on physical artifacts." According to St-Jean, gaining precise, quantized control over how light flows could expand possibilities not only in metrology but also in quantum information processing. It may even help lead to more resilient quantum photonic computers. Small departures from perfect quantization could also be useful. Even tiny deviations might reveal subtle environmental disturbances, opening the door to extremely sensitive new types of sensors. Engineering the Future of Photonics "Observing a quantized drit of light is uniquely challenging, for photonic systems are inherently out of equilibrium," St-Jean noted. "Unlike electrons, light demands precise control, manipulation and stabilization." The team's achievement relied on advanced experimental engineering. Their work suggests new opportunities for designing next generation photonic devices capable of transmitting and processing information in powerful new ways.