3 min readHere’s what you’ll learn when you read this story:
- Electrons are influenced by a magnetic field display known as the quantum Hall effect (QHE), which helps scientists make hyper-accurate measurements.
- Now, scientists have observed a similar behavior in photons, which could open the door to a host of new applications.
- The light-based QHE is so useful because it’s based on fundamental principles of the universe, which allows it to serve as an invaluable measuring mechanism.
Early in the morning on February 5th, 1980, German scientist Klaus von Klitzing noticed that when a strong magnetic field is applied at a right angle to an electric current, a voltage is created in a sideways direction. Interestingly, this voltage did not increase smoothly, but at highly specific values. Von Klitzing had just experimentally proven the quantum Hall effect (QHE)—a useful quantum quirk that helps scientists measure magnetic fields with immense precision and determine material doping levels. The discovery eventually won von Klitzing the Nobel Prize in Physics five years later.
A fascinating aspect of von Klitzing’s voltage plateaus is that they were a fundamental constant, meaning that changes in material, shape, or amount of imperfections didn’t impact these flat regions. That’s because this quantum behavior was intrinsic to two fundamental properties of the universe: the Planck constant and the electron charge. As a result of this bedrock nature, the quantum Hall effect became an immensely powerful tool in metrology, the science of measurement.
While the usefulness of this quantized Hall effect was immediately apparent, scientists wondered if the phenomenon was unique to electrons. After all, electrons respond to the presence of electric and magnetic fields, whereas photons (for example) lack any electric charge, meaning they don’t naturally react with these fields. However, a new study—led by an international team of scientists and published in the journal Physical Review X—details the first-ever observation that light (i.e. photons) does in fact display quantized drift, meaning the quantum Hall effect is not limited to electrons.
“Light drifts in a quantized manner, following universal steps analogous to those seen with electrons under strong magnetic fields,” Philippe St-Jean, a co-author of the study from the University of Montreal, said in a press statement. “Observing a quantized drift of light is uniquely challenging, for photonic systems are inherently out of equilibrium. Unlike electrons, light demands precise control, manipulation and stabilization.”
In November of 2018, the General Conference on Weights and Measures voted to officially redefine the kilogram based on the Planck constant (using the QHE) rather than a physical object stored in a vault in France, as had been done for 130 years. This means that labs around the world can execute calibrations with pinpoint accuracy during experiments.
“Today, the kilogram is defined on the basis of fundamental constants using an electromechanical device that compares electric current to mass,” St-Jean said in a press statement. “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.”
This precise level of quantized light control not only opens up new doors in metrology, but may also help create hyper-accurate sensors (by allowing for the detection of deviations from perfect quantization) and improve photonic quantum systems.
More than four decades after von Klitzing’s famous discovery, the quantum Hall effect still retains the ability to surprise.
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Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.