Physicists prove simplest quantum paradox using pulses of light in 37 dimensions

Quantum mechanics has always had a way of making even the sharpest minds stop and scratch their heads. In the everyday world, you expect objects to follow straightforward rules. A ball thrown into the air will fall back down. A coin flip will land either heads or tails. Yet when you shrink the scale to the world of atoms and particles, the rules stop working in the way you think they should. Instead, reality takes on a stranger flavor—where measurement changes outcomes and certainty becomes slippery.

A recent study by physicist Zhenghao Liu and his colleagues at the Technical University of Denmark shines new light on this mystery. The study finding were published in the journal Science Advances.

The group set out to test a particularly bold idea about the foundations of quantum theory: contextuality. This is the notion that the behavior of a quantum particle depends on the specific conditions under which it is measured, not on some hidden internal rulebook. Put simply, reality at the quantum level may not exist in a fixed way until you probe it.

To explore this, the researchers leaned on a famous thought experiment known as the GHZ paradox, named after physicists Daniel Greenberger, Michael Horne, and Anton Zeilinger. The paradox is often described as a “no-win” situation for anyone trying to explain quantum outcomes with classical logic.

Imagine trying to solve a puzzle where every move seems consistent—until the end, when the pieces simply won’t fit. That is what happens if you assume that hidden variables secretly govern quantum systems. The GHZ paradox shows that these assumptions eventually lead to contradictions, meaning the quantum world simply doesn’t play by the same rules as the everyday one.

What Liu’s team accomplished was finding the most efficient way to demonstrate this paradox. They discovered that you only need three distinct measurement settings, or “contexts,” to show a clear clash between quantum behavior and classical reasoning. That number turns out to be the lowest possible according to the laws of quantum theory. In other words, they found the simplest and cleanest version of the paradox.

The real challenge came in bringing this idea out of theory and into the lab. To do this, the researchers turned to light. They used a laser that produces short, sharp bursts—called coherent pulsed light—and then passed those bursts through a network of optical fibers and modulators. These tools allowed them to precisely shape and manipulate the light over time.

But this was no ordinary setup. The team pushed the system into what’s called a 37-dimensional space. In daily life, you think in three dimensions—length, width, and height. Here, the scientists were dealing with 37 possible states at once, each representing a unique way light can be structured and measured. The goal was to create a playground where the paradox could unfold at an unprecedented scale.

The setup worked like this: modulators adjusted the light’s properties in extremely fast cycles, fibers created loops that combined signals in complex ways, and a sensitive detection system known as homodyne detection measured the final output with extreme accuracy. By designing the experiment this way, they could mimic a high-dimensional quantum system without needing exotic new hardware.

When the experiment ran, the data landed exactly where quantum theory predicted. Certain probabilities added up perfectly within the framework of quantum mechanics but flatly refused to match any classical explanation.

This meant the outcomes couldn’t be written off as the result of hidden variables that existed before measurement. The particles behaved as quantum mechanics insists they must—context-dependent, surprising, and utterly defiant of classical intuition.

Even more striking was that this played out in 37 dimensions. Most previous experiments testing similar ideas stayed in just two or three dimensions. By leaping into such a high-dimensional space, Liu and his colleagues proved that the bizarre features of quantum systems only grow more pronounced as the complexity increases.

The team had managed to “measure a pulse of light in 37 dimensions” and confirm that quantum mechanics is “more nonclassical than thought.” In other words, the weirdness wasn’t watered down by complexity. It became stronger.

This achievement matters for more than just proving a theoretical point. By creating the leanest version of the GHZ paradox, the team drew a sharper line between classical and quantum behavior. It’s a bit like finding the minimum set of moves needed to prove that a card trick isn’t magic but rather a new rule of reality.

Equally important is the method itself. Using pulses of light in a looping fiber system opens new ways to study high-dimensional quantum systems without needing to build more complicated machines. It’s flexible, efficient, and adaptable.

Scientists could use this same platform to test other hard-to-reach quantum ideas or to design new communication protocols that rely on many-dimensional states of light.

The broader significance is that even after decades of exploring quantum mechanics, surprises still emerge. Just when you think the limits are clear, researchers uncover a new layer that challenges your picture of how reality works.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

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