New laser technique reveals nearly 20 previously hidden states of matter

The quantum world is already full of surprises, but a new discovery has added an entire wing to what scientists call the “quantum zoo.”

Using a new kind of laser technique, researchers have uncovered nearly 20 previously hidden states of matter—some of which may be the building blocks for a new generation of quantum computers. These states exist in a material called twisted molybdenum ditelluride, or tMoTe₂, and they don’t require an external magnet to appear.

The discovery, published in Nature, builds on decades of searching for exotic forms of quantum matter. In the past, scientists predicted these states through theory and computer models, but they hadn’t been able to find them all in real materials.

Now, thanks to a collaboration led by Columbia University’s Xiaoyang Zhu, these elusive states have finally stepped into the light. “Some of these states have never been seen before,” said Zhu, the Howard Family Professor of Nanoscience. “And we didn’t expect to see so many either.”

At the heart of this breakthrough is a phenomenon called the fractional quantum anomalous Hall effect. To understand it, you need to know about its ancestor—the classical Hall effect. Discovered in 1879, the Hall effect describes how electrons moving through a strip of metal shift toward the edges when exposed to a magnetic field, creating a measurable voltage difference.

When this experiment is done in two dimensions at extremely low temperatures, something stranger happens: the voltage jumps in fixed steps, a phenomenon called the quantum Hall effect. Sometimes, those steps break into smaller ones—fractions of an electron’s charge—giving rise to the fractional quantum Hall effect. This bizarre behavior was so significant that Columbia’s Horst Stormer shared the 1998 Nobel Prize in Physics for helping uncover it.

The “anomalous” twist comes when these effects appear without any external magnet. That’s exactly what happens in twisted molybdenum ditelluride, where the arrangement of atoms creates its own internal magnetic field.

In 2023, physicist Xiaodong Xu at the University of Washington—working with researchers from Cornell and Shanghai Jiao Tong University—found that twisting atom-thin layers of molybdenum ditelluride into a special pattern called a moiré lattice could produce the fractional quantum anomalous Hall effect without magnets. This was a huge leap, because magnets can disrupt superconducting materials used in quantum technology.

Xu’s team discovered two such magnet-free fractional states. That alone was remarkable. But Zhu and his colleagues suspected there were more waiting to be found. The secret lies in the moiré pattern. When the layers are slightly rotated relative to each other, they form a honeycomb-like grid at the atomic scale.

This structure changes the way electrons move, encouraging them to team up in unusual ways that create fractional charges. In other words, the twist turns the material into a playground for exotic quantum phases.

Last summer, Yiping Wang, a postdoctoral fellow at Columbia, got a sample of twisted molybdenum ditelluride from Xu’s lab. While Zhu was traveling, she decided to try a special laser method known as pump-probe spectroscopy, developed by fellow researcher Eric Arsenault.

This technique uses two laser pulses. The first pulse, the “pump,” briefly excites electrons and “melts” the quantum states in the material. The second, the “probe,” measures how those states recover over time. By tracking these changes in the material’s dielectric constant, the researchers could spot extremely subtle energy levels—many invisible to standard experiments.

What Wang saw lit up her screen. Peaks appeared at fractions that scientists had only theorized before. Among them were fractional fillings such as -4/3, -3/2, -5/3, -7/3, -5/2, and -8/3. These are strong candidates for predicted exotic phases, including fractional topological insulators and non-Abelian anyons—exotic particles thought to be crucial for stable topological quantum computing. “This discovery also establishes pump-probe spectroscopy as the most sensitive technique in detecting quantum states of matter,” Zhu said.

The team didn’t just confirm known states—they revealed nearly 20 new ones. These included fractional fillings between 0 and -1, as well as many on the electron-doped side, where the material has more electrons than usual.

The most intriguing are the newly observed fractional fillings of the Chern bands—energy bands with unique topological properties. These may host non-Abelian states, a rare class of quantum matter where swapping particles changes the system in ways that depend on the order of the swaps.

This property could help create quantum computers that are far more resistant to errors. “We hope these results and our technique inspire others to explore,” Zhu said. “There are just so many.”

The pump-probe experiments also revealed how these correlated quantum states break apart and recover. The melting happens on two very different timescales. Some states collapse in just 2–4 trillionths of a second, a speed linked to pure electronic changes. Others take much longer—about 180–270 trillionths of a second—due to the movement of atomic vibrations, or phonons.

The difference between electron-doped and hole-doped states, where electrons are removed instead of added, comes from the distinct shapes of the material’s conduction and valence bands. These differences could be important for tuning the material for future technologies.

The fractional quantum anomalous Hall effect isn’t just another curiosity in the quantum zoo—it’s a potential gateway to practical quantum technology. Topological quantum computers, which rely on stable, error-resistant quantum states, have long been a goal for physicists. Until now, creating the right states has required magnets, which interfere with most quantum computing hardware.

The fact that these new fractional states exist without magnets means they could be integrated into devices more easily. The discovery also provides a powerful new way to find and study exotic quantum matter in other materials. “Every new state is like finding a new species,” said Wang. “You can study it, understand it, and maybe even use it for something entirely new.”

The idea of a “quantum zoo” might sound whimsical, but it captures the excitement in the field. For decades, many predicted states existed only in mathematical models. With each new experimental technique, scientists uncover more of them, expanding our understanding of how electrons can organize themselves.

In twisted molybdenum ditelluride, the zoo just got a lot bigger. What’s next will depend on how these new states are explored and whether they can be harnessed for technology. Given the pace of discoveries, the zoo’s latest residents may soon be joined by even stranger creatures.

Note: The article above provided above by The Brighter Side of News.

Like these kind of feel good stories? Get The Brighter Side of News' newsletter.