The unpredictable quantum world just got stranger thanks to Brown University physicists and the discovery of unexpected behavior in particles called fractional excitons.
Odd quantum behaviors like existing in multiple locations simultaneously, instantaneous communication over large distances, and passing through solid barriers have long intrigued physicists. Now, the recent Brown University discoveries are shedding light on what seemingly impossible properties exist at the tiny quantum scale.
“Our findings point toward an entirely new class of quantum particles that carry no overall charge but follow unique quantum statistics,” said co-author Jia Li, an associate professor of physics at Brown. “The most exciting part is that this discovery unlocks a range of novel quantum phases of matter, presenting a new frontier for future research, deepening our understanding of fundamental physics, and even opening up new possibilities in quantum computation.”
Quantum Effects
In 1879, American physicist Edwin Hall discovered the Hall effect, in which a magnetic field applied to a material with an electric current generates measurable voltage differences at right angles to both the magenetic field and the current. Today, the Hall effect is an important component in engineering video game controllers.
At the quantum level, the quantum Hall effect occurs, where extremely low temperatures contrasted with high magnetic fields enable the “sideways” voltage to increase in distinctly separate jumps. Even stranger is the fractional quantum Hall effect, where those steps grow by only a fraction of an electron’s charge.
The Brown team developed a structure from two pieces of the two-dimensional nanomaterial graphene insulated from each other with hexagonal boron nitride crystal. This platform allowed the researchers to finely control electrical charges and create excitons. The physicists created the excitons by combining an electron with a hole, the absence of an electron. With the excitons prepared, the team then exposed the system to magnetic fields millions of times stronger than Earth’s to observe the strange characteristics of novel fractional excitons.
Unexpected Particles
The excitons that the Brown team observed defied typical categorization. Generally, fundamental particles are either bosons or fermions. Bosons can share the same quantum state and co-exist with others of their kind, while no two fermions can occupy the same state due to the Pauli exclusion principle. A far smaller number of particles fit into the anyon category, which lies somewhere in the middle. The fractional excitons, however, displayed behaviors specific to each while not entirely resembling any type, acting almost as a hybrid.
“This unexpected behavior suggests fractional excitons could represent an entirely new class of particles with unique quantum properties,” lead author Naiyuan Zhang said. “We show that excitons can exist in the fractional quantum Hall regime and that some of these excitons arise from the pairing of fractionally charged particles, creating fractional excitons that don’t behave like bosons.”
Quantum Computing Applications
This new type of particle isn’t just a scientific curiosity; it may have very important real-world applications. These particles could enhance information storage and manipulation, improving the speed and reliability of quantum computers.
“We’ve essentially unlocked a new dimension for exploring and manipulating this phenomenon, and we’re only beginning to scratch the surface,” Li said. “This is the first time we’ve shown that these types of particles exist experimentally, and now we are delving deeper into what might come from them.”
Moving forward, the Brown physicists are working to understand how these particles can be applied to real-world uses. The team’s next study will focus on how the fractional excitons interact and how humans can effectively control their behavior. A thorough understanding of their behavior could lead to exciting applications in the quantum computing field, while tighter control will be required to execute those ideas.
“This feels like we have our finger right on the knob of quantum mechanics,” co-author D. E. Feldman said. “It’s an aspect of quantum mechanics that we didn’t know about or, at least, we didn’t appreciate before now.”
“The paper “Excitons in the Fractional Quantum Hall Effect” appeared on January 08, 2025 in Nature.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.