In a recent investigation, researchers have discovered a novel type of quantum particles identified as fractional excitons. These particles exhibit surprising properties that have the potential to deepen the scientific community’s comprehension of quantum mechanics.
Within the enigmatic world of quantum physics, subatomic particles often defy conventional physical laws. They can simultaneously occupy multiple locations, penetrate solid obstacles, and even transmit information instantaneously over great distances. While such behavior may appear far-fetched, scientists are currently examining various properties in the quantum domain that were once deemed impossible.
Recently, physicists at Brown University have made an exciting observation concerning a new class of quantum particles known as fractional excitons. These unusual particles display unexpected behaviors that could broaden the understanding of quantum phenomena.
“Our research indicates the existence of a completely new category of quantum particles that lack an overall charge but adhere to distinct quantum statistics,” explained Jia Li, an associate professor of physics at Brown. “The most thrilling aspect of this finding is that it opens up a variety of innovative quantum phases of matter, marking a new frontier for future studies, enhancing our grasp of fundamental physics, and even paving new avenues for advancements in quantum computing.”
Alongside Li, three graduate students—Naiyuan Zhang, Ron Nguyen, and Navketan Batra—and Dima Feldman, a physics professor at Brown, contributed to this research. Zhang, Nguyen, and Batra share the title of co-first authors for the paper published in Nature.
The focus of the team’s research is the fractional quantum Hall effect, which builds on the classical Hall effect. In the classical Hall effect, a magnetic field applied to a conducting material generates a sideways voltage. The quantum Hall effect occurs under conditions of extreme cold and high magnetic fields, producing this sideways voltage in distinct increments. Meanwhile, in the fractional quantum Hall effect, the increments become more unusual, increasing by fractional amounts—corresponding to a fraction of an electron’s charge.
To conduct their experiments, the researchers created a structure consisting of two fine layers of graphene, a two-dimensional nanomaterial, separated by a hexagonal boron nitride insulator. This arrangement allowed them to precisely manage the movement of electrical charges and generate excitons—particles formed when an electron pairs with a “hole,” or the absence of an electron. They then subjected this system to extraordinarily strong magnetic fields, millions of times stronger than Earth’s, enabling them to observe the distinctive behaviors of the fractional excitons.
In general, fundamental particles are categorized into two types: bosons and fermions. Bosons can occupy the same quantum state without limitations, while fermions adhere to the Pauli exclusion principle, which prohibits two fermions from sharing the same quantum state.
However, the fractional excitons identified in this experiment do not neatly fit into either category. Although they displayed the expected fractional charges, their behavior exhibited traits of both bosons and fermions, akin to a blend of the two. This makes them resemble anyons—particles that occupy a middle ground between fermions and bosons—but the fractional excitons possess unique characteristics that differentiate them from anyons, too.
“The unexpected behavior we observed suggests that fractional excitons may signify a brand new class of particles with distinctive quantum characteristics,” remarked Zhang. “We demonstrate that excitons can exist within the fractional quantum Hall regime and that some of these excitons are produced by the pairing of fractionally charged particles, resulting in fractional excitons that do not behave like bosons.”
The recognition of this new class of particles might eventually enhance how information is stored and processed at the quantum level, leading to the development of swifter and more dependable quantum computers, according to the team.
“We have essentially uncovered a new dimension for exploring and manipulating this phenomenon, and we are merely starting to unravel its complexities,” Li noted. “This marks the first occurrence in which we have experimentally demonstrated the existence of these types of particles, and now we aim to investigate further the potential implications of their existence.”
The next phase of the research will involve examining how these fractional excitons interact and if their properties can be manipulated.
“It feels as though we are right at the threshold of advanced quantum mechanics,” Feldman expressed. “This aspect of quantum mechanics was previously unknown to us or, at least, not fully appreciated until now.”
