Where do you see patterns amidst chaos? This has now been proven within the incredibly small quantum domain. Researchers have described an experiment that validates a theory proposed four decades ago, which suggests that electrons trapped in quantum space tend to travel along shared routes instead of creating a disordered mess of paths.
Where do you see patterns amidst chaos? An international team, co-led by physicist Jairo Velasco, Jr. from UC Santa Cruz, has demonstrated this in the tiny quantum domain. Their latest findings, published on November 27 in Nature, outline an experiment that substantiates a 40-year-old theory indicating that confined electrons within quantum spaces will follow common trajectories instead of forming chaotic trajectories.
Electrons showcase both particle and wave characteristics — they do not merely roll around like balls. Their behavior is often surprising; under certain circumstances, their waves can overlap in ways that guide their movement into specific patterns. The physicists refer to these shared paths as “unique closed orbits.”
To achieve this in Velasco’s lab, a sophisticated blend of advanced imaging techniques and meticulous control over electron dynamics within graphene was necessary. Graphene is a frequently used material in research due to its unique characteristics and 2D structure, which makes it an excellent medium for studying quantum behaviors. In their experiments, Velasco’s team employed the sharp probe of a scanning tunneling microscope to initially trap electrons and then to closely observe their movements on a graphene surface without interfering physically.
According to Velasco, the advantage of electrons following closed orbits in a confined area is that the properties of the subatomic particles would maintain better integrity as they travel from one point to another. He explained that this has significant implications for electronics in everyday life, where information encoded in an electron’s characteristics could be transferred without degradation, potentially leading to highly efficient, low-power transistors.
“One of the most exciting prospects of this discovery is its potential for information processing,” Velasco noted. “By slightly disturbing, or ‘nudging,’ these orbits, electrons could move predictably across devices, transmitting information from one end to another.”
Quantum scars leave their mark
In the realm of physics, these distinctive electron paths are labeled as “quantum scars.” This concept was first introduced in a 1984 theoretical study by Harvard physicist Eric Heller, who demonstrated through computer simulations that confined electrons would trace high-density orbits if reinforced by wave interference.
“Quantum scarring is not just a quirky phenomenon; it’s a glimpse into the unusual quantum realm,” stated Heller, who is also a co-author of the paper. “Scarring represents a localization around orbits that return to themselves. In classical physics, these returns have no lasting impact — they quickly fade from memory. However, they are forever remembered in the quantum realm.”
With Heller’s theory now validated, researchers have a solid basis to investigate possible applications. Current transistors, which are already on the nanoelectronic scale, could become even more efficient by implementing designs based on quantum scars, improving devices like computers, smartphones, and tablets that depend on densely packed transistors for enhanced processing capability.
“For future work, we aim to expand our visualization of quantum scars to devise techniques for controlling and utilizing scar states,” Velasco shared. “Harnessing chaotic quantum phenomena could lead to innovative methods for the selective and adaptable delivery of electrons on the nanoscale — paving the way for new forms of quantum control.”
Classical chaos vs. quantum chaos
Velasco’s team uses a visual model commonly known as “billiards” to illustrate the differences between linear and chaotic systems in classical mechanics. A billiard is a confined area that reveals how particles inside move, and a frequently analyzed shape in physics is a “stadium,” which features straight edges and rounded ends. In classical chaos, a particle would bounce around at random and unpredictably, eventually covering the entire surface.
For their experiment, the team constructed a stadium billiard on one-atom-thick graphene, measuring approximately 400 nanometers in length. Using the scanning tunneling microscope, they observed quantum chaos firsthand: finally witnessing the arrangement of electron orbits formed within the stadium billiard created in Velasco’s lab.
“I am thrilled that we successfully captured images of quantum scars in an authentic quantum system,” exclaimed Zhehao Ge, the first author and a UC Santa Cruz graduate student who completed this study. “I hope these findings will deepen our understanding of chaotic quantum systems.”
