Insider Brief
- Scientists reported that heavy electrons in the compound CeRhSn follow unusual quantum rules tied to Planckian scaling, a finding that could inform new types of quantum computing, according to a study in npj Quantum Materials.
- The researchers found that electrons in CeRhSn behave as if they are hundreds of times heavier due to strong interactions, entering a “non-Fermi liquid” state that reflects quantum criticality and collective entanglement.
- Experiments revealed directional differences in electron behavior linked to the crystal’s lattice geometry, but the effect appeared only along one axis, highlighting both the promise and current limits of heavy-electron systems for future quantum technologies.
- Image: Heavy electrons with quantum entanglement on CeRhSn. (Takuto Nakamura and Shin-ichi Kimura)
Scientists in Japan have discovered that so-called “heavy” electrons in a special crystalline material follow unusual quantum rules, a finding that may one day support new types of quantum computers, according to a study published in npj Quantum Materials.
The team studied CeRhSn, a compound where electrons behave as if they carry hundreds of times their normal mass. This “heaviness” does not come from the electrons themselves but from how they interact strongly with other particles inside the material. According to the researchers, those interactions slow the electrons down and make them appear heavier.
Instead of following the predictable behavior of normal metals, the heavy electrons in CeRhSn enter what scientists call a “non-Fermi liquid” state. In simple terms, the electrons stop acting like individual particles and start moving in a collective, entangled way. The study reports that this unusual state appears to obey a universal speed limit called Planckian scaling, which ties the time it takes for energy to dissipate to fundamental constants of nature.
In ordinary conductors like copper, electrons scatter in a way that can be calculated with standard physics. But at the edge of magnetism, superconductivity, or other collective phases, those rules break down. According to the researchers, CeRhSn sits right at this edge, making it a prime example of what physicists call “quantum criticality.”
The significance, according to the team, is that quantum critical materials may offer new routes for building quantum technologies. While most current quantum computers use superconducting circuits or trapped ions, heavy-electron compounds could provide an alternative platform where information is stored in the collective motion of electrons.
Dr. Shin-ichi Kimura of The University of Osaka, who led the research, said in a news release, “Our findings demonstrate that heavy fermions in this quantum critical state are indeed entangled, and this entanglement is controlled by the Planckian time. This direct observation is a significant step towards understanding the complex interplay between quantum entanglement and heavy fermion behavior.”
Testing the Material With Light
To probe CeRhSn, the team grew single crystals of the material in a controlled furnace and then polished them for study. They shined polarized light along different crystal directions and recorded how the electrons responded across a wide range of energies.
The experiments showed a distinct directional difference. In the plane where the cerium atoms form a kagome-like pattern—a triangular lattice with inherent frustration—the electrons followed Planckian scaling below about 80 Kelvin, or -193°C. Along the vertical axis, however, the electrons did not follow the same rule. The researchers interpret this anisotropy, or direction dependence, as evidence that the geometry of the lattice strongly shapes how the electrons behave.
Limits of the Current Work
While the findings demonstrate that heavy electrons can follow universal scaling laws, they do not yet provide a recipe for building a quantum computer. According to the study, the scaling behavior appeared only along one direction in the crystal, underscoring the material’s complexity.
The researchers also note that different experimental probes sometimes yield conflicting results. For example, while optical conductivity measurements suggested Planckian behavior, other measurements such as heat capacity report different values. Reconciling these differences will require further experiments.
Toward Future Quantum Devices
Quantum computing today is built on platforms that manipulate single quantum states and properly managing entanglement. Although there is work to do, the study points to a different possibility: harnessing the collective entanglement of many strongly interacting electrons. While speculative, the researchers argue that observing Planckian scaling in heavy-electron systems adds weight to this idea.
The researchers suggest that CeRhSn may represent a new class of quantum critical material, distinct from compounds where magnetism dominates. They propose studying other materials with similar lattice structures to see if the same directional scaling appears. Pressure, chemical substitution, or magnetic fields could also be used to test how far the Planckian regime extends.
If the phenomenon proves robust, scientists report they could eventually try to design materials where the collective state of heavy electrons can be stabilized and controlled. Such systems might support qubits that are less sensitive to noise than those in existing technologies.
