Researchers discovered that gold “super atoms” can act much like the atoms used in advanced quantum systems—except they’re significantly easier to scale up.
These miniature clusters can be tailored at the molecular scale, providing a flexible and robust platform for future quantum technologies.
Gold Clusters as Scalable Quantum Building Blocks
Quantum technologies—from computing to sensing—rely on the behavior of electrons, particularly their spin. One of the most precise quantum methods uses electron spins in gas-phase atoms, offering high accuracy but poor scalability for larger devices. Researchers at Penn State and Colorado State have shown that gold clusters can replicate gas-phase atom spin behavior in a more scalable form.
“For the first time, we show that gold nanoclusters exhibit the same essential spin characteristics as today’s leading quantum information platforms,” said Ken Knappenberger, department head and professor of chemistry at the Penn State Eberly College of Science and lead author of the study. “We can also actively adjust a key feature called spin polarization in these clusters, which is usually fixed in a material.” Because they’re easy to synthesize in relatively large quantities, this work provides strong proof-of-concept that gold clusters could support a wide range of quantum applications.”
The findings—detailed in two papers in ACS Central Science and The Journal of Physical Chemistry Letters—lay out the spin behavior of the gold clusters with high precision.
How Electron Spin Drives Quantum Capabilities
“An electron’s spin affects not only key chemical processes but also quantum technologies such as computing and sensing,” said Nate Smith, a chemistry graduate student in the Penn State Eberly College of Science and first author on one of the studies. “The way an electron spins—and how that orientation lines up with the spins of other electrons—can directly influence the precision and stability of quantum information systems.”
An electron rotates around its axis much like Earth does, though electrons can spin in either a clockwise or counterclockwise direction. When many electrons in a material spin the same way and their orientations align, they become correlated. Materials with a high degree of this alignment exhibit strong spin polarization.
“Materials with strongly correlated, highly spin-polarized electrons can keep those electrons aligned for much longer, which helps the materials maintain accuracy over extended periods,” Smith said.
Limits of Trapped Ions and the Push for New Approaches
The most effective approach for achieving ultra-low error rates in quantum information systems uses trapped atomic ions—charged atoms held in a gaseous environment. In these setups, electrons can be excited into Rydberg states, which provide long-lived and precisely controlled spin polarizations. These systems also support superposition, allowing electrons to exist in multiple states simultaneously until measured—a key principle of quantum computing.
“These trapped gas-phase ions are inherently sparse, making them very difficult to scale,” said Knappenberger. “In solid materials, atoms are densely packed, which sacrifices that dilute nature. While scaling up gives you all the necessary electronic properties, it also makes the system highly sensitive to environmental interference, which can scramble the encoded information and increase error rates. Our study shows that gold clusters can replicate all the advantages of trapped gaseous ions while offering the scalability needed for practical quantum devices.”
Gold Nanoclusters and Their Promise for Quantum Technology
Researchers have traditionally explored gold nanostructures for applications in optics, sensing, therapeutics, and catalysis, but they have studied their magnetic and spin-related properties far less. In the recent research, the team examined monolayer-protected clusters—gold cores encased in molecules called ligands. Researchers can finely tune the structure of these clusters and produce them in relatively large quantities.
“Researchers call these clusters superatoms because their electronic behavior resembles that of a single atom, and now we see that their spin properties behave similarly as well,” Smith said. “We identified 19 distinct Rydberg-like spin-polarized states that replicate the superposition states achievable in trapped, gas-phase ions. This shows that the clusters possess the essential characteristics for performing spin-based operations.”
Controlling Spin Polarization via Chemical Engineering
The researchers measured spin polarization in the gold clusters using methods similar to those applied to individual atoms. One cluster exhibited 7 percent spin polarization, while another, with a different ligand, reached nearly 40 percent—comparable to some of the top-performing two-dimensional quantum materials.
“This shows that an electron’s spin properties are closely linked to the vibrations of the ligands,” said Knappenberger. In conventional quantum materials, spin polarization typically stays fixed, but our findings show that we can widely tune this property by changing the ligands on gold clusters.
The team now aims to explore how modifying specific ligand features influences spin polarization and how they can use these adjustments to precisely control quantum behavior.
“Physics and materials science have largely driven the quantum field, but this work shows how chemists can use synthesis techniques to create materials with customizable quantum properties,” Knappenberger added. “This opens a new frontier in quantum information science.”
Read the original article on: SciTechDaily
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