Deep in the clean rooms of the University of Hamburg, Roland Wiesendanger and Harim Jang placed individual iron atoms one by one onto a bismuth-silver surface, building a quantum experiment from the ground up. What they discovered—published in Nature Physics—could help quantum computers finally work reliably in the messy real world.
The challenge is fundamental: quantum computers harness the strange rules of quantum mechanics to process information in ways classical computers cannot. But qubits, the quantum units of information, are fragile. Temperature fluctuations, electromagnetic noise, magnetic field shifts—even tiny environmental disturbances can corrupt their delicate quantum states and introduce errors that cascade through calculations. For decades, this sensitivity has been the central obstacle to practical quantum computing.
Enter Majorana modes. These are exotic quantum states with a remarkable property: they store information in the overall topology of a system rather than in specific locations. Theory suggests they should be naturally resistant to the noise and defects that plague ordinary qubits. But theory and reality often diverge in quantum physics. Wiesendanger, Jang, and their colleagues set out to test whether Majorana modes actually deliver on this promise.
They engineered a hybrid material platform consisting of a superconducting niobium substrate, a silver layer just a few nanometers thick, and a single atomic layer of bismuth-silver alloy on top. Using a scanning tunneling microscope—an ultra-sharp probe that can manipulate individual atoms—they precisely positioned iron atoms into perfectly linear chains atop the bismuth-silver surface. The bismuth atoms themselves formed a crystal lattice, but the underlying silver layer introduced nanoscale disorder, creating the kind of imperfections that would normally degrade quantum states.
Then came the crucial observation: at both ends of the iron chains, the researchers detected pronounced zero-energy states—the unmistakable signature of Majorana quasiparticles—even though disorder was present throughout the substrate. The Majorana modes persisted. They were robust.
"Our primary objective was to realize Majorana quasiparticles, exotic quantum states describing particles as their own antiparticles, using a novel material platform," Wiesendanger and Jang explained. "This pursuit has attracted intense interest lately, as Majorana states have been predicted to be very robust and therefore promising for realizing fault-tolerant qubits for so-called topological quantum computation, where quantum information can be processed with high tolerance to external perturbations."
The implications are substantial. If Majorana modes can indeed resist disorder and environmental noise—as this work suggests—they offer a path toward quantum computers that work reliably outside laboratory conditions. Topological quantum computing, built on these robust states, could finally deliver on the promise of quantum advantage without requiring the extreme isolation from noise that current systems demand.
The work represents a proof of concept in a crucial direction: showing that exotic quantum states predicted by theory can survive contact with real-world messiness. It's a small but meaningful step toward quantum computers that can be deployed in hospitals, research facilities, and industries—machines that calculate, not just in pristine conditions, but in the imperfect world we actually inhabit.