Innovative quantum technology with great potential
Although there are various approaches for developing quantum computers, no major breakthroughs have been made. Now, in a new project funded by the Werner Siemens Foundation, researchers at the universities of Basel and Bern hope to change this with their innovative strategy for building stable, energy-efficient quantum units.
Quantum computers are something like the Holy Grail of information technology. They have the potential to perform calculations so much faster than today’s conventional computers that entirely new applications would be possible. For instance, quantum computers could enable the discovery of novel drugs and revolutionary new materials—or they could be used to crack even the most obscure encryptions, make financial markets predictable and simulate complex climate models.
However, there’s still a long way to go before these scenarios become reality. While quantum computers have already been built, they’re either test or niche devices. Not only are they unable to keep pace with existing supercomputers,they’re also not even close to replacing our everyday digital devices. This lack of progress is simply because quantum computers are both costly and complex—indeed, the core technology is so sophisticated it surpasses our human imagination.
The computing elements in quantum computers are quantum bits, or “qubits”—the equivalent of “bits”, which are the basic units of information in conventional computers. Bits have only two states: off (0) or on (1). By contrast, qubits can have a value anywhere between 0 and 1, theoretically making it possible for them to be simultaneously in an infinite number of states. This explains how quantum computers are able to perform several arithmetic operations at the same time, rather than one after the other.
Instability a major obstacle
Researchers have various approaches for constructing qubits—and hence for storing quantum information. For instance, some research groups use neutral atoms, others work with ions, while still others experiment with tiny superconducting circuits. Because quantum states are extremely volatile and unstable, qubits must be shielded from the environment as much as possible and are generally cooled to temperatures only slightly above absolute zero, at minus 273.15 degrees Celsius. However, computing errors begin to creep in soon after processing begins. That’s why most qubits in current solutions are used for running operations to identify and eliminate errors.
Now, researchers at the universities of Basel and Bern are exploring a highly innovative approach for building more stable qubits—at the new WSS Research Center for Molecular Quantum Systems (MolQ), which has received a grant of fifteen million Swiss francs over the next eleven years from the Werner Siemens Foundation (WSS). “Our goal is to place what are known as topologically protected qubits on superconductors,” says Ernst Meyer, professor of physics at the University of Basel and head of the new research centre. “The novel aspect in our approach is linking topological protection with superconductivity.”
Superconducting materials are characterised by their ability to enable electricity to flow with no resistance. Topological material states are harder to grasp. One way to understand them is by comparing them to a doughnut and a roll. The doughnut has a hole, the roll has none, and it’s impossible to convert one form into the other through small, continuous deformations. Their basic feature—hole or no hole—is invariant and protected against external influences.
Research into topological phases was singled out for the 2016 Nobel Prize in Physics—and at the new research centre, this complex property of matter will be harnessed to generate stable quantum bits. Their unique topological structure is what prevents the novel qubits from losing their basic properties, even when exposed to external factors like malfunctions or defects. With this stability, topological superconductors could pave the way to building quantum computers that are both more reliable and more energy-efficient than those constructed with other technologies.
Molecules with extraordinary properties
Finding ways to create such topological structures is the job of researchers at the Department of Chemistry, Biochemistry and Pharmaceutical Sciences at the University of Bern. There, Privatdozent Shi-Xia Liu and Professor Emeritus Silvio Decurtins are using the tools of chemistry to fabricate novel molecules, then manipulating their properties. “These are compact molecules with a flat structure made of carbon and hydrogen atoms, similar to the more commonly known graphene,” Shi-Xia Liu explains.
The structure is then enhanced with nitrogen atoms and halogens—bromine or chlorine, for example. “The remarkable property in these new molecules is that they can acquire single electrons,” Silvio Decurtins says. Unpaired electrons have what is known as “spin”, an intrinsic form of angular momentum; the researchers use the magnetic moment coupled with the electron’s spin to build qubits.
For this step, the synthesised molecules made in Bern are sent to Basel and the teams led by Ernst Meyer and Dominik Zumbühl, the latter also professor of physics at the University of Basel and deputy head of MolQ. The researchers fuse the molecules to a superconducting substrate, commonly lead, niobium or silver-niobium. Once placed on the metal surface, each molecule acquires an additional electron from the superconductor—and thus a magnetic moment. The molecular arrangement is studied using high-resolution microscopy, then compared with theoretical calculations made by Ulrich Aschauer from the University of Salzburg.
Storage at the edges
The chemical bonds on the superconductor enable the individual molecules to be arranged into molecular lattices—so-called molecular islands—with precisely controlled size, structure and order. The clou is that, when arranged just so, the charges and magnetic moments generate what are known as superconducting edge currents. “An electric charge flows loss-free on the edge currents around the molecular islands—we can use them to store information, as a novel qubit,” Ernst Meyer explains. Another advantage is that the edge currents shield the magnetic field of the molecular islands, creating a stable topological system.
Additional steps are needed to build a quantum computer based on this approach: the individual qubits must be linked to form larger structures, as the ultimate aim is to form circuits. By manipulating electromagnetic fields, the coupled qubits can be stimulated to interact with each other and perform logical arithmetic operations. “We still have a great deal more research to conduct before we achieve these results,” Ernst Meyer says.
Experiment and theory
To find the most suitable molecules, materials and arrangements the researchers will be conducting numerous experiments and investigations. Aiding them in this work are several high-performance microscopes and devices at the University of Basel’s Department of Physics—including scanning tunnelling microscopy (STM) and atomic force microscopy (AFM), which are used to observe molecules in high resolution. Remarkably, the devices can even set chemical reactions in motion. Also essential is acquiring an in-depth understanding of the processes in these quantum systems. Ernst Meyer says this is why a foundational part of the project is the integration of theory and experiment.
Physics professors Daniel Loss and Jelena Klinovaja from the University of Basel are responsible for the theoretical work in the MolQ team. Both researchers are leading experts in the theoretical modelling of quantum computers and topological qubits. At the new WSS Research Center, their work will include calculating which molecular structures are particularly conducive to generating superconducting edge currents. Their theory-based predictions will help determine how qubits interact with each other, how long they remain stable and which arithmetic operations they can perform.
The advantages of the planned molecular quantum systems are far-reaching. First, the researchers work at minuscule scales from the very outset. “One of our molecules is about one nanometre long,” Shi-Xia Liu says—a measurement that corresponds to one millionth of a millimetre. One qubit, which the researchers estimate will consist of roughly twenty to one hundred molecules, would be between four and ten nanometres wide and long. All of which means there’s theoretically room for an enormous number of qubits on a tiny quantum chip.
Greener electronics
A second advantage is that quantum computers built with MolQ technology would consume significantly less energy thanks to superconducting information processing. Electrical resistance is what causes today’s electronic devices to heat up—a phenomenon familiar to anyone who uses a laptop or smartphone. The capability to manufacture devices that operate without this energy loss would be a real breakthrough, as ten percent of global power consumption is used for data processing. This amount is likely to rise sharply in the coming decades, especially in view of the increasingly powerful supercomputers being developed as well as the surge in applications for artificial intelligence.
The third strong point of the envisioned system is that topological protection could prove to be groundbreaking. Physicists use the term “coherence time” to refer to how long qubits maintain their quantum states. “Today’s qubit platforms have coherence times of nanoseconds to microseconds,” Ernst Meyer says. “We believe our topologically protected qubits will attain coherence times in the millisecond range.” Put in other terms: this would make it possible for a computer to perform at least one thousand times more operations before an error occurs.
The researchers are well aware of the fierce competition in the development of quantum computers, with big companies like IBM, Google and Microsoft investing hundreds of millions of dollars in R&D. Which technology will prevail in the end remains to be seen. But one thing is already clear: the innovative and interdisciplinary approach at the new WSS Research Center for Molecular Quantum Systems holds great potential.
Facts and figures
Funding from the Werner Siemens Foundation
15 million Swiss francs
Project duration
2025 to 2035
Project leaders
Prof. Dr Ernst Meyer, Department of Physics, University of Basel
Prof. Dr Dominik Zumbühl, Department of Physics, University of Basel
Partners
Experimental physics:
Prof. Dr Ernst Meyer, Prof. Dr Dominik Zumbühl, Department of Physics, University of Basel
Theoretical physics:
Prof. Dr Jelena Klinovaja, Prof. Dr Daniel Loss, Department of Physics, University of Basel
Synthetic chemistry:
PD Dr Shi-Xia Liu, Prof. Dr Silvio Decurtins, Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern
Theoretical chemistry:
Prof. Dr Ulrich Aschauer, Department of Chemistry and Physics of Materials, University of Salzburg
> MolQ Website
