After 12 years of hard work, scientists at Empa have managed to develop novel carbon materials with surprising, hitherto impossible magnetic and electronic properties, which could be used to construct quantum computers with unique architectures in the future.
Artistic rendering of a graphene nanoribbon adsorbed on a gold surface and probed with the sharp tip of a scanning tunneling microscope. These tailor-made carbon structures exhibit quantum effects that are stable and can be manipulated even at room temperature. That could be a silver bullet for building entirely new kinds of quantum computers. Image Credit: Empa.
A million-dollar grant from the Werner Siemens Foundation for the next decade currently offers this visionary project an extraordinarily long research horizon, significantly boosting the chances for success.
A remarkably large grant will enable a group of Empa scientists to take up an ambitious project over the next decade. The Werner Siemens Foundation is financing Empa's CarboQuant project with 15 million Swiss francs. The objectives of the project are to lay the foundations for innovative quantum technologies that may even work at room temperature — contrary to existing technologies, most of which need cooling to near absolute zero.
With this project, we are taking a big step into the unknown. Thanks to the partnership with the Werner Siemens Foundation, we can now move much further away from the safe shore of existing knowledge than would be possible in our 'normal' day-to-day research. We feel a little like Christopher Columbus and are now looking beyond the horizon for something completely new.
Oliver Gröning, Project Lead and Researcher, Empa
The mission into the uncharted, presently being handled by Empa researchers Oliver Gröning, Pascal Ruffieux and Gabriela Borin-Barin under the leadership of Roman Fasel, was preceded by 12 years of rigorous research activity. The scientists from nanotech@surfaces laboratory headed by Fasel at Empa frequently publish their research papers in well-known journals such as Science, Nature and Angewandte Chemie.
In 2010, for the first time, the team successfully synthesized graphene strips, referred to as nanoribbons, from smaller precursor molecules. With their unique synthesis method, the Empa team can currently create carbon nanomaterials with atomic precision, thereby precisely establishing their quantum properties.
Graphene is said to be a promising building material for futuristic computers; it is composed of carbon and looks like the well-known graphite. The material is, however, merely one atomic layer thin and promises faster, more robust computer architectures than the semiconductor materials that are presently available.
Earlier in 2017, the research team, in partnership with colleagues from the University of California, Berkeley, constructed the first transistor from graphene nanoribbons. This was reported by them in Nature Communications.
A First Milestone: Magnetic Carbon
But then the scientists realized an effect that had formerly only been predicted hypothetically and appeared even more intriguing: Their minute, tailor-made carbon nanomaterials displayed properties of magnetism. In 2020, the effect discovered by them was described in the journal Nature Nanotechnology — and followed up with a more detailed article in October 2021.
At present, using their carbon nanomaterials, they had shown for the first time a physical effect foreseen by the future Nobel Prize winner in physics F.D.M. Haldane almost 40 years ago: spin fractionalization.
Spin fractionalization only develops when numerous spins (i.e., fundamental quantum magnets) can be assembled into a common, coherent quantum superposition. Empa scientists have accomplished just that in their accurately synthesized molecular chains.
The purpose of CarboQuant is to build on these extraordinary spin effects in graphene nanoribbons.
So far, we see spin states at very specific locations in the nanoribbons, which we can generate and detect. The next step will be to manipulate these spin states deliberately, for example, to reverse the spin at one end of the nanoribbon and thus elicit a corresponding reaction at the other end.
Oliver Gröning, Project Lead and Researcher, Empa
This would offer Empa scientists something very exclusive to deal with: a quantum effect that is stable and can be controlled even at room temperature or necessitating just minimal cooling. That could be a silver bullet for the construction of completely new types of quantum computers.
0 and 1 at the Same Time
But, what makes quantum computers calculate faster than conventional computers? Classical computing machines compute in bits. Each part can possess one of two possible states: 0 or 1.
In the quantum realm, however, these states can be superimposed: 0 or 1, or both states are possible simultaneously.
That is why circuits in a quantum computer, called qubits, can carry out not just one computational operation after another, but numerous ones concurrently. Gröning is already eager to carry out the experiment: "If we manage to control the spin states in our nanoribbons, we can use them for quantum electronic devices."
While a few members of the team continue to explore spin effects in a high vacuum, other team members will concentrate on the real-world suitability of the graphene nanoribbons.
"We have to get the components out of the protected environment of the high vacuum and prepare them in such a way that even in ambient air and at room temperature, they do not disintegrate. Only then can we equip the nanoribbons with contacts — which is the prerequisite for practical applications without the need of an elaborate infrastructure," Gröning says.
High-Frequency Radiation and Intense Laser Pulses
The voyage into this uncharted, new world will in any case be very challenging. Already the preliminary phase — the control and time-resolved computation of spin states — necessitates a totally new set of equipment that the scientists will have to design and construct.
We need to combine the scanning tunneling microscope (STM), in which we synthesize the nanoribbons and look at their structure, with ultra-fast measurements of their electronic and magnetic properties.
Oliver Gröning, Project Lead and Researcher, Empa
That can be achieved by high-frequency electrical signals at high magnetic fields and by irradiation with very short, strong laser pulses.
To accomplish this, two new measurement platforms are being arranged at Empa, which will also play crucial roles in the team's other research endeavors and which are co-funded by the European Research Council (ERC) and the Swiss National Science Foundation (SNSF).
"This shows that synergies always emerge from different projects," says Gröning, "but also that ambitious goals can only be achieved with the support of different players at multiple levels."
The researchers estimate that it will take two to three years just to set up these new analytical instruments and to carry out the first test runs.
A Very Distinct Project
CarboQuant is an exclusive project, owing to its long-term and substantial funding, says Oliver Gröning. The scientists at Empa's nanotech@surfaces lab currently have surprisingly great and long-term creative freedom on the way to their pioneering goal: a probable building material for advanced quantum computers.
We don't yet see the island that might be out there. But we can guess it, and if there is something out there, we are confident that we will find it, thanks to the support of the Werner Siemens Foundation and our national and international research partners.
Oliver Gröning, Project Lead and Researcher, Empa