Safe, efficient and sustainable quantum technologies based on carbon – this is the vision of the CarboQuant project. With the support of the Werner Siemens Foundation and the Swiss National Science Foundation (SNSF), Empa researchers are investigating quantum effects in carbon nanostructures. In a first milestone, a new high-tech laboratory was inaugurated at Empa on 30 January 2025.

Research in the new lab focuses primarily on so-called nanographenes and graphene nanoribbons: pieces of the two-dimensional carbon material graphene that are just a few atoms in size. These special molecules were synthesized only a few years ago, many of them in Empa's nanotech@surfaces laboratory. Their structure can be precisely defined down to a single atom, allowing targeted introduction of different quantum effects. Empa researchers want to use such nanographenes to produce novel sensors, communication technologies or components for quantum computers.

Controlling quantum magnetism

At the heart of the new CarboQuant lab are two state-of-the-art scanning tunneling microscopes. Scanning tunneling microscopy – invented in Switzerland at the beginning of the 1980s – uses electric current and quantum physics to make individual atoms visible. With the new devices, Empa researchers can not only see their nanographene molecules, but also control their quantum states. High-frequency microwave radiation makes it possible to manipulate individual so-called spins – a type of quantum magnetism that electrons and other particles possess, and which can also manifest itself in certain nanographenes.

Spin is considered a particularly promising physical property for quantum computing and other technologies. In the simplest case, it has two basic states, “up” and “down” – similar to a classic computer bit, which can be 1 or 0. The main difference is that quantum effects allow the two states to be superimposed, so that the spin can assume any combination of “up” and “down”. It is this ambiguity that should make quantum computers and other quantum-based technologies so powerful – if we succeed in understanding and controlling them.

To understand and to implement

This is exactly what Empa researchers are setting out to do in the new CarboQuant lab. This puts them at the forefront of science. “Scanning tunneling microscopy with electron spin resonance has only been used for the manipulation of spins in the last ten years, and mostly for individual atoms,” says Roman Fasel, co-head of CarboQuant and head of nanotech@surfaces.

To apply this novel technology to nanographenes for the first time, CarboQuant has succeeded in recruiting one of the few experts in the world: South Korean researcher Yujeong Bae is taking over as head of the new Empa research group for quantum magnetism. “By combining microwave technologies with scanning tunneling microscopy, we can detect and control any superposition state of spins in a coherent manner. This coherent control is a core of quantum technologies. We are aiming to demonstrate this quantum control in nanographenes for the first time,” explains the researcher.

Working with carbon-based materials offers a decisive advantage: “While individual atoms only have one spin, nanographenes make it possible to create several linked spins,” says Bae. Making several spins “talk” to each other is a decisive step on the way to functioning quantum technologies – after all, a single bit does not make a computer.

This still requires two large stainless steel machines in the lab, with their ultra-high vacuum chambers, strong magnetic fields and helium tanks that cool them down to almost absolute zero. “In the long term, we want to have quantum-based devices that work outside of these high-tech systems, perhaps even under ambient conditions, e.g. for optical effects,” says Oliver Gröning, co-head of CarboQuant and deputy head of nanotech@surfaces.

First, however, the researchers need to understand and learn to control the quantum effects. The first, imminent goal of the project is therefore a materials platform, a kind of toolbox, for research into carbon-based quantum materials and their properties. With the opening of the new lab, the researchers have come a good deal closer to this goal.

CarboQuant

Empa's CarboQuant project focuses on developing carbon-based nanostructures with precisely controlled quantum effects for use in electronic components that operate at room temperature. The aim is to build a technology platform and refine characterization methods to advance the fundamental understanding and practical implementation of these nanomaterials. The CarboQuant project runs from 2022 to 2032 and is supported by the Werner Siemens Foundation.