Quantum Microscope ‘Made In Jülich'

Physicists at Forschungszentrum Jülich have developed a unique scanning tunneling microscope with magnetic cooling for studying quantum effects

They depict materials with atomic precision and are versatile: researchers have been using scanning tunneling microscopes for many years to explore the world of the nano-cosmos. Physicists at Forschungszentrum Jülich have now optimized such a device for researching quantum effects. Thanks to magnetic cooling, your scanning tunneling microscope has no moving parts and works almost vibration-free at extremely low temperatures of up to 30 millikelvin. The instrument can help researchers in the future to discover the unusual properties of quantum materials, which are of crucial importance for the development of quantum computers and sensors.

The area near absolute zero is particularly exciting for physics. Thermal fluctuations are reduced to a minimum at the low temperatures. The laws of quantum physics come into play and reveal special properties of materials. Electric current then flows without any loss and without any resistance. Another example is what is known as superfluidity: individual atoms merge into a collective state and move past one another without friction.

Such extremely low temperatures are also the prerequisite for researching quantum effects for quantum computing and making them usable. Researchers around the world and at Forschungszentrum Jülich are currently pursuing this goal at full speed. Quantum computers could be vastly superior to conventional supercomputers in certain tasks. But the development is still at the very beginning. A central challenge is the search for materials and processes that make complex architectures with stable quantum bits possible.

"I think a versatile microscope like ours is the means of choice for this fascinating task because it enables the imaging and manipulation of matter at the level of individual atoms and molecules in a variety of ways," explains Ruslan Temirov from Forschungszentrum Jülich.

For this purpose, over many years of work, he and his team have equipped a scanning tunneling microscope with magnetic cooling. “Our new microscope differs from all the others in the same way that an electric car differs from a combustion engine,” explains the Jülich physicist. So far, a kind of liquid fuel, a mixture of two helium isotopes, has been used to bring microscopes to such low temperatures. “During operation, this cooling mixture continuously circulates through thin pipes, which leads to increased background noise,” says Temirov.

The cooling device of the Jülich microscope, on the other hand, is based on the process of adiabatic demagnetization. The principle is not new. It was already used in the 1930s to achieve temperatures below 1 Kelvin for the first time in the laboratory. “To cool the device, we only change the strength of the electrical current that flows through an electromagnetic coil. Our microscope has no moving parts and works practically vibration-free, ”reports Ruslan Temirov.

The Jülich team were the first to construct a scanning tunneling microscope with this technology. “The new cooling technology has several advantages in practice. Not only does the image quality benefit from this, the operation of the device and the entire structure are also simplified, ”says institute director Stefan Tautz. With its modular design, the Jülich quantum microscope is also open to technical advances, as upgrades are easy to implement. “Adiabatic cooling is a real quantum leap for scanning tunneling microscopy. The advantages are so significant that we are now developing a commercial prototype in the next step, ”explains Stefan Tautz. Quantum technologies are currently the focus of research. The interest of numerous research groups in such an instrument should therefore be certain.