Carbon rings control quantum states without loss

Control Ring instead of Steering Wheel Tiny Carbon Rings Control Quantum States

2026-07-10 Source: Martin Luther University Halle-Wittenberg (MLU) | Translated by AI 2 min Reading Time

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Using carbon rings measuring just a few nanometers, quantum states can be controlled precisely, as researchers can now prove...

This is a tiny donut-shaped carbon molecule. It develops stable toroidal moments under electrical voltage, something the world of quantum computing can look forward to, as researchers at Martin Luther University Halle-Wittenberg believe...(Image: MLU) — This is a tiny donut-shaped carbon molecule. It develops stable toroidal moments under electrical voltage, something the world of quantum computing can look forward to, as researchers at Martin Luther University Halle-Wittenberg believe...
(Image: MLU)

The fact that nanometer-sized carbon rings can control quanta makes a previously hardly usable class of electromagnetic dipoles possible. More specifically, these are so-called toroidal moments. And physicists at the Martin Luther University Halle-Wittenberg (MLU) (Germany) have now found a way, through computer simulations, to generate these in nanostructures without loss and even to control them, as can be noted. The results, published in the journal "npj Computational Materials," offer promising new perspectives for quantum computing technology. The study was supported by the German Research Foundation. Let's take a closer look:

There Are Not Only Electric and Magnetic Dipoles

In physics, two well-known types of dipoles are distinguished: electric dipoles, which generate electric signals in a battery or antenna, and magnetic dipoles, such as a current-carrying coil or a conventional bar magnet. However, beyond these classical dipoles, there exists a third type of charge-current distribution that has been challenging to achieve at the molecular level: the aforementioned toroidal dipoles. The MLU researchers explain it as follows: A current-carrying coil encloses a magnetic field that disappears outside the coil. However, if the ends of the coil are connected, a toroidal system is created, which is charge-neutral and does not generate external electric or magnetic fields.

In Tiny "Donuts," Electrons Swirl in 3D

Until now, it was known in research that stable toroidal moments could exist. However, how to generate and control them at the nanoscale was unclear, as further explained. Problems arise when trying to shrink these to the nanoscale. Classical toroidal coils only function well if they are large enough—about with a radius of one centimeter. However, if the coil becomes too small, the current does not flow efficiently in a circle but only with high losses, according to the experts. With computer simulations, they were able to show how toroidal moments can be generated in so-called nanotori. These are ring-shaped structures made of carbon atoms that resemble tiny donuts. When a constant electric field is applied to these structures, the electrons move in a 3D vortex around the ring, thus forming a toroidal moment. These moments can not only be generated losslessly but also controlled, driven, and switched.

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