Martina Havenith-Newen, Sebastian Kruss, and Marialore Sulpizi (from left) work together in the RESOLV Cluster of Excellence.
Photo Credit: © RUB, Marquard
Scientific Frontline: Extended "At a Glance" Summary: Light-Induced Quantum Friction
The Core Concept: Light-induced quantum friction is an unexpected phenomenon in which irradiating nanoscale particles—specifically fluorescent carbon nanotubes in aqueous solutions—with visible light decelerates their movement rather than accelerating or heating them.
Key Distinction/Mechanism: Contrary to classical expectations where light imparts kinetic energy, this deceleration is caused by the direct coupling between excitons (mobile electronic excitations within the solid nanotube) and the fluctuating dipole moments of the surrounding water molecules. This dynamic creates a microscopic momentum transfer that acts as surface resistance, effectively braking the particle and decreasing its diffusion constant as light intensity increases.
Major Frameworks/Components:
- Fluorescent Carbon Nanotubes: Ultra-thin carbon meshes (100,000 times thinner than a human hair) serving as the solid nanoscale framework.
- Excitons: Electronic excitations whose mobility along the nanotube is responsible for the direct exchange with the fluid environment.
- Terahertz (THz) Spectroscopy: An advanced measurement technique utilized to observe real-time friction and energy dissipation after electronic excitation.
- Atomistic Simulations: Computational models used to numerically visualize the momentum transfer and collective molecular movements at the liquid-solid interface.
Branch of Science: Physical Chemistry, Theoretical Physics, Quantum Physics, Nanotechnology, and Materials Science.
Future Application: The ability to tune nanoscale friction through optical electronic excitation offers groundbreaking potential for precisely steering microscopic transport processes, which is highly applicable to the development of advanced nanomaterials, nanomachines, and precise delivery systems.
Why It Matters: This discovery fundamentally alters established models of interfacial processes by demonstrating that water acts as an active, dynamically resistant partner rather than a passive solvent. It highlights how the strict boundaries between solid-state physics and liquid dynamics blur entirely at the quantum nano-level.
A research team in Bochum has made an unexpected observation: light can slow down movements in the nanoworld. This is due to quantum friction, a phenomenon that has been previously poorly understood.
Light is expected to heat particles up or set them in motion. However, an interdisciplinary team at Ruhr University Bochum, Germany, has now proven the opposite. In an aqueous solution, fluorescent carbon nanotubes move much more slowly once they are irradiated with light. During this process, the diffusion constant decreases with light intensity, an effect linked to direct coupling between electrons in the solid and the molecules of the liquid. The research teams of Sebastian Kruss, Marialore Sulpizi, and Martina Havenith describe the previously unknown phenomenon in the scientific journal Nature on June 10, 2026. “This discovery of light-induced quantum friction fundamentally changes our understanding of interfacial processes,” says Kruss.
Experiment: Light as an Invisible Brake
The nanotubes used in the experiments consist of a carbon mesh and are 100,000 times thinner than a human hair. They fluoresce when irradiated with visible light.
The team observed the movement of the nanotubes under a microscope. Once the tubes were excited by light, they behaved as though the surrounding water had suddenly become more viscous. “Our experiments show that the diffusion decreases when we increase the light intensity,” says Kruss, a professor of physical chemistry. “What’s fascinating is that this effect vanishes entirely when we use nanotubes in which the electronic excitations that lead to the fluorescence—known as excitons—are slowed down at defects. This means it is the mobility of the excitons along the nanotube that is in direct exchange with the environment and creates this decelerating effect.”
Theory: Understanding the Transfer of Momentum
Numerical calculations were required to understand how an exciton inside a nanotube can decelerate the movement of the entire object in water. To do this, the team used atomistic simulations to make the processes at the interface visible. “By doing so, we were able to show that the fluctuating dipole moments of the excitons in the nanotubes directly couple with the collective movements of the water molecules,” explains Marialore Sulpizi, a professor of theoretical physics. “A tiny but measurable transfer of momentum takes place. The water is not a smooth medium for the illuminated nanotube; instead, there is resistance on the surface that slows the movement.”
Spectroscopy: Water as an Active Partner
One key topic investigated by the Excellence Cluster RESOLV (Ruhr Explores Solvation) in Bochum is the fact that water is much more than just a passive solvent. Using terahertz (THz) spectroscopy, the team was able to experimentally demonstrate the immediate coupling between the nanotube and the water.
“With THz spectroscopy, we were able to determine how the friction and energy dissipation into water occur in real time after the excitation of electronic states in the nanotube,” says Professor Martina Havenith, spokesperson for RESOLV. “It is a textbook example of how solvation interactions with the environment dominate physical properties like friction. The knowledge that we can control the friction at the interface with the liquid via electronic excitation in the solid opens entirely new doors in materials science and nanotechnology.”
The discovery of light-induced quantum friction shows that the boundaries between solid-state physics and liquids blur at the nanoscale. Controlling this friction with light offers potential for applications in which transport processes on very small length scales must be precisely steered.
Additional information: In addition to research groups from Ruhr University Bochum, researchers from the Fraunhofer Institute for Microelectronic Circuits and Systems IMS were also involved in the work.
Funding: The work was funded by the German Research Foundation as part of the Excellence Cluster RESOLV.
Published in journal: Nature
Title: Light-induced quantum friction of carbon nanotubes in water
Authors: Tanuja Kistwal, Krishan Kanhaiya, Adrian Buchmann, Chen Ma, Jana Nikolić, Julia Ackermann, Phillip Galonska, Sanjana S. Nalige, Vahideh Sardari, Aishwarya Sudarsan, Martina Havenith, Marialore Sulpizi, and Sebastian Kruss
Source/Credit: Ruhr-Universität Bochum
Edited by: Scientific Frontline
Reference Number: chm061426_01
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