Researchers at TU Wien have developed a quantum system using ultracold rubidium atoms that allows energy and mass to flow with perfect efficiency, defying usual resistance. Confined to a single line, the atoms collide endlessly without slowing down, mimicking a Newton's cradle. The discovery, published in Science, highlights a novel form of transport in quantum gases.
In a breakthrough experiment, scientists at Vienna University of Technology (TU Wien) have engineered a quantum 'wire' from thousands of rubidium atoms cooled to ultracold temperatures. By using magnetic and optical fields to restrict the atoms' movement to a straight line, the team observed transport of energy and mass that remains undiminished despite numerous collisions.
This setup challenges conventional physics, where flows like electricity or heat typically face resistance from friction and scattering. Instead, the atomic gas exhibits a perfect conductivity, with motion propagating cleanly through the system.
"In principle, there are two very different types of transport phenomena," explains Frederik Møller from the Atominstitut at TU Wien. "We speak of ballistic transport when particles move freely and cover twice the distance in twice the time—like a bullet traveling in a straight line."
The observed behavior, however, transcends ballistic and diffusive transport. "By studying the atomic current, we could see that diffusion is practically completely suppressed," Møller notes. "The gas behaves like a perfect conductor; even though countless collisions occur between the atoms, quantities like mass and energy flow freely, without dissipating into the system."
The effect resembles a quantum Newton's cradle, where momentum transfers directly without loss. "The atoms in our system can only collide along a single direction," Møller says. "Their momenta are not scattered but simply exchanged between collision partners. Each atom's momentum remains conserved—it can only be passed on, never lost."
This prevents the gas from reaching thermal equilibrium, offering insights into quantum resistance. "These results show why such an atomic cloud does not thermalize—why it doesn't distribute its energy according to the usual laws of thermodynamics," Møller adds. "Studying transport under such perfectly controlled conditions could open new ways to understand how resistance emerges, or disappears, at the quantum level."
The findings appear in a paper titled 'Characterizing transport in a quantum gas by measuring Drude weights,' published in Science in 2025 by authors including Philipp Schüttelkopf, Mohammadamin Tajik, and Jörg Schmiedmayer.
