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| The team Frederik Møller, Philipp Schüttelkopf and Jörg Schmiedmayer Photo Credit: © Technische Universität Wien |
At TU Wien, researchers have created a one-dimensional “quantum wire” made from a gas of ultracold atoms, where mass and energy flow without friction or loss.
In physical systems, transport takes many forms, such as electric current through a wire, heat through metal, or even water through a pipe. Each of these flows can be described by how easily the underlying quantity—charge, energy, or mass—moves through a material. Normally, collisions and friction lead to resistance causing these flows to slow down or fade away. But in a new experiment at TU Wien, scientists have observed a system where that doesn’t happen at all.
By confining thousands of rubidium atoms to move along a single line using magnetic and optical fields, they created an ultracold quantum gas in which energy and mass move with perfect efficiency. The results, now published in the journal Science, show that even after countless collisions, the flow remains stable and undiminished, thus revealing a kind of transport that defies the rules of ordinary matter.
The Atom Chip with the atoms trapped and levitated below.
Image Credit: © Technische Universität Wien
Two Kinds of Transport
“In principle, there are two very different types of transport phenomena,” says 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.”
There is also diffusive transport, which arises from many random collisions. Heat conduction is one such diffusive process: when some hot particles meet cooler ones, they gradually share energy and momentum until, on average, all have the same temperature. “This kind of transport is not linear,” says Møller. “To cover twice the distance, you typically need four times as long.”
In the TU Wien experiment, the atoms behaves very differently. “By studying the atomic current, we could see that diffusion is practically completely suppressed,” says Møller. “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.”
Like a Newton’s Cradle
This unusual behavior can be understood through an analogy to a Newton’s cradle, the familiar desk toy with a row of swinging metal balls. When one ball is pulled back and released, it transfers its momentum straight through the others to the ball on the opposite end, which swings out as if untouched.
“The atoms in our system can only collide in a single direction,” explains Møller. “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.”
Just like in the Newton’s cradle, motion in the atomic wire continues without damping. Momentum and energy can travel across the gas indefinitely rather than dissipating as in normal matter. “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” says Møller. “Studying transport under such perfectly controlled conditions could open new ways to understand how resistance emerges, or disappears, at the quantum level.”
Published in journal: Science
Title: Characterizing transport in a quantum gas by measuring Drude weights
Authors: Philipp Schüttelkopf, Mohammadamin Tajik, Nataliia Bazhan, Federica Cataldini, Si-Cong Ji, Jörg Schmiedmayer, and Frederik Møller
Source/Credit: Technische Universität Wien
Reference Number: qs112825_01