Physicists at MIT have directly imaged the frictionless flow of atoms along the edges of a material, confirming long-held theories about electron behavior in the quantum Hall effect. By recreating the effect’s conditions with ultracold atoms, the team observed these particles effortlessly navigating around obstacles, defying everyday experience with friction.

In the everyday world, friction is an ever-present force and a major source of energy loss in everything from mechanical systems to electronic circuits. It’s also part of the reason your laptop gets hot when you are running lots of applications — or why a drill bit gets so hot it could burn you when boring through, say, concrete with an impact driver.

Quantum oddities

In quantum mechanics, particles can behave in ways that defy our classical intuitions under specific conditions — and friction seemingly vanish. A prime example is the quantum Hall effect, observed in two-dimensional electron systems at extremely low temperatures and under strong magnetic fields. In such conditions, the electrons’ movement becomes quantized, meaning they can only occupy specific energy levels. This quantization leads to a resistance to the flow of current across the material, while simultaneously allowing for the dissipationless flow of current along the edges, giving rise to the “edge states.” Such states were observed in the MIT study, which was published in Nature Physics.

Developing nearly frictionless motion has long captivated scientists. In 2015, researchers announced that nearly frictionless motion had been developed in the nanorealm. Research on such low friction states can also extend to the everyday physical realm. When cooled below 2.17 Kelvin, liquid helium becomes a superfluid that can flow without friction. And Maglev trains use powerful magnets to levitate above the tracks, practically eliminating friction between the train and rails. Some investors have strived to go further. The concept of a perpetual motion machine, though it would violate the Laws of Thermodynamics, has inspired generations of inventors.

The quantum Hall effect in electronic systems, which gives rise to frictionless flow in edge states, is typically constrained to laboratory environments. It requires extremely low temperatures and strong magnetic fields—conditions that are challenging to achieve and maintain in everyday contexts. The fabrication and integration of two-dimensional materials that exhibit this effect pose additional hurdles for practical applications.

Atoms mimic electrons in a laser-generated ‘world’

The MIT experiment takes a novel approach that departs from traditional electronic systems by using ultracold atoms to simulate and directly observe the physics of edge states, a phenomenon that typically requires the challenging conditions of the quantum Hall effect in electronic systems. To achieve this, MIT physicists manipulated a cloud of roughly one million sodium atoms, confining them in a laser-controlled trap. By manipulating this trap, they mimicked the effects of a strong magnetic field on electrons, essentially recreating the environment needed for edge states to emerge. This approach provides valuable insights into quantum behavior but, like the quantum Hall effect itself, faces its own set of challenges for real-world applications, including the difficulties of maintaining such extreme conditions.

This setup exploited the Coriolis effect, causing the atoms to behave as if they were charged particles in a magnetic field. The researchers then introduced an “edge” to this system using a ring of laser light, forming a circular boundary around the spinning atoms.

The atoms then flowed along the laser-created edge in a single direction, without any resistance. When the team introduced obstacles in the form of points of light along the atoms’ path, the flow continued unimpeded. As Richard Fletcher, an assistant professor at MIT, described it in a press release: “You can imagine these are like marbles that you’ve spun up really fast in a bowl, and they just keep going around and around the rim of the bowl. There is no friction.”

Implications

The research MIT research has significant implications beyond fundamental physics. The research on frictionless particle flow could lead to the development of super-efficient novel materials and devices. The researchers suggest that this phenomenon could be harnessed in future electronic devices. “You could imagine making little pieces of a suitable material and putting it inside future devices, so electrons could shuttle along the edges and between different parts of your circuit without any loss,” Fletcher said.