Physicists Turn Quantum Chaos Into Something Surprisingly Useful

Quantum mechanics controls reality on the smallest levels, but when scaled up, it’s often difficult to gauge how and why this realm matters in the practical world. That said, physicists will on occasion uncover an oddly practical use for spooky quantum phenomena, and when they do, technology is often the biggest beneficiary. Such is the case with a new finding pertaining to superradiance—an aspect of quantum mechanics that has traditionally led to more headaches than solutions.

Superradiance is a phenomenon in which a group of quantum particles collaborate to produce significantly stronger signals. It remains a serious nuisance for some physicists, as the phenomenon can quickly destabilize quantum systems—and, by extension, the operation of key quantum technologies.

However, researchers from Austria and Japan devised a novel method to exploit superradiance to produce powerful, long-lasting microwave signals. The team reported its results today in Nature Physics. The team notes that the discovery paves the way for technological advances in medicine, navigation, and quantum communication, according to a statement.

“This discovery changes how we think about the quantum world,” Kae Nemoto, study co-author and a physicist at the Okinawa Institute of Science and Technology (OIST) in Japan, said in the release. “That shift opens entirely new directions for quantum technologies.”

Questionable quantum teamwork

Physicist Robert Dicke proposed the idea of superradiance in 1954. Since then, physicists have identified and even utilized superradiance for a variety of systems, including semiconductors, experimental X-ray lasers, and even to explain the chaos near fast radio bursts and black holes.

Superradiance typically occurs when a group of excited atoms become entangled after interacting with a light source. That produces a short, yet intense, burst of light—emitting substantially more energy from the system than if a single particle were bouncing about by itself.

Order from chaos

For the experiment, researchers trapped tiny atomic defects inside a microwave cavity. The cavities contained tiny chambers with electron spins, which served as “miniature magnets” to represent different quantum states. Then, they observed how the system changed over time, applying the data to extensive computer simulations to better describe the physics at work.

The researchers noticed an odd “train of narrow, long-lived microwave pulses” that followed a superradiant burst, which they investigated further in their simulations. They found that, surprisingly, the “seemingly messy interactions between spins actually fuel the emission,” Wenzel Kersten, study lead author and a physicist at the Vienna University of Technology in Austria, said in the release.

“The system organizes itself, producing an extremely coherent microwave signal from the very disorder that usually destroys it,” Kersten added.

A reversal of concepts

Because superradiance releases so much energy, scientists have long suspected—and partly confirmed through experiments—that it creates technical challenges for quantum technology.

The new study supplants this view, suggesting instead that, with the right approach, the next generation of quantum technologies could benefit from the “very interactions once thought to disrupt quantum behavior,” Nemoto said.

For instance, the strong, self-sustained microwave signal could help operate ultra-precise clocks, communication links, and navigation systems. These signals are also highly sensitive to the slightest changes in magnetic or electric fields, a feature with potential applications for a myriad of devices.