Quantum physics comes in from the cold

  Last updated March 14, 2018 at 6:47 pm


Canadian researchers have developed a new way to create a quantum effect, paving the way for ‘warmer’ quantum technologies.

In quantum physics, ‘mmany-body localisation’ is a state caused when quantum interactions trap particles in web-like mesh of random locations. Credit:Ed Grant

Quantum physics is a dynamic and exciting field, with its technological applications promising, among other things, vastly quicker and more powerful computers. But the quantum world is also a tricky place, filled with complex phenomena that continue to defy complete understanding.

One such phenomenon is “many-body localisation”, a state caused when quantum interactions trap particles in web-like mesh of random locations. While particles are trapped, their energy is protected from degradation due to heat. This could have ready applications in quantum computation — for example, safeguarding the state of qubits, the units of quantum information.

In recent years researchers have been striving to understand the effect better, but they have assumed that it only occurs in quantum systems that are almost as cold as absolute zero (-273 °C).

Now, new research at the University of British Columbia in Vancouver has demonstrated a new way to achieve many-body localisation — and it doesn’t require the system to be quite so chilly.

“We have found that a common atmospheric gas, when excited in a particular way with a laser, spontaneously reorganises to form a plasma with very unusual properties,” explains Ed Grant, chemical physicist who co-authored the study with theoretical physicist John Sous. One such property is that the plasma appears to spontaneously self-assemble into a many-body localised state.

This plasma, made up of electrons, ions and Rydberg molecules (electronically excited nitrosonium molecules), contains an enormous amount of energy per molecule — enough to fragment it into atoms — and yet it remains very cool, with its temperature hovering just a few degrees above absolute zero.

“So far, most evidence for many-body localisation has been found using atoms arrayed in space by crossed laser fields,” says Grant. “But arrangements like these last only as long as the light is on and are as easily disrupted as ripping a piece of tissue paper.”

The system created in this experiment, however, “stands at a precipice of annihilation and dissipation, yet lingers in this paradoxical state for as long as we can observe it,” says Grant.

The plasma doesn’t need a web of laser fields or a near-absolute-zero environment to achieve a state of many-body localisation, instead achieving it naturally. Beginning at a higher temperature, the plasma spontaneously “quenches” (rapidly loses energy) to become a highly disordered system in a state of many-body localisation.

“This could give us a much easier way to make a quantum material, which is good news for practical applications,” says Grant.

The research was published in Physical Review Letters.

About the Author

Lauren Fuge
Lauren Fuge is an Adelaide-based author and science communicator.