A famous thought experiment in science is based around the feasibility of building a perpetual motion machine – a contraption which continues to operate without external input.
But as with many other concepts, scientists turn to the wacky world of quantum mechanics to make the impossible possible. Quantum properties which make perpetual motion a reality may have a use in future technologies, new research finds.
“Time crystals” are a newly discovered phase of matter. Like other crystal structures found in rocks and metals, time crystal atoms are arranged in a regularly repeating pattern, or “lattice”.
The “time” element has nothing to do with time travel – unfortunately. Time crystal atoms are themselves in never-ending motion despite no external input of energy, seemingly breaking the laws of physics. The atoms are constantly oscillating or spinning.
New research, published in Nature Communications, details the creation of the first two-body time-crystal system. The authors argue that, not only do the coupled time crystals behave exactly as they theoretically should, the coupled system presents opportunities for future technologies.
“Everybody knows that perpetual motion machines are impossible. However, in quantum physics perpetual motion is okay as long as we keep our eyes closed,” explains the paper’s lead author, Dr Samuli Autti, from Lancaster University in the UK. “By sneaking through this crack, we can make time crystals.”
Spanning institutions from the UK, Russia and Finland, the international team created time crystals by cooling helium-3 – a rare isotope of helium with a missing neutron – to 0.0001K or -273.15°C, within one-10,000th of a degree above absolute zero. At that temperature, the helium-3 creates a superfluid, which is a liquid with zero viscosity.
Once created, the two time crystals formed within the superfluid were brought together to interact.
Time crystals were first theorised in 2012 by Nobel Laureate Frank Wilczek, and identified in 2016. Since they were first created, time crystals have perplexed physicists, and a potential use for the strange, squirmy substance has been elusive.
“It turns out putting two of them together works beautifully, even if time crystals should not exist in the first place. And we already know they also exist at room temperature,” says Autti.
A two-level system is the basic building block of a quantum computer. The fact that coupled time crystal dynamics follows the textbook description of a two-level system (with a bit of quantum spice) is an exciting development. The authors suggest that this may mean time crystals may be the key to developing room temperature quantum computers.