A shimmering crystal gets its colorful appearance from the precise arrangement of its atoms in space. In 2012, Nobel Prize-winning physicist Frank Wilczek proposed that a similar kind of order could exist not in space, but in time. He suggested that certain quantum systems could organize themselves into repeating patterns that continue indefinitely without needing energy from the outside. He called these systems time crystals. They exist in their lowest energy state while still exhibiting constant, repeating motion. Scientists confirmed their existence experimentally in 2016.
Researchers at Aalto University’s Department of Applied Physics have now achieved a major milestone by linking a time crystal to an external system for the first time. The study, led by Academy Research Fellow Jere Mäkinen, shows how the team converted a time crystal into an optomechanical system. This approach could lead to technologies such as highly precise sensors or improved memory systems for quantum computers, potentially enhancing their performance.
The findings were published in Nature Communications.
“Perpetual motion is possible in the quantum realm so long as it is not disturbed by external energy input, such as by observing it. That is why a time crystal had never before been connected to any external system,” Mäkinen says. “But we did just that and showed, also for the first time, that you can adjust the crystal’s properties using this method.”
Creating and Sustaining a Time Crystal
To build the system, the researchers used radio waves to inject magnons into a Helium-3 superfluid cooled to temperatures near absolute zero. Magnons are quasiparticles, i.e. groups of particles behaving as if they were individual particles instead. Once the radio wave input was switched off, the magnons organized themselves into a time crystal.
This time crystal continued its motion for an unusually long period, lasting up to 108 cycles or several minutes before fading to a level that could no longer be measured. As it gradually weakened, the time crystal interacted with a nearby mechanical oscillator. The nature of this interaction depended on the oscillator’s frequency and amplitude.
Linking Time Crystals to Optomechanics
“We showed that changes in the time crystal’s frequency are completely analogous to optomechanical phenomena widely known in physics. These are the same phenomena that are used, for example, in detecting gravitational waves at the Laser Interferometer Gravitational-Wave Observatory in the U.S. By reducing the energy loss and increasing the frequency of that mechanical oscillator our setup could be optimized to reach down near the border of the quantum realm,” Mäkinen says.
This connection to optomechanics is significant because it provides a way to control and tune the behavior of time crystals, something that had not been possible before.
Potential for Quantum Computing and Sensing
Time crystals could play an important role in advancing quantum technologies. Their ability to persist far longer than typical quantum systems makes them especially promising.
“Time crystals last for orders of magnitude longer than the quantum systems currently used in quantum computing. The best-case scenario is that time crystals could power the memory systems of quantum computers to significantly improve them. They could also be used as frequency combs which are employed in extremely high-sensitivity measurement devices as frequency references,” says Mäkinen.
The work was carried out using the Low Temperature Laboratory, part of OtaNano, Finland’s national infrastructure for nano-, micro- and quantum technologies. The team also used computational resources provided by the Aalto Science-IT project.