Scientists blew up lots of atoms like balloons to create an extreme version of an “impossible” state of matter.
By blasting rubidium atoms with lasers, physicists excited them into a bloated Rydberg state in an experiment that resulted in an exotic state of matter known as a time crystal.
This, the team says, opens up a new way to investigate the properties of time crystals, as well as phenomena such as quantum fluctuations, correlations and synchronization – an important factor in the design of quantum computers.
First described by American theoretical physicist Frank Wilczek in 2012, time crystals are particle motions that repeat in the time dimension, much like crystals like diamond and quartz are particle patterns repeating in space.
While the original theory described patterns repeating in an “eternal” fashion, the “temporary” versions were experimentally realized and observed in different ways by different teams of physicists. Oscillation patterns that differ from any external rhythms stored on the crystal can be measured in them.
This new kind of time crystal was generated from a room-temperature gas with rubidium atoms enclosed in a glass container.
A team of physicists led by Xiaoling Wu, Zhuqing Wang and Fan Yang at Tsinghua University in China used laser light to excite an atom into Rydberg states. Then energy is added to the atom in such a way that the outermost electrons follow larger orbits around the nucleus, essentially inflating the atom to a hundred times its normal radius.
That’s still pretty small from our perspective, but it has an interesting effect on the way the atoms interact when they’re all grouped together in a glass box.
“If the atoms in our glass container are prepared in such Rydberg states and their diameter becomes huge, then the forces between these atoms also become very large,” explains physicist Thomas Pohl from the Vienna University of Technology.
“And that in turn changes the way they interact with the laser. If you choose the laser light in such a way that it can excite two different Rydberg states in each atom at the same time, then a feedback loop is created that causes spontaneous oscillations between the two atomic states, which in turn leads to oscillatory absorption of light.”
So, when the team blew up their rubidium gas with laser light, something exciting happened. Although the laser was at a constant intensity, when they measured the light at the far end of the container, they saw signs of atomic oscillation, as the atoms ticked back and forth between an excited state and a less excited state.
These oscillations appeared organically and thus met the definition of a time crystal.
“This is actually a static experiment in which there is no specific rhythm stored in the system,” says Pohl. “The interactions between light and atoms are always the same, the laser beam has a constant intensity. But surprisingly, it turned out that the intensity that reaches the other end of the glass cell begins to oscillate in very regular patterns.”
This has potential applications in technology that requires highly regular, self-sustaining oscillations. Such a system could be used, for example, by metrology – the science of measurement. And quantum information processing based on Rydberg atoms would be a powerful tool for computing applications.
“We have created a new system here that provides a powerful platform for advancing our understanding of the time crystal phenomenon in a way that is very close to Frank Wilczko’s original idea,” says Pohl.
The research was published in Natural physics.