Scientists have blown up a bunch of atoms like balloons to make an extreme version of an ‘impossible’ state of matter.
By blasting rubidium atoms with lasers, physicists have excited them into a swollen Rydberg state in an experiment that results in the exotic state of matter known as a time crystal.
This, the team says, opens up a new way to explore the properties of time crystals, as well as phenomena such as quantum fluctuations, correlation 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 movements that repeat in a time dimension, similar to how crystals like diamond and quartz are particle patterns that repeat in space.
While the original theory described patterns that repeat in a ‘permanent’ fashion, ‘temporary’ versions have been experimentally realized and observed in different ways by different teams of physicists. In these, oscillatory patterns can be measured that are distinct from any external rhythm imposed on the crystal.
This new type of time crystal is created from a gas of rubidium atoms at room temperature sealed 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 the atom into Rydberg states. This is when energy is added to the atom in such a way that the outermost electrons describe larger orbits around the nucleus, essentially inflating the atom to hundreds of times its normal radius.
This is still very small from our perspective, but it has an interesting effect on the way atoms interact when they are all packed together in a glass box.
“If the atoms in our glass container are prepared in such Rydberg states and their diameter becomes large, 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 generated that causes oscillations spontaneous exchange between two atomic states, in turn, leads to absorption of light.
So when the team excited their rubidium gas with laser light, something exciting happened. Although the laser had a constant intensity, when they measured the light at the far end of the container, they saw signs of atomic wobble as the atoms moved back and forth between an excited state and a less excited state.
These oscillations had appeared organically, thus meeting the definition of a time crystal.
“This is really a static experiment in which no specific pace is imposed on the system,” says Pohl. “The interactions between the light and the atoms are always the same, the laser beam has a constant intensity. But surprisingly, it turned out that the intensity arriving at the other end of the glass cell starts to oscillate in very regular patterns.”
This has potential applications in technology that requires very regular and stable oscillations. Metrology, for example – the science of measurement – can use such a system. And quantum information processing based on Rydberg atoms would be a powerful tool for computer applications.
“We have created a new system here that provides a powerful platform for deepening our understanding of the time crystal phenomenon in a way that comes very close to Frank Wilczek’s original idea,” says Pohl.
The research was published in Nature Physics.