Physicists have made atoms hundreds of times larger than normal, to create a spectacular version of exotic matter once thought impossible.
The strange phase of matter, also called a time crystal, was created by firing lasers at rubidium atoms until they swelled into an excited form.
The researchers say they have opened up a new avenue for investigating the properties of the mysterious crystals, which cycle periodically between two states, seemingly endlessly, in perpetual motion and never losing energy.
The new technique, described July 2 in the journal Nature Physics, could also help scientists build better quantum computers.
“We have created a new system here that provides a powerful platform to deepen our understanding of the time crystal phenomenon in a way that comes very close to Frank Wilczek’s original idea,” co-author Thomas Pohl, a physicist at the University of Vienna, said in a statement.
Time crystals were first proposed in 2012 by Nobel Prize-winning physicist Wilczek. They are groups of particles that repeat in time, much like other crystals (such as table salt or diamonds) repeat in space.
Related: Physicists connect two time crystals in seemingly impossible experiment
This is exciting for physicists. Usually the laws of physics, which are symmetric over space and (In most cases) time, producing results that are the same regardless of their direction in space and time.
But crystals break this symmetry and arrange themselves in a desired spatial direction. This means that even if the laws of nature are still symmetrical, they create different outcomes depending on the direction in which they act on crystals.
In the same way that crystals break symmetry in space, time crystals break it in time. They exist at the lowest possible energy allowed by quantum mechanics, and oscillate between two states without slowing down.
These remarkable properties have led to many claims that time crystals are perpetual motion machines that violate the second law of thermodynamics, but this is not the case. The crystals, driven by lasers, simply cannot lose or gain energy—all the laser light hitting them does is cause them to repeat their two-step shuffle. This means that, as with many systems containing only a handful of atoms, the second law does not apply to them.
Since Wilczek’s proposal, a number of time crystals have been created, each offering unique windows into this bizarre phase of matter. To build their time crystal, the researchers behind the new study used rubidium atoms excited into what are known as Rydberg states.
By firing laser light into a glass container filled with rubidium atoms, the physicists pumped the gas with tons of excess energy. The laser light excited the electrons inside the atoms, causing the spaces between their nuclei and the electrons’ outer shells to swell to hundreds of times their normal size. This caused something very interesting to happen.
“If the atoms in our glass container are prepared in such Rydberg states and their diameter becomes enormous, then the forces between these atoms also become very large,” Pohl said. “And that in turn changes the way they interact with the laser. If you choose 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. This in turn also leads to oscillatory light absorption.”
In other words, a time crystal had appeared in the glass box.
“This is actually a static experiment where no specific rhythm is imposed on the system,” Pohl added. “The interactions between light and atoms are always the same, the laser beam has a constant intensity. But surprisingly, it turns out that the intensity arriving at the other end of the glass cell starts to oscillate in very regular patterns.”
Now that they’ve created their new type of time crystal, the researchers will continue to experiment with it and test it for further applications. They’ve suggested that it could be used to create new, highly sensitive sensors, in addition to helping scientists better understand quantum synchronization — a phenomenon in which multiple quantum systems can be brought into phase, which will help in the development of better quantum computers.