Physicists have created a system of two connected time crystals, which are strange quantum systems stuck in an infinite loop that do not follow the normal laws of thermodynamics. By connecting two time crystals, physicists hope to use the technology to eventually build a new kind of quantum computer.
“It’s a rare privilege to be able to study an entirely new phase of matter,” Samuli Autti, the project’s lead scientist from Lancaster University in the UK, told Live Science in an email.
From Crystal to Time Crystal
We encounter regular crystals all the time in everyday life, from ice in a cocktail to diamonds in jewellery. While crystals are pretty, to a physicist they represent a breakdown of nature’s normal symmetries.
The laws of physics are spatially symmetrical. This means that the basic equations of heaviness or electromagnetism or quantum mechanics apply equally to the entire volume of universe. They also work in every direction. So a lab experiment rotated 90 degrees should give the same results (everything else is the same, of course).
But in a crystal, this beautiful symmetry is broken. The molecules of a crystal arrange themselves in a preferred direction, resulting in a repeating spatial structure. In the jargon of physicists, a crystal is a perfect example of “spontaneous symmetry breaking” – the basic laws of physics remain symmetrical, but the arrangement of the molecules is not.
In 2012, Massachusetts Institute of Technology physicist Frank Wilczek noted that the laws of physics also have time symmetry. This means that each experiment is repeated at a later time time should bring the same result. Wilczek made an analogy with normal crystals, but in the dimension of time, and called this spontaneous symmetry that breaks through time a time crystal. A few years later, physicists were finally able to build one.
Related: “X-particles” from the beginning of time discovered in the Large Hadron Collider
“A time crystal is constantly moving and periodically repeating itself in time in the absence of external encouragement,” Autti said. This is possible because the Time Crystal is in its lowest energy state. The basic rules of quantum mechanics prevent the movement from completely stilling, and so the time crystal remains “stuck” in its endless cycle.
“That means they are perpetuum mobile and therefore impossible,” Autti noted.
The laws of thermodynamics suggest that systems in equilibrium tend to be more entropy, or disordered—a coffee cup left outside always cools, a pendulum eventually stops swinging, and a ball rolling on the ground eventually comes to a standstill. But a time crystal resists this or simply ignores it because the rules of thermodynamics don’t seem to apply to it. Instead, time crystals are governed by quantum mechanics, the rules that govern the zoo of subatomic particles.
“In quantum physics, a perpetual motion machine is fine as long as we keep our eyes closed, and it’s only allowed to start slowing down as we watch the motion,” Autti said, citing the fact that the exotic quantum mechanical states are important for the Time required Crystals cannot continue to function once they interact with their environment (for example, when we observe them).
This implies that physicists cannot observe time crystals directly. The moment they try to see one, the quantum rules that allow them to exist break down and the time crystal grinds to a halt. And this concept goes beyond observation: any sufficiently strong interaction with the external environment that destroys the time crystal’s quantum state will cause it to cease to be a time crystal.
This is where Autti’s team came in, trying to find a way to interact with a quantum time crystal through classical observations. Quantum physics rules on the smallest scale. But bugs and cats and planets and black holes are better described by the deterministic rules of classical mechanics.
“The continuum from quantum physics to classical physics is still poorly understood. How one becomes the other is one of the outstanding mysteries of modern physics. Time crystals span part of the interface between the two worlds. Maybe we can learn how to remove the interface by studying time crystals closely,” Autti said.
In the new study, Autti and his team used “magnons” to build their time crystal. Magnons are “quasiparticles” that are created in the collective state of a group of particles atoms. In this case, the team of physicists took helium-3 — a helium atom with two protons but only one neutron — and cooled it to ten-thousandths of a degree above absolute zero. At this temperature, the helium-3 turned into a Bose-Einstein condensate, in which all atoms share a common quantum state and work together.
In this condensate, all of the spins of the electrons in the helium-3 were connected and working together, creating waves of magnetic energy called magnons. These waves swept back and forth forever, making her a time crystal.
Autti’s team took two groups of magnons, each acting as their own time crystal, and brought them close enough to affect each other. The combined system of magnons acted like a time crystal with two different states.
Autti’s team hopes their experiments can clarify the relationship between quantum physics and classical physics. Her goal is to build time crystals that interact with their environment without the quantum states dissolving, allowing the time crystal to keep running while it is being used for something else. It wouldn’t mean free energy – the motion associated with a time crystal doesn’t have kinetic energy in the usual sense, but it could be used for quantum computing.
It is important to have two states as this is the basis for the calculation. In classical computing systems, the basic unit of information is a bit, which can take on either the 0 or 1 state, while in quantum computing, each “qubit” can reside in more than one place at a time, allowing for much more computational energy.
“This could mean that time crystals can be used as building blocks for quantum devices that also work outside of the laboratory. In such an endeavor, the two-level system that we have now created would be a fundamental building block,” Autti said.
This work is currently still very far from a functioning quantum computer, but opens up interesting research approaches. If scientists can manipulate the two-time crystal system without destroying its quantum states, they could potentially build larger systems of time crystals to serve as real computing devices.
Originally published on Live Science.
https://www.livescience.com/time-crystals-linked Physicists link two time crystals in seemingly impossible experiment