Time crystals that persist indefinitely at room temperature could have applications in precision timekeeping
We’ve all seen crystals, whether it’s a simple grain of salt or sugar, or a beautiful and elaborate amethyst. These crystals are made up of repeating atoms or molecules in a symmetrical three-dimensional pattern called a lattice, in which the atoms occupy specific points in space. By forming a periodic lattice, the carbon atoms in a diamond, for example, break the symmetry of the space in which they are found. Physicists call this “symmetry breaking”.
Scientists have recently discovered that a similar effect can be seen over time. Symmetry breaking, as the name suggests, can only occur where some kind of symmetry exists. In the time domain, a cyclically changing force or source of energy naturally produces a temporal pattern.
Symmetry breaking occurs when a system moved by such a force experiences a moment of deja vu, but not with the same period as that of the force. Over the past decade, “time crystals” have been researched as a new phase of matter, and more recently observed under elaborate experimental conditions in isolated systems. These experiments require extremely low temperatures or other harsh conditions to minimize unwanted external influences, called noise.
For scientists to learn more about time crystals and utilize their technological potential, they must find ways to produce time crystal states and keep them stable outside of the laboratory.
Cutting-edge research conducted by UC Riverside and published this week in Nature Communication has now observed time crystals in a system that is not isolated from its surrounding environment. This major achievement brings scientists one step closer to developing time crystals for use in real-world applications.
“When your experimental system exchanges energy with its surroundings, dissipation and noise work hand in hand to destroy the temporal order,” said lead author Hossein Taheri, assistant research professor of electrical and computer engineering. to Marlan and Rosemary Bourns of UC Riverside. College of Engineering. “In our photonics platform, the system balances gain and loss to create and preserve time crystals.”
The all-optical time crystal is made using a disc-shaped magnesium fluoride glass resonator one millimeter in diameter. When bombarded with two laser beams, the researchers observed subharmonic spikes, or frequency tones between the two laser beams, which indicated a breakdown in time symmetry and the creation of time crystals.
The UCR-led team used a technique called self-injection locking of the two lasers onto the resonator to achieve robustness against environmental effects. The time repeating state signatures of this system can be easily measured in the frequency domain. The proposed platform therefore simplifies the study of this new phase of matter.
Without the need for low temperature, the system can be moved outside of a complex laboratory for field applications. One such application could be very precise time measurements. Since frequency and time are mathematical inverses of each other, the precision of frequency measurement enables accurate time measurement.
“We hope this photonic system can be used in compact and lightweight radio frequency sources with superior stability as well as in precision timekeeping,” Taheri said.
Nature Communications’ open access article, “All-optical dissipative discrete time crystals”, is available here. Taheri was joined in the research by Andrey B. Matsko at NASA’s Jet Propulsion Laboratory, Lute Maleki at OEwaves Inc. in Pasadena, California, and Krzysztof Sacha at Jagiellonian University in Poland.