All-Optical Crystals Perform as Precision Timekeepers

A team led by researchers at the University of California, Riverside (UC Riverside) has demonstrated time crystals that can persist indefinitely at room temperature, despite noise and energy loss. The team, which includes researchers from the NASA Jet Propulsion Laboratory, OEwaves Inc., and Jagiellonian University (Poland), investigated time crystals — periodic states that exhibit spontaneous symmetry breaking — in a system that is not isolated from the time crystals’ ambient environment.

Until now, time crystals have been observed under complex experimental conditions in isolated systems. These experiments have required extremely low temperatures or other rigorous conditions to minimize the effect of external influences.

To study time crystals and their potential uses more effectively, the team aimed to create stable time crystalline states outside the laboratory.

Crystals are made of atoms or molecules repeating in a symmetrical 3D lattice pattern, in which atoms occupy specific points in space. A phenomenon called “breaking symmetry” occurs when, for example, carbon atoms in a diamond form a periodic lattice, breaking the symmetry of the space in which they sit. Scientists have recently discovered that symmetry can be broken in time as well as space.

“When your experimental system has energy exchange with its surroundings, dissipation and noise work hand-in-hand to destroy the temporal order,” professor Hossein Taheri said. “In our photonic platform, the system strikes a balance between gain and loss to create and preserve time crystals.”

When the researchers blasted a 1-mm, disk-shaped magnesium fluoride glass resonator with two laser beams, they observed subharmonic spikes, or frequency tones, between the two beams that indicated breaking of temporal symmetry and the creation of time crystals. To reinforce the robustness of the photonic platform, the researchers relied on the simultaneous self-injection locking of two independent pump lasers to two same-family cavity modes with arbitrary free spectral range frequency separation and a dissipative optical soliton.

Through a theoretical study and experimental demonstration, the researchers showed that in a high-Q resonator driven at two frequencies, strongly interacting photons can spontaneously generate one or more temporal solitons, which crystallize in the rotating optical lattice formed by the beating between the pumps. The solitons can give rise to discrete time crystals that possess temporal long-range order.

Time crystals that can persist indefinitely outside of a laboratory setting, at room temperature, could have applications in precision timekeeping and quantum computing. An international research team has introduced a photonic platform that uses these crystals as core components. Courtesy of James Lee, Unsplash.

The researchers believe that their platform, which operates at room temperature, lends itself to simplified investigations of unexplored time crystalline properties, such as phase transitions and mutual interactions, and hints at the diversity of systems hosting time crystals. The results also show that integrated optics can provide a robust, flexible platform for mimicking physical condensed matter phenomena associated with time crystals.

Paired with monolithic microfabrication and well-developed techniques of quantum integrated photonics, this study could pave the way for extricating the time crystalline phase of matter from complex laboratory setups and using time crystals in real-world applications — such as in quantum computation.

Without the need for a low temperature, the system can additionally be moved outside a complex lab for field applications. One such application could be highly accurate measurements of time. Because frequency and time are mathematical inverses of each other, accuracy in measuring frequency leads to accurate time measurement.

“We hope that this photonic system can be utilized in compact and lightweight radio frequency sources with superior stability as well as in precision timekeeping,” Taheri said.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-022-28462-x).