In physics, a crystal can be defined as any system that hosts a repeating pattern in its microscopic structure. In conventional crystals, this pattern repeats in space—but more exotic behavior can emerge in materials whose configurations repeat over time. Known as "time crystals," these systems were first demonstrated experimentally in 2016. Since then, researchers have been working to understand the full extent of their possible applications.
A reliable timekeeper
In their study, Viotti's team explored how time crystals could be used to design a practical quantum clock. In existing high-precision designs, devices often operate by cooling trapped ions or atoms to ultra-low temperatures using lasers, then exciting their electrons to higher energy levels. The frequencies of the photons emitted as these electrons decay back to lower energy states, provide an extremely stable reference signal.
Because these optical frequencies are far higher than the microwave frequencies used in older atomic clocks, they enable far more precise timekeeping. However, this improved accuracy comes at a cost: these systems are complex, energy-intensive, and can be challenging to deploy outside specialized lab settings.
By contrast, time crystals don't require continuous energy-intensive excitation to sustain their oscillations. Instead, a repeating pattern in a collective observable can emerge and persist due to intrinsic interactions within the system, providing a natural, built-in rhythm.
