Researchers at TU Dortmund University have shown that multiple time crystals can form inside a single semiconductor and spontaneously synchronize their oscillations. The team, led by Prof. Alex Greilich, reports in Nature Communications that the crystals, embedded in a gallium arsenide semiconductor with small amounts of indium and silicon, lock to a common frequency when illuminated together. The work builds on an earlier demonstration that a continuous time crystal could persist for hours in such a material.
Time crystals are systems whose internal rhythm repeats without any external periodic drive. In this experiment, localized electrons interact with roughly a million nearby nuclear spins at temperatures near -270 °C. A pump laser aligns the electron spins, which transfer polarization to the nuclei; in a weak magnetic field, the nuclear polarization rotates, and feedback between electrons and nuclei sustains the oscillations. A second laser monitors the evolving rhythm.
The researchers found that separate oscillators, which would normally differ slightly due to microscopic variations in the material, fall into sync when many regions are excited at once. The coupling is carried by spin-polarized electrons, allowing synchronization across distances up to 40 micrometers—more than a thousand times the size of a single oscillator. Beyond that separation, the time crystals oscillate independently. The team likens the effect to Christiaan Huygens' 1665 observation of pendulum clocks synchronizing through a shared support, though here the link is electronic rather than mechanical. The results reveal long-range, non-local coupling between spin systems and may inform future networks of controllable spin oscillators.