Phys. Rev. Letters: Discrete Time Crystals in Actively Mode-locked Lasers

As part of an international collaboration with the Universitat de les Illes Balears and the University of Auckland, the group of Prof. Svetlana Gurevich has published its joint research in the renowned journal Phys. Rev. Letters. The study combines theoretical and experimental efforts which were led by the two PhD students, Elias Koch (Münster) and Ruiling Weng (Palma), respectively. It demonstrates for the first time that a semiconductor laser operating in the multi-pulse mode-locked regime can spontaneously reorganize its emission into a new dynamical state. Instead of producing evenly spaced pulses, the laser undergoes a sharp transition and begins emitting pulses at half the original repetition rate, effectively “skipping” every other pulse. This behavior is a clear signature of a discrete time crystal, a phase of matter that breaks the time-translation symmetry of the driving system. Time crystals were long considered impossible and have only recently been observed in highly controlled and often complex experimental platforms. A key advance of this work is that the phenomenon emerges in a simple, tunable, and robust laser system, making it considerably more accessible than previously demonstrated implementations. Beyond the period-doubling behavior, the system reveals an additional layer of complexity: two equivalent chiral states can coexist, forming distinct temporal patterns. These switching states are separated by sharp boundaries analogous to domain walls in conventional crystals (c.f. illustration). The findings not only provide new insight into how complex laser systems self-organize in time, but also open new perspectives for future applications. Time-crystal dynamics in lasers could enhance ultra-precise timing technologies, improve frequency-comb generation (with applications in spectroscopy, metrology, and GPS), and provide new tools to control light in advanced photonic devices.

R. Weng, E. R. Koch, J. Yelo-Sarrión, J. Batle, N. G. R. Broderick, J. Javaloyes, and S. V. Gurevich, "Discrete Time Crystals in Actively Mode-Locked Lasers", Physical Review Letters 136(19), 193801 (2026). 
DOI: 10.1103/k1cn-ngy6