Crystals, periodic arrangements of atoms over large scales, are well-known for their structured appearance with smooth facets. Frank Wilczek, a physicist at MIT and Nobel laureate, proposed in 2012 that, similar to crystals in space, there should also be “time crystals” where a physical property changes periodically in time without corresponding interference. This idea generated scientific debate and even made its way into popular culture, featuring in movies like Avengers: Endgame (2019).
While some potential time crystals have been demonstrated since 2017, they involved systems subjected to temporal excitations with specific periodicities, reacting with a different period twice as long. The realization of a time crystal behaving periodically in time without time-dependent excitation was achieved in 2022 in a Bose-Einstein condensate. Still, the crystal had a short lifespan, lasting just a few milliseconds.
The physicists in Dortmund, led by Dr. Alex Greilich, have developed a unique crystal using indium gallium arsenide, where nuclear spins serve as a reservoir for the time crystal. In this crystal, continuous illumination leads to the formation of nuclear spin polarization through interactions with electron spins. This design allows for the creation and maintenance of the time crystal in a controlled manner.
The crystal is highly durable: It can live millions of times longer than could be shown in previous experiments. The researchers in Dortmund have validated a highly intriguing phenomenon postulated by Nobel laureate Frank Wilczek about a decade ago. This concept, which has even made its way into science fiction movies, involves the creation of time crystals, and scientists have now provided experimental evidence supporting this idea.
The key to the time crystal phenomenon lies in the nuclear spin polarization generated by continuous illumination. This polarization then spontaneously triggers oscillations, creating a time crystal. Notably, the experiments with this crystal have demonstrated remarkable longevity, with a lifetime of at least 40 minutes – a duration ten million times longer than previously achieved and potentially even longer.
Furthermore, the researchers can manipulate the crystal’s period by systematically adjusting experimental conditions. In some areas, the crystal loses its periodicity, known as “melting,” leading to chaotic behavior that can persist over extended periods. This marks the first instance where scientists have employed theoretical tools to analyze the chaotic behavior of such systems.
Journal Reference:
- Greilich, A., Kopteva, N.E., Kamenskii, A.N. et al. Robust continuous time crystal in an electron–nuclear spin system. Nat. Phys. (2024). DOI: 10.1038/s41567-023-02351-6