Can Time Itself Form Crystal?
Nature follows many rhythms: the Earth’s orbit around the sun brings about the seasons, and the swing of a pendulum keeps a clock ticking. These patterns can often be described with simple mathematical equations, the journal Physical Review Letters reported.
But rhythms can also appear in a very different way—spontaneously, without any external driver—arising from the intricate interplay of many particles. Out of what might seem like uniform disorder, a repeating pattern in time emerges. This phenomenon is called a “time crystal.”
Researchers at TU Wien (Vienna) have now shown that time crystals can form through a mechanism not previously considered. Quantum correlations between particles, once thought to hinder their formation, can actually help stabilize these structures. This offers a surprising perspective on the physics of many-particle quantum systems.
When a liquid freezes, its particles undergo a spatial transformation. In the liquid state, they move randomly with no fixed structure. Once frozen, they lock into position within a crystal, forming an ordered, repeating pattern. A liquid is uniform—it has the same properties everywhere and in every direction. A crystal, by contrast, breaks this symmetry, producing a structured arrangement where certain directions differ from others.
This raises a profound question: could a similar type of symmetry breaking occur in time? Might a quantum system that appears completely disordered in time, with each moment equivalent to the next, nevertheless give rise to a repeating temporal pattern?
“This question has been the subject of intensive research in quantum physics for over ten years,” says Felix Russo from the Institute of Theoretical Physics at TU Wien, who is conducting research for his doctoral thesis in Prof. Thomas Pohl’s team. In fact, it has been shown that so-called time crystals are possible – systems in which a temporal rhythm is established without the beat being imposed from outside.
“However, it was thought that this was only possible in very specific systems, such as quantum gases, whose physics can be well described by mean values without having to take into account the random fluctuations that are inevitable in quantum physics,” says Felix Russo. “We have now shown that it is precisely the quantum physical correlations between the particles, which were previously thought to prevent the formation of time crystals, that can lead to the emergence of time-crystalline phases.”
The complex quantum interactions between the particles induce collective behavior that cannot be explained at the level of individual particles – similar to how the smoke from an extinguished candle can sometimes form a regular series of smoke rings; a phenomenon whose rhythm is not dictated from outside and which cannot be understood from single smoke particles.
“We are investigating a two-dimensional lattice of particles held in place by laser beams,” says Felix Russo. “And here we can show that the state of the lattice begins to oscillate – due to the quantum interaction between the particles.”
The research offers the opportunity to better understand the theory of quantum many-body systems – paving the way for new quantum technologies or high-precision quantum measurement techniques.
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