A schematic illustration of the experiment. The rectangles on the right depict the microwave pulses. The pointed spheres denote the carbon-13 nuclei’s spins.
| Photo Credit: Moon, L.J.I., Schindler, P.M., Sun, Y. et al. Nat. Phys. (2025).
Scientists have discovered a new phase of matter called a time rondeau crystal that shows an unusual kind of order in time, rather than in space like solids and liquids. The phase is related to, but distinct from, a time crystal.
In normal matter, the arrangement of atoms can be either ordered or disordered. For example a (solid) crystal has a repeating structure while a liquid doesn’t. The order in a crystal comes from breaking the perfect symmetry of space: instead of looking the same everywhere, it repeats in a regular pattern.
A time crystal, predicted in 2012 and observed in later experiments, shows a similar idea in time rather than space. When a system is periodically imparted some energy — like pushing a swing at regular intervals — it might oscillate at a different rhythm, such as every two pulses instead of one. Now the system can be said to be behaving in a repeating way in time, forming a crystal pattern in time rather than in space.
A time rondeau crystal (TRC), which an international research team reported on October 14 in Nature Physics, takes this concept further. In a time crystal, the motion is perfectly regular, like a clock ticking at a fixed beat. In a TRC, the system has a mix of order and randomness: it keeps a repeating pattern over long times, but between those repeating moments the motion is disordered or irregular.
The researchers created a TRC using the spins of the nuclei of carbon-13 atoms in diamond. They controlled the spins, which is an implicit property of these particles, using microwave pulses. They didn’t impart the pulses at strictly periodic intervals — there was some randomness — but the randomness itself had structure. They caused the nuclei’s spins to be partly unpredictable in the short term but predictable when observed over longer intervals.
The time rondeau crystal’s order was found to be metastable, i.e. it lasted for several seconds, which was far longer than the timescales at which microscopic processes happened in the diamond, but which faded as the system heated up.
A TRC is thus a state of matter in which long-term regularity and short-term randomness coexist in time, like a melody with unpredictable variations that also keeps returning to a familiar refrain. It shows that time itself can host patterns richer than simple repetition, and that even in disorder, order may lie hidden.
The discovery matters because it expands physicists’ understanding of what ‘order’ means in physics. Researchers have believed time order could only exist in strictly periodic systems like time crystals. The TRC shows however that new, more complex forms of time-wise organisation are also possible, even when the timing of the external drive is not regular. According to the study’s authors, this opens the door to exploring many new kinds of “temporal orders” lying between perfect order and complete randomness.
Physicists expect such systems to have practical uses as well. For instance, a TRC can be used to encode information in its beats or to create new kinds of quantum sensors that respond to specific frequencies.
mukunth.v@thehindu.co.in
Published – October 15, 2025 02:15 pm IST
