Only recently have time crystals, a particularly intriguing form of matter, been shown to exist, but physicists have already achieved a significant milestone: they have created and seen an interaction between two time crystals.
Two time crystals swapped quasiparticles in a helium-3 superfluid without losing their coherence, a feat that, according to the researchers, opens up new avenues for developing sectors like quantum information processing, where coherence is crucial.
"A significant accomplishment is managing the interaction of two time crystals. No one has ever seen two time crystals in the same system before, much less seen them interact, "said Samuli Autti, a physicist and the study's principal author from Lancaster University in the UK.
Anyone hoping to use a time crystal for real-world uses, including quantum information processing, has controlled interactions at the top of their wish list.
I find time crystals to be rather intriguing. Although they have the same appearance as regular crystals, they have an extra, unusual quality.
Similar to the atomic lattice of a diamond or quartz crystal, the atoms in regular crystals are organised in a set, three-dimensional grid pattern. Although the arrangement of these repeating lattices might vary, they only repeat spatially, not very much else.
The atoms in time crystals exhibit somewhat distinct behaviour. They rotate in an oscillating motion, first in one direction and then the other. These oscillations, sometimes known as "ticking," are synced to a set, regular frequency. In time crystals, the structure repeats in both space and time, unlike in ordinary crystals where it just repeats in space.
Theoretically, time crystals tick at their ground state, which is the lowest energy conceivable and is stable and coherent for very long times. If their coherence could be maintained in a regulated interaction, this may be used.
So Autti arranges a time crystal playtime with his coworkers from the UK and Finland. First, they produced a B-phase superfluid, a zero-viscosity fluid with low pressure, by cooling helium-3, a stable isotope of helium with two protons but only one neutron, to within a tenth of a degree of absolute zero.
The two time crystals appeared in this medium as spatially separate magnon quasiparticle Bose-Einstein condensates. Magnons are collective excitations of electron spin, similar to a wave moving through a lattice of spins, rather than actual particles.
The oscillation was altered to the opposite phase without compromising coherence when the scientists allowed the two time crystals to contact.
The results were in line with the Josephson effect, a feature of superconductivity where a current passes between two pieces of superconducting material separated by a thin insulator called the Josephson junction. These configurations are only one of several being investigated for the production of qubits, the fundamental pieces of data in a quantum computer.
Even while it's merely a very basic interaction, it does provide a starting point for attempts to design and manage many more complex ones.
The researchers said in their paper that their findings "demonstrate that time crystals obey the general dynamics of quantum mechanics and offer a basis for further investigating the fundamental properties of these phases, opening pathways for potential applications in developing fields, such as quantum information processing."
The durable time crystals described here are an example of a long-lived coherent quantum system with controllable interactions that offers a foundation for creating new quantum devices based on spin-coherent phenomena.
The study was published in the journal Nature Materials.
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