The existence of time crystals – a particularly fascinating state of matter – was confirmed only a few short years ago, but physicists have already made a pretty big breakthrough: they have induced an interaction and observed between two time crystals.
In a superfluid helium-3, crystals exchange quasi-particles twice without limiting their coherence; an achievement that, say the researchers, opens up opportunities for emerging fields, such as processing quantum information, where coherence is vital.
“Monitoring the interaction of two time crystals is an important achievement. Before anyone had observed two time crystals in the same system, let alone seeing them interact,” said physicist and lead author Samuli Autti of Lancaster University in the United Kingdom. .
“Controlled interactions are the number one item on the wish list of anyone looking to use a time crystal for practical applications, such as processing quantum information.”
Time crystals are pretty fascinating. They look just like normal crystals, but they sport an extra, peculiar property.
In regular crystals, the atoms are arranged in a solid, three-dimensional lattice structure, like the atomic lattice of a diamond or quartz crystal. These repeating grids may differ in configuration, but they do not move very much: they repeat only spatially.
In time crystals, the atoms behave a little differently. They oscillate, spinning first in one direction, and then the other. These oscillations – referred to as ‘ticking’ – are locked at a regular and specific frequency. So, where the structure of regular crystals repeats in space, in time crystals it repeats itself in space and time.
Theoretically, time crystals tick at their lowest possible energy state – known as the earth state – and are therefore stable and coherent over long periods of time. This could be exploited, but only if its coherence could be maintained in a controlled interaction.
That, Autti and his colleagues from the UK and Finland set up a timely crystal playdate. First, they cool helium-3 – a stable isotope of helium with two protons, but just one neutron – to within ten thousandths of a degree of absolute zero, making a B-phase redundant, a low-viscosity zero-viscosity liquid.
In this medium, the two time crystals appeared as spatially distinct Bose-Einstein condensates of magnon quasi-particles. Magnons are not real particles, but consist of a collective excitation of the spin of electrons – like a wave propagated by a grid of spins.
When the physicists allowed the two time crystals to reach, they exchanged magnons – which altered the oscillation in the opposite phase without sacrificing coherence.
The results were consistent with a phenomenal superconductivity, known as the Josephson effect, in which a current flows between two pieces of superconducting material separated by a thin insulator, known as the Josephson node. These structures are one of several that are being investigated for the creation of qubits, the basic units of information in a quantum computer.
It’s just a very simple interaction, but it opens the door to try to make and control a lot more saber.
“Our results demonstrate that time crystals follow the general dynamics of quantum mechanics and provide a basis for further exploring the fundamental properties of these phases, opening paths for possible applications in developing fields, such as processing quantum information,” the researchers wrote in their paper.
“Long-lived coherent quantum systems with tunable interactions, such as the robust time crystals studied here, provide a platform for building new quantum devices based on spin-coherent phenomena.”
The study was published in Natural materials.
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