Physicists have just taken as stunning move towards quantum devices that sound like something beyond the science fiction.
For the first time, isolated groups of particles acting like bizarre states of matter known as time crystals have been linked into a single, evolving system that could be extremely useful in quantum computing.
Following the first observation of the interaction between two-time crystals, explained in a paper two years ago, this is the next step towards potentially harnessing time crystals for experimental purposes, such as quantum information processing.
Time crystals, only officially discovered and confirmed a few years ago in 2016, were once thought to be physically not possible. They are a phase of matter very much similar to normal crystals, but for one additional, peculiar, and very unique property.
In well-ordered crystals, the atoms are arranged in a fixed, three-dimensional grid structure, like the atomic lattice of a diamond or quartz crystal. These repeating lattices can be different in configuration, but any movement they exhibit comes exclusively from external pushes.
In time crystals, the atoms act a bit differently. They show patterns of movement in time that can't be so easily explained by an external push or shove. These oscillations – referred to as 'ticking' – are locked to a regular and certain frequency.
Theoretically, time crystals click at their lowest possible energy state – known as the ground state – and are therefore stable and coherent over long periods of time. So, where the formation of regular crystals repeats in space, in time crystals it repeats in space and time, thus exhibiting perpetual ground state motion.
"Everybody knows that perpetual motion machines are not possible," says Physicist and Author Samuli Autti of Lancaster University in the UK.
The time crystals, the group of scientists have been working with containing quasiparticles called magnons. Magnons are not true particles, but contains collective excitation of the spin of electrons, like a wave that propagates through a lattice of spins.
Magnons appear when helium-3 – a stable isotope of helium with two protons but only one neutron – is cooled to within one ten thousandth of a degree of absolute zero.
This forms what is called a B-phase superfluid, a zero-viscosity fluid with low pressure.
In this medium, time crystals created as spatially distinct Bose-Einstein condensates, each containing a trillion magnon quasiparticles.
A Bose-Einstein condensate is created from bosons cooled to just a bit above absolute zero (but not reaching absolute zero, at which point atoms stop moving).
This causes them to sink to their lowest-energy state, moving very slowly, and coming together close enough to overlap, making a high-density cloud of atoms that acts like one 'super atom' or matter wave.
When the two-time crystals were allowed come together, they exchanged magnons. This exchange influenced the oscillation of each of the time crystals, forming a single system with an option of functioning in two, distinct states.
In quantum physics, objects that can get more than one state exist in a mix of those states before they've been pinned down by a simple measurement. So, having a time crystal operating in a two-state system gives a rich new picking as a basis for quantum-based technologies.
Time crystals are a fair method from being deployed as qubits, as there are a significant number of hurdles to solve first. But the pieces are starting to dropping into place.
Earlier this year, a group of physicists announced that they had successfully created room temperature time crystals that don't need to be separated from their ambient surroundings.
More sophisticated interactions between time crystals, and the clear control thereof, will need to be developed further, as will noticing interacting time crystals without the need for cooled super fluids. But scientists are hopeful.
This research has been published in Nature Communications.
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