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Scientists have long believed that time crystals – a concept proposed in 2012 by physicist Frank Wilczek – could not exist. However, the first time crystal was not created until 2016. Today, a team claims to have succeeded in connecting two time crystals to a single system. This breakthrough brings us one step closer to a practical application of this strange phase of matter.
A time crystal is a macroscopic quantum system in periodic motion in its basic state (the lowest energy state). Specifically, it is a structure composed of a group of particles arranged in a repeating pattern, like a classical crystal, but which moves and returns to their original state periodically, like an oscillator. While the arrangement of standard crystals only repeats itself in space, it is repeated with time crystals also in time.
Because they are able to go from one state to another indefinitely without the supply of energy, these crystals break one of the most important laws of physics, the second law of thermodynamics. , which states that any transformation of a system is necessarily accompanied by an increase in entropy. In constant flux, these crystals nevertheless remain stable. Due to this long-term stability and consistency, they can be very useful in quantum computing.
A two-level system composed of magnons
Two years ago, the same team of scientists had for the first time witnessed an interaction between two time crystals. No one had ever observed two time crystals in the same system, let alone interacting with each other. In a new experiment, this time they succeeded in coupling two temporal crystals built up of quasi-particles called “magnons”, to form a single macroscopic system with two levels. However, such a system is the basic element of a quantum computer.
” It turns out that putting two of them together works wonders, even though Time Crystals should not exist in the first place. And we already know that they are also found at room temperature said Samuli Autti, a researcher at Lancaster University’s Department of Physics and lead author of the paper describing the experiment.
The magnons are not really particles, but rather forms of collective excitation of the electrons’ spin, like a wave propagating through a network of spins – they are also considered “spin waves”. These magnons were created by cooling helium-3 – a rare isotope of helium, which lacks a neutron – to about ten thousandths of a degree from absolute zero (0.0001 K or -273.15 ° C). At this temperature, helium 3 has several phases, including two supernatants (designated A and B).
The researchers created two time crystals, which spatially separated Bose-Einstein condensates, each composed of 1012 magnons, in the superfluid B phase. ” In this system, the observable lifetime of the time crystal can be extended up to a thousand seconds (109 periods of motion), in the absence of a driving force “, They clarify in their article.
Time crystals that could serve as qubits
As a reminder, a Bose-Einstein condensate is a substance state in which the particles (bosons), at a sufficiently low temperature, all occupy the lowest energy quantum state (the ground state), which gives specific properties. The atoms move extremely slowly and approach each other until they overlap; this produces a kind of high-density “cloud of atoms” that acts as a single wave of matter.
When the two time crystals were brought into contact, they exchanged magnons. This exchange then changed the oscillation of each of them, creating a unified system consisting of two discrete states. This represents a major breakthrough for all technologies that rely on quantum physics. In fact, any quantum system can by definition be in several states at the same time, and only the measurement can determine one of these states – the system is in a single quantum state, but each measurement can give a different result associated with its probability.
This combination of two time crystals thus opens new paths for the development of quantum computers. Especially since another team of researchers recently proved that time crystals can be created at room temperature in a system that is not isolated from its surrounding environment.
However, there is still a lot of research to be done before these strange crystals will one day be used as qubits. In particular, the team needs to find a way to make the temporal crystals interact without using superfluids and to control these interactions more finely.