The first time crystals are ready. And that’s great news for quantum computers.

When Frank Wilczek, an American theoretical physicist and winner of the 2004 Nobel Prize in Physics, proposed the theoretical formulation of time crystals, many of his colleagues raised their hands in the air. The idea he was suggesting seemed to conflict with both the conservation of energy principle and the second law of thermodynamics, so couldn’t be possible.

The principle of conservation of energy, or the first law of thermodynamics, fundamentally states that energy is neither created nor destroyed; becomes. And the second law of thermodynamics holds that the entropy of an isolated thermodynamic system always increases with the passage of time until reaching a state of thermodynamic equilibrium in which it is maximum.

Defining what entropy is in a formal and rigorous way would overly complicate this article, but we can guess with some precision what it is about if we look at it as the degree of disorder naturally present in a physical system. Furthermore, the second law of thermodynamics has a very important consequence: you cannot reverse a physical phenomenon.

What is a time crystal and why it seems like an impossible object (but it is not)

First of all, a time crystal is simply a crystal, so it is a good idea to start by reviewing what this object is from a physicochemical point of view. We can define a crystal as a structure of matter whose atoms are arranged in a certain way. homogeneous and orderlyshaping a pattern that is repeated periodically throughout space.

They are very abundant in nature; in fact, gemstones, sugar and salt are crystals, among many other objects that originate in a completely natural way. However, from a physicochemical point of view, glass is not a crystal because, in reality, it is an object. with an amorphous atomic structure.

During one of his classes at MIT (Massachusetts Institute of Technology), Frank Wilczek had the idea that there could be a different type of crystal whose atomic structure, instead of repeating itself in space, repeats itself periodically. over time. It is difficult to imagine something like this, and, as we have seen in the first paragraphs of this article, the scientific community received the idea with great suspicion because it seemed to contravene the laws of physics.

Furthermore, making a time crystal like the ones proposed by Wilczek required finding a way to break spontaneously. time symmetry, and at that time this purpose seemed unfathomable. A stable object isolated from any disturbance remains unchanged over time, hence it preserves the temporal translation symmetry. However, a time crystal should simultaneously be able to preserve its stability and change its crystal structure periodically.

This idea has an implication that is easy to intuit: if we observe the time crystal at different times, we should perceive that its structure is not always the same. It should vary periodically, a behavior that inevitably leads us to identify it as a new state of matter different from the solid, liquid, gas and plasma phases. Under certain conditions, other much more unusual states of matter are also possible, such as Bose–Einstein condensatebut to a greater or lesser extent we are all familiar with these four phases.

Despite the initial suspicion of the scientific community, some researchers reflected on what Wilczek proposed and realized that under certain highly unlikely conditions, but possible, some objects could theoretically exhibit the behavior of a time crystal. They should be able to change their structure periodically and return to their initial configuration at regular intervals.

There is no doubt that this idea is very exotic, but it has an even more strange implication: this is only possible if this constant and eternal phase transition does not require investing energy. In some way we would be facing an impossible ideal: a form of perpetual motion machine that benefits from the principle of conservation of energy, but clearly violates the second law of thermodynamics.

The first time crystals are ready (and they are very promising)

Despite all the objections that the laws of physics with which we are familiar put to the existence of time crystals, the research group of the University of Lancaster, in the United Kingdom, led by the physicist Samuli Autti has managed to fine-tune the first. According to this scientist, his starting point has been the idea that “in the field of quantum physics, perpetual motion is feasible, and once we have accepted this idea, time crystals are possible.”

In the article that this research group has published in Nature Communications explains that his time crystals They are made up of magnons.. And the funny thing is that these elements are not particles; they are quasiparticles of spin 1 capable of transporting energy and momentum in a crystal. This definition is complicated, but we can get a rough idea of ​​what a magnon is if we identify it as the result of the simultaneous excitation of the spin of a set of electrons.

This explanation of Francis Villatoro helps us to strengthen this idea a little better: «We can say that a magnon is the quantum equivalent to a wave of spins, just as a phonon is the quantum equivalent to an elastic wave in a solid». The strategy that these physicists have devised to recreate the magnons is to cool helium-3, which is a stable isotope of heliumuntil it acquires a temperature very close to absolute zero (-273.15 degrees Celsius).

Under these conditions, helium-3 acquires the properties of a superfluid and favors the spontaneous appearance of time crystals, so that each one of them is made up of a trillion magnons. And it’s a billion of us, not the Anglo-Saxons. In his article Autti and his research colleagues assure that the time crystals they have recreated exhibit the same properties formulated theoretically by Frank Wilczek, so there is no doubt that we are facing a very important milestone. And it is relevant due to the theoretical scope of its possible applications.

Researchers working on the design of time crystals are confident that they can be used to measure time and distance with extreme precision. If so, they could probably be used to fine-tune more precise GPS, more advanced telecommunications equipment, or more robust cryptography systems. But this is not all. In addition, the team of researchers led by Autti argues that time crystals can help us process quantum information because it is possible to use them to make higher quality qubits.

These scientists predict that fine-tuning quantum bits using time crystals will endow them with greater coherence, understanding this property as its ability to prolong the state in which quantum hardware preserves the characteristics that allow it to outperform classical computers during the execution of some algorithms. And it is that when quantum decoherence appears, quantum effects disappear, and with them the advantages that they bring in the context of quantum computing also disappear.

In addition, these researchers claim that time crystals can be created and manipulated at room temperature, so, in theory, they could allow the fine-tuning of qubits that, unlike superconductors, would not have to be cooled to a temperature close to absolute zero. Everything we have seen in this article sounds very good. Surprisingly well.

Even so, it is most prudent that we moderate our expectations because in order to be able to use time crystals to make qubits challenges need to be solved that have yet to be tackled by scientists. Nevertheless, we can be reasonably optimistic. Just a decade ago, a good part of the scientific community opposed the existence of time crystals, and we already have them here. Let’s cross our fingers that the first practical applications will be ready very soon.

Cover image: IBM

More information: Nature Communications