what they are, why they are so revolutionary and how quantum computers are already helping us achieve them

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In just nine years time crystals have gone from physical impossibility to practical reality. And it is surprising that such a sudden change has taken place in such a short time. When the American theoretical physicist, and winner of the Nobel Prize in Physics in 2004, Frank Wilczek proposed his theoretical formulation In 2012, a good part of the scientific community raised their hands to their heads. And he had reason to.

Wilczek’s “occurrence” was contrary to the laws of physics, especially the Second principle of thermodynamics. This fundamental law states that the entropy of an isolated thermodynamic system always increases with time until a state of thermodynamic equilibrium is reached in which entropy is maximum.

This formal definition is counterintuitive, largely because the word entropy appears twice in it. explain rigorously what is entropy It would only complicate the article even more, but, fortunately, we can intuit this concept in a simple way, provided that, yes, we agree to sacrifice a little rigor. Entropy is usually formulated as the degree of disorder naturally present in a physical system.

When Frank Wilczek proposed the theoretical formulation of time crystals, in 2012, a good part of the scientific community raised their hands to their heads

This description is an oversimplification, but it invites us to explore an essential consequence of the second law of thermodynamics: the impossibility of reversing a physical phenomenon. In addition, what Wilczek proposed also seemed to violate the first law of thermodynamics, or principle of conservation of energy, which fundamentally establishes that energy is neither created nor destroyed; becomes.

There is no doubt that the time crystals did not get off to a good start, but today, and in an unexpected turn of events, they represent a new line of research. extraordinarily promising that keeps many research groups engaged, such as the one led by the Spanish physicist Paul Hurtado at the University of Granada.

What is a time crystal

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.

Making a time crystal like the ones proposed by Wilczek required finding a way to spontaneously break the time symmetry.

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.

quantum computer

The operating principle of quantum computers positions them as a very attractive tool for simulating and recreating time crystals. Quantum computing researchers are looking for applications for this equipment, and this is one of the most promising.

This idea has an implication that is easy to intuit: if we observe the time crystal at different instants we should perceive that its structure it 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.

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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 a 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, which we have discussed above.

In 2017, the first experimental tests were carried out by acting on the spin of a quantum system

During the last five years, several research groups, including the group in which the Spanish physicist Pablo Hurtado participates, have been working hard to propose strategies that seek to allow us to build a time crystal. And the first results are very promising. In fact, there is already on the table several proposals that have yielded a very encouraging result in computational simulations.

But this is not all. In 2017 the first experimental tests were carried out acting on the spin of a quantum system by subjecting it to an external force that changes periodically over time. It is clear that the physics involved in fine-tuning time crystals is in its infancy.

Much remains to be done, and much more research will still be necessary, but a scientific article posted just a few days ago and in which researchers from Google and the American universities of Princeton and Stanford, among other institutions, participate, invites us to contemplate the future of time crystals with reasonable optimism.

Quantum computers, our allies in the search for time crystals

At the beginning of last July, a group of researchers led by the American physicist Joe Randall published a scientific article very promising. In it he exposes how he has used a quantum simulation platform to describe the creation of a discrete time crystal acting on the spin of the diamond particles.

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According to these researchers, quantum computers are an exceptional tool when it comes to recreating time crystals

And just a few days later it has seen the light other item in which a second research group has used Google’s quantum computer to recreate a time crystal that manages to evade the second law of thermodynamics. According to these researchers, their strategy describes an object capable of changing phase at regular intervals, thus breaking the temporal symmetry and without investing the slightest energy in the process. In theory we are facing a full-fledged time crystal.

According to these researchers, quantum computers are an exceptional tool when it comes to recreating time crystals because their operating principle allows them to tackle this problem in an efficient and natural way. What they propose is very interesting because it puts us one step closer to obtaining a time crystal that meets all the conditions established by the theoretical formulation, and, furthermore, represents a practical application in which quantum computers seem to have a lot to say.

googlesycamore

The Sycamore processor with which Google achieved quantum supremacy in 2019 has 54 qubits. The chip in this photo is the Bristlecone processor, which has 72 qubits.

Probably in the coming months we will see more progress in this very promising area, and perhaps the idea of ​​building a time crystal inside the a quantum processorlike Google’s Sycamore, but there is something important that we have not yet explored in this article: what is a time crystal for in practice?

Researchers working on the design of time crystals are confident that they can be used to measure time and distance with extreme precision.

Answering this question requires us to delve into the realm of speculation, but 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 set up more precise GPS, more advanced telecommunications equipment or more robust cryptography systems, among other applications.

It is even possible that time crystals help us detect gravitational waves more precisely, and also allow us to understand a little better what happens inside black holes and what are the properties of the space-time continuum that permeates the entire universe. We still can’t take any of this for granted, and researchers they admit it honestlybut there is no doubt that this is a very promising area of ​​research that may bring us big surprises in the medium term.

Cover image: IBM Research

Images: IBM Research | Google

Via: Quanta Magazine

More information: arXiv.org

In just nine years time crystals have gone from physical impossibility to practical reality. And it is surprising that such…

In just nine years time crystals have gone from physical impossibility to practical reality. And it is surprising that such…

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