MOSCOW, July 14- RIA News. Russian and American scientists working at Harvard have created and tested the world's first quantum computer, consisting of 51 qubits. The device is still the most complex computing system of its kind, said a professor at Harvard University, co-founder of the Russian Quantum Center (RQC) Mikhail Lukin.

The physicist announced this, speaking at the International Conference on Quantum Technologies ICQT-2017, which is held under the auspices of the RCC in Moscow. This achievement allowed Lukin's group to become a leader in the race to create a full-fledged quantum computer, which has been unofficially for several years between several groups of the world's leading physicists.

Quantum computers are special computing devices whose power grows exponentially due to the use of the laws of quantum mechanics in their work. All such devices consist of qubits - memory cells and at the same time primitive computational modules capable of storing a range of values \u200b\u200bbetween zero and one.

Today, there are two main approaches to the development of such devices - classical and adiabatic. Proponents of the first of them are trying to create a universal quantum computer, in which qubits would obey the rules by which ordinary digital devices work. Working with such a computing device, ideally, would not be very different from how engineers and programmers operate conventional computers. An adiabatic computer is easier to create, but it is closer in its principles of operation to analog computers of the early 20th century, and not to digital devices of our time.

Last year, several teams of scientists and engineers from the United States, Australia and a number of European countries announced that they were close to creating such a machine. The leader in this informal race was the team of John Martinis from Google, which is developing an unusual "hybrid" version of a universal quantum computer that combines elements of an analog and digital approach to such calculations.

Lukin and his colleagues at RCC and Harvard bypassed Martinis's group, which, as Martinis told RIA Novosti, is now working on a 22-qubit computing machine, using exotic "cold atoms" rather than superconductors, like scientists from Google.

As Russian and American scientists have found, a set of atoms held inside special laser "cells" and cooled to ultra-low temperatures can be used as qubits of a quantum computer, maintaining stability under a fairly wide range of conditions. This allowed physicists to create the largest quantum computer so far, of 51 qubits.

Using a set of similar qubits, Lukin's team has already solved several physical tasks, extremely difficult to simulate with "classic" supercomputers. For example, Russian and American scientists were able to calculate how a large cloud of particles connected with each other behaves, to detect previously unknown effects arising inside it. It turned out that with the damping of excitation in the system, some types of oscillations can remain and be held virtually indefinitely, which scientists did not suspect before.

To check the results of these calculations, Lukin and his colleagues had to develop a special algorithm that made it possible to carry out similar calculations in a very crude form on ordinary computers. The results were broadly consistent, confirming that the 51-qubit system of Harvard scientists works in practice.

In the near future, scientists intend to continue experiments with a quantum computer. Lukin does not exclude that his team will try to run Shor's famous quantum algorithm on him, which allows him to break most of the existing encryption systems based on the RSA algorithm. According to Lukin, an article with the first results of a quantum computer has already been accepted for publication in one of the peer-reviewed scientific journals.

Russian and American scientists at Harvard have created and tested the world's first 51-qubit quantum computer - the most sophisticated computing system of its kind.

This was stated by a professor at Harvard University, co-founder of the Russian Quantum Center (RQC) Mikhail Lukin, rIA Novosti reports.

The physicist spoke about this at the International Conference on Quantum Technologies ICQT-2017 in Moscow.

This achievement allowed Lukin's group to become a leader in the "race" to create a full-fledged quantum computer, which has been unofficially for several years between several groups of the world's leading physicists.

Quantum computers are special computing devices whose power grows exponentially due to the use of the laws of quantum mechanics in their work.

All such devices consist of qubits - memory cells and at the same time primitive computational modules capable of storing a range of values \u200b\u200bbetween zero and one.

Today, there are two main approaches to the development of such devices - classical and adiabatic.

Proponents of the first of them are trying to create a universal quantum computer, in which qubits would obey the rules by which ordinary digital devices work.

Working with such a computing device, ideally, would not be much different from how engineers and programmers operate conventional computers.

An adiabatic computer is easier to create, but it is closer in its principles of operation to analog computers of the early 20th century, and not to digital devices of our time.

Last year, several teams of scientists and engineers from the United States, Australia and a number of European countries announced that they were close to creating such a machine.

The leader in this informal race was the team of John Martinis from Google, which is developing an unusual "hybrid" version of a universal quantum computer that combines elements of an analog and digital approach to such calculations.

Lukin and his colleagues at RCC and Harvard bypassed Martinis's group, which is now working on a 22-qubit computing machine, using exotic "cold atoms" rather than superconductors, like scientists from Google.

As Russian and American scientists have found, a set of atoms held inside special laser "cells" and cooled to ultra-low temperatures can be used as qubits of a quantum computer, maintaining stability under a fairly wide range of conditions. This allowed physicists to create the largest quantum computer so far, of 51 qubits.

Using a set of similar qubits, Lukin's team has already solved several physics problems that are extremely difficult to simulate with "classical" supercomputers.

For example, Russian and American scientists were able to calculate how a large cloud of particles connected with each other behaves, to detect previously unknown effects arising inside it. It turned out that with the damping of excitation in the system, some types of oscillations can remain and be held virtually indefinitely, which scientists did not suspect before.

To check the results of these calculations, Lukin and his colleagues had to develop a special algorithm that made it possible to carry out similar calculations in a very crude form on ordinary computers. The results were broadly consistent, confirming that the 51-qubit system of Harvard scientists works in practice.

In the near future, scientists intend to continue experiments with a quantum computer. Lukin does not exclude that his team will try to run Shor's famous quantum algorithm on him, which allows him to break most of the existing encryption systems based on the RSA algorithm.

According to Lukin, an article with the first results of a quantum computer has already been accepted for publication in one of the peer-reviewed scientific journals.

The costs of the Russian Field project are partially covered by funds provided by the Russkiy Mir Foundation

Recently, the Harvard group of physicist Mikhail Lukin managed to create - in fact, a semblance of matter, which consists not of atoms, but of light quanta. This fundamental discovery, - previously the possibility of photonic matter was discussed only theoretically, - has direct practical application: on the basis of interacting photons, it is possible to create computational logic for quantum computers. While this is a matter of the distant future, but now Lukin's group is working on the creation of communication devices for systems of absolutely secure communication.

Mikhail Lukin is a professor at Harvard University and concurrently head of the International Advisory Council of the Russian Quantum Center. He is one of the most cited physicists of Russian origin. His group is engaged not only in basic research in photonics, but also in its technological applications. Moreover, not only in the field of quantum communications or quantum computing, but also in application to medicine: this summer, Lukin's group created diamond ones, with the help of which it is possible to selectively and controllably kill cancer cells. Lenta.ru talked with the scientist about how a new discovery can bring the appearance of full-fledged quantum computers closer, whether fundamental physics can easily turn into medical startups and about what it is doing for Skolkovo, working in Boston.

"Lenta.ru": Your last article talks about the creation of photonic matter. What it is?

Let me try to explain with a simple example. Imagine two laser beams that you cross with each other. The photons of these beams do not interact in any way, they pass through each other, without affecting each other in any way, like two waves on the surface of the lake. This is due to the fact that individual quanta of light, photons, are fundamentally non-interacting particles. However, if you cross the same laser beams not in a vacuum, but in a certain medium, for example, in glass, the situation will change. The light of different beams will interact: the beams will deflect each other a little, or the speed in one beam will change depending on the intensity of the other.

Why is this happening? The fact is that light itself changes the environment in which it propagates. Usually very weak, but changes. The changed medium conducts electromagnetic radiation in a different way - and it is through the medium that photons interact.

All this has been known for a long time. The field of physics that deals with such interactions has been around for almost half a century and is called nonlinear optics. By the way, Soviet scientists made a great contribution to it. However, until now, no one has been able to force individual quanta of light, rather than laser beams, to interact.

In principle, in theory, many thought about this earlier. About 20-30 years ago, there were theoretical predictions about what kind of medium for the propagation of light to make in order to make the photons inside it interact. The possibility of the existence of such exotic objects, photon pairs - essentially photonic molecules, was predicted. In this article in Nature, about which you are talking, we described how we finally managed to get such pairs. They, in fact, are called photonic matter - due to the fact that they strongly resemble molecules, but they do not consist of atoms, but of photons.

It should be added here that the study of interacting photons is interesting not only in itself. It has direct practical application in information technology and communications. The point is this. On the one hand, the fact that photons usually do not interact is their great advantage as a carrier of information. But on the other hand, if we want to somehow process the information that is transmitted using light, then it is necessary to make some kind of switches, some kind of logical elements. And for this it is necessary that the photons somehow interact with each other. Now, light is mainly used only to transmit information, and to manipulate it, it needs to be translated into some kind of electrical signal. It is inconvenient, slow and inefficient. So if we can get the photons to interact with each other, we can create all-photonic information-processing devices.

How is the environment in which photonic matter exists?

In our setup, it consists of cooled rubidium atoms, forming a fairly dense atomic gas. In this environment, light travels very slowly. That is, compared to vacuum, the speed of light decreases in any medium, this is understandable, but in in this case photons almost stop - their speed is about one hundred meters per second. We published the method of such "stopping the light" back in 2001 (Lenta.ru about this work).

Images: Ofer Firstenberg et al., Nature, 2013

Propagating in such a medium, the photons seem to be pulling a plume of atomic excitations. Due to this, in fact, the light slows down. But the most interesting thing is that atoms in this medium begin to interact with each other so strongly that these interactions are transferred to photons, and they, photons, seem to begin to be attracted to each other. As a result, photons, firstly, acquire an effective mass and, secondly, due to mutual attraction, they form a connected state that resembles a molecule. The laws describing the behavior of photons in such a medium are very similar to the laws describing the behavior of particles with mass, massive atoms.

The photonic molecule that we managed to obtain is just the beginning, because in principle, more complex objects can be created from them. First of all, we are now interested in analogs of crystal structures, photonic crystals.

Do you mean photonic matter containing more than two photons?

Not only more, but also at regular intervals. To get this state, photons must be repelled, not attracted. Basically, we know how to achieve this, and I think small crystals can certainly be made in the near future.

The pairs of photons you received, as far as I understand, are fairly stable. That is, they, like any photons, cannot be stopped, they must move in the medium, but they exist in a pair for a relatively long time, do not collapse, do not turn, say, into one photon of increased energy. In this case, as you said, in the medium between them, only the force of attraction arises, without repulsion. Why is this happening?

The point is that it is a quantum system. Think of Bohr's atomic model, which celebrates its centenary this year. Indeed, in an ordinary atom there is also a positively charged nucleus, there is an electron and there are no repulsive forces between them, only attraction. Nevertheless, the electron does not fall on the nucleus, as we know.

This happens due to the quantization of energy, which allows the electron to move around the nucleus, as it were, without collapsing. The exact same story happens with our photons. In principle, there is only an attractive force between them, but due to the fact that this is a quantum system, it does not collapse, it is in a stable state. The situation is very similar to that of molecules with two atoms. That is, the name "photonic matter" for these pairs of particles is quite justified - the analogy here is quite deep.

In the same issue Nature, where your article appeared, the work of Fukuhara was published, where a similar pairing effect was demonstrated not on photons, but on magnons - virtual magnetic particles.

Yes, it was done by the group of Emmanuel Bloch from the Max Planck Institute. This is indeed a very unusual coincidence, because the systems we work on are completely different, but the effects we observe are remarkably similar.

Bloch's group worked with atoms fixed in an optical trap. This is a fairly well-known system that, using several lasers, allows you to create an optical lattice in which atoms sit in potential holes, relatively speaking, like eggs in a box. In the initial state, all these atoms have one spin, that is, their magnetic polarization is directed in the same direction. By acting on this medium with light, Bloch and colleagues achieved that a pair of atoms changed their spin to the opposite one, and then this inversion began to propagate in a wave along the lattice.

In this case, a pair of bound particles also appeared, only in their case magnons, and not photons. The fact that magnons can exist in a bound state was known, in principle, before. But Bloch's group was the first to trace the propagation of these bound particles in a medium. The wave function of such a bound state of particles is very similar to what we saw for photons. It turns out that this is such a fairly universal effect.

Emmanuel and I recently met at a conference. At breakfast, when I showed him my data, a rather funny situation arose: our data turned out to be so similar in completely different physical processes that all that remained was to say "wow."

Yes, but pairs of magnons, unlike photonic matter, are much less convenient for use in communications. Please tell us what can be done with photonic matter in practical terms?

The applied goal of our work is the creation of photonic logic. In systems where individual photons can interact with each other, we can create, say, single-photon switches or single-photon transistors. One of the specific challenges is to approach the creation of a quantum repeater - a device that allows you to transfer quantum information without destroying its quantum nature.

What is a Quantum Repeater? You certainly know about, in which information is transmitted using single photons in a superposition of two states. In theory, single photon transmission of the key is an absolutely reliable encryption technology, because any attempt by an attacker to tamper with the system and intercept the message will be visible. This, in fact, is what makes quantum cryptography interesting. However, there are losses in any channels, therefore, the currently existing quantum communication is limited to the distance at which most of the photons are not lost - these are tens, maximum - hundreds of kilometers.

In principle, the problem of losses also exists in classical communication, but there it is solved with the help of ordinary repeaters that receive the signal, “clean it up” a little, repeat it in an amplified form and send it further through the optical network. For quantum communication, analogs of such devices are needed. But the problem is that if you send information encoded in a single photon, you cannot “amplify” it ( a typical example is the detection of a photon with an unknown polarization - if the measurement basis does not coincide with the photon polarization basis, the information will simply be lost - approx. "Lenta.ru").

A quantum repeater should be able to do two basic things. First, he must be able to store the quantum information that is transmitted with photons. To achieve this, we, in fact, worked on what is called "stopping the light." This, in fact, was the practical motivation for our work - we tried to stop the impulse by writing its information into atomic excitation.

Secondly, to make this repeater, it is necessary to learn how to make logical switches for photons, photonic logic. And those experiments that have now been published, they are directly related to the creation of such logic for quantum repeaters.

Are photon pairs acting as qubits in this computer?

No, individual photons are qubits. And the logic will be built on the basis of their connection and separation into photonic molecules. Since we can link photons in pairs, we figure out how to create a switch where, say, the presence of one photon can stop the propagation of another. It is already possible to build computational logic on this.

Of course, there is a lot of work to be done here. To create a switch, we have to improve the interaction between photons many times over. But we have already shown the basic principle, and it works. Now you can think in a more practical way. In fact, in an independent experiment, we have already greatly improved even the quality of interaction (performance) that was obtained in the published experiments.

We hope that the use of photonic matter will not be limited to quantum repeaters. In the future, on their basis, it will be possible to create full-fledged quantum computers that perform computations. This is still a very distant horizon, because for this it is necessary to create hundreds, maybe even thousands of qubits. And the quantum repeater is our current, quite tangible, practical goal.

You are not only concerned with photonic matter. In August, we talked about how your group came up with unexpected uses for diamonds with nitrogen vacancies. Usually they are used as qubits, but you made thermometers out of them not even cells, but their separate parts. Where did this idea come from?

Nowadays a variety of systems are used as carriers of qubits. These can be, for example, cooled superconducting resonators, individual ions, or cooled atoms in an optical trap. Or, in the case of this work, electrons in the so-called NV centers. Physically, an NV center is just a hole in the crystal lattice of a diamond that exists next to an impurity - a nitrogen atom. These impurities also exist in ordinary diamonds, but we can create them artificially using irradiation, for example, with nitrogen atoms. Moreover, these centers can be made in very small particles, diamond nanocrystals.

The electrons of the NV center, if it is located close to the surface, are very sensitive to the external environment, to its temperature and magnetic field. Roughly speaking, the rate of their quantum evolution depends on these parameters. On the one hand, this is a problem for quantum computers - the state of the system becomes fragile, it becomes difficult to preserve it in such a qubit. But, on the other hand, such NV centers can be used as extremely sensitive sensors.

Their uniqueness is that they can be very small, that is, we can measure fields and temperature in very small volumes. Naturally, we tried to use such nanocrystals for applications where microscopic size is an advantage. For example, for spectroscopy of complex biomolecules at room temperature or for measuring the temperature of individual parts of a cell. In that article, we studied the possibilities of using diamond NV centers precisely as microscopic thermometers.

Such nanocrystals are not only a completely new tool for biologists. It is also potentially a method for the controlled destruction of cancer cells. And in this sense, an example of how a completely fundamental research, such as "blue sky research", can lead to the development of real applications. There are already a couple of startups that are trying to commercialize this technique.

Are these your startups?

One of them was created by my former postdoc, the other by my former student. I am involved in them only as an external advisor. That is, I know a little what is happening there. It's very interesting to see how research turns into real applications.

You are the head of the scientific advisory board of the Russian Quantum Center in Skolkovo, but you do not work in Russia yourself. Although many of your colleagues have just moved here. How did it happen?

When, in fact, Skolkovo was being created, they tried to offer me to create a large laboratory in Moscow. But I am not a supporter of building large empires at all, it seems to me that when there are huge groups in which hundreds of people work, then the leader can no longer really be engaged in science, he must first of all be a manager. And in my memory it never ended with something good.

My position was that if there is an active center in Moscow, in which good scientists will work, with their ideas, their groups, then I will be happy to interact and cooperate with them. I did not want to create my own laboratory in Moscow. But I said that I could help create an RCC, and, in particular, I promised to help find good peoplethat laboratories could create. Well, give advice on how to organize it.

What was created in less than two years, what I saw this summer, is already impressive. There are several theoretical and experimental groups that are already starting to do serious experiments. In the summer we published a joint article with Alexey Akimov's group in Science.

We talked with him about this publication. He now works in Skolkovo, but this installation, on which, in fact, the article was made, was collected in America.

This is true. Nevertheless, now there is already a scientific life here, there are already quite interesting work... I mean the groups of Akimov, Kalachevsky, Lvovsky, Zheltikov and Ustinov (Lenta.ru wrote about the creation of the latter in the laboratory).

I've spent quite a lot of time and effort helping to make this all work correctly. Now main questionWhat worries me is the question of what the future holds for the quantum center and similar projects in general. This question is important because ...

Because people want to plan their lives ...

Not only. The fact is that one Quantum Center cannot solve all problems. There must be at least some group of such institutions or centers. They must have at least some kind of long-term perspective - this is the only way to create a real scientific environment.

Personally, the most surprising thing about this story is how many of the world's leading scientists have agreed to help create this center. And they helped, and they helped completely free of charge. As far as I understand, this is a unique case for Russian reality. Maybe that's why it turned out to be something good to do.

MOSCOW, July 14- RIA News. Russian and American scientists working at Harvard have created and tested the world's first quantum computer, consisting of 51 qubits. The device is still the most complex computing system of its kind, said a professor at Harvard University, co-founder of the Russian Quantum Center (RQC) Mikhail Lukin.

The physicist announced this, speaking at the International Conference on Quantum Technologies ICQT-2017, which is held under the auspices of the RCC in Moscow. This achievement allowed Lukin's group to become a leader in the race to create a full-fledged quantum computer, which has been unofficially for several years between several groups of the world's leading physicists.

Quantum computers are special computing devices whose power grows exponentially due to the use of the laws of quantum mechanics in their work. All such devices consist of qubits - memory cells and at the same time primitive computational modules capable of storing a range of values \u200b\u200bbetween zero and one.

Today, there are two main approaches to the development of such devices - classical and adiabatic. Proponents of the first of them are trying to create a universal quantum computer, in which qubits would obey the rules by which ordinary digital devices work. Working with such a computing device, ideally, would not be very different from how engineers and programmers operate conventional computers. An adiabatic computer is easier to create, but it is closer in its principles of operation to analog computers of the early 20th century, and not to digital devices of our time.

Last year, several teams of scientists and engineers from the United States, Australia and a number of European countries announced that they were close to creating such a machine. The leader in this informal race was the team of John Martinis from Google, which is developing an unusual "hybrid" version of a universal quantum computer that combines elements of an analog and digital approach to such calculations.

Lukin and his colleagues at RCC and Harvard bypassed Martinis's group, which, as Martinis told RIA Novosti, is now working on a 22-qubit computing machine, using exotic "cold atoms" rather than superconductors, like scientists from Google.

As Russian and American scientists have found, a set of atoms held inside special laser "cells" and cooled to ultra-low temperatures can be used as qubits of a quantum computer, maintaining stability under a fairly wide range of conditions. This allowed physicists to create the largest quantum computer so far, of 51 qubits.

Using a set of similar qubits, Lukin's team has already solved several physics problems that are extremely difficult to simulate with "classical" supercomputers. For example, Russian and American scientists were able to calculate how a large cloud of interconnected particles behaves, to detect previously unknown effects arising inside it. It turned out that with damping of excitation in the system, some types of oscillations can remain and be held virtually indefinitely, which scientists did not suspect before.

To check the results of these calculations, Lukin and his colleagues had to develop a special algorithm that made it possible to carry out similar calculations in a very crude form on ordinary computers. The results were broadly consistent, confirming that the 51-qubit system of Harvard scientists works in practice.

In the near future, scientists intend to continue experiments with a quantum computer. Lukin does not exclude that his team will try to run Shor's famous quantum algorithm on him, which allows him to break most of the existing encryption systems based on the RSA algorithm. According to Lukin, an article with the first results of a quantum computer has already been accepted for publication in one of the peer-reviewed scientific journals.

On Friday morning, July 14, at the International Conference on Quantum Technologies, Mikhail Lukin, a co-founder of the Russian Quantum Center and a professor at Harvard University, spoke about the creation by his research group of a fully programmable 51-qubit quantum computer. At first glance, this result can be called a sudden breakthrough in this area - such giants as Google and IBM are just approaching the 50-qubit mark in a quantum computer. Just yesterday, a detailed description of the experiment appeared on the arXiv.org preprint server. Editorial staff N + 1 decided to figure out what happened and what to expect from the new quantum computer.

Briefly about quantum computers - universal and non-universal

What is a 51-qubit computer like?

Let's deal with the system created by physicists in new job... The role of qubits in it is played by cold rubidium atoms captured in an optical trap. The trap itself is an array of 101 optical tweezers (focused laser beam). The atom is held in an equilibrium position with tweezers due to the electric field gradient - it is attracted to the area with the maximum electric field strength, which is located at the focal point of the tweezers. Since all the tweezers are lined up, all the atom-qubits of the computer are also lined up.

"Zero" for each of the rubidium atoms is its basic, unexcited state. “One” is a specially prepared Rydberg state. This is such an excited state in which the outer electron of rubidium is very far from the nucleus (at the 50th, 100th, 1000th orbital), but still remains associated with it. Due to the large radius, Rydberg atoms begin to interact (repel) at much greater distances than ordinary ones. This repulsion makes it possible to transform a row of 51 rubidium atoms into a chain of strongly interacting particles.

To control the states of qubits, a separate laser system is used, capable of exciting them to the Rydberg state. The main and most important feature of the new computer is the ability to directly address each of the 51 qubits. There are also more complex ensembles of atoms in which entangled quantum states are observed (recently we have about 16 million atoms entangled by interaction with one photon), and quantum simulations have been performed on more than a hundred cold atoms. But in all these cases, scientists did not have the ability to precisely control the system. This is why the new system is called a fully programmable quantum computer.

Every computation on a quantum computer is, in a sense, a simulation of a real quantum system. The bulk of the new work is devoted to modeling a well-known quantum system - the Ising model. It describes a chain (in this case) of particles with nonzero spins (magnetic moments) interacting with their neighbors. The Ising model is often used to describe magnetism and magnetic transitions in solids.

The experiment was constructed as follows. First, the particles were cooled and captured in optical tweezers. This is a probabilistic process, so at first the array of particles was chaotic. Then, using a sequence of measurements and corrections, a defect-free array of more than 50 cold atoms in the ground unexcited state was created. At the next stage, the optical tweezers were turned off and at the same time turned on the system that excited the atoms to the Rydberg state. For some time, the system evolved under the influence of van der Waals forces - atoms occupied the most "convenient" positions for them, after which the tweezers were turned on again and the result of evolution was studied.

Physicists observed different evolutionary results depending on how close the cold atoms were before the exciting pulse. This is due to the fact that Rydberg atoms are capable of suppressing the excitation of neighbors to Rydberg states (due to strong repulsion). Scientists have observed systems in which atoms after evolution turned out to be ordered so that between each pair of neighboring Rydberg atoms there was strictly one, strictly two or strictly three ordinary atoms.

Interestingly, the formation of highly ordered structures after free evolution occurred with a very high probability - even in the case of an array of 51 cold atoms.

To see how the evolutionary process takes place, scientists turned on tweezers and "photographed" the system at different times. It turned out that in some cases the evolution to a state of equilibrium proceeded very slowly: the system oscillated for a long time between several states. This result can be confirmed by rough classical modeling involving the interaction between neighboring and following neighboring atoms in the analysis.

Is it helpful?

This is one of those cases where quantum modeling predicts a real new effect. It is worth noting that it is impossible to accurately simulate a system of 51 cold atoms using a classical computer. Just to describe all its possible states will require 2 51 bits of RAM (about a petabyte). This effect was confirmed only by rough modeling on a classical computer.

It is interesting that exactly the opposite situation arises in quantum chemical calculations - classical computers give only an approximate estimate of the properties for complex systemsspending huge computing resources on it. At the same time, direct analysis of these undoubtedly quantum systems gives an accurate result.

And what else is it useful for?

At the end of the preprint, the authors traditionally provide a list of areas in which new development can be useful. Some of them can be listed: the creation of superpositions consisting of a large number of particles, the study of topological states in spin systems. Physicists point out separately that the algorithm is well suited for solving problems of optimizing systems, the sizes of which obviously exceed the reach of conventional computers. These tasks include simulation of chemical reactions and training.

The system created by Mikhail Lukin and his colleagues works now as a quantum simulator - it simulates systems similar to itself. However, it is worth noting that physicists have already managed to create logical CNOT-valves used to create entanglement on individual pairs of Rydberg atoms. Therefore, we can say that some of the simplest algorithms can be implemented in the new system (for example, Deutsch's algorithm, or Shor's algorithm for very small numbers). However, at this stage, these algorithms will not be useful.

Mikhail Lukin (left) and John Martinis (right) - head of the 49-qubit quantum computer team at Google

Russian quantum center

In a sense, the new device is already capable of solving problems that are inaccessible to classical computers - it cannot be accurately simulated by conventional computers. But it is too early to talk about useful quantum superiority, which is already useful in applied problems. Many scientists point out that the race for quantum supremacy now does not carry anything useful from the point of view of applied computational problems.

It is worth noting that experiments with atoms in optical lattices already several years ago surpassed the limits of accurate modeling by classical computers. They use dozens of interconnected particles. For example, with their help, quantum cooperative phenomena related to superfluidity and superconductivity. Is this quantum superiority?

Vladimir Korolev