Scientific research on quantum computing

Main article: Quantum computers and quantum communication

Research in Russia

Main article: Quantum computers and networks in Russia

2024: A revolutionary method of creating a quantum computer has been developed

On March 27, 2024, British researchers from University College London announced the development of a new method for creating quantum computers. The proposed approach is expected to design scalable quantum systems that can solve the world's most complex problems.

One approach to creating a quantum computer is to accurately position individual "impurity" atoms in a silicon crystal, which allows them to be manipulated by quantum properties to form qubits - quantum bits. The advantage of this method is the use of silicon microelectronics technologies. Phosphorus is usually used as the impurity atoms, but in this case the positioning accuracy is about 70%. British researchers propose replacing phosphorus with arsenic: this, it is claimed, makes it possible to place atoms with almost 100% accuracy.

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Pixabay

To accurately position and manipulate individual atoms, the project participants used a special microscope. They formed an array of single arsenic atoms in the form of a 2 × 2 matrix that functions as a qubit.

Based on our calculations, we concluded that individual arsenic atoms can be placed more reliably than phosphorus atoms, and we were able to successfully demonstrate this. We can place arsenic atoms with an accuracy of 97%, but in the near future the indicator may be increased to 100%, says Dr. Taylor Stock, one of the authors of the study.

The proposed method in its original form requires manual positioning of each atom. In the future, this process is planned to be automated, which will allow the construction of universal quantum computers, numbering millions or even billions of qubits.^[1]

2022

Universal Quantum Computer Architecture Created

On October 28, 2022, the University of Innsbruck in Austria announced the development of a new architecture for universal quantum computers of the next generation. The proposed model is expected to improve the performance and reliability of such computing systems.

Quantum computers work with so-called qubits, or quantum bits. They can simultaneously take the value of logical zero and logical one. Thanks to this, as the number of qubits increases, the speed grows exponentially. But there are also serious difficulties. Since quantum information cannot be copied, it cannot be stored in memory, as in a classical computer. And therefore, all qubits in a quantum computing system must be able to interact with each other. In addition, quantum computers are very sensitive to interference.

New universal quantum computer architecture created

In 2015, researchers Wolfgang Lechner, Philipp Hauke and Peter Zoller proposed a new architecture for a quantum computer, which is now named after them - LHZ. The idea is that physical qubits do not encode logical bits, but relative consistency. This means that not all qubits must interact with each other. Now scientists have shown that the proposed concept can be used, among other things, in universal quantum computers.

The new architecture also involves effective hardware error correction. With the usual approach, significant resources must be allocated to protect quantum information, which significantly increases the number of qubits required. The proposed model provides for the use of two-stage correction, in which errors of one type are eliminated at the hardware level, and the other - at the software level.

The developed technology will speed up complex quantum calculations of a certain type, for example, Fourier transformations and the execution of the Shore algorithm.^[2]

Technology created to scale quantum computers to millions of qubits

At the end of September 2022, information appeared that the German researchers from Juelich Research Center the Rhine-Westphalian Technical University from Aachen created technology to scale quantum computers to millions. qubits

In order for quantum computers to be useful in practical application, millions of quantum bits are needed. Scalability is one of the biggest challenges for September 2022 when developing future devices. One problem is that qubits have to be very close together on a chip to connect them together. Researchers have moved closer to solving this problem by a significant step. They managed to transfer electrons, carriers of quantum information, to several micrometers on a quantum chip. Their quantum bus could be a key component that makes it possible to make a jump to millions of qubits.

Scientists create technology to scale quantum computers to millions of qubits

Quantum computers could potentially vastly outperform conventional computers when performing certain tasks. But there is still a long way to go before they can help solve real problems. Many applications require quantum processors with millions of quantum bits.

At some point, the number of signal lines becomes a bottleneck. The lines take up too much space compared to the size of tiny qubits. And a quantum chip cannot have millions of inputs and outputs - in a modern classical chip there are only about 2 thousand of them. Scientists have been conducting research for several years to find a solution to this problem. Their common goal is to integrate parts of the control electronics directly into the chip. Manufacturing processes largely coincide with those of conventional silicon processors. This is considered an advantage when it comes to the realization of a very large number of qubits.

Therefore, in order to spread qubits, in 2018, scientists put forward the idea of ​ ​ a quantum shuttle. This component should allow the exchange of quantum information between qubits that are at a great distance from each other.

As a next step, physicists now want to show that qubit information encoded in an electron is not lost during transportation. Theoretical calculations have already shown that this is possible in silicon in certain speed ranges. Thus, the quantum bus paves the way for a scalable quantum computer architecture that can also serve as the basis for several million qubits.^[3]

Scientists achieve more than 99% quantum accuracy with silicon

On April 11, 2022, it became known that a study by Princeton University scientists paves the way for the use of silicon-based technologies in quantum computing and will contribute to increasing their use as an alternative to other quantum computing technologies such as superconductors and captured ions.

Illustration: securitylab.ru

During the study, scientists were able to achieve an accuracy level of more than 99.8% using a two-cube silicon quantum device. The precision of being able qubit (the smallest unit information in) quantum computer to perform error-free operations is key for practical high-performance quantum computing.

Researchers around the world are trying to figure out which technologies, superconducting qubits, trapped ions or silicon spin qubits, are most suited to the role of basic elements of quantum computing. And, importantly, experts are studying which technologies are most suitable for commercial use.

With the help of a silicon device, the so-called double quantum dot, Princeton University scientists were able to capture two electrons and force them to interact with each other. Thus, they managed to use the spin state of each electron as a qubit, and the interaction between the electrons allowed these qubits to entangle.

Qubit is a kind of quantum bit that is the smallest unit of data in computer technology. Like a bit, a qubit is encoded with information that may have a value of zero or one.

However, unlike a bit, a qubit can use the principles of quantum mechanics, which allows it to perform tasks that a regular bit cannot. For example, it can have a superposition of zeros and ones, that is, it can be both zero and one. Thanks to this, quantum computers are more productive than conventional ones.

In spin qubits, "spin" means the momentum of an electron. This is a quantum property, manifested in the form of a tiny magnetic dipole that can be used to encode information. An example is a compass arrow indicating the south and north poles and rotating according to the Earth's magnetic field.

Spin is a property of an electron used in silicon-based quantum devices. By comparison, conventional computers operate by controlling the negative charge of an electron.

In general, silicon spin qubits are preferable to other types of qubits.

"The idea is that each system should scale to multiple qubits. At the beginning of April 2022, other qubit systems have real physical limitations of scalability. Size can be a real problem for these systems. There are not many places where all this can be squeezed in, "- study leader Adam Mills explained.

Silicon spin qubits are composed of single electrons and are extremely small. The device used in the study had a diameter of only 100 nm, while the diameter of conventional superconducting qubits exceeds 300 microns, so they cannot fit a lot on the chip.

Another feature of silicon spin qubits is that conventional electronics are based on silicon technology. According to the authors of the study, only a solid-state system that can be scaled using the standard semiconductor industry is suitable for creating a million or ten million qubits for practical application.^[4]

2021

Honda Research Institute has developed technology for synthesizing nano-materials

On December 27, 2021, the company Honda announced that scientists Honda Research Institute located in (USA Honda Research Institute USA, Inc. - HRI-US), using, synthesis method created atomically thin "nano-tapes." This achievement may affect the future development of quantum - the electronic engineers field of physics, which studies the influence of quantum mechanics on the behavior of electrons in matter. Synthesis technology could allow for the creation of two-dimensional materials that would enable the application of quantum technologies, particularly quantum computing and sensing, at temperatures higher than those required for the materials used. More. here

Launched a quantum computer with qubits having a "third state"

In December 2021, Rigetti Computing announced the Aspen-M quantum computer equipped with an 80-qubit processor, which includes two units of 40 superconducting qubits. Read more here.

Experts have bypassed the main obstacle to creating a quantum computer

Experts have bypassed the main obstacle to creating a quantum computer. This became known on November 16, 2021. In particular, the researchers managed to simultaneously control several spin qubits on a single quantum chip.

One of the obstacles in creating a quantum computer is the inability to simultaneously control many qubits.

Controlling one qubit usually negatively affects the other due to simultaneous exposure to control pulses.

Unlike companies like Google and IBM working on superconducting technologies for quantum processors, the researchers focused on semiconductor or so-called spin qubits.

In general terms, spin qubits consist of electron spins trapped in semiconductor nanostructures called quantum dots, so that individual spin states can be controlled and entangled with each other, the researchers explained.

Spin qubits can retain their quantum states for a long time, potentially allowing them to make faster and more accurate calculations compared to other types of platforms. Since spin qubits are very small, a lot of them fit on one chip. This is of great importance, since the more qubits, the more processing power.

The researchers were able to create and manage four qubits on a single chip with rows of 2×2. One of their main tasks was to force the Qubits to communicate with each other.

Now that we have good qubits, you need to combine them into a scheme that can control many qubits, but at the same time complex enough to correct errors in quantum calculations. Until now, studies in the field of spin qubits have made it possible to create schemes with rows of qubits of 2×2 and 3×3. The problem is that you can only manage one qubit at a time, the researchers explained.

The quantum circuit created by the researchers is made of a semiconductor substance called gallium arsenide, and its size does not exceed the size of the microbe. However, the main thing is that the chip allowed experts to simultaneously control and measure all qubits.

In quantum computing, it is very important to control and measure simultaneously. Qubits are very sensitive, and if measured one by one, even tiny ambient noise can disrupt quantum information on the system.

Another significant obstacle is that all 48 of the chip's control electrodes need to be manually tuned and kept tuned. It takes a lot of time for a person, so a specialist is looking for ways to use optimization algorithms and machine learning to automate this process^[5].

Scientists find 'missing piece of puzzle' in development of quantum computers

Scientists have found the "missing piece of the puzzle" in the development of quantum computers. This became known on August 16, 2021.

The discovery of scientists will be a real breakthrough in the creation of quantum processors worth millions of qubits.

Vaccine and drug development, artificial intelligence, transport and logistics, the science of climate change - all these areas will take a huge step forward when a full-scale quantum computer appears.

As of August 2021, quantum processors, which are the main components of quantum computers, are relatively small (less than 100 qubits). Although the first quantum processors played a decisive role in demonstrating the potential of quantum computing, processors with more than 1 million qubits are needed for application in globally significant areas.

In the course of the study, specialists from the University of South Wales (Australia) managed to get closer to creating such a powerful quantum processor. According to scientists, they discovered the "missing piece of the puzzle" to improve the architecture of quantum chips.

The problem with qubit-based quantum computing approaches is that qubits are controlled by wires that take up space on the chip and generate heat.

{{quote 'For August 2021, the management of electronic spin qubits depends on the generation of microwave magnetic fields by passing current through a wire near the qubit. This creates some real problems if we want to scale to the millions of qubits that a quantum computer will need to solve globally significant problems, such as the development of new vaccines, "explained study leader Dr. Jarryd Pla. }}

Led by Pla, the team of researchers found an interesting solution to this problem and suggested not using wires, but generating a magnetic field over the entire chip.

First, the researchers removed the wire near the qubits and decided to generate microwave magnetic fields throughout the system.

That is, in fact, we could generate control fields for four million qubits. There are two key changes here. The first is that we didn't have to use a lot of electricity to get a strong field, which means we didn't generate a lot of heat. The second innovation is that the field is homogeneous throughout the chip, so the same level of control applies to all millions of qubits, "Pla explained.

The researchers developed a prototype of the technology and tested it on qubits.

We were unusually happy when the experiment was a success. The problem of controlling millions of qubits has bothered me for a very long time, as it was the main obstacle to the creation of a full-scale quantum computer, said University of South Wales professor Andrew Dzurak.

Now that this obstacle has been removed, the next step should be to use this hike to create a simpler silicon quantum processor. According to the researchers, this will simplify the production of devices with a large number of qubits in the future^[6].

Quantum processor turned into a time crystal with ordered eigenstates

On August 4, 2021, it became known that researchers from Google and several the American universities reported the creation of a true discrete time crystal with ordered eigenstates. This state was obtained on qubits of quantum from processor Sycamore Google. Scientists demonstrated that the time crystal they created met a number of criteria that allowed it to be considered a true time crystal. The preprint of the article is published on arXiv.org. More. here

Intel and QuTech have made a breakthrough in solving the problem of quantum interconnections

Intel and QuTech - a joint project of the Delft University of Technology and the Organization for Applied Scientific Research of the Netherlands - on May 14, 2021 announced the publication of key results of research in the field of quantum computing aimed at eliminating the "bottleneck of interconnections" between quantum chips that are located in cryogenic dissolution refrigerators, and complex electronics for controlling qubits, which operates at room temperature. The innovations, presented in the industry scientific journal Nature, mark an important stage in solving one of the major challenges of scaling quantum computing with the Intel Horse Ridge cryogenic controller chip. Read more here.

Scientists carried out quantum teleportation at 44 km

On January 5, 2021, it became known that scientists from the Fermi National Accelerator Laboratory, a national laboratory of the US Department of Energy associated with the University of Chicago, together with partners from five institutions, took a significant step towards the implementation of the quantum Internet: they carried out quantum teleportation.

In particular, the researchers managed to transfer the quantum state by 44 km with an accuracy of more than 90% over fiber-optic networks similar to those that form the basis of the existing Internet.

We are delighted with these results. This is a key achievement towards creating a technology that will redefine the development of global communication, says physicist Panagiotis Spenzuris of Fermilab Particle Physics and Accelerator Laboratory, based at the California Institute of Technology (Caltech).

Both the accuracy of data transmission and the distance of transmission are crucial when it comes to creating a real, working quantum internet^[7].

2020

Created material that will make a quantum computer resistant to interference

An ultra-thin material that allows you to reproduce quasiparticles on the basis of which a quantum computer that is resistant to interference can be built has been developed by an international group of scientists at the University of Aalto (Finland), on December 18, 2020, the HPCwire portal specializing in supercomputers^[8]

Qubits, which are the basis of a quantum computer and are used for ultra-high-speed computing, have a very high sensitivity to noise and interference created by surrounding materials. This influence leads to errors in calculations.

A new type of qubit - topological qubits that can be created using zero-energy Majorana states (MZMs) - groups of electrons bound in a certain way and behaving like a particle called the Majorana fermion can help solve this problem. Its existence was suggested by the Italian physicist Ettore Maiorana in the 1930s.

"The topological quantum computer is based on topological qubits, which are supposed to be much more noise-resistant than other qubits. However, topological qubits have not yet been obtained in the laboratory, "explained the lead researcher of the project, Professor Peter Liljeroth.

To create MZM, researchers had to create a two-dimensional material with the property of topological superconductivity. This phenomenon occurs at the boundary of the magnetic electric insulator and the superconductor.

Having grown islands of magnetic material one atom thick on top of a superconducting crystal and measured the obtained properties using a scanning tunneling microscope, scientists came to the conclusion that they created MZM.

In addition, they confirmed their findings through computer simulations. As the next stage of their work, the researchers see the creation of a topological qubit.

A quantum device SQUID was created in Los Alamos

On August 1, 2020, it became known that scientists from the National Laboratory in Los Alamos (DOE/Los Alamos National Laboratory) created a device for carrying out changes on the verge of quantum laws and realities. The development is based on the behavior of clouds of "ultra-cold" atoms.

In the created installation, atoms cooled to ultra-low temperatures fall under the radiation of one, laser shining in a certain plane. A second angled laser "draws" patterns on the beam surface of the first that direct the ultracold atoms into two semicircles separated by small gaps known as Josephson transitions.

The installation, called Superconducting QUantum Interference Device (SQUID), can be used as part of a quantum computer and as an ultra-sensitive sensor to detect the slightest rotation. As SQUID rotates and Josephson transitions move towards each other, the number of atoms in the semicircles changes as a result of quantum mechanical interference of currents through Josephson transitions. By counting the atoms in each part of the semicircle, the researchers can very accurately determine the rotational speed of the system.

In the device we created, quantum interference in electron currents can be used to create one of the most sensitive magnetic field detectors, "said Changhyun Ryu, a physicist from the Physics and Materials Application group at Los Alamos National Laboratory. - In the instrument, we use neutral atoms, not charged electrons, and instead of reacting to magnetic fields, our system is sensitive to mechanical rotation.

In addition to the motion sensor, SQUID is supposed to be used as an additional computational component of modern quantum computers.

We are talking about creating the first prototype of a quantum device (SQUID), which has a long way to go before it can become part of quantum computers or conventional devices and gadgets. But, since we are talking about studying patterns on the verge of quantum and ordinary laws of physics, researchers predict good prospects for this direction^[9].

In China, a quantum communication session was held at a distance of 1120 kilometers

On June 16, 2020, it became known that a Chinese group of physicists, who had previously demonstrated the quantum distribution of the key between the satellite and the observatory, conducted a quantum cryptography session using entanglement between two ground stations at a distance of 1120 kilometers. The work is presented in the journal Nature.

Quantum key distribution is theoretically an absolutely secure way to exchange secret keys between remote users. The method is based on the fundamental laws of quantum physics: the process of measuring a quantum system changes its state. An attacker who tries to steal a key must somehow measure it, but the measurement introduces anomalies that legitimate protocol participants also see. Thus, users can reveal and check part of the received key and make sure that no one but themselves has measured it.

Experimental key distribution was demonstrated in the laboratory using 421 kilometer long fiber. Earlier, outside the laboratory, Chinese scientists led by Professor Jian-Wei Pan managed to transfer the key from the satellite to the ground station at a distance of 1200 kilometers, which is a record for June 2020.

However, real-world cryptography based on quantum key distribution targets users on Earth. When using quantum repeaters, you can create a network of nodes that are up to 100 kilometers from each other. Unfortunately, each repeater carries a security risk and can be attacked by an attacker. Another way of distributing the key over long distances involves satellite communication using quantum entanglement.

The same group of Chinese scientists led by Professor Pan conducted a quantum key distribution session based on entanglement between two ground stations, the distance between which was 1120 kilometers. Entangled pairs of photons were separated and sent via communication channels from the Micius satellite to two ground-based observatories in Delingha and Nanshan.

An important engineering achievement, without which the experiment would not have taken place, is the creation of a highly efficient telescope and processing optics. Scientists have managed to increase the efficiency of collecting data from each satellite-Earth communication channel by about half compared to the previous experiment. The best data were obtained on a clear night and without fog, when the atmosphere had the highest transmittance.

Distance between satellite and ground observatories and attenuation as a function of time. Source: Juan Yin, et al./Nature, 2020

To test the constructed cryptographic system, to begin with, physicists verified entanglements using the Clauser-Horn-Shimoni-Holt (CHSH) test, which was carried out on satellite-derived photons. The test confirmed the presence of quantum correlations with an accuracy of eight standard deviations.

To directly distribute the key, the scientists used the BBM92 protocol, in which two users receive one photon each from a stream of entangled pairs of photons. They then randomly select the basis for measuring each photon, obtain the measurement result, and select only those outcomes where they measured in the same basis. The bases are negotiated via a classical communication channel. Then they use part of the key to estimate the error rate, which indicates the presence of eavesdropping.

Quantum Key Distribution Protocol Based on BBM92 Entanglement, Source: wikipedia.org

Physicists have made sure that the resulting keys are safe - ground receivers are immune to noise errors, that is, the occurrence of anomalies clearly indicates eavesdropping. The authors note that the results are an important step towards absolutely reliable cryptography for intercontinental remote users.

Earlier, the same group of scientists created entanglement at a distance of more than 50 kilometers using fiber between two laboratories in Hefei. While China is ahead of the planet, we are gradually joining the quantum communications race: in 2016, a quantum communications banking line was created in Russia, and in 2017, scientists from Moscow State University presented a quantum phone. As of June 2020, the Russian Quantum Center, Sberbank and the Skolkovo Foundation are building a quantum secure communication line with a total length of about 250 kilometers on the territory of the innovation center in Russia^[10].

2019: First quantum teleportation performed

On December 27, 2019, it became known that scientists were able to successfully transfer information from one chip to another using quantum entanglement.

According to experts, information processing technologies using the laws of quantum physics will have a huge impact on modern society. For example, quantum computers will be able to solve problems that even the most powerful modern supercomputers are unable to cope with, and the quantum Internet will protect the data transmitted in it from cyber attacks. However, these technologies rely on so-called "quantum information" encrypted in quantum particles, which are extremely difficult to measure and control.

As reported, scientists at the University of Bristol (UK), together with colleagues from the Danish Technical University, have created a chip capable of generating and manipulating individual particles of light in programmable nanochemes. The chip can encrypt information in light particles generated in nanochemes and process "quantum information" with high performance and very low noise.

The real breakthrough was an experiment in which specialists from the Laboratory of Quantum Engineering at the University of Bristol for the first time in the world successfully performed quantum teleportation of information from one chip to another. It is quantum teleportation that is the cornerstone of quantum communications and computing, scientists note.

Quantum teleportation involves transferring the quantum state of a particle from one place to another using quantum entanglement (a phenomenon in which the quantum states of several objects turn out to be interdependent). Teleportation is needed not only for quantum communications, but is also the basis for optical quantum computing.

Establishing a link between the two chips by creating quantum entanglement proved to be a daunting task for scientists. However, they managed to ensure that the photons on both chips came to the same quantum state. The main thing was the teleportation experiment, during which the individual quantum state of the particle after quantum measurement was transmitted from one chip to another^[11] was^[12]

2018: Australians create quantum 'processor' based on phosphorus atom

In March 2018, it became known that the UNSW Sydney group of scientists (University of New South Wales) Australia from under the guidance of Professor Michelle Simmons for the first time in the world created a quantum "processor" based on a phosphorus atom, in practice showing that qubits (single-atom quantum physical bits) can interact with each other already at a distance of 16 nanometers from each other, demonstrating the so-called "quantum entanglement" phenomenon. However, the principle of operation of the presented device and modern computer processors ones differ dramatically.

According to Michelle Simmons, a quantum computer based on logical qubits will surpass any traditional computer. Photo: CNews.ru

As you know, in modern mass computing, bits can take only two values: "1" or "0," while quantum bits, or qubits, can also be in intermediate states. In this case, changing one qubit always affects the state of the "neighbors" associated with it. This phenomenon is called quantum entanglement and allows you to build a logical qubit - a group of physical qubits connected to each other. The "processor," obtained by connecting several logical qubits, can provide the highest performance characteristic of quantum computers, and will also allow you to find and correct errors arising in physical qubits under the influence of external factors.

It was previously believed that the interaction between physical qubits is possible at a distance of 20 nanometers. However, Australian scientists were able to achieve the formation of a logical qubit at a distance of 16 nanometers between phosphorus atoms. According to Michelle Simmons, a quantum computer consisting of 30 such qubits will surpass any existing traditional computers, and a 300-qubit copy will overtake all existing computers in the world combined.

The findings are expected to improve the existing model and accelerate the emergence of prototype devices based on monatomic phosphorus qubits. In particular, a group of Australian scientists expects to get the current model of 10 related qubits within the next 5 years.^[13]

2017

Scientists in the United States have created a 53-qubit quantum computer

In early December 2017, it became known that scientists from the University of Maryland at College Park (UMD) and the National Institute of Standards and Technology (NIST) USA created a model of a quantum system consisting of 53 qubits, which are used to simulate quantum matter.

The UMD-NIST simulator was created by deploying 53 individual ytterbium ions held in place by gilded electrodes

According to the authors of the project, the UMD-NIST simulator was created by deploying 53 separate ytterbium ions held in place by gilded "razor-sharp" electrodes. At the same time, the number of atoms, according to scientists, can be further increased, which, in turn, will lead to an increase in the number of qubits.

UMD-NIST can operate at room temperature and normal atmospheric pressure - this property is typical for all qubit systems based on ions. In the presented model, qubits are reliably isolated from environmental influences.

Each ion qubit is a stable atomic clock that can be fully reproduced, "said Professor of Physics Christopher Monroe, UMD team leader. They are effectively coupled together with external laser beams. This means that the same device can be reprogrammed and reconfigured externally to adapt to any type of quantum simulation or future quantum computer application that emerges.

Modern transistor computers experience difficulties when dealing with more than twenty interacting quantum objects in connection with the phenomenon of quantum magnetism - because of it, interaction can lead to magnetic alignment or mixing of competing interests. In particular, 53 interacting quantum magnets create about quadrillion possible magnetic configurations, and this amount doubles with the addition of a new magnet, scientists say.

According to the lead author of the study, Jiehang Zhang, it will soon be possible to control 100 or more qubits. Zhang and colleagues published the results of their research in the journal Nature.^[14]

Scientists from Russia and the United States have created a 51-qubit quantum computer

In July 2017, it became known that a group of scientists from Harvard University and the Massachusetts Institute of Technology, led by Mikhail Lukin, a professor of physics from Harvard and co-founder of the Russian Quantum Center, created and tested a programmable quantum computer based on 51 qubits, thus becoming the leader among participants in the "quantum race."

According to Mikhail Lukin, he and his colleagues used qubits based on "cold atoms" that were held by optical "tweezers" - specially organized laser beams. Most modern quantum computers rely on the use of superconducting qubits based on Josephson contacts.

A group of American scientists led by a Russian physicist has created a 51-qubit quantum computer. Photo: indicator.ru

Lukin and his colleagues managed to solve with the help of their quantum computer the problem of modeling the behavior of quantum systems from many particles, which was practically unsolvable with the help of classical computers. Moreover, as a result, they were able to predict several previously unknown effects, which were then tested using conventional computers. As a result, scientists managed to find a way to approximate calculations that helped to get a similar result on a classical computer.

In the near future, scientists intend to continue experiments with a quantum computer, perhaps they will try to use this system to test quantum optimization algorithms that allow them to surpass existing computers.

Quantum calculator 'overtook' humanity's first computer

Physicists from the Chinese University of Science and Technology (Shanghai), the University of Würzburg and St. Andrews University have improved the work of one of the types of quantum computers - the boson sampler. According to the authors, the device now outperforms ENIAC (the first universal classic computer) by about 220 times in a specific class of tasks. Scientists believe that boson samplers will be able to demonstrate the superiority of quantum systems over modern classical computers in the near future. The study is published in the journal Nature Photonics, briefly reported by Xinhua^[15].

It is believed that quantum computers are able to significantly surpass ordinary, classical computers - this will allow solving problems previously inaccessible to scientists. For example, computing the properties of various molecules is very difficult for computers - they are based on the laws of quantum mechanics. However, the superiority of quantum computers over traditional systems has only been partially demonstrated. So, at the end of 2015, Google showed that D-Wave quantum annealing systems can repeatedly overtake computers when solving specially created optimization problems.

For quantum computers, performance and acceleration, compared to classical systems, directly depends on the number of qubits - quantum bits that exist in the superposition of the "zero" and "one" states. Scientists expect that quantum computers will need about 50 qubits to achieve superiority - now in laboratory devices the number of qubits does not exceed 10-15. However, in some special quantum computers, fewer controlled quantum particles can be dispensed with - for example, 20-30 photons are enough for boson samplers.

Bosonic samplers are computers with which you can quickly build a distribution of random variables. In them, several photons move along branching and intersecting optical paths, interfering with each other. You can read more about them in the news about the previous result of this scientific group - the entanglement of 10 photons for the sampler at once. Among the applications of the device is the calculation of the oscillatory spectra of molecules, necessary, for example, for the analysis of the chemical composition of materials

In addition to the number of photons involved in the operation of the sampler, the speed of its operation is also influenced by the frequency of reading photon states. In the new work, scientists were able to significantly increase it - about 24 thousand times compared to previous experiments. According to the authors, the key to achieving the result was the development of high-quality single-photon sources based on semiconductor nanocrystals. These modules are excited by picosecond laser pulses (lasting a trillionth of a second) and generate 25.6 million polarized single photons per second, the best indicator of brightness in the world.

As an optical table with different optical paths for photons, the authors used a programmable integrated optical circuit - it determined the distribution that the sampler generated. It included 36 beam splitters - translucent mirrors. Scientists tested the operation of the device with three, four and five photons creating the distribution. For three-photon devices, the generation frequency was about five thousand hertz (in previous works this value did not exceed two tenths of hertz). According to the authors, if you use single-photon detectors on superconducting nanonets in the installation, then this value can be further increased by 26 times.

With the increasing speed of reading and generating distributions, physicists have the opportunity to use more photons in the boson sampler. So, if in the previous work with a 10-photon sampler the generation frequency was 11 pieces per hour, then in a new installation the frequency of the same order can be achieved already with 14 photons. According to the authors, if we improve the scheme for generating single photons, accelerating their generation by almost 75 percent, then we can expect a reading speed of 20-photon events of 130 pieces per hour.

Physicists compare the performance of the new system with the first human-made computer, ENIAC. Scientists estimate that the created three-photon sampling scheme exceeds the speed of solving the same problem with ENIAC by 220 times. The authors claim to have created the first single photon computer that was able to overtake a classic computer.

2016

Scientists were able to transmit information using a single photon

Princeton University scientists have developed a device that allows a single electron to transmit quantum information to a photon. The study was published in late 2016 in the journal Science and could be a real breakthrough in the field of quantum computer technology^[16].

"We now have the ability to directly transmit the quantum state to a photon. Previously, this was impossible to do using semiconductor devices, since the quantum state was lost before it could transmit information, "explained Princeton University scientist Xiao Mi

See more - Photonic Integrated Circuit (FIS)

Compact quantum computer created

A group of scientists from the University of Maryland at College Park in the United States has created a compact quantum computer that can be reprogrammed,^[17] reports^[18]. The machine consists of five qubits.

The publication reports that the qubits are captured using an ion trap and can be controlled by a laser. In addition to being computational elements, qubits are also memory cells at the same time.

Scientists have shown that the created computer is capable of performing various quantum algorithms. Moreover, when moving from one algorithm to another, there is no need to make changes to the design of the system.

The creators claim that the accuracy of calculations of a quantum computer is 98 percent, which is a very high figure. According to experts, in the future it can be scaled by connecting a similar design, which will allow performing more complex tasks.

2013: Challenges in Building a Quantum Computer

There were many problems in the way of creating a quantum computer in 2013. First of all, it was necessary to learn how to bring qubits to certain initial states, combine them into entangled systems, isolate these systems from the influence of external interference, and read the results of quantum calculation.

Also, developers of a quantum computer will have to choose the optimal element base for the manufacture of qubits. There are several competing approaches, and one of them is superconducting qubits with Josephson transitions, similar to the first computer information carriers - ferrite rings. True, qubits are about a thousand times smaller than the magnetic bits of the era that preceded the appearance of integrated circuits. Developments in this area are occupied by many foreign institutes and laboratories of large companies. Having a working prototype of a universal quantum computer opens up huge opportunities in the development of new materials, decoding the most complex codes, modeling complex systems, creating universal artificial intelligence and many other areas. With the advent of qubit state reading technology, Russia could also get involved in this promising work on the cutting edge of science and computer technology.

In essence, quantum computing systems represent the pinnacle of the development of parallel computing. These systems are capable of solving the most complex computing problems that are not available to traditional computers. In particular, quantum computers allow modeling of natural processes in the interests of specialists in chemistry, materials science and molecular physics. With the advent of quantum computers, scientists will finally be able to create a catalyst for absorbing carbon dioxide from the atmosphere, superconductors capable of operating at room temperature, and new drugs for so far incurable diseases.

However, despite significant progress in research and active discussions about the success of scientists, the problem of overcoming natural obstacles to the creation of viable large-scale quantum systems capable of demonstrating the required computational accuracy remains relevant. One such obstacle is the problem of producing homogeneous and stable qubits (basic elements of quantum computing systems).

Qubits require extremely gentle treatment. Random noise and even random observation of a qubit can lead to data loss. For the stable operation of qubits, an extremely low ambient temperature is necessary - at the level of 20 milliKelvin, which is 250 times colder than the temperature of outer space. Such a temperature regime presents the strictest requirements for the design of bodies of quantum systems, which include qubits. In an effort to realize the full potential of quantum computing systems, Intel experts from the Component Research Group (CR) in Oregon and the Experimental Production Complex (ATTD) in Arizona are working hard to create innovative architectures and enclosures to meet the unique requirements and tasks of quantum computing systems.

2012: Created a quantum computer inside a diamond

Diamonds or diamonds - an integral part of many movies - can now become the main component of quantum computers. On April 5, 2012, the world famous journal Nature published an article by a group of scientists from various countries who managed to build a workable quantum computer inside the diamond. Unlike the precursor samples, it first managed to solve the problem of unstable coherence.

As stated in the article, scientists involved natural defects in the crystal lattice of diamond to encode information in the form of quantum bits or qubits. Unlike the usual bits in modern computers, qubits are able to be not only in states 0 or 1, but also in a superposition (in other words, simultaneously in states 0 and 1). The latter variant was until recently considered unstable, and the computational elements of previously existing prototypes of quantum computers tended to quickly return from superposition to classical states. The consequence of the so-called unstable coherence is noise and errors, which lead to a sharp decrease in the reliability of such devices.

In other words, the negative effect indicated above should be sought to minimize at all costs. The use of a solid crystal (in this case diamond) as the working medium of a quantum computer has made it possible to achieve more stable superposition states. The reason lies on the surface - the spin of the nucleus is more stable than the spin of the electron, which was focused on earlier. According to Professor Daniel Lidar, who simultaneously holds positions at USC Viterbi School of Engineering and USC Dornsife College of Letters, Arts and Sciences, the characteristic time for switching states in the cores is measured in milliseconds, and this is a lot. Electrons are much faster, but the state of superposition in computer systems based on them is much easier to destroy.

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