A quantum computer is a computing device that uses the phenomena of quantum superposition and quantum entanglement to transmit and process data. A full-fledged universal quantum computer is still a hypothetical device, the very possibility of constructing which is associated with a serious development of quantum theory in the field of many particles and complex experiments; developments in this area are associated with the latest discoveries and achievements of modern physics. At the moment, only a few experimental systems have been practically implemented that execute a fixed algorithm of low complexity.
According to the editors of Science Alert, a group of specialists from the University of Vienna was able to develop the first-ever quantum router and even conducted the first tests of the new device. This is the first device that can not only receive entangled photons, but also transmit them. In addition, the scheme used in the router can form the basis for the creation of the quantum Internet.
L. Fedichkin, PhD in Physics and Mathematics (Institute of Physics and Technology of the Russian Academy of Sciences.
Using the laws of quantum mechanics, you can create a fundamentally new type of computers that will allow you to solve some problems that are inaccessible even to the most powerful modern supercomputers. The speed of many complex calculations will skyrocket; messages sent over the lines of quantum communication can neither be intercepted nor copied. Prototypes of these quantum computers of the future have already been created.
American mathematician and physicist of Hungarian descent Johann von Neumann (1903-1957).
American theoretical physicist Richard Phillips Feynman (1918-1988).
American mathematician Peter Shor, an expert in the field of quantum computing. Proposed a quantum algorithm for fast factorization of large numbers.
Quantum bit, or qubit. The states and correspond, for example, to the direction of the spin of an atomic nucleus up or down.
Quantum register is a string of quantum bits. One- or two-qubit quantum gates perform logical operations on qubits.
INTRODUCTION, OR A LITTLE ABOUT THE PROTECTION OF INFORMATION
Which software do you think has the most licenses sold in the world? I will not dare to insist that I know the correct answer, but I definitely know one wrong one: this notany version of Microsoft Windows. The most common operating system is outpaced by a modest product from RSA Data Security, Inc. - a program that implements the RSA public key encryption algorithm, named after its authors - American mathematicians Rivest, Shamir and Adelman.
The fact is that RSA is built into most operating systems sold, as well as many other applications used in various devices - from smart cards to cell phones. In particular, it is also available in Microsoft Windows, which means that it is wider than this popular operating system. To detect traces of RSA, for example, in the Internet Explorer browser (a program for viewing www-pages on the Internet), just open the Help menu, enter the About Internet Explorer submenu and view a list of used products of other companies. Another common browser, Netscape Navigator, also uses the RSA algorithm. In general, it is difficult to find a well-known high-tech firm that would not buy a license for this program. Today RSA Data Security, Inc. has already sold over 450 million (!) licenses.
Why is RSA so important?
Imagine that you need to quickly exchange a message with a person far away. Thanks to the development of the Internet, such an exchange has become available to most people today - you just need to have a computer with a modem or network card. Naturally, when exchanging information over the network, you would like to keep your messages secret from strangers. However, it is impossible to completely protect an extended communication line from eavesdropping. This means that when sending messages, they must be encrypted, and when receiving, they must be decrypted. But how can you and your interlocutor agree on which key you will use? If you send the key to the cipher on the same line, then an eavesdropping attacker can easily intercept it. You can, of course, transmit the key through some other communication line, for example, send it by telegram. But this method is usually inconvenient and, moreover, not always reliable: another line can also be tapped. It is good if you and your addressee knew in advance that you would exchange encryptions, and therefore transferred the keys to each other in advance. What if, for example, you want to send a confidential offer to a prospective business partner or buy a product you like with a credit card in a new online store?
In the 1970s, encryption systems were proposed to solve this problem, using two types of keys for the same message: open (not requiring secrecy) and closed (highly secret). The public key is used to encrypt the message, and the private key is used to decrypt it. You send your correspondent a public key, and he encrypts his message with it. All an attacker who intercepts a public key can do is encrypt his letter and forward it to someone. But he will not be able to decipher the correspondence. Knowing the private key (it is initially stored with you), you can easily read the message addressed to you. To encrypt reply messages, you will use the public key sent by your correspondent (and he keeps the corresponding private key for himself).
This is the kind of cryptographic scheme used in RSA, the most widely used public key encryption method. Moreover, to create a pair of public and private keys, the following important hypothesis is used. If there are two large (requiring more than a hundred decimal digits for their notation) simple numbers M and K, then finding their product N \u003d MK will not be difficult (for this it is not even necessary to have a computer: a sufficiently accurate and patient person can multiply such numbers with a pen and paper). But to solve the inverse problem, that is, knowing a large number N, decompose it into prime factors M and K (the so-called factorization problem) - almost impossible! It is with this problem that an attacker who decides to "crack" the RSA algorithm and read the information encrypted with it will face: to find out the private key, knowing the public one, you will have to calculate M or K.
To test the validity of the hypothesis about the practical complexity of factoring large numbers, special competitions have been and are still being held. The decomposition of only a 155-digit (512-bit) number is considered a record. The calculations were carried out in parallel on many computers for seven months in 1999. If this task were performed on one modern personal computer, it would take about 35 years of computer time! Calculations show that using even thousands of modern workstations and the best computational algorithms known today, one 250-digit number can be factorized in about 800 thousand years, and a 1000-digit number - in 10 25 (!) Years. (For comparison, the age of the universe is ~ 10 10 years.)
Therefore, cryptographic algorithms like RSA, operating with sufficiently long keys, were considered completely reliable and were used in many applications. And everything was fine until then ... until quantum computers came along.
It turns out that using the laws of quantum mechanics, it is possible to build computers for which the factorization problem (and many others!) Will not be difficult. It is estimated that a quantum computer with only about 10,000 quantum bits of memory is able to factor a 1000-digit number into prime factors in just a few hours!
HOW IT ALL BEGAN?
It was not until the mid-1990s that the theory of quantum computers and quantum computing was established as a new field of science. As is often the case with great ideas, it is difficult to pick out a discoverer. Apparently, the Hungarian mathematician I. von Neumann was the first to draw attention to the possibility of developing quantum logic. However, at that time, not only quantum, but also ordinary, classical, computers had not yet been created. And with the advent of the latter, the main efforts of scientists were directed primarily at the search and development of new elements for them (transistors, and then integrated circuits), and not at the creation of fundamentally different computing devices.
In the 1960s, the American physicist R. Landauer, who worked at the IBM corporation, tried to draw the attention of the scientific world to the fact that computation is always some kind of physical process, which means that it is impossible to understand the limits of our computational capabilities without specifying what physical implementation they are. correspond. Unfortunately, at that time, among scientists, the prevailing view of computation as some kind of abstract logical procedure, which should be studied by mathematicians, not physicists.
As computers proliferated, quantum scientists came to the conclusion that it was practically impossible to directly calculate the state of an evolving system consisting of only a few dozen interacting particles, such as a methane molecule (CH 4). This is explained by the fact that for a complete description of a complex system, it is necessary to keep in the computer memory an exponentially large (in terms of the number of particles) number of variables, the so-called quantum amplitudes. A paradoxical situation arose: knowing the equation of evolution, knowing with sufficient accuracy all the potentials of interaction of particles with each other and the initial state of the system, it is practically impossible to calculate its future, even if the system consists of only 30 electrons in a potential well, and there is a supercomputer with random access memory , the number of bits of which is equal to the number of atoms in the visible region of the Universe (!). And at the same time, to study the dynamics of such a system, you can simply set up an experiment with 30 electrons, placing them in a given potential and initial state. This, in particular, was pointed out by the Russian mathematician Yu. I. Manin, who pointed out in 1980 to the need to develop a theory of quantum computing devices. In the 1980s, the same problem was studied by the American physicist P. Benev, who clearly showed that a quantum system can perform calculations, as well as the English scientist D. Deutsch, who theoretically developed a universal quantum computer superior to the classical analogue.
The Nobel Prize Laureate in Physics R. Feynman, who is well known to regular readers of Science and Life, has attracted much attention to the problem of developing quantum computers. Thanks to his authoritative appeal, the number of specialists who paid attention to quantum computing has increased many times.
Yet for a long time it remained unclear whether the hypothetical computing power of a quantum computer could be used to speed up solving practical problems. But in 1994, P. Shor, an American mathematician and employee of Lucent Technologies (USA), stunned the scientific world by proposing a quantum algorithm that allows fast factorization of large numbers (the importance of this problem was already discussed in the introduction). In comparison with the best of the classical methods known today, Shor's quantum algorithm gives a multiple acceleration of computations, and the longer the factorized number, the greater the gain in speed. The fast factorization algorithm is of great practical interest for various special services that have accumulated banks of unencrypted messages.
In 1996, Shor's colleague at Lucent Technologies, L. Grover, proposed a quantum fast search algorithm in an unordered database. (An example of such a database is a telephone book, in which the names of subscribers are arranged not alphabetically, but in an arbitrary way.) The task of searching, choosing the optimal element among numerous options is very common in economic, military, engineering problems, and in computer games. Grover's algorithm allows not only to speed up the search process, but also to approximately double the number of parameters taken into account when choosing the optimum.
The real creation of quantum computers was hampered by essentially the only serious problem - errors, or interference. The fact is that the same level of interference spoils the process of quantum computing much more intensively than classical ones. The ways of solving this problem were outlined in 1995 by P. Shor, who developed a scheme for encoding quantum states and correcting errors in them. Unfortunately, the topic of error correction in quantum computers is as important as it is difficult to cover in this article.
DEVICE OF A QUANTUM COMPUTER
Before describing how a quantum computer works, let us recall the main features of quantum systems (see also Science and Life No. 8, 1998; No. 12, 2000).
To understand the laws of the quantum world, one should not directly rely on everyday experience. In the usual way (in the everyday sense), quantum particles behave only if we constantly "peep" at them, or, more strictly speaking, we constantly measure what state they are in. But as soon as we “turn away” (stop observing), quantum particles immediately pass from a completely definite state at once into several different hypostases. That is, an electron (or any other quantum object) will be partially located at one point, partially at another, partially at a third, etc. This does not mean that it is divided into slices, like an orange. Then it would be possible to reliably isolate some part of the electron and measure its charge or mass. But experience shows that after measurement, the electron always turns out to be "safe and sound" at one single point, despite the fact that before that he managed to visit almost everywhere simultaneously. This state of an electron, when it is located at several points in space at once, is called superposition of quantum states and are usually described by the wave function introduced in 1926 by the German physicist E. Schrödinger. The magnitude of the value of the wave function at any point, squared, determines the probability of finding a particle at this point at a given moment. After measuring the position of the particle, its wave function contracts (collapses) to the point where the particle was detected, and then starts to spread again. The property of quantum particles to be simultaneously in many states, called quantum parallelism , is successfully used in quantum computing.
Quantum bit
The main cell of a quantum computer is a quantum bit, or, in short, qubit(q-bit). This is a quantum particle with two basic states, which are denoted 0 and 1, or, as is customary in quantum mechanics, and. Two values \u200b\u200bof a qubit can correspond, for example, the ground and excited states of an atom, up and down directions of the spin of an atomic nucleus, direction of current in a superconducting ring, two possible positions of an electron in a semiconductor, etc.
Quantum register
The quantum register works almost the same as the classical one. This is a string of quantum bits, over which one- and two-bit logical operations can be carried out (similar to the use of NOT, 2AND-NOT, etc. in a classical register).
The basic states of a quantum register formed by L qubits include, as in the classical one, all possible sequences of zeros and ones of length L. There can be 2 L different combinations in total. They can be considered as writing numbers in binary form from 0 to 2 L -1 and denoted. However, these basic states do not exhaust all possible values \u200b\u200bof the quantum register (in contrast to the classical one), since there are also superposition states specified by complex amplitudes related by the normalization condition. Most of the possible values \u200b\u200bof the quantum register (except for the basic ones) simply do not have a classical analogue. The states of the classical register are just a pitiful shadow of the wealth of states in a quantum computer.
Imagine that an external influence is carried out on the register, for example, electrical impulses are applied to a part of the space or laser beams are directed. If it is a classical register, a pulse, which can be viewed as a computational operation, will change L variables. If it is a quantum register, then the same pulse can simultaneously transform to variables. Thus, a quantum register is, in principle, capable of processing information one times faster than its classical counterpart. This immediately shows that the small quantum registers (L<20) могут служить лишь для демонстрации отдельных узлов и принципов работы квантового компьютера, но не принесут большой практической пользы, так как не сумеют обогнать современные ЭВМ, а стоить будут заведомо дороже. В действительности квантовое ускорение обычно значительно меньше, чем приведенная грубая оценка сверху (это связано со сложностью получения большого количества амплитуд и считывания результата), поэтому практически полезный квантовый компьютер должен содержать тысячи кубитов. Но, с другой стороны, понятно, что для достижения действительного ускорения вычислений нет необходимости собирать миллионы квантовых битов. Компьютер с памятью, измеряемой всего лишь в килокубитах, будет в некоторых задачах несоизмеримо быстрее, чем классический суперкомпьютер с терабайтами памяти.
It should be noted, however, that there is a class of problems for which quantum algorithms do not provide significant acceleration in comparison with classical ones. One of the first to show this was the Russian mathematician Yu. Ozhigov, who built a number of examples of algorithms that cannot be accelerated by a single clock on a quantum computer.
Nevertheless, there is no doubt that computers operating according to the laws of quantum mechanics are a new and decisive stage in the evolution of computing systems. It remains only to build them.
QUANTUM COMPUTERS TODAY
Prototypes of quantum computers exist today. True, so far it has been experimentally possible to collect only small registers consisting of only a few quantum bits. For example, recently a group led by the American physicist I. Chang (IBM) announced the assembly of a 5-bit quantum computer. This is undoubtedly a great success. Unfortunately, the existing quantum systems are not yet able to provide reliable computations, since they are either insufficiently controllable, or very susceptible to noise. However, there are no physical restrictions on the construction of an effective quantum computer, it is only necessary to overcome technological difficulties.
There are several ideas and suggestions on how to make reliable and easily controllable quantum bits.
I. Chang develops the idea of \u200b\u200busing the spins of the nuclei of some organic molecules as qubits.
Russian researcher M.V. Feigelman, working at the Institute for Theoretical Physics. LD Landau RAS, suggests assembling quantum registers from miniature superconducting rings. Each ring acts as a qubit, and states 0 and 1 correspond to the direction of the electric current in the ring - clockwise and counterclockwise. Such qubits can be switched using a magnetic field.
At the Physico-Technological Institute of the Russian Academy of Sciences, a group led by Academician K.A. Valiev proposed two options for placing qubits in semiconductor structures. In the first case, the role of a qubit is played by an electron in a system of two potential wells created by a voltage applied to mini-electrodes on the semiconductor surface. States 0 and 1 are the positions of an electron in one of these wells. The qubit is switched by changing the voltage on one of the electrodes. In another variant, the qubit is the nucleus of a phosphorus atom inserted at a certain point in the semiconductor. States 0 and 1 are the directions of the nuclear spin along or against the external magnetic field. The control is carried out using the combined action of magnetic pulses of the resonant frequency and voltage pulses.
Thus, research is being actively pursued and it can be assumed that in the very near future - in about ten years - an effective quantum computer will be created.
A LOOK INTO THE FUTURE
Thus, it is quite possible that in the future, quantum computers will be manufactured using traditional methods of microelectronic technology and contain many control electrodes, resembling a modern microprocessor. In order to reduce the noise level, which is critical for the normal operation of a quantum computer, the first models will most likely have to be cooled with liquid helium. The first quantum computers are likely to be bulky and expensive devices that could not fit on a desk and were maintained by a large staff of system programmers and hardware adjusters in white coats. First, only government agencies will gain access to them, then rich commercial organizations. But the era of conventional computers began in about the same way.
And what will become of classic computers? Will they die? Hardly. Both classical and quantum computers have their own areas of application. Although, in all likelihood, the ratio in the market will gradually shift towards the latter.
The introduction of quantum computers will not lead to the solution of fundamentally unsolvable classical problems, but will only speed up some calculations. In addition, quantum communication will become possible - the transmission of qubits over a distance, which will lead to the emergence of a kind of quantum Internet. Quantum communication will provide a protected (by the laws of quantum mechanics) from eavesdropping connection of everyone with each other. Your information stored in quantum databases will be more secure from copying than it is now. Firms producing programs for quantum computers will be able to protect them from any, including illegal, copying.
For a deeper understanding of this topic, you can read the review article by E. Riffel, V. Polak "Fundamentals of Quantum Computing" published in the journal "Quantum Computers and Quantum Computing" published in Russia (No. 1, 2000). (By the way, this is the first and so far the only journal in the world devoted to quantum computing. Additional information about it can be found on the Internet at http://rcd.ru/qc.). Having mastered this work, you will be able to read scientific articles on quantum computing.
A little more preliminary mathematical training will be required when reading the book by A. Kitaev, A. Shen, M. Vyaly "Classical and quantum computing" (Moscow: MTsNMO-CheRo, 1999).
A number of fundamental aspects of quantum mechanics, essential for quantum computing, are analyzed in the book by V.V.Belokurov, O.D. Timofeevskaya, O. A. Khrustalev "Quantum teleportation is an ordinary miracle" (Izhevsk: RKhD, 2000).
The RKhD Publishing House is preparing to publish the translation of A. Steen's review on quantum computers as a separate book.
The following literature will be useful not only cognitively, but also historically:
1) Yu. I. Manin. Computable and non-computable.
M .: Sov. radio, 1980.
2) I. von Neumann. Mathematical foundations of quantum mechanics.
Moscow: Nauka, 1964.
3) R. Feynman. Simulation of physics on computers // Quantum computer and quantum computing:
Sat. in 2 volumes - Izhevsk: RKhD, 1999.Vol. 2, p. 96-123.
4) R. Feynman. Quantum mechanical computers
// Ibid, p. 123.-156.
See in issue on the same topic
Quantum computing, at least in theory, has been talked about for decades. Modern types of machines that use non-classical mechanics to process potentially unthinkable amounts of data are big breakthroughs. According to the developers, their implementation turned out to be perhaps the most complex technology ever created. Quantum processors operate at levels of matter that humanity only knew about 100 years ago. The potential for such calculations is enormous. Using the bizarre properties of quanta will speed up the calculations, so many problems that are currently beyond the power of classical computers will be solved. And not only in the field of chemistry and materials science. Wall Street is also showing interest.
Investing in the future
CME Group has invested in Vancouver-based 1QB Information Technologies Inc., which develops software for quantum processors. According to investors, such calculations are likely to have the greatest impact on industries that handle large amounts of time-sensitive data. Financial institutions are an example of such consumers. Goldman Sachs has invested in D-Wave Systems, and In-Q-Tel is funded by the CIA. The first produces machines that do what is called "quantum annealing," that is, they solve low-level optimization problems using a quantum processor. Intel is also investing in this technology, although it considers its implementation to be a matter of the future.
Why is this needed?
The reason quantum computing is so exciting is because of its perfect combination with machine learning. It is currently the main application for such calculations. Part of the very idea of \u200b\u200ba quantum computer is using a physical device to find solutions. Sometimes this concept is explained by the example of the game Angry Birds. The tablet CPU uses mathematical equations to simulate gravity and the interaction of colliding objects. Quantum processors turn this approach upside down. They drop a few birds and watch what happens. Birds are recorded into the microchip, they are thrown, what is the optimal trajectory? Then all possible solutions are checked, or at least a very large combination of them, and the answer is given. In a quantum computer, not a mathematician, the laws of physics work instead.
How does it work?
The basic building blocks of our world are quantum mechanical. If you look at molecules, the reason why they are formed and remain stable is the interaction of their electronic orbitals. All quantum mechanical calculations are contained in each of them. Their number grows exponentially with the number of simulated electrons. For example, for 50 electrons, there are 2 possibilities to the 50th power. This is phenomenal, so it cannot be calculated today. Connecting information theory to physics can point the way to solving such problems. A 50-qubit computer can do it.
Dawn of a new era
According to Landon Downs, president and co-founder of 1QBit, a quantum processor is the ability to harness the computing power of the subatomic world, which is essential for making new materials or creating new drugs. A transition from a paradigm of discovery to a new era of design is taking place. For example, quantum computing can be used to model catalysts that extract carbon and nitrogen from the atmosphere and thereby help stop global warming.
At the forefront of progress
The technology community is extremely excited and busy. Teams around the world at startups, corporations, universities, and government labs are racing to build machines that take different approaches to processing quantum information. Superconducting qubit chips and trapped ion qubits have been created by researchers from the University of Maryland and the US National Institute of Standards and Technology. Microsoft is developing a topological approach called Station Q, which aims to use a non-Abelian anion that has yet to be conclusively proven to exist.
The year of the likely breakout
And this is just the beginning. As of the end of May 2017, the number of quantum-type processors that definitely do something faster or better than a classical computer is zero. Such an event will establish "quantum supremacy", but it has not happened yet. Although it is likely that this may happen this year. Most insiders say the clear favorite is the Google group led by UC Santa Barbara physics professor John Martini. Its goal is to achieve computational superiority with a 49-qubit processor. By the end of May 2017, the team successfully tested the 22-qubit chip as an interim step towards disassembling a classic supercomputer.
How did it all start?
The idea of \u200b\u200busing quantum mechanics to process information has been around for decades. One of the key events happened in 1981 when IBM and MIT co-hosted a conference on the physics of computing. The famous physicist proposed building a quantum computer. According to him, for modeling, one should use the means of quantum mechanics. And this is a great task because it does not seem so easy. In a quantum processor, the principle of operation is based on several strange properties of atoms - superposition and entanglement. A particle can be in two states at the same time. However, when measured, it will appear in only one of them. And it is impossible to predict which one, except from the standpoint of the theory of probability. This effect is at the heart of the thought experiment with Schrödinger's cat, which is simultaneously alive and dead in a box until the observer sneaks into it. Nothing in everyday life works like this. Nevertheless, about 1 million experiments conducted since the beginning of the 20th century show that superposition does exist. And the next step is figuring out how to use this concept.
Quantum processor: job description
Classic bits can take the value 0 or 1. If you pass their string through the "logical gates" (AND, OR, NOT, etc.), then you can multiply numbers, draw images, etc. A qubit can take on the values \u200b\u200b0, 1 or both at the same time. If, say, 2 qubits are entangled, then this makes them perfectly correlated. A quantum processor can use logic gates. T. n. a Hadamard gate, for example, puts a qubit in a state of perfect superposition. When superposition and entanglement are combined with cleverly placed quantum gates, the potential of subatomic computing begins to unfold. 2 qubits allow you to explore 4 states: 00, 01, 10 and 11. The principle of operation of a quantum processor is such that performing a logical operation makes it possible to work with all positions at once. And the number of available states is 2 to the power of the number of qubits. So, if you make a 50-qubit universal quantum computer, then theoretically you can explore all 1.125 quadrillion combinations simultaneously.
Kudits
A quantum processor in Russia is seen a little differently. Scientists from the Moscow Institute of Physics and Technology and the Russian Quantum Center have created “kudits”, which are several “virtual” qubits with different “energy” levels.
Amplitudes
A quantum processor has the advantage that quantum mechanics is based on amplitudes. Amplitudes are similar to probabilities, but they can also be negative and complex numbers. So, if you need to calculate the probability of an event, you can add up the amplitudes of all possible options for their development. The idea behind quantum computing is to try to tune in such a way that some paths to wrong answers have positive amplitudes and some negative ones, so that they cancel each other out. And the paths leading to the correct answer would have amplitudes that are in phase with each other. The trick is that you need to organize everything without knowing in advance which answer is correct. So the exponentiality of quantum states combined with the potential for interference between positive and negative amplitudes is an advantage of this type of computation.
Shor's algorithm
There are many tasks that the computer cannot solve. For example, encryption. The problem is that it is not easy to find the prime factors of a 200-digit number. Even if the laptop runs great software, it may take years to find the answer. So another milestone in quantum computing was an algorithm published in 1994 by Peter Shor, now professor of mathematics at MIT. His method is to find the factors of a large number using a quantum computer that did not yet exist. Essentially, the algorithm performs operations that indicate areas with the correct answer. The next year, Shore discovered a method for quantum error correction. Then many realized that this is an alternative way of computing, which in some cases can be more powerful. Then there was a surge of interest from physicists in the creation of qubits and logic gates between them. And now, two decades later, humanity is on the verge of creating a full-fledged quantum computer.
Last week, news broke that Google has made a breakthrough in quantum computing -
the company understood how such a computer would cope
with their own mistakes. Quantum computers have been talked about for several years: it, for example, on the cover of Time magazine. If such computers appear, it will be a breakthrough akin to the appearance of classical computers - or even more serious. Look At Me explains what quantum computers are good at and what exactly Google did.
What is a quantum computer?
A quantum computer is a mechanism at the intersection of computer science and quantum physics, the most difficult branch of theoretical physics. Richard Feynman, one of the greatest physicists of the 20th century, once said: "If you think you understand quantum physics, then you do not understand it." Therefore, keep in mind that the explanations that follow are incredibly simplistic. It takes people many years to understand quantum physics.
Quantum physics deals with elementary particles smaller than an atom. The way these particles work and how they behave contradicts many of our ideas about the universe. A quantum particle can be in several places at the same time - and in several states at the same time. Imagine that you toss a coin: while it is in the air, you cannot tell whether it will come up heads or tails; this coin is like heads and tails at the same time. This is how quantum particles behave. This is called the principle of superposition.
A quantum computer is still a hypothetical device that will use the principle of superposition (and other quantum properties)
for computing. An ordinary computer works with transistors,
which perceive any information as zeros and ones. Binary code can describe the whole world - and solve any problems within it. The quantum analogue of the classical bit is called the cubit (qubit, qu - from the word quantum, quantum)... Using the principle of superposition, the cubit can be simultaneously located
in state 0 and 1 - and this will not only significantly increase the power compared to traditional computers, but also allow you to solve unexpected problems,
which ordinary computers are not capable of.
The superposition principle is the only one
what will quantum computers be based on?
No. Due to the fact that quantum computers exist only in theory, scientists so far only speculate how they will work. For example, it is believed that quantum computers will also employ quantum entanglement.
This is a phenomenon that Albert Einstein called "creepy" ( he was generally against quantum theory, because it does not fit with his theory of relativity)... The meaning of the phenomenon is that two particles in the Universe can be interconnected, and vice versa: say, if helicity
(there is such a characteristic of the state of elementary particles, we will not go into details) of the first particle is positive, then the helicity of the second will always be negative, and vice versa. This phenomenon is called "creepy" for two reasons. First, this connection works instantly, faster than the speed of light. Second, entangled particles can be located at any distance from each other.
from a friend: for example, at different ends of the Milky Way.
How can a quantum computer be used?
Scientists are looking for applications for quantum computers and at the same time figuring out how to build them. The main thing is that a quantum computer will be able to very quickly optimize information and generally work with big data that we accumulate, but do not yet understand how to use it.
Let's imagine this option (greatly simplified, of course): you are about to shoot a bow at a target and you need to calculate how high to aim to hit. Let's say you need to calculate the height from 0 to 100 cm. A conventional computer will calculate each trajectory in turn: first 0 cm, then 1 cm, then 2 cm, and so on. A quantum computer will calculate all the options at the same time - and instantly give out the one that will allow you to hit exactly the target. Many processes can be optimized in this way:
from medicine (say, diagnose cancer earlier) before aviation (for example, do more complex autopilots).
There is also a version that such a computer will be able to solve problems that a regular computer is simply not capable of - or that would take thousands of years of computation. A quantum computer will be able to work with the most complex simulations: for example, calculate whether there are intelligent beings in the Universe other than humans. It is possible that the creation of quantum computers will lead
to the emergence of artificial intelligence. Imagine what the advent of conventional computers has done to our world - quantum computers can be about the same breakthrough.
Who is developing quantum computers?
Everything. Governments, military, technology companies. Almost anyone will benefit from creating a quantum computer. For example, among the documents released by Edward Snowden, there was information that the NSA has a project "Deployment in complex goals", which includes the creation of a quantum computer to encrypt information. Microsoft is seriously engaged in quantum computers - the first research in this area, they began in 2007. IBM is in the process of development and a few years ago announced that they had created a chip with three cubits. Finally, Google and NASA collaborate
with D-Wave, which claims to release
"The first commercial quantum processor" (or rather, the second, now their model is called D-Wave Two)but it doesn't work like quantum yet -
we recall that they do not exist.
How close are we to creating
quantum computer?
Nobody can say for sure. Technology Breakthrough News (as a recent Google news) appear constantly, but we can be as very distant
from a full-fledged quantum computer, and very close to it. Let's say there are studies that suggest that it is enough to create a computer for everything
with several hundred cubits to make it work like a full-fledged quantum computer. D-Wave claims to have built an 84 kubit processor -
but critics who have analyzed their processor claim that it works,
like a classical computer, not like a quantum one. Google collaborating
with D-Wave, they believe that their processor is just in the very early stages of development and will eventually work like a quantum one. Anyway, now
quantum computers have one major problem - bugs. Any computers make mistakes, but classical computers can easily cope with them, while quantum computers do not yet. Once the researchers figure out the errors, there will be only a few years before the advent of the quantum computer.
Making it difficult to fix errors
in quantum computers?
Simplified, errors in quantum computers can be divided into two levels. The first one is the mistakes that any computers make, including classic ones. An error may appear in the computer's memory when 0 involuntarily changes to 1 due to external noise such as cosmic rays or radiation. These errors are easy to solve, all data is checked for such changes. And this problem in quantum computers was just recently dealt with at Google: they stabilized a chain of nine cubits
and saved her from mistakes. There is, however, one caveat to this breakthrough: Google has dealt with classic errors in classical computing. There is a second level of error in quantum computers, and it is much more difficult to understand and explain.
Cubits are extremely unstable, they are subject to quantum decoherence - this is a violation of communication within a quantum system under the influence of the environment. A quantum processor must be isolated as much as possible from environmental influences (although decoherence sometimes occurs as a result of internal processes)to keep errors to a minimum. At the same time, quantum errors cannot be completely eliminated, but if they are made rare enough, a quantum computer can work. At the same time, some researchers believe that 99% of the power of such a computer will just be directed
to eliminate errors, but the remaining 1% is enough to solve any problems.
According to physicist Scott Aaronson, Google's achievement can be considered the third
half of the seven steps required to create a quantum computer — in other words, we are halfway there.
