Quantum computer: any complex consists of a set of simple
Off-topic changes made
The post is written as follows:
1. Trying to look at the potential (almost fantastic) capabilities of quantum computers.
2. Review of new research and achievements
3. To explain the phenomenon of quantum coupling in a simple example.
4. Literature
')
While condensing visual materials using JPEG and MPEG , a strange thought suddenly occurred to me: in the case of a virtual picture or video, it is a compression of a two-dimensional object. But what about a three-dimensional object (for example, the description and compression of the information equivalent of an anthropomorphic object)?
All data compression programs work on the same principle. The program scans the image line by line and searches for adjacent pixels that have the same color. It is clear that the description of the three-dimensional object required a tremendous amount of information. In a large computer Tianhe-1A ( TH-1A ), designed for parallel data processing, contains the equivalent of 50 thousand processors. And what happens if you get to work in parallel the equivalent of 32 billion processors ?
How can you use the "pixels" of three-dimensional objects for moving? Similar to the image: you can not shove a piece of paper, and especially a book in the telephone wire, but you can send a fax . There are successful experiments on the teleportation of photons ( Zeilinger , Francesco De Martini , 1997). But people and everything else is made up of many particles. So the next natural step would be to imagine how to apply quantum teleportation to such a large aggregate of particles, which would allow the transfer of macroscopic objects from one place to another.
There are three problems that need to be overcome in order to be able to download the information of the human brain into a computer.
- A way to translate and seal brain information into a computer language is needed. Work is currently underway on the Blue Brain Project computer project . The project is scheduled to be completed by 2023. A conversion of brain signals into teams involved in the SQUID sensor scanners. Can a scanner remove all information from the brain? Is this possible, but not now? ..
- need a computer with a sufficiently large amount of memory . For example, the human brain has 10 to 14 degrees of synapses. Each synapse requires one byte of computer memory. This is approximately 1 tib.
- a philosophical problem - there is something in biology that we have not yet discovered, or have not yet understood .
The joint measurement of two photons was an impressive achievement, but in experiments with photons it is possible to manipulate only one pair of interlinked particles. Three-dimensional macro-objects have over a billion billion billion particles. Thus, the creation of two containers of linked particles is far beyond the limits of modern possibilities. Today, it is not even possible to imagine the joint dimension of billions and billions of particles.
Science and technology are constantly pushing the boundaries of the impossible and teleportation of macroscopic bodies looks unlikely. But how to know? Descartes also seemed unlikely to talk at a distance of 100 km ...
To a simple question: “When will a quantum computer be made - tomorrow, after 10 years, or never?”, Google’s magic gives rise to amazing results: 130,000 thousand links.
The following news is attracting particular attention: Lockheed Martin, the largest US arms maker, has acquired the first commercial model of the D-Wave One quantum computer with a Rainier processor. The corporation studied the quantum computer very meticulously before making a purchase and looked at it for over a year. The strangest thing in this whole story is that the scientific community still does not have complete confidence that the quantum computer in question is working . But the competence of the buyer seems to be no doubt.
<img src = "
"alt =" image "/>
In second place was a critic of a quantum computer, an employee of MIT Scott Aaronson (Scott Aaronson). All questions, according to Mr. Aaronson, would be removed by a single publication in a peer-reviewed journal, which would provide clear evidence that the processor implements key quantum effects (entanglement, superposition states), and direct comparisons of quantum and classical calculations.
It would seem that it could be simpler - here, they connected two qubits, and this is a breakthrough, here, they connected the qubit to a resonator-memory, and this means that success is near, etc. However, the discussion on the possibility of creating a quantum computer that broke out in early February 2012 on the Internet ( blog The Lost Letter of Mathematician Gödel, Gödel's Lost Letter) showed that everything is not so simple ...
Started discussion Scot Aronson. He offered a prize of $ 100 thousand to someone who can prove, based on the laws of nature, the fundamental impossibility of creating a scalable quantum computer. The motive of such an extraordinary act was an irresistible desire, living in every real researcher, to see the fundamental limitations imposed by nature, in this case, on the speed of information processing.
To understand the sense of a prize of $ 100 thousand, Aronson explains the context of his question:
- at the end of the XVIII - beginning of the XIX century, people tried to create machines that would produce as much useful work as possible, consuming as little heat as possible (ie, fuel) and found a certain limit set by the second law of thermodynamics - the efficiency of a heat engine must be less 1 (if greater than or equal to 1 - then this is the "perpetual motion")
- A computer that turns a difficult task for a person into a simple one is also a kind of information engine. Just like a heat engine, a computer can have its own information efficiency associated with the degree of reduction in the complexity of the task and the degree of complexity of the computer itself. Are there fundamental limitations to the information efficiency of computers? The answer to this question could be the first postulate of quantum informatics (similar to the second law of thermodynamics).
Actually the answer to this question is waiting for Scot Aronson.
Meanwhile, on September 19, 2012, the intriguing report of the research team of Dr. Andrea Morello and Professor Dzurak from the UNSW School of Electrical Engineering and Telecommunications was published in the journal Nature. Scientists were able to isolate, measure and control an electron belonging to one atom, and all thanks to the prototype of a new device that implements a quantum bit on a single phosphorus atom in a silicon chip.
<img src = "
"alt =" image "/>
As Dr. Morello notes: “This quantum is equivalent to a button on your keyboards. None of these materials have been able to achieve such great successes than silicon - a material that has the advantage, since it is well understood from a scientific point of view and is very well received by industry. Our technology is the same that is already used in countless everyday electronic devices. ”
The next goal of the team is to combine pairs of quantum bits to create two qubit logic gates . This experience will allow you to create a base processing unit for a quantum computer.
On what stage of evolution a quantum computer resides, in particular - what a valve and the essence of information coding - need a little refreshment in the memory of the living, accessible, sometimes ironic pages of the famous "Code" by Charles Petzold.
In solid-state systems , qubits have become successfully encoded relatively recently.
- in one paper, the spin states of the nuclei of phosphorus atoms were changed .
- another study used NV centers in artificial diamond (an experiment by the conglomerate DeBeers, a leading developer and supplier of advanced materials based on synthetic diamonds)
Also, there is an increase in the number of qubit in this technology:
- at the turn of the 21st century single-qubit quantum processors were created in many scientific laboratories;
- In November 2009, NIST physicists in the USA for the first time managed to assemble a programmable quantum computer consisting of two qubits;
- April 2012. NIST created a quantum simulator capable of reproducing interactions between several hundred quantum bits (qubits);
- in the April issue of the journal Nature, Stephan Ritter summed up the research of a team of scientists led by the Director of the Institute for Quantum Optics Max Planck, Professor Gerhard Rempe, who built the first elementary quantum network. In the experiment, the long-range quantum coupling was created in about a microsecond and remained on the order of 100 microseconds. In the long run, in his opinion, the entire Internet could turn into such a coherent quantum system;
- at the end of May 2012, a group of European scientists under the leadership of Anton Zeilinger (Anton Zeilinger) managed to transfer the quantum state of two entangled photons between the two Canary Islands - La Palma and Tenerifen ( distance over 143 km ). Quantum teleportation was carried out simply through the atmosphere. Fiber optics was not used due to unresolved routing problems (it is possible to transmit photons in a quantum state only within a single optical fiber). The efforts of researchers are aimed not only at increasing the distance of effective data transfer, but also at developing the concept of a global network - the Internet of the future, which will be based on certain quantum properties of particles;
- Chinese physicists presented a router on one qubit.
- computers consisting of 16 \ 128 \ 1024-qubit (developed by D-Wave) are on the way.
A quantum computer is currently the “blue bird” of modern calculators. There is a perception among teapots ( thanks to the writers ) that such a machine will be able to manipulate three-dimensional objects, in a split second to crack the most sophisticated ciphers, the secrecy of which is based on the existence of so-called. algorithmically complex tasks, very quickly determine the chemical formulas of compounds with the required pharmaceutical properties or the biological code leading to a particular disease (search on an unordered database), according to the Canadian company D-Wave, in other words, to solve any complex tasks that are not under the power of a classic computer.
The basic units, or "letters", of modern calculations are the two bit states "0" and "1". To encode them, only the electron charge is sufficient. But the electron has other properties that are used in quantum bits to extend the "alphabet". The transition from bits to qubits, thus able to significantly increase the computing power of computers.
A quantum bit corresponds to a single electron in a certain state. Agree to encode the electron charge and the encoding of the trajectory of the electron on two closely spaced channels - this is not the same thing. In the latter case, two different states are possible: the electron moves either along the upper or the lower channel. According to quantum theory, a particle can be in several states at the same time, that is, it can pass through two channels at once. Such mixed states form the extended “alphabet” of quantum computations.
Therefore, a quantum computer works many times faster with factorials of very large numbers (while for ordinary electronics such tasks are too resource-intensive). The best of multi-core processors allow you to encrypt or decrypt 150-digit numbers. But if the task was to decipher a 1000-digit number, then all the computational resources of the world would be needed to do this. For a quantum computer, this task can take only a few hours.
To calculate a quantum computer uses the so-called quantum algorithms that use quantum mechanical effects, such as quantum parallelism and quantum entanglement. The meaning of this phenomenon is that the quantum states of particles can be related to each other, even if they are spaced apart
Often, Einstein’s dialogue with Bohr is cited as the quintessence of the debate about quantum entanglement:
- God does not play dice.
- do not tell God what to do.
The outcome of the dispute:
- Bor created the Copenhagen system, which was forbidden to think about quantum entanglement
- Einstein, Podolsky and Rosen formulated the EPR paradox . They conducted a thought experiment with two dodecahedra of a quantum company with Betelgeuse, described in the famous article “Can you have complete?” (1935)
This article and the EPR paradox in general were creatively rethought by Roger Penrose in "Mind Shadows". The company with Betelgeuse took the system with a common spin 0 (initial state), divided it into two atoms (each with a spin) and suspended each atom carefully into the center dodecahedron.
Then the dodecahedrons were carefully packed and sent by mail (one to Earth, and the other to the Alpha Centauri system), while ensuring that the spin states of these atoms are completely unchanged until one of the recipients measures the spin. of the buttons located at the vertices of the dodecahedrons.
The most important thing here is to achieve complete identity in the orientation of the two dodecahedrons. When the button is pressed simultaneously, nothing happens. However, the following event may occur, after which the company has appointed a premium: a bell will ring, followed by an impressive firework, accompanied by the complete destruction of this particular dodecahedron.
Button presses are spatially separated events: according to the theory of relativity, no exchange of signals conveying information about which buttons users click on is impossible. Quantum theory, on the contrary, fully admits the existence of some kind of “connection” connecting the dodecahedrons through space-like separated events. Generally speaking, this “connection” cannot be used to transmit directly “usable” information, and in this sense there is no operational conflict between the SR and the CT. There is only a conflict with the spirit of SRT - which, in fact, is an excellent illustration of one of the most profound Z-puzzles of quantum theory, the phenomenon of quantum nonlocality. Two atoms in the center of the dodecahedra form a linked state, and, according to the rules of standard CT, they cannot be considered as separate independent objects.
Now the most important thing is that when users begin to press buttons, this “long-range communication” should be present, and its nature is such that a signal transmission at a distance of about four light years occurs, apparently, instantly. The secret of the company is that they simply take and hang one atom at the center of each dodecahedron, whose spin is equal, no more, no less.
Pressing the button activates the measurement of an atom located in the center of the corresponding dodecahedron. The possible results of measuring a particle with spin are only four; they correspond to four mutually orthogonal states. When you press any button, the measuring device will certainly be oriented in the direction (from the center of the dodecahedron) to this same button.
The bell rings (the result is “yes”) if an atom is detected in the measurement in the second of four possible locations. In other words, the other three states do not cause any reaction (the answer is “no”). If the answer is no, the three remaining beams are brought together (say, by changing the direction of the non-uniform magnetic field to the opposite), which is not accompanied by any destructive effects, and we can again press any other button, thereby selecting the new direction of change. fields.
As a key assumption, we assume that there is no long-range "connection" between the earth and alpha dodecahedron. We will assume that after the dodecahedrons have left the “assembly shop”, they exist separately and completely independently of each other.
Predictions of a quantum mechanical formalism cannot be described in terms of objects considered separately from one another. "Linked" in this outlandish way objects remain linked regardless of the distance they happen to move away from each other.
Schrödinger first called these particles "entangled" or linked. Today, most experiments with entangled particles use photons. This is due to the relative simplicity of obtaining entangled photons and their transfer to the detectors.
In 1983, Richard Feynman expressed the idea that it is possible in principle (in the language of mathematics) to describe processes of any complexity that occur in nature by using for computing (information processing) processes of the same complexity as, for example, processes occurring in the quantum world.
After that, for a long time, the efforts of researchers in the field of quantum informatics were divided, roughly speaking, into two directions.
On the one hand, physical devices (qubits) that could hold and process quantum information were actively created, but at the same time all experiments ultimately boiled down to testing a small number of qubits (up to 10), setting a goal to "demonstrate the fundamental possibility" rather than create a real computer. On the other hand, applied mathematicians , who developed quantum algorithms that significantly reduce the number of operations performed (exactly this number depending on the length of the input number determines the complexity of the algorithm) for solving problems that are practically “unsolvable” by classical (non-quantum) methods, did not idle . However, all the proposed algorithms assumed the existence of a “spherical horse in a vacuum,” in other words, ideal qubits and logical operations perfectly performed on them.
At the end of the 90s of the last century, it became clear that the success of quantum informatics depends on the “non-sphericity of the horse” and the presence of the “atmosphere”, that is, on the ability to implement quantum algorithms in real conditions, in the presence of noise. Noise interferes with any calculations , both quantum and classical, since it introduces an error into all elements of the computational process (initial data, logical operations, data reading, etc.). Errors arising from classical calculations, learned to correct even in the time of Shannon. With quantum systems, everything is much more complicated - they are more sensitive to external noise, and classical error correction methods are not applicable to them due to the fundamental properties of nature (measurement-reading destroys the state of a quantum bit). Skeptics believed that all the effectiveness of ideal quantum algorithms would be reduced to "no" when trying to extract information from a quantum system.
However, in 1997, Peter Shor is the author of the most well-known quantum algorithm, and John Preskill and several other researchers developed such error correction methods in quantum systems that do not lead to a significant lengthening of the algorithm itself (more precisely, they require performing a polynomial number of correction operations). In addition, quantum information coding schemes have been proposed, allowing for error-resistant computing. After that, everyone calmed down a bit, skeptics died down, and optimists began to create new physical implementations of qubits, new (non-digital) concepts of quantum computing with even greater zeal, and try to build a quantum computing device containing more than two qubits. However, in more than 10 years of this century, to overcome the so-called. “Quantum gap” (i.e., to keep more than 10 qubits in superposition) was not possible (the Canadian company D-Wave claims that it managed to create a quantum computer with the number of qubits of about 1000, but the published companies do not allow to unconditionally believe this statement).
Skeptics and pessimists once again perked up and put the question to the core - or maybe a quantum computer is completely impossible?
Skeptic Gilles Qalayi believes that an increase in the number of qubits will lead to a catastrophic increase in errors, the correction of which will take as much time as the solution of the problem on a classical computer. His main argument is the possibility of the generation of noise by “wrong” quantum correlations, which in a large system will be distributed according to the domino principle and cover all qubits. In other words, what makes a quantum computer such a powerful and attractive computing tool, namely, quantum correlations, leads to an equally powerful and rapid increase and spread of noise.
The optimist Aram Harrow believes, following Einstein, that nature is cunning but not insidious ("God is subtle but not malicious"). Harrow believes that in those specific systems that have been created to date, correlated noise is either unlikely or can be taken into account and eliminated as a systematic error. Given the linearity of the equations of quantum mechanics, Harrow sees no reason for the catastrophic propagation of noise (subject to the regular application of error correction procedures).
Other scientists are actively involved in the discussion. The weighty arguments of the parties are not yet sufficient for revealing the secrets of nature, but the debaters do not lose hope of winning the dispute, looking for new facts.
Modeling, construction and operation of a quantum computer is possible with the following interdisciplinary approach:
- programming ( computer architecture , parallel computing )
- particle physics
- overloking
- cryptology
Sources:
Brian Green "Cosmos Fabric"
Richard Penrose "Shadows of the Mind"
ko.com.ua/100000_ili_kakovoj_budet_cena_otkrytiya_62001
ru.wikipedia.org/wiki/quantum_computer
www.supercomputers.ru
blogs.computerra.ru
a lot of literature on this topic here here and here
according to the author of the theory of B. Green’s strings, the phenomenon of quantum coupling at a popular level is well described in recent books:
Siegfried T. The Bit and the Pendulum. New York: John Wiley, 2000;
Johnson G. A Shortcut Through Time. New York: Knopf, 2003.
The post is written as follows:
1. Trying to look at the potential (almost fantastic) capabilities of quantum computers.
2. Review of new research and achievements
3. To explain the phenomenon of quantum coupling in a simple example.
4. Literature
')
While condensing visual materials using JPEG and MPEG , a strange thought suddenly occurred to me: in the case of a virtual picture or video, it is a compression of a two-dimensional object. But what about a three-dimensional object (for example, the description and compression of the information equivalent of an anthropomorphic object)?
All data compression programs work on the same principle. The program scans the image line by line and searches for adjacent pixels that have the same color. It is clear that the description of the three-dimensional object required a tremendous amount of information. In a large computer Tianhe-1A ( TH-1A ), designed for parallel data processing, contains the equivalent of 50 thousand processors. And what happens if you get to work in parallel the equivalent of 32 billion processors ?
How can you use the "pixels" of three-dimensional objects for moving? Similar to the image: you can not shove a piece of paper, and especially a book in the telephone wire, but you can send a fax . There are successful experiments on the teleportation of photons ( Zeilinger , Francesco De Martini , 1997). But people and everything else is made up of many particles. So the next natural step would be to imagine how to apply quantum teleportation to such a large aggregate of particles, which would allow the transfer of macroscopic objects from one place to another.
There are three problems that need to be overcome in order to be able to download the information of the human brain into a computer.
- A way to translate and seal brain information into a computer language is needed. Work is currently underway on the Blue Brain Project computer project . The project is scheduled to be completed by 2023. A conversion of brain signals into teams involved in the SQUID sensor scanners. Can a scanner remove all information from the brain? Is this possible, but not now? ..
- need a computer with a sufficiently large amount of memory . For example, the human brain has 10 to 14 degrees of synapses. Each synapse requires one byte of computer memory. This is approximately 1 tib.
- a philosophical problem - there is something in biology that we have not yet discovered, or have not yet understood .
The joint measurement of two photons was an impressive achievement, but in experiments with photons it is possible to manipulate only one pair of interlinked particles. Three-dimensional macro-objects have over a billion billion billion particles. Thus, the creation of two containers of linked particles is far beyond the limits of modern possibilities. Today, it is not even possible to imagine the joint dimension of billions and billions of particles.
Science and technology are constantly pushing the boundaries of the impossible and teleportation of macroscopic bodies looks unlikely. But how to know? Descartes also seemed unlikely to talk at a distance of 100 km ...
Riddle
To a simple question: “When will a quantum computer be made - tomorrow, after 10 years, or never?”, Google’s magic gives rise to amazing results: 130,000 thousand links.
The following news is attracting particular attention: Lockheed Martin, the largest US arms maker, has acquired the first commercial model of the D-Wave One quantum computer with a Rainier processor. The corporation studied the quantum computer very meticulously before making a purchase and looked at it for over a year. The strangest thing in this whole story is that the scientific community still does not have complete confidence that the quantum computer in question is working . But the competence of the buyer seems to be no doubt.
<img src = "
"alt =" image "/>In second place was a critic of a quantum computer, an employee of MIT Scott Aaronson (Scott Aaronson). All questions, according to Mr. Aaronson, would be removed by a single publication in a peer-reviewed journal, which would provide clear evidence that the processor implements key quantum effects (entanglement, superposition states), and direct comparisons of quantum and classical calculations.
It would seem that it could be simpler - here, they connected two qubits, and this is a breakthrough, here, they connected the qubit to a resonator-memory, and this means that success is near, etc. However, the discussion on the possibility of creating a quantum computer that broke out in early February 2012 on the Internet ( blog The Lost Letter of Mathematician Gödel, Gödel's Lost Letter) showed that everything is not so simple ...
Started discussion Scot Aronson. He offered a prize of $ 100 thousand to someone who can prove, based on the laws of nature, the fundamental impossibility of creating a scalable quantum computer. The motive of such an extraordinary act was an irresistible desire, living in every real researcher, to see the fundamental limitations imposed by nature, in this case, on the speed of information processing.
To understand the sense of a prize of $ 100 thousand, Aronson explains the context of his question:
- at the end of the XVIII - beginning of the XIX century, people tried to create machines that would produce as much useful work as possible, consuming as little heat as possible (ie, fuel) and found a certain limit set by the second law of thermodynamics - the efficiency of a heat engine must be less 1 (if greater than or equal to 1 - then this is the "perpetual motion")
- A computer that turns a difficult task for a person into a simple one is also a kind of information engine. Just like a heat engine, a computer can have its own information efficiency associated with the degree of reduction in the complexity of the task and the degree of complexity of the computer itself. Are there fundamental limitations to the information efficiency of computers? The answer to this question could be the first postulate of quantum informatics (similar to the second law of thermodynamics).
Actually the answer to this question is waiting for Scot Aronson.
Quantum achievements
YuMeanwhile, on September 19, 2012, the intriguing report of the research team of Dr. Andrea Morello and Professor Dzurak from the UNSW School of Electrical Engineering and Telecommunications was published in the journal Nature. Scientists were able to isolate, measure and control an electron belonging to one atom, and all thanks to the prototype of a new device that implements a quantum bit on a single phosphorus atom in a silicon chip.
<img src = "
"alt =" image "/>As Dr. Morello notes: “This quantum is equivalent to a button on your keyboards. None of these materials have been able to achieve such great successes than silicon - a material that has the advantage, since it is well understood from a scientific point of view and is very well received by industry. Our technology is the same that is already used in countless everyday electronic devices. ”
The next goal of the team is to combine pairs of quantum bits to create two qubit logic gates . This experience will allow you to create a base processing unit for a quantum computer.
On what stage of evolution a quantum computer resides, in particular - what a valve and the essence of information coding - need a little refreshment in the memory of the living, accessible, sometimes ironic pages of the famous "Code" by Charles Petzold.
In solid-state systems , qubits have become successfully encoded relatively recently.
- in one paper, the spin states of the nuclei of phosphorus atoms were changed .
- another study used NV centers in artificial diamond (an experiment by the conglomerate DeBeers, a leading developer and supplier of advanced materials based on synthetic diamonds)
Also, there is an increase in the number of qubit in this technology:
- at the turn of the 21st century single-qubit quantum processors were created in many scientific laboratories;
- In November 2009, NIST physicists in the USA for the first time managed to assemble a programmable quantum computer consisting of two qubits;
- April 2012. NIST created a quantum simulator capable of reproducing interactions between several hundred quantum bits (qubits);
- in the April issue of the journal Nature, Stephan Ritter summed up the research of a team of scientists led by the Director of the Institute for Quantum Optics Max Planck, Professor Gerhard Rempe, who built the first elementary quantum network. In the experiment, the long-range quantum coupling was created in about a microsecond and remained on the order of 100 microseconds. In the long run, in his opinion, the entire Internet could turn into such a coherent quantum system;
- at the end of May 2012, a group of European scientists under the leadership of Anton Zeilinger (Anton Zeilinger) managed to transfer the quantum state of two entangled photons between the two Canary Islands - La Palma and Tenerifen ( distance over 143 km ). Quantum teleportation was carried out simply through the atmosphere. Fiber optics was not used due to unresolved routing problems (it is possible to transmit photons in a quantum state only within a single optical fiber). The efforts of researchers are aimed not only at increasing the distance of effective data transfer, but also at developing the concept of a global network - the Internet of the future, which will be based on certain quantum properties of particles;
- Chinese physicists presented a router on one qubit.
- computers consisting of 16 \ 128 \ 1024-qubit (developed by D-Wave) are on the way.
A quantum computer is currently the “blue bird” of modern calculators. There is a perception among teapots ( thanks to the writers ) that such a machine will be able to manipulate three-dimensional objects, in a split second to crack the most sophisticated ciphers, the secrecy of which is based on the existence of so-called. algorithmically complex tasks, very quickly determine the chemical formulas of compounds with the required pharmaceutical properties or the biological code leading to a particular disease (search on an unordered database), according to the Canadian company D-Wave, in other words, to solve any complex tasks that are not under the power of a classic computer.
Some theory
The basic units, or "letters", of modern calculations are the two bit states "0" and "1". To encode them, only the electron charge is sufficient. But the electron has other properties that are used in quantum bits to extend the "alphabet". The transition from bits to qubits, thus able to significantly increase the computing power of computers.
A quantum bit corresponds to a single electron in a certain state. Agree to encode the electron charge and the encoding of the trajectory of the electron on two closely spaced channels - this is not the same thing. In the latter case, two different states are possible: the electron moves either along the upper or the lower channel. According to quantum theory, a particle can be in several states at the same time, that is, it can pass through two channels at once. Such mixed states form the extended “alphabet” of quantum computations.
Therefore, a quantum computer works many times faster with factorials of very large numbers (while for ordinary electronics such tasks are too resource-intensive). The best of multi-core processors allow you to encrypt or decrypt 150-digit numbers. But if the task was to decipher a 1000-digit number, then all the computational resources of the world would be needed to do this. For a quantum computer, this task can take only a few hours.
To calculate a quantum computer uses the so-called quantum algorithms that use quantum mechanical effects, such as quantum parallelism and quantum entanglement. The meaning of this phenomenon is that the quantum states of particles can be related to each other, even if they are spaced apart
Often, Einstein’s dialogue with Bohr is cited as the quintessence of the debate about quantum entanglement:
- God does not play dice.
- do not tell God what to do.
The outcome of the dispute:
- Bor created the Copenhagen system, which was forbidden to think about quantum entanglement
- Einstein, Podolsky and Rosen formulated the EPR paradox . They conducted a thought experiment with two dodecahedra of a quantum company with Betelgeuse, described in the famous article “Can you have complete?” (1935)
This article and the EPR paradox in general were creatively rethought by Roger Penrose in "Mind Shadows". The company with Betelgeuse took the system with a common spin 0 (initial state), divided it into two atoms (each with a spin) and suspended each atom carefully into the center dodecahedron.
Then the dodecahedrons were carefully packed and sent by mail (one to Earth, and the other to the Alpha Centauri system), while ensuring that the spin states of these atoms are completely unchanged until one of the recipients measures the spin. of the buttons located at the vertices of the dodecahedrons.
The most important thing here is to achieve complete identity in the orientation of the two dodecahedrons. When the button is pressed simultaneously, nothing happens. However, the following event may occur, after which the company has appointed a premium: a bell will ring, followed by an impressive firework, accompanied by the complete destruction of this particular dodecahedron.
Button presses are spatially separated events: according to the theory of relativity, no exchange of signals conveying information about which buttons users click on is impossible. Quantum theory, on the contrary, fully admits the existence of some kind of “connection” connecting the dodecahedrons through space-like separated events. Generally speaking, this “connection” cannot be used to transmit directly “usable” information, and in this sense there is no operational conflict between the SR and the CT. There is only a conflict with the spirit of SRT - which, in fact, is an excellent illustration of one of the most profound Z-puzzles of quantum theory, the phenomenon of quantum nonlocality. Two atoms in the center of the dodecahedra form a linked state, and, according to the rules of standard CT, they cannot be considered as separate independent objects.
Now the most important thing is that when users begin to press buttons, this “long-range communication” should be present, and its nature is such that a signal transmission at a distance of about four light years occurs, apparently, instantly. The secret of the company is that they simply take and hang one atom at the center of each dodecahedron, whose spin is equal, no more, no less.
Pressing the button activates the measurement of an atom located in the center of the corresponding dodecahedron. The possible results of measuring a particle with spin are only four; they correspond to four mutually orthogonal states. When you press any button, the measuring device will certainly be oriented in the direction (from the center of the dodecahedron) to this same button.
The bell rings (the result is “yes”) if an atom is detected in the measurement in the second of four possible locations. In other words, the other three states do not cause any reaction (the answer is “no”). If the answer is no, the three remaining beams are brought together (say, by changing the direction of the non-uniform magnetic field to the opposite), which is not accompanied by any destructive effects, and we can again press any other button, thereby selecting the new direction of change. fields.
As a key assumption, we assume that there is no long-range "connection" between the earth and alpha dodecahedron. We will assume that after the dodecahedrons have left the “assembly shop”, they exist separately and completely independently of each other.
Predictions of a quantum mechanical formalism cannot be described in terms of objects considered separately from one another. "Linked" in this outlandish way objects remain linked regardless of the distance they happen to move away from each other.
Schrödinger first called these particles "entangled" or linked. Today, most experiments with entangled particles use photons. This is due to the relative simplicity of obtaining entangled photons and their transfer to the detectors.
Quantum skeptics and optimists
In 1983, Richard Feynman expressed the idea that it is possible in principle (in the language of mathematics) to describe processes of any complexity that occur in nature by using for computing (information processing) processes of the same complexity as, for example, processes occurring in the quantum world.
After that, for a long time, the efforts of researchers in the field of quantum informatics were divided, roughly speaking, into two directions.
On the one hand, physical devices (qubits) that could hold and process quantum information were actively created, but at the same time all experiments ultimately boiled down to testing a small number of qubits (up to 10), setting a goal to "demonstrate the fundamental possibility" rather than create a real computer. On the other hand, applied mathematicians , who developed quantum algorithms that significantly reduce the number of operations performed (exactly this number depending on the length of the input number determines the complexity of the algorithm) for solving problems that are practically “unsolvable” by classical (non-quantum) methods, did not idle . However, all the proposed algorithms assumed the existence of a “spherical horse in a vacuum,” in other words, ideal qubits and logical operations perfectly performed on them.
At the end of the 90s of the last century, it became clear that the success of quantum informatics depends on the “non-sphericity of the horse” and the presence of the “atmosphere”, that is, on the ability to implement quantum algorithms in real conditions, in the presence of noise. Noise interferes with any calculations , both quantum and classical, since it introduces an error into all elements of the computational process (initial data, logical operations, data reading, etc.). Errors arising from classical calculations, learned to correct even in the time of Shannon. With quantum systems, everything is much more complicated - they are more sensitive to external noise, and classical error correction methods are not applicable to them due to the fundamental properties of nature (measurement-reading destroys the state of a quantum bit). Skeptics believed that all the effectiveness of ideal quantum algorithms would be reduced to "no" when trying to extract information from a quantum system.
However, in 1997, Peter Shor is the author of the most well-known quantum algorithm, and John Preskill and several other researchers developed such error correction methods in quantum systems that do not lead to a significant lengthening of the algorithm itself (more precisely, they require performing a polynomial number of correction operations). In addition, quantum information coding schemes have been proposed, allowing for error-resistant computing. After that, everyone calmed down a bit, skeptics died down, and optimists began to create new physical implementations of qubits, new (non-digital) concepts of quantum computing with even greater zeal, and try to build a quantum computing device containing more than two qubits. However, in more than 10 years of this century, to overcome the so-called. “Quantum gap” (i.e., to keep more than 10 qubits in superposition) was not possible (the Canadian company D-Wave claims that it managed to create a quantum computer with the number of qubits of about 1000, but the published companies do not allow to unconditionally believe this statement).
Skeptics and pessimists once again perked up and put the question to the core - or maybe a quantum computer is completely impossible?
Skeptic Gilles Qalayi believes that an increase in the number of qubits will lead to a catastrophic increase in errors, the correction of which will take as much time as the solution of the problem on a classical computer. His main argument is the possibility of the generation of noise by “wrong” quantum correlations, which in a large system will be distributed according to the domino principle and cover all qubits. In other words, what makes a quantum computer such a powerful and attractive computing tool, namely, quantum correlations, leads to an equally powerful and rapid increase and spread of noise.
The optimist Aram Harrow believes, following Einstein, that nature is cunning but not insidious ("God is subtle but not malicious"). Harrow believes that in those specific systems that have been created to date, correlated noise is either unlikely or can be taken into account and eliminated as a systematic error. Given the linearity of the equations of quantum mechanics, Harrow sees no reason for the catastrophic propagation of noise (subject to the regular application of error correction procedures).
Other scientists are actively involved in the discussion. The weighty arguments of the parties are not yet sufficient for revealing the secrets of nature, but the debaters do not lose hope of winning the dispute, looking for new facts.
findings
Modeling, construction and operation of a quantum computer is possible with the following interdisciplinary approach:
- programming ( computer architecture , parallel computing )
- particle physics
- overloking
- cryptology
Sources:
Brian Green "Cosmos Fabric"
Richard Penrose "Shadows of the Mind"
ko.com.ua/100000_ili_kakovoj_budet_cena_otkrytiya_62001
ru.wikipedia.org/wiki/quantum_computer
www.supercomputers.ru
blogs.computerra.ru
a lot of literature on this topic here here and here
according to the author of the theory of B. Green’s strings, the phenomenon of quantum coupling at a popular level is well described in recent books:
Siegfried T. The Bit and the Pendulum. New York: John Wiley, 2000;
Johnson G. A Shortcut Through Time. New York: Knopf, 2003.
Source: https://habr.com/ru/post/156105/
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