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You've probably seen Schrödinger's cat-a cat in a superimposed state of life and death. Now, let’s say hello to the scientists of the Schrodinger series-these researchers are currently in a state of excitement and fear.
Schrödinger's famous thought experiment has entered people's lives through some new form, because quantum researchers have stood at the top of an achievement through long-term exploration: to create a quantum computer that cannot be matched by traditional computers. Opponents insist that quantum computers are a scientific fantasy that is difficult to realize; quantum researchers have spent years refuting this view. Now, they can finally feel comfortable with themselves before others.
But media reports that over-exaggerated progress also flooded in. For example, on February 17, 2014, Time magazine announced the characteristics of quantum computing. The editors also declared on the cover that this "infinity machine" (InfinityMachine) is extremely revolutionary and "promises to solve the problems faced by humanity. The most complicated question." Since then, many media descriptions have become equally exaggerated.
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Graeme Smith, a quantum computing researcher at the University of Colorado at Boulder, explained the challenges facing the field. "In the past, if you were working in this field, you would be optimistic about telling everyone its bright future. But the situation has changed, and now, even researchers like me cannot believe what the media reports say. ——The quantum computer can solve every problem in an instant. The question of what the quantum computer can do seems to be exaggerated without a limit."
People are so excited because quantum computers are expected to achieve an important milestone sometime this year. In the competition between the Google research team and the IBM research team, scientists are expected to demonstrate "quantum hegemony." This means that the system will be able to solve the problem that existing traditional computers are helpless due to insufficient storage capacity or computing power.
Although the title party claims that "quantum hegemony" will make "the arrival of quantum computing" inevitable, its achievements will not be as significant as the mainstream media boast. First of all, the algorithm used by Google to demonstrate quantum hegemony did not accomplish anything of practical significance: the problem designed by the researchers did not involve the existing computational scope of traditional computers.
Building a quantum computer that can solve the computational problems that people really care about in the real world requires years of arduous research. In fact, both Google and IBM's quantum computing engineers say it will take decades to build a quantum "dream machine" that can solve the most difficult computing problems.
Even then, people in the industry would not expect quantum computers to replace traditional computers-although it is generally believed that the failure of traditional computing Moore's Law will give quantum computers a chance to dominate the world. In all current quantum computer designs, they are matched with traditional computers that perform a large number of preprocessing and postprocessing steps. In addition, since the hardware and software that can enable quantum computers to perform tasks smoothly have just started, the daily programming tasks that traditional computers can quickly perform at present may become very slow in quantum computing.
"I don't think anyone would expect quantum computers to replace traditional computers." Quantum researcher Stephen Jordan said. Jordan has worked at the National Institute of Standards and Technology (NIST) for many years and recently joined the Microsoft Institute in Redmond, Washington. Perhaps, quantum machines are only suitable for certain computing tasks that have huge benefits that traditional computers cannot easily handle.
The view of quantum computers can be traced back to a speech by Richard Feynman, the 1981 Nobel Prize winner and physicist. He proposed that the properties of subatomic particles can be used to simulate the behavior of other subatomic particles. But a better starting point in this area is a paper by Peter Shor (formerly AT&T Bell Labs, now at the Massachusetts Institute of Technology) in 1994, which shows a quantum computer—assuming people can Create a quantum computer-how to quickly find large numbers of prime factors to decipher common public key encryption systems. Such a computer can basically break the Internet.
Many people have noticed this article, especially the US security agencies involved in encryption technology, they soon began to invest in quantum hardware research. In the past 20 years, the relevant investment in this field has reached billions of dollars, and the main investor is the government. Nowadays, the existing technology is more and more commercialized, and venture capitalists are also taking action. This situation is likely to be related to the current hype about quantum technology.
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So how does a quantum computer work?
It is very difficult to give a simple and easy-to-understand answer. Because of this, in April 2016, Canadian Prime Minister Justin Trudeau answered this question as easily as other laymen before he was named a geek hero. At a news conference, Trudeau explained: "Ordinary computers... use 1 or 0, which is a binary system. And quantum states can be programmed with more complex information in 1 bit." This explanation is fast It is a household name.
If Trudeau has more time, he may continue to say that the main basic unit of a quantum computer is a "qubit"-a qubit is a quantum object and can be in an infinite variety of states. They are assumed when measuring qubits. The probability of being in one of two states is related. Any object with quantum characteristics (such as electrons or photons) can be used as a qubit, as long as the computer can isolate and control it.
Once each qubit is formed inside a computer, it complies with some mechanism that can transfer electromagnetic energy to it. In order to run a specific program, the computer quickly moves the qubits at a specific frequency and duration according to a script sequence (such as microwave transmission). These pulses correspond to the "instructions" of the quantum program. Each instruction allows the undetermined state of the qubit to evolve in a specific way.
These pulse operations are not performed on only one qubit, but on all qubits in the system. Usually each qubit or a group of qubits receives a different pulse "instruction". The process of quantum bit interaction in quantum computers is called entanglement; in a sense, this process is related to their future. It is worth mentioning that quantum researchers have found ways to use the continuous changes in the state of qubits in computers to perform effective calculations.
After the program is completed (that is, after thousands or even millions of pulses are sent out), the state of the qubits is measured, revealing the final calculation result. This causes each qubit to become 0 or 1, which is the collapse of the well-known wave function in quantum mechanics.
The qubit must be isolated from even the smallest amount of external interference (at least before the calculation is completed). If not, quantum computing will be a very simple project. But it is difficult to achieve isolation, which is why until a few years ago, the largest quantum machine had at most a dozen qubits, and only the simplest algorithms could be executed.
Due to the surrounding noise, qubits are prone to errors. To solve this problem, quantum computers need spare qubits. If there is a problem with a qubit, the system will mobilize the spare qubit to restore the wrong qubit to the correct state.
Conventional computers also have this kind of error correction process. But the number of qubits required by quantum systems is huge. Engineers estimate that to obtain a reliable quantum computer, each qubit used may require 1,000 or more spare qubits. Because many advanced algorithms require thousands of qubits to run, the total number of qubits required for a practical quantum machine (including those related to error correction) can easily reach millions.
In contrast, the latest quantum computing chip released by Google contains only 72 qubits. The computational value of these qubits will depend on their error proneness.
In 2014, Google hired a team at the University of California, Santa Barbara to conduct quantum computer research. In November 2017, IBM announced the successful construction of a 50-qubit quantum computer. The chips used by these two companies, as well as the Berkeley, California-based startup Rigetti Computing and Intel (which recently announced the launch of a 49-qubit array), have been specially designed to possess quantum characteristics due to the superconducting circuit loops they contain . These chips must be kept at extremely low temperatures, so a cooling system the size of a closet like a Hollywood sci-fi movie prop is needed.
There is a completely different quantum hardware architecture, in which the quantum particles, ions, can be suspended in a system operating at room temperature. The startup IonQ (located at the University of Maryland Parker campus) co-founded by Duke University physicist Jungsang Kim and Christopher Monroe at the University of Maryland is working on building a Machines using ytterbium ions.
Microsoft is pursuing the third strategy, namely topological quantum computing. It is theoretically feasible, but currently there is no effective hardware.
None of these systems is close to the quantum computer platform from D-Wave Systems in Canada that has gained the most public attention in recent years. Although well-known companies such as Google and Volkswagen have adopted D-Wave machines, most people in the field of quantum research are still skeptical of these devices. These scientists believe that what the traditional computer cannot do, the D-Wave system is also impossible to do; and also questioned whether the system really achieved quantum acceleration.
Google-IBM-Rigetti’s superconducting strategy seems to be leading the way in this hardware competition, but it is not yet clear which form of hardware will ultimately win; there is also a possibility that these three methods will coexist. Quantum programmers say they don’t care which design wins in the end, they just want to play the role of qubits.
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There are many unknown factors in quantum computing, one of which is how fast a machine can provide additional qubits. With the development of traditional computer technology, Moore's Law can ensure that the number of transistors doubles every two years or so. However, due to the complexity of the electronics associated with quantum machines, it is currently impossible to make similar predictions. Many engineers expect that in the future, we will stop at machines with a relatively small number of qubits (possibly only a few hundred). Given that basic demonstrations of quantum hegemony may not provide useful results, and it will take many years for mature systems to appear, engineers are focusing on algorithms that can be run in small quantum systems that have recently come out.
The consensus that people are about to form is: Although surprises may appear at any time, progress cannot be achieved overnight.
"Those who claim that quantum computers can solve real-world problems soon, or claim that using quantum computers to make big money, I don't think they are telling the truth." Wim van Da, a physicist at the University of California, Santa Barbara Wimvan Dam said, "To achieve these goals, you need a larger system. But this does not mean that the current progress in this area is not exciting."
In the 20 years since Peter Sholl of the Massachusetts Institute of Technology developed the factorization algorithm, quantum computing has become closely related to cryptography. However, in recent years, people’s concerns about cracking Internet encryption have eased, partly because the quantum community has realized that there is still a long way to go to implement the machine described by Shore, and partly because it can resist The "post-quantum cryptography" of quantum attacks is on the rise. Even now, the National Institute of Standards and Technology is evaluating various candidate methods for post-quantum encryption infrastructure.
With Feynman's unique insights into quantum computing, researchers are not completely limited to encryption, but tend to use computers to simulate atoms and molecules. The researchers said that in the National Institute of Standards and Technology's quantum algorithm concentration, physical and chemical simulation algorithms are the most, and the benefits are also considerable. For example, imagine what a superconducting metal near room temperature would look like.
But be careful not to overstate it. According to Andrew Childs, a physicist and computer scientist at the University of Maryland, the first generation of quantum computers can only solve relatively simple physical and chemical problems. "You can appropriately use a small number of qubits to answer questions that can also be answered in the field of polymer physics," he said, "but to understand more, such as high temperature superconductivity, more qubits are needed."
Although the researchers caution against being overly optimistic about the new quantum computer, they do not rule out that future breakthroughs will be able to solve more problems with less energy. The more programmers practice, the better the algorithm will be, which is why IBM puts its quantum machines online for researchers.
"I can write on this white paper the names of all quantum algorithm researchers on the planet. This is the problem." Chad Rigetti of Berkeley Rigetti Quantum Computing said, "We need to be on the algorithm To make greater progress, it is necessary to provide tens of thousands of students with learning machines, which will help promote the development of this field."
As far as these students are concerned, standing on the tide of the new era, and showing the huge potential of amazing new discoveries in the future, which makes them happy. Daniel Freeman, a graduate student in the physics department at the University of California, Berkeley, said that quantum machines are still in the early stages of development as a feature of this research field, not a flaw.
He said: "We are in a position that is almost equivalent to the nascent period of traditional computing 100 years ago, and has not even entered the vacuum tube stage. But I think this is really cool."
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Details
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