# Quantum computers surpass ordinary computers

At any time now, quantum computers will solve a problem that classical computers cannot solve. At least, this is what we have been hoping for. Scientists and companies are working towards this computational milestone called quantum supremacy, and this milestone seems to be outside of our capabilities.

In short, it is difficult to control the quantum properties of particles. Even if we can use them for calculations, “quantum supremacy” is a misleading term. The first argument for quantum supremacy is almost certainly a man-made issue, and there will be no actual or consumer use. Nonetheless, this is a crucial milestone when it comes to benchmarking these devices and determining what they can actually do. So what is holding us back to the future?

John Presskill, professor of theoretical physics at the California Institute of Technology, invented the term “quantum supremacy.” “We are at a critical stage.”

You may first want to know what a quantum computer is, or basically, what a computer is. Computers are devices that abstract data and store them as input. They operate through command systems and mathematical algorithms. Generally, data is stored as operable bits, two physical devices of choice, allowing the system of these bits to produce some desired output. On quantum computers, algorithms are mapped to a different architecture; in addition to bits, there are two devices called qubits, which follow the strange rules of quantum mechanics.

Each qubit is a bit like a double-sided dice, you can install it with a piece of iron to adjust the probability of you rolling on either side. Performing quantum calculations is like rolling dice. But you can entangle qubits, which are like magnetized iron plates, so the dice must be treated as a single-sided dice with its own set of probabilities. This can cause interference-making certain sides of the dice more likely to roll, while other sides are less likely to roll. Quantum computing applies gates to these dice energy pulses. These energy pulses will further affect the position of the weight inside the dice and change the dice you will roll. Applications involve mapping some information to each side, and often require many dice to get interesting results.

Scientists and technology companies pursue quantum computers not only because of their natural scientific interest as experiments that push the limits, but also because of the way they may have an impact on artificial intelligence, cybersecurity, and healthcare. It is speculated that some algorithms running on quantum structures will be faster than those running on classical computers. The most famous is the Shore algorithm, which can resolve very large numbers faster than classical computers. An algorithm that can quickly decompose numbers is very important, because most of our modern encryption algorithms are based on the premise that classic computers can easily multiply two numbers, but it takes a long time to decompose them. A computer capable of running Shor’s algorithm will make this encryption strategy insecure. Others hope that quantum computers can find applications in artificial intelligence (such as quantum neural networks) or help solve chemical problems (such as finding new drugs to treat diseases), which are much more efficient than traditional computers.

But a quantum computer worthy of excitement or worry should be better than an ordinary computer to do the same job. This is why scientists and companies, especially Google, list quantum advantage as a key milestone for their devices.

Proposals for quantum supremacy usually follow the same premise. Build complex and random quantum circuits and measure the values. You will get many answers. Now, use statistical tests to ensure that the answers using these outputs have completed the experiment correctly. Theoretical physicists believe that quantum computers will show advantages in such tasks-basically, as the complexity of the problem increases, the time required for classical computers to calculate problems will increase faster than quantum computers.

From a business perspective, this task seems to be man-made. Quantum advantage shows that quantum computers are better at becoming quantum computers than classical computers. That is not something you can use to treat diseases.

But from a theoretical point of view, this is profound. There is a hypothesis called Church-Turing theory, which believes that any computer problem can be solved with an abstract computer invented by mathematician Alan Turing in 1936. This theoretical computer simplifies all calculation problems into symbols on tape. Then, there is an extended Turing theory of the church-no actual computational model can complete tasks faster than these Turing machines. Theoretical computer scientists gave strong evidence that the extended Church-Turing theory was wrong in the early 1990s. A machine that has achieved quantum advantage will experimentally prove that this view is wrong. It will prove that there are indeed some computer problems, supercomputers are not the most effective way to calculate these problems, and computers based on another architecture, namely quantum computers, can solve these problems.

Quantum supremacy, from a scientific point of view, is to provide scientists with a specific method to determine whether quantum computers will and will not be useful, and to compare them with classical computers. Until the early 1990s, theoretical computer scientists were still designing some artificial problems for quantum computers, and later useful tasks such as the Shore algorithm appeared. Fefferman said: “Don’t say’you spent billions of dollars to solve this man-made problem’, the answer is that we must first lay the foundation.”

It is not useless in itself, because this experiment can make quantum computers a useful random number generator, which can find applications in cryptography, gambling, simulation, and other fields.

But how did you reach this milestone? According to a report by the Massachusetts Institute of Technology Technology Review last year, Google has received help from NASA and hopes to be the first. The team is building and testing a chip, and they hope that this chip can have enough qubits to prove quantum supremacy. Some researchers study the same quantum superiority problem on classical computers for comparison, and devote themselves to computational theory to ensure that a rigorous proof of superiority is obtained.

Researchers will need to verify the results of quantum computer calculations in some way, even if they are only performing calculations that non-quantum computers cannot.

With the vast resources and ideas of NASA, Google, IBM, and other organizations on this issue, you may wonder why it took so long. Currently, the largest commercial quantum device has about 20 qubits, although IBM, Google and IonQ have tested 50-, 72- and even 160-qubit devices respectively. But every step of building and operating a quantum computer is difficult. In addition to silicon transistors on microchips, scientists must use lasers to make their devices. These lasers can capture individual atoms, superconducting materials can conduct current without resistance, thereby exhibiting manipulable quantum properties, or other The underlying structure. This usually requires keeping the processor at a temperature close to absolute zero — at this temperature, the particles have the smallest possible heat. Controlling this system proved to be very difficult, because a small amount of energy from the external environment can cause qubits to collapse into very expensive and very regular bits.

In these limited systems, researchers can only perform a small number of quantum operations, known as “gates,” before the quantum state collapses. Entangling too many qubits can cause the system to collapse. Every time a qubit is added, the complexity of the machine doubles. The electromagnetic pulse of the control system must be perfectly designed.

At the same time, quantum computer scientists are not just trying to defeat classical computers that simulate quantum computers. They try to beat any possible solution that someone can come up with programming a classic computer, which is more difficult to prove. Researchers will need to verify the results of quantum computer calculations in some way, even if they only complete calculations that non-quantum computers cannot.

Graeme Smith, assistant professor at the University of Colorado at Boulder, told Gizmodo: “I bet someone will announce (quantum supremacy) soon, but since it is difficult to verify this fact, people will question whether they have achieved this goal.”

Maybe you have noticed the pattern. No one has yet reached the supremacy of quantum because it is difficult.

IBM scientists are working on a task that may be easier to achieve. They tried to prove “quantum advantage.” “The difference is subtle. Quantum advantage means that quantum computers can perform calculations that classical computers cannot complete in a reasonable time. Quantum advantage simply means that quantum computers can beat classical computers in certain calculations, even if only slightly better. Some researchers Some mathematical proofs have been devised to prove that a quantum computer is always better than a classical computer running the same algorithm. But in this case, the classical computer is subject to a limitation similar to one of the core limitations of today’s quantum computers: it can only perform a few operations at a time , Just like qubits, qubits can only perform a few operations until they collapse.

However, quantum advantage is more advantageous than quantum advantage. Quantum advantage is a high goal, but if the industry is just looking for a faster algorithm, then these quantum advantages may allow quantum computers to be more widely used in the industry faster.

For companies like Google and IBM, these terms carry a lot of public relations work. “Google will say that the goal is supreme, and IBM will say that the goal is the advantage. This will not lead to a huge difference in hardware.”

In the end, when a company that makes quantum computers inevitably announces that it has achieved “quantum hegemony” or “quantum superiority,” this will not be a radical change for the industry. They still refer to relatively small, error-prone devices-what researchers call NISQ, or “noisy medium-scale quantum” machines. These machines will still face the same limitations as prior to the existence of superior devices, such as the short time that qubits can maintain their quantum state, or the number of calculations that qubits can perform before they lose their quantum properties.

A postdoctoral researcher at Lawrence Berkeley National Laboratory said “Quantum hegemony is a stepping stone to our progress, which can solve more interesting problems.” But there are some specific goals to make quantum computers the future code cracking and molecular simulation equipment. “It requires orders of magnitude more qubits and longer gate depths,” she explained-qubits can do more calculations before losing their quantum behavior.

Sara Moradian, a postdoctoral researcher at the University of California, Berkeley, said that to achieve this state, better hardware is needed, including more precise optics for quantum computers that use lasers to trap atoms. Those who are engaged in superconducting quantum computer research hope to see improvements in system wiring and better overall control. Both of these systems need to find a way to increase the scale and size significantly, which is not as easy as adding more bricks to the LEGO tower. Quantum computers also need to correct errors, or store the information of a single qubit across multiple entangled physical qubits to correct possible errors.

Devices are still a breakthrough tool in the study of quantum physics. Maybe they will find useful applications in the short term, whether they show “quantum supremacy”, “quantum advantage”, or even just “quantum usefulness”. “There are many other quantum devices under development, such as sensors and cryptographic tools, which may be applied faster.”

However, for the sake of start-up funding, it is hoped that scientists and technical experts can prove quantum advantages and find useful quantum computer applications as soon as possible.

Quantum hegemony is coming soon, and the pursuit of it will continue to promote scientific progress in a fundamental and far-reaching way. But the quantum advantage of proving a problem will not bring a quantum computer closer to your desk. We must continue to emphasize the uncertainty in this area, especially in terms of short-term potential.

Quantum computers emphasize that science and technology have different goals and provide two very different perspectives to understand quantum supremacy. Technology can feel like a never-ending advance towards better products. But science is slow, unpredictable, and usually more rigorous-it requires people to cover all the foundations in order to understand how these breakthrough new devices actually work before we can claim that quantum computers are actually better one.