# What is a quantum computer.

How are quantum computers different from ordinary computers? We will tell you what qubits are, how quantum computers work and where they will be useful.

The news regularly reports that someone has developed another quantum computer and this will change the future of computing. Google recently announced that its D-Wave quantum computer, which it describes as “quantum superiority,” solves problems a hundred million (!) Times faster than conventional computers. If this is true, then what are the qubits that provide such incredible performance?

A bit of history

For the first time they started talking about quantum computing back in 1980, but then the matter did not advance beyond theory. The physical embodiment of quantum computers was a few years ago. In 2010, at the Technical University of Munich, scientists demonstrated the first working five-qubit computer, and he performed the first tasks for calculating ordinal elements at the IBM research center at Stanford University.

Nowadays, quantum computers are called very productive machines that can surpass even supercomputers used by IT giants or, for example, space agencies like NASA, in speed and computation volume. But any such computer is based on qubits - let's start with them.

What is a qubit

If ordinary computers are measured by the frequency of the processor and RAM, and operate with bits, then quantum computers use qubits for this. A qubit is a basic element of computation, which is a system in which the number of particles is equal to the momentum, and the phase variable (energy state) is the coordinate. while the bits in traditional computers take on the value of either zero or one, qubits can be in both of these values simultaneously and in different combinations. In practice, this makes it possible to create numerous combinations and develop computational speeds comparable to the performance of supercomputers. We have already written about the latter in the article " The first supercomputers: at the dawn of the era of big data ".

A qubit is the smallest possible unit of information in quantum computers that can be simultaneously in several states of space and time. At the same time, the qubits themselves have interesting properties that ultimately determine the incredible computing power that is inherent in quantum computers - first of all, this is superposition and entanglement.

Superposition refers to the ability of qubits to simultaneously be in multiple states. It is the same if, when the coin is tossed up, both "heads" and "tails" fell simultaneously. High-precision lasers or microwave beams are used to superimpose the qubits. In practice, superposition allows a huge variety of different results to be calculated using qubits.

Entangled pairs are pairs where both qubits are in the same quantum state. And if the state of one qubit changes, the second one "repeats" after it. This property speeds up computations many times over that quantum computers are capable of. On the other hand, critical errors often occur due to the confusion in these calculations.

Why is there an ambiguous attitude towards quantum computers?

The main advantage of quantum computers over conventional computers is the speed of computation. Since we live in a world where data is heating up at a high speed, obviously, we need tools that process this data: sort, extract information of a certain type from it, analyze it, train artificial intelligence systems with it. In traditional computing environments, performance grows according to Moore's Law: the number of transistors on processor chips doubles every two years. It's a little different with quantum computers. They are already demonstrating a leap in performance, although not in all tasks that a person needs to solve.

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Why quantum computers aren't universal

Speed and performance are good, but in many cases, accuracy comes first. And here, quantum computers still lag behind traditional computing systems. Qubits often make it impossible to obtain an accurate, unambiguous solution to a problem. and correcting errors eats up additional resources.

Another problem is the complexity of building quantum algorithms. Large teams of engineers are working to adapt classical algorithms to quantum ones. Without this, it is impossible to speed up the execution of even the simplest tasks.

In fact, there are a small number of quantum computers that do not yet stand out in some incredible abilities over the same supercomputers. Problems that can be solved using qubits can be as simple as possible for an office PC, but require a lot of the resources of a quantum computer.

D-Wave and Quantum Superiority

Back to Google and its loud claim of "quantum supremacy". The IT giant to the whole world has declared that its D-Wave solves problems that ordinary computers cannot cope with. Google focused on the Sycamore programmable quantum processor, which is capable of reaching the quantum state of 53 qubits. Supposedly thanks to him, a quantum computer coped with a task in 200 seconds, which would take an ordinary computer 10 thousand years!

This event could have been the greatest technological breakthrough, but, as often happens, the skepticism of competitors got in the way. IBM said that Google, to put it mildly, embellished reality and was seriously mistaken in its performance calculations. and Summit's iBeam computer can do the same calculations as D-Wave, but in two and a half days (not 10 thousand years). Other companies also joined in with criticism and declared that such inventions should be properly assessed not by pretty numbers, but by their real usefulness.

It doesn't really matter who is the first to achieve "quantum supremacy". The main thing is that today there is nothing behind this term that could change our life. The widely advertised D-Wave still knows how to solve ... one problem and at the same time is not able to add 2 + 2 without complex manipulations! Therefore, it is still too early to say that quantum computers will soon change our lives.

Source: dwavesys.com

Where can quantum computers be used?

Quantum computers are the high level in the world of computing. Accordingly, it is inappropriate to use them for solving everyday tasks (and, as we found out above, it is premature). But it is already clear that quantum computers will be needed wherever it is necessary to make accurate economic forecasts, look for formulas for new drugs, develop space flights or simulate the behavior of matter at the molecular level. The first tasks assigned to quantum computers were not easy: in 2016, Google simulated a hydrogen molecule on a nine-qubit computer, and a year later Microsoft announced a quantum programming language integrated into Visual Studio. From more mundane examples, the experience of the Volkswagen automobile concern is interesting. Its engineers have presented a service that calculates the optimal trajectories for buses and taxis in cities.

We are sure that we will soon learn about other, most incredible scenarios for using quantum computers.

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