Quantum computers: how they work

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Quantum computers: how they work
Quantum computers: how they work

Experts predict that ordinary computers will soon be replaced by quantum ones, which are several times more powerful than modern computing systems. But what are quantum computers?

Quantum computers

According to experts' forecasts, very soon, after 10 years, microcircuits in computers will reach atomic measurements. It seems logical that the era of quantum computers is coming, with the help of which the speed of computing systems can increase by several orders of magnitude.

The idea of ​​quantum computers is relatively new: in 1981, Paul Benioff first theoretically described the principles of the quantum Turing machine.

In the 1930s, Alan Turing first described a theoretical device that was an endless ribbon divided into small cells. Each cell can contain the character 1 or 0, or it remains empty.

The control device moves along the tape, reading characters and writing new ones. A set of such symbols is used to compose a program that the machine must execute.

In Benioff's quantum Turing machine, the principles of operation remain the same, with the difference that both the tape and the control device are in a quantum state.

This means that the symbols on the tape can be not only 0 and 1, but also superpositions of both numbers, that is, 0 and 1 at the same time. Thus, if the classical Turing machine is capable of simultaneously performing only one computation, then the quantum one deals with several computations in parallel.

Today's computers operate on the same principle as normal Turing machines - with bits that are in one of two states: 0 or 1. Quantum computers have no such restrictions: information in them is encrypted in quantum bits (qubits), which can contain superposition of both states.


Physical systems realizing qubits can be atoms, ions, photons, or electrons, which have two quantum states. In fact, if you make elementary particles carriers of information, you can use them to build a computer memory and processors of a new generation.

Thanks to the superposition of qubits, quantum computers are designed from the ground up to perform parallel computations. This parallelism, according to physicist David Deutsch, allows quantum computers to perform millions of calculations at the same time, while modern processors only work with one single one.

A 30-qubit quantum computer will be as powerful as a supercomputer running at 10 teraflops (trillion operations per second). The power of modern desktop computers is measured in only gigaflops (billion operations per second).

Another important quantum mechanical phenomenon that can be exploited in quantum computers is called entanglement. The main problem with reading information from quantum particles is that during the measurement process they can change their state, and in a completely unpredictable way.

In fact, if we read information from a qubit in a superposition state, we get only 0 or 1, but never both numbers at the same time. This means that instead of a quantum one, we will be dealing with a normal classical computer.

To solve this problem, scientists must use measurements that do not destroy the quantum system. Quantum entanglement provides a potential solution.

In quantum physics, if you apply an external force to two atoms, they can be "entangled" together in such a way that one of the atoms has the properties of the other. This, in turn, will lead to the fact that, for example, when measuring the spin of one atom, its "entangled" twin will immediately assume the opposite spin.

This property of quantum particles allows physicists to know the value of a qubit without directly measuring it.

One day, quantum computers may replace silicon chips, just as transistors replaced vacuum tubes. However, modern technologies do not yet allow building full-fledged quantum computers.


However, with each passing year, researchers are announcing new advances in quantum technology, and the hope that one day quantum computers will be able to outperform conventional computers continues to grow.


Researchers at the Massachusetts Institute of Technology managed for the first time to distribute one qubit between three nuclear spins in each molecule of liquid alanine or trichloroethylene molecule. This distribution made it possible to use "entanglement" for non-destructive analysis of quantum information.


In March, scientists at Los Alamos National Laboratory announced the creation of a 7-qubit quantum computer in a single drop of liquid.


Demonstration of Shor's algorithm computation by specialists from IBM and Stanford University on a 7-qubit quantum computer.


At the Institute of Quantum Optics and Quantum Information at the University of Innsbruck, for the first time, it was possible to create a kube (a combination of 8 qubits) using ion traps.


Canadian company D-Wave has demonstrated the first 16-qubit quantum computer capable of solving a variety of problems and puzzles such as Sudoku.

Since 2011, D-Wave has been offering for $ 11 million a D-Wave One quantum computer with a 128-qubit chipset that performs only one task - discrete optimization.

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