What is a quantum computer?

The closer we get to a quantum computerThe more it becomes a philosophical question, the more it becomes a philosophical question. The first obstacle is that the word "computer" has a very specific meaning. In the 1980s, an American mathematician had a vision of a computer as a device that manipulates information as a series of ones and zeros, or bits. In essence, this is what a classical computer does. A quantum computer, on the other hand, is a device that manipulates information as a series of quantum mechanical states: 0 and 1, or off and on, or up and down. This is what a quantum computer does.

By the way, the word "computer" is an abbreviation for "computing machine" and not a reference to quantum mechanics. When we say "quantum computer", we mean "a machine that uses quantum mechanics to compute". Physicists often use the word "quantum computer" as a synonym for "quantum information processor".

What is the difference between a quantum computer and a classical computer?

Quantum mechanics tells us that we cannot measure a quantum system without perturbing it. A quantum computer uses this perturbing part of the measurement process as the "bit" that controls the next step of the calculation.

Classical computers, which use electrical charges to represent 0 and 1, do not have this bit. We must insist on this point: a classical computer has nothing. The presence or absence of a bit is the fundamental difference between a quantum computer and a classical computer.

What is quantum entanglement?

Quantum entanglement means that two quantum systems are connected in such a way that the state of one of them depends on the state of the other. For example, if one of these quantum systems is in the state of 0, the other must be in the state of 1. And vice versa.

Quantum entanglement is the quantum mechanical link between two quantum systems. It is the mechanism that allows the quantum computer to be faster than any classical computer. The difference between quantum entanglement and classical linking is that classical linking is established by wires or other devices, while quantum linking is established by quantum systems performing measurements on each other.

What is the role of quantum entanglement in quantum computing?

Let us return to the three-qubit quantum computer discussed earlier. If we write 1 for the state of the first qubit, 0 for the state of the second qubit, and 0 for the state of the third qubit, there are two sets of three combinations of ones and zeros that are the same, except that the third combination is upside down:

1 0 0 1 0 1 0 1

0 1 0 1 0 0 0 0

The difference between these two sets of combinations does not depend on the order in which they are written. The order does not matter. But the difference between these two sets of combinations is exactly the same as the difference between the next two sets of combinations:

0 0 0 1 0 0 0 0

0 1 0 1 0 1 0 1

This is the difference called quantum entanglement. The difference does not depend on the order in which the combinations are written. And this is exactly the same difference as in the classical case. That is, there is also entanglement in the classical case.

Why is quantum entanglement useful for quantum computing?

Suppose we have two classical bits, which we will call "left" and "right". We will assume that the state of the left bit is always 0, while the state of the right bit is 1 with probability 0.5. And the states of the two bits are connected. We will assume that when the left bit is in the state of 0, the right bit is in the state of 1 with probability 0.5. This is the classical entanglement.

Now, suppose we want to know whether the bit on the left is in the state of 0 or in the state of 1. We can simply check whether the bit on the right is in the state of 1 or in the state of 0. This is the procedure used in the classical computer. In this case, the bit on the left does not influence the bit on the right and the two bits are separated.

In the quantum case, the situation is different. Suppose there is a three-qubit quantum computer, with the three qubits called "left", "middle" and "right". Suppose that the state of the left qubit is 1, the state of the middle qubit is 0, and the state of the right qubit is 1. Then the probability of getting the result "1" is 0.5, and the probability of getting the result "0"

In theory, a quantum computer will make cubits replace bits, which will help computers perform more complex mathematical calculations in less time. And at the same time they will be able to make the binary system we already know obsolete. So a whole new logic will have to be reinvented for the use of new computers.

This new system will have a great impact on a global level, since it will practically destroy the binary system, and, therefore, the security we know could be violated by quantum computers, even the Pentagon itself could be exposed. That is why, before they go to market, all important agencies and companies will have to adapt to the new change, since in the hands of the wrong people it will cause them to lose thousands of dollars.

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