You all used to our computers in the morning to read the news from a smartphone, work laptop, and in the evening watching movies on the tablet. All these devices have one thing in common — silicon processor with billions of transistors. The principle of operation of these transistors is quite simple — depending on the supplied voltage, we obtain at the output a different voltage, or which is interpreted as a logical 0, or logical 1. In order to carry out a division operation, there is a bitwise shift if we, for example, the number 1101 then shifted 1 bit to the left would be 01101, and if we now shift it by 1 bit to the right will be 01110. And the main problem lies in the fact that the same division may need a few dozen of such operations. Yes, given the fact that billions of transistors, this operation takes a nanosecond, but if a lot of operations — we lose on the computing time.
The principle of operation of quantum computers
A quantum computer offers a completely different method of computation. Let's start with definitions:
Quantum computer — computing device that uses the phenomena of quantum superposition and quantum entanglement for data transmission and processing.
Clearer clearly did not. Quantum superposition tells us that the system with some probability exists in all possible States for it (the sum of all probabilities, of course, equal 100% or 1). Let us examine this with an example. Information in quantum computers is stored in qubits — if the ordinary bits can be 0 or 1, a qubit can be 0, 1, and 0 and 1 simultaneously. So if we have 3 of a qubit, for example 110, the expression in bits is equivalent to 000, 001, 010, 011, 100, 101, 110, 111.
What it gives us? Yes, everything! For example, we have numeric password of 4 characters. How to hack a normal processor? Simple brute force from 0000 to 9999. 9999 in the binary system has the form 10011100001111, that is, to write it we need 14 bits. So if we have a quantum PC with 14 qubits — we already know the password: after all, one of the possible States of such a system is the password! As a result, all tasks that now days I think even supercomputers, on the quantum systems will be addressed immediately necessary to find a substance with certain properties? No problem, make a system with the same number of qubits the number of requirements to the substance — the answer will already be in your pocket. You need to create an AI (artificial intelligence? Simple: while normal PCs will cycle through all combinations, a quantum computer will work at lightning speed, by choosing the best answer.
Everything seemed to be great, but there is one important problem — how do we know the result of the calculation? Normal PC it's simple — we can take and consider it by connecting directly to the CPU: logical 0 and 1 there most definitely are interpreted as the absence and the presence of charge. But with the qubits, this will not do — because every time he is in an arbitrary state. And here we come to the aid of quantum entanglement. Its essence lies in the fact that you can get a few particles that are related to each other (scientifically speaking — if, for example, the spin projection of one confusing particles is negative, then the other will be positive). How it looks on your fingers? Let's say we have two boxes, which is a piece of paper. We split the box any distance, opened one of them and see that the piece of paper in her in horizontal stripes. This automatically means that the other paper is in a vertical strip. But the problem is that as soon as we found out the condition of one piece of paper (or particles), the quantum system collapses the uncertainty disappears, the qubits are transformed into ordinary bits.
Therefore, calculations on quantum computers are essentially disposable: we create a system, which consists of entangled particles (where their second "half", as we know). We carry out the calculation, and then "open the box with a piece of paper", we know the state of entangled particles, and therefore the state of the particles in a quantum computer, and therefore the result of the calculation. So for new calculations need to re-create the qubits — simply "to close the box with a piece of paper" will not work — we already know what is drawn on paper.
The question is again a quantum computer can instantly pick up any passwords — how to protect information? Surely with the advent of such devices will disappear. Of course not. Comes to the aid of so-called quantum encryption: it is based on the fact that when you try to "read" the quantum state, it collapses, making any hacking impossible.
Home quantum computer
And the last question — once quantum computers are so cool, powerful, and unbreakable — why are we not using them? The problem is simple — the inability to realize a quantum system in a conventional home. In order for a qubit to exist in a state of superposition indefinitely need very specific conditions: this is a complete vacuum (no other particles), the temperature close to zero Kelvin (for superconductivity), and the complete absence of electromagnetic radiation (for lack of influence on the quantum system). Agree to create such conditions in mildly difficult, but the slightest deviation will lead to the fact that the state of superposition disappears and the calculation results will be incorrect. The second problem is to make the qubits interact with each other in the interaction, their lifetime decreases catastrophically. In the end, with a high for the day is quantum computers with few tens of qubits.
However, there are quantum computers from D-Wave, which have 1000 qubits, but generally speaking, these quantum computers, they are not, because they do not use the principles of quantum entanglement, so they may not work according to classical quantum algorithms:
However, such devices are significantly (thousands of times) more powerful than a PC that can be considered a breakthrough. However, the user will replace the device they Oh so soon — first we need to learn to create the conditions for the operation of such devices at home, or, conversely, "forced" to work these devices in the usual conditions. The steps in the second direction have already been made — in 2013, was created the first dvuhserijnyj quantum computer on a diamond with impurities, operating at room temperature. But alas — it's just a prototype, and 2 of a qubit is not enough for computing. So wait quantum PC for a very long time.