What is a quantum computer?

A few days ago, Google's quantum computing research has attracted a lot of attention, and there are voices in the currency circle that if the development of quantum computers may endanger the security of cryptocurrencies, what exactly is a quantum computer? Jerry, I spent some time researching, but because the quantum-related information is really hard to understand, I want to explain it with my own understanding. If there are any mistakes, I hope you can correct me.

Speaking of quantum Quantum, most people probably heard the word from the movie "Ant-Man". Quantum material force is a kind of knowledge in the microscopic world. It is very different from the physics of the macroscopic world and is independent. I have learned in physics class, what about Planck's constant, wave-particle duality, double-chariot seam experiment, etc., mainly to show that at the microscopic scale, these particles (such as electrons or photons) will have some difficult to explain This is also the key point, so if you can't understand the content of the meeting, it is absolutely normal!

Well, back to the quantum computer, first of all we need to know that the computer uses bits (Bit) to perform binary operations, each bit is either 0 or 1, but quantum computers are based on qubits (Qubit or Qbit) to do operation, and Qubit is a superposition state, that is, a state in which the bits of a quantum computer store 0 and 1 at the same time (I know it is very strange, but you can continue to accept it first), and because of the bits of this superposition state, the quantum computer has It has more powerful computing power than ordinary computers, so why does it exist in two states at the same time? This is about the properties of quantum.

Particles with quantum properties can be used as qubits, such as atomic nuclei, photons or electrons. Because electrons have spin (Spin) properties, we can judge its spin direction. The lowest energy is 0 and the highest is 1. Here So far, it is no different from ordinary bits, but the special feature of qubits is the "superposition", the qubits are both 0 and 1 when they are "unobserved" (yes, they are two states at the same time) the existence of ), so the real difference of qubits is the existence of quantum superposition state and probability. In short, qubits can represent 0 and 1 at the same time, which also means that if a qubit can be designed to read Effectively, 1 Qbit can replace the computing power of a traditional computer (2bit).

This may not seem like much, but when the number of qubits increases, the results are very different. 2Qbit can contain 4bits of information, and 3Qbit can perform 8bit operations, which means that an N-bit quantum computer can perform N of 2. The calculation of the amount of information to the power is why scientists have such great expectations for quantum computers. Because of the characteristics of quantum, the operation of quantum computer is equal to the operation of multiple possibilities at the same time, so it can be imagined as the concept of parallel universe (the concept of parallel universe is originally a hypothesis discussed from quantum mechanics).

But not all operations of quantum computer are fast. In fact, it is only for some special operations. If it is general operations or watching movies, your computer or mobile phone is faster. In other words, quantum computers may not replace you and me. Of course, quantum computers are still in the open. It is difficult for us to infer how the future will be. Don't worry if you still don't understand quantum computers and quantum mechanics after reading this article. Scientist Feynman also said: "I can tell you with certainty that no one really understands quantum mechanics", and my high school experience is, don't ask, Back it up and calculate it!