Quantum computer is a type of physical device that follows the laws of quantum mechanics to perform high-speed mathematical and logical operations, store and process quantum information. When a device processes and calculates quantum information and runs quantum algorithms, it is a quantum computer. The concept of quantum computers originated from the study of reversible computers. The purpose of studying reversible computers is to solve the energy consumption problem in computers.
Ordinary digital computers operate on a binary system of 0s and 1s, called bits. But quantum computers are far more powerful. They can operate on quantum bits (qubits) and can calculate values between 0 and 1. Imagine an atom placed in a magnetic field. It spins like a top, so its axis of rotation can point either upward or downward. Common sense tells us that the rotation of atoms may be upward or downward, but not both at the same time. But in the strange world of quantum, an atom is described as the sum of two states, an atom spinning up and an atom spinning down. In the wonderful world of quantum, every object is described by the sum of all its incredible states.
Imagine a string of atoms arranged in a magnetic field, spinning in the same way. If a laser beam were shined over this string of atoms, the laser beam would jump off the group of atoms, rapidly flipping the spin axis of some atoms. By measuring the difference between the incoming and outgoing laser beams, we have performed a complex quantum "calculation" involving the rapid movement of many spins.
From a mathematical abstract point of view, quantum computers perform calculations with sets as the basic operation unit, and ordinary computers perform calculations with elements as the basic operation unit (if there is only one element in the set, there is no difference between quantum computing and classical computing).