The principle of quantum overlap and implication has produced great computing power. A 2-bit register in an ordinary computer can only store one of four binary numbers (00,01,1,1) at a time, while a 2-bit qubit register in a quantum computer can store these four numbers at the same time, because each qubit can represent two values. If there are more qubits, the computing power will increase exponentially. Quantum bits are the theoretical cornerstone of quantum computing. In a conventional computer, information units are represented by binary 1 bits, which are either in a "0" state or in a "1" state. In a binary quantum computer, an information unit is called a qubit, which is not only in the "0" state, but also in the "1" state. It can also be in a super-posing state. The superposition state is an arbitrary linear superposition of "0" state and "1" state, which can be either "0" state or "1" state. "0" state and "1" state exist at the same time with a certain probability. By measuring or interacting with other objects, it presents "0" state or "1" state. Any two-state quantum system can be used to realize qubits. For example, the gro und state and the 1 excited state of electrons in hydrogen atoms, the+1/2 and-1/ 2 components of proton spin in any direction, and the left-right rotation of circularly polarized light.

A quantum system contains several particles, which move according to the laws of quantum mechanics, and it is said that the system is in a quantum state in the state space. The state space consists of several eigenstates (i.e. basic quantum states), which are referred to as basic states or basic vectors for short. The state space can be represented by Hilbert space (linear complex vector space). That is, Hilbert space can represent all possible quantum States of quantum system. For the convenience of representation and operation, Dirac proposed to use the symbol X > to represent the quantum state, which is a column vector called KET. Its * * * yoke transposition is represented by < x, which is a line vector and is called bra. The superposition state of a qubit can be described by the unit vector of two-dimensional Hilbert space (that is, two-dimensional complex vector space), and its simplified schematic diagram is shown in the right figure. Quantum computing is likely to make the computing power of computers greatly exceed that of today's computers, but there are still many obstacles. One problem of large-scale quantum computing is that it is difficult to improve the accuracy of the required quantum devices.

The world's first commercial quantum computer

Canadian quantum computing company D-Wave officially released the world's first commercial quantum computer "D-Wave One" in May, 201,and the dream of quantum computer is a big step closer to us. The slogan of D-Wave Company is "Yes, you can have one". In fact, as early as the beginning of 2007, D-Wave demonstrated Orion, the world's first commercial practical quantum computer, but strictly speaking, that system was not a real quantum computer at that time, but a special machine that could solve problems with some quantum mechanics methods.

After four years, D-Wave One was finally reborn and officially unveiled. It uses a 128- qubit processor, which is four times that of the previous prototype, and its theoretical operation speed has far exceeded that of any existing supercomputer. In addition, D-wave will upgrade it to 5 12 qubit in June of 20 13. But don't get too excited. This big guy can only handle the specific task of optimization now. General tasks are far from rivals of traditional silicon processors, and programming needs to be relearned. In addition, in order to reduce the energy level of qubits as much as possible, it is necessary to make qubits from niobium in low-temperature superconducting state, and the working temperature of D wave should be kept near absolute zero (20 mK).

Finally, the price. 20 1 1 year, NASA and Google bought a D-wave quantum computer with 5 12 qubits for about $0/0/0. This is absolutely sky-high, but it is also the inevitability of the beginning of new technologies. Just like the first electronic computer ENIAC cost 400,000 dollars (400,000 dollars in the 1940s).