1. The quantum computer in "The Wandering Earth 2"
The most popular movie in China in 2023 is "The Wandering Earth 2". In "The Wandering Earth 2", there is an artificial intelligence robot MOSS. Its predecessor is the "550W" super quantum computer . "MOSS" is created by it. Name ("550W" reversed 180 degrees is "MOSS").
Moss (the English name of moss), this plant grows in a dark and humid environment, is a metaphor for the situation of human beings, hoping that after the loss of the sun, human beings on earth can still live tenaciously.
MOSS is responsible for managing the affairs of the space station. It is the assistant executor of the "Wandering Earth" program and the executor of the "Tinder" program, and has the authorization of the joint government. It can make the most correct decision in the shortest time, and it is a perfect intelligent body. As long as the data exists, MOSS exists. MOSS has no life span, no cognitive limitations, and eliminates perceptual thinking consciousness, leaving only rational algorithms .
After his wife and daughter died in a car accident, the scientist Tu Hengyu transferred his daughter's thoughts to "550W". Since then, the super quantum computer has begun to learn human emotions and consciousness. Later, when MOSS analyzed the human data on the earth, it came to the conclusion that " it is indeed a luxury to keep human beings rational forever ", and " the best choice to continue human civilization is to destroy human beings ". 
During the crisis of star gravity, MOSS chose to abandon the earth to start the "fire" plan. Later, a bottle of vodka thrown by Liu Peiqiang was ignited, and MOSS was destroyed, and finally the earth was rescued.
2. The core technology of quantum computer
The power of a quantum computer comes from the quantum processor, which is the heart of a quantum computer. Quantum processors are composed of many qubits, and qubits are the basis of quantum processors. Therefore, qubits are the most basic and critical components to support quantum computers, so what exactly are qubits ?
The biggest difference between a quantum computer and a classical computer is that the smallest information unit used by the two is different . The smallest unit of information used by a classical computer is a bit (binary digit), which is called a classical bit. The smallest information unit used by quantum computers is qubit , which is qubit (quantumbinary digit) in English. 
Classical computers perform computations using two information states, 0 and 1, and a classical bit has either the value 0 or 1 . In classical computers, different levels are used to represent the two states of 0 and 1. The low level (0V) represents the information state of 0, and the high level (5V) represents the information state of 1. These two level states It can be achieved by " on " and " off " in the circuit . In a classical computer, 8 bits make up a byte (byte). The byte is the most commonly used unit in a classical computer. For example, the size of an SD card is 4MB, the storage size of a mobile phone is 32GB, and the size of a computer hard disk is 1TB. Among these units "B" is byte. The internal circuit schematics of NAND FLASH and NOR FLASH are shown in the figure below, and each unit cell in the figure is a bit . 
Quantum computers use qubits to perform calculations, and qubits can also use two states of 0 and 1 to represent information (this feature is the same as classical bits), but qubits can also be in a " superposition " of 0 and 1. special status. This is an important characteristic of qubits, and the huge difference between quantum computers and classical computers at this stage also comes from this!
The characteristics of the qubit come from the characteristics of quantum mechanics . The qubit has the following important characteristics:
1. Superposition , the qubit is in the superposition state of 0 and 1 before measurement, and can be detected by an arrow pointing to a certain point on the Bloch sphere. express.
2. Probabilistic . Once the qubit is measured, it will use probability to determine whether it is in state 0 or state 1.
3. Fragility , after the measurement, the quantum state is destroyed, and the state of the qubit becomes a definite state, either in state 0 or in state 1. At this time, information that is either 0 or 1 can be read from the qubit.
3. Eliminate demons
Superposition ? probability ? Quantum entanglement ? What are these! It's really confusing! Let's not be intimidated by these concepts, and then have resistance to quantum computers, so first of all, let's eliminate the demons together !
Quantum computers are not a panacea.
Traditional computers solve problems in all aspects of our daily work and life, and greatly improve our work efficiency and the essence of life. At present, food, clothing, housing and transportation are basically inseparable from traditional computers. Since traditional computers are so powerful, why do we need quantum computers? Can quantum computers really crush traditional computers in various fields ? 
Is the gap between quantum computers and traditional computers really like the gap between Wuling Hongguang and Rolls-Royce ? 
Actually not ! Among the tasks that traditional computers are good at, quantum computers cannot effectively complete most of them. For example, quantum computers cannot complete video playback or run games independently! Quantum computers are not a " panacea ", and quantum computers cannot solve all problems! 
Why Quantum Computers
Although quantum computers are not omnipotent, for some special problems, such as the simulation of complex physical phenomena , traditional computers will be very difficult to deal with, often requiring a lot of time (some problems even take up to 10,000 years). However, some of these problems happen to be handled by quantum computers quickly. If these problems are solved by quantum computers, the processing efficiency will be greatly improved .
For example, random numbers are widely used in the fields of computer and cryptography. At present, the random numbers produced by traditional computers are called "pseudo-random numbers". These random numbers will be applied to computing and communication infrastructure, and some are used in Encrypt data to protect everything from everyday conversations to financial transactions to state secrets. But these "pseudo-random numbers" can be cracked if the computing power is sufficient! At this time, the advantages of quantum computers can be reflected: generating purely random numbers (which cannot be cracked) . 
Not only that ! Quantum computers will solve problems in the fields of materials, biology, mathematics, and physics in the future. With the help of quantum computers, humans can simulate the folding of some protein molecules to help treat Alzheimer's disease and Parkinson's disease.
4. Physical properties of qubits
The three characteristics of qubits are mentioned above: superposition, probability, and fragility . The reason for these three characteristics is that qubits follow some physical characteristics of quantum mechanics . These physical properties are also the soul of our quantum computing. We need to use quantum mechanical properties to solve problems with quantum mechanical properties.
Several main physical properties of qubits: superposition, uncertainty, non-cloning, indistinguishability, entanglement, and fragility . (It’s enough to have a general understanding of these physical properties, so don’t worry too much about these theoretical knowledge)
Superposition (both life and death)
Quantum superposition is a very wonderful property of quantum mechanics, that is, as a quantum object or particle, it can be in different states at the same time . For example, tossing a coin, the result of the toss must be one of two states, either heads or tails. If the coin is spinning in the air, the state of the coin at this time is both heads and tails . The famous "Schrödinger's cat" theory was once vividly expressed as " a cat can be both alive and dead at the same time ". 
Uncertainty (depending on luck)
The principle of uncertainty proposed by Heisenberg, these words are easily misunderstood, and people will mistakenly think that "the measurement is not accurate, not really inaccurate", but it is not the case . The inaccuracy principle should be called uncertainty . The uncertainty principle is not a problem of methods or measuring instruments, but a natural law of the movement of microscopic substances in the quantum world. Uncertainty is one of the biggest characteristics of quantum mechanics, everything is governed by probability , just like whether you can win a lottery ticket, you can only rely on luck ! 
Unclonability (unique)
In 1982, Wootters, Zurek and Dieks proposed the famous single quantum non-clonable theorem in the paper "Single Quantum State Unclonable": Quantum Mechanics cannot achieve the exact same for any unknown quantum state copy. This theory is the same as the German philosopher Leibniz's theory that " there are no two identical leaves in the world ". Everything in the world is different and unique!
Indistinguishability (true and false Monkey King)
The principle of indistinguishability points out that it is impossible to accurately measure two non-orthogonal quantum states at the same time, that is to say, we cannot distinguish particles in the same quantum world , for example, there are two electrons A and B together , we cannot tell the difference between these two electrons, so we cannot determine which electron is A and which electron is B. Just like the real and fake Monkey King in Journey to the West , we cannot tell the difference!
Entanglement (you are me)
Quantum entanglement is a strange phenomenon of quantum mechanics. No matter how far apart the two quanta are in an entangled state, there is a correlation . When one quantum state changes, the other state will be corresponding instantaneously. Change. When two particles are in a state of quantum entanglement, a measurement on one of them immediately tells the result of the other particle without detection .
If the particles in the quantum world are regarded as small balls, we imagine such an experiment: there are two small balls A and B, they fly in opposite directions (the distance between them will become larger and larger), if we observe Ball A finds that ball A spins "clockwise", then we can immediately know that ball B spins "counterclockwise". 
Vulnerability (glass heart)
For the movement of quantum, the influence of all external motion forces can cause it to collapse , and all advanced instruments cannot be accurately measured. Quantum cannot eliminate the influence of external instruments, and it collapses as soon as it is observed. Tiny quantum is the easiest Changes occur instantly due to external influences, and the quantum collapses in an instant. Quantum states are so fragile that measuring, observing, touching or perturbing any of these states will collapse them into classical states . We can think of this feature as a "glass heart" that breaks when touched!
5. Representation of qubits
Bits in a conventional computer are represented by 0 and 1, so how should qubits be represented? There are three representations of qubits: Dirac notation, Bloch sphere representation, and waveform representation .
Dirac notation
Dirac notation is a language designed to meet the precise needs of expressing states in quantum mechanics, and is often used when representing qubits in mathematical expressions. 
As shown in the figure above, | 0 ⟩ represents the 0 state of the qubit, | 1 ⟩ represents the 1 state of the qubit, and the superposition state of the qubit is represented by Dirac as shown in the figure below. 
We talked about the representation of a single qubit earlier, so how to use the Qiu Lak symbol to represent multiple qubits, assuming that there are 4 qubits, the states are | 1 ⟩, | 0 ⟩, | 1 ⟩, this definite state can be written as | 1 ⟩| 0 ⟩| 1 ⟩, or simply | 101 ⟩, as shown in the figure below. 
Bloch sphere representation
In quantum mechanics, the Bloch sphere named after Felix Bloch, an expert in spin physics and nuclear magnetic resonance, is a geometric representation of the pure state space in a two-state system Law. Operations on single qubits commonly used in quantum information processing can be precisely described in Bloch sphere pictures. Any single qubit state can be represented by a point on the Bloch sphere, and the representation of the Bloch sphere is shown in the figure below.
waveform representation
The probability amplitude and phase can be represented using a waveform diagram of a period, and the state of the qubit can be illustrated in terms of probability amplitude and phase. When representing the state of multiple qubits, the waveform representation is more convenient to use. When using waves to represent qubits, the respective probability amplitudes and phases of | 1 ⟩ and | 0 ⟩ can be represented by a periodic wave. The complex number a and the complex number B each represent a train of waves.
The waveform of the complex number a is shown in the figure below.
6. Realization of qubits
6.1 Qubit physical bearer entity
In traditional computers, the physical load of bits is electrons . The circuit uses electrons to generate voltage , and changes the voltage value (high level and low level) through switch control , and finally realizes 0 and 1. The schematic diagram of the level control circuit is as follows.
There are many qubit implementation methods used in quantum scientific research and quantum computers, which can be used as the physical carrying entities of qubits: photons, optical coherent states, electrons, atomic nuclei, optical grids, Joseph junctions, single charged quantum dots, quantum dots . 
Common qubit physical implementation methods are as follows :
Since there are many types of qubit implementation methods, the following introduces two common technologies, Josephson junction and photon .
6.2 Josephson junction
superconducting qubit is realized through Josephson junction circuit . The Josephson junction is a structure composed of a superconductor (SC1)-insulator (insulator)-superconductor (SC2), and the thickness of the insulating layer is usually on the order of nanometers. No current will be generated after a voltage is applied across the Josephson junction, because this structure is an open circuit. When the insulating dielectric thin layer (insulator) is thin enough, electrons can tunnel between SC1 and SC2, and flow from one end to the other to generate current. The Josephson knot is shown below.
a is the superconducting Josephson junction
b is the representation of the Josephson junction in the circuit
c is the circuit model of the Josephson junction
Superconducting qubits are mainly divided into three categories according to different degrees of freedom: charge qubits, flux qubits, and phase qubits . These three kinds of superconducting qubits are all plagued by different noises, resulting in very short decoherence times. The noise sources mainly include charge fluctuations, magnetic flux fluctuations, and quasi-particle noise. The circuit diagrams of the three superconducting qubits are as follows.
a is the charge qubit
b is the flux qubit
c is the phase qubit
A superconducting quantum chip will integrate multiple superconducting qubits, encode quantum information on the qubits, and perform quantum logic gate operations through microwave control, thereby realizing quantum computing. The figure below is a superconducting quantum chip with 5 qubits. The five cross-shaped devices marked Q0−Q4 in the figure are superconducting qubits .
China's superconducting quantum computer achievements The
superconducting quantum chips developed in China include: the 62-bit superconducting qubit chip Zuchongzhi (Zuchongzhi) independently developed by the Quantum Information of the Chinese Academy of Sciences and Pan Jianwei's team; the 26-bit qubit "Tianmu No. guide quantum chip. 
6.3 Photons
Photons can be used as the physical carrying entity of qubits, and qubits can be realized by using the polarization state of photons, the number of photons in light pulses, and the time when photons appear . When using photon polarization state, horizontal polarization is | 0 ⟩ vertical polarization is | 1 〉; when using light pulse photon number, no photon is | 0 〉 photon is | 1 〉; when photon appearance time is used, there is no delay 0 ⟩ with a delay of | 1 ⟩.
An optical quantum computer uses photons as qubits , emits a single photon through a single photon source, uses the vibration direction (polarization) of light as a qubit, and performs quantum operations by inputting it into an optical quantum circuit to achieve quantum computing.
China's Optical Quantum Computer Achievements In
December 2020, the University of Science and Technology of China announced that the school had successfully built a photonic quantum computing prototype " Jiuzhang ", and the qubits of "Jiuzhang" were realized with photons.
7. Current status of quantum computer technology
In the early 1980s, quantum computer probability appeared. After decades of development, the application of technology based on quantum mechanics and the development of quantum computers are still in their infancy, and there are still many difficulties that need to be solved by the technology of all mankind. Current quantum computer technology is in its infancy . 
Quantum computer, as a new tool for human beings, can only be regarded as a "single fire" at present. However, "a single spark can start a prairie fire." Through in-depth research and exploration of quantum computers, it will inevitably ignite the flaming torch that leads mankind to the unknown world. Lead mankind to the sea of stars !