quantum mechanics

[liàng z ǐ lì xué]

Announce discuss Upload video

Physical Theory

open 3 entries with the same name

Collection

see My Collection

zero Useful+1

zero

synonym Quantum Theory (Physical theory) generally refers to quantum mechanics (physical theory)

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Quantum Mechanics, a physical theory, is a branch of physics that studies the movement law of microscopic particles in the material world. It mainly studies the basic theory of the structure and properties of atoms, molecules, condensed matter, atomic nuclei and basic particles. Together with the theory of relativity, it forms the theoretical basis of modern physics. Quantum mechanics is not only one of the basic theories of modern physics, but also Chemistry And many modern technologies.

At the end of the 19th century, people found that the old classical theory could not explain the microscopic system, so through the efforts of physicists, they created quantum mechanics at the beginning of the 20th century to explain these phenomena. Quantum mechanics fundamentally changes human understanding of the structure of matter and its interactions. Except gravity described by general relativity, all basic interactions can be described within the framework of quantum mechanics (quantum field theory).

Chinese name: quantum mechanics
Foreign name: English: Quantum Mechanics
Disciplines: Secondary discipline

Origin: 1900
founder: dirac 、 Schrodinger 、 Heisenberg
Founder of Old Quantum: Plonk ， Einstein ， Bohr

catalog

▪ Solid State Physics
▪ Quantum Informatics
nine Explanation of quantum mechanics
▪ Quantum mechanical problems
▪ explain
ten The overthrow of randomness is a rumor

Brief History of Discipline

Announce

edit

Quantum mechanics is a theory that describes microscopic matter, and relativity It is considered as the two basic pillars of modern physics. Many physical theories and sciences such as Atomic physics , solid state physics Nuclear physics and Particle physics And other related disciplines are based on quantum mechanics.

Quantum mechanics is the description of atoms and Subatomic Scaly physics theory^[1] 。 The theory was formed in the early 20th century, which completely changed people's understanding of the composition of matter. In the micro world, particles are not billiards, but buzzing and jumping Probability cloud , they do not only exist in one location, nor will they reach point B through a single path from point A^[1] 。 According to quantum theory, particles often behave like wave , the "wave function" used to describe the behavior of a particle predicts the possible properties of a particle, such as its position and speed, rather than certain properties^[1] 。 There are some strange concepts in physics, such as entanglement and Uncertainty principle From quantum mechanics^[1] 。

Electronic cloud

At the end of the 19th century, classical mechanics and Classical electrodynamics The shortcomings in describing micro systems are becoming more and more obvious. Quantum mechanics was developed by Max Planck 、 Niels Bohr 、 Werner Heisenberg 、 Erwin Schrodinger 、 Wolfgang Pauli 、 Louis de Broglie 、 Max Born 、 Enrico Fermi 、 Paul Dirac 、 Albert Einstein 、 Compton And a large number of physicists.

The development of quantum mechanics has revolutionized people's understanding of the structure of matter and its interactions. Quantum mechanics has been able to explain many phenomena and predict new and unimaginable phenomena, which were later proved by very accurate experiments. Except through General relativity In addition to the gravity described, all other physics Basic interaction Can be described within the framework of quantum mechanics（ Quantum field theory ）。

Quantum mechanics has no support free will , only in the micro world that matter has Probability wave Isoexistance Uncertainty , but it still has stable objective law , not based on human will, deny Fatalism 。 First, there is still an insurmountable distance between the randomness on the micro scale and the general macro scale; Second, it is difficult to prove whether this randomness is irreducible. Things are a diverse whole combined by their independent evolution, chance And Inevitability existence Dialectical relationship 。 Whether there is randomness in nature is still an open question. What determines this gap is Planck constant , many in statistics Random event Strictly speaking, it is a decisive example.

In quantum mechanics, the state of a physical system is determined by wave function Represents any of the wave functions linear Superimposition still represents a possible state of the system. Corresponding to operator The effect on its wave function; The modular square of the wave function represents the physical quantity Appearing probability density 。

Quantum mechanics is Old quantum theory Developed on the basis of. The old quantum theory includes Plonk Quantum hypothesis Einstein The light quantum theory and Bohr The atomic theory.

In 1900, Plonk Put forward the radiation quantum hypothesis electromagnetic field The exchange of energy with matter is realized in the form of discontinuity (energy sub). The size of energy sub is proportional to the radiation frequency, and the proportional constant is called Planck constant , which leads to Planck formula , correctly giving Blackbody radiation Energy distribution.

In 1905, Einstein introduced Light quanta （ photon ）And gives the energy momentum And the frequency and wavelength of radiation photoelectric effect 。 Later, he proposed that the vibration energy of solid is also quantization , which explains that Specific heat of solid Question.

Plonk

In 1913, Bohr rutherford Based on the original nuclear atom model, the atomic quantum theory is established. According to this theory, electrons in atoms can only move in discrete orbits, and when moving in orbits, electrons neither absorb nor release energy. Atom has certain energy, and its state is called“ Stationary state ”And atoms can absorb or radiate energy only when they move from one stationary state to another. Although this theory has many successes, there are still many difficulties to further explain the experimental phenomenon.

After people realized that light has the duality of waves and particles, in order to explain some phenomena that cannot be explained by classical theories, French physicists De Broglie It was proposed in 1923 Matter wave This concept. It is believed that all microscopic particles are accompanied by a wave, which is called De Broglie wave 。

De Broglie's matter wave equation:

，

, where

, can be

obtain

。

Because microscopic particles have Wave particle duality The motion law of micro particles is different from that of macro objects, and the quantum mechanics describing the motion law of micro particles is also different from that of macro objects classical mechanics 。 When the size of a particle changes from micro to macro, the law it follows also changes from quantum mechanics to classical mechanics.

Wave particle duality

In 1925, based on the understanding that physical theory only deals with observable quantities, Heisenberg abandoned the concept of unobservable orbits, and started from the observable radiation frequency and intensity, and Born 、 Jordang Set up together Matrix mechanics ； In 1926, Schrodinger found the motion equation of the microscopic system based on the understanding that quantum is the reflection of the fluctuation of the microscopic system, and thus established Wave dynamics And shortly thereafter proved that wave dynamics and Matrix mechanics Mathematical equivalence of; Dirac and Jordan independently developed a general transformation theory and gave a concise and perfect mathematical expression of quantum mechanics.

When a microscopic particle is in a certain state, its mechanical quantities (such as coordinates, momentum angular momentum , energy, etc.) generally have no definite value, but a series of possible values, each of which appears with a certain probability. When the state of the particle is determined, the probability that the mechanical quantity has a certain possible value is completely determined. This is 1927, heisenberg Resulting Uncertainty relation At the same time, Bohr proposed Concurrent principle And further explains quantum mechanics.

Quantum mechanics and Special relativity The combination of the two results in relativistic quantum mechanics. through dirac , Heisenberg (also known as Heisenberg, the same below) and Pauli People's work has developed Quantum electrodynamics 。 After the 1930s, the quantization theory describing various particle fields was formed—— Quantum field theory , which forms the theoretical basis for describing basic particle phenomena.

Heisenberg also proposed Uncertainty principle The formula of the principle is as follows:

。

Two Great Schools

Announce

edit

Copenhagen School

For a long time Bohr Leaded Copenhagen School It is regarded as the first school of physics in the 20th century by Chinese scholars. But according to Houyude These existing evidences are lack of historical support.^[10] Feynman Having questioned Bohr's contribution, other physicists believe that Bohr's role in establishing quantum mechanics has been overestimated. In essence, the Copenhagen School is a philosophical school.^[10]

Gottingen School of Physics

Gottingen School of Physics Is the school of physics that established quantum mechanics. yes Gaussian Laid Gottingen School of Mathematics Academic tradition meets physics It is the inevitable outcome of the stage with special development needs.^[9] Born And Frank Is the core figure of this school.^[10]

Fundamentals

Announce

edit

The basic mathematical framework of quantum mechanics is based on: quantum state Description and statistical interpretation of Equation of motion Based on the correspondence rules between observed physical quantities, measurement postulates, and identical particle postulates.

Schrodinger

dirac

Heisenberg

State function

Bohr

In quantum mechanics, the state of a physical system is determined by State function Indicates that the arbitrary linear superposition of the state function still represents a possible state of the system. The change of state over time follows a linear differential equation , this equation predicts the behavior of the system, physical quantity By satisfying certain conditions and representing certain operations operator express; The operation of measuring a physical quantity of a physical system in a certain state corresponds to the action of the operator representing the quantity on its state function; The possible value of the measurement is determined by the Eigenequation Determined, measured expected value By a integral equation calculation. (Generally speaking, quantum mechanics does not predict a single result with certainty for one observation.

Instead, it predicts a set of different possible outcomes and tells us the probability of each outcome. That is to say, if we make the same measurement for a large number of similar systems, and each system starts in the same way, we will find that the measurement result is that A occurs a certain number of times, and B occurs a different number of times, etc. People can predict the result as an approximation of the number of occurrences of A or B, but cannot predict the specific results of individual measurements.) The modular square of the state function represents the probability of the occurrence of the physical quantity as its variable. According to these basic principles and other necessary assumptions, quantum mechanics can explain the relationship between atoms and Subatomic Various phenomena.

according to Bra-ket notation Represents, state function, using< Ψ| And| Ψ> Of the state function probability density use ρ=<Ψ|Ψ> Is expressed by (?/2mi)（ Ψ* ▽ Ψ－Ψ ▽ Ψ*） The probability is the space integral of the probability density.

State function It can be expressed as the state vector expanded in the orthogonal space set, such as

, where | i>is the spatial basis vector orthogonal to each other,

It is Dirac function and satisfies the orthogonal normalization property. State function satisfies Schrodinger Wave equation,

After separating variables, we can get the evolution equation in the non explicitly time-dependent state

, En is energy Eigenvalue , H is Hamiltonian operator 。

So the quantization of classical physical quantities comes down to the solution of Schrodinger wave equation.

Microsystem

System status

In quantum mechanics, there are two kinds of changes in the state of the system. One is that the state of the system evolves according to the equation of motion, which is a reversible change; The other is to measure the irreversible changes that change the state of the system. Therefore, quantum mechanics can not give a definite prediction of the physical quantity that determines the state, but can only give the probability of the value of the physical quantity. In this sense, Classical physics The law of causality has failed in the micro field.

Accordingly, some physicists and philosophers assert that quantum mechanics rejects causality, while others believe that the causality of quantum mechanics reflects a new kind of causality - probabilistic causality. In quantum mechanics, the wave function representing the quantum state is defined in the whole space, and any change of the state is realized in the whole space at the same time.

Microsystem

quantum mechanics

Since the 1970s, experiments on the correlation of distant particles have shown that the event of spacelike separation is related to the prediction of quantum mechanics. This connection is the same as Special relativity The view that physical interaction can only be transmitted between objects at a speed not greater than the speed of light is contradictory. Therefore, in order to explain the existence of this correlation, some physicists and philosophers proposed that there is a global causality or global causality in the quantum world, which is different from the local causality based on the special theory of relativity, and can determine the behavior of related systems on the whole at the same time.

For quantum mechanics quantum state The concept of "0" represents the state of micro system and deepens people's understanding of physical reality. The properties of microscopic systems are always shown in their interactions with other systems, especially observation instruments.

When people describe the observation results in the language of classical physics, they find that under different conditions, the microscopic system is mainly represented by wave patterns or particle behavior. The concept of quantum state expresses the possibility of wave or particle generated by the interaction between micro system and instrument.

Bohr theory

Electronic cloud

Bohr Bohr, an outstanding contributor to quantum mechanics, pointed out that the concept of quantization of electronic orbits. Bohr believes that the atomic nucleus has a certain energy level. When the atom absorbs energy, the atom will transition Higher level or excited state When an atom emits energy, it transitions to a lower energy level or ground state, Atomic energy level The key to whether the transition occurs is the difference between the two energy levels. According to this theory, it can be calculated from the theory Rydberg constant , which is in good agreement with the experiment.

But Bohr's theory also has limitations. For larger atoms, the calculation error is large, and Bohr still retains the macro world Middle track In fact, the coordinates of electrons in space are uncertain. The more electrons gather, the higher the probability of electrons appearing here. On the contrary, the lower the probability. Many electrons gather together, which can be vividly called Electronic cloud 。

Pauli principle

In principle, it is impossible to completely determine the state of a quantum physical system, so the distinction between particles with identical intrinsic characteristics (such as mass, charge, etc.) in quantum mechanics is meaningless. In classical mechanics, the position and momentum of each particle are completely known, and their tracks can be predicted. Each particle can be determined by a measurement. In quantum mechanics, the position and momentum of each particle are determined by wave function Therefore, when the wave functions of several particles overlap each other, the practice of "attaching a label" to each particle loses its meaning.

this Identical particle (identity particles) Symmetry , as well as the statistical mechanics , has far-reaching impact. For example, when exchanging two particles "1" and "2", we can prove that the state of a multi particle system composed of identical particles is not symmetric, that is, it is antisymmetric. The particles in symmetric state are called Boson The antisymmetric particles are called Fermion 。 in addition spin The exchange of is also symmetrical: particles with half spin (such as electrons proton and neutron ）It is antisymmetric, so it is fermion; A particle with an integer spin (such as a photon) is symmetric and therefore boson.

The relationship between the spin, symmetry and statistics of this abstruse particle can only be derived from relativistic quantum field theory, which also affects the phenomena in non relativistic quantum mechanics. One result of the antisymmetry of fermions is Pauli exclusion principle That is, two fermions cannot occupy the same state. This principle has great practical significance. It means that in our material world composed of atoms, electrons cannot occupy the same state at the same time, so after the lowest state is occupied, the next electron must occupy the next lower state until all states are satisfied. This phenomenon determines the physical and chemical properties of substances.

The heat distribution of the states of fermions and bosons is also very different: bosons follow Bose Einstein statistics And fermions follow Fermi Dirac statistics 。

historical background

Announce

edit

At the end of the 19th century and the beginning of the 20th century, classical physics has developed to a quite perfect level, but it has encountered some serious difficulties in the experiment. These difficulties are regarded as "several dark clouds in a clear sky", and it is these dark clouds that have triggered changes in the physical world. Here are some difficulties:

Blackbody radiation problem

Max Planck

At the end of the 19th century, many physicists Blackbody radiation Very interested. Blackbody It is an idealized object that can absorb all the radiation on it and convert it into thermal radiation. The spectral characteristics of this thermal radiation are only related to the temperature of the blackbody. This relationship cannot be explained using classical physics. By treating atoms in objects as tiny harmonic oscillators, Max Planck To obtain a black body radiation Planck formula 。 But when guiding this formula, he had to assume that the energy of these atomic harmonic oscillators is not continuous (which is contrary to the view of classical physics), but discrete: En=nh ν

Here n is an integer and h is a natural constant. (The correct formula proved later should replace n with n+1/2. See zero point energy.). In 1900, Planck was very careful when describing the quantization of his radiant energy. He only assumed that the absorbed and radiated radiant energy was quantized. Today, this new natural constant is called Planck constant To commemorate Planck's contribution. Its value:

value

Photoelectric effect experiment

photoelectric effect^[2]

Due to ultraviolet radiation, a large number of electrons escape from the metal surface. It is found that the photoelectric effect has the following characteristics:

a. There is a certain critical frequency. Only when the frequency of the incident light is greater than the critical frequency can there be photoelectron Escape.

b. The energy of each photoelectron is only related to the frequency of light.

c. When the frequency of the incident light is greater than the critical frequency, photoelectrons can be observed almost immediately as soon as the light is illuminated.

For the above three characteristics, c is a quantitative problem, while a and b cannot be explained by classical physics in principle.

Atomic spectroscopy

Spectral analysis has accumulated a wealth of data. Many scientists have sorted and analyzed them, and found that Atomic spectrum It is a discrete linear spectrum rather than a continuous distribution. The wavelength of the spectral line also has a very simple rule.

After Rutherford's model was discovered, according to classical electrodynamics, accelerating charged particles will continue to radiate and lose energy. Therefore, electrons moving around the atomic nucleus will eventually fall into the atomic nucleus due to a large loss of energy. So the atom collapses. The real world shows that atoms exist stably.

Equipartition theorem of energy

When the temperature is very low Equipartition theorem of energy Not applicable.

Light quantum theory

Quantum theory is the first Blackbody radiation Breakthrough in problems. Planck put forward the concept of quantum - h in order to theoretically deduce his formula, but it did not attract many people's attention at that time. Einstein used quantum hypothesis to put forward the concept of light quantum, thus solving the problem of photoelectric effect. Einstein also further applied the concept of energy discontinuity to the vibration of atoms in solids, successfully solving the phenomenon that the specific heat of solids tends to zero at T → 0K. The concept of light quanta has been directly verified in Compton scattering experiments.

Bohr's quantum theory

Bohr creatively used the concept of Planck Einstein to solve the problems of atomic structure and atomic spectrum, and put forward his quantum theory of atoms. It mainly includes two aspects:

a. Atoms can only exist stably in a series of states corresponding to discrete energies. These states become stationary.

b. When an atom transitions between two stationary states, the absorption or emission frequency v is unique, which is given by hv=En Em.

Bohr's theory has achieved great success, opening the door to people's understanding of atomic structure for the first time. However, with the further deepening of people's understanding of atoms, its problems and limitations are gradually discovered.

De Broglie wave

Inspired by Planck and Einstein's quantum theory of light and Bohr's atomic quantum theory, considering that light has wave particle duality, de Broglie, based on the principle of analogy, assumes that physical particles also have wave particle duality. He proposed this hypothesis, on the one hand, in an attempt to unify physical particles and light, and on the other hand, in order to understand the discontinuity of energy more naturally, so as to overcome the shortcoming of artificial nature of Bohr quantization condition. The direct proof of the fluctuation of physical particles was in 1927 Electron diffraction experiment Implemented in.

Quantum physics

Quantum mechanics itself was established in 1923-1927. Two equivalent theories, matrix mechanics and wave dynamics, were proposed almost simultaneously. The proposition of matrix mechanics is closely related to Bohr's early quantum theory. On the one hand, Heisenberg inherited the reasonable core of early quantum theory, such as the concepts of energy quantization, stationary state, transition, etc., and abandoned some concepts without experimental basis, such as the concept of electronic orbit. The matrix mechanics of Heisenberg, Born and Yordam, which is physically observable, endows each physical quantity with a matrix. Their algebraic operation rules are different from those of classical physical quantities, and they follow the algebra that cannot be easily multiplied.

Wave dynamics The idea comes from matter waves. Inspired by matter waves, Schrodinger found a quantum system of matter waves Equation of motion -Schrodinger equation is the core of wave dynamics. Later Schrodinger also proved that matrix mechanics and wave dynamics are completely equivalent, which are two different forms of expressions of the same mechanical law. In fact, quantum theory can also be expressed more generally, which is the work of Dirac and Jordan.

Quantum physics The establishment of the "" is the crystallization of the joint efforts of many physicists, which marks the first collective victory of physics research.

Experimental phenomenon

Announce

edit

photoelectric effect

In 1905, Albert Einstein By extending Planck's quantum theory, it is proposed that not only the interaction between matter and electromagnetic radiation is quantized, but also quantization is a theory of basic physical characteristics. Through this new theory, he was able to explain the photoelectric effect. Heinrich Rudolf Hertz and Philipp Lenard The experiment of et al. found that electrons can be knocked out of metal by light. And they can measure the kinetic energy of these electrons. No matter the intensity of the incident light, only when the frequency of the light exceeds a threshold (cut-off frequency) can electrons be emitted. The kinetic energy of the ejected electrons increases linearly with the frequency of light, and the intensity of light only determines the number of electrons emitted. Einstein put forward the theory of quantum of light (the name of photon came into being later) to explain this phenomenon. The quantum energy of light is h ν

In the photoelectric effect, this energy is used to eject electrons from the metal (escape work

）And accelerating electrons (kinetic energy):

Einstein photoelectric effect equation:

=h ν-

Here m is the mass of the electron, v Is its velocity, and v is the frequency of incident light.

Atomic energy level transition

Early 20th century Rutherford Model It was considered the correct atomic model at that time. The model assumes that negatively charged electrons move around positively charged atomic nuclei just as planets move around the sun. In this process, the coulomb force and centrifugal force must be balanced. This model has two problems that cannot be solved. First, according to classical electromagnetism, this model is unstable. according to electromagnetics The electron is constantly accelerated during its operation, and its energy should be lost by emitting electromagnetic waves, so that it will fall into Nucleus 。 Secondly, the atomic emission spectrum consists of a series of discrete emission lines. For example, the emission spectrum of hydrogen atom consists of an ultraviolet series (Lyman system) and a visible series（ Balmer system ）And other infrared series. According to the classical theory, the emission spectrum of atoms should be continuous.

In 1913, Niels Bohr A Bohr model named after him is proposed, which gives a theoretical principle for atomic structure and spectral lines. Bohr believes that electrons can only operate in the orbit of a certain energy En. If an electron jumps from a high energy orbit (En) to a low energy orbit (Em), the frequency of light it emits is.

By absorbing photons of the same frequency, we can jump from low-energy orbit to high-energy orbit.

Bohr model can explain the hydrogen atom, and the improved Bohr model It can also explain the ions with only one electron, namely He+, Li2+, Be3+, etc. But can't accurately explain the physical phenomenon 。

Electronic volatility

De Broglie assumes that electrons are accompanied by a wave, and he predicts that when electrons pass through a small hole or crystal, they should have an observable diffraction phenomenon. In 1925, when Davidson and Germer were conducting electron scattering experiments in nickel crystals, they first obtained the diffraction phenomenon of electrons in crystals. When they learned about de Broglie's work, they carried out this experiment more accurately in 1927. The experimental results are in full agreement with the formula of de Broglie wave, which strongly proves the wave nature of the electron.^[3]

The fluctuation of electrons is also reflected in the interference phenomenon of electrons passing through the double slits. If only one electron is emitted at a time, it will randomly excite a small bright spot on the sensitive screen after passing through the double slits in the form of waves. When a single electron is emitted multiple times or multiple electrons are emitted at a time, the light and dark interference fringes will appear on the sensitive screen. This proves once again the volatility of electrons.^[4]

The position of the electronic punch on the screen has a certain distribution probability With time, we can see the special stripe image of double slit diffraction. If a light slit is closed, the image formed is the distribution probability of the wave unique to a single slit.

There can never be half an electron. In the double slit interference experiment of this electron, it is that the electron passes through two slits at the same time in the form of wave, and interferes with itself. It cannot be wrongly considered as the interference between two different electrons. It is worth emphasizing that the superposition of wave functions here is the superposition of probability amplitude rather than that of the classical example“ State superposition principle ”It is a basic hypothesis of quantum mechanics.^[5]

Related concepts

Announce

edit

Waves and particles

Quantum theory interpretation of vibrating particles

The particle nature of matter is determined by energy E and momentum P scribe, wave The characteristics of γ And its wavelength λ The scale factor of these two groups of physical quantities is related by Planck constant h (h=6.626 * 10 ^ (- 34) J · s).

E=h γ, E=mc ^ 2, two simultaneous equations, m=h γ/ C ^ 2 (this is the relativistic mass of the photon, because the photon cannot rest, so the photon has no static mass) and p=mv

Then p=vh γ/ C ^ {2} (p is momentum)

quantum mechanics

The general form of the partial differential wave equation of one-dimensional plane wave of particle wave is

d ξ/ dx=（1/ γ）（d ξ/ dt） [5]

three-dimensional The classical wave equation of plane particle waves propagating in space is

d ξ/ dx+d ξ/ dy+d ξ/ dz=（1/ γ）（d ξ/ dt） [6]

The wave equation is a description of the wave properties of microscopic particles by using the wave theory in classical mechanics. Through this bridge, the wave particle duality in quantum mechanics is well expressed.

The u in the formula 1,1 'or [6] of the classical wave equation implies a discontinuous quantum relationship E=h γ Relationship with de Broglie λ= H/p, because u= γλ， Therefore, you can select u=v λ Multiply the factor (h/h) containing Planck's constant h by the right side of

u=（ γ h）（ λ/ h）

De Broglie

=E/p

Equal relation u=E/p, so that Classical physics And Quantum physics The connection between continuity and discontinuity (localization) is unified

Particle wave de Broglie matter wave

De Broglie relationship λ= H/p, and quantum relation E=h γ (and Schrodinger equation ）These two relations actually represent the unified relationship between wave and particle. De Broglie matter waves are waves of real matter particles, photons, electrons, etc

Heisenberg Uncertainty Principle

That is, the uncertainty of the momentum of the object multiplied by the reduced Planck constant whose uncertainty of position is greater than or equal to 1/2.

measurement process

A major difference between quantum mechanics and classical mechanics lies in the position of measurement process in theory. In classical mechanics, the position and momentum of a physical system can be determined and predicted with infinite precision. At least in theory, measurement has no effect on system itself and can be carried out with the infinite precision. In quantum mechanics, the measurement process itself affects the system.

To describe the measurement of an observable quantity, it is necessary to linearly decompose the state of a system into a set of eigenstates of the observable quantity linear combination 。 The measurement process can be regarded as a projection on these eigenstates, and the measurement result is the eigenvalue corresponding to the projected eigenstates. If we measure every copy of an infinite number of copies of the system, we can obtain the probability distribution of all possible measured values, and the probability of each value is equal to the square of the absolute value of the corresponding eigenstate coefficient.

It can be seen that the measurement sequence of two different physical quantities A and B may directly affect their measurement results. In fact, such is the incompatibility observable.

Uncertainty

The most famous incompatibility observable is the position x and momentum p of a particle. Their uncertainty Δ X and Δ Product of p, greater than or equal to Planck constant Half of:

Heisenberg The "uncertainty principle" discovered in 1927, also known as the "uncertainty relationship" or "uncertainty relationship", means that the mechanical quantities (such as coordinates and momentum, time and energy) represented by two noncommutative operators cannot have certain measured values at the same time. The more accurate one is, the less accurate the other is. It shows that the "interference" of the measurement process on the behavior of microscopic particles leads to the non interchangeability of the measurement sequence, which is a basic law of microscopic phenomena. In fact, physical quantities such as the coordinates and momentum of particles are not information waiting for us to measure. Measurement is not a simple "reflection" process, but a "transformation" process. Their measured values depend on our measurement methods. It is the mutual exclusion of measurement methods that leads to uncertainty.^[6]

probability

By decomposing a state into a linear combination of observable eigenstates, the Probability amplitude c i 。 The absolute value square of this probability amplitude | c i | two Is to measure the eigenvalue n i This is also the probability that the system is in the eigenstate. Ci can be calculated by projecting onto each eigenstate. Therefore, for a Ensemble When a certain observable quantity of the identical system is measured in the same way, generally the results obtained are different; Unless the system is already in the eigenstate of the observable quantity.

Through the same measurement of each system in the same state in the ensemble, the measured value of ni can be obtained statistical distribution 。 All experiments are faced with the problem of statistical calculation of the measured value and quantum mechanics.

Quantum Entanglement

Often, the state of a system composed of multiple particles cannot be separated into the state of a single particle. In this case, the state of a single particle is called entanglement. Entangled particles have amazing properties that defy common intuition. For example, the measurement of a particle can lead to the wave packet Immediately collapses, thus affecting another, remote particle entangled with the measured particle. This phenomenon does not violate Special relativity Because at the level of quantum mechanics, before measuring particles, you can't define them. In fact, they are still a whole. But after measuring them, they will leave the state of quantum entanglement.

Quantum decoherence

As a basic theory, quantum mechanics should, in principle, be applicable to physical systems of any size, that is, not limited to microscopic systems, so it should provide a way to transition to macroscopic "classical" physics. The existence of quantum phenomena raises a question, that is, how to explain the classical phenomena of macroscopic systems from the perspective of quantum mechanics. What cannot be seen directly is how the superposition state in quantum mechanics can be applied to the macro world. In 1954, in a letter to Max Bonn, Einstein proposed how to explain the positioning of macro objects from the perspective of quantum mechanics. He pointed out that only the phenomenon of quantum mechanics was too "small" to explain this problem.

Another example of this problem is Schrodinger Proposed Schrodinger's Cat Thought experiment.

It was not until about 1970 that people began to realize that the above thought experiments were actually impractical, because they ignored the inevitable interaction with the surrounding environment. Facts have proved that the superposition state is very easy to be affected by the surrounding environment. For example, in Double slit experiment Medium, electronic or photon Collision with air molecules or emission of radiation can affect the phase relationship between various states that are critical to the formation of diffraction. In quantum mechanics, this phenomenon is called quantum decoherence. It is caused by the interaction between the system state and the surrounding environment. This interaction can be expressed as the entanglement between each system state and the environment state. The result is that only when considering the whole system (i.e. experimental system+ environmental system ）Only superposition is effective. If only the system state of the experimental system is considered in isolation, then only the "classical" distribution of the system is left. Quantum decoherence It is the main way for quantum mechanics to explain the classical properties of macroscopic quantum systems today.

Quantum decoherence is the realization of quantum computer The biggest roadblock. In a quantum computer, multiple quantum states need to be kept superposed as long as possible. The short decoherence time is a very big technical problem.

Theoretical evolution

Announce

edit

The Emergence and Development of Theory

Quantum mechanics is a physical science that describes the structure, movement and change law of the micro world of matter. It is a major leap in the development of human civilization in the 20th century. The discovery of quantum mechanics has triggered a series of epoch-making scientific discoveries and technological inventions, which have made important contributions to the progress of human society.

At the end of the 19th century, when great achievements were made in classical physics, a series of phenomena that could not be explained by classical theories were discovered one after another. Wien, a German physicist, discovered the thermal radiation theorem by measuring the energy spectrum of thermal radiation. German physicist Plonk In order to explain the energy spectrum of thermal radiation, a bold hypothesis was put forward: in the process of the generation and absorption of thermal radiation, the energy is exchanged one by one with hf as the smallest unit. This assumption of energy quantization not only emphasizes the discontinuity of thermal radiation energy, but also directly contradicts the basic concept of "radiation energy is independent of frequency, determined by amplitude", and cannot be included in any classical category. At that time, only a few scientists seriously studied this problem.

Einstein In 1905, he put forward the theory of light quanta. In 1914, American physicist Millikan published the experimental results of photoelectric effect, which verified Einstein's theory of light quanta.

Einstein

1913 Denmark In order to solve the instability of Rutherford's atomic planet model (according to the classical theory, the electrons in the atom will radiate energy when moving around the atomic nucleus in a circle, leading to the reduction of the orbital radius until they fall into the atomic nucleus), physicist Bohr proposed the hypothesis of steady state: the electrons in the atom can not operate in the orbits of any classical mechanics like stars, and the orbits are stable Action Fpdq must be an integer multiple of h（ Quantization of angular momentum ）, i.e. fpdq=nh, n is called Quantum number 。 Bohr also proposed that the atomic luminescence process is not a classical radiation, but a discontinuous transition process of electrons between different stable orbital states. The frequency of light is determined by the energy difference between orbital states

Determine, that is, frequency rule. In this way, Bohr atom theory explained the discrete spectral lines of hydrogen atom with its simple and clear images, and intuitively explained the periodic table of chemical elements with the electronic orbital state, leading to the discovery of element No. 72, hafnium, which triggered a series of major scientific advances in the following ten years. This is unprecedented in the history of physics.

Because of the profound connotation of quantum theory Copenhagen School They conducted in-depth research on correspondence principle, matrix mechanics Incompatibility principle , uncertainty relationship Complementary principle 。 The probability interpretation of quantum mechanics has made contributions.

In April 1923, the American physicist Compton published the phenomenon of frequency reduction caused by the scattering of X-rays by electrons, namely the Compton effect. According to the classical wave theory, the scattering of waves by stationary objects does not change the frequency. According to Einstein's light quanta, this is the result of the collision of two "particles". The light quanta not only transfer energy but also momentum to the electron when colliding, which makes the light quantum theory get experimental proof.

Light is not only an electromagnetic wave, but also a particle with energy momentum. In 1924, American born Austrian physicist Pauli published the "incompatibility principle": no two electrons in an atom can be at the same time quantum state 。 This principle explains the shell structure of electrons in atoms. This principle applies to the fundamental particles (usually called fermions, such as protons, neutrons quark Etc.) Quantum statistical mechanics ——- Base point of Fermi statistics. In order to explain the fine structure of spectral lines Anomalous Zeeman effect Pauli suggested that for the electronic orbital state originally in, the fourth quantum number should be introduced in addition to the existing three quantum numbers corresponding to the classical mechanical quantities (energy, angular momentum and its components). This quantum number was later called“ spin ”, is an expression Elementary particle An intrinsic physical quantity.

In 1924, French physicist de Broglie put forward the expression Wave particle duality Einstein of—— De Broglie relationship ：E=hV，p=h/ λ， The energy and momentum of physical quantities characterizing particle property are equal to the frequency and wavelength characterizing wave property through a constant h.

In 1925, German physicists Heisenberg and Bohr established the first mathematical description of quantum theory - matrix mechanics. In 1926, Austrian scientists proposed partial differential equation ——Schrodinger equation gives another mathematical description of quantum theory - wave dynamics. In 1948, Feynman The path integral form of quantum mechanics is established.

Quantum mechanics is of universal significance in the scope of high-speed and microscopic phenomena. It is one of the foundations of modern physics. Surface physics Semiconductor physics 、 Condensed matter physics Particle physics, low temperature Superconductor Physics The development of quantum chemistry, molecular biology and other disciplines has important theoretical significance. The emergence and development of quantum mechanics indicates that human understanding of nature has achieved a significant leap from the macro world to the micro world.

Boundary with classical physics

In 1923, Niels Bohr Proposed Correspondence principle It is believed that quantum numbers (especially Number of particles ）The quantum system that reaches a certain limit can be accurately described by classical theory. The background of this principle is that, in fact, many macroscopic systems can be described very accurately by classical theories, such as classical mechanics and electromagnetism. Therefore, it is generally believed that in a very "large" system, the characteristics of quantum mechanics will gradually degenerate to the characteristics of classical physics, and the two do not conflict. Therefore, the correspondence principle is an important auxiliary tool for establishing an effective quantum mechanical model.

The mathematical basis of quantum mechanics is very extensive, which only requires that the state space is Hilbert space The observable quantity is a linear operator. However, it does not specify which Hilbert space and which operators should be selected in the actual situation. Therefore, in reality, we must choose the corresponding Hilbert space and operator to describe a specific quantum system. The correspondence principle is an important auxiliary tool for making this choice. This principle requires that the predictions made by quantum mechanics gradually approximate the predictions of classical theory in an increasingly large system. The limit of this large system is called "classical limit" or "corresponding limit". Therefore, we can use heuristics to build a model of quantum mechanics, and the limit of this model is the corresponding model of classical physics.

Combination with special relativity

In its early development, quantum mechanics did not take special relativity into account. For example, when using the harmonic oscillator model, a non relativity Of Harmonic oscillator 。 In the early days, physicists tried to link quantum mechanics with special relativity, including using the corresponding klein-gordon equation , or Dirac equation Instead of Schrodinger equation. Although these equations have been successful in describing many phenomena, they still have defects, especially their inability to describe the generation and elimination of particles in the relativistic state. Through the development of quantum field theory, the real relativistic quantum theory came into being. Quantum field theory not only quantizes observable quantities such as energy or momentum, but also quantizes the field of medium interaction. The first complete quantum field theory is Quantum electrodynamics It can completely describe the electromagnetic interaction.

It is generally described Electromagnetic system A complete quantum field theory is not required. A simpler model is to treat a charged particle as a quantum mechanical object in a classical electromagnetic field. This method has been used since the beginning of quantum mechanics. For example, the electronic state of the hydrogen atom can be approximately calculated using the classical 1/r voltage field. However, when the quantum fluctuations in the electromagnetic field play an important role, such as a charged particle emitting a photon, this approximation method fails.

Strong weak interaction

Strong interaction Of Quantum field theory yes Quantum chromodynamics This theory describes the particles composed of atomic nuclei（ quark and Gluon ）Interaction between. Weak interaction Combined with electromagnetic interaction Electroweak interaction Medium.

Universal gravitation

So far, only Universal gravitation It cannot be described using quantum mechanics. Therefore, in the black hole Near, or looking at the whole universe as a whole, quantum mechanics may encounter its applicable boundary. Use quantum mechanics, or use General relativity , can't explain that a particle arrived at the black hole singularity The physical condition of the. General relativity predicts that the particle will be compressed to an infinite density; Quantum mechanics predicts that, because the position of the particle cannot be determined, it cannot reach the infinite density and can escape from the black hole. Therefore, the two most important new physical theories in the 20th century, quantum mechanics and general relativity, contradict each other. Seeking an answer to this contradiction is an important goal of theoretical physics（ Quantum gravity ）。 But so far, it is obviously very difficult to find the quantum theory of gravity. Although, some subclassical approximation theories have made some achievements, such as hawking radiation But so far, we can not find a whole theory of quantum gravity. Research in this area includes String theory Etc.

Applied discipline

Announce

edit

In many modern technical equipment, Quantum physics The effect of has played an important role. From laser electron microscope 、 atomic clock reach nuclear magnetic resonance The principle and effect of quantum mechanics are the key to the development of medical image display devices. Research on semiconductors has led to diode and triode The invention of electronics industry Paved the road. stay nuclear weapon The concept of quantum mechanics also played a key role in the process of invention.

In the above inventions, the concept and mathematical description of quantum mechanics seldom play a direct role, but solid physics, chemistry material science perhaps Nuclear physics The concepts and rules of play a major role. In all these disciplines, quantum mechanics is the basis. The basic theories of these disciplines are all based on quantum mechanics. The following can only list some of the most significant applications of quantum mechanics, and these listed examples are certainly not complete.

Atomic physics

Atomic Physics and Chemistry

The chemical properties of any substance are determined by the electronic structure of its atoms and molecules. All relevant Nucleus The electronic structure of the atom or molecule can be calculated by the multiparticle Schrodinger equation and the electron equation. In practice, people realize that it is too complicated to calculate such equations, and in many cases, it is enough to determine the chemical properties of substances as long as simplified models and rules are used. In establishing such a simplified model, quantum mechanics plays a very important role.

A very common model in chemistry is Atomic orbital 。 In this model, the multi particle state of the molecule's electrons is formed by adding the single particle states of the electrons of each atom together. This model contains many different approximations (such as ignoring the repulsive force between electrons, the separation of electron motion from atomic nucleus motion, etc.), which can approximately and accurately describe the atomic energy level 。 In addition to the relatively simple calculation process, this model can also intuitively give the image description of electron arrangement and orbit.

With atomic orbitals, people can use very simple principles（ Hongde rule ）To distinguish the electronic layout. chemical stability The rules (octet law, magic number) of are also easily derived from this quantum mechanical model.

By adding several atomic orbitals together, this model can be extended to molecular orbitals. Since molecules are generally not spherically symmetric, this calculation is much more complicated than atomic orbitals. The branch of theoretical chemistry, quantum chemistry and Computer Chemistry , a discipline that uses the approximate Schrodinger equation to calculate the structure and chemical properties of complex molecules.

Nuclear physics

Nuclear physics It is the branch of physics that studies the properties of atomic nuclei. It has three major fields: studying various subatomic particles and their relationships, classifying and analyzing the structure of atomic nuclei, and driving the corresponding progress of nuclear technology.

Solid State Physics

Why is diamond hard, brittle and transparent, while graphite, which is also composed of carbon, is soft and opaque? Why do metals conduct heat and electricity Metallic luster ？ What is the working principle of LED, diode and triode? Why is iron ferromagnetic? What is the principle of superconductivity?

The above examples can make people imagine the diversity of solid state physics. In fact, condensed matter physics is the largest branch of physics Condensed matter physics From the microscopic point of view, only through quantum mechanics can we correctly explain the phenomena in. Using classical physics, we can only offer some explanations on the surface and phenomenon at most.

Some phenomena with particularly strong quantum effects are listed below:

Lattice phenomenon	Phonons, heat conduction
Electrostatic phenomenon	Piezoelectric effect
conductance	Insulator, conductor
magnetic	Ferromagnetism
Cryogenic state	Bose Einstein condensation
Low dimensional effect	Quantum wire, quantum dot

Quantum Informatics

The focus of the research is a reliable method to deal with quantum states. Because quantum states can be superimposed. In theory, quantum computers can perform highly parallel operations. It can be applied to cryptography Medium. theoretically, Quantum cryptography It can generate theoretically absolutely secure passwords. Another current research project is to utilize quantum states Quantum entanglement Transmitted to distant quantum teleportation 。

Explanation of quantum mechanics

Announce

edit

Quantum mechanical problems

In the sense of dynamics, the equation of motion of quantum mechanics is that when the state of a system at a certain time is known, its future and past state at any time can be predicted according to the equation of motion.

The Prediction of Quantum Mechanics and Classical physics The predictions of the equation of motion (particle motion equation and wave equation) are different in nature. In classical physics theory, the measurement of a system does not change its state. It has only one change and evolves according to the equation of motion. Therefore, the equation of motion can make certain predictions about the mechanical quantities that determine the state of the system.

Quantum mechanics can be regarded as one of the most rigorous physical theories that have been verified. So far, all the experimental data can not overthrow quantum mechanics. Most physicists believe that it correctly describes the physical properties of energy and matter in almost all cases. Nevertheless, there are still conceptual weaknesses and flaws in quantum mechanics, except for the above Universal gravitation In addition to the lack of quantum theory, the interpretation of quantum mechanics has been controversial so far.

explain

If the mathematical model of quantum mechanics and the complete description of physical phenomena within its scope of application, we find that the meaning of probability of each measurement result is different from that of probability in classical statistical theory. Even the measurements of identical systems will be random. This is different from the probability results in classical statistical mechanics. In classical statistical mechanics, the difference in measurement results is due to the fact that the experimenter cannot completely replicate a system, not because the measuring instrument cannot accurately measure. In the standard interpretation of quantum mechanics, the randomness of measurement is fundamental, which is obtained from the theoretical basis of quantum mechanics. Although quantum mechanics cannot predict the results of a single experiment, it is still a complete description of nature, which makes people have to draw the following conclusion: there is no objective system characteristics that can be obtained through a single measurement in the world. The objective characteristics of a quantum mechanical state can only be obtained by describing the statistical distribution reflected in the whole set of experiments. Einstein ("quantum mechanics is incomplete", "God does not roll dice") and Niels Bohr were the first to debate this issue. Bohr maintenance Uncertainty principle and Complementary principle 。 After years of intense discussions, Einstein We had to accept the uncertainty principle, while Bohr weakened his complementarity principle, which finally led to today's Copenhagen Interpretation 。

Today, most physicists accept the view that quantum mechanics describes all the known characteristics of a system, and that the measurement process cannot be improved, not because of our technical problems. One result of this interpretation is that the measurement process perturbs the Schrodinger equation, making the system collapse to its eigenstate. In addition to the Copenhagen interpretation, some other interpretation methods have been proposed. include:

one David Bohm A nonlocal theory with hidden variables is proposed（ Implicit variable theory ）。 In this interpretation, the wave function is understood as a leading wave of particles. As a result, the experimental results predicted by this theory are different from relativity The predictions of the Copenhagen interpretation are exactly the same, so it is impossible to identify the two interpretations by experimental means. Although the prediction of this theory is decisive, due to the uncertainty principle, the exact state of hidden variables cannot be inferred. The result is the same as the Copenhagen interpretation, which is also a probabilistic result. So far, it is uncertain whether this explanation can be extended to relativistic quantum mechanics. Louis de Broglie and others have also proposed a similar explanation of the hidden coefficient.

two Hugh Everett III The proposed multi world interpretation believes that all Quantum Theory All the possible predictions made are realized at the same time, and these realities become parallel universes that have nothing to do with each other. In this interpretation, the general wave function Without collapse, its development is decisive. However, as observers, we cannot exist in all parallel universes at the same time. Therefore, we only observe measurements in our universe, while parallel in other universes, we observe measurements in their universes. This interpretation does not require special treatment of measurement. Schrodinger equation What is described in this theory is also the sum of all parallel universes.

three Microscopic action Principle:^[7] (See《 Quantum handwriting 》）There are micro forces between micro particles (micro forces can evolve into both macro mechanics and micro mechanics). Micro effects are a deeper theory behind quantum mechanics. The reason why micro particles exhibit volatility is an indirect objective reflection of micro forces, The difficulties and puzzles faced by quantum mechanics under the principle of microscopic interaction are understood and explained.

4. Another direction of interpretation is to change the classical logic into a quantum logic to eliminate the difficulty of interpretation.

The following lists the explanations of quantum mechanics, the most important experiments and thought experiments:

1. Einstein Podowski Rosen paradox and related Bell inequality , which clearly shows that the theory of quantum mechanics cannot be explained by "local" hidden variables; The possibility of non local hiding coefficient is not excluded.

two Double slit experiment It is a very important quantum mechanics experiment. From this experiment, we can also see the measurement problems and interpretation difficulties of quantum mechanics, which is the simplest and most obvious demonstration Wave particle duality The test of.

three Schrodinger's Cat

The overthrow of randomness is a rumor

Announce

edit

There is a news report called "Schrodinger's cat is finally saved, and Nature Research has observed the quantum transition process for the first time". Titles such as "Yale University experiment overthrows the randomness of quantum mechanics" and "Einstein got it right again" appeared one after another. As if the invincible quantum mechanics had capsized overnight, many young scholars lamented that fatalism had returned. However, is that really the case? Let's explore^[8] 。

1. Randomness of quantum mechanics^[8]

According to the summary of Feng Neumann, a master of mathematics and physics, quantum mechanics has two basic processes, one is the deterministic evolution according to Schrodinger equation, the other is the random collapse of quantum superposition state caused by measurement. Schrodinger equation is the core equation of quantum mechanics. It is deterministic and has nothing to do with randomness. Then the randomness of quantum mechanics only comes from the latter, that is, from measurement^[8] 。

This measurement of randomness is the most incomprehensible part for Einstein. He used the metaphor of "God can't roll dice" to oppose measurement of randomness, and Schrodinger also imagined measuring the life and death superposition of a cat to oppose it^[8] 。

However, numerous experiments have proved that to directly measure a quantum superposition state, the result is that it is randomly located on one of the eigenstates (probability is the coefficient modulus square of each eigenstate in the superposition state), which is the most important measurement problem in quantum mechanics. In order to solve this problem, many interpretations of quantum mechanics have been born, among which the three mainstream interpretations are the Copenhagen interpretation, the multi world interpretation and the consistent historical interpretation^[8] 。

The Copenhagen interpretation holds that measurement will lead to quantum state collapse, that is, quantum state will be destroyed instantaneously and fall to an eigenstate randomly; Multi world interpretation I felt that the Copenhagen interpretation was too profound, so I made a more profound one, thinking that every measurement is a split of the world, and all the results of the eigenstates exist, but they are completely independent of each other (orthogonal), and can not interfere with each other. We are just randomly in a certain world; The consistent historical interpretation introduces the quantum decoherence process, which solves the problem from superposition state to classical probability distribution. However, the debate about which classical probability to choose still returns to the Copenhagen interpretation and the multi world interpretation^[8] 。

Logically, the combination of multi world interpretation and consistent historical interpretation seems to be the most perfect way to interpret measurement problems. Multiple worlds form a total superposition state, which retains the certainty of "God's perspective" and the randomness of a single world perspective. But physics is a science based on experiments. These interpretations predict the same physical results, which cannot be falsified, so the physical meaning is equivalent. Therefore, the academic circle mainly adopts the Copenhagen interpretation, that is, the word collapse represents the randomness of the measured quantum states^[8] 。

2. Thesis content of Yale University^[8]

This Nature paper of Yale University first lays a foundation for the knowledge of quantum mechanics, that is, quantum transition is a deterministic process in which the quantum superposition state evolves completely according to the Schrodinger equation, that is, the probability amplitude on the ground state | G>is continuously transferred to the excited state | E>according to the Schrodinger equation, and then is continuously transferred back to form an oscillation (the frequency is called Rabi frequency), It belongs to the first kind of process summarized by von Neumann.

This paper measures such a deterministic quantum transition, so it's no surprise to get a deterministic result. The selling point of the article is how to prevent the measurement from destroying the original superposition state, or how to prevent the quantum transition from stopping due to the sudden measurement. This is not a mysterious technology, but a "weak measurement" method widely used in the field of quantum information.

This experiment uses a three-level system artificially constructed by superconducting circuit, and the signal-to-noise ratio is much worse than the real atomic energy level^[8] 。

The weak measurement technology used in the experiment is to divide the number of particles in the original ground state | G>(superconducting current is used in this experiment) a little, and let it form a superposition state with | D>. At the same time, the number of particles remaining in | G>continues to overlap with | B>. The two superposition states are (almost) independent and (almost) do not affect each other. For example, by strongly controlling the two transition Rabi frequencies through light (microwave), we can make the probability amplitude close to 1 at | B>and close to 1 at | D>. By measuring the superposition state of | G>and | B>, we can find that the number of particles collapses above | B>. At this time, although the superposition states of | G>and | D>do not collapse, we can also know that the probability amplitude is above | D>. When we measure the superposition states of | G>and | D>, the result is that the particle number collapses on | D>. So measuring the superposition state of | G>and | B>is itself a measurement that causes random collapse, but this measurement does not cause collapse of the superposition state of | G>and | D>(only slight changes), and it can also monitor the evolution of the superposition state of | G>and | D>, which becomes a weak measurement relative to the superposition state of | G>and | D>^[8] 。

If the three-level system has only one particle, then when the number of particles collapsing on | B>is 1, the number of particles collapsing on | D>and | G>is zero. However, this three-level system is artificially prepared with superconducting current, which is equivalent to having a lot of electrons available. When some electrons collapse on | B>, there are still some electrons in the superposition state of | D>and | G>. So the multi particle system also ensures that the weak measurement experiment can be carried out. This is very similar to the cold atom experiment, that is, a large number of atoms have the same energy level system, and the probability of superposition state can be reflected in the relative atomic number^[8] On.

3. God still rolls the dice^[8]

To sum up, in this nature paper, experimental techniques are used to weaken the measurement of a deterministic process, actively avoiding the measurement of the process that can lead to random results. Everything conforms to the prediction of quantum mechanics, and has no impact on the measurement randomness of quantum mechanics. So Einstein didn't turn over, and God still rolled the dice^[8] 。

This nature paper just verifies the correctness of quantum mechanics again. Why does it cause such a big misunderstanding? I have to complain here. This is closely related to the wrong target set by the authors in the abstract and introduction. It is estimated that in order to make big news, they found the idea of quantum transition instantaneity proposed by Bohr in 1913 as a target, but this idea was rejected as early as the Heisenberg equation in 1925 and Schrodinger equation in 1926 (that is, the formal establishment of quantum mechanics), They also clearly stated in the paper that the experiment actually verified Schrodinger's view that transitions are continuous deterministic evolution. Bohr was probably moved out to create an opposite effect to Einstein, continue the century debate and attract more attention. But on the issue of quantum transition, it is Bohr's earliest idea that is wrong. Heisenberg and Schrodinger are right. It is none of Einstein's business.

The author of the English report of this paper is Phillip Ball. Although he has written many excellent science news, he probably met the blind spot of knowledge this time. The whole report was also mystifying, and missed the key point. He also drew Heisenberg to accompany Bohr to carry the pot for the transient transition (I wonder if Heisenberg equation and Schrodinger equation are essentially equivalent?). Then the Chinese media translated it, and other We media gave free play to it, and it became the "accident scene" of science communication^[8] 。

Since quantum technology aims at the second information revolution, its value will be determined by its future application, and it should not be affected by the atmosphere of sensationalism in order to publish top journals. Even if it is favored for a while, it will be buried by history soon^[8] 。

Novice on the road

Growth task Getting Started with Editing Edit Rule Edit by myself

I have questions

Content query Online Service Official post bar Feedback

Complaints and suggestions

Report bad information Failed to appeal through entries Complaint of infringement information Blocking query and unblocking

Jinggong Network Anbei No. 1100000200001