Complete collection of detailed information of quantum electrodynamics

Quantum electrodynamics is the most mature branch of quantum field theory.

It studies the quantum properties of electromagnetic interaction (that is, the emission and absorption of photons), the generation and annihilation of charged particles, the scattering between charged particles, the scattering between charged particles and photons, and so on. It summarizes the basic principles of electromagnetic interaction in atomic physics, molecular physics, solid state physics, nuclear physics and particle physics.

Chinese name: quantum electrodynamics mbth: research category of quantum electrodynamics: quantum interaction between electromagnetic field and charged particles belongs to a discipline: applied discipline of physics: terminology category of quantum mechanics: general situation of mathematical science, development process, radiation field, correction and discipline overview Quantum electrodynamics is the longest and most mature branch in the development of quantum field theory, referred to as QED for short. It mainly studies the basic process of interaction between electromagnetic field and charged particles. In principle, its principle summarizes the electromagnetic interaction process in atomic physics, molecular physics, solid state physics, nuclear physics and particle physics. It studies the quantum properties of electromagnetic interaction (that is, the emission and absorption of photons), the generation and annihilation of charged particles (such as positive and negative electrons), the scattering between charged particles and the scattering between charged particles and photons. It is outstanding in modern physics because of its wide range of applications, simple and clear basic assumptions and high accuracy in agreement with experiments. Development process 1925 Shortly after the establishment of quantum mechanics, P.A.M Dirac put forward the quantum theory of radiation in 1927, and W.K. Heisenberg and W. Pauli put forward the quantum theory of radiation in 1929, which laid the theoretical foundation of quantum electrodynamics. In the scope of quantum mechanics, the interaction between charged particles and electromagnetic field can be regarded as perturbation to deal with the absorption and stimulated emission of light, but it cannot deal with the self-emission of light. Because if the electromagnetic field is regarded as a classical field, there is no radiation field before the photon is emitted. Excited electrons in atoms are steady in quantum mechanics. Without the radiation field as a disturbance, it will not jump. Self-luminescence is an established fact. In order to explain this phenomenon and give its occurrence probability quantitatively, we can only deal with it flexibly in quantum mechanics. One method is to use the correspondence principle to treat the excited electrons in the atom as the sum of many harmonic oscillators, and to identify the oscillating current that produces radiation as some transition matrix elements corresponding to quantum mechanics, so as to calculate the transition probability of self-emission. From this method, M Planck radiation formula can be obtained, which in turn shows that the treatment of correspondence principle is feasible. Another method is to use Einstein's theory about the relationship between self-emission probability and absorption probability. Although the results obtained by these methods can be consistent with the experimental results, they are theoretically contradictory to the quantum mechanical system-the steady-state life of quantum mechanics is infinite. Dirac, Heisenberg and Pauli quantized the radiation field. In addition to obtaining a clear expression of wave-particle duality of light, it also solves the above contradiction. After the quantization of electromagnetic field, both electric field intensity and magnetic field intensity become operators. Their components satisfy a certain reciprocity relation, and their "expected value" (that is, the average value measured by experiments) should satisfy the uncertainty relation of quantum mechanics, so it is impossible for them to have a definite value (that is, the mean square error is zero at the same time). As a special case, they cannot be determined to be zero at the same time. In the absence of photons (called radiation field vacuum state), the average value of sum is zero. But the average value of sum is not zero (otherwise mean square; The difference will be zero at the same time). This is the vacuum fluctuation of quantized radiation field. It is very similar to the zero energy of the harmonic oscillator in quantum mechanics. After quantization, the generation and annihilation of fields become a universal and basic process. Therefore, when an atom is in an excited state, although there are no photons, electrons can still jump to a low-energy state and generate photons. Based on the quantum theory of radiation field, we can calculate the cross section of charged particles interacting with electromagnetic field, such as Compton effect, photoelectric effect, bremsstrahlung, electron pair generation and electron pair annihilation. These results are obtained by using perturbation theory to approximate the lowest order nonzero, which is in good agreement with the experiment. But no matter what kind of process, when calculating the results of high-order approximation, it is bound to encounter divergence difficulties, that is, it will get infinite results. This was first pointed out by Oppenheimer in 1930. In the following ten years, although quantum electrodynamics has been developing continuously in the research of many basic electromagnetic processes, as well as the penetration of high-energy radiation in matter and the cascade shower of cosmic rays, it is still in a relatively stagnant state in solving the divergence difficulties in basic theory. Under the new theoretical expression, the higher-order corrections of various processes are calculated. Due to the improvement of experimental conditions and accuracy, these results meet the increasingly high requirements of the theory. Quantum electrodynamics is a gauge field theory. Unified electromagnetic interaction and weak interaction is an important development stage of quantum field theory. The standard model of weak current unified theory and quantum chromodynamics describing strong interaction belong to gauge field theory. Their establishment is inspired by the theory and method of quantum electrodynamics. Renormalization theory established from the study of quantum electrodynamics is not only used in particle physics, but also a useful tool in statistical physics (see phase and phase transition, renormalization group).