Quantum optics uses radiationQuantum TheoryResearchray radiationIt is a subject of basic physical problems in the generation, coherent statistical properties, transmission, detection and interaction of light and matter.The term quantum optics comes into beinglaserIt was put forward later.
Quantum opticsquantumtheoretical research lightThe generation, transmission, detection and interaction of light and matter.In the 19th century, especially in lightElectromagnetic theoryAfter establishment, the reflectionrefraction、interference、diffractionandpolarizationEquivalencyPropagation of lightRelated phenomenawave theory Has achieved complete success (seeWave optics）。Found at the end of the 19th century and the beginning of the 20th centuryBlackbody radiationRegularity andphotoelectric effectAnd so onOptical phenomenonIn explaining these phenomena involving the generation of light and the interaction between light and matter, the old wave theory encountered insurmountable difficulties.In 1900, MPlonkIn order to solve the problem of blackbody radiation law, the hypothesis of energy sub is proposed, and thePlanck formula, well explain the black body radiation law (seePlanck hypothesis）。
All these have laid the foundation for quantum optics.The advent of lasers in the 1960s greatly promoted the development of quantum opticsLaser theoryThe semi classical theory and the fullQuantum Theory。Semi classical theory regards matter as obeying the laws of quantum mechanicsparticleThe laser field obeys the classical Maxwell electromagnetic equations.This theory can better solve many problems related to the interaction between laser and matter, but it cannot explain andradiation fieldPhenomena related to quantization, such as the coherence statistics of laser and that of matterSpontaneous emissionBehavior, etc.In the full quantum theory, the laser field is regarded as a quantized photon group, and this theoretical system canquantumThe fluctuation phenomenon and various phenomena involving the interaction between laser and matter are described strictly and comprehensively.The generation mechanism of laser, including spontaneous emission andStimulated radiationmoredetailedThe research on laser transmission, detection and statistics is the main research topic of quantum optics.
Figure 1a shows the vibration sent by the point light source S through the double slit P1, P2E1(t+τ)，E2(t）Overlay Q points on the screen, light intensityI(Q) It can be expressed as
Figure 1a
In the formula, 〈〉 represents the timetCalculate the statistical average, τ represents the relative time delay of the light passing through the slit P1 and P2, с is the speed of light.The first two items at the right end of equation (1) areE1，E2, the last two areE1，E2 The interference term after the superposition of Q points describes the interference fringe on the screen.If the slit is removed as shown in Figure 1b, usePhotocellReceive the light intensity of Q, Q 'points, and output random photocurrent signalsn(t+τ)，n'(t)，。The experiment shows that these two random signals have a certain correlation.Their product averages timen(t+τ)n'(t）>0 is related to the relative time delay τ, which is also called photon coincidence counting.Because only whenn(t+τ) Andn'(t）When none is zero, the product is not zero.The interference fringe in Figure 1a consists of the interference term<E1(t+τ)E(t）>To describe;Of Figure 1dPhotocurrentThe correlation of the output is the reflection of the quantum statistical fluctuation property of the radiation source, which should ben(t+τ)n'(t）>.Take these two quantitiesnormalization, we getradiation fieldFirst and second order ofcorrelation functiongThe definitions of 1 (τ) and g2 (τ) are shown in Figure 2 below. The second-order correlation functions of various radiation sources are giveng2 (τ) versus delay time τ.The upper curve isBlackbody radiationSource, when τ → 0,g2 (τ) → maximum 2, the photon coincidence count is also the largest, which indicates that photons tend to arrive at the same time, which is the photon bunching effect of blackbody radiation.But when τ increases, g2 (τ) decreases to asymptotic value 1, and the photon coincidence count also decreases accordingly, showing no bunching.The middle curve is a single-mode laser source, regardless of τ value, g2 (τ) value is 1, showing no bunching.This is because single-mode lasers obeyPoisson distribution ；Black body radiation obeys Planck distribution.statistical distribution Different, showing the second order of statistical distributioncorrelation functionG2 (τ) is also different.Another case is the anti aggregation represented by the following curveBeam sourceUnder certain conditions, it obeys the sub Poisson distribution.When τ → 0, g2 (τ) → 0, that is, when SQ=SQ ', no photons can arrive at points Q and Q' at the same time, and the photon coincidence count is zero, which is the anti bunching effect.Why can't the light wave emitted by S reach the Q and Q 'points satisfying the condition τ=(SQ-SQ')/с=0 at the same time, from the classicwave theory Look, this is incredible.But from the light quantum point of view, a single photon either enters the Q pointPhotocellIs received, then n=0, n '≠ 0; or the photocell entering the Q' point is received, then n ≠ 0, n '=0, so after averaging, there is 〈 n (t) n' (t) 〉=0, g2 (τ)=0, so anti bunching is a kind ofQuantum effectIt can only be understood from quantum optics.
Figure 3 Quantum Optics Legend
Figure 1d
Spontaneous emission
Figure 4 Quantum Optics Legend
As for the interaction between light and atoms, nothing is more fundamental thanSpontaneous emissionAndStimulated radiationAn excited atom emits a photon due to the external field,transitionreachground state, this is called stimulated radiation;If there is no external field, the atom will also spontaneously emit a photon back to the ground state, which is called spontaneous emission.Although the perturbation theory of quantum mechanics according to the semiclassical theory can be derivedabsorption coefficientAnd stimulated radiationcoefficient。However, to derive the spontaneous emission coefficient, we need to use the concept of damping oscillator of classical field. Ifradiation fieldQuantization also leads to zero field fluctuation energy that is not available in a classical field. Due to the effect of zero field, excited atomsSpontaneous emissionThe outgoing photon returns to the ground state.In addition, due to the quantization of the field, there is a virtual transition process.In the real process shown in Figure 3a, the electron transitions from high energy state 2 to low energy state 1 and emits photonshv；However, the virtual process shown in Fig. 3b is that the electron is transferred from low-energy state 1transitionTo high energy state 2, a photon is also emittedhv。It seems that the energy is not conserved, but the action time is very short, which does not violate theUncertainty relationConsidering the atomic energy level shift after the virtual process, the calculation is in good agreement with the experiment.Closely related to spontaneous radiation is the radiation linetype.The earliest calculation of the atomic spontaneous emission linetype was based on the assumption that the atom is in theexcited stateThe outfield is zero.In fact, if it is not the action of the external field, how can the atom reachExcited stateWhat about?It can only be said that the external field is very weak, and the influence on the radiation linetype can be ignored. This naturally raises the question of what the atomic radiation linetype is when the external field is excited strongly, which is also a good test of the field quantization theory.With the help ofAtomic beamTechnology and tunable laser technology have been applied to sodium atomResonant transitionExperimental and theoretical verification.And familiarLorentz There is only one different peak in the linetype, and the fluorescence linetype under the action of strong field has three peaks. Figure 4a is the theoretical curve;Figure 4b shows the experimental curve, which is in good agreement.
Figure 5 Research Experiment
Figure 6 Quantum Optics
Except for single atomicSpontaneous emissionIn addition, there are severalatomCoherent spontaneous emission generated when together, also known asSuperradiance。This is because multiple atoms and the commonradiation fieldThey interact to form a cooperative whole.CooperativeNThe atomic radiation is in phase, and the total amplitude is proportional toN, the total spontaneous emission power is proportional toN2. This is the main feature of coherent spontaneous emission.For incoherentSpontaneous emissionAs the phase of N atoms is random, the total spontaneous emission power and excited stateAtomic numberN is proportional.
as forStimulated radiation, the main basis for laser generation is stimulated radiation andOpen resonator。The role of the resonant cavity is to extend the lifetime of stimulated radiation photons in the cavity, so that they do not escape out of the cavity quickly. It is a complex quantum mechanical open system including the working material, cavity, and optical pump (seeLaser)。This needs to be handledDamping systemOfdissipation, undulatingQuantum statisticsmethod.From radiation to atomic totalityQuantum TheoryStarting to derive Langevin equationFokker—PlonkEquationdensity matrix Equation.The following is typical of the annihilation andGeneration operatorb. B+Langevin equation。
The appearance of laser has undoubtedly promoted the development of quantum optics.The generation, transmission, detection and statistical properties of lasers are still very interesting topics in current quantum optics, such asOptical bistability、Optical solitary wave、Squeezed stateEtc.
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photoelectric effect
Fig. 7 M Planck proposed the energy quantum hypothesis
As we all know, lightquantumThe theory was first studied by A. Einstein in 1905photoelectric effect[Note: Photoelectric effect phenomena includeExternal photoelectric effect、Internal photoelectric effectEinstein himself won the Nobel Prize in Physics for his research on the phenomenon of external photoelectric effect and his theoretical correct quantum explanation of it;This is the first major turning historical event in the history of quantum optics, and the first Nobel Prize in physics in the history of quantum optics.Although Einstein's lifelong contribution to science is multifaceted (for example, he established the special theory of relativity andGeneral relativityBut he himself won the only Nobel Prize in Physics].
The proposal of the theory of light quanta and its successful explanationphotoelectric effectExperimental results of phenomenon, promote photoelectricDetection theory、Photoelectric detection technologyWith the rapid development of photoelectric detection devices and other disciplines;Therefore, in this sense, Einstein is the father of photoelectric detection theory.Moreover, the proposition of quantum theory eventually led to the establishment of quantum optics, so it is said that it is the source and starting point of the development of quantum optics;In this sense, Einstein was the pioneer and founder of quantum optics.More importantly, the concept of light quanta put forward by Einstein in his optical quantum theory has developed several times to form the concept of photon, which eventually led to the establishment of the theory of photonics, and thus led to the rapid development of photon technology, photon engineering and photon industry;It can be seen that the light quantum theory is the beginning of photonics, photon technology, photon engineering and photon industry;Therefore, Einstein is the leader of photonics, photon technology, photon engineering and photon industry.In addition, Einstein was studyingenergy levelSystematicBlackbody radiationQuestions have been raisedStimulated radiation、Stimulated absorptionAndSpontaneous emissionThese three concepts are formally introduced into Einstein's stimulated emission coefficient, stimulated absorption coefficient and spontaneous emission coefficient;In particular, the concept of stimulated radiation was proposed, which eventually led to the invention of laser, the appearance of laser andLaser theoryThe birth of the, until the formation of today's laser technology, laser engineering and laser industry;So Einstein is the father of laser and the pioneer of laser theory.
Theoretical system
During the 50 years from 1906 to 1959, although many important achievements have been made in the research of the theory of light quanta, its overall development is still relatively slow.Its most obvious feature is lightQuantum TheoryA complete theoretical system has not yet been formed.
The nobel prize in physics
Figure 8 Quantum Optics Experiment
The first set in the world since 1960Ruby laserSince then, the scientific research work in this field has entered an unprecedented and active period of rapid development.As a result, it directly led to the birth and development of quantum optics. [Note: It is a major turning point in the history of quantum optics, providing an important experimental technical guarantee for the rapid development of quantum optics. At the same time, the inventors of lasers also won the Nobel Prize in Physics. This is the second Nobel Prize in physics in the history of quantum optics.It should be emphasized that lasers themselves belong to quantum devices, not classical devices!The behavior of lasers does not fully comply with the theoretical rules of classical physics.
Push deeper
It is E.T. Jaynes and F.W. Cummings who really put the theoretical research work of quantum optics on the right track and further.In 1963, E.T. Jaynes and FW. Cummings proposed to represent single mode light field and single ideal twoenergy levelThe Jaynes Cummings model of atom single photon interaction (hereinafter referred to as the standard J-C model) marks the formal birth of quantum optics.Since then, people have done a lot of fruitful theoretical and experimental research around the standard J-C model and its various forms of promotion.
The first climax
Figure 9 Quantum Optics Research Conference
With the deepening and deepening of research work, with the expansion of research objects, research contents and research scope, as well as the updating and improvement of research methods and means, a series of new and significant breakthroughs have emerged in the field of quantum optics today.Especially in 1997, S. Chu, C. C. Tannoudji and WD. Phillips et alLaser coolingHe won the 1997 Nobel Prize in Physics with the capture, which pushed the research work in the field of quantum optics to the first climax (note: this is the third Nobel Prize in physics in the history of quantum optics).
The second climax
Since 1997, many new signs of development have appeared in the field of quantum optics.In particular, in 2001Royal Swedish Academy of SciencesDecided to award the 2001 Nobel Prize in Physics to theBose Einstein condensateThe three scientists who made outstanding contributions pushed the research work in the field of quantum optics to the second new climax (note: this is the fourth Nobel Prize in physics in the history of quantum optics).
The third climax
Figure 10 Related Books
In 2005, the Royal Swedish Academy of Sciences again decided to award the 2005 Nobel Prize in Physics to the Nobel Prize for Optical Coherent States andspectroscopyThree scientists who have made outstanding contributions to the research.The optical coherent state (i.e. Glouber coherent state) is found, and the light field is further established on this basiscoherenceAll ofQuantum TheoryGlouber, an American scientist, won 50% of this year's Nobel Prize in Physics alone, while the other two scientists shared the other 50% of this year's Nobel Prize in Physics.This is enough to explain the importance, position and role of quantum optics research and the degree of attention that the international scientific community attaches to the subject of quantum optics;Just imagine that in a short period of eight years, the quantum optics discipline was awarded three Nobel Physics Prizes!Thus, the research work in the field of quantum optics has been pushed to the third new climax (note: this is the fifth Nobel Prize in physics in the history of quantum optics).
It is necessary to summarize and review the past brilliant achievements in the field of quantum optics, and analyze and look forward to the latest development trends in the field of quantum optics as well as the development trends and directions in the field of quantum optics in the 21st century, so that people can get new inspiration in the new exploration in the future, and strive to achieve greater breakthroughs in the early 21st century.
Academic achievements
Figure 11 Discussion on quantum optics
PhotogenicquantumThe theory was first studied by A. Einstein in 1905photoelectric effectPhotoelectric effect phenomena includeExternal photoelectric effect、Internal photoelectric effectThe inverse effect of the photoelectric effect and so on. Einstein obtained it by studying the phenomenon of external photoelectric effect and theoretically making a correct quantum explanation for itThe nobel prize in physics；It is the first major turning historical event in the history of quantum optics and the first Nobel Prize in physics in the history of quantum optics.Although Einstein's lifelong contribution to science is multifaceted (for example, he establishedSpecial relativityAnd general relativity, etc.), but he only won the only Nobel Prize in physics.
Father of Laser
It must be pointed out that the theory of light quanta successfully explainedphotoelectric effectThe experimental results of the phenomenon promote the photoelectricDetection theoryThe rapid development of photoelectric detection technology and photoelectric detection devices;Therefore, in this sense, Einstein is the father of photoelectric detection theory.Moreover, the proposition of the quantum theory eventually led to the establishment of quantum optics, so it is the source and source of the development of quantum opticsstarting point；Therefore, in this sense, Einstein was the pioneer and founder of quantum optics.More importantly, the concept of light quanta put forward by Einstein in his theory of light quantum has developed several times to form the concept of today's photon, which eventually led to the establishment of the theory of photonics, and thus led to the rapid development of photon technology, photon engineering and photon industry;It can be seen that the light quantum theory is the beginning of photonics, photon technology, photon engineering and photon industry;Therefore, in this sense, Einstein wasphotonics、Photonic technology、Photonic EngineeringAnd the leader of the photon industry.In addition, Einstein was studyingenergy levelSystematicBlackbody radiationThe question was raisedStimulated radiation、Stimulated absorptionandSpontaneous emissionThese three concepts are formally introduced into Einstein's stimulated emission coefficient, stimulated absorption coefficient and spontaneous emission coefficient;In particular, the concept of stimulated radiation eventually led to the invention of lasers, the emergence of lasers andLaser theoryThe birth of the, until the formation of today's laser technology, laser engineering and laser industry;Therefore, in this sense, Einstein himself is the father of laser and the pioneer of laser theory.
Theoretical rules
During the 50 years from 1906 to 1959Quantum TheoryAlthough many important achievements have been made in the research work of, its overall development is still relatively slow.Its most obvious feature is that the quantum theory of light has not yet formed a complete theoretical system.
The first set in the world since 1960Ruby laserSince then, the scientific research work in this field has entered an unprecedented and active period of rapid development.This directly led to the birth and development of quantum optics. [Note: This is a major turning point in the history of quantum optics, providing an important experimental technical guarantee for the rapid development of quantum optics. At the same time, the inventors of lasers also won the Nobel Prize in Physics. This is the second Nobel Prize in physics in the history of quantum optics.The laser itself is a quantum device, and its behavior does not fully comply with the theoretical rules of classical physics.
More breakthroughs
Therefore, in this case, it is necessary to summarize and review the past brilliant achievements in the field of quantum optics, and analyze and look forward to the latest developments in the field of quantum optics, as well as the development trend and direction of the field of quantum optics in the 21st century, so that people can receive new inspiration in new exploration and strive to achieve greater breakthroughs in the early 21st century.
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Important branches
Quantum optics was originally developed fromQuantum electrodynamicsIt is developed and evolved from theory.It is not only an important branch of quantum electrodynamics theory, but also a comprehensiveQuantum TheoryThe result of further development.At the same time, quantum optics also forms the theoretical basis of photonics, a new applied basic discipline.The main task of quantum optics is to study the physical essence of various classical and non classical phenomena of the light field, and reveal various linear andnonlinear effect It reveals the physical mechanism of the interaction between light field and matter (atoms, molecules or ions) and the relationship between light field and matter structure, and reveals the basic characteristics, mechanism, laws and deep structure of photons themselves.
Although a series of significant progress and brilliant achievements have been made in the field of quantum optics, the structure of quantum optics theory itself is far from perfect.
Three aspects
First, so far, people have onlyplane waveThe field has been successfully quantized, andSpherical wave field、Cylindrical wave fieldandGaussianThe quantization of non plane wave fields, such as laser beams, has been powerless;
Second, quantum optical theory is only a non relativistic theory, while the real relativistic quantum optical theory has not been established, which shows obvious limitations when in-depth studying the quantum optical properties of micro high-speed or ultra high-speed moving particles;
Third, the self interaction of photons andphotonThe research on the structure ofproduceAnd form effective research methods and research means.It is believed that quantum optics is at an important crossroads on the eve of greater brilliant development. It has made a series of significant progress and some brilliant achievements. However, in the 21st century, the achievements and achievements in the field of quantum optics will be more colorful, especially inPhotonic structureThe research of the problem will push the scientific research work in the field of quantum optics to the peak.
Law of development
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Gradual development
Figure 12 Einstein is the leader of photonics and photon technology
It was discovered at the end of the 19th century and the beginning of the 20th centuryBlackbody radiationRegularity andphotoelectric effectAnd so onOptical phenomenonWhen explaining the phenomena involving the generation of light and the interaction between light and matter, the oldwave theory Encounter insurmountable difficulties.
In 1900, MPlonkThe energy quantum hypothesis is proposed to solve the problem of blackbody radiation law, and thePlanck formula, which well explains the black body radiation law (seePlanck hypothesis）。
The advent of lasers in the 1960s greatly promoted the development of quantum opticsLaser theoryThe semi classical theory andFull quantum theory。Semiclassical theory regards matter as obeying the law of quantum mechanicsparticleAnd the laser light field complies with the classicMaxwell's electromagnetic equations。This theory can better solve many problems about the interaction between laser and matter, but it cannot explain the interaction between laser and matterradiation fieldPhenomena related to quantization, such as coherent statistics of laser and materialSpontaneous emissionBehavior, etc.In the wholeQuantum TheoryThe laser field is regarded as quantizedPhoton groupThis theoretical system canquantum fluctuation Phenomena and various phenomena involving the interaction between laser and matter are strictly and comprehensively described.Mechanism of laser generation, including spontaneous emission andStimulated radiationMore detailed research, as well as research on laser transmission, detection and statistics, are the main research topics of quantum optics[1]。
