Quantum isModern PhysicsImportant concepts of.That is, if a physical quantity has the smallest indivisible basic unit, it is quantized, and the smallest unit is called quantum.
The word "quantum" comes from the Latin word quantus, meaning "how much", which stands for "a certain amount of substance". It was originally created byGermanyphysical scientistM. PlanckIt was proposed in 1900.He assumedBlackbody radiationInRadiant energyIt is discontinuous and can only take energyBasic unitOfintegerTherefore, the experimental phenomenon of blackbody radiation is well explained.
Later research shows that not only does the energy show this discontinuous separation property, but alsophysical quantitysuch asangular momentum、spin, electric charge, etcquantizationPhenomenon.This is the same asNewtonian mechanicsRepresented byClassical physicsThere are fundamental differences.Quantization is mainly shown inmicrocosmicThe physical world.Describe the micro physical worldOur physical theory is quantum mechanics.
Since Planck put forward the concept of quantum, a complete theory of quantum mechanics has been initially established in the first half of the 20th century through the improvement of Einstein, Bohr, de Broglie, Heisenberg, Schrodinger, Dirac, Bohn and others.Most physicists regard quantum mechanics as the basic theory to understand and describe nature.
If a physical quantity existsleastIndivisibleBasic unit, then this physical quantity is quantized, and the smallest unit is called quantum.The English name of quantum comes from the Latin quantus, meaning "there isHow many?”, stands for "a considerable amount of certain substance".In physics, we often use the concept of quantum, which means thatdivisionThe basic individual of.For example, "quantum of light"（photon）It's a certain frequencylightThe basic unit of energy.And extendedquantum mechanics、quantum opticsAnd become different professional research fields.Its basic concept is that all tangible properties are "quantifiable"."Quantization" refers to thenumerical valueIs discrete, rather than continuous arbitrary value.For example, inatomMedium, electronicenergyIt is quantizable.This determines the general problems of atomic stability and emission spectrum.Most physicists regard quantum mechanics as understanding anddescribeNature's Basicstheory。
popularIn other words, quantum is the smallest that can show the characteristics of a certain substance or physical quantityunit。
Development history
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Proposing concepts
stayClassical physicsMedium, according toEquipartition theorem of energy: Energy iscontinuityAny value can be taken if it changes.In the late 19th century, scientists found manyphysical phenomenonIt cannot be explained by classical theory.At that time, the German physics communityfocusingtoBlackbody radiationResearch on the problem.Around 1900, M·PlonkTrying to solve the problem of blackbody radiation, he boldly put forward the quantum hypothesis and obtainedPlanck radiation law, still used today.Planck proposed that, like the atom as the constituent unit of all substances“Energon”（quantum）Is the smallest unit of energy。Objects can only absorb or emit electromagnetic radiation in the form of energy quantum.Planck first presented energy quantization at the meeting of the German Physical Society on December 14, 1900numerical value, a moleculemole(mol) andelementary chargeEtc.Its value is more accurate than before, and the proposed theory has also successfully solved the problem of blackbody radiation, marking thatquantum mechanicsThe birth of.
In 1928, British physicistdirac Completed the mathematical equivalence proof between matrix mechanics and wave dynamics, systematically summarized the theory of quantum mechanics, and integrated the two theoretical systems——relativityAnd quantum mechanicsQuantum field theoryThe prologue of.Quantum theory isModern PhysicsOne of the two cornerstones ofmicrocosmicThe theoretical basis is provided for understanding macro phenomena.
The proposal of the quantum hypothesis forcefullyto attackHasClassical physics, promote physics to enter the micro level and lay the foundationModern Physics。However, until now, some of the physicists' assumptions about quantum mechanics have not been fully proved, and there is still much to study.
Planck proposed a simple formula that can be well consistent with the observation results,experimental physicist I believe that there must be a scientific principle that has not yet been revealed.[2]
Planck found that the blackbody radiation formula can be derived theoretically if the following assumptions are made:radiation, objects can only absorb orlaunchIt, h, is calledPlanck constant。In other words, objects absorb or emitelectromagnetic radiationIt can only be carried out in a quantum way. The energy of each quantum is E=h ν, which is called action quantum.
fromclassical mechanicsThe concept of energy discontinuity is absolutely not allowed[2]。But when interpreting this formula, we can treat atoms in objects as tiny quantaHarmonic oscillator, we have to assume theseQuantum harmonic oscillatorThe total energy of is not continuous, that is, the total energy can only be discrete values（Classical physicsIs the opposite).Planck further assumed that the radiation energy absorbed and emitted by a single quantum harmonic oscillator was quantized, which seriously impacted classical physics.Quantum theoryinvolveForm of material movementAnd fundamental changes in the laws of motion.
First of all, note thatQuantum hypothesisIt is possible to solve other problems encountered in classical physicsEinstein。He tried to explain it with quantum hypothesisphotoelectric effectThe problems encountered inLight quantaConceptradiation fieldIt is composed of light quanta.The relationship between the energy E of each light quantum and the frequency ν of radiation is E=h ν.After the concept of light quanta is adopted, the problems in photoelectric effect will be solved immediately.
Only then did Planck's concept of energy discontinuity gradually attract physicists' attention[2]。So, a cautious physicistPlonkSet off the quantum in the early 20th centuryPhysics revolutionThe curtain of.
quantum mechanics
quantum mechanicsIt was founded in overcoming the difficulties and limitations of early quantum theory.Inspired by Planck Einstein's light quantum theory and Bohr's atomic theory, French physicist LDe BroglieThe particle theory of light andFluctuation theoryAnd noted thatgeometrical optics Similarity with classical particle mechanics. Assume the physical object (static mass) according to the analogy methodm≠ 0)particleLike light, it hasWave particle duality, and these two aspects must have similar relations, and Planck constant must appear in them.He assumed thatPhysical particleAssociated waves (called“Matter wave”）Frequency andwavelengthThey are ν=E/h, λ=h/p, which are called de Broglie relations.On the one hand, he proposed this assumption as an attempt to regard light andm≠ 0);On the other hand, it is also to better understand the discontinuity of microscopic particle energy to overcomeBohr theoryDefects with artificial nature.De Broglie put the atomStationary stateAndstanding waveThat is to say, to bind the energy of moving physical particlesquantizationAnd standing wave in finite spacewavelength(orfrequency）Is connected with the discreteness of[2]。
AustriaPhysicist ESchrodingerTaking note of de Broglie's work, he proposed awave equation ——Schrodinger equation, is a pair of wave functionsSpatial coordinatesSecond order ofwechat BusinessOfpartial differential equation 。Schrodinger discrete the atomenergy levelAnd differential equations under certain boundary conditionsEigenvalueThe problems are connected, and the success shows thathydrogen atom、Harmonic oscillatorEnergy level sum ofspectrumThe law of.Almost at the same time, W. Heisenberg and MBornAnd E. Jordan established matrix mechanics.The proposition of matrix mechanics, andBohrOfQuantum theoryIt has a very close relationship, especially Bohr's correspondence principle thought has an important influence on Heisenberg (seeCorrespondence principle）。It inherits the reasonable core of quantum theory (such as discrete energy levels and stationary states of atomsQuantum transition, frequency condition, etc.), while abandoning some traditional concepts without experimental basis (such as the concept of particle orbital motion).Heisenberg especially emphasized that in any physical theory, onlyobservationOfphysical quantity(such as wavelength, spectral term, quantum number, spectral line intensity, etc.).In matrix mechanics, every physical quantity (such ascoordinate、momentum, energy, etc.)matrix, theirAlgebraic operationThe rule is different from the classical physical quantityproductGenerally not satisfiedCommutative law。Soon Schrodinger discovered thatMatrix mechanicsandWave dynamicsIs completelyequivalenceOf.Followed by Pdirac And E. Jordan proposed a method calledTransformation theoryIt is pointed out that matrix mechanics and wave dynamics are just two of the infinite expressions of the laws of quantum mechanics[2]。
quantum mechanicsIs to study atoms, molecules and evenNucleusThe basic theory of the structure and properties of elementary particles is one of the basic theories of modern physics.The classical physics before the 20th century was only suitable for describing the motion of matter under general macro conditionsMicrocosm(Atoms andSubatomicSome macroscopic phenomena under certain conditions can only be explained on the basis of quantum mechanics.On the other hand, material properties andMicrostructureIt can only be explained on the basis of quantum mechanics[2]。All problems involving material properties and microstructure are based on quantum mechanics[2]。
Black radiation quantum equation
The successful interpretation of blackbody radiation is the first trial since the birth of the concept of quantization.
When an object is heated toelectromagnetic waveIn the form of infrared radiation.When the object becomes hot, the red wavelength part begins to become visible.majoritythermal radiationIt is infrared, unless the object becomes as hot as the surface of the sun, but this condition could not be achieved in the laboratory at that time, and onlymeasurementpartBlackbodyspectrum。
Energy EradiationThe frequency f and temperature T can be written as:
hIs Planck's constant andkyesBoltzmann constant。Both are the basis of physics.The quantum of basic energy is hf.However, this unit does not normally exist and does not need quantization.
The basic idea of quantum communication was proposed by Bennett in the 1980s and 1990s, including quantum key distribution (QKD) and quantum teleportation.Quantum key distributionA secure communication password can be established, and the point-to-point secure classical communication can be achieved through one-time encryption.The security here has been strictly proved mathematically, which is beyond the reach of classical communication so far.The existing quantum key distribution technology can realize the quantum key distribution of the order of one hundred kilometers, supplemented by optical switch and other technologies, and can also realize the quantum key distribution network.Quantum state teleportation is based onQuantum entanglementThe distribution and quantum joint measurement of can realize the spatial transfer of quantum state (quantum information) without moving the physical carrier of quantum state, which is like transferring the contents of sealed letters from one envelope to another without moving any information carrier itself.This is unimaginable in classical communication.be based onTeleportation of quantum statesandQuantum storage technologyOfquantum repeater It can realize quantum key distribution and network at any distance.
The realization of quantum communication is based onQuantum state transmission。In order to facilitate the transmission, the existing quantum communication experiments generally use photons as the carrier of quantum states, which is expressed in the form of photon state transmission.The encoding space of quantum information is mainly light polarization.[3]
scientific research
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In September 2022, American scientists showed that the magnon in the magnetic semiconductor chromium bromide could pair with the exciton, and the exciton quasiparticle would emit light.This result can be regarded as quantum transduction, that is, converting one "quantum" energy into another.[4]
In October 2022,The first quantum scalable algorithm comes out[5]。
In July 2023, researchers from the University of Science and Technology of China and other institutions successfully realized the preparation and verification of 51 superconducting quantum bits, set a new world record for the number of truly entangled bits in all quantum systems, and demonstrated the measurement based variational quantum algorithm for the first time.Relevant research results were published online in Nature on July 12.[6]
