Physics:Quantum Formulas Collection

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This page provides a list of the most important formulas in quantum mechanics, useful as a quick reference for students, teachers, and researchers. The formulas are organized by topic and include names, mathematical expressions, and short explanations of what they mean and how they are used. While this collection focuses on key results, science is always evolving, and new discoveries may override or extend these formulas. You, the reader, are welcome to suggest additions or corrections to keep this resource up to date.

Key Formulas in Quantum Mechanics

This table lists key formulas in quantum mechanics, showing their names, expressions, and applications.

Equation Name Formula Description Applications
Angular Momentum Components Lz=m Z-component of angular momentum. Quantized orbits.
Compton Effect: Change in Wavelength Δλ=hmec(1cosθ) Shift in photon wavelength after scattering. Compton scattering, evidence for photon momentum.
Cutoff Wavelength λmin=hcK0 Minimum wavelength in bremsstrahlung. X-ray production.
De Broglie Wavelength p=hλ=k Wavelength associated with a particle's momentum. Matter waves, electron diffraction.
Occupancy Probability P(E)=1e(EEF)/kT+1 Fermi-Dirac distribution. Electron statistics in metals.
Density of States N(E)=82πm3/2E1/2/h3 Number of states per energy interval (3D free electron gas). Solid-state physics, Fermi gas.
Dirac Equation (βmc2+ck=13αkpk)Ψ=itΨ Relativistic quantum equation for fermions. Particle physics, electrons.
Electric Dipole Potential Energy V=𝐩𝐄 Energy of dipole in electric field. Molecular physics.
Electrostatic, Coulomb Potential Energy V=q1q24πϵ0r Coulomb potential. Atomic interactions.
Free Particle Schrödinger's Equation (1D) 22md2dx2Ψ=EΨ For free particle in 1D. Free particle motion.
Free Particle Schrödinger's Equation (3D) 22m2Ψ=EΨ For free particle in 3D. Scattering problems.
Harmonic Oscillator Potential Energy V=12kx2 Potential for harmonic oscillator. Vibrational modes, quantum optics.
Heisenberg's Uncertainty Principle ΔxΔpx2
ΔEΔt2
Limits on simultaneous knowledge of position/momentum and energy/time. Fundamental limit in measurements, quantum tunneling.
Hydrogen Atom, Orbital Energy En=me48ϵ02h2n2=13.6eVn2 Energy levels of hydrogen atom. Atomic spectroscopy, Bohr model.
Hydrogen Atom, Radial Probability Density P(r)=4r2a3e2r/a Probability density for electron position (ground state). Atomic orbitals.
Hydrogen Atom Spectrum, Rydberg Equation 1λ=RH(1n221n12) Wavelengths of spectral lines. Hydrogen emission/absorption spectra.
Infinite Potential Well Energy Levels En=(hn2L)212m Energy levels for particle in a box. Quantum confinement, nanostructures.
Klein-Gordon Equation (1c22t2+2)Ψ=(m0c)2Ψ Relativistic equation for bosons. Scalar particles.
Law of Probability Conservation for Quantum Mechanics tV|Ψ|2dV+S𝐣d𝐀=0 Conservation of probability. Quantum dynamics.
Magnetic Dipole Potential Energy V=𝐦𝐁 Energy of dipole in magnetic field. Magnetic resonance.
Moseley's Law f=cλ=MKα(Z1)2
MKα=2.47×1015 Hz
Frequency of K-α X-ray line. Atomic number determination, X-ray spectroscopy.
Normalization Integral 𝐫R|Ψ|2dV=1 Normalizes the wavefunction. Probability calculations.
One-Dimensional Box Potential Energy V={0x[a,b]x[a,b] Potential for particle in a box. Quantum wells.
Orbital Electron Magnetic Dipole Components μorb,z=mμB Z-component of orbital magnetic moment. Zeeman effect.
Orbital Electron Magnetic Dipole Moment μorb=e𝐋/2m Magnetic moment due to orbital motion. Atomic magnetism.
Orbital, Electron Magnetic Dipole Moment Potential U=μorb𝐁ext=μorb,zBext Potential in external field. Magnetic interactions.
Spin, Electron Magnetic Dipole Moment μ𝐬=em𝐒=ge2m𝐒 Spin magnetic moment. Electron spin resonance.
Photoelectric Effect: Maximum Kinetic Energy Ekmax=hfΦ Maximum kinetic energy of photoelectrons. Photoelectric effect experiments, solar cells.
Photon Momentum p=hfc=hλ Momentum of a photon. Quantum optics, Compton scattering.
Planck–Einstein Equation E=hf=hcλ Relates energy of a photon to its frequency or wavelength. Wave-particle duality, photon energy calculations.
Planck's Radiation Law (Frequency Form) I(ν,T)=2hν3c21ehνkT1 Spectral radiance for blackbody in frequency. Blackbody radiation, stellar spectra.
Planck's Radiation Law (Wavelength Form) I(λ,T)=2hc2λ51ehcλkT1 Spectral radiance for blackbody in wavelength. Thermal radiation analysis.
Probability Current (Non-Relativistic) 𝐣=2mi(Ψ*ΨΨΨ*) Flow of probability. Current in quantum systems.
Probability Density Function ρ(𝐫,t)=|Ψ(𝐫,t)|2 Probability density. Locating particles.
Schrödinger's Equation (General Form) H^Ψ=EΨ Fundamental equation of quantum mechanics. Solving quantum systems.
Spin Angular Momentum Magnitude S=s(s+1) Magnitude of spin. Particle spin properties.
Spin Projection Quantum Number ms{12,+12} Spin along z-axis for electrons. Spintronics, NMR.
Time-Dependent Schrödinger's Equation (1D) (22m2x2+V)Ψ=itΨ Time evolution in 1D. Dynamics of quantum systems.
Time-Dependent Schrödinger's Equation (3D) (22m2+V)Ψ=itΨ Time evolution in 3D. Quantum simulations.
Time-Independent Schrödinger's Equation (1D) (22md2dx2+V)Ψ=EΨ Stationary states in 1D. Bound states, potentials.
Time-Independent Schrödinger's Equation (3D) (22m2+V)Ψ=EΨ Stationary states in 3D. Atomic and molecular physics.
Wavefunction of a Trapped Particle, One Dimensional Box Ψn(x)=Asin(nπxL) Wavefunction for particle in a box. Bound states, quantum wells.
Work Function Φ=hf0 Minimum energy to eject an electron. Photoelectric effect, surface physics.

2. Organized by topic

Below are the same formulas grouped

Quantum mechanics (QM)

Core Dynamical Equations

Time-Dependent Schrödinger Equation i,tΨ=H^Ψ

Time-Independent Schrödinger Equation H^ψ=Eψ

Time-Evolution Operator U(t)=eiH^t/

Operators and Measurement Theory

Canonical Commutation Relation (Heisenberg) [x,p]=i

Expectation Value A=ψ|A|ψ

Born Rule (Measurement Probability) P(a)=|a|ψ|2

Harmonic Oscillator

Annihilation Operator a=12mω,(mωx+ip)

Energy Levels En=ω(n+12)

Perturbation Theory & Quantum Transitions

First-Order Energy Correction En(1)=n|V|n

Fermi Golden Rule (Transition Rate) Γ=2π,|Vfi|2,ρ(E)

Continuity Equation & Probability Current

Probability Current j=2mi(ψψψψ)

Open quantum systems

  • Density Matrix (Statistical Mixture) ρ=ipi,|ψiψi|
  • Lindblad Master Equation (Markovian Open Systems) ρ˙=i[H^,ρ]+k𝒟[Lk]ρ
  • von Neumann Entropy S=Tr(ρlogρ)

Quantum information science (QIS)

I(A:B)=S(A)+S(B)S(AB)

Φ(ρ)=kAkρAk (quantum channels)

  • Bell states |ψ±, |ϕ±
  • CNOT gate definition
  • Qubit superposition |ψ=α|0+β|1

Quantum optics (QO)

a,a creation–annihilation operators

Hint=𝐝𝐄

  • Coherent state |α=e|α|2/2nαnn!|n
  • Jaynes–Cummings Hamiltonian H=ωaa+12ω0σz+g(aσ+aσ+)

Quantum statistical mechanics

  • Partition function Z=Tr(eβH)
  • Thermal state ρβ=eβH/Z
  • Response function χ(ω)

Quantum field theory (QFT)

  • Canonical commutation [ϕ(x),π(y)]=iδ(xy)
  • Klein–Gordon equation (+m2)ϕ=0
  • Dirac Lagrangian
  • Relativistic dispersion E2=p2c2+m2c4

3. Multi column version

  • itΨ=HΨ
  • Hψ=Eψ
  • ΔxΔp/2
  • [x,p]=i
  • P(a)=|a|ψ|2
  • ρ=pi|ψiψi|
  • S=Tr(ρlogρ)
  • En=ω(n+1/2)
  • a=(mωx+ip)/2mω
  • Γ=2π|Vfi|2ρ(E)
  • I(A:B)=S(A)+S(B)S(AB)
  • Bell states |ψ±
  • CNOT =|00|I+|11|X
  • ρ˙=i[H,ρ]+𝒟[L]ρ
  • [ϕ(x),π(y)]=iδ(xy)
  • (+m2)ϕ=0
  • Z=Tr(eβH)

4. Wave Packet spreading example

Free particle dispersion: σx(t)=σx(0)1+(t2mσx(0)2)2 → Used in cold-atom clouds, ultrafast electron microscopy.

Two-level Rabi oscillation

Population oscillation: Pe(t)=sin2(Ωt/2) → Atomic clocks, qubit control.

Harmonic oscillator example

Ground state energy: E0=12ω → Zero-point fluctuations in quantum optics.

Formula Description Applications
itΨ=H^Ψ Time-dependent Schrödinger equation Dynamics, atoms, molecules
H^ψ=Eψ Time-independent Schrödinger equation Spectra, tunneling, bound states
ΔxΔp2 Heisenberg uncertainty Measurement limits, wave packets
[x,p]=i Canonical commutator Quantization, oscillators
A=ψ|A|ψ Expectation value Predictions, statistics
P(a)=|a|ψ|2 Born rule Measurement probabilities
U^(t)=eiHt/ Time-evolution operator Quantum gates, scattering
ρ=ipi|ψiψi| Density matrix Decoherence, open systems
S=Tr(ρlogρ) von Neumann entropy Entanglement, thermodynamics
Tr(ρA) Expectation via density matrix Ensembles, thermal states
dρdt=i[H,ρ]+k𝒟[Lk]ρ Lindblad master eq. Decoherence, dissipation
𝒟[L]ρ=LρL12{LL,ρ} Dissipator Relaxation, noise
Z=Tr(eβH) Partition function Thermodynamics, blackbody
ψ(x)=12πdpeipx/ϕ(p) Fourier relation Wavepackets, scattering
j=2mi(ψ*ψψψ*) Probability current Continuity, tunneling
a^=12mω(mωx+ip) Annihilation operator QHO, quantum optics
En=ω(n+12) HO spectrum Phonons, cavities
ϕn(x)= HO eigenfunctions Basis for perturbation theory
H^spin=γ𝐁𝐒 Spin Hamiltonian NMR, ESR, qubits
χ(ω)=0dteiωtC(t) Response function Conductivity, noise
k=2mE/ Free-particle wavenumber Beams, dispersion
ψ(x)=ncnϕn(x) Basis expansion Computation, spectral theory
H=H0+λV Perturbation theory split Approximations, resonances
En(1)=n|V|n 1st-order energy shift Stark, Zeeman effects
Γ=2π|f|V|i|2ρ(Ef) Fermi golden rule Transition rates
(a|b)=Tr(ab) Hilbert-Schmidt inner product Superoperators, channels
Φ(ρ)=kAkρAk CPTP map (quantum channel) Noise, quantum info
I(A:B)=S(A)+S(B)S(AB) Mutual information Correlations, QIT
|ψ±=12(|01±|10) Bell states Entanglement, teleportation
UCNOT=|00|I+|11|X CNOT gate Quantum computing
[ϕ(x),π(y)]=iδ(xy) Canonical QFT commutator Field quantization
E2=p2c2+m2c4 Relativistic dispersion QFT, particles
=ψ¯(iγμμm)ψ Dirac Lagrangian Fermions, QED
ϕ+m2ϕ=0 Klein-Gordon eq. Bosons, relativistic waves

See also

Table of contents (136 articles)

Index

Full contents

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