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=mℓℏ Z-component of angular momentum. Quantized orbits.
Compton Effect: Change in Wavelength Δλ=hmec(1−cos⁡θ) 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=ℏk Wavelength associated with a particle's momentum. Matter waves, electron diffraction.
Occupancy Probability P(E)=1e(E−EF)/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+c∑k=13αkpk)Ψ=iℏ∂∂tΨ Relativistic quantum equation for fermions. Particle physics, electrons.
Electric Dipole Potential Energy V=−𝐩⋅𝐄 Energy of dipole in electric field. Molecular physics.
Electrostatic, Coulomb Potential Energy V=q1q24πϵ0r Coulomb potential. Atomic interactions.
Free Particle Schrödinger's Equation (1D) −ℏ22md2dx2Ψ=EΨ For free particle in 1D. Free particle motion.
Free Particle Schrödinger's Equation (3D) −ℏ22m∇2Ψ=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 ΔxΔpx≥ℏ2
ΔEΔt≥ℏ2
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)=4r2a3e−2r/a Probability density for electron position (ground state). Atomic orbitals.
Hydrogen Atom Spectrum, Rydberg Equation 1λ=RH(1n22−1n12) 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 (−1c2∂2∂t2+∇2)Ψ=(m0cℏ)2Ψ Relativistic equation for bosons. Scalar particles.
Law of Probability Conservation for Quantum Mechanics ∂∂t∫V|Ψ|2dV+∫S𝐣⋅d𝐀=0 Conservation of probability. Quantum dynamics.
Magnetic Dipole Potential Energy V=−𝐦⋅𝐁 Energy of dipole in magnetic field. Magnetic resonance.
Moseley's Law f=cλ=MKα(Z−1)2
MKα=2.47×1015 Hz
Frequency of K-α X-ray line. Atomic number determination, X-ray spectroscopy.
Normalization Integral ∫𝐫∈R|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=−mℓμB 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=−μorb⋅𝐁ext=−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=hf−Φ 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)=2hν3c21ehνkT−1 Spectral radiance for blackbody in frequency. Blackbody radiation, stellar spectra.
Planck's Radiation Law (Wavelength Form) I(λ,T)=2hc2λ51ehcλkT−1 Spectral radiance for blackbody in wavelength. Thermal radiation analysis.
Probability Current (Non-Relativistic) 𝐣=ℏ2mi(Ψ*∇Ψ−Ψ∇Ψ*) 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=ℏs(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) (−ℏ22m∂2∂x2+V)Ψ=iℏ∂∂tΨ Time evolution in 1D. Dynamics of quantum systems.
Time-Dependent Schrödinger's Equation (3D) (−ℏ22m∇2+V)Ψ=iℏ∂∂tΨ Time evolution in 3D. Quantum simulations.
Time-Independent Schrödinger's Equation (1D) (−ℏ22md2dx2+V)Ψ=EΨ Stationary states in 1D. Bound states, potentials.
Time-Independent Schrödinger's Equation (3D) (−ℏ22m∇2+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 iℏ,∂tΨ=H^Ψ

Time-Independent Schrödinger Equation H^ψ=Eψ

Time-Evolution Operator U(t)=e−iH^t/ℏ

Operators and Measurement Theory

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

Expectation Value ⟨A⟩=⟨ψ|A|ψ⟩

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

Harmonic Oscillator

Annihilation Operator a=12ℏmω,(mωx+ip)

Energy Levels En=ℏω(n+12)

Perturbation Theory & Quantum Transitions

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

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

Continuity Equation & Probability Current

Probability Current j=ℏ2mi(ψ∇ψ−ψ∇ψ)

Open quantum systems

  • Density Matrix (Statistical Mixture) ρ=∑ipi,|ψi⟩⟨ψi|
  • Lindblad Master Equation (Markovian Open Systems) ρ˙=−iℏ[H^,ρ]+∑k𝒟[Lk]ρ
  • von Neumann Entropy S=−Tr(ρlog⁡ρ)

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=−𝐝⋅𝐄

  • Coherent state |α⟩=e−|α|2/2∑nαnn!|n⟩
  • Jaynes–Cummings Hamiltonian H=ℏωa†a+12ℏω0σz+g(a†σ−+aσ+)

Quantum statistical mechanics

  • Partition function Z=Tr(e−βH)
  • Thermal state ρβ=e−βH/Z
  • Response function χ(ω)

Quantum field theory (QFT)

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

3. Multi column version

  • iℏ∂tΨ=HΨ
  • Hψ=Eψ
  • ΔxΔp≥ℏ/2
  • [x,p]=iℏ
  • P(a)=|⟨a|ψ⟩|2
  • ρ=∑pi|ψi⟩⟨ψi|
  • S=−Tr(ρlog⁡ρ)
  • En=ℏω(n+1/2)
  • a=(mωx+ip)/2ℏmω
  • Γ=2πℏ|Vfi|2ρ(E)
  • I(A:B)=S(A)+S(B)−S(AB)
  • Bell states |ψ±⟩
  • CNOT =|0⟩⟨0|⊗I+|1⟩⟨1|⊗X
  • ρ˙=−iℏ[H,ρ]+∑𝒟[L]ρ
  • [ϕ(x),π(y)]=iℏδ(x−y)
  • (◻+m2)ϕ=0
  • Z=Tr(e−βH)

4. Wave Packet spreading example

Free particle dispersion: σx(t)=σx(0)1+(ℏt2mσx(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=12ℏω → Zero-point fluctuations in quantum optics.

Formula Description Applications
iℏ∂∂tΨ=H^Ψ Time-dependent Schrödinger equation Dynamics, atoms, molecules
H^ψ=Eψ Time-independent Schrödinger equation Spectra, tunneling, bound states
ΔxΔp≥ℏ2 Heisenberg uncertainty Measurement limits, wave packets
[x,p]=iℏ Canonical commutator Quantization, oscillators
⟨A⟩=⟨ψ|A|ψ⟩ Expectation value Predictions, statistics
P(a)=|⟨a|ψ⟩|2 Born rule Measurement probabilities
U^(t)=e−iHt/ℏ Time-evolution operator Quantum gates, scattering
ρ=∑ipi|ψi⟩⟨ψi| Density matrix Decoherence, open systems
S=−Tr(ρlog⁡ρ) von Neumann entropy Entanglement, thermodynamics
Tr(ρA) Expectation via density matrix Ensembles, thermal states
dρdt=−iℏ[H,ρ]+∑k𝒟[Lk]ρ Lindblad master eq. Decoherence, dissipation
𝒟[L]ρ=LρL†−12{L†L,ρ} Dissipator Relaxation, noise
Z=Tr(e−βH) Partition function Thermodynamics, blackbody
ψ(x)=12πℏ∫dpeipx/ℏϕ(p) Fourier relation Wavepackets, scattering
j=ℏ2mi(ψ*∇ψ−ψ∇ψ*) Probability current Continuity, tunneling
a^=12ℏmω(mωx+ip) Annihilation operator QHO, quantum optics
En=ℏω(n+12) HO spectrum Phonons, cavities
ϕn(x)=… HO eigenfunctions Basis for perturbation theory
H^spin=−γ𝐁⋅𝐒 Spin Hamiltonian NMR, ESR, qubits
χ(ω)=∫0∞dteiωtC(t) Response function Conductivity, noise
k=2mE/ℏ 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=2πℏ|⟨f|V|i⟩|2ρ(Ef) Fermi golden rule Transition rates
(a|b)=Tr(a†b) 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=|0⟩⟨0|⊗I+|1⟩⟨1|⊗X CNOT gate Quantum computing
[ϕ(x),π(y)]=iℏδ(x−y) Canonical QFT commutator Field quantization
E2=p2c2+m2c4 Relativistic dispersion QFT, particles
ℒ=ψ¯(iγμ∂μ−m)ψ Dirac Lagrangian Fermions, QED
◻ϕ+m2ϕ=0 Klein-Gordon eq. Bosons, relativistic waves

See also

Table of contents (185 articles)

Index

Full contents

9. Quantum optics and experiments (5) ↑ Back to index
14. Plasma and fusion physics (8) ↑ Back to index
Conceptual illustration of plasma physics in a fusion context, showing magnetically confined ionized gas in a tokamak and the collective behavior governed by electromagnetic fields and transport processes.
Conceptual illustration of plasma physics in a fusion context, showing magnetically confined ionized gas in a tokamak and the collective behavior governed by electromagnetic fields and transport processes.
Author: Harold Foppele