Physics:Quantum fermion

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Short description: Type of subatomic particle


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A fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have half-integer spin and obey the Pauli exclusion principle. These particles include all quarks, leptons, and composite particles made from an odd number of fermions, such as protons, neutrons, many nuclei, and many atoms.

Fermions differ from bosons, which obey Bose–Einstein statistics. In relativistic quantum field theory, particles with integer spin behave as bosons, while particles with half-integer spin behave as fermions.

Elementary Fermions one of the basic building blocks of matter in the Standard Model.
Fermions form one of the two major classes of subatomic particles, the other being bosons. Composite particles may behave as fermions or bosons depending on their internal structure.


Description

Fermions possess conserved baryon or lepton quantum numbers in addition to their spin properties. Because of the Pauli exclusion principle, no two identical fermions can occupy exactly the same quantum state at the same time.[1]

If several fermions occupy the same spatial region, at least one quantum property, such as spin orientation, must differ between them. This exclusion principle is responsible for much of the structure and stability of ordinary matter, including electron shells in atoms.

Fermions are generally associated with matter, while bosons are usually associated with force mediation. However, under special conditions fermions can collectively display bosonic behaviour. Examples include superconductivity and superfluidity.

Composite fermions such as protons and neutrons are the primary building blocks of ordinary baryonic matter.

The term fermion was introduced by English physicist Paul Dirac in honour of Italian physicist Enrico Fermi.[2]

Elementary fermions

Standard Model of particle physics
Elementary particles of the Standard Model
Background
Particle physics
Standard Model
Quantum field theory
Gauge theory
Spontaneous symmetry breaking
Higgs mechanism
Constituents
Electroweak interaction
Quantum chromodynamics
CKM matrix
Standard Model mathematics
Limitations
Strong CP problem
Hierarchy problem
Neutrino oscillations
Physics beyond the Standard Model

The Standard Model recognizes two families of elementary fermions:

In total there are 24 elementary fermions when antiparticles are included.

Quarks

The six known quarks are:

Quarks carry color charge and participate in the strong interaction. They combine to form hadrons such as protons and neutrons.

Leptons

The six leptons are:

Leptons do not participate in the strong interaction. Neutrinos interact only weakly and gravitationally.

Types of fermions

Mathematically, several forms of fermions are known:

Most Standard Model fermions are believed to behave as Dirac fermions, although the exact nature of neutrinos remains uncertain.[3]: 106 

In 2015, Weyl fermions were experimentally realized in Weyl semimetals.

Composite fermions

Composite particles can behave as fermions or bosons depending on the number of constituent fermions.

Examples include:

  • a proton, containing three quarks
  • a neutron, containing three quarks
  • the nucleus of carbon-13
  • helium-3 atoms
  • deuterium atoms

A composite particle containing an odd number of fermions behaves overall as a fermion and has half-integer spin.

The fermionic or bosonic behaviour of composite systems is most evident when their constituents remain spatially separated. At shorter distances, the internal structure becomes important.

Fermion pairing

Under certain conditions, fermions can pair together and collectively behave like bosons.

Superconductivity

In superconductors, electrons form Cooper pairs through interactions mediated by phonons. These paired electrons can move collectively without electrical resistance.

Superfluidity

In helium-3, fermionic helium atoms pair through spin interactions and form a superfluid state at extremely low temperatures.

= Composite fermions

Quasiparticles observed in the fractional quantum Hall effect are called composite fermions. They consist of electrons bound to quantized vortices.

Physical interpretation

Fermions are responsible for the structure of matter because the Pauli exclusion principle prevents identical fermions from collapsing into the same state. This principle explains:

  • atomic shell structure
  • chemical behaviour
  • stability of white dwarfs and neutron stars
  • degeneracy pressure
  • the organization of matter at microscopic scales

Properties

  • half-integer spin
  • obey Fermi–Dirac statistics
  • follow the Pauli exclusion principle
  • include quarks and leptons
  • form ordinary matter
  • can combine into composite fermions
  • may form paired bosonic states in superconductors and superfluids

See also

Table of contents (184 articles)

Index

Full contents

1. Foundations (11)↑
  1. Physics:Quantum basics
  2. Physics:Quantum Postulates
  3. Physics:Quantum Hilbert space
  4. Physics:Quantum Observables and operators
  5. Physics:Quantum mechanics
  6. Physics:Quantum mechanics measurements
  7. Physics:Quantum state
  8. Physics:Quantum system
  9. Physics:Quantum superposition
  10. Physics:Quantum probability
  11. Physics:Quantum Mathematical Foundations of Quantum Theory
2. Conceptual and interpretations (13)↑
  1. Physics:Quantum Interpretations of quantum mechanics
  2. Physics:Quantum Wave–particle duality
  3. Physics:Quantum Complementarity principle
  4. Physics:Quantum Uncertainty principle
  5. Physics:Quantum Measurement problem
  6. Physics:Quantum Bell's theorem
  7. Physics:Quantum Hidden variable theory
  8. Physics:Quantum nonlocality
  9. Physics:Quantum contextuality
  10. Physics:Quantum Darwinism
  11. Physics:Quantum A Spooky Action at a Distance
  12. Physics:Quantum A Walk Through the Universe
  13. Physics:Quantum The Secret of Cohesion and How Waves Hold Matter Together
  14. Physics:Quantum measurement problem
3. Mathematical structure and systems (13)↑
  1. Physics:Quantum Density matrix
  2. Physics:Quantum Exactly solvable quantum systems
  3. Physics:Quantum Formulas Collection
  4. Physics:Quantum A Matter Of Size
  5. Physics:Quantum Symmetry in quantum mechanics
  6. Physics:Quantum Angular momentum operator
  7. Physics:Quantum Runge–Lenz vector
  8. Physics:Quantum Approximation Methods
  9. Physics:Quantum Matter Elements and Particles
  10. Physics:Quantum Dirac equation
  11. Physics:Quantum Klein–Gordon equation
  12. Physics:Quantum pendulum
  13. Physics:Quantum configuration space
4. Atomic and spectroscopy (14)↑
    Quantum atomic structure and spectroscopy: orbitals, energy levels, and emission and absorption spectra.
  1. Physics:Quantum Atomic structure and spectroscopy
  2. Physics:Quantum Hydrogen atom
  3. Physics:Quantum number
  4. Physics:Quantum Multi-electron atoms
  5. Physics:Quantum Fine structure
  6. Physics:Quantum Hyperfine structure
  7. Physics:Quantum Isotopic shift
  8. Physics:Quantum defect
  9. Physics:Quantum Zeeman effect
  10. Physics:Quantum Stark effect
  11. Physics:Quantum Spectral lines and series
  12. Physics:Quantum Selection rules
  13. Physics:Quantum Fermi's golden rule
  14. Physics:Quantum beats
5. Wavefunctions and modes (9)↑
    A quantum wavefunction showing probability amplitude in space; the square of its magnitude gives the probability density.
  1. Physics:Quantum Wavefunction
  2. Physics:Quantum Superposition principle
  3. Physics:Quantum Eigenstates and eigenvalues
  4. Physics:Quantum Boundary conditions and quantization
  5. Physics:Quantum Standing waves and modes
  6. Physics:Quantum Normal modes and field quantization
  7. Physics:Number of independent spatial modes in a spherical volume
  8. Physics:Quantum Density of states
  9. Physics:Quantum carpet
6. Quantum dynamics and evolution (17)↑
  1. Physics:Quantum Time evolution
  2. Physics:Quantum Schrödinger equation
  3. Physics:Quantum Time-dependent Schrödinger equation
  4. Physics:Quantum Stationary states
  5. Physics:Quantum Perturbation theory
  6. Physics:Quantum Time-dependent perturbation theory
  7. Physics:Quantum Adiabatic theorem
  8. Physics:Quantum Scattering theory
  9. Physics:Quantum S-matrix
  10. Physics:Quantum tunnelling
  11. Physics:Quantum speed limit
  12. Physics:Quantum revival
  13. Physics:Quantum reflection
  14. Physics:Quantum oscillations
  15. Physics:Quantum jump
  16. Physics:Quantum boomerang effect
  17. Physics:Quantum chaos
7. Measurement and information (9)↑
  1. Physics:Quantum Measurement theory
  2. Physics:Quantum Measurement operators
  3. Physics:Quantum Projective measurement
  4. Physics:Quantum POVM
  5. Physics:Quantum Weak measurement
  6. Physics:Quantum Measurement collapse
  7. Physics:Quantum entanglement
  8. Physics:Quantum Zeno effect
  9. Physics:Quantum limit
8. Quantum information and computing (10)↑
  1. Physics:Quantum information theory
  2. Physics:Quantum Qubit
  3. Physics:Quantum Entanglement
  4. Physics:Quantum Gates and circuits
  5. Physics:Quantum Computing Algorithms in the NISQ Era
  6. Physics:Quantum Noisy Qubits
  7. Physics:Quantum random access code
  8. Physics:Quantum pseudo-telepathy
  9. Physics:Quantum network
  10. Physics:Quantum money
9. Quantum optics and experiments (5)↑
    Experimental quantum physics: qubits, dilution refrigerators, quantum communication, and laboratory systems.
  1. Physics:Quantum Nonlinear King plot anomaly in calcium isotope spectroscopy
  2. Physics:Quantum optics beam splitter experiments
  3. Physics:Quantum Ultra fast lasers
  4. Physics:Quantum Experimental quantum physics
  5. Physics:Quantum optics
    6. Template:Quantum optics operators
10. Open quantum systems (9)↑
  1. Physics:Quantum Open systems
  2. Physics:Quantum Master equation
  3. Physics:Quantum Lindblad equation
  4. Physics:Quantum Decoherence
  5. Physics:Quantum dissipation
  6. Physics:Quantum Markov semigroup
  7. Physics:Quantum Markovian dynamics
  8. Physics:Quantum Non-Markovian dynamics
  9. Physics:Quantum Trajectories
11. Quantum field theory (20)↑
    Structural dependency map of quantum field theory.
  1. Physics:Quantum field theory (QFT) basics
  2. Physics:Quantum field theory (QFT) core
  3. Physics:Quantum Fields and Particles
  4. Physics:Quantum Second quantization
  5. Physics:Quantum Harmonic Oscillator field modes
  6. Physics:Quantum Creation and annihilation operators
  7. Physics:Quantum vacuum fluctuations
  8. Physics:Quantum Propagators in quantum field theory
  9. Physics:Quantum Feynman diagrams
  10. Physics:Quantum Path integral formulation
  11. Physics:Quantum Renormalization in field theory
  12. Physics:Quantum Renormalization group
  13. Physics:Quantum Field Theory Gauge symmetry
  14. Physics:Quantum Non-Abelian gauge theory
  15. Physics:Quantum Electrodynamics (QED)
  16. Physics:Quantum chromodynamics (QCD)
  17. Physics:Quantum Electroweak theory
  18. Physics:Quantum Standard Model
  19. Physics:Quantum triviality
  20. Physics:Quantum confinement problem
12. Statistical mechanics and kinetic theory (9)↑
  1. Physics:Quantum Statistical mechanics
  2. Physics:Quantum Partition function
  3. Physics:Quantum Distribution functions
  4. Physics:Quantum Liouville equation
  5. Physics:Quantum Kinetic theory
  6. Physics:Quantum Boltzmann equation
  7. Physics:Quantum BBGKY hierarchy
  8. Physics:Quantum Relaxation and thermalization
  9. Physics:Quantum Thermodynamics
13. Condensed matter and solid-state physics (13)↑
  1. Physics:Quantum Band structure
  2. Physics:Quantum Fermi surfaces
  3. Physics:Quantum Semiconductor physics
  4. Physics:Quantum Phonons
  5. Physics:Quantum Electron-phonon interaction
  6. Physics:Quantum Superconductivity
  7. Physics:Quantum Topological phases of matter
  8. Physics:Quantum well
  9. Physics:Quantum spin liquid
  10. Physics:Quantum spin Hall effect
  11. Physics:Quantum phase transition
  12. Physics:Quantum critical point
  13. Physics:Quantum dot
14. Plasma and fusion physics (8)↑
    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.
  1. Physics:Quantum Fusion reactions and Lawson criterion
  2. Physics:Quantum Plasma (fusion context)
  3. Physics:Quantum Magnetic confinement fusion
  4. Physics:Quantum Inertial confinement fusion
  5. Physics:Quantum Plasma instabilities and turbulence
  6. Physics:Quantum Tokamak core plasma
  7. Physics:Quantum Tokamak edge physics and recycling asymmetries
  8. Physics:Quantum Stellarator
15. Timeline (8)↑
  1. Physics:Quantum mechanics/Timeline
  2. Physics:Quantum mechanics/Timeline/Pre-quantum era
  3. Physics:Quantum mechanics/Timeline/Old quantum theory
  4. Physics:Quantum mechanics/Timeline/Modern quantum mechanics
  5. Physics:Quantum mechanics/Timeline/Quantum field theory era
  6. Physics:Quantum mechanics/Timeline/Quantum information era
  7. Physics:Quantum mechanics/Timeline/Quantum technology era
  8. Physics:Quantum mechanics/Timeline/Quiz
16. Advanced and frontier topics (16)↑
  1. Physics:Quantum topology
  2. Physics:Quantum battery
  3. Physics:Quantum Supersymmetry
  4. Physics:Quantum Black hole thermodynamics
  5. Physics:Quantum Holographic principle
  6. Physics:Quantum gravity
  7. Physics:Quantum De Sitter invariant special relativity
  8. Physics:Quantum Doubly special relativity
  9. Physics:Quantum arithmetic geometry
  10. Physics:Quantum unsolved problems
  11. Physics:Quantum Yang-Mills mass gap
  12. Physics:Quantum gravity problem
  13. Physics:Quantum black hole information paradox
  14. Physics:Quantum dark matter problem
  15. Physics:Quantum neutrino mass problem
  16. Physics:Quantum matter-antimatter asymmetry problem

Notes

  1. ↑ Weiner, Richard M. (4 March 2013). "Spin-statistics-quantum number connection and supersymmetry". Physical Review D 87 (5): 055003–05. doi:10.1103/physrevd.87.055003. ISSN 1550-7998. Bibcode: 2013PhRvD..87e5003W. https://journals.aps.org/prd/abstract/10.1103/PhysRevD.87.055003. Retrieved 28 March 2022. 
  2. ↑ Notes on Dirac's lecture Developments in Atomic Theory at Le Palais de la Découverte, 6 December 1945, UKNATARCHI Dirac Papers BW83/2/257889. See note 64 on page 331 in "The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom" by Graham Farmelo
  3. ↑ Morii, T.; Lim, C. S.; Mukherjee, S. N. (1 January 2004). The Physics of the Standard Model and Beyond. World Scientific. ISBN 978-981-279-560-1. 


Author: Harold Foppele





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