Semiclassical physics

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Semiclassical physics, or simply semiclassical refers to a theory in which one part of a system is described quantum-mechanically whereas the other is treated classically. For example, external fields will be constant, or when changing will be classically described. In general, it incorporates a development in powers of Planck's constant, resulting in the classical physics of power 0, and the first nontrivial approximation to the power of (−1). In this case, there is a clear link between the quantum-mechanical system and the associated semi-classical and classical approximations, as it is similar in appearance to the transition from physical optics to geometric optics.


Three examples of a semiclassical approximation include:

In quantum field theory, in the semiclassical approximation only Feynman diagrams with at most a single closed loop (see for example one-loop Feynman diagram) are considered, this corresponds to the powers of Planck's constant. In chaos theory, the observation semiclassical approximations is a topic of current research.

See also[edit]


  • R. Resnick; R. Eisberg (1985). Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles (2nd ed.). John Wiley & Sons. ISBN 978-0-471-87373-0. 
  • P.A.M. Dirac (1981). Principles of Quantum Mechanics (4th ed.). Clarendon Press. ISBN 978-0-19-852011-5. 
  • W. Pauli (1980). General Principles of Quantum Mechanics. Springer. ISBN 3-540-09842-9. 
  • R.P. Feynman; R.B. Leighton; M. Sands (1965). Feynman Lectures on Physics. 3. Addison-Wesley. ISBN 0-201-02118-8. 
  • C.B. Parker (1994). McGraw-Hill Encyclopaedia of Physics (2nd ed.). McGraw-Hill. ISBN 0-07-051400-3.