Fourier Transform, Dirac Commutator, Energy Conservation, and Correspondence Principle for Electrical Engineers

Christopher J. Ryu, Erhan Kudeki, Dong Yeop Na, Thomas E. Roth, Weng C. Chew

Research output: Contribution to journalArticlepeer-review


The canonical commutation relation is a fundamental postulate of the quantum theory regarding the operators needed in quantum description of physical observables. It is shown that the Fourier transform is derivable from this seemingly simple postulate along with the basic properties of the position and momentum operators. Further discussions on the canonical commutation relation reveal its connection to a more fundamental notion that energy must be conserved. This discussion also unveils the mathematical homomorphism between the classical and quantum theories for systems represented by sum separable Hamiltonians. Another link between the classical and quantum theories is established by the correspondence principle which states that the classical theory emerges from quantum theory in the limit of vanishingly small Planck constant. Finally, the quantum Maxwell's equations, which have been derived in our previous works, are presented and briefly discussed, and the 3-D mode transform is derived that can be interpreted as a generalization of the Fourier transform. We present both the details and meanings of the 3-D mode transform which will serve as a foundation for a full 3-D quantum finite-difference time-domain method.

Original languageEnglish (US)
Pages (from-to)69-83
Number of pages15
JournalIEEE Journal on Multiscale and Multiphysics Computational Techniques
StatePublished - 2022


  • Commutator
  • classical limit
  • coherent state
  • correspondence principle
  • fourier transform
  • mode transform
  • quantum mechanics

ASJC Scopus subject areas

  • Modeling and Simulation
  • Mathematical Physics
  • Physics and Astronomy (miscellaneous)
  • Computational Mathematics


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