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The word quantum is the neuter singular of the Latin interrogative adjective quantus, meaning "how much"."Quanta", the neuter plural, short for "quanta of electricity" (electrons), was used in a 1902 article on the photoelectric effect by Philipp Lenard, who credited Hermann von Helmholtz for using the word in the area of electricity.
Quantum mechanics is a fundamental theory that describes the behavior of nature at and below the scale of atoms. [2]: 1.1 It is the foundation of all quantum physics, which includes quantum chemistry, quantum field theory, quantum technology, and quantum information science. Quantum mechanics can describe many systems that classical physics cannot.
In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. [ 1 ] [ 2 ] [ 3 ] In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. [ 2 ]
A fundamental physical constant occurring in quantum mechanics is the Planck constant, h. A common abbreviation is ħ = h /2 π , also known as the reduced Planck constant or Dirac constant . Quantity (common name/s)
The idea of quantum field theory began in the late 1920s with British physicist Paul Dirac, when he attempted to quantize the energy of the electromagnetic field; just as in quantum mechanics the energy of an electron in the hydrogen atom was quantized. Quantization is a procedure for constructing a quantum theory starting from a classical theory.
These are the principal quantum number, the orbital angular momentum quantum number, and the magnetic quantum number. Together with one spin-projection quantum number of the electron, this is a complete set of observables. The figure can serve to illustrate some further properties of the function spaces of wave functions.
A quantum version of an adiabatic process can be modeled by an externally controlled time dependent Hamiltonian (). If the system is isolated, the dynamics are unitary, and therefore, is a constant. A quantum adiabatic process is defined by the energy entropy being constant.
Quantum engineering uses quantum mechanics as a toolbox for the development of quantum technologies, such as quantum sensors or quantum computers. Many devices that people utilize rely on quantum mechanical effects and have revolutionized the society through medicine, optical communication, high-speed internet, and high-performance computing ...