Nonclassical light explained
Nonclassical light is light that cannot be described using classical electromagnetism; its characteristics are described by the quantized electromagnetic field and quantum mechanics.
The most common described forms of nonclassical light are the following:
- Photon statistics of Nonclassical Light is Sub-Poissonian[1] in the sense that the average number of photons in a photodetection of this kind of light shows a standard deviation that is less than the mean number of the photons.
- Squeezed light exhibits reduced noise in one quadrature component. The most familiar kinds of squeezed light have either reduced amplitude noise or reduced phase noise, with increased noise of the other component.
- Fock states (also called photon number states) have a well-defined number of photons (stored e.g. in a cavity), while the phase is totally undefined.
Glauber–Sudarshan P representation
See main article: Glauber–Sudarshan P representation. The density matrix for any state of light can be written as:
\widehat{\rho}=\intP(\alpha)|{\alpha}\rangle\langle{\alpha}|\rm{d}2\alpha,
where
\scriptstyle|\alpha\rangle
is a
coherent state. A
classical state of light is one in which
is a
probability density function. If it is not, the state is said to be
nonclassical.
Aspects of
that would make it nonclassical are:
The matter is not quite simple. According to Mandel and Wolf: "The different coherent states are not [mutually] orthogonal, so that even if
behaved like a true probability density [function], it would not describe probabilities of mutually exclusive states."
References
General references
- Glauber . Roy J. . Coherent and Incoherent States of the Radiation Field . Physical Review . American Physical Society (APS) . 131 . 6 . 1963-09-15 . 0031-899X . 10.1103/physrev.131.2766 . 2766–2788.
Notes and References
- M. Fox, Quantum Optics: An Introduction, Oxford University Press, New York, 2006
