Nonclassical light
In optics, 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 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 have a well-defined number of photons, while the phase is totally undefined.
Glauber–Sudarshan P representation
The density matrix for any state of light can be written as:where 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:
- a negative value at any point;
- being more singular than a Dirac delta function.