Vacuum Noise | previous | next | feedback |
Definition: quantum noise of the vacuum state, or quantum noise introduced into an optical system via a vacuum input
Vacuum noise is quantum noise related to the zero-point fluctuations of the electric field in the vacuum state. Such fluctuations exist even though the vacuum states has a photon number of zero.
Figure 1: When a beamsplitter is used to attenuate a beam, vacuum noise enters via the open port.
Despite being quite weak, vacuum noise can affect the noise properties or even the essential function of optical devices. For example, parametric generation can be considered as the effect of amplifying vacuum noise to macroscopic power levels in a high gain optical parametric amplifier. Also, the process of spontaneous emission can (in a semiclassical picture) be interpreted as being stimulated by vacuum noise.
Any linear losses acting on a light beam introduce vacuum noise, rather than simply attenuating the quantum noise together with the average amplitude. This is most obvious for attenuation with a beam splitter, which can be understood to mix a portion of the input beam with vacuum noise from the unused input port (Figure 1). However, vacuum noise is also introduced by any other kind of linear attenuation. In effect, linear attenuation brings e.g. squeezed light closer to a coherent state.
See also: quantum noise, coherent states, squeezed states of light, spontaneous emission, fluorescence
Categories: fluctuations and noise, quantum optics
