One of the most intriguing consequences of quantum mechanics is that
empty space is not really empty at all. The Heisenberg uncertainty principle
predicts that it is never possible to be absolutely precise about the energy
of a system, including even that of empty space, or more correctly, the
vacuum. This fuzziness manifests itself as what are called vacuum fluctuations
– a sort of background quantum noise. Vacuum fluctuations have real effects
on forms of energy such as light.
A light beam consists of an oscillating electromagnetic field. In the
classical, or wave description of light, these oscillations may be pictured
as a smooth wave with a well-defined amplitude (the height of the wave crest,
which relates to the intensity of the light) and a definite phase (which
relates to the position of the wave and the wavelength).
If we apply quantum mechanics to light, we can then visualise light
as a stream of ‘wave packets’ called photons. These wave packets obey the
uncertainty principle, so a well-defined wave is not permitted. There are
fluctuations in the amplitude and phase of the wave which are basically
the result of the vacuum fluctuations, as defined by the uncertainty principle.
These fluctuations can be a nuisance because they impose a limit on the
precision of optical measurements. For example, some optical measurements
depend on detecting the interference patterns produced when two light waves
meet – a technique called optical inter-ferometry. Fluctuations in the phase
produce optical ‘noise’, smearing out the patterns and so making any sensitive
measurement difficult.
Recently, physicists working on optical systems have succeeded in generating
light with fewer fluctuations than…
