184 Comments

• Digg
• Bury

point is, a classical beam of light - the sort of thing that comes out of a normal laser - can contain any number of photons, eg. the probability of finding 0,1,2,3,4,5,.... photons in the beam follows a fixed pattern, which only depends overall on how bright the beam of light was.you also can make non-classical light beams that contain only even numbers of photons, eg. if you count the number of photons in the beam, you might find 0,2,4,6,8,... but never 1,3,5,7,.... That kind of beam corresponds to a "squeezed vacuum" because the normal measurements of light amplitude depend on the difference between the probabilities of finding N and N+1 photons, so if you have a beam where all the odd probabilities are zero, then P(N)*P(N+1) = 0 and the normal detection methods for the amplitude go haywire. The only normal way you can have P(N)*P(N+1) = 0 for a classical beam of light is to have no light at all -> vacuum. but there are photons in the non-classical beam -> "squeezed vacuum"The noise depends on P(N),P(N+2) and so you can tell you have a squeezed vacuum by the noise distribution. The point is they can store these non-classical beams of light in their gas cloud as well as the classical ones, so it's storing all the correlations in the beam of light.

• Reply