"A special case of squeezed light, known as the squeezed vacuum, forms when the average amplitude of the light is zero."
I love this. Don't ask me what it means.
I love this. Don't ask me what it means.
Exotic as the name seems, squeezed states are just Heisenberg’s uncertainty principle in action. In quantum optics, a light field is described by two “quadratures,” one for phase (P) and one for amplitude (X). Per Heisenberg, the minimum uncertainty of those two quadratures in a given measurement is given by the relation ΔXΔP = ħ/2. In other words, for a given measurement, the better you know the phase, the more potential error there is in the amplitude, and vice versa.
For a coherent state, such as a laser field, the phase and amplitude uncertainties are equal, giving rise to a circularly symmetric “fuzzball” of potential error between the two quadratures. But using nonlinear-optics techniques, the circle can be “squeezed” into an ellipse. That means that uncertainty in one quadrature—the one that’s relevant to your sensor—can be reduced, while the uncertainty in the other, less relevant quadrature are increased.
I think in the case described here, the zero average amplitude thing has to do with something a little bit different.
Except there are ways to go below that, like a Casimir cavity.
I find these things confusing because when people explain Casimir cavities they never bother to say why the justification for zero point energy existing in the first place doesn’t apply within the cavity.
Of course in nature there is no such thing as a "classical wave", so this description has to break down at some point. This is the case for vacuum fluctuations which simply do not have a classical explanation.