Physicists Successfully Store and Retrieve Nothing

[SF]

By Adrian Cho
ScienceNOW Daily News
29 February 2008
It sounds like a headline from the spoof newspaper The Onion, but for physicists, this is actually an achievement: Two teams have stored nothing in a puff of gas and then retrieved it a split second later. Storing a strange form of vacuum builds on previous efforts in which researchers stopped light in its tracks (ScienceNOW, 22 January 2001) and may mark a significant step toward new quantum information and telecommunication technologies.

http://sciencenow.sciencemag.org/cgi/content/full/2008/229/1

 

[strangerep]

Two teams have stored nothing in a puff of gas and then retrieved it a split second later. Storing a strange form of vacuum builds on previous efforts in which researchers stopped light in its tracks (ScienceNOW, 22 January 2001) and may mark a significant step toward new quantum information and telecommunication technologies.

For the benefit of other readers, the article is about "storing" a "squeezed vacuum"
state of light.

The notion of "squeezed" states basically refers to the possibility that, given a minimum
uncertainty state, where $\Delta p \Delta q =$ (minimum), one can play with
the individual uncertainties in position and momentum (e.g: increasing $\Delta p$
but decreasing $\Delta q$, while still maintaining the minimum uncertainty
product. It's called "squeezing" because if you draw a diagram of this in phase space,
a circle gets squeezed to an ellipse (while maintaining total area).

This idea applies to state of zero photons (normally called a "vacuum"). If a
"vacuum" state has (determinately) zero energy-momentum, it must have totally
indeterminate position. If confined in space (so that its position uncertainty
decreases, its momentum uncertainty must increase). The experiment just
confirms the well-known fact that the details of what's happing at the
so-called "dark" ports in a quantum optics experiment are important
quantum mechanically. There is not just a single unique universal notion of
"vacuum state" in general.

Wikipedia has more: http://en.wikipedia.org/wiki/Squeezed_state

The squeezing transformations correspond to certain "canonical transformations"
in classical Hamiltonian dynamics (which can mix position and momentum
variables without changing the form of Hamilton's equations). The full group of
these canonical transformations is not always well-represented when one passes
to a quantum theory. E.g., in (infinite-dimensional) QFT based on unitary irreps
of the Poincare group, one finds that there are physically-important
transformations (field displacements, Bogoliubov transformations) that are
useful in generalized coherent states, superconductivity, and more,
but are not implemented sensibly in the usual Hilbert-Fock space.

 

[Demystifier]

The squeezed vacuum is actually not a vacuum. It contains a large (but uncertain) number of quanta. Its mean energy is larger than the ground state energy. Hence it is not "nothing".

 

[jnorman]

yawn... this kind of story just makes physicists look like idiots, just like their earlier story on "stopping light". some droll sort of scientific sensationalism, which after written for the masses by some semi-scientist makes little sense and generally the story has next to nothing to do with the actual experiment or its results.