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Physicists Successfully Store and Retrieve Nothing

  1. Mar 3, 2008 #1


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    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.

  2. jcsd
  3. Mar 3, 2008 #2


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    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 [itex]\Delta p \Delta q =[/itex] (minimum), one can play with
    the individual uncertainties in position and momentum (e.g: increasing [itex]\Delta p[/itex]
    but decreasing [itex]\Delta q[/itex], 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.
    Last edited: Mar 3, 2008
  4. Mar 4, 2008 #3


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    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".
  5. Mar 4, 2008 #4
    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.
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