Wednesday, November 30, 2011

[Mind's Eye] plucking light from 'nothing'

I tend to like science that doesn't require building vast entities
like the LHC at CERN. Stuff I could do on the kitchen table is more
my scene and hopefully simple enough to show my grandson, at least in
Wilson, C., Johansson, G., Pourkabirian, A., Simoen, M., Johansson,
J., Duty, T., Nori, F., & Delsing, P. (2011). Observation of the
dynamical Casimir effect in a superconducting circuit Nature, 479
(7373), 376-379 DOI: 10.1038/nature10561
is an example - though I actually can't do this one.

I went through undergraduate chemistry "knowing" about virtual
particles, though I mistakenly thought they were accounting devices
rather than real. I "knew" too that vacuums were full of such stuff.
The thought experiments all seemed undoable. Here's a description of
the plucking light from vacuum job.

"In addition, there is also the dynamic Casimir effect. This occurs if
the mirrors are moving very fast so that the electromagnetic field in-
between has no time to adjust. Instead, the ripples in the field
caused by the fast mirror movement lead to the emission of a light
particle. Basically, the mirrors create light out of the
electromagnetic field in a similar way that a guitar player generates
sounds from plucking a string. The problem with the experimental
realization of the dynamic Casimir effect is that the mirrors need to
move seriously fast. Otherwise the system has time to adjust to the
new geometry of the mirrors, and no light will be excited. We are
talking about speeds close to the speed of light!

Such fast mirror movements are simply not possible with mechanical
mirrors. What is needed is an analogue that changes the dimension of
the vacuum by other means. Fortunately, such systems exist in
superconducting circuits, where magnetic fields applied to a so-called
SQUID circuit on a chip achieve the same moving mirror function for
electromagnetic fields. Moreover, fast-changing magnetic fields are no
problem to create. In the present experiment the mirrors 'move' at a
quarter of the speed of light, which corresponds to a driving
frequency for the magnetic field of more than 10 gigahertz. The
dynamic Casimir is clearly observed, with light being generated at the
expected frequencies.

This is certainly a beautiful study confirming the intriguing
properties of quantum mechanics. And what's more, it doesn't need
Hawking's black holes to experiment with them, all that's needed is a
table-top setup of superconducting circuits. This ease of
experimentation will make sure we will learn much more about these
virtual fluctuations in vacuum from future experiments."

As a kid I used to hear that money could not be produced from thin air
and such - these days it seems more and more of what was nothing
actually is something.


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