that contain computer chips as well as extremely strong encryption of computer data,
which is called quantum cryptography.
Quantum communication, cryptography
and computing all are based on the concept
that quantum particles such as photons can
be in more than one physical state at the
same time. Electricity, by contrast, is either
on or off – one or the other, but not both.
By existing in more than one state at the
same time, photons can hasten computer-to-computer communication and make
smarter computers that can come up with
complex encryption that foreign spies and
wanton hackers cannot break.
Holding an ion
Another device that can be used both
for sensing and for quantum communication was developed by researchers at the
National Institute of Standards and Technology (NIST) in Bolder, Colo., and their
colleagues at the University of Erlangen-Nuremberg in Germany. It can trap and
hold individual ions above three cylindrical steel electrodes with hollow bores protruding from the device. They call it a
“stylus trap” because the steel cylinders
trap the ion, and each cylinder reminds the
researchers of a stylus.
Laser light and cold temperatures were
used to trap the ions using techniques that
have been demonstrated previously. The
fact that the ions are held above the electrodes is unique. This architecture allows
for greater access to the ions.
Using the ion as a probe for electromagnetic fields, the device can be used to
measure forces, especially those oscillating between approximately 100 kHz and
10 MHz. It is about a million times more
sensitive than the mechanical sensitivity
of a cantilever of an atomic force microscope. Individual photons theoretically
could be transferred to the trapped ions
with 95 percent efficiency for quantum
cryptography, and fluorescent light emitted by the ions could be used in quantum
computing. This device is detailed in the
June 28, 2009, issue of Nature Physics by
senior author David Wineland of NIST
and his colleagues.
Ripping a nanozipper
An even more exotic-looking force-sens-ing device was created by the Oskar Painter
group at Caltech. The device consists of
two nanoscale strands of silicon with peri-
odic oval holes down the length of the
strands. Connected side by side, the strands
reminded the researchers of a zipper found
on a piece of clothing. The zipper strands
even opened up like a zipper when the scientists focused a laser beam down the center of the strands.
However, the researchers said that the
zipper does not open as a result of the
beam’s path straight down the center. The
mechanism is more exotic than that. Some
of the photons enter and circulate in the
periodic oval holes, and this circulation is
what ultimately opens the zipper cavity.
The zipper strands could be used in force
sensing; for example, two molecules could
be attached to opposite strands, and the
force required to open the strands and
thereby pull the molecules apart could be
calculated from there. The strands also
could be used for photonic communication
and photonic circuits, as well as for studying fundamental forces.
Applications aside, the cavity is also a
marvel of physics. The force of a single
photon traveling straight through the cavity
is comparable to a force 10 times that of