that contain computer chips as well as extremely strong encryption of computer data,which is called quantum cryptography.
Quantum communication, cryptographyand computing all are based on the conceptthat quantum particles such as photons canbe in more than one physical state at thesame time. Electricity, by contrast, is eitheron or off – one or the other, but not both.By existing in more than one state at thesame time, photons can hasten computer-to-computer communication and makesmarter computers that can come up withcomplex encryption that foreign spies andwanton hackers cannot break.
Holding an ion
Another device that can be used both
for sensing and for quantum communica-
tion was developed by researchers at the
National Institute of Standards and Tech-
nology (NIST) in Bolder, Colo., and their
colleagues at the University of Erlangen-
Nuremberg in Germany. It can trap and
hold individual ions above three cylindri-
cal steel electrodes with hollow bores pro-
truding 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 wereused to trap the ions using techniques thathave been demonstrated previously. Thefact that the ions are held above the electrodes is unique. This architecture allowsfor greater access to the ions.
Using the ion as a probe for electromagnetic fields, the device can be used tomeasure forces, especially those oscillating between approximately 100 kHz and10 MHz. It is about a million times moresensitive than the mechanical sensitivityof a cantilever of an atomic force microscope. Individual photons theoreticallycould be transferred to the trapped ionswith 95 percent efficiency for quantumcryptography, and fluorescent light emitted by the ions could be used in quantumcomputing. This device is detailed in theJune 28, 2009, issue of Nature Physics bysenior author David Wineland of NISTand 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 sci-
entists focused a laser beam down the cen-
ter 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 study-
ing 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