PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 737 July 14, 2005
by Phillip F. Schewe, Ben Stein
        
CIRCUIT ELEMENTS FOR OPTICAL FREQUENCIES.   Researchers at the
University of Pennsylvania propose to shrink circuits in order to save
space and power and, more importantly, to accommodate electronic
applications at much higher frequencies than are possible with current
models, applications that include nano-optics, optical information storage,
and molecular signaling.
        Electric circuit elements, among them resistors, capacitors, and
inductors, come in a variety of sizes to deal with a variety of
applications at a range of frequencies. The familiar electrical grid, for
example, operates at a frequency of 60 Hz.  A circuit designed to process
radio signals operates at the 100-megahertz range.  A typical frequency
domain for computers is 1 GHz.  Higher still, microwave applications often
operate at the 10-GHz (10^10 Hz) level.  Nader Engheta
(engheta{at}ee.upenn.edu, 215-898-9777) and his Penn group would like to
extend the circuit concepts up to optical frequencies, around 10^15 Hz.  To
do this, instead of just shrinking the classic circuit elements to fraction
of the typical wavelength of the optical signal being processed (around 500
nm), the Penn proposal is to make nano-inductors,  nano-capacitors and
nano-resistors out of sub-wavelength nano-particles, fashioned from
appropriate materials on a substrate with lithographic techniques.
Possible applications would include direct processing of optical signals
with nano-antennas, nano-circuit-filters, nano-waveguides, nano-resonators,
and even nano-scaled negative-index optical structures.  (Engheta et al.,
Physical Review Letters, upcoming article;
http://www.ee.upenn.edu/~engheta/)
        
STRENGTHENING QUANTUM CRYPTOGRAPHY BY PUTTING ON BLINDERS.  A Korea-UK team
(contact Myungshik Kim, Queen's University, Belfast, m.s.kim{at}qub.ac.uk , or
Chilmin Kim, Paichai University) has introduced a method for preventing
several clever attacks against quantum cryptography, a form of message
transmission that uses the laws of quantum physics to make sure an
eavesdropper does not covertly intercept the transmission.  Making the
message sender and receiver a little blind to each other's actions, the
researchers have shown, can bolster their success against potential
eavesdroppers.
        In quantum cryptography, a sender (denoted as Alice) transmits a
message to a receiver (called Bob) in the form of single photons each
representing the 0s and 1s of binary code. If an eavesdropper
(appropriately named Eve) attempts to intercept the message, she will
unavoidably disturb the photon through the Heisenberg uncertainty
principle, which says that even the gentlest observation of the photon will
perturb the particle. This will be instantly detectable by Alice and Bob,
who can stop the message and start again.  Quantum cryptography is already
being used in the real world and is even available commercially as a way
for companies to transmit sensitive financial data.  But in its real-world
implementation, a weak pulse of light (rather than a perfect stream of
single photons) is sent down a transmission line that is "lossy,"
or absorbs photons.  So feasible attacks on quantum cryptography include
the pulse-splitting attack (in which Eve splits a transmitted pulse into
two pulses and examines one of them for information), the pulse-cloning
attack (in which a transmitted pulse is copied to relatively high accuracy
and then inspected for its information), and the "man-in-middle"
or impersonation attack, in which Eve could impersonate Alice or Bob by
intercepting the transmission and acting as sender or receiver.
A new paper proposes a solution to these three attacks by proposing a
technique called "blind polarization."  In this technique, Alice
and Bob verify their identities to each other in a rather paradoxical way,
by performing some actions that is their own private information. Yet these
actions make the message completely indecipherable to a third party. Alice
creates a pair of pulses, but with random polarizations (polarization
indicates the direction or angle in which each pulse's electric field
points relative to some reference, such as a horizontal line)  Alice sends
the pulses to Bob, who does not know the polarizations.  Nonetheless,
without measuring the polarization values, Bob is able to rotate the
polarization of one pulse by one amount and the other pulse by another
amount, but he doesn't tell Alice which pulses got which treatment.  Alice
receives the pulses, and then encodes them with a message (representing the
binary value 0 or 1, which could stand for "no" or "yes),
then blocks one of the pulses, without telling Bob which one was blocked. 
Bob then reverses the various polarizations by a certain amount to get the
desired message.  The various polarization adjustments are designed in such
a way that either pulse Alice sends will yield the desired information. 
According to researcher Myungshik Kim, Alice has her own private
information on which pulse is blocked, while Bob has his own private
information on which pulse he rotated by a given amount.  Once Alice begins
the transmission, there is no way for Eve to have this private information
which makes their protocol effective against the man-in-middle and other
attacks. (Kye et al., Physical Review Letters, upcoming article).  This
paper is the latest in a wave that plugs up potential vulnerabilities in
quantum cryptography (for an example of using "quantum decoys" to
thwart attacks, see Lo et al, Physical Review Letters, 17 June 2005)

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