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Skriven 2005-07-14 23:29:51 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 737
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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@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@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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 * Origin: Big Bang (1:106/2000.7)