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Physicist
Joshua Bienfang sets up the NIST quantum key distribution
system to receive a string of photons from colleagues
stationed on the top floor of the NIST Administration
Building (shown in the background.) The black instrument
on the left is an 8-inch telescope used in collecting
the incoming photons.
Photo by Gail Porter/NIST |
The fastest
known cryptographic system based on transmission of single
photons—the smallest pulses of light—has been
demonstrated by a team at the Commerce Department’s
National Institute of Standards
and Technology (NIST). The transmissions cannot be intercepted
without detection, so that messages encrypted with the system
can be kept secret.
The
NIST “quantum key distribution” (QKD) system transmits
a stream of individual photons to generate a verifiably secret
key—a random series of digital bits, each representing
0 or 1, used to encrypt messages—at a rate of 1 million
bits per second (bps). This rate is about 100 times faster
than previously reported systems of this type.
The
demonstration, described in the May 3 issue of Optics
Express,* is the first major reported result from
a new NIST testbed built to demonstrate quantum communications
technologies and cryptographic key distribution. The testbed
provides a measurement and standards infrastructure for research,
testing, calibrations and technology development. Scientists
tested the QKD system by generating an encryption key that
could be sent back and forth between two NIST buildings that
are 730 meters apart. They are using the testbed to develop
data-handling techniques associated with this type of encryption.
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Alan
Mink works on a programmable printed circuit board used
to process data for the new NIST quantum key distribution
system.
©Robert Rathe |
Acadia
Optronics LLC of Rockville, Md., consulted on the system design
and hardware. Partial funding for the project was provided
by the Defense Advanced Research Projects Agency.
Quantum
systems—exploiting the laws of quantum mechanics—are
expected to provide the next big advance in data encryption.
The beauty of quantum key distribution is its sensitivity
to measurements made by an eavesdropper. This sensitivity
makes it possible to ensure the secrecy of the key and, hence,
the encrypted message. The keys are generated by transmitting
single photons that are polarized, or oriented, in one of
four possible ways. An eavesdropper reading the transmission
causes detectable changes at the receiver. When such changes
are observed, the associated key is not used for encryption.
Compared
to previously described QKD systems, the major difference
in the NIST system is the way it identifies a photon from
the sender among a large number of photons from other sources,
such as the sun. To make this distinction, scientists time-stamp
the QKD photons, then look for them only when one is expected
to arrive.
“To
be effective, this observation time has to be very short,”
says NIST physicist Joshua Bienfang. “But the more often
you can make these very brief observations, then the faster
you can generate keys. We have adapted some techniques used
in high-speed telecommunications to increase significantly
the rate at which we can look for photons.”
The
NIST team has packaged data-handling electronics operating
in the gigahertz (1 billion bits per second) range in a pair
of programmable printed circuited boards that plug into standard
PCs. Photon losses caused by imperfections in the photon sources
and detectors, optics, and procedures reduce the key generation
rate. However, 1 million bps makes QKD practical for a variety
of new applications, such as large network distributions or
streaming encrypted video.
“We
are processing data much faster with this hardware than can
currently be done with software,” says NIST electrical
engineer Alan Mink. “You would need a computer processing
at more than 100 GHz (about 50 times faster than current PCs)
to do it with software and you still couldn’t do it
fast enough because the operating system would slow you down.”
The NIST
quantum system uses an infrared laser to generate the photons
and telescopes with 8-inch mirrors to send and receive the
photons over the air. The data are processed in real time
by printed circuit boards designed and built at NIST, so that
a computer produces ready-made keys. NIST researchers also
developed a high-speed approach to error correction.
Further
research is planned to improve the system, primarily by addressing
the need for faster photon detectors, the principal barrier
to the development of practical systems for more widespread
use. The group plans to incorporate NIST-developed photon
sources and detectors. More information about NIST’s
quantum information program can be found at http://qubit.nist.gov.
As a
non-regulatory agency of the U.S. Department of Commerce’s
Technology Administration, NIST develops and promotes measurement,
standards and technology to enhance productivity, facilitate
trade and improve the quality of life.
For
further information on quantum cryptography see:
http://www.nist.gov/public_affairs/releases/quantumkeys_background.htm
*Optics
Express is the online rapid publication journal of the
Optical Society of America. See: http://www.opticsexpress.org.
Reporters/Editors:
For high-resolution files of the photos on this page contact
Gail Porter, (301)
975-3392.
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