Is Ready for Its Close-Up
Advances in detectors and sources have gotten quantum communication ready for rollout.
Photonics plays a key role in this technology, thanks to the ability to impose a quantum state
on particles of light and to detect that state at a point many miles away.
BY HANK HOGAN
Run across Switzerland, a pilot quantum key distri-
bution (QDK) network was the longest running test
bed of the technology. CERN = European Organi-
zation for Nuclear Research; UNIGE = University of
Geneva; Hepia = Engineering School of Geneva.
Jet d’Eau is Geneva’s landmark water fountain.
Courtesy of ID Quantique.
Quantum communication may be ready for its big debut, but tech- nical issues – such as how to increase transmission distance or construct
a quantum repeater – still must be worked
out. There are also questions about the
commercial viability of the most near-term
application, quantum key distribution
(QDK). However, there is a clear need,
particularly in highly secure settings.
“Key distribution and key generation
are key to the success of any transmission
security network,” said Karl Fuchs, vice
president of technology for satellite communications vendor iDirect Government
Technologies of Herndon, Va. The company sells products and services to the
US military and other demanding customers.
The biggest performance hit arises from
disseminating the initialization key, the
basis for all subsequent encryption, Fuchs
said. Consequently, overall system performance and security would improve
with faster and more secure key switching.
Quantum key distribution achieves the
security objective absolutely by taking advantage of the ability to detect an eavesdropper via changes in the measured
quantum characteristics of a photon.
The operative words here are “a photon,” as in a single photon. Current commercially available quantum key distribution schemes require single-photon
sources and detectors. The former can be
approximated well enough by attenuating
a laser so that, on average, much less than
one photon is present in any given clock
cycle. That clock rate, in turn, is set by
the speed of single-photon detectors, and
here, progress has been made in the past
Raw Key Exchange
Raw Key Exchange
SwissQuantum Network Structure
This flow diagram shows the data path of the pilot QKD network in Switzerland. Courtesy of ID Quantique.
For example, Toshiba Research Europe
Ltd. of Cambridge, UK, a subsidiary of
Japan’s Toshiba Corp., has developed
technology that allows conventional avalanche photodiodes to run 100 times faster
in single-photon mode than previously
possible. The advance involves comparing
detector output from the current clock
cycle to the one before, said Zhiliang