Tokyo, May 31, 2005 --- NEC Corporation (President: Akinobu
Kanasugi, "NEC"), National Institute of Information and
Communications Technology (President: Makoto Nagao, "NICT"),
POWEREDCOM, Inc. (President and CEO: Sam Nakane, "POWERDCOM Inc."),
and Japan Science and Technology Agency (President: Kazuki Okimura,
"JST") have jointly succeeded in realizing fortnight-long,
continuous quantum cryptography final-key (note
1) generation at an average rate of 13 kbps over a 16-km-long
commercial optical network.
These results have been achieved by NEC under the NICT project
"Research and Development on Quantum Cryptographic Technology"
through employment of a low-noise photon receiver, in addition to
an alternative-shift phase modulation method (note
2), which was developed by NEC and the Imai Quantum Computation
Information Project (Exploratory Research for Advanced Technology
("ERATO"), JST.)
The main features of this research are as follows:
| 1. |
This experiment is carried
out under general environment conditions by using optical fiber
commercially settled on the outside and quantum cryptosystems in an
office environment. |
| 2. |
Continuous generation of the
final-key, which is used in encryption and decryption and ensures
unconditional safety, from the raw-key (note
1.) over a 14 day period is enabled in parallel with single
photon transmission, realizing the world's longest continuous
final-key generation period. |
| 3. |
Over 16.3-km-long access
optical fiber, the average quantum error rate is 7.5 % and the
average final-key generation rate is 13.0 kbps. |
Previous quantum cryptography
systems have not been able to achieve long-time continuous key
generation due to fiber delay variations, reflection and scattering
in fiber. In order to solve these problems, the following novel
technologies have been newly developed and their validity has been
confirmed through continuous key generation experiments employing
POWERDCOM's optical fiber.
|
| (a) |
Wavelength division multiplexing ("WDM")
technologies enable transmission of synchronizing signals and
quantum signals in the same optical fiber. Crosstalk (note
3) from synchronizing signals is suppressed by filters. Use of
an automatic phase-alignment mechanism realizes compensation of
group velocity dispersion (note
4) between the synchronizing signals and quantum signals.
Consequently, stable phase modulation and photon detection is
achieved despite fiber delay being varied. |
| (b) |
Burst mode (note 5), using NEC's
proprietary alternative-shift phase modulation method, achieves
avoidance of the scattering of light in fiber and reflection light
from the connection point, leading to stable key
generation. |
Achieved through a newly developed quantum cryptography system
adopting a novel method, this continuous key generation enables
secure network communication supported by the principles of quantum
mechanical physics. As this system continuously generates
final-keys under general conditions, it enables quantum
cryptography transmissions in commercial optical networks, and is
expected to contribute to the realization of an optical fiber
network system requiring advanced safety levels to prevent against
code-breaking in the future.
Present cryptography systems do not guarantee unconditional
safety as their security is based on the limited calculation
abilities of present computers, however, quantum cryptography
provides unconditionally secure network communication and safety,
even when these capabilities are infinite. This is because quantum
cryptography is not reliant on calculation capability but on the
principle of physics. Therefore, its development is now attracting
considerable attention on a global scale.
NEC's quantum cryptography research is accelerating with each
new achievement putting us ahead of the competition, thus allowing
us to contribute to overall development in the field of quantum
cryptography.
About NEC Corporation
NEC Corporation (NASDAQ: NIPNY) (FTSE: 6701q.l) is one of the
world's leading providers of Internet, broadband network and
enterprise business solutions dedicated to meeting the specialized
needs of its diverse and global base of customers. Ranked as one of
the world's top patent-producing companies, NEC delivers tailored
solutions in the key fields of computer, networking and electron
devices, by integrating its technical strengths in IT and Networks,
and by providing advanced semiconductor solutions through NEC
Electronics Corporation. The NEC Group employs more than 140,000
people worldwide and had net sales of 4,855 billion yen (approx.
$45.4 billion) in the fiscal year ended March 2005. For additional
information, please visit the NEC home page at: http://www.nec.com/
* Newsroom: http://www.nec.co.jp/press/en/newsroom/index.html
***
Notes:
| (1) |
Final-key / Raw-key: The final-key is generated from the
raw-key by eliminating bits that have possibilities of errors and
eavesdropping. The raw-key is a set of random bits generated by
single-photon transmission and detection. The final-key is
essential for transmitting coded information. |
| (2) |
Alternative-shift phase modulation method: This is an NEC
proprietary method used in place of the conventional
Faraday-Mirror. It uses polarization rotation and loop back in the
fiber-loop and phase-modulation. |
| (3) |
Crosstalk: In ordinary power signals and single-photon signal WDM,
spontaneous emission from the ordinary power signals of the light
source and nonlinear effects, for example Spontaneous Raman
Scattering, influence single-photon signal as crosstalk. This
crosstalk is neglected in ordinary optical communication systems;
however, it degrades the performance in quantum cryptography
systems. |
| (4) |
Group velocity dispersion: Optical signal speed in fiber
depends on its wavelength due to wavelength dispersion in fiber.
Therefore, transmission delay difference between different
wavelength signals depends on fiber length. |
| (5) |
Burst mode: Optical signals are launched intermittently enabling
signal and noise to be isolated. |
NEC Press Contacts:
In Japan
Diane Foley
NEC Corporation
d-foley@ax.jp.nec.com
+81-3-3798-6511