Cambridge 8 October 2008
Researchers at the Cambridge Research Lab of Toshiba Research Europe Ltd announced
today that they have increased the bit rate of quantum key distribution (QKD) more
than hundred-fold. The breakthrough will allow QKD to be applied to optical fibre
networks connecting many users.
Quantum Key Distribution (QKD) is a new technology for distributing secret digital
keys on optical fibre. Unlike today's algorithm based techniques, the secrecy of
the keys formed by QKD can be tested and guaranteed. The Toshiba system uses a QKD
protocol satisfying the most stringent security assumptions to form keys secure
from all types of hacking on the communication channel.
Up until now the real-world applicability of QKD has been hampered by its relatively
low bit rate which is typically less than 10 kbit/sec for a 20 km fibre
link. While sufficient for secure point-to-point links, such bit rates are too low
for networks with many users. This is because in a network the secure key rate must
be shared between many pairs of users. The Toshiba breakthrough allows a 100 times
increase, to over 1 Mbit/sec for a 20 km link, enabling use on networks
with thousands of users.
The advance stems from a single photon detector developed by Toshiba, which can
work over 100-times faster than the conventional device. As the detector is based
on a compact and robust semiconductor device, it is suitable for use in real-world
networks.
In a parallel development, the Toshiba team has also designed and successfully implemented
hardware (based on their older kb/s technology) in the first QKD network launched
today in Vienna. This network is the product of a collaboration of 41 QKD R&D
teams across Europe funded by the EC through the Integrated Project SECOQC.
Dr Andrew Shields, who leads the Quantum Information Group at CRL, commented “Together,
the dramatic increase in bit rate and the possibility of network deployment, herald
a breakthrough in the applicability of QKD technology. We plan now to develop a
fully functional prototype of the high bit rate QKD system for use in quantum networks.”
TECHNICAL BACKGROUND
Cryptography, the science of information security, is essential to protect electronic
business communication and e-commerce, enabling, for example, confidentiality, identification
of users and validation of transactions. All of these applications rely upon digital
keys, which are shared between the legitimate users, but must be kept secret from
everyone else. Maintaining the ability to distribute keys securely is thus one of
the most important battlefields in the cryptography arms race. It is essential to
be able to distribute keys between users securely. Furthermore, in order to protect
the system from crypto-analysis or key theft it is important to change the keys
frequently.
QKD relies on sending encoding single photons (particle of light) along the fibre.
Any attempt by a hacker to intercept these photons scrambles their encoding, alerting
the users that their key is not secret. The Toshiba QKD system uses a one-way architecture
and the decoy protocol, which has been proven to satisfy ‘unconditional secrecy’,
meaning that the security does not rely on assumptions about the technology available
to an eavesdropper. This is the most stringent security criterion.
Current QKD systems are limited by the semiconductor devices (avalanche photodiodes)
used to detect the single photons. One photon triggers an avalanche of millions
of electrons in this semiconductor device which can be sensed by electrical circuitry
in the QKD system. The problem in present systems is that some of these avalanche
electrons can be trapped in the device and later stimulate a second spurious detection
count. As these noise counts cause errors in the key, current detectors must be
operated with long dead times to allow the decay of any trapped electrons. This
limits the clock rate of current QKD systems to around 10 MHz and thus the
secure key bit rate to under 10 kbit/sec for a 20 km fibre.
The Toshiba team has devised a method to detect much weaker electron avalanches.
This strongly reduces the chance for an electron to be trapped, allowing the detector
to be operated at much faster rates. Using this method Toshiba has increased the
clock rate of their QKD system to 1.036 GHz, approaching the value used in
conventional optical communications. This allows a raw bit rate of 9 Mbit/sec
over 20 km of fibre, which in turn provides 1.02 Mbit/sec of secure key.
This is the first time that a secure bit rate exceeding 1 Mbit/sec has been
achieved.
The new system also displays record bit rates for longer optical fibre lengths.
For a 100 km fibre the secure bit rate is 10.1 kbit/sec. This is over
an order of magnitude higher than previously reported values.
As the detector is based on a compact and robust semiconductor device, it is suitable
for real-world applications. Toshiba plan now to develop a fully functional prototype
of the high bit rate QKD system.
Part of this work was funded by the EC Framework 6 Information Society Technologies
programme through the Integrated Project SECOQC.
For further information about the work of Toshiba CRL, go to
http://www.toshiba-europe.com/research/crl/
About Toshiba
Toshiba is a world leader and innovator in pioneering high technology, a diversified
manufacturer and marketer of advanced electronic and electrical products spanning
information & communications equipment and systems; digital consumer products;
electronic devices and components; power systems, including nuclear energy; industrial
and social infrastructure systems; and home appliances.
Toshiba was founded in 1875, and today operates a global network of more than 740
companies, with 198,000 employees worldwide and annual sales surpassing US$76 billion.
Visit Toshiba's web site at www.toshiba.co.jp/index.htm
About Toshiba Research Europe Ltd
Toshiba Corporation is fully committed to the research and development of future
technologies. This commitment has resulted in Toshiba having a record number of
world firsts, including the first laptop PC (1985), the first single chip MPEG4
videophone LSI (1998) and the first DVD player (Oct. 1996). Over the 3 years to
end March 2010, the Corporation anticipates a total global R&D expenditure of
JPY1,290bn.
Toshiba Corporation established its first overseas research centre in 1991, with
the opening of Toshiba Cambridge Research Centre Ltd in the UK. This was renamed
Toshiba Research Europe Ltd (TREL) in August 1998, when a new telecommunications
laboratory in Bristol was launched. TREL now has two research laboratories in the
UK; the Cambridge Research Laboratory (CRL) in Cambridge, and Telecommunications
Research Laboratory (TRL) in Bristol.
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