Toshiba shows practical quantum cryptography

[R.A. Hettinga]

<http://www.zdnet.co.uk/print/?TYPE=story&AT=39181033-39020357t-10000013c>

Toshiba shows practical quantum cryptography
Rupert Goodwins
ZDNet UK
December 13, 2004, 18:15 GMT

Toshiba Research Europe demonstrated last week what it claims is the
world's first reliable automated quantum cryptography system and run it
continuously for over a week.

 The system, which relies on single photons to transmit an untappable key
over standard optical fibres, is capable of delivering thousands of keys a
second and can be effective over distances of more than 100km.

 Although no price or launch date has been set yet, Toshiba is already in
talks with a number of telcos and end users in preparation for
commercialisation of the technology -- which offers the possibility of
significantly more secure networking.

 "We're talking to a number of potential end users at the minute," Dr
Andrew Shields, group leader of Toshiba's Cambridge-based Quantum
Information Group told ZDNet UK. "We're planning to do some trials in the
City of London next year, and are targeting users in the financial sector.
We've also had some interest from telcos, including MCI with whom we've
been running the installed fibre tests."

 The system works by transmitting a long stream of photons modulated to
represent ones and zeros, most of which are lost along the way. These
photons can be modulated in one of two ways through two different kinds of
polarisation, but according to Heisenberg's Uncertainty Principle it is
impossible to know both the kind of polarisation and the data represented
by the photon. The receiver has to assume one to get the other, which it
will frequently get wrong.

 The receiver picks up and attempts to decode a few out of those that make
it, and reports back to the sender which ones it received and decoded thus
making up a key that both ends know. Any interceptor can't know what the
value of those photons is, because by reading them in transit it will
destroy them, and it can't replace them after reading them because it can
never know their exact details.

 Although Toshiba has been developing special hardware to create and
analyse single photon transactions by quantum dots -- effectively
artificial atoms integrated with control circuitry -- the current
cryptographic equipment uses standard parts, including Peltier-effect
cooled detectors operating at very low noise levels. The next generation of
equipment is expected to use this new technology.

 Toshiba is also looking at ways to increase the range of the systems
beyond the limitations of a single fibre -- because a photon can't be
intercepted and retransmitted, it's not possible for the technology to
incorporate repeaters to overcome the losses in multiple segments. However,
says Shields, there is a possibility that repeaters may be created using
quantum teleportation -- a new and still experimental effect where the
quantum state of a particle can be transmitted across distances without it
needing to be fully measured.

 Toshiba Research Europe Ltd is part of the European SECOQC project, which
is working towards the development of a global network for secure
communication using quantum technology.


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R. A. Hettinga <mailto: rah at ibuc.com>
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
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"... however it may deserve respect for its usefulness and antiquity,
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experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'