Scientists working at Toshiba's Research Centre Laboratory at Cambridge University in the UK have developed a photodetector that identifies and "holds" individual photons as they travel along a fibre optic cable, opening up the possibility of uncrackable codes able to carry the most secret and sensitive data without fear of compromise. Martyn Warwick reports.
The researchers have also devised a "gate" that opens and closes in a tenth of a billionth of a second allowing the captured photons to form an orderly queue before being let through, one at a time, to deliver with their individual parts of a message. To put that figure in perspective, the photodetector window is open for just 50 picoseconds; the length of time it takes light to travel just 15 millimetres.
Details of the research, which is based on attributes of quantum physics, are published in the latest edition of "Physical Review X". The article covers the technology used to isolate and "read" pulses of quantum light concealed in massive streams of the billions of photons that are sent across fibre optic data networks every second.
The new technique permits the faintest of photons to be identified and isolated even though their presence and signatures are obscured in the welter of much brighter coloured light hurtling across fibre optic networks. As an analogy, it is akin to being able to distinguish the dim light from a single star in a galaxy many thousands of light years from earth whilst looking at and through the sun.
The Quantum Key Signal Distribution photons (QKD) can be seen and read because the new techniques allow such rapid switching across all light sources on any given fibre that everything is seen and nothing is rendered invisible and unreadable by the brightness and strength of other light sources operating on different wavelengths.
The Cambridge experiments are currently purely laboratory-based but the tests were carried out over 90 kilometres of fibre.
The previous longest distance achieved by other scientists was just ten metres.
So, it'll be a while before we see QKD in commercial networks, but it will happen, not least because the technique is comparatively inexpensive compared to the cost of erecting and policing massive high-security firewalls.
Estimates are that that QKD could be deployed for a few tens of thousands of pounds, a sum well within the bounds of many big business corporations. And, of course, the price will fall as more and more systems are deployed.
That said, governments and government agencies are the most likely to be the first to take advantage of the remarkable data security provided by QKD but the big banks and other financial services corporations won't be far behind.
And, as to whether or not the new technology will ever make it into the consumer space, well, you pays your money and you takes your choice. Every analysts and pundit seems to have a different take on it.
The great thing about Quantum Key Distribution systems is, because they are based on quantum cryptography, they provide a darned near failsafe method of distributing genuinely and verifiably secret digital keys whilst also providing significant cost advantages over other methodologies.
What's more, QKD potentially allows for key distribution over standard telecom fibre links well in excess of 100 kilometres at bit rates high enough to generate a Megabit per second of key material - and that's enough for coverage in major cities and conurbations.
The Toshiba's Reseach Centre Laboratory experiments are based on a "one-way" architecture, within which the photons travel from sender to receiver. It is claimed that this design is secure from all types of both covert and overt surveillance because quantum physics theory states that were some unauthorised person or entity break into a fibre optic cable and attempt to hold and to measure single photons, the very act of trying to measure will affect their quantum state and so result in irrevocable errors in the information carried by a single photon. Thus, by measuring the error rate in the secret key, it is possible to tell if there has been any attempt to eavesdrop.
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