Polymer serves up single photons

[Chris Trott]

Hi,

I generally prefer to be a lurker on these types of lists, but I figured I
might as well stick my head out at some point.. I was just reading a digest
from Septembers list and found this..

>"Quantum cryptography in theory allows someone to send a secret key and
>know
>for sure that the key has not been seen by anyone but the intended
>recipient. Each bit of information in the key is represented by attributes
>of a photon, which makes it impossible for an eavesdropper to both read and
>replace all the photons in a string.

> Although commercial quantum cryptography systems exist, they use photon
>sources that sometimes represent information using a single photon and
>sometimes a few photons. Sources that reliably emit just a single photon at
>a time are needed to ensure perfect security. The goal is a reliable,
>inexpensive device that emits single photons on demand at room temperature.

> Researchers from the Georgia Institute of Technology, the University of
>Tennessee, and Oak Ridge National Laboratory have made a room-temperature,
>single-photon source using polymer molecules.

> The device consists of precisely oriented single molecules of a
>semiconducting polymer that are applied to a surface using a simple
>spray-on technique, said Tae-Hee Lee, now a researcher at Stanford
>University. "We proved that [a] simple, one-step polymer processing
>technique can generate strong and stable single-photon sources," said Lee.
>The method is an inexpensive way of generating single photons, he said.

> The single-photon source could be used in quantum cryptography devices and
>eventually for quantum computing, said Lee.

> The polymer is similar to materials used to make new types of organic
>light-emitting diodes. The researchers' prototype contains
>10-nanometer-long single-chain molecules oriented perpendicular to a glass
>surface. This orientation allows them to emit photons, and because they are
>individual molecules, they emit one photon at a time."

This sounds remarkably like existing magnetic tape that we all know and
love, but using photons instead of magnetism.  Surely the security in
quantum cryptography is in the nature of entanglement, rather than in the
storage of bits in photons. How would this tape reveal that a message has
been intercepted if it consistently serves the same photons up ? Surely an
interceptor could read it (as many times as they wishes) and pass it on,
with the receiver none the wiser ?

Cheers,

Chris




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