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Communications Science Technology

Storing Photons In a Solid State Device 68

bondisthebest writes in with a report from IEEE Spectrum: "Physicists in Switzerland, led by Nicolas Gisin of the University of Geneva, reported last week in Nature that they have made a solid-state device capable of storing photons for as long as 1 microsecond. The invention will aid in the development of light-based quantum-cryptography networks, which are theoretically impervious to hacking but are currently limited in range to a few dozen kilometers, primarily because of a lack of a suitable way to store the quantum state of photons."
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Storing Photons In a Solid State Device

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  • by Dutch Gun ( 899105 ) on Wednesday December 24, 2008 @05:13PM (#26226099)

    I'll bet if you also chill your 3 year old to near absolute zero, you can get him to stop fidgeting for much longer than that.

    Anyhow... *cough*, I had to follow an extra link to see what this might be good for. Apparently, one could theoretically build a quantum repeater, required for quantum networks, which supposedly would be impervious to hacking, because supposedly one can't read the quantum data without actually changing it's state to some degree.

    But then there's this:

    Quantum repeaters will be an essential component for long-range quantum information networks because photons degenerate--their quantum state changes--as they travel and need to be regenerated periodically in a way that preserves their original information. No one has been able to make a reliable quantum repeater yet. One of the prerequisites for such a device is a quantum memory that can store photons (and their quantum state) without destroying entanglement. Entanglement, a property important to quantum networks, allows two photons to be linked in such a way that, if someone measures one of the photons, the quantum state of the other becomes known as well. When a photon travels through optical fiber, entanglement degeneration occurs by approximately 300 kilometers.

    So, if they could somehow figure out how to build a repeater, doesn't that by definition mean they could read the data, then recreate and retransmit it? Or is the act of repeating and retransmitting the quantum data different than "reading" the data? I don't quite understand how this is supposed to work (not too surprising, I'm not a physicist). Can anyone explain this supposed paradox to me?

  • by SmlFreshwaterBuffalo ( 608664 ) on Wednesday December 24, 2008 @05:41PM (#26226283)

    I think "reading" is referring to actually retrieving something of value from the data. If retransmitting requires some sort of processing to occur, then the processor would have to read the data in order to retransmit it. But if retransmitting can be done at the quantum level (the goal of this as far as I can tell), then there is nothing actually reading the data, it's merely propagated through.

    A (rather bad) analogy would be if someone were to speak to you in a language you do not know, and you repeated the words (data) verbatim. You retransmitted the words, but did not need to process them (i.e. read the data). That is, you didn't need to know what the words meant to repeat them.

  • by mark-t ( 151149 ) <> on Wednesday December 24, 2008 @06:08PM (#26226463) Journal

    Sure, if somebody finds a way to hack the physical universe in which we live and change its laws of operation, I suppose its possible.

    Quantum cryptography is secure by virtue of actual physical laws. Unless we are all living in the Matrix or some weird-ass crap like that, I'd say it's a pretty safe bet that it's secure. Even the mere _attempt_ to hack it would be immediately obvious to both the sender and the receiver.

  • by Dutch Gun ( 899105 ) on Wednesday December 24, 2008 @11:12PM (#26227941)

    So will this tech be able to build a stronger chess computer? Will I ever be able to win?

    Forget chess. We've already beaten grandmasters with computers. The next AI challenge is programming a decent Go player. []

What is algebra, exactly? Is it one of those three-cornered things? -- J.M. Barrie