[tt] the physics arXiv blog

[Eugen Leitl]

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From: the physics arXiv blog <howdy at arxivblog.com>
Date: Mon, 31 Mar 2008 17:40:49 -0500 (CDT)
To: eugen at leitl.org
Subject: the physics arXiv blog
Reply-To: the physics arXiv blog <howdy at arxivblog.com>


[1]the physics arXiv blog

   [2]A new class of photon gun

   Posted: 31 Mar 2008 12:21 AM CDT

   [3]Photon gun 

   Photons are easy to produce, at least en masse. But making them one at
   a time in a controlled fashion is much harder. Until recently the only
   trick physicists had for this was to reduce the brightness of a beam
   until it contained only one photon at a time, on average.

   Of course, the "on average" clause allows for any manner of
   multiphoton sin: the photons may be produced in pairs or bunches or
   not at all. That's a serious problem for techniques such as quantum
   cryptography because any extra photons are equivalent to a leak of
   information that an eavesdropper can use to crack the code.

   Enter the photon gun brigade, a growing band of physicists attempting
   to build devices that can fire identical, single photons on demand.
   The single photon part of this problem has been cracked by a number of
   groups who have built guns that work by inducing atoms, ions,
   molecules or quantum dots to fluoresce in a cavity.

   What has turned out to be more difficult, but just as important, is
   making each of these single photons identical. What tends to happen is
   that the cavites vibrate in various ways and this subtly distorts the
   wavelength of the photons they produce. The result is that each photon
   is very slightly different, which spoils their ability to interfere
   and become entangled with each other.

   Here's the breakthrough: Andrew Shields, at Toshiba's research labs in
   Cambridge, UK, plus a few pals from a nearby university, say they can
   create the photons using a quantum dot that they zap with two
   precisely timed voltage pulses. The first pulse injects charge
   carriers into the diode while the second suddenly shifts the quantum
   dot's emission characteristics so that it can emit light. When that
   happens, the dot emits a photon of a specific energy.

   But the key is to use such short voltage pulses that the photon
   doesn't have time to be influenced by its surroundings. And that means
   the quantum dot always emits photons of precisely the same wavelength.

   So it looks as if Shields and co have a neat new trick up their
   sleeves, albeit one that has to be performed at 4K. But it's also an
   entirely new mechanism for producing photons of this kind so
   improvements are gonna be forthcoming. How long before we see a
   commercial version?

   Ref: [4]arxiv.org/abs/0803.3700: Indistinguishable Photons from a
   Diode

   [5][arXivblog?i=kaUnLe] 
   [6][arXivblog?i=NgUGvRF] [7][arXivblog?i=zrrrBhF]
   [8][arXivblog?i=zW1gref] [9][arXivblog?i=7TgyeBF]
   [10][arXivblog?i=CWohyEf] [11][arXivblog?i=pzFQoLF]
   [12][arXivblog?i=H8MmV2f] [13][arXivblog?i=9XyxsDF] 
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References

   1. http://arxivblog.com/
   2. http://feeds.feedburner.com/~r/arXivblog/~3/261071841/
   3. http://arxivblog.com/wp-content/uploads/2008/03/photon-gun.jpg
   4. http://arxiv.org/abs/0803.3700
   5. http://feeds.feedburner.com/~a/arXivblog?a=kaUnLe
   6. http://feeds.feedburner.com/~f/arXivblog?a=NgUGvRF
   7. http://feeds.feedburner.com/~f/arXivblog?a=zrrrBhF
   8. http://feeds.feedburner.com/~f/arXivblog?a=zW1gref
   9. http://feeds.feedburner.com/~f/arXivblog?a=7TgyeBF
  10. http://feeds.feedburner.com/~f/arXivblog?a=CWohyEf
  11. http://feeds.feedburner.com/~f/arXivblog?a=pzFQoLF
  12. http://feeds.feedburner.com/~f/arXivblog?a=H8MmV2f
  13. http://feeds.feedburner.com/~f/arXivblog?a=9XyxsDF
  14. http://arxivblog.com/
  15. http://www.feedburner.com/fb/a/emailunsub?id=8632699&key=kesJ612ZsV
  16. http://feeds.feedburner.com/arXivblog
  17. http://feeds.feedburner.com/arXivblog

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-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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