[tt] the physics arXiv blog

Tue Jul 8 21:08:47 UTC 2008

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From: the physics arXiv blog <howdy at arxivblog.com>
Date: Tue, 8 Jul 2008 14:36:14 -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]Simple mod turns diode into photon counter

   Posted: 08 Jul 2008 12:53 AM CDT

   [3]Avalanche photodetection 

   Counting photons is a tricky business. They're slippery beasts that
   arrive silently, often and in packs, in ways that are almost
   impossible to count.

   One of the most widely used of devices that can spot the arrival of a
   single photon is the avalanche photodiode. These cheap and easy to use
   devices rely on the ability of diodes to allow the flow of electrons
   when the voltage across them is in one direction but prevent that flow
   when the bias is reversed. But  if the reverse bias is increased
   beyond a specific threshold then a breakdown occurs and a reverse
   current suddenly starts to flow.

   Choose the right material for your photodiodes and this breakdown can
   be triggered by a the arrival of a single photon  smashing into an
   electron which goes on to hit other electrons causing a chain
   reaction. The result is an avalanche of current that signals the
   arrival of your photon.

   Avalanche photodiodes are widely use to detect single photons but have
   an important limitation: they cannot distinguish between the arrival
   of a single photon and the arrival of two or more photon's
   simultaneously.

   But that is set to change. Today, [4]our old friend Andrew Shields, at
   Toshiba's research labs in Cambridge UK, explains how to soup up a
   bog-standard avalanche photodiode so that it can count photons as they
   arrive. That's like turning a Fiat 500 into a Ferrari.

   He says that the trick is to measure the characteristics of the
   avalanche current in the very first instants that it forms. At this
   early stage, say Shields and friends, the avalanche current  is
   proportional to the number photons that have struck.

   Simple really but with enormous potential. The ability to count
   photons is one of the key enabling technologies for optical quantum
   computing. A number of schemes are known in which it is necessary to
   count the arrival of 0,1 or 2 photons at specific detectors.

   Various people, including Shields himself, have  come up with complex,
   cooled devices that can count photons. But this is a major step
   forward. Avalanche photodiodes are cheap, widely available and easy to
   use. With such a cheap detector now available (as well as decent
   photon guns), we could see dramatic progress in this field in the
   coming months.

   If you haven't quite seen the significance of this, imagine
   overclocking your calculator and matching the performance of a
   workstation. Or polishing up the 3 inch reflector in your attic and
   outclassing Hubble with your images.

   Impressive stuff.

   Ref: [5]arxiv.org/abs/0807.0330: An Avalanche-Photodiode-Based
   Photon-Number-Resolving Detector

   [6][arXivblog?i=CbruoH] 
   [7][arXivblog?i=bqXrpJ] [8][arXivblog?i=4oNL8J]
   [9][arXivblog?i=TFw0jj] [10][arXivblog?i=qMNBYJ]
   [11][arXivblog?i=NPCVlj] [12][arXivblog?i=0ZrNCJ]
   [13][arXivblog?i=lAQelj] [14][arXivblog?i=pjp32J] 
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References

   1. http://arxivblog.com/
   2. http://feeds.feedburner.com/~r/arXivblog/~3/329535400/
   3. http://arxivblog.com/wp-content/uploads/2008/07/avalanche.jpg
   4. http://arxivblog.com/?p=338
   5. http://arxiv.org/abs/0807.0330
   6. http://feeds.feedburner.com/~a/arXivblog?a=CbruoH
   7. http://feeds.feedburner.com/~f/arXivblog?a=bqXrpJ
   8. http://feeds.feedburner.com/~f/arXivblog?a=4oNL8J
   9. http://feeds.feedburner.com/~f/arXivblog?a=TFw0jj
  10. http://feeds.feedburner.com/~f/arXivblog?a=qMNBYJ
  11. http://feeds.feedburner.com/~f/arXivblog?a=NPCVlj
  12. http://feeds.feedburner.com/~f/arXivblog?a=0ZrNCJ
  13. http://feeds.feedburner.com/~f/arXivblog?a=lAQelj
  14. http://feeds.feedburner.com/~f/arXivblog?a=pjp32J
  15. http://arxivblog.com/
  16. http://www.feedburner.com/fb/a/emailunsub?id=8632699&key=kesJ612ZsV
  17. http://feeds.feedburner.com/arXivblog
  18. 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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