[FPSPACE] >Single photons bounced off orbiting satellite

[LARRY KLAES]

>From: the physics arXiv blog <howdy at arxivblog.com>
>Reply-To: the physics arXiv blog <howdy at arxivblog.com>
>To: ljk4 at msn.com
>Subject: the physics arXiv blog
>Date: Mon, 17 Mar 2008 16:32:05 -0500 (CDT)
>
>the physics arXiv blog
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>Single photons bounced off orbiting satellite
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>Posted: 17 Mar 2008 06:41 AM CDT

>http://feeds.feedburner.com/~r/arXivblog/~3/252946761/
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>Quantum physicists have been sending qubits through the atmosphere encoded 
>in individual photons for years now. The work is the foundation of a new 
>type of quantum communication that is perfectly secure from eavesdropping.
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>But there are challenges in setting up a global system of quantum 
>communication. Not least is the problem of decoherence, in which noise 
>destroys the quantum nature of the information as it travels though the 
>atmosphere. This has limited the distance record for this kind of 
>transmission to 144km (although longer distances are possible through 
>optical fibres).
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>The obvious way around this is to send the signals through space via a 
>satellite. When sent straight up, the photons need only travel through 8 
>kilometres of atmosphere and so are much less likely to decohere.
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>On Friday, Anton Zeilingers group in Vienna announced that they had taken 
>the first step in this direction by bouncing single photons off an orbiting 
>satellite soome 1400km above the Earth.
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>The team used a 1.5 metre telescope called the Matera Laser Ranging 
>Observatory in Italy to bounce single photons off the Ajisai geodetic 
>satellite, an orbiting disco ball that is used for laser ranging 
>measurements.
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>Quantum communication with entangled photons can only be done by sending 
>and detecting them one at a time so the experiment is a crucial step in 
>making space-based quantum communication possible.
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>However, the team also tried bouncing photons off several other disco balls 
>such as Lageos II, without success.
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>But give them their due. The experiment proves that it is possible to use 
>existing laser ranging equipment to send and receive single photons from 
>orbiting satellites.
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>Our findings strongly underline the feasibility of Space-to-Earth quantum 
>communication with available technology, says the team.
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>Of course, this isnt a demonstration of quantum communication itself in 
>space. That will require an orbiting source of entangled photons.
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>So all they need now is somebody to build and launch a satellite that can 
>produce and transmit entangled photons. Any takers?
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>Ref:  arxiv.org/abs/0803.1871: Experimental Verification of the Feasibility 
>of a Quantum
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>Channel between Space and Earth
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