[Laser] Quantum teleportation achieved over 16 km

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Quantum teleportation achieved over 16 km
May 20, 2010 by Lin Edwards

(Graphic) A birds-eye view of the 16-km free-space quantum  
teleportation experiment. Charlie sends photon 1 to Alice for BSM.  
Classical information, including the results of the BSM and the signal  
for time synchronization, is sent through the free-space channel with  
photon 2, to Bob, before decoding and triggering of the corresponding  
unitary transformation. b, Sketch of the experimental system. See the  
original paper for more details. Image copyright: Nature Photonics,  
doi:10.1038/nphoton.2010.87

(PhysOrg.com) -- Scientists in China have succeeded in teleporting  
information between photons further than ever before. They transported  
quantum information over a free space distance of 16 km (10 miles),  
much further than the few hundred meters previously achieved, which  
brings us closer to transmitting information over long distances  
without the need for a traditional signal.

Quantum teleportation is not the same as the teleportation most of us  
know from science fiction, where an object (or person) in one place is  
?beamed up? to another place where a perfect copy is replicated. In  
quantum teleportation two photons or ions (for example) are entangled  
in such a way that when the quantum state of one is changed the state  
of the other also changes, as if the two were still connected. This  
enables quantum information to be teleported if one of the  
photons/ions is sent some distance away.

In previous experiments the photons were confined to fiber channels a  
few hundred meters long to ensure their state remained unchanged, but  
in the new experiments pairs of photons were entangled and then the  
higher-energy photon of the pair was sent through a free space channel  
16 km long. The researchers, from the University of Science and  
Technology of China and Tsinghua University in Beijing, found that  
even at this distance the photon at the receiving end still responded  
to changes in state of the photon remaining behind. The average  
fidelity of the teleportation achieved was 89 percent.

The distance of 16 km is greater than the effective aerosphere  
thickness of 5-10 km, so the group's success could pave the way for  
experiments between a ground station and a satellite, or two ground  
stations with a satellite acting as a relay. This means quantum  
communication applications could be possible on a global scale in the  
near future.

The public free space channel was at ground level and spanned the 16  
km distance between Badaling in Beijing (the teleportation site) and  
the receiver site at Huailai in Hebei province. Entangled photon pairs  
were generated at the teleportation site using a semiconductor, a blue  
laser beam, and a crystal of beta-barium borate (BBO). The pairs of  
photons were entangled in the spatial modes of photon 1 and  
polarization modes of photon 2. The research team designed two types  
of telescopes to serve as optical transmitting and receiving antennas.

The experiments confirm the feasibility of space-based quantum  
teleportation, and represent a giant leap forward in the development  
of quantum communication applications.

The paper is available in full online at Nature Photonics.

More information: Xian-Min Jin, Experimental free-space quantum  
teleportation, Nature Photonics, Published online: 16 May 2010.  
doi:10.1038/nphoton.2010.87

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