By Hamish Johnston
Just yesterday we reported that physicists in China had shattered the record for quantum teleportation through free space by sending quantum states 97 km across a lake.
Now, a different team led by Anton Zeilinger (right) of the University of Vienna has extended this distance to 143 km by teleporting quantum states across the stretch of sea separating two of the Canary Islands. The team claims that its triumph takes the prospect of quantum teleportation to and from satellites one step closer.
Quantum teleportation involves sending a quantum state between two parties – from Alice to Bob – without actually sending a particle in that state. The process involves one quantum channel of communication between the two, along which one half of an entangled pair of photons is sent from Alice to Bob. Also required is a conventional communication channel, through which Alice can send Bob information about a measurement that she has made on a particle in the quantum state that she wants to teleport to Bob. Bob then uses this information to manipulate his entangled photon so that it is in the teleported state.
Zeilinger and co-workers teleported quantum states from La Palma to Tenerife, and to pull it off they had to develop several new technologies including a new source of entangled photon pairs and “ultra-low-noise” single-photon detectors. Timing also proved to be a challenge, because the 10 ns uncertainty in GPS timing signals was not good enough to achieve the teleportation. Instead, the team had to develop a new “entanglement-assisted clock synchronization” technique that relies on the detection of the entangled photons by Alice and Bob.
Beyond the technical challenges, the team say it had to contend with “exceptionally bad weather conditions” from May to July 2011 when the experiment was done, which included everything from sandstorms to snow.
The fact the team was able to overcome these technical and meteorological challenges bodes well for the ultimate goal of the research – the ability to teleport quantum states back and forth to satellites in low Earth orbits (LEOs). Although most LEO satellites are positioned about three times the distance between Tenerife and La Palma, the atmosphere is much thinner – and therefore much less disruptive – for most of that distance. As a result, teleportation to a satellite might actually be easier than sending photons across a stretch of sea.
This latest result is described in a preprint on the arXiv server.