Austrian researchers set new world distance record for ‘quantum teleportation’
May 21, 2012
Anton Zeilinger’s group (Institute for Quantum Optics and Quantum Information at the University of Vienna) has just submitted an arXiv paper claiming that they’ve demonstrated “quantum teleportation“ over a distance of 143 km (89 miles) in the Canary Islands. If confirmed, this sets a new world’s distance record in quantum teleportation, and also sets the stage for a future global quantum network for secure satellite communications.
On May 9, researchers at the University of Science and Technology of China in Shanghai claimed that they had demonstrated quantum teleportation at a distance of 97 km (60 mi) across a lake in China. The previous published distance record was 16 km.
Quantum teleportation is actually not about teleporting matter — it’s the process of transferring the exact information about a particle from one place to another, using quantum entanglement, without the particle traveling through the intervening space.
In a related development, Space-QUEST, Zeilinger’s project on quantum entanglement for space experiments, demonstrated the exchange of a single photon between a low-Earth-orbit satellite and an Earth-based telescope in March 2008.
This wasn’t active communications, because the satellite only had a mirror, no quantum laser source. Their next step would be to install an active quantum laser on an external payload of the International Space Station, the researchers say.
Global space-based quantum networks
These new research projects validate the ability to send and receive photons under the same kinds of atmospheric interference conditions that would be required for a link between the earth and an orbiting satellite.
Successful demonstration of quantum entanglement at these distances is important as proof-of-concept for future space-based, global quantum networks, and to test the limits of entanglement at relativistic distances (in outer space). A key question: does entanglement remain valid at these length scales, or is it affected by gravity or physical distance?
In that connection, DARPA has just released a Broad Agency Announcement (BAA) soliciting “macroscopic quantum communications proposals which can combine the security of quantum communications with the distances/rates of macroscopic telecommunications. Proposed research should investigate innovative approaches that enable revolutionary advances in secure quantum communications.”
The DARPA announcement calls for some serious out-of-the-box thinking. The Chinese demonstration of quantum teleportation confirmed only 1171 teleported photons in four hours, experiencing a loss of 35–53 dB at a distance of 97 km. The Austrian demonstration confirmed only 605 teleported photons in about 6.5 hours, experiencing a loss of 28–39 dB at a distance of 143 km.
Contrast that with the new DARPA program: they’re asking for researchers to demonstrate sustained transmission of secure quantum key rates of 1-10 Gigabits per second — at distances of 1,000–10,000 km — a real quantum leap (pun intended).
And they’re asking for these communications to be insensitive to the lossy, environmental decoherence that a dirty atmosphere presents to any experiment. According to DARPA: “Current techniques for quantum communication are highly sensitive to loss, with an increase in loss leading to a corresponding drop in bit rate (e.g., 10 dB of loss results in a factor of 10 decrease in secure bit rate). Successful programs are expected to present a method for decoupling loss from secure bit rate.”
The program has two secondary goals: to conclusively demonstrate that secure quantum communications can be extended to entirely new domains, even underwater and through dirty air, and to extend macroscopic quantum communications to entirely new domains beyond the realm of key distribution.
Ref.: X. Ma et al., Quantum teleportation using active feed-forward between two Canary Islands, arxiv.org/pdf/1205.3909.pdf
Ref.: Juan Yin et al., Teleporting Independent Qubits Through A 97 Km Free-Space Channel, arxiv.org/abs/1205.2024
Also see: Rapid-fire single photons for quantum information processing