Quantum teleportation hits record distance

Physicists at the University of Vienna and the Austrian Academy of Sciences recently managed to achieve quantum teleportation over a record distance.

The international team – led by Austrian physicist Anton Zeilinger – successfully transmitted quantum states over a distance of 143 km between the two Canary Islands of La Palma and Tenerife. The previous record, set by researchers in China just a few months ago, was 97 km.

According to Zeilinger, the experiment marks a major step towards implementing satellite-based quantum communication.

“Our experiment shows how mature ‘quantum technologies’ are today, and how useful they can be for practical applications. The next step is satellite-based quantum teleportation, which should enable quantum communication on a global scale,” he explained.

“We have now taken a major step in this direction and will use our know-how in an international cooperation, which involves our colleagues at the Chinese Academy of Sciences. [Our ultimate] goal is to launch a quantum satellite mission.”

Interestingly, Zeilinger says breaking the distance record wasn’t his primary goal. Rather, the experiment provides a basis for an eventual worldwide information network, in which quantum mechanical effects enable the exchange of messages with greater security – allowing certain calculations to be performed more efficiently than with conventional technologies. 

In such a (theoretical) future, a “quantum Internet” – facilitated by quantum teleportation – will be a key protocol for the transmission of information between quantum computers. This process apparently works even if the location of the recipient is not known. Such an exchange can be used either for the transmission of messages, or as an operation in future quantum computers. 

However, the photons that encode the quantum states must be transported reliably over long distances without compromising the fragile quantum state. Indeed, the photons had to be sent directly through the turbulent atmosphere between the two islands. Unfortunately, the use of optical fibers was not suitable for teleportation experiments over such great distances, as signal loss would be too severe. 

As such, the scientists were forced to implement a series of technical innovations. Support came from a theory group at the Max Planck Institute for Quantum Optics in Garching (Germany) and an experimental group at the University of Waterloo (Canada).

”An important step for our successful teleportation was a method known as ‘active feed-forward’, which we have used for the first time in a long-distance experiment. It helped us to double the transfer rate,” explained Xiao-song Ma, one of the scientists involved in the experiment.

“In an active feed-forward protocol, conventional data is sent alongside the quantum information, enabling the recipient to decipher the transferred signal with a higher efficiency.”

Rupert Ursin, who has been working with Zeilinger on long-distance experiments since 2002, added: “Our latest results are very encouraging with a view to future experiments in which we either exchange signals between Earth and satellites or send messages from one satellite to another. Satellites in ‘low-Earth orbit’ fly between 200 and 1200 km above the surface of the Earth.

“On the way through the atmosphere from La Palma to Tenerife, our signals have been attenuated by a factor of roughly one thousand. Nevertheless, we managed to perform a quantum teleportation experiment. In satellite-based experiments, the distances to be travelled are longer, but the signal will have to pass through less atmosphere. We have now created a sound basis for such experiments.”