Quantum Temple

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.