Physicists in the US have teleported information
between distant ions for the first
time. The breakthrough is a significant milestone
in the quest for a workable quantum
computer, say the researchers.
Quantum teleportation involves “entangling”
two particles so that a measurement
made on one particle instantly determines the
state of the other, regardless of how far apart
they are. This is difficult in practice because
the particles tend to destroy their entanglement
by interacting with the environment.
In spite of this limitation, researchers have
been able to teleport information between
photons or between atoms that are situated
close together.

Now, Christopher Monroe of the University
of Maryland and the National Institute
of Standards and Technology (NIST) and coworkers
have managed to achieve atomic
teleportation over much larger distances by
using photons as intermediaries. The researchers
placed two ytterbium ions in separate
vacuum chambers 1 m apart and applied
microwave pulses to drive the ions into a
superposition of quantum states. Next they
shone a laser onto the ions to make them
emit single photons representing the superposition.
These photons each travelled 2m
to a meeting point at a beamsplitter, which
transferred the photons’ entanglement to
the ions. When the physicists performed a
measurement on one of the ions and sent the
outcome to the other, the latter ion embodied
the former’s initial state.
To check that teleportation had taken
place, the researchers used a process called
quantum tomography, in which they made
many measurements of the ytterbium atoms
and compared the results with theoretical
predictions. They found that their experiment
had a teleportation success rate of 90%
(Science 323 486).
Monroe says that this type of system is
attractive for quantum memories, which can
help boost quantum signals so that they can
travel further. “Our method combines the
unique advantages of both photons and
atoms,” he explains. “Photons are ideal for
transferring information fast over long distances,
whereas atoms offer a valuable medium
for long-lived quantum memory.”