Perhaps the first step towards the development of a quantum internet has been taken by researchers who quantum entangled two stationary atoms over 20 kilometres of fibre optic wire.
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Two stationary rubidium atoms have been quantum entangles
across a record distance. Image: ezphoto |
Ludwig Maximilian University (LMU) physicists have just
broken the record for quantum entanglement by successfully connecting two
rubidium atoms over a 33-kilometer (20-mile) fibre optic connection. The
accomplishment is a significant step towards the creation of a quantum
internet, which would enable instantaneous information transfer between network
nodes.
The coupling of two particles so that modifying one
instantly modifies the other is known as quantum entanglement. Moreover, one
may automatically determine the state of the other particle by measuring the
state of one.
The study authors explain how they entangled two atoms kept
in different buildings on the LMU campus, around 700 metres (2,300 ft) apart,
in a paper published in the journal Nature. The 33 kilometres (20 miles) of
fibre optic cable that connected the two locations was routed through many
coils.
After the two atoms were excited by a laser pulse, each of
them released a photon. Most importantly, this mechanism causes the atom's spin
to become quantum entangled with the photon's polarisation upon emission.
Because photons with wavelengths inside the visible light
range of the electromagnetic spectrum often only travel a few kilometres down
the cable before disappearing, previous attempts to transport such particles
through fibre optics have failed.
In order to raise the
photons' wavelength from 780 to 1,517 nanometers—roughly equivalent to the
telecom wavelength of 1,550 nanometers—the researchers employed
"polarization-preserving quantum frequency conversion." This is the
optimal frequency range for light transmission via fibre optics.
Because of this, the photons were able to make it through
their record-breaking journey down the cable and be detected by a receiver. At
this moment, the photons were measured jointly, entangled as a result. The two
atoms eventually became entangled with one another as a result of this
procedure because each photon was already entangled with the rubidium atom from
which it was released.
The two atoms could function as "quantum memory"
nodes in a larger communication network once they are entangled. The fact that
fibre optic cables were used to accomplish this is significant because it opens
the door to the potential of building such a network utilising already-existing
telecom infrastructures.
Lead author Tim van Leent said in a statement, "The
significance of our experiment is that we actually entangle two stationary
particles, that is to say, atoms that function as quantum memories."
"This opens up many more application possibilities, but it is much more
difficult than entangling photons."
More specifically, "the experiment is an important step on the path to the quantum internet based on existing fibre optic infrastructure," according to co-author Harald Weinfurter.