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THE dream of teleporting atoms and molecules—and maybe even larger
objects—has become a real possibility for the first time. The advance is
thanks to physicists who have suggested a method that in theory could be used to
“entangle” absolutely any kind of particle.

Quantum entanglement is the bizarre property that allows two particles to
behave as one, no matter how far apart they are. If you measure the state of one
particle, you instantly determine the state of the other. This could one day
allow us to teleport objects by transferring their properties instantly from one
place to another. Until now, physicists have only been able to entangle photons,
electrons and atoms, using different methods in each case. For instance, atoms
are entangled by forcing them to interact inside an optical trap, while photons
are made to interact with a crystal.

“These schemes are very specific,” says Sougato Bose of the University of
Oxford. But Bose and Dipankar Home, of the Bose Institute in Calcutta, have now
demonstrated a single mechanism that could be used to entangle any particles,
even atoms or large molecules.

To see how it works, consider the angular momentum or “spin” of an electron.
To entangle the spins of two electrons, you first need to make sure they’re
identical in all respects but their spin. Then you shoot the electrons
simultaneously into a beam splitter. This device “splits” each electron into a
quantum state called a superposition, which gives it an equal probability of
travelling down either of two paths. Only when you try to detect the electron do
you know which path it took. If you split two electrons simultaneously, both
paths could have one electron each (which will happen half of the time) or
either path could have both.

Bose and Home show mathematically that whenever one electron is detected in
each path, they will be entangled. While a similar effect has been demonstrated
before for photons, the photons used were already entangled in another way, even
before they reached the beam splitter. “One of the advances we have made is that
these two particles could be from completely independent sources,” says
Bose.

The technique should work for any objects—atoms, molecules and who
knows what else—as long as you can split the beam into a quantum
superposition. Anton Zeilinger, a quantum physicist at the University of Vienna
in Austria, has already shown that this quantum state is possible with
buckyballs—football-shaped molecules of C₆₀. Although entangling
such large objects is beyond our technical abilities at the moment, this is the
first technique that might one day make it possible.

Any scheme that expands the range of particles that can be entangled is
important, says Zeilinger. Entangling massive particles would mean they could
then be used for quantum cryptography, computing and even teleportation. “It
would be fascinating,” he says. “The possibility that you can teleport not just
quantum states of photons, but also of more massive particles, that in itself is
an interesting goal.”