快猫短视频

FOR the first time, photons have forged an intimate relationship without even
meeting. This bizarre consequence of quantum mechanics鈥攅ntanglement
swapping鈥攈as been demonstrated by Austrian physicists working on quantum
teleportation
(see 鈥淏eyond Reality鈥�, 快猫短视频, 14 March, p 26).

When photons or atoms become 鈥渆ntangled鈥�, their fates are linked. Measure the
properties of one and you know about the other, no matter how distant it might
be. But until now, scientists could entangle objects only by creating them in
pairs or by making them collide or interact at close range. In a forthcoming
issue of Physical Review Letters, Anton Zeilinger and his colleagues at
the University of Innsbruck describe how they managed to entangle a pair of
photons without the two coming into contact.

The scheme uses two pairs of entangled photons created by shooting a laser
beam into a crystal. Photon 1 is entangled with photon 2, but is blissfully
ignorant of the doings of photons 3 and 4. Zeilinger took photons 2 and 3 and
mixed up their paths so that it was impossible to tell them apart. By measuring
2 and 3 together, he forced photons 1 and 4 to entangle, even though they were
shooting off in opposite directions.

Zeilinger says it should be possible to entangle particle pairs no matter how
far apart they are. 鈥淚t鈥檚 mind-boggling that you can entangle two objects
without having them interact,鈥� he says.