In the weird world of quantum
physics, two linked particles can share a single fate, even
when they're miles apart.
Now, two physicists have mathematically described how this
spooky effect, called entanglement, could also bind particles
If their proposal can be tested, it could help process
information in quantum computers and
test physicists' basic understanding of the universe.
"You can send your quantum state into the future without traversing the middle time,"
said quantum physicist S. Jay Olson of Australia's University of
Queensland, lead author of the new study.
In ordinary entanglement, two particles (usually electrons or
photons) are so intimately bound that they share one quantum state
-- spin, momentum and a host of other variables -- between them.
One particle always "knows" what the other is doing. Make a
measurement on one member of an entangled pair, and the other
Physicists have figured out how to use entanglement to encrypt
messages in uncrackable codes and build ultrafast computers.
Entanglement can also help transmit encyclopedias' worth of
information from one place to another using only a few atoms, a
protocol called quantum teleportation.
In a new paper posted on the physics preprint website arXiv.org,
Olson and Queensland colleague Timothy Ralph perform the math to
show how these same tricks can send quantum messages not only from
place to place, but from the past to the future.
The equations involved defy simple mathematical explanation, but
are intuitive: If it's impossible to describe one particle without
including the other, this logically extends to time as well as space.
"If you use our timelike entanglement, you find that [a quantum
message] moves in time, while skipping over the intermediate
points," Olson said. "There really is no difference mathematically.
Whatever you can do with ordinary entanglement, you should be able
to do with timelike entanglement."
Olson explained them with a Star
Trek analogy. In one episode, "beam me up" teleportation expert
Scotty is stranded on a distant planet with limited air supply. To
survive, Scotty freezes himself in the transporter, awaiting
rescue. When the Enterprise arrives decades later, Scotty steps out
of the machine without having aged a day.
"It's not time travel as you would ordinarily think of it, where
it's like, poof! You're in the future," Olson said. "But you get to
skip the intervening time."
According to quantum physicist Ivette Fuentes of the University
of Nottingham, who saw Olson and Ralph present the work at a
conference, it's "one of the most interesting results" published in
the last year.
"It stimulated our imaginations," said Fuentes. "We know
entanglement is a resource and we can do very interesting things
with it, like quantum teleportation and quantum cryptography. We
might be able to exploit this new entanglement to do interesting
One such interesting thing could involve storing information in
black holes, said physicist Jorma
Louko, also of the University of Nottingham.
"They show that you can use the vacuum, that no-particle state,
to store a lot of information in just a couple of atoms, and
recover that info from other atoms later on," Louko said. "The
details of that have not been worked out, but I can foresee that
the ideas that these authors use could be adapted to the black hole
Entanglement in time could also be used to investigate
as-yet-untested fundamentals of particle physics. In the 1970s,
physicist Bill Unruh predicted that, if a spaceship accelerates through the empty
space of a vacuum, particles should appear to pop out of the void.
Particles carry energy, so they would be, in effect, a warm bath.
Wave a thermometer outside, and it would record a positive
Called the Unruh effect, this is a solid prediction of quantum
field theory. It's never been observed, however, as a spaceship
would have to accelerate at as-yet-unrealistic speeds to generate
an effect large enough to be testable. But because timelike
entanglement also involves particles emerging from vacuums, it
could be used to conduct more convenient searches, relying on time
rather than space.
Finding the Unruh effect would provide support for quantum field
theory. But it might be even more exciting not to see the effect,
"It would be more of a shocking result," Olson said. "If you
didn't see it, something would be very wrong with our