Quantum teleportation achieved



photo credit: The Star Trek transporter - we're not there yet, but getting close to settling one of physic's great debates.


One of the hurdles to teleportation has been overcome, with the reliable movement of quantum information between two objects separated by a short distance. The achievement is still a very, very long way from the movements familiar from science fiction, but strengthens our confidence in the theory of quantum entanglement, one of the most controversial aspects of modern physics. It may, moreover, assist the much closer goal of quantum computing.

Certain subatomic particles always exist in paired states. For example, two electrons may have opposite spins. This is fine initially, but creates a famous paradox if one particle is interfered with in such a way that its spin is changed. According to entanglement theory the other particle will instantly respond to the changes wrought on its pair so that the two remain opposite. 

However, the distance between the two this means that the information of what has happened to the one particle must be transmitted infinitely fast – faster than the speed of light. Einstein famously mocked the idea as “spooky action at a distance”, and suggested our understanding of quantum mechanics must be in error. However, with quantum theory's subsequent success physicists have grown more comfortable with the idea that entanglement exists, although many argue it cannot be used to transmit information.

In 1964 physicist John Stewart Bell came up with an idea for an experiment to test whether entanglement is real. At the time the test was impractical, but with publication in Science a team from the Delft University of Technology, Netherlands have got close to conducting Bell's test.

The Delft team trapped electrons in very low temperature diamonds, which team leader Ronald Hanson describes as “miniprisons”. This allowed them to measure the spin for each electron very reliably. Alterations to this spin were reflected in the spin of an entangled electron trapped in a similar diamond prison on the next bench.

The small distance between the two diamonds makes it hard to demonstrate that the transfer of information is occurring instantly, rather than at light speed. Consequently, the next step will be to entangle caged electrons and expand their separation across town or around the world. Entanglement between islands more than 100km apart has already been demonstrated, but only statistically, rather than with 100% success. 

Besides finally settling one of 20th Century physics greatest debates, reliable quantum teleportation could make possible the ultimate in secure communication channels, which would also be infinitely fast as well. Although this is starting to sound awfully close to Ursula Le Guin's ansible, most physicists dispute the possibility of such a device.

As usual, the result does not come out of nowhere. Other teams have also been able to teleport quantum information, but only in a minority of cases. Last year Hanson's team announced they had achieved quantum teleportation using diamond entrapment, but without the 100% reliability of the most recent work.

Комментарии (0)Просмотров (383)