Thursday, June 23, 2011

Quantum magic trick

NewScientist reports on a new experiment:
Despite quantum theory's knack for explaining experimental results, some physicists have found its weirdness too much to swallow. Albert Einstein mocked entanglement, a notion at the heart of quantum theory in which the properties of one particle can immediately affect those of another regardless of the distance between them. He argued that some invisible classical physics, known as "hidden-variable theories", must be creating the illusion of what he called "spooky action at a distance".

A series of painstakingly designed experiments has since shown that Einstein was wrong: entanglement is real and no hidden-variable theories can explain its weird effects. ...

They found that the resulting statistics could only be explained if the combination of properties that was tested was affecting the value of the property being measured. "There is no sense in assuming that what we do not measure about a system has [an independent] reality," Zeilinger concludes.

Steinberg is impressed: "This is a beautiful experiment." If previous experiments testing entanglement shut the door on hidden variables theories, the latest work seals it tight. "It appears that you can't even conceive of a theory where specific observables would have definite values that are independent of the other things you measure," adds Steinberg.
The abstract is in Nature, and the full paper is here.

There are dozens of papers like this, claiming to have finally proved that Einstein was wrong in 1935. I thought that everyone was convinced that Einstein was wrong by 1936, so I am not sure what the big deal is. Von Neumann had already published a quantum mechanics book in 1932 with an argument against hidden variable theory.

Meanwhile, another story tells of an extreme entanglement attempt:
Physicists in China have broken their own record for the number of photons entangled in a "Schrödinger's cat state". They have managed to entangle eight photons in the state, beating the previous record of six, which they set in 2007. The Schrödinger's cat state plays an important role in several quantum-computing and metrology protocols. However, it is very easily destroyed when photons interact with their surroundings, prompting the researchers to describe its creation in eight photons as "state of the art" in quantum control.

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