![\"ghost-imaging\"](\"http:\/\/arxivblog.com\/wp-content\/uploads\/2008\/12\/ghost-imaging-150x150.jpg\" "\\"ghost-imaging\\"")
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Ghost imaging is a curious phenomenon that has had numerous physicists scratching their heads in recent years.<\/p>\n
It works like this: take two beams of entangled photons and aim the first at an object. The transmitted photons from the object are then collected by a single pixel detector.<\/p>\n
The second beam is aimed at a CCD array without ever having hit the object.<\/p>\n
It turns out it is possible to reconstruct an image of the object–a so-called ghost image–by matching the data from the two detectors, even though the single pixel detector has no spatial resolution.<\/p>\n
When this was first demonstrated in 1995, everybody was amazed by the strange power of quantum entanglement.<\/p>\n
But later, various groups showed that entangled beams weren’t necessary at all and that ordinary light from a pseudothermal source would do the job just as well.<\/p>\n
While interesting, that doesn’t actually rule out the possibility that the two beams may be correlated in some entangled-like quantum way, however.<\/p>\n
So the question of whether quantum entanglement is responsible or not has remained open. Until now.<\/p>\n
Yaron Silberberg and pals from the Weizmann Institute of Science in Israel, have carried out an ingenious experiment that settles the matter.<\/p>\n
They use only one beam, which they use to illuminate the object, and collect the transmitted photons using a single pixel detector. They then calculate theoretically what the second beam should look like and combine the single pixel data with this “virtual beam”.<\/p>\n
And get this: they still see a ghost image. That’s a 2D image from a single pixel detector! And a pretty convincing demonstration that quantum entanglement cannot be responsible.<\/p>\n
The question now is: what kind of classical information processing allows the reconstruction of a 2d image from a single pixel sensor? That’s a real puzzle.<\/p>\n