Ghost imaging is a curious phenomenon that has had numerous physicists scratching their heads in recent years.
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.
The second beam is aimed at a CCD array without ever having hit the object.
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.
When this was first demonstrated in 1995, everybody was amazed by the strange power of quantum entanglement.
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.
While interesting, that doesn’t actually rule out the possibility that the two beams may be correlated in some entangled-like quantum way, however.
So the question of whether quantum entanglement is responsible or not has remained open. Until now.
Yaron Silberberg and pals from the Weizmann Institute of Science in Israel, have carried out an ingenious experiment that settles the matter.
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”.
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.
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.
Ref: arxiv.org/abs/0812.2633: Ghost Imaging with a Single Detector