Quantum Camera Now Snaps Objects That Are Not Seen

A normal digital camera can take snaps of objects that are not visible to its lens, US researchers noted. The "ghost imaging" technique help satellites take snapshots through clouds or smoke.

Recently, Tanya Shih of the University of Maryland, Baltimore, and colleagues at the US Army Research laboratory, also in Maryland, have been able to take first ghost images of an opaque object - a toy soldier.

Ghost imaging works a bit like taking a flash-lit photo of an object using a normal camera. Although the images are formed from photons that come out of the flash, and passes into the lens.

In Shih's experiments, a toy soldier was placed 45 centimeters away from a light source, which was split into two beams. One was pointed at the toy and the other at a digital camera. A photon detector was then placed close to the soldier which only takes record when the photon bounced off.

Photons from the light source constantly travel down both paths made by a splitter, either towards the soldier and the photon detector, or towards the camera.

When this takes place, there is a direct relationship between where one of the photons hit the soldier, and where the other one hits the camera's sensor, says Shih, due to a quantum effect called "two-photon interface."

Therefore, when the camera records only pixels from photons that hit the detector simultaneously, a "ghost image" of the objects is formed. The soldier's image appeared after about 1000 coincidental photons were recorded.