29 August 2014

Quantum camera takes pic using only entangled photons

by Will Parker

Using a new quantum imaging technique, a picture has been captured without the camera detecting the light that was used to illuminate the subject. Instead, the detector relies on entangled photons that have never touched the subject (in this case, a silhouette of a cat).

Normally, an image of an object is obtained by sensing the light that is either reflected or transmitted through that object. However, in the new technique, detailed in Nature, the scientists used entangled pairs of photons.

In the experiment, the laser illuminates two separate crystals, creating one pair of twin photons (consisting of one infrared photon and a "sister" red photon) in either crystal. The object is placed in between the two crystals.

The arrangement is such that if a photon pair is created in the first crystal, only the infrared photon passes through the imaged object. Its path then goes through the second crystal where it fully combines with any infrared photons that would be created there.

"With this crucial step, there is now, in principle, no possibility to find out which crystal actually created the photon pair," explained researcher Gabriela Barreto Lemos (pictured). "Moreover, there is now no information in the infrared photon about the object. However, due to the quantum correlations of the entangled pairs the information about the object is now contained in the red photons - although they never touched the object. Bringing together both paths of the red photons [from the first and the second crystal] creates bright and dark patterns, which form the exact image of the object."

All of the infrared photons (the only light that illuminated the object) are discarded; and the picture is obtained by detecting only the red photons that never interacted with the object. Additionally, the camera used in the experiment is blind to the infrared photons that have interacted with the object.

Lemos, from the University of Vienna, is confident that her team's new quantum imaging technique could find application where low light imaging is crucial, in fields such as biological or medical imaging.

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Source: University of Vienna