IMAGE.ENTANGLED
This beautiful sunset was captured in the conventional way that works by collecting light reflected from the image. But scientists have now been able to obtain a picture of a cat by using light that never fell on the cat in a demonstration of one of the principles of quantum physics. REUTERS

Scientists have obtained an image using light that never fell on the object, in what is a demonstration of quantum entanglement or Einstein's spooky action at a distance.

The findings published in Nature can have practical applications never imagined before.

Usually images are formed when light that falls on an object is reflected and captured by the camera. In the present experiment, one wavelength of laser light illuminated the object and a totally different wavelength of light that never set its eye on the object delivered the image to the camera.

The magic is explained by the fact that the two beams or photons (light particles) used are entangled partners. Quantum physics says that entangled particles which share a common history have an entwined future forever.

The first step is entanglement which requires the parent beam to be sent into a special crystal that splits the beam into two constituent, entangled pairs of photons (light beams). In this case, a red and yellow pair of entangled photons was obtained. The yellow photon beam was made to fall on the image – a cat stencil – which was transparent to the red light. The red light never saw the image.

But it is the red light that delivered the image to the camera. The camera was insensitive to yellow light, reports The National Geographic.

The cat was intact.

The explanation for this 'magical' image is the interference between the two photon pairs. Quantum particles, due to a principle called quantum superposition, exist in every theoretically possible state at the same time. But the act of measurement fixes a single state on the particle. With entanglement, when you measure one half of the entangled pair, the other half instantly assumes the exact opposite state so that together the probability of either state remains the same.

The changes in yellow light are instantaneously transferred to its entangled pair, the red light.

The cat image alludes to this mystical tenet of quantum mechanics – the Schrodinger cat experiment where a cat is simultaneously dead and alive, illustrating how at any point the particle (or cat) has many probabilities of existence, but the act of measurement fixes it in one.

Sensitive bio-samples can be imaged without damaging tissues using conventional ways. These can be illumined at one wavelength and imaged using another (harmful) wavelength.

The problem in observing these phenomena in the classical world where our labs and equipments operate is that background disturbances upset the entanglement.

The current record distance measured for spooky action at a distance is 144 kilometres from La Palma to Tenerife in the Canary Islands.

The latest work was led by the Institute for Quantum Optics and Quantum Information in Vienna, Austria.