Conventional imaging devices like cameras and x-ray machines create pictures by detecting photons that interact with the things being imaged. Now researchers have developed a new quantum imaging technique that shines a beam of photons on an object but then, instead of using these photons to form a picture, uses instead a completely different beam that has never come near the object. If this sounds a bit spooky, it is: what connects the two sets of photons and allows this technique to work is the bizarre quantum physics phenomenon known as entanglement.
The advantage of a quantum entanglement camera like this is that you can illuminate an object using photons with a certain wavelength and then use entangled photons with a different wavelength to form the image. The scientists have already begun investigating possible biotechnological applications such as capturing images of sensitive samples that would be destroyed by conventional imaging techniques.
Entanglement is a fundamentally quantum mechanical relationship between two particles—in this case, photons—created in a kind of extreme, nonlinear crystal that can split individual photons into twin photons. The twin photons behave like distinct and separate photons but also share a separated-at-birth synchronicity unique to the submicroscopic quantum world.
Observation of the first twin photon’s polarization instantaneously forces the second photon into a parallel (or, depending on the setup, perpendicular) polarization state. The paradoxical quality of quantum entanglement, recognized in the 2012 Physics Nobel Prize, is still a mind-bending frontier of fundamental physics. But entanglement’s technological applications, from quantum cryptography to quantum computing, are becoming a reality.
The current research, published in this week’s issue of the journal Nature, harnesses a recently discovered quantum interferometer setup that can effectively create a pair of entangled photons that don't exist at the same time. These photons find themselves in an existential cage match in which only one will survive. The observation of one photon, via this new kind of “time entanglement,” necessarily destroys the other. (Readers seeking college credit for wrapping their heads around the present discovery have our support.)
Gabriela Barreto Lemos is a postdoctoral researcher in the lab of prominent quantum researcher Anton Zeilinger at the Vienna Center for Quantum Science and Technology, in Austria. Barreto Lemos, Zeilinger, and four other researchers turned the above quantum interferometer into a kind of remote-viewing quantum camera, one whose pixels are generated by photons that never come into contact with the object being imaged.
In their experiment, green laser light is twice split into entangled infrared twins, one of which is in the short-wave infrared (SWIR), the other of which is in the near infrared (NIR). One of the SWIR photons then illuminates the object being imaged. Both SWIR photons are ultimately discarded, never to be observed.
But their NIR twins are the ones in the existential cage match: If the imaged object blocks its corresponding SWIR counterpart, then the NIR counterpart gets to exist. It ultimately appears as a pixel on the quantum camera’s image. If SWIR passed through the object, its NIR twin doesn’t exist. Its absence is recorded by the camera as a dark spot.
The end-result is that NIR photons create the image, although no NIR photons illuminated the object. And SWIR photons exclusively illuminated the object, although no SWIR photons are ever detected or observed.
One application of the quantum entanglement camera, Barreto Lemos says, is that the light that illuminates an object can be completely separate from the light that forms the image in the camera.
For instance, imaging some kinds of biological samples with mid-infrared light can be both revealing and valuable. But low-light mid-infrared cameras are also expensive and sometimes unreliable. By contrast, low-light near-infrared cameras (“night vision”) are cheap and more robust—and even found in many consumer cameras and camcorders today.
“You could have this [experiment] at visible and mid-infrared wavelengths,” Barreto Lemos says. “The combination of wavelengths is very flexible.”
Margo Anderson is the news manager at IEEE Spectrum. She has a bachelor’s degree in physics and a master’s degree in astrophysics.