Boo! No need to be scared. Quantum ghost imaging has nothing to do with detecting actual ghosts. It instead can be used to image hyper light-sensitive materials such as your eyes. So, if you ever need an eye exam or eye surgery this technology in the future can be used to better understand your eye.
What is it?
Quantum ghost imaging relies on the quantum principle of entanglement which we covered in last week's newsletter on quantum teleportation. For a quick review, entanglement refers to the phenomenon where two particles are linked across any distance. This principle is what makes quantum ghost imaging special since it allows for the separation of the object's illumination and image acquired. To explain we will bring back the fan (Sabrina's) favorites Alice and Bob.
Alice knows her friend has an embarassing picture of her on their phone, but won't send it to Alice. Alice recruits her friend Bob to get her the picture. Alice knows she can't send herself the photo from the phone or else her friend will find out. Instead, Bob asks the friend to see the photo. Alice and Bob are entangled meaning when Bob sees the image he can just send Alice a description of the image for her to recreate it. This is because things that Bob interacts with influence Alice as well due to the properties of their entanglement. Now Alice has successfully recovered the embarrassing photo without her friend knowing.
Getting into the Science
This is the idea of ghost imaging- it is as if a ghost took the picture. But, instead of Alice and Bob, we are working with photons. Two entangled photons hit the beam splitter sending one towards the object to be imaged (idler) and one to a camera through the delay line (imager). Once the idler interacts with the item to get a spacial measurement, it is picked up by the single photon detector. This detector then sends the information to the camera. When the signal and imager reach the camera at the exact same time, a pixel of the recreated image is displayed. Pixel-by-pixel the image is reconstructed using the spacial correlation between the idler and imager photons. This means that a camera is never actually pointed at the object with the need for bright image illumination. Instead, based on how the idler hits the object, it can be reconstructed spatially using the connection to the imager photon.
Why Should I Care?
Many objects are hyper light-sensitive, like your eyes or specific drugs that become toxic with light exposure. This imaging technique uses the lowest photon (light) dosage possible to create an image at less than a photon per image pixel. With further development, this technology not only has wide medical usage, but military and security applications as well.
Further Reading and Resources
https://opg.optica.org/ao/viewmedia.cfm?uri=ao-62-23-6275&seq=0
https://www.sciencedaily.com/releases/2023/08/230808151247.htm
https://www.youtube.com/watch?v=HrlcXEri4b0 (Very helpful video with image shown above!)
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