When forming an image of an object, such as a photograph taken by a cell phone, light that has interacted with the object and either passed through or bounced off it is captured by the detector in the phone.
Schematic diagram of the implemented quantum ghost imaging setup. (a) Entangled bi-photons are produced via spontaneous parametric downconversion (SPDC) at the NLC. The entangled photons are spatially separated, and each is imaged onto a SLM. Required holograms are displayed on each SLM. Coincidence measurements are done between both paths, and the coincidences are used to reconstruct an image of the object. For each object, two measurements are taken, as numerically simulated in (b). These two images are then combined such that the argument reveals the total phase. (c) shows the digital phase-only objects used in the experiment, while the simulated image reconstructions are shown in (d) showing how the digital objects are expected to perform. Credit: Optica (2023). DOI: 10.1364/OPTICA.472980 Some 25 years ago, scientists devised another, less direct way to do this. In the conventional form, information gathered from two detectors are instead used, by combining information from one capturing the light that has interacted with the object and one that has not interacted with the object at all. It is the light that has never interacted with the object that is used to obtain the image, though, resulting the technique taking on the name "ghost imaging." When entangled light is used, the quantum properties can be exploited to do this at very low light levels which can be a large advantage when looking at light-sensitive samples in biological imaging where too much light can damage or change the sample and thus destroying what one wishes to look at—this being quite a conundrum in the field. Using either direct or indirect imaging, the images being formed is a result of how much light is let through and thus a result of the transparency of the object. There is, however, another type of interaction that objects can have with light which can reveal some important information and show rich features. This is the speeding up or slowing down of the light that passes…