Interaction-free ghost-imaging of structured objects.

Quantum - or classically correlated - light can be employed in various ways to improve resolution and measurement sensitivity. In an "interaction-free" measurement, a single photon can be used to reveal the presence of an object placed within one arm of an interferometer without being absorbed by it. With a technique known as "ghost-imaging", entangled photon pairs are used for detecting an opaque object with significantly improved signal-to-noise ratio while preventing over-illumination. Here, we integrate these two methods to obtain a new imaging technique which we term "interaction-free ghost-imaging" (IFGI). With this new technique, we reduce photon illumination on the object by up to 26.5% while still maintaining at least the same image quality of conventional ghost-imaging. Alternatively, IFGI can improve image signal-to-noise ratio by 18% when given the same number of interacting photons as in standard ghost-imaging. IFGI is also sensitive to phase and polarisation changes of the photons introduced by a structured object. These advantages make IFGI superior for probing light-sensitive materials and biological tissues.