Experimental realization of sub-shot-noise quantum imaging

The properties of quantum states have led to the development of new technologies, ranging from quantum information to quantum metrology(1-12). A recent field of research to emerge is quantum imaging, which aims to overcome the limits of classical imaging by making use of the spatial properties of quantum states of light(13-18). In particular, quantum correlations between twin beams represent a fundamental resource for these studies(19-32). One of the most interesting proposed schemes takes advantage of the spatial quantum correlations between parametric down-conversion light beams to realize sub-shot-noise imaging of weak absorbing objects(14), leading ideally to noise-free imaging. Here, we present the first experimental realization of this scheme, showing its potential to achieve a larger signal-to-noise ratio than classical imaging methods. This work represents the starting point for this quantum technology, which we anticipate will have applications when there is a requirement for low-photon-flux illumination (for example for use with biological samples).