Experimental realization of sub-shot-noise quantum imaging

Properties of quantum states have disclosed new technologies, ranging from quantum information to quantum metrology. Among them a recent research field is quantum imaging, addressed to overcome limits of classical imaging by exploiting spatial properties of quantum states of light . In particular quantum correlations between twin beams represent a fundamental resource for these studies. One of the most interesting proposed scheme exploits spatial quantum correlations between parametric down conversion light beams for realizing sub-shot-noise imaging of the weak absorbing objects, leading ideally to a noise-free imaging. Here we present the first experimental realisation of this scheme, showing its capability to reach a larger signal to noise ratio (SNR) with respect to classical imaging methods. This work represents the starting point of this quantum technology that can have relevant applications, especially whenever there is a need of a low photon flux illumination (e.g. as with certain biological samples)

Practical quantum cryptography based on two-photon interferometry.

We propose an experimental realization of cryptographic-key-sharing scheme exploiting quantum correlations between pair photons. Our experimental setup consists of an external source of correlated photon pairs which propagate to two widely separated unbalanced Mach-Zehnder interferometers. The probability of detection of photon pairs in any two outputs of the interferometers can be fully modulated by phase plates in either interferometer. © 1992 The American Physical Society