Dr Ivano Ruo-Berchera

Quantitative phase and amplitude imaging enhanced by quantum correlation in a non-interferometric scheme

Recovering the relevant amplitude and phase information on a sample in a quantitative way is fundamental in many sensing and imaging applications. At the same time, it is important to keep the photon dose as low as possible to avoid alteration of the sample, especially in biological studies. Quantum imaging is a valuable pathway to extract more information per photon than classical scheme can do. Quantum entanglement and squeezing have demonstrated to significantly improved phase estimation and imaging in interferometric setups beyond the classical limits. However, only recently a genuine quantum advantage has been demonstrated in a non-interferometric phase imaging scheme [1], where the phase is retrieved only by measuring its effect on the intensity of the free-propagating field. This represents a turning point as non-interferometric phase imaging/retrieval methods, (e.g. diffraction imaging, wave-front sensing, ptychography) are vastly used in the classical domain, opening the way to new applications of quantum technologies. More in detail, in [1] we exploit a quantitative phase retrieval method based on the so-called “transport of intensity equation" (TIE), that provides the absolute value of the phase without prior knowledge of the object and operates in wide-field mode, so it does not need time-consuming raster scanning. The TIE works also with partial coherence light proving to be perfectly compatible with multimode quantum light sources used in sub-shot-noise imaging approaches [2,3]. In fact, the quantum enhancement derives from the reduction of the shot-noise in the measured intensity distribution obtained by exploiting spatially quantum correlated beams. Besides a general improvement of the phase image quality at a fixed number of photons irradiated through the object, resulting in better discrimination of small details, we demonstrate experimentally 40% reduction of the uncertainty in the quantitative phase estimation for each point of the image. And on top of that, here we show that both phase and amplitude full-field quantitative imaging can be attained in the same measurement scheme, and both with a significant practical quantum advantage. Thanks to its versatility, wide-field and real-time properties, this amplitude and phase imaging method represents an important step forward in quantum imaging of delicate samples. By state-of-the-art technology, it can find application in optical microscopy and in perspective to X-ray imaging, reducing the photon dose necessary to achieve a fixed signal-to-noise ratio both in phase and amplitude wide- field measurements. [1] Ortolano, G., Paniate, A., Boucher, P. et al. Quantum enhanced non-interferometric quantitative phase imaging. Light Sci Appl 12, 171 (2023). [2] I. Ruo-Berchera, A. Meda, E. Losero, et al. Improving resolution-sensitivity trade off in sub-shot noise quantum imaging. Applied Physics Letters 116, 214001 (2020)