**Quantum Optics INRIM**

**Quantum Imaging and Sensing**

**Quantum Imaging and Sensing**

Quantum imaging and sensing aim at exploiting entanglement and quantum correlation to step over classical limitation in sensitivity and resolution. Conventional optical measurements are affected by fundamental limits that comes from the quantum fluctuation of the optical field. Shot noise turns out from the discretization of the energy in photons and from the randomness of the photon emission from conventional (classical) sources. However, quantum mechanics does not prevent to build sources which are more stable, e.g. producing a regular stream of equidistant photons or entangled beams where photons are perfectly correlated in any degree of freedom. Engineering these states, manipulate and efficiently detect them, allows to reduce uncertainty in measurements and to go beyond classical paradigms such as the Rayleigh diffraction limit and shot-noise limit.

In the group, we have realized several “first” experimental demonstration of quantum imaging and sensing protocols: wide field sub shot noise imaging and microscopy without resorting to post-selection; quantum enhanced target detection in a preponderant background, known as ‘quantum illumination’; super-resolution fluorescence microscopy with photon antibunching from NV centers; absolute calibration of CCD cameras by quantum correlations; quantum reading and lossy channel discrimination. We also enjoy exploring possible real application of quantum inspired techniques, for example ‘ghost imaging’.

## Recent highlights

### Twin beam quantum-enhanced correlated interferometry for testing fundamental physics

S. T. Pradyumna et al., Communications Physics 3, Article number: 104 (2020)

Quantum metrology deals with improving the resolution of instruments that are otherwise limited by shot noise and it is therefore a promising avenue for enabling scientific breakthroughs. The advantage can be even more striking when quantum enhancement is combined with correlation techniques among several devices. Here, we present and realize a correlation interferometry scheme exploiting bipartite quantum correlated states injected in two independent interferometers. The scheme outperforms classical analogues in detecting a faint signal that may be correlated/uncorrelated between the two devices. We also compare its sensitivity with that obtained for a pair of two independent squeezed modes, each addressed to one interferometer, for detecting a correlated stochastic signal in the MHz frequency band. Being the simpler solution, it may eventually find application to fundamental physics tests, e.g., searching for the effects predicted by some Planck scale theories.

### Quantum differential ghost microscopy

Quantum correlations become formidable tools for beating classical capacities of measurement. Preserving these advantages in practical systems, where experimental imperfections are unavoidable, is a challenge of the utmost importance. Here we propose and realize a quantum ghost imaging protocol stemming from the differential ghost imaging, a scheme elaborated so far in the limit of bright thermal light, particularly suitable in the relevant case of faint or sparse objects. The extension toward the quantum regime represents an important step as quantum correlations allow low-brightness imaging, desirable for reducing the absorption dose. Furthermore, we optimize the protocol in terms of signal-to-noise ratio, to compensate for the detrimental effects of detection noise and losses. We perform the experiment using spontaneous parametric down conversion light in a microscope configuration. The image is reconstructed exploiting nonclassical intensity correlation in the low photon flux regime, rather than photon pairs detection coincidences. On the one side, we validate the theoretical model and on the other we show the applicability of this technique by imaging biological samples.

### Experimental quantum reading with photon counting

G. Ortolano et al., SCIENCE ADVANCES 20 Vol 7, Issue 4 (2020)

The final goal of quantum hypothesis testing is to achieve quantum advantage over all possible classical strategies. In the protocol of quantum reading, this is achieved for information retrieval from an optical memory, whose generic cell stores a bit of information in two possible lossy channels. We show, theoretically and experimentally, that quantum advantage is obtained by practical photon-counting measurements combined with a simple maximum-likelihood decision. In particular, we show that this receiver combined with an entangled two-mode squeezed vacuum source is able to outperform any strategy based on statistical mixtures of coherent states for the same mean number of input photons. Our experimental findings demonstrate that quantum entanglement and simple optics are able to enhance the readout of digital data, paving the way to real applications of quantum reading and with potential applications for any other model that is based on the binary discrimination of bosonic loss.

## Most relevant pubblications

G. Brida, M. Genovese, I. Ruo-Berchera, Experimental realization of sub-shot-noise quantum imaging, Nature Photonics 4, 227- 230 (2010).

Lopaeva, E. D., Ruo Berchera, I., Degiovanni, I. P., Olivares, S., Brida, G., and Genovese, M., Experimental Realization of Quantum Illumination, Phys.Rev. Lett.

**110**, 153603 (2013).

Ruo Berchera I., Degiovanni, I. P., Olivares, S., Genovese, M., Quantum Light in Coupled Interferometers for Quantum Gravity Tests, Phys. Rev. Lett.

**110**, 21360 (2013). DOI: 10.1103/PhysRevLett.110.213601.

D. Gatto Monticone, K. Katamadze, P. Traina, E. Moreva, J. Forneris, I. Ruo-Berchera, P. Olivero, I.P. Degiovanni, G. Brida,M. Genovese, "Beating the Abbe Diffraction Limit in Confocal Microscopy via Nonclassical Photon Statistics", Phys. Rev. Lett. 113, 143602 (2014).

Meda A., Caprile A., Avella A., Ruo Berchera I., Degiovanni I.P., Magni A., Genovese M. Magneto-optical imaging technique for hostile environments: The ghost imaging approach Applied Physics Letters 106 (26), 262405 (2015).

Avella, A., Ruo-Berchera, I., Degiovanni, I. P., Brida, G., Genovese, M., Absolute calibration of an EMCCD camera by quantum correlation, linking photon counting to the analog regime, Optics Lett. 41(8), 1841-1844 (2016);

Samantaray, N., Ruo-Berchera, I., Meda, A., Genovese, M., Realization of the first sub-shot-noise wide field microscope, Light: Science & Applications 6, e17005 (2017);

Meda, A., Losero, E., Samantaray, N., Scafitimuto F., Pradyumna S., Avella A., Ruo-Berchera, I., Genovese, M. Photon-number correlation for quantum enhanced imaging and sensing, 19(9), 094002(2017);

E Losero, I Ruo-Berchera, A Meda, A Avella, M Genovese, Unbiased estimation of an optical loss at the ultimate quantum limit with twin-beams, Scientific Reports

**8**, 7431 (2018).

Ruo-Berchera, IP Degiovanni, Quantum imaging with sub-Poissonian light: challenges and perspectives in optical metrology, Metrologia

**56**, 024001(2019).

E Losero, I Ruo-Berchera, A Meda, A Avella, O Sambataro, M Genovese, Quantum differential ghost microscopy, Physical Review A 100 (6), 063818 (2019)

I Ruo-Berchera, A Meda, E Losero, A Avella, N Samantaray, M Genovese, Improving resolution-sensitivity trade off in sub-shot noise quantum imaging, Applied Physics Letters 116 (21), 214001(2020).

Pradyumna, S.T., Losero, E., Ruo-Berchera, I. et al. Twin beam quantum-enhanced correlated interferometry for testing fundamental physics. Commun Phys 3, 104 (2020).

G Ortolano, E Losero, S Pirandola, M Genovese, I. Ruo-Berchera, "Experimental quantum reading with photon counting" Sci. Adv. 2021; 7 : eabc7796 (2021),