In the study “Quantum Conformance Test”, published on 22nd December 2021 in the prestigious journal Science Advances (DOI: 10.1126/sciadv.abm3093), a team of researchers led by Ivano Ruo Berchera and composed by Giuseppe Ortolano, phD student from Politecnico di Torino (first author of the research), and by INRiM Researchers Pauline Boucher, Ivo Pietro Degiovanni, Elena Losero, Marco Genovese (Director of the Quantum Optics research sector of INRiM), has shown that, through optical measurements optimized thanks to quantum correlations, called 'entanglement', it will be possible to reduce errors in the verification of conformity of certain products and production processes.
Conformity tests are often performed with measurements on a random subset of the final products. Important examples are optical transmittance measurements and spectroscopy, useful for the characterization of chemical concentrations and biological samples.
Since each substance absorb light in a different way for different optical frequencies, its concentration can be estimated by means of an optical transmissivity measurement, i.e., measuring the intensity before and after the test object. However, the production process is affected by statistical fluctuations so that the concentrations, and consequently the optical intensity transmitted, will be distributed around a reference value.
Intrinsic fluctuations in conventional light sources typically used for optical measurements, including lasers, reduce the accuracy in the characterization of the products. This limitation is particularly relevant in case of photosensitive samples, for which it is fundamental to use low-intensity light and to keep small the number of products tested over the whole production. Exactly in this scenario, the researchers have shown how, through the experimental realization of the “Quantum Conformance Test”, making use of quantum “entangled” light sources can notably reduce the probability of having classification errors at a fixed irradiated energy on the samples, improving in a substantially the efficiency of the monitoring.
In short, one of two entangled beams of light interacts with the tested object while the other one is used to measure the light fluctuation with high precision. The experiment shows how the quantum conformance test can be realized with present technology available in laboratories, thus in perspective transportable toward practical applications in the near future.