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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - QSB (Quantum Sensing for Biology)

Teaser

Summary

The overall issue being addressed in this research is the development of a practical quantum sensing technology which allows one to probe fragile tissues and biological materials in a completely non-invasive way. In fact, the idea is to design more sophisticated quantum sources and quantum measurements which are extremely more accurate than the current classical setups, so that the quantum setup can be implemented with very few photons. In the long run, this research is important for the society because it may lead to the development of completely non-invasive quantum devices for biological analyses and bio-medical applications, e.g., in hospitals, where the radiation dose absorbed by patients is still a non-trivial problem to solve. The realistic and short-term objective of this research is to make the first steps in this direction by developing a biologically-driven theory of quantum channel discrimination and estimation. In particular, this is applied to the development of a non-invasive prototype of quantum photometer, which is able to read the concentration of bacteria in samples by employing just a few photons.

Work performed

The work has been directed to two main directions: One purely theoretical aimed at developing new tools for investigation; the other aimed at developing practical applications for quantum sensing. From the point of view of the tools, I have contributed to review and further develop the theory of channel simulation which allows one to simplify the most general protocols of quantum metrology, quantum channel discrimination, and quantum communication. This technique is very powerful because it allows one to derive simple bounds for the ultimate performance achievable in all these tasks. This work has been done in collaborations with other authors and published in a couple of papers: â€œChannel Simulation in Quantum Metrologyâ€ published as [Quantum Meas. Quantum Metrol. 5, 1-12 (2018)], and â€œTheory of channel simulation and bounds for private communicationâ€ published as [Quantum Sci. Technol. 3, 035009 (2018)]. Then, I have investigated the discrimination of discord (i.e., quantum correlations beyond entanglement) in separable Gaussian states, comparing different types of quantum measurements, in particular, local and nonlocal. This work clarifies the optimal detection strategies for detecting quantum correlations in Gaussian states. It has been published as a proceeding to the conference Quantum Communications and Quantum Imaging XVI, SPIE Optical Engineering + Applications (19 - 23 August 2018, San Diego CA, United States). A preprint is available on the arXiv (arXiv:1807.01992).

From the point of view of the applications, I have investigated the quantum discrimination of bosonic loss using symmetric and asymmetric hypothesis testing. In both approaches, I found that an entangled resource is able to outperform any classical strategy based on coherent-state transmitters in the regime of low photon numbers. In the symmetric case, I then considered the low energy detection of bacterial growth in culture media. Assuming an exponential growth law for the bacterial concentration and the Beer-Lambert law for the optical transmissivity of the sample, I found that the use of entanglement allows one to achieve a much faster detection of growth with respect to the use of coherent states. This performance was also studied by assuming an exponential photo-degradable model, where the concentration is reduced by increasing the number of photons irradiated over the sample. This work called â€œSymmetric and asymmetric discrimination of bosonic loss: Toy applications to biological samples and photo-degradable materialsâ€ has been published as [Phys. Rev. A 98, 053836 (2018)].

Still in terms of more practical applications, my work â€œThermal quantum metrology in memoryless and correlated environmentsâ€ published as [Quantum Sci. Technol. 4, 015008 (2019)] has addressed the theoretical development of an optimal yet practical model of quantum spectro-photometer. In bosonic quantum metrology, the estimate of a loss parameter is typically performed by means of pure states, such as coherent, squeezed or entangled states, while mixed thermal probes are discarded for their inferior performance. In this work I instead showed that thermal sources with suitable correlations can be engineered in such a way to approach, or even surpass, the error scaling of coherent states in the presence of general Gaussian decoherence. These findings pave the way for practical and optimal quantum metrology with thermal sources in optical instruments, most importantly photometers, or at different wavelengths (e.g., far infrared, microwave or X-ray) where the generation of quantum features, such as coherence, squeezing or entanglement, may be extremely challenging

Final results

The project will extend the current theory of quantum channel discrimination, clarifying the performance achievable by the different types of quantum sources and quantum detectors. This investigation is driven by biological applications where it is already generating results. In particular, I have already shown the non-invasive feature of quantum setups in detecting the growth of very fragile bacteria, which may be rapidly photo-degraded by light. For the end of the project, the expected results will be the development of fully non-invasive quantum devices for biomedical applications, in particular of a commercially viable prototype of quantum spectro-photometer. In the long run I also foresee practical applications at different wavelengths (e.g., far infrared, microwave or X-ray) where the generation of quantum features, such as coherence, squeezing or entanglement, may be challenging. Potential impact of the project will be for biological and medical instrumentation, which may be developed into more powerful quantum versions.