Abstract
Quantum light offers unique opportunities to extend the capabilities of optical spectroscopy beyond the limits imposed by classical light sources. In particular, entangled photon pairs exhibit strong correlations in time and frequency that can be exploited to probe molecular dynamics under extremely low excitation conditions, opening new perspectives for the investigation of photosynthetic systems, biomolecules, and quantum materials. However, despite considerable theoretical interest, quantum spectroscopy has remained largely confined to proof-of-principle demonstrations because of the limited availability of suitable quantum light sources, the lack of realistic theoretical models for complex molecular systems, and the long acquisition times required by existing experiments. The project CoRrElated photonS for advanCed ENtangleD quantum spectrOscopy (CRESCENDO) was established to overcome these challenges by developing a comprehensive platform for quantum spectroscopy based on entangled photon pairs. Through a collaborative effort between POLIMI, UNIBO, and CNR, the project combined experimental quantum photonics, ultrafast spectroscopy, and advanced quantum dynamical simulations to establish both the theoretical and experimental foundations of spectroscopy with correlated photons.
Results achieved
By the conclusion of the project, CRESCENDO successfully achieved its three primary objectives: 1. Quantum light sources and diagnostics The project developed advanced methodologies for the generation and characterization of spectrally entangled photon pairs produced by spontaneous parametric down-conversion. POLIMI implemented Fourier-transform techniques based on TWINS birefringent interferometers to reconstruct the joint spectral intensity of photon pairs and introduced hyperspectral momentum-space imaging capable of simultaneously resolving their spatial and spectral properties. These developments provided efficient diagnostic tools for optimizing quantum light sources and clarified the influence of phase-matching geometry, angular collection, and optical alignment on the preservation of spectral correlations and entanglement. 2. Computational methods for quantum spectroscopy UNIBO and CNR developed a new generation of computational approaches for simulating nonlinear spectroscopic signals in realistic molecular systems. The project established an advanced protocol for pump-probe spectroscopy based on nonadiabatic quantum dynamics and successfully applied it to biologically relevant systems such as NADH, revealing the role of transient charge-transfer states in ultrafast excitation-energy transfer. In parallel, the consortium reformulated the theory of entangled two-photon absorption in the time domain, making it compatible with wavepacket propagation methods and therefore applicable to realistic molecular systems for the first time. Applications to uracil, perylene diimide oligomers, and retinal models demonstrated the ability of these methods to predict quantum spectroscopic signatures of complex vibronic dynamics. 3. Experimental quantum spectroscopy The project achieved its most significant milestone with the realization of time- and frequency-resolved fluorescence spectroscopy based on entangled photon pairs generated by a continuous-wave laser. Unlike conventional ultrafast spectroscopy, the method exploits the intrinsic temporal correlations of photon pairs to perform fluorescence lifetime measurements without high-intensity pulsed excitation. The system accurately measured fluorescence lifetimes of standard fluorophores, produced spectro-temporal maps capable of separating overlapping fluorescent species, and was successfully applied to photosynthetic light-harvesting complexes and bacterial membranes, resolving different functional states under physiologically relevant low-light conditions. Importantly, acquisition times were reduced from tens of minutes reported in previous quantum spectroscopy demonstrations to less than one minute, bringing quantum-light spectroscopy significantly closer to practical applications. Long-term Impact and Sustainability CRESCENDO established one of the first integrated experimental and theoretical platforms for realistic quantum spectroscopy. While demonstrating that entangled photons can perform spectro-temporal measurements under extremely low flux, the project also developed the computational framework required to interpret these experiments in complex molecular systems. The results, published in leading international journals including Nature Communications, demonstrate that quantum light can become a practical tool for studying light-sensitive biological and molecular systems under conditions inaccessible to conventional ultrafast spectroscopy. Beyond its direct scientific achievements, CRESCENDO has created a strong interdisciplinary collaboration between quantum optics, ultrafast spectroscopy, and theoretical chemistry that provides a solid foundation for future quantum-enhanced spectroscopic methodologies. The experimental platforms, computational tools, and expertise developed during the project position the consortium to pursue next-generation quantum spectroscopy experiments and contribute to the emerging field of quantum technologies for molecular science.Project details
Unibo Team Leader: Marco Garavelli
Unibo involved Department/s:
Dipartimento di Chimica Industriale "Toso Montanari"
Coordinator:
Politecnico di MILANO(Italy)
Total Unibo Contribution: Euro (EUR) 64.072,00
Project Duration in months: 24
Start Date:
28/09/2023
End Date:
28/02/2026
