Multidimensional spectroscopy has been instrumental for probing dynamical processes in a wide variety of material systems ranging from atoms, molecules to biological complexes. These techniques traditionally rely on sequences of coherent laser pulses with electric fields with well-defined envelopes and phases. Quantum light sources have been developed for broad applications such as quantum information processing, secure communication, and lithography. Employing quantum light in multidimensional spectroscopy is opening up many exciting opportunities to enhance the signal-to-noise ratio, improve the combined temporal, spatial, and spectral resolutions, and simplify nonlinear optical signals by selecting desired transition pathways. In second and third order signals, we show how photoelectron signals generated by time-energy entangled photon pairs can monitor ultrafast excited state dynamics of molecules with high joint spectral and temporal resolutions, not limited by the Fourier uncertainty of classical light. Two-entangled-photon absorption scales linearly with the pump intensity, allowing the study of fragile biological samples with low photon fluxes. We present a quantum dynamical study on the charge migration in molecules by coupling to an optical cavity, which can activate and enhance the targeted charge migration modes that are suppressed in the bare molecule.

Novel X-ray pulse sources from free-electron lasers and high-harmonic generation setups enable the monitoring of molecular events on unprecedented temporal, spatial and energetic scales. The attosecond duration of X-ray pulses, their large bandwidth, tunable energy range, and the atomic selectivity of core X-ray excitations offer a uniquely high spatial and temporal selectivity for non- linear spectroscopies. We show how the orbital angular momentum of twisted X-ray light can be leveraged to detect electronic and vibrational coherences and time evolving chirality emerging at conical intersections.

1. Kizmann, M., Yadalam, H. K., Chernyak, V. Y., Mukamel, S.: Quantum interferometry and pathway selectivity in the nonlinear response of photosynthetic excitons. PNAS 120, e2304737120
   (2023). https://doi.org/10.1073/pnas.2304737120
2. “Ultrafast X-ray Probes of Elementary Molecular Events,” Daniel Keefer, Stefano M. Cavaletto, Jérémy R. Rouxel, Marco Garavelli, Haiwang Yong, Shaul Mukamel, Annual Review of Physical Chemistry 2023 74:1, 73-97. https://doi.org/10.1146/annurev-physchem-062322-051532
3. “Manipulating two-photon-absorption of cavity-polaritons by entangled light,” Bing Gu and Shaul Mukamel. Journal of Physical Chemistry Letters, 11, 19, 8177–8182 (2020) https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.0c02282
4. “Cavity control of molecular spectroscopy and photophysics,” Bing Gu, Yonghao Gu, Vladimir Y. Chernyak, and Shaul Mukamel, Accounts of Chemical Research (2023). https://doi.org/10.1021/acs.accounts.3c00280
5. “Distinguishability and “which pathway” information in multidimensional interferometric spectroscopy with a single entangled photon-pair,” Shahaf Asban and Shaul Mukamel. Science Advances, 7: eabj4566 (2021) DOI: 10.1126/sciadv.abj4566