Monitoring Wavepacket Dynamics at Conical Intersections by Entangled Two-Photon Absorption

Abstract

In this theoretical study, we show how ultrafast electron–nuclear dynamics in a molecule can be monitored by two-photon absorption of time–energy entangled photon pairs generated by spontaneous parametric down-conversion with a narrow-band pump. The dynamics is tracked by a controllable signal-idler delay. Time correlation of the entangled photons enables an ultrafast measurement even with a monochromatic pump. The frequency anticorrelation of the photon pair allows the projection of the intermediate excited-state wavepacket onto an energy-selected vibrational level on a higher-lying electronic state with high energy resolution. Such joint high temporal and energy resolution is not possible with classical light. We demonstrate our scheme for a conical intersection model with four electronic states and two vibrational modes. The ultrafast nuclear wavepacket dynamics around the conical intersection is imprinted onto the time- and frequency-resolved entangled two-photon absorption signals. Electronic population dynamics is obtained by the frequency-integrated signal.

Nonadiabatic Conical Intersection Dynamics in the Local Diabatic Representation with Strang Splitting and Fourier Basis

“…n mn BO (9) as the nuclear state |n⟩ is an eigenstate of all position operators. eq 9 is the typical approximation invoked in a DVR method.…”

“…Conical intersections (CIs), a cone-like structure formed in molecular configuration space where adiabatic potential energy surfaces (APES) of electronic states intersect, play a critical role in understanding and explaining virtually all photochemical and photophysical phenomena such as vision, photostability of DNA and RNA nucleobases, Jahn–Teller distortion, photoisomerization, light-driven dynamics, singlet fission, ultrafast spectroscopy, and polaritonic chemistry. − In the vicinity of CIs, electronic and nuclear motion become strongly correlated as their energy scales becomes comparable, and hence, the Born–Oppenheimer approximation that separates the electronic and nuclear motion breaks down. One intriguing aspect of CIs lies in their capacity to facilitate ultrafast transitions between electronic states, often occurring on femtosecond time scales.…”

Entangled Photons Enabled Ultrafast Stimulated Raman Spectroscopy for Molecular Dynamics

“…The multi-photon interactions with complex molecules were studied recently in a context of quantum-light spectroscopy. Several experiments indicated the extraordinary transitions with entangled two-photon absorption (ETPA)-the inhomogeneous line broadening can be circumvented for an efficient population of highly-excited states of molecules 1,18,[22][23][24][25][26][27][28][29][30][31][32][33][34] . The multi-photon interaction has been studied much in atoms, it is however an open issue in molecules so far.…”

Raman Spectroscopy of Conical Intersections Using Entangled Photons

“…This can be partially overcome by using multidimensional probe schemes, which are based on two independent time variables. 22,27 Quantum states of light provide a different avenue for increasing the time−bandwidth limit. Entanglement and nonclassical statistics of photons create a new parameter space and provide new control knobs.…”

“…Entangled photons allow for simultaneous resolution in the time and frequency domains, where classical light is bound to the Fourier limit. Such a quantum advantage has been explored in recent theoretical studies of photochemical reactions of molecules, which included the non-adiabatic dynamics monitored from two-photon absorption. Femtosecond coherent Raman spectra using entangled photons were reported recently as a proof-of-principle demonstration of enhanced resolutions for monitoring fast molecular dynamics. , However, for molecular systems with a CI, there has not yet been a conclusive study, and it is still an open issue.…”