Quantum coherent dissipation: A glimpse of the “cat”

Time-resolved spectra of I2 in a krypton crystal by G-MCTDH simulations: nonadiabatic dynamics, dissipation and environment driven decoherence

Time- and frequency-resolved pump-probe spectra of I₂ in a krypton crystal are calculated and analyzed using high-dimensional multi-state quantum dynamics by the Gaussian-based multi-configuration time-dependent Hartree (G-MCTDH) method.

Quantum dynamics and spectroscopy of dihalogens in solid matrices. II. Theoretical aspects and G-MCTDH simulations of time-resolved coherent Raman spectra of Schrödinger cat states of the embedded I2Kr18 cluster

This study presents quantum dynamical simulations, using the Gaussian-based multiconfigurational time-dependent Hartree (G-MCTDH) method, of time-resolved coherent Raman four-wave-mixing spectroscopic experiments for the iodine molecule embedded in a cryogenic crystal krypton matrix [D. Picconi et al., J. Chem. Phys. 150, 064111 (2019)]. These experiments monitor the time-evolving vibrational coherence between two wave packets created in a quantum superposition (i.e., a "Schrödinger cat state") by a pair of pump pulses which induce electronic B Πu30⁺⟵XΣg+1 transitions. A theoretical description of the spectroscopic measurement is developed, which elucidates the connection between the nonlinear signals and the wave packet coherence. The analysis provides an effective means to simulate the spectra for several different optical conditions with a minimum number of quantum dynamical propagations. The G-MCTDH method is used to calculate and interpret the time-resolved coherent Raman spectra of two selected initial superpositions for a I₂Kr₁₈ cluster embedded in a frozen Kr cage. The time- and frequency-dependent signals carry information about the molecular mechanisms of dissipation and decoherence, which involve vibrational energy transfer to the stretching mode of the four "belt" Kr atoms. The details of these processes and the number of active solvent modes depend in a non-trivial way on the specific initial superposition.

Quantum dynamics and spectroscopy of dihalogens in solid matrices. I. Efficient simulation of the photodynamics of the embedded I2Kr18 cluster using the G-MCTDH method

The molecular dynamics following the electronic BΠu30⁺⟵XΣg+1 photoexcitation of the iodine molecule embedded in solid krypton are studied quantum mechanically using the Gaussian variant of the multiconfigurational time-dependent Hartree method (G-MCTDH). The accuracy of the Gaussian wave packet approximation is validated against numerically exact MCTDH simulations for a fully anharmonic seven-dimensional model of the I₂Kr₁₈ cluster in a crystal Kr cage. The linear absorption spectrum, time-evolving vibrational probability densities, and I₂ energy expectation value are accurately reproduced by the numerically efficient G-MCTDH approach. The reduced density matrix of the chromophore is analyzed in the coordinate, Wigner and energy representations, so as to obtain a multifaceted dynamical view of the guest-host interactions. Vibrational coherences extending over the bond distance range 2.7 Å < R_I-I < 4.0 Å are found to survive for several vibrational periods, despite extensive dissipation. The present results prepare the ground for the simulation of time-resolved coherent Raman spectroscopy of the I₂-krypton system addressed in Paper II.

Simulation of Femtosecond Phase-Locked Double-Pump Signals of Individual Light-Harvesting Complexes LH2

Recent phase-locked femtosecond double-pump experiments on individual light-harvesting complexes LH2 of purple bacteria at ambient temperature revealed undamped oscillatory responses on a time scale of at least 400 fs [ Hildner et al. Science 2013 , 340 , 1448 ]. Using an excitonic Hamiltonian for LH2 available in the literature, we simulate these signals numerically by a method that treats excitonic couplings and exciton-phonon couplings in a nonperturbative manner. The simulations provide novel insights into the origin of coherent dynamics in individual LH2 complexes.

Long-Lived Electronic Coherence of Iodine in the Condensed Phase: Sharp Zero-Phonon Lines in the B↔X Absorption and Emission of I2 in Solid Xe

Our study of B←X absorption of molecular iodine (I2) isolated in a low-temperature crystalline xenon has revealed an exceptionally long-lived electronic coherence in condensed phase conditions. The visible absorption spectrum shows prominent vibronic structure in the form of zero-phonon lines (ZPLs) and phonon side bands (PSBs). The resolved spectrum implies weak interaction of the chromophore to the lattice degrees of freedom. The coherence extends past the vibrational period of the excited state molecule, unlike that observed in any condensed phase environment for I2 so far. The ZP transitions from the relaxing B-state populations were resolved in the hot luminescence when the 532 nm laser was used for excitation.

Ultrafast dynamics of halogens in rare gas solids

We perform time resolved pump-probe spectroscopy on small halogen molecules ClF, Cl2, Br2, and I2 embedded in rare gas solids (RGS). We find that dissociation, angular depolarization, and the decoherence of the molecule is strongly influenced by the cage structure. The well ordered crystalline environment facilitates the modelling of the experimental angular distribution of the molecular axis after the collision with the rare gas cage. The observation of many subsequent vibrational wave packet oscillations allows the construction of anharmonic potentials and indicate a long vibrational coherence time. We control the vibrational wave packet revivals, thereby gaining information about the vibrational decoherence. The coherence times are remarkable larger when compared to the liquid or high pressure gas phase. This fact is attributed to the highly symmetric molecular environment of the RGS. The decoherence and energy relaxation data agree well with a perturbative model for moderate vibrational excitation and follow a classical model in the strong excitation limit. Furthermore, a wave packet interferometry scheme is applied to deduce electronic coherence times. The positions of those cage atoms, excited by the molecular electronic transitions are modulated by long living coherent phonons of the RGS, which we can probe via the molecular charge transfer states.

Effective chromophore potential, dissipative trajectories, and vibrational energy relaxation: Br2 in Ar matrix

The intramolecular wave packet dynamics on the electronic B (3pi0) potential of Br2 in solid argon is induced and interrogated by femtosecond pump-probe spectroscopy. An effective potential of the chromophore in the solid is derived from the wave packet period for different excitation photon energies. Deep in the potential well, it is consistent with vibrational energies from wavelength-resolved spectra. It extends to higher energies, where the vibrational bands merge to a continuum, and even beyond the dissociation limit, thus quantifying the cage effect of the argon matrix. This advantage of pump-probe spectroscopy is related to a reduced contribution of homogeneous and inhomogeneous line broadenings. The vibrational energy relaxation rates are determined by a variation of the probe window spatial position via the probe quantum energy. A very large energy loss in the first excursion of the wave packet is observed near the dissociation limit. This strong interaction with the argon matrix is directly displayed in an experimental trajectory.