Ultrafast dynamics in the vicinity of quantum light-induced conical intersections

Abstract

Nonadiabatic effects appear due to avoided crossings or conical intersections (CIs) that are either intrinsic properties in field-free space or induced by a classical laser field in a molecule. It was demonstrated that avoided crossings in diatomics can also be created in an optical cavity. Here, the quantized radiation field mixes the nuclear and electronic degrees of freedom creating hybrid fieldmatter states called polaritons. In the present theoretical study we go further and create CIs in diatomics by means of a radiation field in the framework of cavity quantum electrodynamics. By treating all degrees of freedom, that is the rotational, vibrational, electronic and photonic degrees of freedom on an equal footing we can control the nonadiabatic quantum light-induced dynamics by means of CIs. First, the pronounced difference between the the quantum light-induced avoided crossing and the CI with respect to the nonadiabatic dynamics of the molecule is demonstrated. Second, we discuss the similarities and differences between the classical and the quantum field description of the light for the studied scenario.The dynamics initiated in a molecule by absorbing a photon is often described in the Born-Oppenheimer (BO) or adiabatic approximation [1], where the electronic and nuclear degrees of freedom are treated separately. However, in some nuclear configurations called conical intersections (CIs) the mixing between the electronic and nuclear motions are very significant [2][3][4][5][6]. Owing to the strong nonadiabatic couplings (NACs) in the close vicinity of these CIs the BO approximation breaks down. It is well-known that these CIs have a significant impact on several important photo-dynamical processes, such as vision, photosynthesis, molecular electronics, and the photochemistry of DNA [7][8][9][10][11]. During the dynamics the CIs can serve as efficient decay channels for the ultrafast transfer of the populations. In the following we call these CIs, which originate from the field free electronic structure, natural CIs.Nonadiabatic effects can also appear when molecules are exposed to resonant laser light. The electric field can couple to two or more electronic states of the molecule via the non-vanishing transition dipole moment(s) [12][13][14][15]. This results either in a light-induced avoided crossing (LIAC) or a light-induced conical intersection (LICI) depending on how many nuclear degrees of freedom are involved in the field induced process [16]. In case of poly atomic molecules a sufficient number of vibrational degrees of freedom are always present to span a twodimensional branching space (BS), which is indispensable to the formation of LICI. In the case of diatomics one always has to find a proper second degree of freedom (DOF) which can act as a dynamical variable to form a BS. As the molecule rotates [17][18][19], the rotational angle between the molecular axis and the light polarization axis can serve as the missing DOF for establishing the BS [20].Nonadiabatic effects can arise in an optical or mi...

Born–Oppenheimer approximation in optical cavities: from success to breakdown

“…25,26 Recently, efforts have been made to study light-induced nonadiabatic phenomena in optical or microwave cavities. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] It has been successfully demonstrated that describing the photon-matter interaction with the tools of cavity quantum electrodynamics (cQED) [47][48][49][50] can provide an alternative way to study the quantum control of molecules with light. In this framework nonadiabatic dynamics arises due to the strong coupling between the molecular dofs and the photonic mode of the radiation eld which can alter the molecular energy levels by controlling the dynamics of basic photophysical and photochemical processes.…”

“…In most of the studies diatomic or polyatomic organic molecules are treated as reduced-dimensional two-level systems by taking into account only one vibrational and photonic dof. [27][28][29]34,35,42 As is already clear from classical light, quantum LICI situations can also only occur if, in addition to the only vibrational dof, the rotational angle between the molecular axis and the polarization vector of the electric eld in the cavity is also accounted for (in case of diatomics) 37,38 or at least two vibrational dofs are considered in the description. 26,44 Furthermore, quantum light-induced collective nonadiabatic phenomena (collective LICI) can also emerge when many molecules are involved in strong coupling to the cavity mode.…”

Three-player polaritons: nonadiabatic fingerprints in an entangled atom–molecule–photon system

“…In such theoretical descriptions, the molecules are usually treated with a reduced number of degrees of freedom or with some simplified models assuming two-level systems [20]. However, it is worth studying single-molecule cavity interactions as well, since a more detailed study of individual objects may also provide meaningful results [22,23,[40][41][42].…”

“…The radiation field can strongly mix the vibrational, rotational, and electronic degrees of freedom, thus creating light-induced avoided crossings (LIACs) or light-induced conical intersections (LICIs) between polaritonic potential-energy surfaces [43]. Recent works discussed how the natural avoided crossings (already present in field-free systems) can be manipulated by placing the molecule into a nano-cavity and influencing the ultrafast dynamics by means of a quantized radiation field [23,42]. Field-dressed rovibronic spectra of diatomics within the framework of cavity quantum electrodynamics (CQED) have also been investigated recently [40], elucidating the significant contribution of molecular rotation to nonadiabatic effects in the spectrum.…”

Reduced Density-Matrix Approach to Strong Matter-Photon Interaction

“…3,22 However, limits and difficulties of few-level approximations have been pointed out, 23−28 and recently, new models have been used to investigate polaritonic chemistry. 15,28−41 Still, many questions remain open, especially whether the collective (ultra)strong coupling, predicted by the Dicke model can actually modify ground state properties of single molecules. 17,42 Another example is the ongoing discussion on the theoretical understanding of super-radiance.…”