Conical Intersections Induced by Quantum Light: Field-Dressed Spectra from the Weak to the Ultrastrong Coupling Regimes

Abstract

A fundamental theoretical framework is formulated for the investigation of rovibronic spectra resulting from the coupling of molecules to one mode of the radiation field in an optical cavity. The approach involves the computation of (1) cavity-field-dressed rovibronic states, which are hybrid light-matter eigenstates of the "molecule + cavity radiation field" system, and (2) the transition amplitudes between these field-dressed states with respect to a weak probe pulse. The predictions of the theory are shown for the homonuclear Na 2 molecule. The field-dressed rovibronic spectrum demonstrates undoubtedly that the Born-Oppenheimer approximation breaks down in the presence of the cavity radiation field. A clear fingerprint of the strong nonadiabaticity is found, which can only emerge in the close vicinity of conical intersections. In this work, the conical intersection is induced by the quantized radiation field, and it is thus called a "light-induced conical intersection" (LICI). Dependence of the cavity-field-dressed spectrum on the cavity-mode wavelength as well as on the light-matter coupling strength is investigated. Essential changes are identified in the spectra from the weak to the ultrastrong coupling regimes.

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

“…Depending on the homogeneity of the atom-field interactions, with inhomogeneity caused either by inhomogeneities in the field or the atomic transition frequencies, the energy level structure and the absorption spectrum could become more complex, as detailed in reference [47]. As for molecules interacting with a cavity radiation mode, Autler-Townes-type splittings, as well as 'intensity borrowing' effects [49,53] and the formation of polaritonic potential energy surfaces, are reflected in the spectrum [40]. The right panels of figure 1 show the light-dressed spectra of an Na 2 molecule and two-state atoms interacting with a single cavity mode.…”

“…Now we turn to the weak-field absorption spectrum of the composite system. Similar to previous works [40,48], the spectrum is determined by first computing the field-dressed states, i.e., the eigenstates of the full 'molecule + atoms + radiation field' system, and then computing the dipole transition amplitudes between the field-dressed states with respect to a probe pulse. The probe pulse is assumed to be weak, inducing primarily one-photon processes, implying that the standard approach [49] of using first-order time-dependent perturbation theory to compute the transition amplitudes should be adequate.…”

“…Since the pioneering experimental work carried out by the group of Ebbesen, in which they observed that strong light-matter coupling could modify chemical landscapes [8], the field of 'molecular polaritons' experienced much activity from both experimental [9][10][11][12][13][14][15][16][17][18][19] and theoretical [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] research groups. Recent achievements on molecules strongly coupled to a cavity mode, such as that strong cavity-matter coupling can alter chemical reactivity [9,38], provide long-range energy or charge transfer mechanisms [12,37], modify nonradiative relaxation pathways through collective effects [35], and modify the optical response of molecules [31,40], support the relevance of such a new chemistry. In most of the works published so far, many organic emitters were put into a cavity and the interest was mainly focused on the investigation of collective phenomena between the quantum radiation field and the molecular ensemble.…”

“…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].…”

Strong Coupling with Light Enhances the Photoisomerization Quantum Yield of Azobenzene

“…For collective effects, the focus has been on polariton formation in full quantum diatomic molecules 35 and on several model dye molecules in a realistic environment 36 . At the single molecule level, the non-adiabatic dynamics schemes developed allowed to predict features arising on the PESs like the creation of avoided crossings and light-induced conical intersections 13,37,38 . Such features modify the shape of PESs, translating into a potentially different photochemical reactivity 27,[39][40][41] .…”