An efficient and flexible approach for computing rovibrational polaritons from first principles

A theoretical framework is presented for the computation of rovibrational polaritonic states of a molecule in a lossless infrared (IR) microcavity. In the proposed approach the quantum treatment of the rotational and vibrational motion of the molecule can be formulated using arbitrary approximations. The cavity-induced changes in electronic structure are treated perturbatively, which allows using the existing polished tools of standard quantum chemistry for determining electronic molecular properties. As a case study, the rovibrational polaritons and related thermodynamic properties of H$_2$O in an IR microcavity are computed for varying cavity parameters and applying various approximations to describe the molecular degrees of freedom. The self-dipole interaction is found to be significant for nearly all light-matter coupling strengths investigated, and the molecular polarizability proved to be important for the correct qualitative behavior of the energy level shifts induced by the cavity. On the other hand, the magnitude of polarization remains small, justifying the perturbative approach for the cavity-induced changes in electronic structure. Comparing results obtained using a high-accuracy variational molecular model with those obtained utilizing the rigid rotor and harmonic oscillator approximations revealed that as long as the rovibrational model is appropriate for describing the field-free molecule, the computed rovibropolaritonic properties can be expected to be accurate as well. Strong light-matter coupling between the radiation mode of an IR cavity and the rovibrational states of H$_2$O lead to minor changes in the thermodynamic properties of the system, and these changes seem to be dominated by non-resonant interactions between the quantum light and matter

Pauli principle in polaritonic chemistry

Consequences of enforcing permutational symmetry, as required by the Pauli principle (spin-statistical theorem), on the state space of molecular ensembles interacting with the quantized radiation mode of a cavity are discussed. The Pauli-allowed collective states are obtained by means of group theory, i.e., by projecting the state space onto the appropriate irreducible representations of the permutation group of the indistinguishable molecules. It is shown that with increasing number of molecules the ratio of Pauli-allowed collective states decreases very rapidly. Bosonic states are more abundant than fermionic states, and the brightness of Pauli-allowed collective states (contribution from photon excited states) increases(decreases) with increasing fine structure in the energy levels of the material ground(excited) state manifold. Numerical results are shown for the realistic example of rovibrating H$_2$O molecules interacting with an infrared (IR) cavity mode

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

A quantum system composed of a molecule and an atomic ensemble, confined in a microscopic cavity, is investigated theoretically. The indirect coupling between atoms and the molecule, realized by their interaction with the cavity radiation mode, leads to a coherent mixing of atomic and molecular states, and at strong enough cavity field strengths hybrid atom-molecule-photon polaritons are formed. It is shown for the Na$_2$ molecule that by changing the cavity wavelength and the atomic transition frequency, the potential energy landscape of the polaritonic states and the corresponding spectrum could be changed significantly. Moreover, an unforeseen intensity borrowing effect, which can be seen as a strong nonadiabatic fingerprint, is identified in the atomic transition peak, originating from the contamination of the atomic excited state with excited molecular rovibronic states

Robust field-dressed spectra of diatomics in an optical lattice

The absorption spectra of the cold Na2 molecule dressed by a linearly polarized standing laser wave is investigated. In the studied scenario the rotational motion of the molecules is frozen while the vibrational and translational degrees of freedom are accounted for as dynamical variables. In such a situation a light-induced conical intersection (LICI) can be formed. To measure the spectra a weak field is used whose propagation direction is perpendicular to the direction of the dressing field but has identical polarization direction. Although LICIs are present in our model, the simulations demonstrate a very robust absorption spectrum, which is insensitive to the intensity and the wavelength of the dressing field and which does not reflect clear signatures of light-induced nonadiabatic phenomena related to the strong mixing between the electronic, vibration and translational motions. However, by widening artificially the very narrow translational energy level gaps, the fingerprint of the LICI appears to some extent in the spectrum

Pauli principle in polaritonic chemistry

Consequences of enforcing permutational symmetry, as required by the Pauli principle (spinstatistical theorem), on the state space of molecular ensembles interacting with the quantized radiation mode of a cavity are discussed. The Pauli-allowed collective states are obtained by means of group theory, i.e., by projecting the state space onto the appropriate irreducible representations of the permutation group of the indistinguishable molecules. It is shown that with increasing number of molecules the ratio of Pauli-allowed collective states decreases very rapidly. Bosonic states are more abundant than fermionic states, and the brightness of Pauli-allowed state space (contribution from photon excited states) increases(decreases) with increasing fine structure in the energy levels of the material ground(excited) state manifold. Numerical results are shown for the realistic example of rovibrating H2O molecules interacting with an infrared (IR) cavity mode

An efficient and flexible approach for computing rovibrational polaritons from first principles

A theoretical framework is presented for the computation of the rovibrational polaritonic states of a molecule in a lossless infrared (IR) microcavity. In the proposed approach, the quantum treatment of the rotational and vibrational motions of the molecule can be formulated using arbitrary approximations. The cavity-induced changes in electronic structure are treated perturbatively, which allows using the existing polished tools of standard quantum chemistry for determining electronic molecular properties. As a case study, the rovibrational polaritons and related thermodynamic properties of H2O in an IR microcavity are computed for varying cavity parameters, applying various approximations to describe the molecular degrees of freedom. The self-dipole interaction is significant for nearly all light–matter coupling strengths investigated, and the molecular polarizability proved important for the correct qualitative behavior of the energy level shifts induced by the cavity. On the other hand, the magnitude of polarization remains small, justifying the perturbative approach for the cavity-induced changes in electronic structure. Comparing results obtained using a high-accuracy variational molecular model with those obtained utilizing the rigid rotor and harmonic oscillator approximations revealed that as long as the rovibrational model is appropriate for describing the field-free molecule, the computed rovibropolaritonic properties can be expected to be accurate as well. Strong light–matter coupling between the radiation mode of an IR cavity and the rovibrational states of H2O leads to minor changes in the thermodynamic properties of the system, and these changes seem to be dominated by non-resonant interactions between the quantum light and matter