Strong coupling of organic molecules to the vacuum field of a nanoscale cavity can be used to modify their chemical and physical properties. We extend the Tavis-Cummings model for molecular ensembles and show that the often neglected interaction terms arising from the static dipole moment and the dipole self-energy are essential for a correct description of the light-matter interaction in polaritonic chemistry. On the basis of a full quantum description, we simulate the excited-state dynamics and spectroscopy of MgH+ molecules resonantly coupled to an optical cavity. We show that the inclusion of static dipole moments and the dipole self-energy is necessary to obtain a consistent model. We construct an efficient two-level system approach that reproduces the main features of the real molecular system and may be used to simulate larger molecular ensembles.
A two level system is considered which has no static dipole moment, e.g. molecule
H2 in its ground electronic state. If strong enough external field is applied, it will dynamically distort such a system and supply it with time (and field) dependent dipole moment. Although it is impossible to do so in the undistorted system which has no coupling to the dipole component of the external field, having induced in it a dipole moment, the rotational and vibrational dynamics of such system can be manipulated using lasers. In this work, a system is considered in which the external perturbation dynamically induces the transition dipole moment between only two distinct levels. The aim of the work is to show how the driving pulse can be analytically designed, that will produce Rabi-like complete population oscillations between the two levels.
It is found that a sufficiently strong electric field can substantially decrease the relaxation rate of high-frequency polarization of a gas corresponding to the resonance dipole-dipole interaction of its molecules. The corresponding decrease in the integrated cross section for intermolecular Weisskopf collisions is calculated using the two-level approximation for the description of quantum dynamics of internal (vibrational) degrees of freedom of molecules, whereas their translational and rotational motions are treated classically. It is shown that the effect is caused by the Stark change of dipole moments of molecules and the ordering of their orientations in a constant electric field. As a result, for a certain magnitude of this field, the contributions of constant and high-frequency dipole moments of a molecule to the change in its density matrix upon a collision are counter-balanced to a considerable extent. The conditions required for the experimental observation of the effect are formulated.