Thermodynamics of ultrastrongly coupled light-matter systems

We study the thermodynamic properties of a system of two-level dipoles that are coupled ultrastrongly to a single cavity mode. By using exact numerical and approximate analytical methods, we evaluate the free energy of this system at arbitrary interaction strengths and discuss strong-coupling modifications of derivative quantities such as the specific heat or the electric susceptibility. From this analysis we identify the lowest-order cavity-induced corrections to those quantities in the collective ultrastrong coupling regime and show that for even stronger interactions the presence of a single cavity mode can strongly modify extensive thermodynamic quantities of a large ensemble of dipoles. In this non-perturbative coupling regime we also observe a significant shift of the ferroelectric phase transition temperature and a characteristic broadening and collapse of the black-body spectrum of the cavity mode. Apart from a purely fundamental interest, these general insights will be important for identifying potential applications of ultrastrong-coupling effects, for example, in the field of quantum chemistry or for realizing quantum thermal machines.

Self-Dissociation of Polar Molecules in a Confined Infrared Vacuum

<p>We study the infrared photodissociation dynamics of a single hydrogen fluoride (HF) molecule in a single-mode cavity vacuum, and compare it with the case of strong cw laser driving. We show that in the absence of additional IR sources, a single cavity mode can efficiently dissociate a polar diatomic molecule prepared in the ground vibrational level. We predict dissociation probabilities of up to 20%, for a vacuum field that is resonant with the fundamental vibration frequency at the onset of the ultrastrong coupling regime. In contrast, similar dissociation rates can only be achieved in free space using resonant laser fields with intensities not smaller than 10¹⁴ W/cm². Our work highlights the fundamental differences that can be expected for reactive dynamical processes inside infrared cavities.</p>

Self-Dissociation of Polar Molecules in a Confined Infrared Vacuum

<p>We study the infrared photodissociation dynamics of a single hydrogen fluoride (HF) molecule in a single-mode cavity vacuum, and compare it with the case of strong cw laser driving. We show that in the absence of additional IR sources, a single cavity mode can efficiently dissociate a polar diatomic molecule prepared in the ground vibrational level. We predict dissociation probabilities of up to 20%, for a vacuum field that is resonant with the fundamental vibration frequency at the onset of the ultrastrong coupling regime. In contrast, similar dissociation rates can only be achieved in free space using resonant laser fields with intensities not smaller than 10¹⁴ W/cm². Our work highlights the fundamental differences that can be expected for reactive dynamical processes inside infrared cavities.</p>

Multidimensional photon correlation spectroscopy of cavity polaritons

The strong coupling of atoms and molecules to radiation field modes in optical cavities creates dressed matter/field states known as polaritons with controllable dynamical and energy transfer properties. We propose a multidimensional optical spectroscopy technique for monitoring polariton dynamics. The response of a two-level atom to the time-dependent coupling to a single-cavity mode is monitored through time-and-frequency–resolved single-photon coincidence measurements of spontaneous emission. Polariton population and coherence dynamics and its variation with cavity photon number and controlled by gating parameters are predicted by solving the Jaynes–Cummings model.

Quantum Trajectories for Squeezed Input Processes: Explicit Solutions

We consider the quantum (trajectories) filtering equation for the case when the system is driven by Bose field inputs prepared in an arbitrary non-zero mean Gaussian state. The a posteriori evolution of the system is conditioned by the results of a single or double homodyne measurements. The system interacting with the Bose field is a single cavity mode taken initially in a Gaussian state. We show explicit solutions using the method of characteristic functions to the filtering equations exploiting the linear Gaussian nature of the problem.

COHERENCE EFFECTS IN MESOSCOPIC HIGHER HARMONIC MULTISTABILITY

The interaction of a mesoscopic system of coherently injected two-level Rydberg atoms with a coherently driven single cavity mode is treated outside the rotating wave approximation (RWA). The additional first harmonic component of the output field (outside RWA) exhibits closed hysteresis loops and multiple-switching processes, compared with the hysteresis cycles for the nonoscillatory (fundamental) component within the RWA. This is achieved via two controls: (i) varying the coherent population excitation and relative phase parameters (θ, ϕ) of the coherently injected atoms, and, (ii) varying simultaneously atom and cavity detuning parameters.