Spectroscopy of atomic rubidium at500−barbuffer gas pressure: Approaching the thermal equilibrium of dressed atom-light states

Abstract

We have recorded fluorescence spectra of the atomic rubidium D-lines in the presence of several hundreds of bars buffer gas pressure. With additional saturation broadening a spectral linewidth comparable to the thermal energy of the atoms in the heated gas cell is achieved. An intensitydependent blue asymmetry of the spectra is observed, which becomes increasingly pronounced when extrapolating to infinitely high light intensity. We interpret our results as evidence for the dressed (coupled atom-light) states to approach thermal equilibrium.

Thermalization of coupled atom-light states in the presence of optical collisions

“…(16) is compatible with existing theories of spin-boson interaction with thermostat particles (due to collisions in our case) discussed by Leggett et al in [28]. In particular, according to our approach in the ideal case, neglecting spontaneous emission terms in (16), the dressedstate population imbalance S z should reach its thermodynamically equilibrium value S (eq) z with the rate 2w due to collisions with buffer gas atoms [see (21)], which is in agreement with experimentally tested approaches to OCs based on the solution of Boltzmann-like (rate) equations [11,26]. In addition, spontaneous emission described by the rates i→j (i,j = 1,2) causes a transfer between levels of different manifolds.…”

“…[11], [29]). In particular, the population of the lower dressed state |2(N) should be much larger [exp(h R /k B T ) times] than that of the upper one in thermal equilibrium.…”

“…Progress toward the achievement of thermal equilibrium in coupled atom-field states was made by some of us in [11]. In particular, the ability to thermalize coupled atom-light (dressed) states due to frequent collisions of rubidium atoms with buffer gas atoms in the presence of optical irradiation has been demonstrated experimentally.…”

“…However, the problem of thermalization of coupled atom-field states has not been studied. Standard theoretical approaches in this case are based on the rate equations for the population of dressed states only, completely ignoring coupling between population and atomic coherences at the same time (see, e.g., [11], [12], and [26]). Such an approach seems unsuitable if we keep in mind the problem of observation of polariton BEC.…”

Absorption spectroscopy of xenon and ethylene–noble gas mixtures at high pressure: towards Bose–Einstein condensation of vacuum ultraviolet photons

“…A possible suitable medium for photon thermalization in the vacuum ultraviolet regime could be high pressure noble gas samples, which exhibit electronic transitions starting from the electronic ground state in this spectral regime, or both mixtures between atoms or molecules and noble gases. Alkali-noble gas collisions are long known to be extremely elastic [25,26], and for the case of rubidium-argon gas mixtures at a few hundred bar of argon pressure the applicability of the thermodynamic Kennard-…”