We investigate the effect of strong interaction in the dressed energy levels of the two level emitters. Strong dipole-dipole interactions give rise to new sidebands in the fluorescence spectrum due to specific couplings among the collective dressed levels which in turn depends on the spatial configuration of atoms. These couplings are the main responsible for the frequencies and variety of sidebands. We explain the general method for finding the dressed energy levels for a system of any number of strongly coupled atoms and we solve this problem for two different spatial configurations of three coupled two-level emitters. We show that the coupling among dressed levels and consequently energies and number of sidebands in the fluorescence spectrum are different for each configuration. Thus the fluorescence spectrum of strongly interacting atoms contains information about the number and configuration of atoms.
We investigate the effect of strong interaction in the dressed energy levels of the two level emitters. Strong dipole-dipole interactions give rise to new sidebands in the fluorescence spectrum due to specific couplings among the collective dressed levels which in turn depends on the spatial configuration of atoms. These couplings are the main responsible for the frequencies and variety of sidebands. We explain the general method for finding the dressed energy levels for a system of any number of strongly coupled atoms and we solve this problem for two different spatial configurations of three coupled two-level emitters. We show that the coupling among dressed levels and consequently energies and number of sidebands in the fluorescence spectrum are different for each configuration. Thus the fluorescence spectrum of strongly interacting atoms contains information about the number and configuration of atoms.
We investigate the resonance fluorescence features of a small ensemble of closely packed and moderately laser-pumped two-level emitters at resonance. The mean distance between any two-level radiators is smaller than the corresponding emission wavelength, such that the dipole-dipole interactions are not negligible. We have found that under the secular approximation, the collective resonance fluorescence spectrum consists of 2 N + 1 spectral lines, where N is the number of emitters from the sample. The 2 N spectral sidebands, symmetrically located around the generalized Rabi frequency with respect to the central line at the laser frequency, are distinguishable if the dipole-dipole coupling strength is larger than the collective spontaneous decay rate. This way, one can estimate the radiators number within the ensemble via measuring of the spontaneously scattered collective resonance fluorescence spectrum. Contrarily, if the dipole-dipole coupling is of the order of or smaller than the cooperative spontaneous decay rate, but still non-negligible, the spectrum turns into a Mollow-like fluorescence spectrum, where the two sidebands' spectral lines broaden proportional to the dipole-dipole coupling strength. Published by the American Physical Society 2024
We investigate two-color photon correlations in the light emitted by two strongly driven, strongly interacting two-level emitters. The correlations are interpreted introducing the collective dressed states picture, which allows us to describe both bunching and antibunching based on the allowed and prohibited transitions. At odds from weakly interacting emitters, the strong interaction lifts the degeneracy of the energy differences between the different states, leading to a temporal breaking of symmetry for the correlations: photons of different frequencies may not be emitted in any order. Finally, we show that most of the virtual processes, which involve pairs of photons, yield nonclassical correlations when the sum of their energies fits any of the interaction-induced sidebands in the emitted spectrum. In particular, depending on the frequency of the emitted photons, correlations strong enough to violate Bell inequalities can appear.
The transmission spectrum of two dipole-coupled atoms interacting with a single-mode optical cavity in the strong coupling regime is investigated theoretically for the lower and higher excitation cases. The dressed states containing the dipole-dipole interaction (DDI) are obtained by transforming the two-atom system into an effective single-atom system. We find that the DDI can enhance the effects resulting from the positive atom-cavity detunings but weakens them for the negative detuning cases for the lower excitation, which causes the spectrum to exhibit two asymmetric peaks with shifted heights and positions. For the higher excitation cases, the DDI augments the atomic saturation and leads to the deforming of the spectrum. Furthermore, the large DDI can cause the atom and the cavity to decouple, producing a singlet of the normal-mode spectrum.
The dressed atom approach provides a tool to investigate the dynamics of an atom-laser system by fully retaining the quantum nature of the coherent mode. In its standard derivation, the internal atom-laser evolution is described within the rotating-wave approximation, which determines a doublet structure of the spectrum and the peculiar fluorescence triplet in the steady state. However, the rotating wave approximation may fail to apply to atomic systems subject to femtosecond light pulses, light-matter systems in the strong-coupling regime or sustaining permanent dipole moments. This work aims to demonstrate how the general features of the steady-state radiative cascade are affected by the interaction of the dressed atom with propagating radiation modes. Rather than focusing on a specific model, we analyze how these features depend on the parameters characterizing the dressed eigenstates in arbitrary atom-laser dynamics, given that a set of general hypotheses is satisfied. Our findings clarify the general conditions in which a description of the radiative cascade in terms of transition between dressed states is self-consistent. We provide a guideline to determine the properties of photon emission for any atom-laser interaction model, which can be particularly relevant when the model should be tailored to enhance a specific line. We apply the general results to the case in which a permanent dipole moment is a source of low-energy emission, whose frequency is of the order of the Rabi coupling.
We investigate cooperative fluorescence in a dilute cloud of strongly driven two-level emitters. Starting from the Heisenberg equations of motion, we compute the first-order scattering corrections to the saturation of the excited-state population and to the resonance-fluorescence spectrum, which both require going beyond the state-of-the-art linear-optics approach to describe collective phenomena. A dipole blockade is observed due to long-range dipole-dipole coupling that vanishes at stronger driving fields. Furthermore, we compute the inelastic component of the light scattered by a cloud of many atoms and find that the Mollow triplet is affected by cooperativity. In a lobe around the forward direction, the inelastic Mollow triplet develops a spectral asymmetry, observable under experimental conditions.
Frequency-resolved quantum correlation of resonance fluorescence is investigated in a two-atom radiating system. In this quantum radiating system, only one atom is driven by a laser field, and the spontaneous transition of the undriven atom resonates with one of the Rabi sidebands of the driven atom. A single-mode empty cavity is applied to serve as a Lorentzian filter to output the superbunched fluorescent photon pairs when its frequency is tuned to halfway between the central peak and one of the side peaks. In the case of large filter width, two-photon correlation signal and its physical correspondence can be bridged analytically in our approach. It reveals that this superbunching effect turns out to be the constructive quantum interference between a pair of coupled two-photon cascaded transitions. Ulteriorly, it is the consequence of the modulations of the unfiltered dressed-state transition amplitudes by the filter. Our analytical formalism also shows that, although the dipole-dipole interaction is usually weak, the interatomic coherence caused by this weak perturbation can also play a crucial role in breaking through the superbunching limit obtained from a single two-level atom in the same parameter regime. In addition to being a treasurable quantum pump to probe into the target quantum system, it is also found in our investigation that this superbunched fluorescence can serve as a promising quantum response in detecting this weak perturbation in the interior of the quantum source. A general case is also considered when the two-atom radiating system is monitored by two filter-detector monitoring systems. It is found that this filtered strong quantum correlation can be maintained even though the two photons are spatially separated.