arXiv subjects

Megha Gopalakrishna

Publications and source records attributed to Megha Gopalakrishna.

3 recordsLinked to original sources

arXiv2024

Few-Photon Fluorescence from Ultracold Bosons in an Optical Cavity

Within a cavity quantum electrodynamics framework, we analyse the fluorescent spectrum of ultracold bosons in resonant and second-harmonic generation (SHG) regimes. Two settings are considered: (i) (few) bosons in an optical lattice and (ii) a trapped two-component dilute Bose-Einstein condensate (2BEC) within the Bogoliubov scheme. Atom-photon dynamics are treated exactly via time-dependent configuration interaction, while cavity leakage is modelled via classical oscillator baths. For optical lattices, bosons in short Bose-Hubbard chains with two levels per site show spectral intensity that increases with atom number at weak interactions but decreases and redshifts at strong interactions once atoms outnumber sites. In the 2BEC case, spectra largely scale with particle number when 2BEC-cavity and inter-particle couplings are rescaled, while strong correlations induce SHG redshifts. These results reveal some generic features of fluorescence in ultracold bosons in optical cavities, and hint at possible experiments and further theoretical developments.

cond-mat.quant-gas↗

arXiv2023

Time resolved optical response of the Dicke's model via the nonequilibrium Green's function approach

Due to their conceptual appeal and computational convenience, two-level systems (TLS) and their generalisations are often used to investigate nonlinear behavior in quantum optics, and to assess the applicability of theoretical methods. Here the focus is on second harmonic generation (SHG) and, as system of interest, on the Dicke model, which consists of several TLSs inside an optical cavity. The main aspect addressed is the scope of non-equilibrium Green's function (NEGF) to describe the effect of disorder and electron-electron (e-e) interactions on the SHG signal. For benchmarking purposes, exact diagonalization (ED) results are also presented and discussed. SHG spectra obtained with NEGF and ED are found to be in very good mutual agreement in most situations. Furthermore, inhomogeneity in the TLS and e-e interactions reduce the strength of SHG, and the reduction is stronger with inhomogeneity than with interactions. This trend is consistently noted across different (small to large) system sizes. Finally, a modified NEGF approach is proposed to account for cavity leakage, where the quantum photon fields are coupled to a bath of classical oscillators. As to be expected, within this mixed quantum-classical scheme a decrease in the intensity of the fluorescent spectra takes place depending on the entity of cavity leakage.

quant-ph↗

arXiv2023

Photon pumping, photodissociation and dissipation at interplay for the fluorescence of a molecule in a cavity

We introduce a model description of a diatomic molecule in an optical cavity, with pump and fluorescent fields, and electron and nuclear motion are treated on equal footing and exactly. The model accounts for several optical response temporal scenarios: a Mollow spectrum hindered by electron correlations, a competition of harmonic generation and molecular dissociation, a dependence of fluorescence on photon pumping rate and dissipation. It is thus a general and flexible template for insight into experiments where quantum photon confinement, leakage, nuclear motion and electronic correlations are at interplay.

quant-ph↗