Detection of collective resonances using optical two-dimensional coherent spectroscopy

Optical two-dimensional coherent spectroscopy (2DCS) is a powerful technique with high sensitivity and temporal resolution that has been established as a vital tool for measuring ultrafast processes and couplings in complex systems such as atomic ensembles, molecules, and 2D materials. In this presentation, we will demonstrate the ability of 2DCS to probe weak transition dipole-dipole interactions through detection of collective resonances in a rubidium (Rb) vapor. Our methodology involves focusing four sequential pulses onto a Rb vapor cell, with each pulse controlled with time delays. This pulse sequence generates a nonlinear fluorescence signal due to collective resonances of multiple atoms. By performing Fourier transform analysis on the resulting signal, a 2D spectrum is generated in the frequency domain. The spectra reveal insights into coupling information and ultrafast processes. We measure collective resonances of Dicke states with up to 8 correlated atoms. These resonances arise from the cooperative behavior of the atomic ensemble and can be harnessed for various multi-atom applications in quantum information processing and quantum technologies. We propose extending the application of 2DCS to measure collective resonances in cold Rb atoms, thereby gaining an understanding of how many-body interactions can vary in two distinct temperature environments.