Observation of effects of inter-atomic interaction on Autler-Townes splitting in cold Rydberg atoms

TL;DR

The paper investigates how inter-atomic interactions among cold Rydberg atoms modify Autler-Townes splitting observed in trap-loss spectroscopy of a $^{87}$Rb MOT. Using a three-level effective model within the Lindblad formalism, including RRI-induced dephasing, AT splitting is mapped across a wide range of Rydberg principal quantum numbers ($n=35$–$117$) and beam intensities. A pronounced broadening of AT signals is found for $n>100$, driven by interaction-induced dephasing, with strong agreement between experiment and theory. These findings illuminate how RRI-induced dephasing shapes AT spectroscopy in cold Rydberg ensembles and inform Rydberg-based quantum technologies.

Abstract

We demonstrate the effect of inter-atomic interaction in highly excited Rydberg atoms via Autler- Townes splitting in cold atoms. We measure the Autler-Townes (AT) splitting of the 5S1/2, F=2 to 5P3/2, F'=3 transition of 87Rb atoms arising due to the strong coupling of the transition via the cooling beams used for the magneto-optical trap (MOT). The AT splitting is probed using a weakly coupled transition from 5P3/2, F'=3 state to highly excited Rydberg states for a wide range of principal quantum numbers (n = 35 - 117). We observe the AT splitting via trap-loss spectroscopy in the MOT by scanning the probe frequency. We observe a drastic increase in the broadening of the AT splitting signal as a result of interaction-induced dephasing effect in cold Rydberg atoms for highly excited Rydberg states with principal quantum number n > 100. We explain our observations using theoretical modelling and numerical simulations based on the Lindblad Master equation. We find a good agreement of the results of the numerical simulation with the experimental measurements.

Figures (7)

• Figure 1: (a) The schematic of the experimental setup for Rydberg excitation of cold atoms in a 87Rb MOT and trap-loss spectroscopy. The fluorescence of the MOT is measured using an EMCCD camera and an Avalanche photo-diode (APD). (b) Energy-level scheme for two-photon Rydberg excitation along with the cooling and repumping laser beams of the MOT. The ground state and the intermediate state are coupled by the strong cooling beams of the MOT with a detuning of $\Delta_c$.
• Figure 2: (Left) AT dressed split states where the probe couples the two dressed states to the Rydberg level $\ket{r}$. $\Omega'$ is the generalized Rabi frequency of the cooling transition. (Right) A typical trap-loss spectrum of 87Rb cold atoms in the MOT due to two-photon excitation to $\ket{r}$. The measurement has been carried out in a MOT with peak atom number density of $\approx 1 \times 10^{10} cm^{-3}$ by exciting the cold atoms to the Rydberg state $35S_{1/2}$. A total cooling beam intensity of $\approx 55 mW/cm^2$ and a probe beam intensity of $15 mW/cm^2$ was used in the measurement.
• Figure 3: (a) The Trap-loss spectra obtained for $\ket{r}=35S_{1/2}$ with different cooling beam intensities. The cooling beam intensities are given in the unit of saturation intensity for $5S_{1/2}, F=2 \rightarrow 5P_{3/2}, F'=3$ transition. The solid lines are the numerically estimated steady-state fraction of atoms left in the MOT ($1-f_R$) as a function of probe detuning $\Delta_p$ for corresponding experimental parameters. The parameter, interaction-induced dephasing $\gamma_r$ is deduced from the fit to the experimental data for different cooling Rabi frequencies $\Omega_c$. The cooling beam detuning $\Delta_c$ was optimized in the modelling using the experimental measurements. The plot in (b) shows the amount of AT splitting vs the generalized Rabi frequency for cooling transition calculated with the corresponding cooling beam intensities.
• Figure 4: The Trap-loss spectra obtained for $\ket{r}=35S_{1/2}$ with different Rydberg/probe beam intensities measured in $W/m^2$ are shown in (a) The numerically estimated steady state fraction of atoms left in the MOT ($1-f_R$) as a function of probe detuning $\Delta_p$ with the shift in detuning and the interaction-induced dephasing fit to the experimental data for different probe Rabi frequencies $\Omega_p$ is shown as the solid line in (a) in comparison with the experimental results. (b) shows the amount AT splitting vs the Rydberg/probe beam intensities.
• Figure 5: The Trap-loss spectra obtained for different principal quantum number n of 87Rb(Left) and the steady state fraction of atoms left in the MOT ($1-f_R$) for the corresponding n levels obtained numerically (solid line). The measurements are carried out in a cold-atomic cloud of magneto-optical trap with cooling detuning of 10 MHz and a generalized Rabi frequency of 23.7 MHz. The probe laser intensity is chosen in such a way as to keep the $\Omega_p$ same for all the measurements($\approx$ 5.2 kHz).