Pulsed Rydberg four-wave mixing with motion-induced dephasing in a thermal vapor

Abstract

We report on time-resolved pulsed four-wave mixing (FWM) signals in a thermal Rubidium vapor involving a Rydberg state. We observe FWM signals with dephasing times up to 7 ns, strongly dependent on the excitation bandwidth to the Rydberg state. The excitation to the Rydberg state is driven by a pulsed two-photon transition on ns timescales. Combined with a cw de-excitation laser, a strongly directional and collective emission is generated according to a combination of the phase matching effect and averaging over Doppler classes. In contrast to a previous report (Huber et al. in Phys Rev A 90: 053806, 2014) using off-resonant FWM, at a resonant FWM scheme we observe additional revivals of the signal shortly after the incident pulse has ended. We infer that this is a revival of motion-induced constructive interference between the coherent emissions of the thermal atoms. The resonant FWM scheme reveals a richer temporal structure of the signals, compared to similar, but off-resonant excitation schemes. A simple explanation lies in the selectivity of Doppler classes. Our numerical simulations based on a four-level model including a whole Doppler ensemble can qualitatively describe the data.

Rydberg polaritons in a thermal vapor

“…We detect the retrieved photons produced via FWM by single-photon counters as we only address quite small atomic ensemble. The retrieval light field shows motion-induced revivals, which can be attributed to the constructive interference between the coherent evolution of different velocity classes [25,26]. All these features can be reproduced by numerical simulations considering the contribution of a whole Doppler ensemble.…”

“…The Lindblad operator L(ρ v ) includes the various decays [29]. The corresponding Hamiltonian with rotating-wave approximation iŝ The temporal structure of the retrieved signals is sensitive to the incident laser intensities in a resonant FWM transition [26]. Hence, we further consider the spatial profiles of the beams.…”

“…We numerically solve the Lindblad equation with the Hamilton operator in a four-level diamond configuration, ∂ ρv ∂t = − i h Ĥv , ρv + L( ρv ) for the velocity group v. The Lindblad operator L( ρv ) includes the various decays [29]. The corresponding Hamiltonian with rotating-wave approximation is The temporal structure of the retrieved signals is sensitive to the incident laser intensities in a resonant FWM transition [26]. Hence, we further consider the spatial profiles of the beams.…”

“…2), we observe motion-induced signal revivals, as discussed in Refs. [25,26]. The atomic coherences differ in both amplitude and phase for the different velocity classes.…”

Optical cavity for enhanced parametric four-wave mixing in rubidium

“…Four-wave mixing continues to be an active area of research, with applications in a number of different contexts and materials. Currently, four-wave mixing is being pursued in applications including quantum information [1,2], Rydberg States [3][4][5], single-photon sources [6], and optical gyroscopes [7]. It has been examined in a wide range of contexts, including hollow core fibers [8], cold atoms [9] and thermal vapors of rubidium and cesium [10,11].…”