High-sensitivity measurement of Rydberg population via two-photon excitation in atomic vapour using optical heterodyne detection technique

Abstract

We demonstrate a technique based on optical heterodyne detection to measure Rydberg population in thermal atomic vapour. The technique used a probe beam far off resonant to the D2 line of rubidium along with a reference beam with frequency offset by 800 MHz in the presence of a coupling laser that couples to Rydberg state via two-photon resonance. The polarizations of the probe, reference and coupling beams are suitably chosen such that only the probe beam goes through a non-linear phase shift due to two-photon process which is measured relative to the phase shift of the reference beam using optical heterodyne detection technique. We show that the technique has a sensitivity to measure the minimum phase shift of the order of few µrad. We have used a suitable model of two-photon excitation of a 3-level atom to show that the minimum phase shift measured in our experiment corresponds to Rydberg population of the order of 10 −5 . The corresponding probe absorption for the given laser parameters is of the order of 10 −7 . We demonstrate that this technique is insensitive to polarization impurity or fluctuations in the beams. The technique is particularly useful in measuring Rydberg population via two-photon excitation in thermal vapour where multi channel plates (MCP) could be relatively difficult to impliment. It can also be used in ultra-cold atomic sample with suitable laser parameters.

Study of the effect of super-atom dephasing on Rydberg blockade in thermal vapor

“…Similarly, partial suppression in the Rydberg excitation has also been reported as an evidence of Rydberg blockade using a thermal atomic beam [37]. High sensitive measurement of the Rydberg population due to two-photon excitation in thermal vapor is reported using the optical heterodyne detection technique [38,39]. A single-photon source based on strongly interacting Rydberg atoms at room temperature has also been reported [40].…”

Deterministic facilitated excitation of the weakly driven atom in heteronuclear Rydberg atom pairs beyond antiblockade

“…The possibility to all-optical detection of highlyexcited state population with high-precision has opened a new avenue to the investigation of different excitation facilitation mechanisms [1][2][3]. If detecting a single twolevel atom of weak driving ω < |δ| (ω denotes the excitation Rabi frequency and δ is the detuning to the upper level), the steady-state excitation probability of the upper-level can be well characterized by a Lorentzian function of detuning δ [4] P A = 4ω 2 1 + 8ω 2 + 4δ 2 (1) with the frequency unit γ.…”