Rabi Oscillations and Excitation Trapping in the Coherent Excitation of a Mesoscopic Frozen Rydberg Gas

Abstract

We demonstrate the coherent excitation of a mesoscopic ensemble of about 100 ultracold atoms to Rydberg states by driving Rabi oscillations from the atomic ground state. We employ a dedicated beam shaping and optical pumping scheme to compensate for the small transition matrix element. We study the excitation in a weakly interacting regime and in the regime of strong interactions. When increasing the interaction strength by pair state resonances we observe an increased excitation rate through coupling to high angular momentum states. This effect is in contrast to the proposed and previously observed interaction-induced suppression of excitation, the so-called dipole blockade.PACS numbers: 03.65. Yz, 32.80.Pj, 32.80.Rm, 34.20.Cf, 34.60.+z Rydberg atoms, with their rich internal structure, have been in the focus of atomic physics for more than a century [1]. In the last decade Rydberg physics were extended to laser-cooled atomic gases which allowed the study of a frozen system with controllable, strong interactions and negligible thermal contributions. This has opened a wide field in both experiment and theory covering such diverse areas as resonant energy transfer [2,3], plasma formation [4,5], exotic molecules [6,7], and quantum random walks [8,9]. In addition, these frozen Rydberg systems have been proposed as a possible candidate for quantum information processing [10,11]. However, the coherent excitation of Rydberg atoms, an important prerequisite for quantum information protocols, has proven a challenging task. While Rabi oscillations between different Rydberg states have been demonstrated and thoroughly analyzed before [12], Rabi oscillations between the ground state and Rydberg states of atoms have not been observed directly so far, mainly owing to the small transition matrix element.In this Letter we report on the experimental realization and observation of Rabi oscillations between the ground and Rydberg states of ultracold atoms. We demonstrate how strong interatomic interactions influence the coherent excitation of a mesoscopic cloud of atoms. We show that an interaction-induced coupling to a larger number of internal states can be used to trap the excitation. Employed in a controlled way, this effect offers future applications in the experimental realization of quantum random walks with exciton trapping [9].Our experiments are performed with a magneto-optical trap (MOT) of about 10 7 87 Rb atoms at densities of 10 10 cm −3 and temperatures below 100 µK. Rydberg excitation is achieved with two counterpropagating laser beams at 780 nm and 480 nm (see Fig. 1). The laser at 780 nm is collimated to a waist of 1.1 mm ensuring a constant Rabi frequency of 2π × 55 MHz over the excitation volume as determined from Autler-Townes splittings [13]. The laser at 480 nm is referenced to a temperature stabilized Zerodur-resonator and its beam is shaped with a diffractive optical element that produces a flattop beam profile which is characterized with an adapted CCD camera with a spatial resolution of 5.6 µm. The m...

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Collective Rydberg excitations of an atomic gas confined in a ring lattice

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Ultrafast laser-driven Rabi oscillations of a trapped atomic vapor

“…However, the spatial extent of the laser beam over the laser-atom interaction region inevitably causes spatial average effect that often leads to vanishing of the oscillatory behavior. To overcome this problem, homogenizing the spatial profile of laser beams [22,23] and * Electronic address: jwahn@kaist.ac.kr adapting chirped laser interaction [24] have been considered. This paper aims quantitative analysis of spatially averaged Rabi oscillation.…”