Electromagnetically induced transparency of an interacting cold Rydberg ensemble

Abstract

We study electromagnetically induced transparency (EIT) of a weakly interacting cold Rydberg gas. We show that the onset of interactions is manifest as a depopulation of the Rydberg state and numerically model this effect by adding a density-dependent non-linear term to the optical Bloch equations. In the limit of a weak probe where the depopulation effect is negligible, we observe no evidence of interaction induced decoherence and obtain a narrow Rydberg dark resonance with a linewidth of <600 kHz, limited by the Rabi frequency of the coupling beam.PACS numbers: 03.67. Lx, 32.80.Rm, 42.50.Gy Ensembles of Rydberg atoms display fascinating manybody behavior due to their strong interactions [1]. These interactions lead to interesting cooperative effects such as superradiance [2,3,4] and dipole blockade [5,6,7,8], which may provide the basis for applications such as single-photon sources [9] and quantum gates [10,11,12]. For quantum information applications one is interested in the coherent evolution of the ensemble. Coherent excitation of Rydberg states has been achieved using adiabatic passage [13,14]. Rabi oscillations between ground and Rydberg states with dipole-dipole interactions have been observed [15,16]. Also, the coherence of a Rydberg ensemble has been measured directly using a spin echo technique [17]. In most experiments on ultracold Rydberg gases, the Rydberg atoms are detected indirectly following field ionization and subsequent detection of electrons (or ions) using a micro channel plate (MCP). However, recently we demonstrated non-destructive optical detection of Rydberg states in room temperature Rb vapor [18,19] using EIT [20,21]. The same technique was subsequently used to detect Rydberg states in a Sr atomic beam [22]. Rydberg EIT has number of potential applications, for example, a Rydberg EIT medium displays a dc electro-optic effect many orders of magnitude larger than other systems [23], and Rydberg EIT enables direct measurement of the coherence of the Rydberg ensemble.In this work we demonstrate EIT involving Rydberg states in an ultra-cold atomic sample. We show that interactions between Rydberg atoms lead to a rapid depopulation of the Rydberg state, and that the EIT spectra are extremely sensitive to small changes in the interaction strength. For example, changing the principal quantum number of the Rydberg state from n to n + 1 produces a significant change in the EIT spectrum. By using a weak probe, where the probability of populating the Rydberg state is low, we can eliminate this depopulation effect and obtain narrow Rydberg dark resonances with a linewidth of < 600 kHz, limited by the Rabi frequency of the coupling beam.The experimental setup and simplified level scheme are shown in figure 1 (a) and (b) respectively. A probe and coupling beam are combined using dichroic mirrors and counter-propagate through a cloud of laser-cooled 85 Rb atoms. The polarization of the beams are chosen to max- imize transition strengths (σ + -σ + ). The probe beam is derived from a diode laser a...

Optical non-linearity in a dynamical Rydberg gas

“…[4]. Atoms are loaded into a magneto-optical trap (MOT), reaching a peak density of ρ = 1.6 × 10 10 cm −3 .…”

“…The use of electromagnetically induced transparency (EIT) to probe cold Rydberg gases [4] provides a complementary technique to ionization for studying the properties of strongly interacting Rydberg gases [5] and opens new perspectives in non-linear optics [6]. The effect of the strong dipole-dipole interactions between Rydberg atoms on EIT is to produce a non-local optical non-linearity [7].…”

Subnatural linewidths in two-photon excited-state spectroscopy

“…Spectroscopy of excited state transitions is of growing interest for a variety of applications including the search for stable frequency references [1,2], state lifetime measurement [3], optical filtering [4], frequency up-conversion [5], multiphoton laser cooling [6], as well as Rydberg gases [7,8] and their application to electro-optics [9][10][11] and nonlinear optics [12]. Twophoton excited state spectroscopy can be achieved without significant transfer of population out of the ground state using electromagnetically induced transparency (EIT) [13] in the ladder configuration [14].…”

Microwave dressing of Rydberg dark states

“…For example, Rydberg EIT has been used to modify the frequency of light [11], study interactions in cold Rydberg gases [12,13,14] and probe electric fields inside vapour cells [15,16] and close to surfaces [17]. A feature of Rydberg states is the large dipole moment to nearby states which scales with the square of the principal quantum number, n 2 .…”