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...

We demonstrate laser frequency stabilization to excited state transitions using cascade electromagnetically induced transparency. Using a room temperature Rb vapor cell as a reference, we stabilize a first diode laser to the D2 transition and a second laser to a transition from the intermediate 5P 3/2 state to a highly excited state with principal quantum number n = 19 − 70. A combined laser linewidth of 280 ± 50 kHz over a 100 µs time period is achieved. This method may be applied generally to any cascade system and allows laser stabilization to an atomic reference in the absence of a direct absorption signal.

Electrometry near a dielectric surface is performed using Rydberg electromagnetically induced transparency. The large polarizability of high-n-state Rydberg atoms gives this method extreme sensitivity. We show that dipoles produced by adsorbates on the dielectric surface produce a significant electric field that responds to an applied field with a time constant of order 1 s. For transient applied fields (with a time scale of less than 1 s) we observe good agreement with calculations based on numerical solutions of Laplace's equation using an effective dielectric constant to simulate the bulk dielectric.

We present an application of the Faraday effect to produce a narrow band atomic filter in an alkali metal vapor. In our experiment two Raman beams separated in frequency by the ground state hyperfine splitting in 87 Rb are produced using an EOM and then filtered using the Faraday effect in an isotopically pure 85 Rb thermal vapor. An experimental transmission spectra for the filter is presented along with a theoretical calculation. The performance of the filter is then demonstrated and characterized using a Fabry-Perot etalon. For a temperature of 70• C and a longitudinal magnetic field of 80 G a suppression to -18 dB is achieved, limited by the quality of the polarizers.In many atomic physics experiments one requires phase coherent laser light at frequencies separated by the ground state hyperfine splitting; examples include stimulated Raman transitions [1]; coherent population trapping [2]; Λ-system and N -system electromagnetically induced transparency (EIT) [3,4] and mesoscopic Rydberg gates [5]. Alternatively, Raman light is also produced in experiments involving Raman scattering processes [6]. In many cases the two components of the Raman light are of unequal intensity and are not spatially separated. We therefore require a filter that will separate the two frequencies into separate beams, producing two sources of light suitable for subsequent applications.A narrow band atomic filter can be realized using the Faraday effect where a longitudinal magnetic field induces a circular birefringence in the medium [7]. Atomic filters exploiting birefringence were first introduced and demonstrated byÖhman [8]. This principle was developed into the Faraday anomalous-dispersion optical filter (FADOF), which has been demonstrated in Cs [9], Rb [10,11,12] and Na [13]. Similarly, the induced-dichroism excited atomic line (IDEAL) filter, which operates without a magnetic field, has been demonstrated in K [14]. More recently, atomic filters have been produced using absorption in a thermal vapor cell [6] and velocity selective optical pumping in an atomic vapor [15]. Narrow band atomic filters have applications in free space laser communications [11], atmospheric measurements using LIDAR [13,16], ocean temperature profiling using LI-DAR [12] and the generation of narrow band quantumnoise-limited light [9]. In our experiment we use an isotopically pure cell such that we can exploit the Faraday effect in 85 Rb to filter Raman light resonant with 87 Rb. The Faraday effect is observed when a magnetic field is applied parallel to the direction of light propagation, causing initially linearly polarized light to be rotated by an angle, θ, given by:where V is the Verdet constant, B the magnitude of the applied magnetic field and L the length of the medium.The Verdet constant is dependent on the properties of the medium, the wavelength of the light and the temperature. Typical commercial Faraday isolators employ a Terbium Gallium garnet crystal with a Verdet constant of 134 Rad T −1 m −1 at 632 nm [17]. The polarization rotation is ...

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