We present an experimental measurement of the cooperative Lamb shift and the Lorentz shift using a nanothickness atomic vapor layer with tunable thickness and atomic density. The cooperative Lamb shift arises due to the exchange of virtual photons between identical atoms. The interference between the forward and backward propagating virtual fields is confirmed by the thickness dependence of the shift, which has a spatial frequency equal to twice that of the optical field. The demonstration of cooperative interactions in an easily scalable system opens the door to a new domain for nonlinear optics.

We study a gas of ultracold atoms resonantly driven into a strongly interacting Rydberg state. The long distance behavior of the spatially frozen effective pseudospin system is determined by a set of dimensionless parameters, and we find that the experimental data exhibits algebraic scaling laws for the excitation dynamics and the saturation of Rydberg excitation. Mean field calculations as well as numerical simulations provide an excellent agreement with the experimental finding, and are evidence for universality in a strongly interacting frozen Rydberg gas.Comment: 6 pages, 3 figure

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 ...

We report on the first observation of electromagnetically induced transparency (EIT) in a ladder system in the presence of a buffer gas. In particular we study the 5S 1/2 -5P 3/2 -5D 5/2 transition in thermal rubidium vapor with a neon buffer gas at a pressure of 6 Torr. In contrast to the line narrowing effect of buffer gas on Λ-systems we show that the presence of the buffer gas leads to an additional broadening of (32 ± 5) MHz, which suggests a cross section for Rb(5D 5/2 )-Ne of σ−19 m 2 . However, in the limit where the coupling Rabi frequency is larger than the collisional dephasing a strong transparency feature can still be observed.The effect of electromagnetically induced transparency (EIT) arises due to coherence in three-level systems as first described in [1,2], and experimentally demonstrated in [3]. Typically, the three-level system consists of two long-lived states (|1 and |3 ), which are coupled by two lasers, labelled probe and coupling with Rabi frequencies Ω p and Ω c (> Ω p ), to a radiative state |2 with a lifetime, 1/Γ 2 . If the two lasers are resonant, i.e., the detunings δ 12 = δ 23 = 0, the imaginary part of the onephoton coherence Im(ρ 12 ) and the absorption coefficient α ∝ Im(ρ 12 ) are zero, rendering the medium fully transparent [4]. For Ω p < Γ 2 the transparency is caused by a destructive interference of the excitation amplitudes into the intermediate state |2 , which results in the occupation of a dark state |∅ |1 with no contribution from the radiative state. The width of the transparency window is determined by the dephasing rate between states |1 and |3 , Γ 13 , and can be much narrower than the natural linewidth, Γ 13 < Γ 2 . For photon storage applications one is interested in reducing the dephasing rate as the narrow resonance results in a large group index [5] and enables long photon storage times [6]. For thermal atoms, the dephasing rate can be reduced by using the hyperfine ground states as the long lived states forming a Λ-system, and a buffer gas to increase the interaction time with the laser beams [7][8][9].Another topic of interest is the ladder or cascade system where |3 is a higher energy excited state [10][11][12]. For example, if state |3 is a Rydberg state [13], this opens interesting possibilities for quantum information [14][15][16] and electrometry [17,18]. In the ladder system the dephasing rate is typically larger than for Λ-systems due to the spontaneous decay of level |3 . Otherwise, EIT in Λ and ladder systems show generally similar properties. However, the addition of a buffer gas changes this behavior dramatically. In Λ-systems the dephasing of * Electronic address: u.m.krohn@durham.ac.uk the ground state coherences due to the collisions with the buffer gas is negligible and, instead the increased transient time due to collisional diffusion allows an extremely narrow linewidth to be observed [7]. In contrast, for cascade systems the collisional dephasing due to the buffer gas becomes the dominant line broadening mechanism and it is predicted that th...