Phases and relativity in atomic gravimetry

The phase observable measured by an atomic gravimeter built up on stimulated Raman transitions is discussed in a fully relativistic context. It is written in terms of laser phases which are invariant under relativistic gauge transformations. The dephasing is the sum of light and atomic contributions which are connected to one another through their interplay with conservation laws at the interaction vertices. In the case of a closed geometry, a compact form of the dephasing is written in terms of a Legendre transform of the laser phases. These general expressions are illustrated by discussing two techniques used for compensating the Doppler shift, one corresponding to chirped frequencies and the other one to ramped variations.Comment: 7 pages, 1 figur

Theoretical Analysis of a Large Momentum Beamsplitter using Bloch Oscillations

In this paper, we present the implementation of Bloch oscillations in an atomic interferometer to increase the separation of the two interfering paths. A numerical model, in very good agreement with the experiment, is developed. The contrast of the interferometer and its sensitivity to phase fluctuations and to intensity fluctuations are also calculated. We demonstrate that the sensitivity to phase fluctuations can be significantly reduced by using a suitable arrangement of Bloch oscillations pulses

Highly multimode memory in a crystal

We experimentally demonstrate the storage of 1060 temporal modes onto a thulium-doped crystal using an atomic frequency comb (AFC). The comb covers 0.93 GHz defining the storage bandwidth. As compared to previous AFC preparation methods (pulse sequences i.e. amplitude modulation), we only use frequency modulation to produce the desired optical pumping spectrum. To ensure an accurate spectrally selective optical pumping, the frequency modulated laser is self-locked on the atomic comb. Our approach is general and should be applicable to a wide range of rare-earth doped material in the context of multimode quantum memory

Spectral phase encoding for data storage and addressing

We propose to use a broad-bandwidth laser source for storing and retrieving multiple holograms in a photorefractive material. Each storage address is defined by a specific spectral encoding of the reference beam. The validity of the spectral encoding method is tested in a preliminary experiment

Spin coherence lifetime extension in Tm3+^{3+}:YAG through dynamical decoupling

We report on spin coherence lifetime extension on Tm$^{3+}$:YAG obtained through dynamically decoupling the thulium spins from their magnetic environment. The coherence lifetime reached with a Carr-Purcell-Meiboom-Gill sequence revealed a 450-fold extension [$\sim$$(230 \pm 30)$ ms] with respect to previously measured values. Comparison to a simple theoretical model allowed us to estimate the correlation time of the fluctuations of the ground level transition frequency to $(172 \pm 30)$ $\mu$s at 1.7 K. For attaining efficient decoupling sequences, we developed a strategy inspired by the \emph{zero-first-order Zeeman} effect to minimize the large inhomogeneous broadening of the ground level spin transition.Comment: 10 pages, 7 figure

Investigation of elastic and depolarizing collisions in strontium using broadband stimulated photon echoes

Elastic and depolarizing collisions between excited strontium (5s 5p 3P1) and noble gases are investigated in a broadband stimulated photon echo (SPE) experiment. The stimulated photon echo signal produced under broadband (incoherent) excitation is calculated in the weak field regime both for correlated and for uncorrelated pulses using a simple statistical model for the light field. The relaxation of the echo signal due to elastic collisions is considered and the complete development of the corresponding propagator is derived. The collisional velocity changes concerning the total population and the alignment are compared precisely in the SPE experiment and the corresponding relaxation rates are measured. A simple long-range Van der Waals potential accounts for population scattering data ; total elastic scattering cross sections are deduced from the comparison of experiment and calculation (σelAr = 583(27) Å2; σ elHe = 190(6) Å2). The collisional model is extended for light perturbers to include both the small angle classical scattering region and the diffractive scattering region. Total rates for destruction of alignment are measured in an auxiliary photon echo experiment (σ (2)He = 91 (4) Å2; ; σ(2) Ne = 102 (14) A2 ; σ(2)Ar = 267 (13 ) Å2 ; σ(2)Kr = 329 (21) Å2 ; σ(2)Xc = 370 (13) Å2). SPE data for depolarization are compared with a calculation based upon a long-range anisotropic model potential.Les collisions élastiques et les collisions dépolarisantes entre le strontium excité (5s 5p 3P1) et les gaz rares sont étudiées dans une expérience d'échos de photons stimulés avec excitation en bande large. Le signal d'écho de photon stimulé produit par une excitation en lumière spectralement large (lumière incohérente) est calculé en régime de champs faibles pour des impulsions corrélées ainsi que pour des impulsions non corrélées, en utilisant un modèle statistique simple pour le champ lumineux. La relaxation du signal d'écho produite par les collisions élastiques est prise en compte et le développement complet du propagateur correspondant est obtenu. Les changements de vitesse collisionnels affectant la population totale et ceux affectant l'alignement sont comparés dans l' expérience d' écho et les taux de relaxation correspondants sont mesurés. Un potentiel à longue portée du type Van der Waals permet de rendre compte de la diffusion élastique observée ; les sections efficaces totales de diffusion élastique sont déduites de la confrontation entre le modèle théorique et les résultats expérimentaux (σ elAr = 583 (27) Å2 ; σelHe = 190 (6) Å2). Dans le cas des perturbateurs légers le modèle collisionnel est complété pour tenir compte aussi bien de la région de diffusion classique à petit angle que de la région de diffusion diffractive. Les sections efficaces de destruction de l'alignement sont mesurées dans une expérience auxiliaire (σ(2)He = 91 (4) Å 2 ; σ(2)Ne = 102(14)Å2; σ (2)Ar = 267 (13) Å2 ; σ(2) Kr = 329 (21) Å2 ; σ(2)Xe = 370 (13) Å2). Les résultats expérimentaux obtenus pour la dépolarisation en échos de photon stimulés sont comparés à un calcul reposant sur l'utilisation d'un modèle de potentiel anisotrope à longue portée

Time-encoded spatial routing in a photorefractive crystal

The spatial routing of a temporally encoded stream of optical pulses is experimentally demonstrated. The holograms that link the temporally shaped addresses to the def lection directions are engraved in a photorefractive crystal. © 1996 Optical Society of America After the holography concept was clearly extended from the space to the time domain, 1 it appeared difficult to cope experimentally with the fast f low of short signals that represents the restored image of a temporal hologram. For instance, when such a hologram is engraved in a persistent spectral-holeburning material embedded in an amorphous material, the retrieved temporal recording can include .1000 subpicosecond pulses, which are sequentially emitted at a rate greater than 1 Tbit͞s. Fast optical gating techniques were necessary for sampling the temporal structure of the signal f low, 2,3 but they were not appropriate for simultaneously analyzing a spatial image. Only recently was a fast stream of two-dimensional spatial images successfully stored and retrieved within the frame of space and time holography. Recently 9 a scheme was proposed ''to direct temporally structured optical signals originally propagating along a common direction into different and distinct output directions according to the precise temporal waveform encoded onto each signal.'' A detailed explanation of the process, making use of holograms engraved in frequency-selective materials, is given in Ref. 9. However, it has been suggested that the same routing process could be implemented in materials that possess no intrinsic frequency selectivity. Here we use a nonfrequency-selective photorefractive crystal to demonstrate experimentally the routing of data in temporally encoded spatial directions. Also, we show that, despite the subpicosecond scale of the address code, long-duration pulses can be processed in such a material, if their coherence time is short enough to match the time-scale requirements of the router. The storage of a temporal structure in a threedimensional holographic material relies on time -space conversion whereK k 2 2k 1 . The interference pattern is engraved in the crystal as a space-dependent variation of the refractive index, which leads to a Bragg grating of vector 2pnK͞v. In the counterpropagating conf iguration, the grating period is close to l͞2. Let E 2d ͑t͒ be a brief pulse that peaks at t 0. The time integral expresses the sampling analysis of the temporal shape E 1a ͑t͒ through the gate E 2d . The gate location, t K ? r͞v, is scanned as a function of the spatial position along directionK; i.e., the temporal shape E 1a ͑t͒ is recorded as the spatial envelope E 1a ͑K ? r͞v͒ of the Bragg grating. An entire address pulse of duration T can be recorded if its spatial extent vT ͞2 is smaller than the length of the engraved interference pattern. In an exact collinear configuration, the sample thickness L limits the address duration to 2L͞v. Storage is still possible when the waves depart from collinear propagation. Then the condition v͓p 2 ͑k 1 ,k 2 ͔͒T , 2d expresses the trade-off among the maximum object duration T , the collinear propagation angular defect p 2 ͑k 1 ,k 2 ͒, and the beam diameter d. After the programming, the crystal is illuminated by a plane-wave input beam of unit wave vectork 3 k 1

Observation of 0π-pulse formation with incoherent light

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Interaction of three-level atoms with stochastic fields

Three broadband laser pulses are used to drive transitions between three levels in Sr vapor. A four-wave mixing signal is monitored as a function of the delay time $t_{12}$ between two of the pulses. For sufficiently strong fields, it is found that the signal, as a function of $t_{12}$, can possess a dip or a spike which is narrower than the correlation time of the radiation fields. A theoretical interpretation of the results is presented in terms of the so-called dark resonance