Generation of high-purity low-temperature samples of K 39 for applications in metrology

We present an all optical technique to prepare a sample of $^{39}$K in a magnetically-insensitive state with 95\% purity while maintaining a temperature of 6 $\mu$K. This versatile preparation scheme is particularly well suited to performing matter-wave interferometry with species exhibiting closely-separated hyperfine levels, such as the isotopes of lithium and potassium, and opens new possibilities for metrology with these atoms. We demonstrate the feasibility of such measurements by realizing an atomic gravimeter and a Ramsey-type spectrometer, both of which exhibit a state-of-the-art sensitivity for cold potassium.Comment: 6 pages + references, 4 figures, accepted for publication in PR

Correlative methods for dual-species quantum tests of the weak equivalence principle

International audienceMatter-wave interferometers utilizing different isotopes or chemical elements intrinsically have different sensitivities, and the analysis tools available until now are insufficient for accurately estimating the atomic phase difference under many experimental conditions. In this work, we describe and demonstrate two new methods for extracting the differential phase between dual-species atom interferometers for precise tests of the weak equivalence principle (WEP). The first method is a generalized Bayesian analysis, which uses knowledge of the system noise to estimate the differential phase based on a statistical model. The second method utilizes a mechanical accelerometer to reconstruct single-sensor interference fringes based on measurements of the vibration-induced phase. An improved ellipse-fitting algorithm is also implemented as a third method for comparison. These analysis tools are investigated using both numerical simulations and experimental data from simultaneous 87 Rb and 39 K interferometers, and both new techniques are shown to produce bias-free estimates of the differential phase. We also report observations of phase correlations between atom interferometers composed of different chemical species. This correlation enables us to reject common-mode vibration noise by a factor of 730, and to make preliminary tests of the WEP with a sensitivity of 1.6 10 6 × − per measurement with an interrogation time of T = 10 ms. We study the level of vibration rejection by varying the temporal overlap between interferometers in a symmetric timing sequence. Finally, we discuss the limitations of the new analysis methods for future applications of differential atom interferometry

Efficient 2D molasses cooling of a cesium beam using a blue detuned top-hat beam

International audienceWe have performed a 2D blue detuned Sisyphus collimation of a cesium beam. Compared to a red detuned Doppler transverse molasses cooling, the setup was found very advantageous because of its faster cooling time allowing a short (1 cm) cooling length and thus finally a denser atomic beam. A fibered laser was developed delivering up to 500 mW fiber coupled optical power. A 2D collimation was realized but this can be done only if the two cooling zones were not overlapping. A beam density enhancement of more than 10 was observed. We found that a simple top-hat beam was more efficient than a Gaussian one. Similar cooling applies to other atom species and leads to a simple method to produce bright collimated atomic beams

Watt-level green random laser at 532 nm by SHG of a Yb-doped fiber laser

We have developed a Watt-level random laser at 532 nm. The laser is based on a 1064 nm random distributed ytterbium-gain assisted fiber laser seed with a 0.35 nm line-width 900mW polarized output power. A study for the optimal length of the random distributed mirror was carried out. An ytterbium-doped fiber master oscillator power amplifier architecture is used to amplify the random seeder laser without additional spectral broadening up to 20 W. By using a periodically poled lithium niobate (PPLN) crystal in a single pass configuration we generate in excess of 1 W random laser at 532 nm by second harmonic generation with an efficiency of 9 %. The green random laser exhibits an instability 70 dB, 0.1 nm linewidth and excellent beam quality. Random distributed fiber lasers (RDFLs) based on distributed Rayleigh scattering, have been thoroughly investigated due to their high performances and unique features [1]. Where traditional laser schemes are based in resonant cavities for feedback generation, RDFLs use the Rayleigh scattering of a long fiber as distributed mirror, generating a modeless-behavior laser [2,3]. The research in this field has led to the generation of ultra-high power RDFLs from hundreds of Watts [4] to kWs [5,6], narrower linewidth RDFLs up to sub-gigahertz [7], polarized output RDFLs [8-10], tunable RDFLs [11-13] and pulsed generation [14,15]. Gain in RDFLs can be generated from Raman scattering [2,16], by rare earth-doped fibers [12,13] or a hybrid of both [17]. However, to date random lasers in the visible based on second harmonic generation (SHG) of RDFLs have been only reported in [18] with the generation of 110 mw at 654nm in a magnesium periodically poled lithium niobate (MgPPLN) crystal. In this letter, we report for the first time, to the best of our knowledge, a Watt-level visible random laser at 532 nm based on SHG of a RDFL, with a polarized output power in excess of 1W, instability 70 dB and excellent beam quality. The RDFL is based on a half open-cavity setup assisted by a 3m-long Yb-doped double-clad fiber as gain medium (see Fig. 1). The core and clad radii of the fiber are respectively 10 and 130 m, and its clad absorption is 4.6 dB/m at 976 nm. The Yb-fiber is forward-pumped through a multi-mode (MM) combiner with a 9W multimode laser diode (LD) at 976nm. Forward pumping has been previously reported as more efficient in Yb-gain assisted RDFL [19]. The wavelength selection is carried out by a high-reflective (99.85%) fiber Bragg grating (FBG) centered at 1064.39 nm and with a 0.57 nm bandwidth. The distributed mirror is based on single-mode fiber (SMF28). Although this fiber operates in multimode regime at 1064 nm, the splice with the 1060 fiber at the output-isolator filters the high order modes. Moreover, the SMF core radius (∼9 m) is comparable to the Yb-fiber one, reducing the losses in the splice. A pump power stripper was used before the SMF fiber in order to remove the residual pump. Fig. 1. Schematic of the 532nm random laser. (RDFL: Random Distributed Fiber Laser, MO: Master Oscillator, PA: Power Amplifier, SHG: Second Harmonic Generation, PM ISO: Polarization Maintaining Isolator) To optimize the length of the distributed mirror, we carried out measurements for different SMF lengths from 1.5Km to 3Km. Figure 2 shows the spectra and the output power before the isolator for the different SMF lengths. As expected, Raman scattering becomes significant for longer fibers, starting to be critical for lengths over 3Km. Moreover, the high attenuation of SMF28 at 1064 nm (∼1.5 dB/Km) reduce the efficiency, making shorter fibers more attractive. However, the key-point for the distributed mirror length selection was determined by the random laser behavior. RDFL dynamics are less investigated in rare-earth doped-fiber gain assisted systems than in the based on Raman gain. In order to contribute to the understanding of this class of laser, we carried out a consistent study of the RDF

Studies of general relativity with quantum sensors

We present two projects aiming to probe key aspects of the theory of General Relativity with high-precision quantum sensors. These projects use cold-atom interferometry with the aim of measuring gravitational waves and testing the equivalence principle. To detect gravitational waves, a large multi-sensor demonstrator is currently under construction that will exploit correlations between three atom interferometers spread along a 200 m optical cavity. Similarly, a test of the weak equivalence principle is currently underway using a compact and mobile dual-species interferometer, which will serve as a prototype for future high-precision tests onboard an orbiting satellite. We present recent results and improvements related to both projects

Studies of general relativity with quantum sensors

We present two projects aiming to probe key aspects of the theory of General Relativity with high-precision quantum sensors. These projects use cold-atom interferometry with the aim of measuring gravitational waves and testing the equivalence principle. To detect gravitational waves, a large multi-sensor demonstrator is currently under construction that will exploit correlations between three atom interferometers spread along a 200 m optical cavity. Similarly, a test of the weak equivalence principle is currently underway using a compact and mobile dual-species interferometer, which will serve as a prototype for future high-precision tests onboard an orbiting satellite. We present recent results and improvements related to both projects

Studies of general relativity with quantum sensors

We present two projects aiming to probe key aspects of the theory of General Relativity with high-precision quantum sensors. These projects use cold-atom interferometry with the aim of measuring gravitational waves and testing the equivalence principle. To detect gravitational waves, a large multi-sensor demonstrator is currently under construction that will exploit correlations between three atom interferometers spread along a 200 m optical cavity. Similarly, a test of the weak equivalence principle is currently underway using a compact and mobile dual-species interferometer, which will serve as a prototype for future high-precision tests onboard an orbiting satellite. We present recent results and improvements related to both projects

The NEWTON-g Gravity Imager: Toward New Paradigms for Terrain Gravimetry

Knowledge of the spatio-temporal changes in the characteristics and distribution of subsurface fluids is key to properly addressing important societal issues, including: sustainable management of energy resources (e.g., hydrocarbons and geothermal energy), management of water resources, and assessment of hazard (e.g., volcanic eruptions). Gravimetry is highly attractive because it can detect changes in subsurface mass, thus providing a window into processes that involve deep fluids. However, high cost and operating features associated with current instrumentation seriously limits the practical field use of this geophysical method. The NEWTON-g project proposes a radical change of paradigm for gravimetry through the development of a field-compatible measuring system (the gravity imager), able to real-time monitor the evolution of the subsurface mass changes. This system includes an array of low-costs microelectromechanical systems-based relative gravimeters, anchored on an absolute quantum gravimeter. It will provide imaging of gravity changes, associated with variations in subsurface fluid properties, with unparalleled spatio-temporal resolution. During the final ∼2 years of NEWTON-g, the gravity imager will be field tested in the summit of Mt. Etna volcano (Italy), where frequent gravity fluctuations, easy access to the active structures and the presence of a multiparameter monitoring system (including traditional gravimeters) ensure an excellent natural laboratory for testing the new tools. Insights from the gravity imager will be used to i) improve our knowledge of the cause-effect relationships between volcanic processes and gravity changes observable at the surface and ii) develop strategies to best incorporate the gravity data into hazards assessments and mitigation plans. A successful implementation of NEWTON-g will open new doors for geophysical exploration