Two-Way Optical Frequency Comparisons Over 100km Telecommunication Network Fibers

By using two-way frequency transfer, we demonstrate ultra-high resolution comparison of optical frequencies over a telecommunication fiber link of 100 km operating simultaneously digital data transfer. We first propose and experiment a bi-directional scheme using a single fiber. We show that the relative stability at 1 s integration time is 7 10^18 and scales down to 5 10^21. The same level of performance is reached when an optical link is implemented with an active compensation of the fiber noise. We also implement a real-time two-way frequency comparison over a uni-directional telecommunication network using a pair of parallel fibers. The relative frequency stability is 10^15 at 1 s integration time and reaches 2 10^17 at 40 000 s. The fractional uncertainty of the frequency comparisons was evaluated for the best case to 2 10^20. These results open the way to accurate and high resolution frequency comparison of optical clocks over intercontinental fiber networks

Agile low phase noise radio-frequency sine wave generator applied to experiments on ultracold atoms

We report on the frequency performance of a low cost (~500$) radio-frequency sine wave generator, using direct digital synthesis (DDS) and a field-programmable gate array (FPGA). The output frequency of the device may be changed dynamically to any arbitrary value ranging from DC to 10 MHz without any phase slip. Sampling effects are substantially reduced by a high sample rate, up to 1 MHz, and by a large memory length, more than 2.10^5 samples. By using a low noise external oscillator to clock the DDS, we demonstrate a phase noise as low as that of the master clock, that is at the level of -113 dB.rad^2/Hz at 1 Hz from the carrier for an output frequency of 3.75 MHz. The device is successfully used to confine an ultracold atomic cloud of rubidium 87 in a RF-based trap, and there is no extra heating from the RF source.Comment: 10 pages, 6 figure

Trapping and cooling of rf-dressed atoms in a quadrupole magnetic field

6 pages, 6 figures; to appear in J. Phys. BInternational audienceWe observe the spontaneous evaporation of atoms confined in a bubble-like rf-dressed trap (Zobay and Garraway, 2001). The atoms are confined in a quadrupole magnetic trap and are dressed by a linearly polarized rf field. The evaporation is related to the presence of holes in the trap, at the positions where the rf coupling vanishes, due to its vectorial character. The final temperature results from a competition between residual heating and evaporation efficiency, which is controlled via the height of the holes with respect to the bottom of the trap. The experimental data are modeled by a Monte-Carlo simulation predicting a small increase in phase space density limited by the heating rate. This increase was within the phase space density determination uncertainty of the experiment

Source laser intense pour le refroidissement du 87Rb par doublement de fréquence d'un laser fibré télécom

to appear in EPJ-ST; COLOQ11 ProceedingsWe built a frequency-doubled laser for 87Rb laser cooling, from a Telecom fiber laser. Thanks to intense technological development, telecom fiber lasers exhibit outstanding properties regarding relative intensity noise and modulation bandwidth. The enhanced doubling efficiency of periodically poled crystals allowed to obtain up to 1.8 W at 780 nm from 10 W at 1560 nm, with a simple pass configuration in a 50-mm long crystal of ppLN:MgO. This technique can also be applied at the wavelength of potassium (767 nm) (Bourdel, 2009) and could be of great interest for the realization of dipole traps

Influence of the Radio-Frequency source properties on RF-based atom traps

We discuss the quality required for the RF source used to trap neutral atoms in RF-dressed potentials. We illustrate this discussion with experimental results obtained on a Bose-Einstein condensation experiment with different RF sources.Comment: 5 figures, 7 page

Tackling the Limits of Optical Fiber Links

International audienceWe theoretically and experimentally investigate relevant noise processes arising in optical fiber links, which fundamentally limit their relative stability. We derive the unsuppressed delay noise for three configurations of optical links: two-way method, Sagnac interferometry, and actively compensated link, respectively designed for frequency comparison, rotation sensing, and frequency transfer. We also consider an alternative two-way setup allowing real-time frequency comparison and demonstrate its effectiveness on a proof-of-principle experiment with a 25-km fiber spool. For these three configurations, we analyze the noise arising from uncommon fiber paths in the interferometric ensemble and design optimized interferometers. We demonstrate interferometers with very low temperature sensitivity of respectively -2.2, -0.03 and 1 fs/K. We use one of these optimized interferometers on a long haul compensated fiber link of 540 km. We obtain a relative frequency stability of 3x10^-20 after 10,000 s of integration time

Etude du refroidissement laser en cellule : contribution au développement d´une horloge atomique miniature à Cs133

Contact à l´Observatoire : Dr. Stephane Guerandel [email protected] aim of the Horace project is the realisation of on-board high frequency performance and compact atomic clocks thanks to cold Cs atoms. In this thesis, we first discuss the original operation of Horace, where all interactions are applied in the micro-wave cavity (cooling, interrogation and detection), according to a pure temporal scheme. We show that the relative frequency stability can be <1.10^(-12)\tau^(-1/2), depending on one hand on the cooling features, as the atomic cloud size and the capture rate, and on the other hand on the frequency performances of the local oscillator at Fourier frequency of a few 10 Hz (aliasing effect). Detection schemes by fluorescence (population) and radiation damping (coherences) are described and discussed. The second part of the thesis depicts a Doppler model in a reflective or diffusive cell, on the basis of the study of the mean laser field in the cell. Then we show that the 3D speckle pattern allows Sisyphus cooling to occur. The third part of the thesis is devoted to the experimental study of sub-Doppler cooling in a optically polished reflective spherical micro-wave cavity, used as a cell. The study demonstrates that more than 3.10^(7) cold atoms are cooled in the 3D speckle light wells. Thermalization times ~30-fold longer than in a Lin per Lin configuration were observed, as predicted by theory. Time-of-flight measurements revealed temperatures as low as ~ 2 microK. The last part of the thesis describes the realisation and the tuning of a spherical microwave cavity, and the main relative frequency shifts expected in the accuracy budget of Horace. Namely this is the phase shift due to the micro-wave switch and the collisional relative frequency shift, both expected at a few 10^(-13) level.L'objectif du projet HORACE est la réalisation d'horloges compactes embarquées de haute performance en fréquence à l'aide d'atomes froids de Cs. Dans ce mémoire, on discute d'abord le mode de fonctionnement original d'HORACE où toutes les interactions appliquées aux atomes de Cs133 ont lieu dans la cavité micro-onde (refroidissement, interrogation, détection), selon une séquence purement temporelle. On montre que la stabilité relative de fréquence peut être <1.10^(-12)\tau^(-1/2), et dépendra des caractéristiques du refroidissement, comme la taille du nuage et le taux de capture, et des performances en fréquence de l'oscillateur local à des fréquences de Fourier de qq. 10 Hz (effet de repliement de spectre). Les méthodes de détection par fluorescence (populations) et par "radiation damping" (cohérences) sont décrits et discutés. La deuxième partie du mémoire présente un modèle de refroidissement Doppler dans une cellule réfléchissante ou diffusante, basé sur une étude du champ laser moyen dans la cellule. On montre alors que la figure de tavelure 3D permet des mécanismes de refroidissement Sisyphe. La troisième partie du mémoire est consacrée à l'étude expérimentale du refroidissement subDoppler dans une cavité micro-onde sphérique polie au niveau optique utilisée comme cellule. L'étude démontre que plus de 3.10^(7) atomes froids sont refroidis dans les puits de potentiels lumineux de la figure de tavelure 3D. Les constantes de temps de thermalisation ~30 fois plus longs que dans une configuration Lin per Lin prédits par le modèle ont été vérifiés expérimentalement. Des températures de ~2 microK ont été mesurées par temps de vol. La dernière partie du mémoire décrit la réalisation et l'accord en fréquence de la cavité micro-onde sphérique, et les principaux déplacements relatifs de fréquence attendus dans le bilan d'exactitude d'Horace. Ces derniers sont dus au déphasage du champ micro-onde pulsé et au déplacement relatif de fréquence collisionnel entre atomes froids au niveau de quelques 10^(-13)

Linking metrology institutes in Europe by optical fibers

International audienc