Realization of advanced 171Yb optical lattice frequency standard

Atomic clocks constitute a fundamental tool for time and frequency metrology and their application is widespread in many technological fields. In particular, the International System of units (SI) defines the second on a microwave transition of Caesium atoms. The realization is made by clocks reaching uncertainties of few parts in 10^−16, making the second to be the quantity realized with the smallest uncertainty in the SI. However, a new generation of atomic clocks, called optical clocks, have already demonstrated to surpass Caesium standards both in accuracy and stability. The research performed during my PhD activity has been focused on the development and characterization of Ytterbium (Yb) optical lattice clocks. These systems operate with a large number of ultra-cold neutral atoms having a clock transition in the visible region of the electromagnetic spectrum. The atomic sample is trapped in an periodical optical potential called optical lattice that gives the advantage to interrogate many quantum absorbers for an extended time, with small perturbations, allowing to achieve an unprecedented stability and accuracy. The main experimental work has been carried out in the laboratories of the Istituto Nazionale di Ricerca Metrologica (INRIM) in Turin, where several atomic clocks are present including the Italian primary frequency standard, the Caesium fountain ITCsF2, and where an Yb optical lattice clock is currently being developed. This thesis describes the functioning of the system along with the full characterization of systematic effects, the complete uncertainty budget and its first absolute frequency measurement against the primary frequency standard. The clock exhibited an accuracy of 1.6 × 10^−16 and the comparison with the Cs fountain resulted in a frequency of f171Yb = 518 295 836 590 863.59(31) Hz, limited by the fountain uncertainty. This measurement is in agreement with the ytterbium frequency recommended as a secondary representation of the second in the SI and constitutes the first measurement of a Yb clock in Europe and the second one in the world against a primary frequency standard. Several upgrades have been applied after the absolute measurement. In particular, the design and realization a system capable to frequency stabilize several lasers on a single optical cavity is illustrated. This cavity has been implemented to lock the lasers used to cool and trap the atomic sample at 399, 556 and 759nm using the offset sideband locking technique, a modified version of the Pound–Drever–Hall method that gives an extended frequency tunability. The system proved to be an easy-to-use and reliable tool for the experimental activity showing a linewidth below 300 Hz at 556nm, which is the wavelength that requires the most stringent performance, and a long term drift below 20 kHz per day at 759nm. That is suitable for operating the lattice laser with a light shift uncertainty below 1 × 10−18. During my PhD I have been guest researcher at the National Institute of Standards and Technology (NIST) of Boulder, Colorado, for nine months in 2016. In these laboratories two Yb optical lattice clocks are operative. I worked on the instability measurement of a composite system exploiting the two clocks to suppress the Dick effect, called zero-dead-time (ZDT) clock, which demonstrated a fractional instability of 3 × 10−17 at 1s. The two clocks can also be operated to extend the interrogation time obtaining a spectroscopic feature after 4 s of 120(20)mHz corresponding to a quality factor Q > 4 × 10^15. I also worked on the characterization of several systematic shifts that allowed to complete the uncertainty budget of the clocks at 1.6 × 10^−18. In particular, I contributed to the characterization of lattice light shifts considering the effect of atomic sample temperature and the identification of a metrological regime called operational magic frequency where frequency shifts are insensitive to changes in trap depth

Absolute frequency measurement of the 1S0 - 3P0 transition of 171Yb

We report the absolute frequency measurement of the unperturbed transition 1S0 - 3P0 at 578 nm in 171Yb realized in an optical lattice frequency standard. The absolute frequency is measured 518 295 836 590 863.55(28) Hz relative to a cryogenic caesium fountain with a fractional uncertainty of 5.4x10-16 . This value is in agreement with the ytterbium frequency recommended as a secondary representation of the second in the International System of Units.Comment: This is an author-created, un-copyedited version of an article accepted for publication/published in Metrologia. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/1681-7575/aa4e62. It is published under a CC BY licenc

Évaluer pour mieux intervenir : évaluer les résultats et les processus pour améliorer les pratiques d’intervention auprès des familles négligentes

Certaines familles sont caractérisées par un grand niveau de vulnérabilité en raison de différents facteurs tels que l’histoire personnelle et familiale, des situations de pauvreté, d’isolement social, etc. Dans ces situations, la capacité des parents à prendre soin de leur enfant peut se révéler plutôt limitée. En Italie, dans le but de soutenir ces familles vulnérables, et celles qui sont négligentes en particulier, les interventions éducatives à domicile en faveur de l’enfant et de sa famille sont fort répandues, mais elles ont très peu fait l’objet d’évaluations scientifiques rigoureuses. Dans cet article, nous présentons les résultats d’une démarche partenariale de recherche-formation-intervention d’une durée de 12 mois impliquant 12 éducateurs et 18 familles considérées comme négligentes. L’évaluation de cette démarche a ainsi permis d’identifier les facteurs clés favorables à l’adaptation de ces familles.Some families face great vulnerability due to various factors such as personal and familiar history, poverty, social isolation, etc. In such situations, the ability of parents to take care of their children can be rather limited. In Italy, in order to support vulnerable families and more particularly neglectful ones, child -and-family educational home interventions are widespread. However, to date there has been little far-reaching evaluation of their effectiveness. This article reports the results of a joint research-training-intervention project that involved 12 educators and 18 deemed negligent families over an intervention period of 12 months. The evaluation permitted identification of the key factors fostering the adaptation of these families

Évaluer pour mieux intervenir : évaluer les résultats et les processus pour améliorer les pratiques d’intervention auprès des familles négligentes

Certaines familles sont caractérisées par un grand niveau de vulnérabilité en raison de différents facteurs tels que l’histoire personnelle et familiale, des situations de pauvreté, d’isolement social, etc. Dans ces situations, la capacité des parents à prendre soin de leur enfant peut se révéler plutôt limitée. En Italie, dans le but de soutenir ces familles vulnérables, et celles qui sont négligentes en particulier, les interventions éducatives à domicile en faveur de l’enfant et de sa famille sont fort répandues, mais elles ont très peu fait l’objet d’évaluations scientifiques rigoureuses. Dans cet article, nous présentons les résultats d’une démarche partenariale de recherche-formation-intervention d’une durée de 12 mois impliquant 12 éducateurs et 18 familles considérées comme négligentes. L’évaluation de cette démarche a ainsi permis d’identifier les facteurs clés favorables à l’adaptation de ces familles.Some families face great vulnerability due to various factors such as personal and familiar history, poverty, social isolation, etc. In such situations, the ability of parents to take care of their children can be rather limited. In Italy, in order to support vulnerable families and more particularly neglectful ones, child -and-family educational home interventions are widespread. However, to date there has been little far-reaching evaluation of their effectiveness. This article reports the results of a joint research-training-intervention project that involved 12 educators and 18 deemed negligent families over an intervention period of 12 months. The evaluation permitted identification of the key factors fostering the adaptation of these families

Multiple lasers stabilization on a single three color optical cavity

We designed and implemented a simple and robust optical system for the frequency stabilization of lasers at different wavelength, used for the cooling and trapping of atoms in a Yb optical lattice clock. We used a single ultra-stable cavity to lock the frequency of three different lasers at 399 nm, 556 nm and 759 nm exploiting the offset sideband locking technique, derived from the common Pound-Drever-Hall method. A linewidth of less than 300Hz is obtained at 556 nm with a fractional frequency stability of 3 × 10−14 at 1s. At 759 nm we measured a long term drift less than 20kHz per day, which is sufficient to keep the lattice light shift fractional uncertainty under 1 × 10−18. The system was tested by simultaneously locking the three lasers to the cavity and operating the clock without any significant reduction in number of atoms

Multiple wavelength stabilization on a single optical cavity using the offset sideband locking technique

We implemented a compact, robust, and stable device for simultaneous frequency stabilization of lasers with different wavelengths used for the cooling and trapping of Yb atoms in an optical lattice clock. The lasers at 399, 556, and 759 nm are locked to a single ultra-stable cavity using the offset sideband locking technique, a modified version of the Pound-Drever-Hall method. For the most demanding stabilization here, the 556 nm laser, this system exhibits a 300 Hz linewidth for an integration time of 80 ms. We observed a long-term drift of less than 20 kHz per day at 759 nm that is suitable for operating the lattice laser with a light shift uncertainty below 1×10-18. We successfully tested the system for operating the clock during a typical working day by simultaneously locking the three lasers to the cavity

Absolute frequency measurement of the 171Yb optical lattice clock at INRIM

We present the absolute frequency measurement of the transition 1S0 - 3P0 at 578 nm in ytterbium 171 realized in an optical lattice frequency standard relative to the cryogenic caesium fountain ITCsF2. The measurement result is 518 295 836 590 863.59(31) Hz with a relative standard uncertainty of 5.9 × 10-16. A contribution of 1.6 × 10-16 is coming from the ytterbium clock and we are working to reduce this contribution to the 1 × 10-17 level

L’éducation familiale visant à soutenir les parents et les enfants

Les articles de ce numéro thématique s'intéressent à l'éducation familiale d'après la perspective des intervenants des services sociaux, de l'éducation, de la santé et du milieu communautaire. Les recherches rapportées dans ces textes s'attardent aux contextes de la France, de l'Italie et du Québec. Ce dossier comprend également deux articles Hors thème qui portent un regard historique: pour l'un, sur un partenariat de recherche sur les familles et pour l'autre, sur les orphelinats en France et au Québec