Hyperpolarizability effects in a Sr optical lattice clock

We report the observation of the higher order frequency shift due to the trapping field in a $^{87}$Sr optical lattice clock. We show that at the magic wavelength of the lattice, where the first order term cancels, the higher order shift will not constitute a limitation to the fractional accuracy of the clock at a level of $10^{-18}$. This result is achieved by operating the clock at very high trapping intensity up to $400$kW/cm$^2$ and by a specific study of the effect of the two two-photon transitions near the magic wavelength

An accurate optical lattice clock with 87Sr atoms

We report a frequency measurement of the 1S0-3P0 transition of 87Sr atoms in an optical lattice clock. The frequency is determined to be 429 228 004 229 879 (5) Hz with a fractional uncertainty that is comparable to state-of-the-art optical clocks with neutral atoms in free fall. Two previous measurements of this transition were found to disagree by about 2x10^{-13}, i.e. almost four times the combined error bar, instilling doubt on the potential of optical lattice clocks to perform at a high accuracy level. In perfect agreement with one of these two values, our measurement essentially dissipates this doubt

Accuracy Evaluation of an Optical Lattice Clock with Bosonic Atoms

We report the first accuracy evaluation of an optical lattice clock based on the 1S0 - 3P0 transition of an alkaline earth boson, namely 88Sr atoms. This transition has been enabled using a static coupling magnetic field. The clock frequency is determined to be 429 228 066 418 009(32) Hz. The isotopic shift between 87Sr and 88Sr is 62 188 135 Hz with fractional uncertainty 5.10^{-7}. We discuss the conditions necessary to reach a clock accuracy of 10^{-17} or less using this scheme.Comment: 3 pages, 4 figures, uses ol.sty fil

Ultra-stable clock laser system development towards space applications

International audienceThe increasing performance of optical lattice clocks has made them attractive for scientific applications in space and thus has pushed the development of their components including the interrogation lasers of the clock transitions towards being suitable for space, which amongst others requires making them more power efficient, radiation hardened, smaller, lighter as well as more mechanically stable. Here we present the development towards a space-compatible interrogation laser system for a strontium lattice clock constructed within the Space Optical Clock (SOC2) project where we have concentrated on mechanical rigidity and size. The laser reaches a fractional frequency instability of 7.9 × 10−16 at 300 ms averaging time. The laser system uses a single extended cavity diode laser that gives enough power for interrogating the atoms, frequency comparison by a frequency comb and diagnostics. It includes fibre link stabilisation to the atomic package and to the comb. The optics module containing the laser has dimensions 60 × 45 × 8 cm3; and the ultra-stable reference cavity used for frequency stabilisation with its vacuum system takes 30 × 30 × 30 cm3. The acceleration sensitivities in three orthogonal directions of the cavity are 3.6 × 10−10/g, 5.8 × 10−10/g and 3.1 × 10−10/g, where g ≈ 9.8 m/s2 is the standard gravitational acceleration

Guidelines for developing optical clocks with 10−1810^{-18} fractional frequency uncertainty

There has been tremendous progress in the performance of optical frequency standards since the first proposals to carry out precision spectroscopy on trapped, single ions in the 1970s. The estimated fractional frequency uncertainty of today's leading optical standards is currently in the $10^{-18}$ range, approximately two orders of magnitude better than that of the best caesium primary frequency standards. This exceptional accuracy and stability is resulting in a growing number of research groups developing optical clocks. While good review papers covering the topic already exist, more practical guidelines are needed as a complement. The purpose of this document is therefore to provide technical guidance for researchers starting in the field of optical clocks. The target audience includes national metrology institutes (NMIs) wanting to set up optical clocks (or subsystems thereof) and PhD students and postdocs entering the field. Another potential audience is academic groups with experience in atomic physics and atom or ion trapping, but with less experience of time and frequency metrology and optical clock requirements. These guidelines have arisen from the scope of the EMPIR project "Optical clocks with $1 imes 10^{-18}$ uncertainty" (OC18). Therefore, the examples are from European laboratories even though similar work is carried out all over the world. The goal of OC18 was to push the development of optical clocks by improving each of the necessary subsystems: ultrastable lasers, neutral-atom and single-ion traps, and interrogation techniques. This document shares the knowledge acquired by the OC18 project consortium and gives practical guidance on each of these aspects

Guidelines for developing optical clocks with 10-18 fractional frequency uncertainty

There has been tremendous progress in the performance of optical frequency standards since the first proposals to carry out precision spectroscopy on trapped, single ions in the 1970s. The estimated fractional frequency uncertainty of today's leading optical standards is currently in the 10−18 range, approximately two orders of magnitude better than that of the best caesium primary frequency standards. This exceptional accuracy and stability is resulting in a growing number of research groups developing optical clocks. While good review papers covering the topic already exist, more practical guidelines are needed as a complement. The purpose of this document is therefore to provide technical guidance for researchers starting in the field of optical clocks. The target audience includes national metrology institutes (NMIs) wanting to set up optical clocks (or subsystems thereof) and PhD students and postdocs entering the field. Another potential audience is academic groups with experience in atomic physics and atom or ion trapping, but with less experience of time and frequency metrology and optical clock requirements. These guidelines have arisen from the scope of the EMPIR project "Optical clocks with 1×10−18 uncertainty" (OC18). Therefore, the examples are from European laboratories even though similar work is carried out all over the world. The goal of OC18 was to push the development of optical clocks by improving each of the necessary subsystems: ultrastable lasers, neutral-atom and single-ion traps, and interrogation techniques. This document shares the knowledge acquired by the OC18 project consortium and gives practical guidance on each of these aspects.EU/Horizon2020/EMPIR/E

Optical clocks, a second generation of atomic frequency standards

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Introduction to frequency measurements

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Horloge à réseau optique au Strontium : une 2ème génération d'horloges à atomes froids

Atomic fountains, based on a microwave transition of Cesium or Rubidium, constitute the state of the art atomic clocks, with a relative accuracy close to 10^-16. However, at present, it appears that it will be difficult to go significantly beyond this level with this kind of device. The use of an optical transition, the other parameters being unchanged, gives hope for a 4 or 5 order of magnitude improvement of the stability and of the relative uncertainty on most systematic effects. As for motional effects on the atoms, they can be controlled on a very different manner if they are trapped in an optical lattice instead of experiencing a free ballistic flight stage, characteristic of the fountains. The keystone of this approach lies in the fact that the trap can be operated in such a way that a well chosen and weakly allowed J = 0 -> J = 0 clock transition can be set free of light shift effects. In this respect, the strontium atom is one of the most promising candidates, the 1^S_0 -> 3^P_0 transition has a natural width of 1 mHz, and several other easily accessible transitions can be used to efficiently laser cool atoms down to 10 microK. This thesis demonstrates the experimental feasibility of an optical lattice clock based on the strontium atom, and reports on a preliminary evaluation of the relative accuracy with the fermionic isotope 87^Sr, at a level of a few 10^-15.Les fontaines atomiques, basées sur une transition micro-onde du Césium ou du Rubidium, constituent l'état de l'art des horloges atomiques, avec une exactitude relative avoisinant 10^-16. Il apparaît cependant clairement aujourd'hui qu'il sera difficile de dépasser significativement ce niveau de performance avec un dispositif de ce type. L'utilisation d'une transition optique, toutes choses étant égales par ailleurs, ouvre la perspective d'une amélioration de 4 ou 5 ordres de grandeur de la stabilité et de l'incertitude relative sur la plupart des effets systématiques. Les effets liés au mouvement des atomes peuvent être, quant à eux, contrôlés d'une façon totalement différente, en les piégeant dans un réseau optique pour éviter la phase de vol balistique caractéristique des fontaines. Le point clef de cette approche réside dans le fait que les paramètres de ce piège peuvent être ajustés de façon à s'affranchir du déplacement lumineux si l'on sélectionne une transition d'horloge faiblement permise J = 0->J = 0. A cet égard, l'atome de strontium est l'un des candidats les plus prometteurs, la transition 1^S_0 -> 3^P_0 présente une largeur naturelle de 1 mHz, et plusieurs autres transitions facilement accessibles peuvent être utilisées en vue d'un refroidissement laser efficace des atomes jusqu'à une température de 10 microK. Ce manuscrit de thèse d'une part démontre la faisabilité expérimentale d'une horloge à réseau optique basée sur l'atome de strontium, et d'autre part expose une évaluation préliminaire de l'exactitude relative avec l'isotope fermionique 87^Sr, à un niveau de quelques 10^-15

Optical clocks: Towards a redefinition of the second? (the operational point of view)

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