Precision time references in space are of major importance to satellite-based fundamental science, global satellite navigation, earth observation, and satellite formation flying. Here we report on the operation of a compact, rugged, and automated optical frequency comb setup on a sounding rocket in space under microgravity. The experiment compared two clocks, one based on the optical D2 transition in Rb, and another on hyperfine splitting in Cs. This represents the first frequency comb based optical clock operation in space, which is an important milestone for future satellite-based precision metrology. Based on the approach demonstrated here, future space-based precision metrology can be improved by orders of magnitude when referencing to state-of-the-art optical clock transitions.

Space-borne frequency comb metrology

Quantum technology based on cold-atom interferometers is showing great promise for fields such as inertial sensing and fundamental physics. However, the finite free-fall time of the atoms limits the precision achievable on Earth, while in space interrogation times of many seconds will lead to unprecedented sensitivity. Here we realize simultaneous 87 Rb– 39 K interferometers capable of operating in the weightless environment produced during parabolic flight. Large vibration levels (10 A 2 g Hz A 1/2), variations in acceleration (0–1.8 g) and rotation rates (5° s A 1) onboard the aircraft present significant challenges. We demonstrate the capability of our correlated quantum system by measuring the Eotvos parameter with systematic-limited uncertainties of 1.1 Â 10 A 3 and 3.0 Â 10 A 4 during standard-and microgravity, respectively. This constitutes a fundamental test of the equivalence principle using quantum sensors in a free-falling vehicle. Our results are applicable to inertial navigation, and can be extended to the trajectory of a satellite for future space missions.

/pdf/dual-matter-wave-inertial-sensors-in-weightlessness-3yow6l0ks1.pdf

Dual matter-wave inertial sensors in weightlessness

Optical clocks operated on satellites are expected to open up new opportunities in time transfer, geodesy, fundamental physics, and satellite navigation. Here we demonstrate an important first step towards this goal: a modular, compact, optical lattice clock (OLC) system that achieves $2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ fractional uncertainty. The clock is operated with bosonic strontium and improves the performance of bosonic OLCs by a factor of 30. This has important implications for future use of bosonic OLCs in fundamental physics and metrology. We make use of the clock's metrological performance to measure, with independent clocks, the isotope shift of the $^{1}S_{0}\ensuremath{\rightarrow}^{3}P_{0}$ transitions of $^{88}\mathrm{Sr}$ and $^{87}\mathrm{Sr}$, with an uncertainty of 12 mHz. The ratio of the transition frequencies is thus determined with $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ fractional uncertainty.

/pdf/towards-an-optical-clock-for-space-compact-high-performance-8q7n99v3kn.pdf

Towards an optical clock for space: Compact, high-performance optical lattice clock based on bosonic atoms

We propose a concept for future space gravity missions using cold atom interferometers for measuring the diagonal elements of the gravity gradient tensor and the spacecraft angular velocity. The aim is to achieve better performance than previous space gravity missions due to a very low white noise spectral behavior and a very high common mode rejection, with the ultimate goals of determining the fine structures of the gravity field with higher accuracy than GOCE and detecting time-variable signals in the gravity field better than GRACE.

A spaceborne gravity gradiometer concept based on cold atom interferometers for measuring Earth's gravity field

We present a diode laser system optimized for laser cooling and atom interferometry with ultra-cold rubidium atoms aboard sounding rockets as an important milestone toward space-borne quantum sensors. Design, assembly and qualification of the system, combing micro-integrated distributed feedback (DFB) diode laser modules and free space optical bench technology, is presented in the context of the MAIUS (Matter-wave Interferometry in Microgravity) mission. This laser system, with a volume of 21 l and total mass of 27 kg, passed all qualification tests for operation on sounding rockets and is currently used in the integrated MAIUS flight system producing Bose–Einstein condensates and performing atom interferometry based on Bragg diffraction. The MAIUS payload is being prepared for launch in fall 2016. We further report on a reference laser system, comprising a rubidium stabilized DFB laser, which was operated successfully on the TEXUS 51 mission in April 2015. The system demonstrated a high level of technological maturity by remaining frequency stabilized throughout the mission including the rocket’s boost phase.

A compact and robust diode laser system for atom interferometry on a sounding rocket

In this paper, we describe the design and the main performances of the PHARAO laser source flight model. PHARAO is a laser cooled cesium clock specially designed for operation in space and the laser source is one of the main sub-systems. The flight model presented in this work is the first remote-controlled laser system designed for spaceborne cold atom manipulation. The main challenges arise from mechanical compatibility with space constraints, which impose a high level of compactness, a low electric power consumption, a wide range of operating temperature, and a vacuum environment. We describe the main functions of the laser source and give an overview of the main technologies developed for this instrument. We present some results of the qualification process. The characteristics of the laser source flight model, and their impact on the clock performances, have been verified in operational conditions.

PHARAO laser source flight model: Design and performances

CNES, LKB and SYRTE are developing a primary frequency standard, called PHARAO, which is specially designed for space applications. The clock signal is referenced on the frequency measurement of the hyperfine transition performed on a cloud of cold cesium PHARAO : LE PREMIER ETALON PRIMAIRE DE FREQUENCE, A ATOMES FROIDS, SPATIAL 3 atoms (∼1 μK). The transition is induced by an external field feeding a Ramsey cavity. In microgravity the interaction time inside the cavity can be adjusted over two orders of magnitude by changing the atomic velocity (5 cm·s−1–5 m·s−1) in order to study the ultimate performances of the clock. An engineering model has been assembled to validate the architecture of the clock. This model has been fully tested on ground for operation faults. Of course the clock performances are reduced by the effect of the gravity on the moving atoms. The main results are a frequency stability of 3.3× 10−13t−1/2. The main systematic effects have been analyzed and their frequency uncertainties contribution is 1.6 × 10−15. The clock has been compared with the primary frequency standard, the mobile fountain of SYRTE. The mean frequency shift is lower than 2 × 10−15. The mechanical and thermal space qualifications have been carried out by testing a representative mechanical model of the clock and by using refined calculations. The design of the clock has been improved and now the flight model is being assembled. The PHARAO clock is a key instrument of the European ESA space mission called ACES. This mission is dedicated to perform space-time measurements in order to test some fundamental physics aspects.

PHARAO : le premier étalon primaire de fréquence, à atomes froids, spatial

In this paper, we describe the design and the main performances of the PHARAO laser source flight model. PHARAO is a laser cooled cesium clock specially designed for operation in space and the laser source is one of the main sub-systems. The flight model presented in this work is the first remote-controlled laser system designed for spaceborne cold atom manipulation. The main challenges arise from mechanical compatibility with space constraints, which impose a high level of compactness, a low electric power consumption, a wide range of operating temperature and a vacuum environment. We describe the main functions of the laser source and give an overview of the main technologies developed for this instrument. We present some results of the qualification process. The characteristics of the laser source flight model, and their impact on the clock performances, have been verified in operational conditions.

/pdf/pharao-laser-source-flight-model-design-and-performances-33mzdlvr5f.pdf

PHARAO Laser Source Flight Model: Design and Performances

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PHARAO laser source flight model: Design and performances

PHARAO : le premier étalon primaire de fréquence, à atomes froids, spatial

PHARAO Laser Source Flight Model: Design and Performances