Atom interferometry is a technology that allows measurements to be performed with extreme precision and accuracy. It has been applied to the measurement of several physical quantities, covering inertial quantities, atomic polarizations and fundamental physical constants, such as the Newtonian gravitational constant G and the fine structure constant α. For the next decade, research in atomic interferometry has set itself major challenges such as the detection of gravitational waves in a frequency range inaccessible to optical interferometers. For that a gain in sensitivity of 3 to 4 orders of magnitude compared to the state of the art is required. The TONICS project aims at bringing together the competences of two teams from LKB and SYRTE to overcome the limits to the accuracy and sensitivity of atomic interferometers. In particular, the effects related to the distortion of the intensity profile of the laser beams. We will work jointly to implement reliable and robust methods to improve the accuracy of our state-of-the-art gravity and atomic recoil measurements. This step is essential to exploit and validate the benefit of novel methods advocated to realize ultra sensitive interferometers, such as large momentum atomic beam splitters (LMT) at high orders and quantum engineering protocols such as spin compression to surpass the standard quantum limit. The TONICS project is based on three parts. 1/ The development of new robust experimental tools to reduce and control the effect of optical aberrations. For this, the SYRTE team will work on designing collimators with high optical quality and the LKB team will study different laser cooling schemes to provide an experimental protocol for producing a dense source of ultra-cold atoms in a cycle time of the order of a second. In parallel, we will work on the improvement of our two experimental set-ups to improve their sensitivity to exploit fully the benefits of these two ingredients. 2/ The development of a common library for the numerical modeling and simulation of the physical mechanisms at the origin of the systematic effects that limit the accuracy of our measurements. This will require cross-testing of both experiments and will allow a reliable evaluation of the systematic biases. This sequence of work will require very frequent exchanges which will probably be facilitated by the recruitment of a common PhD student and the creation of a common website. 3/ Optimization of the coherence of the large momentum beam splitters based on a combination of the double Raman diffraction technique developed by the SYRTE team and the Bloch oscillation technique in an accelerated optical lattice, which remain the area of expertise of the LKB team. The study of a symmetric atomic interferometer using these LMTs will enable us to evaluate its performance. Our objective is to demonstrate a contrast higher than 30% with a separation of 200 ħk. We are aiming at performances that surpass the state of the art. The goal of the SYRTE team is an absolute gravity measurement with an accuracy of less than 10-8 m.s-2 and a long-term stability better than 10-10 m.s-2. A continuous, absolute gravity meter with long-term stability of this level will meet the needs of the geophysical community that are not covered by existing technologies. The objective of the LKB team is to measure the recoil velocity of the two rubidium isotopes with a relative uncertainty of a few 10-11. This should validate the recent determination of the fine-structure constant and/or will explain the significant discrepancy with the value deduced from the Cs recoil measurement. This level of uncertainty is also required to be able to observe on the electron, a possible effect that could be behind the persistent discrepancy between the theoretical and experimental values of the muon's magnetic moment anomalous.

The GRADUS project aims at developing a novel type of gravity sensors based on atom interferometry, which will measure in a single device both the gravity acceleration and its gradient. These sensors will combine the appealing features of both absolute atom gravimeters and gravity gradiometers: accuracy and long term stability (perfectly known and stable scale factors, being tied to the wavelength of light beamsplitters), quantum noise limited sensitivity for the gradiometric measurements (thanks to the rejection of common mode vibration noise). Two such sensors will be studied and compared in the frame of this project, which will rely on different interferometer geometries. The first one is an industrial prototype sensor realized by MUQUANS, which is based on mature interferometer techniques (laser cooled free falling atoms and Raman beamsplitters) while the second one, under development at SYRTE, will explore more advanced - but less mature - interferometer methods: ultracold atoms launched in a fountain geometry as the interferometer sources on one hand, large momentum transfer (LMT) beamsplitters on the other hand. While comparable performances are expected in terms of gravity acceleration measurements for both instruments (which are expected to be ultimately limited by ground vibration noise), the use of these new methods will allow for a drastic improvement of the gravity gradient determination. The precise assessment of their potential for high precision measurements is essential for maximizing the efficiency of the transfer of knowledge we foresee at the end of the project. We indeed anticipate that GRADUS will pave the way to the industrial development of a new generation of sensors, with decisive competitive advantages in terms of measurement capabilities, accuracy and portability.

In this project, we propose to build a transportable optical clock based on ytterbium atoms and to explore applications of this device to geodesy and geodynamics. The frequency of an atomic clock being sensitive to the geopotential caused by mass distribution , measuring the frequency shift between two clocks can be interpreted in terms of potential difference, or height difference. The perspective of controlling the clock frequency at the level of 18 significant digits is now a reality, which opens the possibility of measuring height differences at the cm level, or equivalent geopotential variations at 0.1 m2/s2 . In parallel, the deployment of optical fiber networks in charge of disseminating an ultrastable reference at 1542 nm is ongoing across Europe, and particularly in France where it takes the form of the Equipex REFIMEVE+. In the future, the transportable clock will enable the resolution of height changes at the 1 cm level between a reference point and any access point to this European networks, even for distances of several thousands of kilometers. Such a measurement is presently unreachable for any instrument, ground-based or in orbit around the Earth. These unprecedented measurements will lead to disruptive applications in operational geodesy and in Earth Sciences. In operational geodesy, accurate and high-resolution measurements of height differences over long distances will enable the correction of biases specific to traditional leveling methods. It will also build homogeneous height references at continental scales. Moreover, a better knowledge of geopotential differences will considerably improve the mapping of the equipotential surfaces of the gravity potential , particularly the reference corresponding to the mean sea level, called the geoid. This will have an impact on the determination of marine references, and on studies of coastal currents. Additionally, considering the original spectrum (range of several 100 km) of clock-based measurements compared to usual gravimetric surveys, the monitoring of geopotential variations in a given location will give access to underground deep mass transfers due to many phenomena (tectonic deformation, volcanism, seismic cycle, or change of the mean sea level …). These aspects can possibly increase public awareness of natural hazards and draw the attention of top decision makers. Countless technological and conceptual challenges must be tackled to transfer a device as precise as an atomic clock from a well-controlled lab environment to outdoor uncontrolled conditions. Several approaches are presented in the ROYMAGE project, notably to preserve the stability and the low uncertainty, to reduce electrical consumption, and to reference all the instruments attached to the clock only to the ultrastable 1542 nm carrier provided by the European fiber network. To this end, we propose innovative techniques of seismometers-assisted vibration compensation, of dual Ytterbium clouds to minimize deadtimes, or of “bootstrapping” of an optical frequency comb permanently attached to the device. The clock will be assembled at SYRTE (Observatoire de Paris), and prior to transport at nodes of the European fiber link, metrological performances will be assessed by comparison to the 6 atomic clocks (strontium, mercury, cesium) already operational in the laboratory. To conclude, the project aims at building the core of the clock, demonstrate the feasibility of the instrument, and evaluate its possible impact for targeted applications. The consortium submitting the proposal gathers specialists of quantum technologies, of geodesy and geophysics, and operational experts in terrestrial and marine geodetic references..

The project FORCA-G aims at studying the short range interactions between a surface and atoms trapped in its vicinity. Using cold atoms confined in the wells of an optical standing wave, the atom-surface potential will be measured with high sensitivity using atom interferometry techniques. The experiment will allow a test of gravity at short distances, which will put stringent bounds on a possible deviation from the known laws of physics, or discover new short range interactions related to gravity, as described by several models based on unification theories. FORCA-G will also allow a measurement of the Casimir Polder interaction (QED vacuum fluctuations) with unprecedented accuracy, clearing the way for promising applications in nanotechnology and micro-machining. It therefore has a major discovery potential in the domain of interplay of some of the most puzzling and fundamental phenomena of present day physics (vacuum fluctuations, gravitation and quantum physics) where the physics of the very small (quantum field theory, unification models) confronts some of the questions posed by the phenomena of the very large (gravitation, astronomy, cosmology).

The project targets to establish a new class of sensors employing interferometers based on atoms trapped in optical lattices. So far only few proof-of-principle experiments exist exploring guided and trapped atom interferometers. Innovative approaches and methods have to be explored in order to achieve new devices with sensitivities and spatial resolutions far beyond state of the art. Our consortium, exploring "Trapped Atom Interferometer in Optical Lattices" (TAOIL), brings together the European experts on atomic sensors and metrology to accomplish this objective in a combined effort of experimentalists and theorists. In this way, we will develop a new class of atomic sensors for high precision measurements in applied and fundamental physics. We will master new methods for separating a split atomic sample far apart while maintaining the quantum coherence, to detect and spatially image exotic quantum forces. We will learn how to tame harmful decoherence effects by either controlling the strength of the two-body interactions or using novel sources of ultra-cold atoms. We will develop the theoretical and the experimental methods to implement an entanglement-enhanced as well as a chaos-enhanced atom-light coupled sensor, an avant-garde approach to the ultra-precise metrology. The accomplishment of the goals set in TAIOL will open new possibilities for a wide range of applications, such as gravimetry and surface force measurements with the perspective of future industrial implementations. Our project addresses in many respects the “Quantum metrology sensing and imaging” area of the call. It targets the development of high sensitivity atomic sensors based on atom interferometry, which will exploit the long coherence times, extending over seconds, of quantum superposition states, thanks to holding the atoms in trapping potentials. In addition, new schemes for efficient and sensitive readout of the interferometer phase will be developed, exploiting quantum entanglement and chaos. The project will lay the foundations for the development of a new class of compact atomic sensors and will open new perspectives for a wide range of applications, extending well beyond quantum physics, such as inertial navigation, resource exploration, geodesy, surface science and fundamental tests of gravitation.