A Gravimetric Support Network for Very Long Baseline Atom Interferometry

With the introduction of portable atom interferometers (AI), a genuinely independent method for the determination of g is available for the first time since the introduction of laser interferometer based instruments. Current AIs offer several advantages and already reach the accuracy of classical sensors. Additionally, a small number of stationary experiments were implemented for research in fundamental physics and geodesy. These instruments, extending the free fall distance of atoms to several meters, allow for longer evolution times of the wave function, thereby increasing the sensitivity of the AI compared to decimetres in portable devices. The construction of an AI with a 9 m interaction zone is currently being completed at Leibniz University Hannover. The knowledge of g and its gradient is required for the evaluation of systematic effects and uncertainties in AI experiments. Therefore, a gravimetric control network connected to one absolute gravimeter pier was established and repeatedly observed during the construction of the Very Long Baseline Atom Interferometry facility (VLBAI). Before the installation of the instrument, this network included the central axis of the VLBAI and one vertical off-axis parallel profile. The latter profile can also be observed during operation of the VLBAI. The effect of local gravity changes, e. g., hydrology, is comparable to 1 nm/s² on both axes. The gravimetric measurements serve as a reference during initial tests of the VLBAI. Repeated observations in the future will be used to characterize the effect of local hydrology and other mass variations along the vertical axis. A model of the research building and groundwater level monitoring supplements the gravimetric network. As the VLBAI is capable of measuring g and its vertical gradient with higher accuracy (<1 nm/s²) than classical instruments, the model will be used to transfer g to a gravimetry laboratory for gravimeter comparisons. We present our strategy for gravimetric control of the VLBAI. This will provide a reference at first and will later be used to establish the VLBAI as a reference for gravimeter comparisons. The results of the first gravimetric campaigns and the comparison with the model of the VLBAI environment show an agreement within the instrumental uncertainties of the relative gravimeters used

Understanding the gravitational and magnetic environment of a very long baseline atom interferometer

By utilizing the quadratic dependency of the interferometry phase on time, the Hannover Very Long Baseline Atom Interferometer facility (VLBAI) aims for sub nm/s$^2$ gravity measurement sensitivity. With its 10 m vertical baseline, VLBAI offers promising prospects in testing fundamental physics at the interface between quantum mechanics and general relativity. Here we discuss the challenges imposed on controlling VLBAI's magnetic and gravitational environment and report on their effect on the device's accuracy. Within the inner 8 m of the magnetic shield, residual magnetic field gradients expect to cause a bias acceleration of only 6$\times$10$^{-14}$ m/s$^2$ while we evaluate the bias shift due to the facility's non-linear gravity gradient to 2.6 nm/s$^2$. The model allows the VLBAI facility to be a reference to other mobile devices for calibration purposes with an uncertainty below the 10 nm/s$^2$ level.Comment: Presented at the Ninth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, May 17-26, 202

Interference of clocks: A quantum twin paradox

The phase of matter waves depends on proper time and is therefore susceptible to special-relativistic (kinematic) and gravitational (redshift) time dilation. Hence, it is conceivable that atom interferometers measure generalrelativistic time-dilation effects. In contrast to this intuition, we show that (i) closed light-pulse interferometers without clock transitions during the pulse sequence are not sensitive to gravitational time dilation in a linear potential. (ii) They can constitute a quantum version of the special-relativistic twin paradox. (iii) Our proposed experimental geometry for a quantum-clock interferometer isolates this effect. © 2019 The Authors

Interference of Clocks: A Quantum Twin Paradox

The phase of matter waves depends on proper time and is therefore susceptible to special-relativistic (kinematic) and gravitational time dilation (redshift). Hence, it is conceivable that atom interferometers measure general-relativistic time-dilation effects. In contrast to this intuition, we show that light-pulse interferometers without internal transitions are not sensitive to gravitational time dilation, whereas they can constitute a quantum version of the special-relativistic twin paradox. We propose an interferometer geometry isolating the effect that can be used for quantum-clock interferometry.Comment: 9 Pages, 2 Figure

Gravity field modelling for the Hannover 10 m atom interferometer

Stable gravimetric measurements over timescales from several days to decades are required to provide relevant insight into geophysical processes or to realise a gravimetric reference frame. Users of absolute gravimeters participate in CIPM or RMO key comparisons with a metrological reference in order to monitor the temporal stability of the instruments and determine the bias to that reference. These comparisons provide the reference values of highest accuracy, around 10 nm/s², compared to the calibration against a single gravimeter operated at a metrological institute. The construction of stationary, large scale atom interferometers paves the way towards a new measurement standard in absolute gravimetry used as a reference with a potential stability better than 1 nm/s² at 1 second integration time. At the Leibniz University Hannover, we are currently building such a very long baseline atom interferometer with a 10 m high vertical free fall zone. Additionally, a 3D model of the instrument and its environment is adapted to derive the change of gravity due to the setup of the instrument. The model is then compared to episodic gravimetric measurements. The knowledge of local gravity and its gradient along and around the baseline is required to establish the instrument's uncertainty budget and enable transfers of gravimetric measurements to nearby devices for comparison and calibration purposes. We report on the progress of the gravimetric measurements and modelling of g inside and near the instrument in parallel to the construction of the atom interferometer

Optomechanical resonator-enhanced atom interferometry

Matter-wave interferometry and spectroscopy of optomechanical resonators offer complementary advantages. Interferometry with cold atoms is employed for accurate and long-term stable measurements, yet it is challenged by its dynamic range and cyclic acquisition. Spectroscopy of optomechanical resonators features continuous signals with large dynamic range, however it is generally subject to drifts. In this work, we combine the advantages of both devices. Measuring the motion of a mirror and matter waves interferometrically with respect to a joint reference allows us to operate an atomic gravimeter in a seismically noisy environment otherwise inhibiting readout of its phase. Our method is applicable to a variety of quantum sensors and shows large potential for improvements of both elements by quantum engineering. © 2020, The Author(s)

Methods for very long baseline atom interferometry

Gravity plays a central role in our understanding of the Earth and the Universe. It is the dominant force at astronomic scales, shaping star systems and galaxies. It is also a pivotal field in the geosciences, allowing access to the physical shape of the Earth, defining height systems, and tracking mass transport, for example water in climate change research, inside volcanoes, or along seismic faults. Finally, it could become a crucial resource for engineering, opening the way to a renewal of underground exploration techniques, both for natural resources and civil engineering legacy. In fundamental physics, gravity nevertheless remains a riddle. From its origins to the first direct detection of gravitational waves in 2015, the theory of general relativity has accumulated successes. Our understanding of the microscopic world, through quantum mechanics and the standard model of particle physics is a similar success story, culminating with the detection of the BEH boson in 2012. Nevertheless, unification theories remain inaccessible and testing both the hypotheses and predictions of our theories remains the safest way towards the discovery of new physics. Here, key research areas relate to tests of the universality of free fall, at the heart of general relativity theory, or the creation of macroscopic superposition states of massive particles, a genuine marker of the quantum world. Novel applications in the geosciences also require improved gravity sensors. For multiple applications in engineering and geodesy, the ideal device is easily transportable and has low energy consumption. Nevertheless, higher-order references are necessary to enable an accurate definition of a gravity standard across the world. Such gravity references could also be combined with state-of-the-art laser gyroscopes into quantum Earth observatories. In this manuscript, we introduce a new generation of matter wave sensors based on very long baseline atom interferometry (VLBAI). Exploring the properties of massive quantum objects at the scales of meters and seconds, they will provide new insights into fundamental physics questions and serve as testbeds for novel atomic inertial sensors on ground and in space. We provide the motivation and working principles for absolute gravity sensing with VLBAI, and discuss in particular the specific trade-offs arising from the use of an extended baseline in atom interferometry. We also present the core design of the Hannover VLBAI facility. Finally, we demonstrate that through a unique and carefully characterized 10 m-long magnetically shielded baseline, this devices offers the required environment for next-generation atomic gravity reference sensors and tests of fundamental physics

Status of gravimetric measurements and modelling along a 10m atom interferometer

Transportable quantum sensors become more common especially in gravimetry and measurements on longer timescales or field campaigns are carried out. Large scale atom interferometers are much rarer and mostly used for experiments in fundamental physics but can also be operated as gravimeter. The extended free fall time of atoms compared to transportable devices paves the way towards a new measurement standard in absolute gravimetry with a potential stability of better than 1 nm/s² at 1 second integration time. In contrast, the reference values at gravimetric key comparisons, which provide the highest accuracy today, achieve an accuracy of 10 nm/s². At the Leibniz University Hannover, we are currently building a very long baseline atom interferometer (VLBAI) with a 10 m vertical free fall zone. The impact of the instrument on the local gravity field and vice versa was determined by gravimetric measurements during the construction. A 3D model of the VLBAI and its environment was created to calculate the gravitational effect of the masses on experiments of the atom interferometer. The model is then compared to episodic gravimetric measurements. The knowledge of local gravity and its gradient is required to establish the instrument´s uncertainty budget and enable the transfer of gravimetric measurements to nearby devices for comparison. We report on the progress of the gravimetric measurements and modelling in parallel to the construction of the VLBAI

Gravity field modelling for the Hannover 10 m atom interferometer

Absolute gravimeters are used in geodesy, geophysics and physics for a wide spectrum of applications. Stable gravimetric measurements over timescales from several days to decades are required to provide relevant insight into geophysical processes. Users of absolute gravimeters participate in comparisons with a metrological reference in order to monitor the temporal stability of the instruments and determine the bias to that reference. However, since no measurement standard of higher-order accuracy currently exists, users of absolute gravimeters participate in key comparisons led by the International Committee for Weights and Measures. These comparisons provide the reference values of highest accuracy compared to the calibration against a single gravimeter operated at a metrological institute. The construction of stationary, large-scale atom interferometers paves the way for a new measurement standard in absolute gravimetry used as a reference with a potential stability up to 1 nm/s 2 at 1 s integration time. At the Leibniz University Hannover, we are currently building such a very long baseline atom interferometer with a 10-m-long interaction zone. The knowledge of local gravity and its gradient along and around the baseline is required to establish the instrument’s uncertainty budget and enable transfers of gravimetric measurements to nearby devices for comparison and calibration purposes. We therefore established a control network for relative gravimeters and repeatedly measured its connections during the construction of the atom interferometer. We additionally developed a 3D model of the host building to investigate the self-attraction effect and studied the impact of mass changes due to groundwater hydrology on the gravity field around the reference instrument. The gravitational effect from the building 3D model is in excellent agreement with the latest gravimetric measurement campaign which opens the possibility to transfer gravity values with an uncertainty below the 10 nm/s2 level.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Niedersächsisches Ministerium für Wissenschaft und Kultur http://dx.doi.org/10.13039/501100010570https://www.bipm.org/kcd

Matter wave interferometry for inertial sensing and tests of fundamental physics

We report on recent developments concerning the commissioning of the Very Long Baseline Atom Interferometry test stand. Stretching over 15 m, the facility with its high-performance magnetic shield, Rb-Yb atom sources, and a low-frequency seismic attenuation system, will allow us to take on the competition with the stability of superconducting gravimeters with absolute measurements. By operating in a differential mode, we anticipate tests of the Universality of Free Fall at levels of parts in 10^(13) and below. We will furthermore report on matter wave sensors enhanced with opto-mechanical resonators as well as fully guided interferometry and discuss the potential of such systems in inertial sensing and fundamental physics. This work is supported by CRC 1128 geo-Q, CRC 1227 DQ-mat, the German Space Agency (DLR) through the Federal Ministry for Economic Affairs and Energy (BMWi) (Grant No. 50WM1641), the Federal Ministry of Education and Research (BMBF) through Photonics Research Germany (Grant No. 13N14875), and QUANOMET