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Frequency stabilized light sources with narrow linewidth are mandatory for atom interferometry based experiments. For compact experiment designs used on space platforms, tunable DFB diode lasers are often used. These lasers combine low energy consumption with small sizes, but lack long-term frequency stability. This paper presents an FPGA based laser frequency stabilization system for highly variable target frequencies using frequency modulated Rb-spectroscopy achieving latencies below 100 μs. The system consists of a DFB laser, a Rb-spectroscopy cell, a laser current controller and an FPGA board with an analog-digital conversion board. The digital part of the frequency stabilization system is a SoC mapped on an FPGA. The SoC consists of a processor, enabling user interaction via network connection, and the dedicated frequency stabilization module. This module consists of a demodulation stage, digital filters, a frequency estimator and a controller. To estimate the frequency, small ramps of the laser frequency are generated using a high-speed DAC connected to the laser current controller. The absorption spectroscopy output of this beam is sampled using a photodiode and a high-speed ADC. After signal conditioning with digital filters, the frequency estimator extracts the present mid-frequency of the laser applying pattern matching with a prerecorded reference spectrum. The frequency controller adjusts the mean laser current based on this estimation. The performance as well as the accuracy of the proposed laser stabilization system and its FPGA resource and power consumption are evaluated.

Die Quanten- und Nanometrologie (QUANOMET) verfolgt die methodische Weiterentwicklung und Innovation immer präziserer und empfindlicherer Messverfahren und ist eine von drei Forschungslinien eines Wissenschaftsbündnisses zwischen der Leibniz Universität Hannover und der Technischen Universität Braunschweig. Wissenschaftler beider Hochschulen berichten, wie das Projekt entstanden ist und welche Ziele es hat.

On 23rd of January 2017 the first Bose-Einstein Condensate (BEC) in Space was created on-board the sounding rocket mission MAIUS-1. The successful launch marks a major advancement in the effort of performing matter wave interferometry with BECs on space vehicles. Its high BEC-flux enables more than 100 experiments during flight, characterizing the creation of BECs in space, their free evolution, state preparation, and the creation of cold atoms in highly dynamic environments. MAIUS-1 opens a new path towards space borne inertial sensing employing interferometers with high accuracy and sensitivity. Two follow-up missions will investigate dual-species interferometry. Recently several missions were proposed ranging from tests of the universality of free fall to gravimetry. Due to their small initial size and low expansion rates BECs are the ideal source for such an interferometric measurement. The findings of the mission will contribute to the NASA CAL project and BECCAL (NASA and DLR). This research is funded by DLR under grant 50WP1435.

Quantenmechanisch korrelierte, also verschränkte Atome eröffnen vielfältige Anwendungen, insbesondere im Bereich der Präzisionsmessungen. Am Institut für Quantenoptik ist es erstmalig gelungen, die Verschränkung nicht nur innerhalb einer Atomwolke, sondern zwischen zwei räumlich getrennten Wolken nachzuweisen. Am HITec sollen solche verschränkten Wolken nicht nur wenige Mikrometer, sondern meterweit aufgetrennt werden, um so Präzisionsmessungen der Gravitation entscheidend zu verbessern.

Mit dem Hannover Institute of Technology (HITec) ist im Juli 2018 ein weltweit einmaliges Forschungszentrum in Betrieb gegangen. Unter Beteiligung der Fachgebiete Physik, Geodäsie und Ingenieurwissenschaften soll hier Grundlagenforschung, angewandte Forschung sowie Technologieentwicklung betrieben werden. Der Technische Leiter und der Geschäftsführer des HITec haben den Entstehungsprozess begleitet.

PTB-Mitteilungen. Band 128 (2018), Heft 3. ISSN 0030-834X

The Space-Time Explorer and Quantum Test of the Equivalence Principle mission (STEQUEST) is devoted to a precise measurement of the effect of gravity on time and matter using an atomic clock and an atom interferometer. The mission was selected by ESA as one of four candidates for the M3 mission within the Cosmic Vision Program (launch in 2022).

Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology, in particular to measure time and to realize the second. In a classical interferometer, an ensemble of atoms is prepared in one of the two input states, whereas the second one is left empty. In this case, the vacuum noise restricts the precision of the interferometer to the standard quantum limit (SQL). Here, we propose and experimentally demonstrate a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. We create a squeezed vacuum state containing an average of 0.75 atoms to improve the clock sensitivity of 10,000 atoms by 2.05 dB. The SQL poses a significant limitation for today's microwave fountain clocks, which serve as the main time reference. We evaluate the major technical limitations and challenges for devising a next generation of fountain clocks based on atomic squeezed vacuum., 9 pages, 6 figures

A large variety of scientific experiments as well as common applications require more and more precise knowledge of gravity g, its derived quantities, and their change in time. For several phenomena the effect on g can be modelled for any given location, e.g., Earth tides and the redistribution of mass in the ocean and the atmosphere. Considering the desired sensitivity of future instruments, these models have to be evaluated for their suitability. The gravitational effect of the instrument itself is typically either neglected or determined once and assumed to be stable. Local changes in gravity, e.g., changes in the groundwater table at a laboratory, are often neglected. The vertical gradient in gravity is assumed to be linear and stable in time and, depending on the size of the experiment, this often is a valid assumption. In case of the Very Long Baseline Atom Interferometer (VLBAI), a 10m vertical atom interferometer currently being installed at Leibniz Universität Hannover/HITec with the scope of precise gravity, gravity gradient measurements and tests of the universality of free fall, higher order corrections have to be estimated. This is especially relevant, since the instruments extends over three floors, experiencing non-linear gravity variations when passing the concrete floor of the building. Additionally, the impact of the instrument itself and its supporting structure has to be evaluated. Since the VLBAI has the potential to serve as a reference providing g for the comparison with classical gravimeters in the future, a transfer of g from the effective measuring height of the atom interferometer to a location accessible with an absolute gravimeter is required. Thus, changes in the local gravity field have to be investigated for their effect on the gradient within the instrument.

Ultra-precise optical clocks in space will allow new studies in fundamental physics and astronomy. Within an European Space Agency (ESA) program, the Space Optical Clocks (SOC) project aims to install and to operate an optical lattice clock on the International Space Station (ISS) towards the end of this decade. It would be a natural follow-on to the ACES mission, improving its performance by at least one order of magnitude. The payload is planned to include an optical lattice clock, as well as a frequency comb, a microwave link, and an optical link for comparisons of the ISS clock with ground clocks located in several countries and continents. Within the EU-FP7-SPACE-2010-1 project no. 263500, during the years 2011-2015 a compact, modular and robust strontium lattice optical clock demonstrator has been developed. Goal performance is a fractional frequency instability below 1x10^{-15}, tau^{-1/2} and a fractional inaccuracy below 5x10^{-17}. Here we describe the current status of the apparatus' development, including the laser subsystems. Robust preparation of cold {88}^Sr atoms in a second stage magneto-optical trap (MOT) is achieved., Comment: 27 Pages, 15 figures, Comptes Rendus Physique 2015

Erratum to: A high-flux BEC source for mobile atom interferometers in: New Journal of Physics 17 (2015) 065001

PTB-Mitteilungen. Band 119 (2009), Heft 2, S. 97 - 166. ISSN 0030-834X

We present the production of dual-species Bose-Einstein condensates of $^{39}\mathrm{K}$ and $^{87}\mathrm{Rb}$. Preparation of both species in the $\left| F=1,m_F=-1 \right\rangle$ state enabled us to exploit a total of three Fesh\-bach resonances which allows for simultaneous Feshbach tuning of the $^{39}\mathrm{K}$ intraspecies and the $^{39}\mathrm{K}$-$^{87}\mathrm{Rb}$ interspecies scattering length. Thus dual-species Bose-Einstein condensates were produced by sympathetic cooling of $^{39}\mathrm{K}$ with $^{87}\mathrm{Rb}$. A dark spontaneous force optical trap was used for $^{87}\mathrm{Rb}$, to reduce the losses in $^{39}\mathrm{K}$ due to light-assisted collisions in the optical trapping phase, which can be of benefit for other dual-species experiments. The tunability of the scattering length was used to perform precision spectroscopy of the interspecies Feshbach resonance located at $117.56(2)\,\mathrm{G}$ and to determine the width of the resonance to $1.21(5)\,\mathrm{G}$ by rethermalization measurements. The transition region from miscible to immiscible dual-species condensates was investigated and the interspecies background scattering length was determined to $28.5\,a_\mathrm{0}$ using an empirical model. This paves the way for dual-species experiments with $^{39}\mathrm{K}$ and $^{87}\mathrm{Rb}$ BECs ranging from molecular physics to precision metrology., 9 pages, 9 figures

We report on the sub-kilohertz optical spectroscopy on the 1S0-3P1 intercombination transition in magnesium at 457 nm. The spectroscopic signal is probed by a time domain atom interferometer. The realization of this time domain atom interferometer with laser cooled and trapped atoms allows extremely long interaction times and leads to resolutions down to 491 Hz (FWHM). This corresponds to a high line Q factor of 1.3×1012. Because of the high accuracy in the determination of the line center, applications with respect to an optical frequency standard are possible. © 1998 The American Physical Society.

Einleitung: Die Optische Stimulation des Innenohres entwickelt sich immer mehr zur alternativen Stimulationsstrategie für Cochlea Implante (CI). Eine dadurch verbesserte frequenzspezifische Aktivierung soll ein besseres Sprachverstehen ermöglichen. Da Laser mittels optischer Faser appliziert[for full text, please go to the a.m. URL], 83. Jahresversammlung der Deutschen Gesellschaft für Hals-Nasen-Ohren-Heilkunde, Kopf- und Hals-Chirurgie

International audience; We present iSense, a recently initiated FET project aiming to use Information and Communication Technologies (ICT) to develop a platform for portable quantum sensors based on cold atoms. A prototype of backpack-size highprecision force sensor will be built to demonstrate the concept.

Einleitung: Als alternative Stimulationsform der Cochlea mit dem Ziel einer höheren Frequenzselektivität ist in letzter Zeit die laseroptische Stimulation mehrfach beschrieben worden. In genetisch modifizierten Hörnerven erfolgt die laseroptische Anregung von Channelrodopsinen mit Auslösung[for full text, please go to the a.m. URL], 82. Jahresversammlung der Deutschen Gesellschaft für Hals-Nasen-Ohren-Heilkunde, Kopf- und Hals-Chirurgie

We present iSense, a recently initiated FET project aiming to use Information and Communication Technologies (ICT) to develop a platform for portable quantum sensors based on cold atoms. A prototype of backpack-size highprecision force sensor will be built to demonstrate the concept.

We perform Ramsey-Bordé spectroscopy on laser-cooled magnesium atoms in free fall to measure the 1S 0→ 3P 1 intercombination transition frequency. The measured value of 655 659 923 839 730 (48) Hz is consistent with our former atomic beam measurement (Friebe et al 2008 Phys. Rev. A 78 033830). We improve upon the fractional accuracy of the previous measurement by more than an order of magnitude to 7×10 -14. The magnesium frequency standard was referenced to a fountain clock of the Physikalisch Technische Bundesanstalt (PTB) via a phase-stabilized telecom fiber link and its stability was characterized for interrogation times up to 8000 s. The high temperature of the atomic ensemble leads to a systematic shift due to the motion of atoms across the spectroscopy beams. In our regime, this leads to a counterintuitive reduction of residual Doppler shift with increasing resolution. Our theoretical model of the atom-light interaction is in agreement with the observed effect and allows us to quantify its contribution in the uncertainty budget. DFG/EXC/QUEST

We have observed 28 heteronuclear Feshbach resonances in ten spin combinations of the hyperfine ground states of a 40K−87Rb mixture. The measurements were performed by observing the loss rates from an atomic mixture at magnetic fields between 0 and 700G. These data were used to significantly refine an interatomic potential derived from molecular spectroscopy, yielding a highly consistent model of the 40K−87Rb interaction. Thus, the measured resonances can be assigned to the corresponding molecular states. In addition, this potential allows for an accurate calculation of the energy differences between highly excited levels and the rovibrational ground level. This information is of particular relevance for the formation of deeply bound heteronuclear molecules. Finally, the model is used to predict Feshbach resonances in mixtures of 87Rb combined with 39K or 41K.

International audience; Cold atomic gases placed in optical lattices enable studies of simple con- densed matter theory models with parameters that may be tuned relatively easily. When the optical potential is randomized (e.g. using laser speckle to create a random intensity distribution) one may be able to observe Anderson localization of matter waves for non-interacting bosons, the so-called Bose glass in the presence of interactions, as well as the Fermi glass or quantum spin glass for mixtures of fermions and bosons.

The lifetime of the metastable 3P2 state of neon has been determined to 14.70(13) s (decay rate 0.06801(62) 1/s) by measuring the decay in fluorescence of an ensemble of Ne-20 atoms trapped in a magneto-optical trap (MOT). Due to low background gas pressure p < 5 10^-11 mbar and low relative excitation to the 3D3 state (0.5% excitation probability) operation only small corrections have to be included in the lifetime extrapolation. Together with a careful analysis of residual loss mechanisms in the MOT a lifetime determination to high precision is achieved., 4 pages, 6 figures