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We report on our development of laser rack systems as “quantum enabling” building blocks of future quantum devices. We present funded projects, where such rack laser systems are integrated into first prototypes.

We report on a transportable and easy-to-operate optical clock utilizing the 2S1/2 - 2D3/2 transition of a single trapped 171Yb+ ion at 436 nm. Developed within a pilot project for quantum technology in Germany lead by industry, the clock is set up in two 19″ racks. In this way, transportation can easily be realized, and the large degree of automatization allows for operation outside highly specialized laboratories for applications beyond basic research. Comparisons to existing high-accuracy optical clock systems enable a verification of the clock's stability and uncertainty budget at the low 10−17 level. During these tests, operation with 99.8% availability over more than 14 days has been achieved.

With a newly-developed generation of control electronics for diode lasers, modern concepts such as intuitive multi-touch operation or computersupported remote control are conquering laser laboratories worldwide. Simultaneously, the reduction of laser noise and drift has reached new records.

We present an overview from first external cavity diode lasers to current and future designs. Based on applications the requirements and realizations of tunable diode lasers are shown with respect to their importance to “Quantum Technology” initiatives.

We present a resonantly frequency-doubled tapered amplified semiconductor laser system emitting up to 2.6 W blue light at 400 nm. The output power is stable on both short and long timescales with 0.12% RMS relative intensity noise, and less than 0.15%/h relative power loss over 16 hours of free running continuous operation. Furthermore, the output power can be actively stabilized, and the alignment of the input beams of the tapered amplifier chip, the frequency doubling cavity and-in case of fiber output-the fiber can be optimized automatically using computer-controlled mirrors.

Single-frequency optical synthesizers (SFOS) provide an optical field with arbitrarily adjustable frequency and phase which is phase-coherently linked to a reference signal. Ideally, they combine the spectral resolution of narrow linewidth frequency stabilized lasers with the broad spectral coverage of frequency combs in a tunable fashion. In state-of-the-art SFOSs tuning across comb lines requires comb line order switching,1, 2 which imposes technical overhead with problems like forbidden frequency gaps or strong phase glitches. Conventional tunable lasers often tune over only tens of GHz before mode-hops occur. Here, we present a novel type of SFOSs, which relies on a serrodyne technique with conditional flyback,3 shifting the carrier frequency of the employed frequency comb without an intrusion into the comb generator. It utilizes a new continuously tunable diode laser that tunes mode-hop-free across the full gain spectrum of the integrated laser diode. We investigate the tuning behavior of two identical SFOSs that share a common reference, by comparing the phases of their output signals. Previously, we achieved phase-stable and cycle-slip free frequency tuning over 28.1 GHz with a maximum zero-to-peak phase deviation of 62 mrad4 when sharing a common comb generator. With the new continuously tunable lasers, the SFOSs tune synchronously across nearly 17800 comb lines (1 THz). The tuning range in this approach can be extended to the full bandwidth of the frequency comb and the 110 nm mode-hop-free tuning range of the diode laser.

We demonstrate demagnetization cooling of a gas of ultracold $^{52}$Cr atoms. Demagnetization is driven by inelastic dipolar collisions which couple the motional degrees of freedom to the spin degree. By that kinetic energy is converted into magnetic work with a consequent temperature reduction of the gas. Optical pumping is used to magnetize the system and drive continuous demagnetization cooling. Applying this technique, we can increase the phase space density of our sample by one order of magnitude, with nearly no atom loss. This method can be in principle extended to every dipolar system and could be used to achieve quantum degeneracy via optical means., 10 pages, 5 figures

We report on progress towards an atom interferometric determination of the Newtonian gravitational constant. Free-falling laser-cooled atoms will probe the gravitational potential of nearby source masses. To reduce systematic errors, we will perform double differential measurements between two vertically separated atom clouds and with different source mass positions.

We describe our experiment MAGIA (misura accurata di G mediante interferometria atomica), in which we will use atom interferometry to perform a high precision measurement of the Newtonian gravitational constant G. Free-falling laser-cooled atoms in a vertical atomic fountain will be accelerated due to the gravitational potential of nearby source masses (SMs). Detecting this acceleration with techniques of Raman atom interferometry will enable us to assign a value to G. To suppress systematic effects we will implement a double-differential measurement. This includes launching two atom clouds in a gradiometer configuration and moving the SMs to different vertical positions. We briefly summarize the general idea of the MAGIA experiment and put it in the context of other high precision G-measurements. We present the current status of the experiment and report on analyses of the expected measurement accuracy.

We demonstrate a Doppler-free spectroscopic method that we test on 87 Rb and 85 Rb vapor. By using a magnetic field to induce a dichroism on the sample, we generate a dispersive signal with low background, which allows us to lock a diode laser even on small spectroscopic features. We elaborate the advantages of this simple and easy method by comparing it to other methods.

We report on the realization of a narrow-band continuous-wave laser source in the deep-ultraviolet. Via two consecutive second-harmonic processes starting from a near-infrared diode laser system, we demonstrate an output power of more than 15 mW at 193 nm. The setup is capable of mode hop-free frequency tuning over a range of 100 GHz und coarse tuning over more than 5 nm. We see direct applications of this laser source in the fields of semiconductor metrology and high-resolution spectroscopy in the deep-ultraviolet.

The general features of atom lithography, such as parallel deposition, large exposure area, nanometer resolution and both direct writing and resist based patterning, make it a promising field. A summary of the present state of neutral atom lithography is presented. The methods and results from various groups are discussed. A more in-depth study of three different types of atom lithography undertaken in our group is given.

We present the realisation of a magneto-optical trap for chromium. 52Cr atoms are loaded directly from a thermal beam. The trap lifetime is enhanced by using two red lasers to repump population that has decayed, via intercombination lines, to metastable levels back into the cooling cycle. We have measured the wavelengths of these intercombination lines and observed coherent Raman spectra. The observed density of 108 cm−3 is currently limited by collisions with the hot beam.

We developed a gravity-gradiometer based on atom interferometry for the determination of the Newtonian gravitational constant \textit{G}. The apparatus, combining a Rb fountain, Raman interferometry and a juggling scheme for fast launch of two atomic clouds, was specifically designed to reduce possible systematic effects. We present instrument performances and show that the sensor is able to detect the gravitational field induced by source masses. A discussion of projected accuracy for \textit{G} measurement using this new scheme shows that the results of the experiment will be significant to discriminate between previous inconsistent values., 9 pages,9 figures, Submitted

We describe a type of phase and frequency detector employing both an analog phase detector and a digital phase and frequency detector. The analog and digital detectors are mutually exclusive so that only one of them is active at any given time, resulting in a phase detector with both the broad capture range of digital circuits and the high speed and low noise of analog mixers. The detector has been used for phase locking the diode lasers generating the sequence of Raman pulses in an atom interferometer. The rms phase error of the phase lock is about 100 mrad in a 5 Hz–10 MHz bandwidth. The limit set on the interferometer phase resolution by the residual phase noise is 1.1 mrad. Since the digital circuitry is implemented with a programmable logic device the detector can be easily adapted to other experiments requiring frequency/phase stabilization of lasers sources.

Cr, different patterns can be generated. Possible applications using the inherent properties of atom lithography, e.g. the fabrication of photonic bandgap material, are discussed.

We have used neutral chromium atoms to write periodic nanometerscale structures in a direct way. We use the force exerted on the induced dipole of the atom in the intensity gradient of an optical standing light field to focus an atomic beam onto a substrate. The generated pattern reflects the symmetry of the optical standing wave.

A continuous-wave deep-ultraviolet light source is demonstrated based on a grating-stabilized diode laser pump system and two consecutive nonlinear conversion stages. Using the crystal Potassium Fluoroberylloborate (KBBF), direct second-harmonic generation to 191 nm could be realized with an output power of up to 1.3 mW. The linewidth at this wavelength is estimated to be around 100 kHz. The emission can be tuned mode hop-free over 40 GHz. Our scheme can be easily extended to 193 nm or – given the availability of suitable fundamental sources – to wavelengths as small as 165 nm. These parameters make our light source an ideal tool for applications in deep-ultraviolet metrology and photoemission spectroscopy.

The use of ultra-precise optical clocks in space ("master clocks") will allow for a range of new applications in the fields of fundamental physics (tests of Einstein's theory of General Relativity, time and frequency metrology by means of the comparison of distant terrestrial clocks), geophysics (mapping of the gravitational potential of Earth), and astronomy (providing local oscillators for radio ranging and interferometry in space). Within the ELIPS-3 program of ESA, the "Space Optical Clocks" (SOC) project aims to install and to operate an optical lattice clock on the ISS towards the end of this decade, as 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. Undertaking a necessary step towards optical clocks in space, the EU-FP7-SPACE-2010-1 project no. 263500 (SOC2) (2011-2015) aims at two "engineering confidence", accurate transportable lattice optical clock demonstrators having relative frequency instability below 1\times10^-15 at 1 s integration time and relative inaccuracy below 5\times10^-17. This goal performance is about 2 and 1 orders better in instability and inaccuracy, respectively, than today's best transportable clocks. The devices will be based on trapped neutral ytterbium and strontium atoms. One device will be a breadboard. The two systems will be validated in laboratory environments and their performance will be established by comparison with laboratory optical clocks and primary frequency standards. In this paper we present the project and the results achieved during the first year., Contribution to European Frequency and Time Forum 2012, Gothenburg, Sweden

We report ultra-stable locking of a commercially available extended cavity diode laser to a vibration-insensitive high finesse Fabry-Perot cavity. A servo bandwidth of 2 MHz is demonstrated. The absolute stability of the diode laser after locking is measured with a three-cornered-hat method. The resulting Allan deviation reaches a level of $2.95\times10^{-15}$ at 1 s, corresponding to only 0.93 Hz linewidth, even without vibration isolation of the reference cavity., 9 pages, 3 figures

This paper reports on the first experimental realization of demagnetization cooling in a gas. In the presence of an external magnetic field, particles with a permanent magnetic dipole moment try to minimize their energy by aligning their dipole along the field, thus generating a macroscopic magnetization of the material. If the field is reduced enough, the particles are able to change their orientation and to do magnetic work during such a demagnetization process. This is done at the expense of their kinetic energy, with a consequent reduction of the temperature of the system. So far such a process has not been detected in gases because at low density the rate of demagnetization is very low. But Cr atoms have such a large magnetic dipole moment (6 muB) that for experimentally accessible densities of 1013 atoms/cm3 and sufficiently low fields (around 250 mG), they can demagnetize on a timescale of a few seconds.

We show that an effective quadratic Zeeman effect can be generated in $^{52}$Cr by proper laser configurations, and in particular by the dipole trap itself. The induced quadratic Zeeman effect leads to a rich ground-state phase diagram, can be used to induce topological defects by controllably quenching across transitions between phases of different symmetries, allows for the observability of the Einstein-de Haas effect for relatively large magnetic fields, and may be employed to create $S=1/2$ systems with spinor dynamics. Similar ideas could be explored in other atomic species opening an exciting new control tool in spinor systems., 4 pages, 2 eps figures

The observation of Bose-Einstein condensation of /sup 52/Cr atoms offers the possibility to experimentally explore a new type of interaction in degenerate quantum gases. Utilizing one of the recently observed Feshbach resonances to tune the strength of the contact interaction, the character of the interaction is varied from mainly contact to purely dipolar.

Our recent measurements on the expansion of a chromium dipolar condensate after release from an optical trapping potential are in good agreement with an exact solution of the hydrodynamic equations for dipolar Bose gases. We report here the theoretical method used to interpret the measurement data as well as more details of the experiment and its analysis. The theory reported here is a tool for the investigation of different dynamical situations in time-dependent harmonic traps., 12 pages. Submitted to PRA

Summary form only given. We present first step results on the way to quantum degenerate gases with chromium atoms. The large magnetic moment (6 /spl mu//sub B/) and the isotopic composition (3 stable bosonic and one stable fermionic isotope with 9.5% n.a.) are suitable for studies of the quantum statistical effects in both Bose and Fermi gases in steep magnetic traps. Furthermore, together with atom lithography, chromium has a technological potential in nanostructure fabrication.

The MAGIA experiment is designed to measure the Newtonian gravitational constant G using atom interferometry. A double differential measurement of the gravitational force produced by heavy source masses on two clouds of atoms allows the determination of G. We present the general idea and actual status of the experiment

Summary form only given. We present our results on the realization of a magneto-optical trap (MOT) for chromium atoms with repumpers on two intercombination lines. The high magnetic moment (6 Bohr magneton) and the isotopic composition of chromium are promising for investigation of collective quantum statistical effects in ultracold Bose- and Fermi gases in steep magnetic traps. Chromium is also interesting in view of its applications in atom lithography.

We have realized a scheme for continuous loading of a magnetic trap (MT). ^{52}Cr atoms are continuously captured and cooled in a magneto-optical trap (MOT). Optical pumping to a metastable state decouples atoms from the cooling light. Due to their high magnetic moment (6 Bohr magnetons), low-field seeking metastable atoms are trapped in the magnetic quadrupole field provided by the MOT. Limited by inelastic collisions between atoms in the MOT and in the MT, we load 10^8 metastable atoms at a rate of 10^8 atoms/s below 100 microkelvin into the MT. After loading we can perform optical repumping to realize a MT of ground state chromium atoms., Comment: 4 pages, 4 figures, version 2, modified references, included additional detailed information, minor changes in figure 3 and in text

We describe two experiments that use neutral atomic beam techniques to write nanostructures. In the chro-mium experiment we have used neutral chromium atoms to write periodic nanometerscale structures in a direct way. In a second experiment we have used a self-assembling monolayer as a resist for metastable helium atoms. 1 INTRODUCTION Requirements for technologically interesting lithography techniques are high spatial resolution, the possibility to form arbitrary structures, and short duty-cycle-times. Simplicity of the setup and the possibility of parallelwriting are advantageous. As standard optical lithography techniques are believed to be limited in principle toresolutions above 1.00 nm, and charged beam techniques face other problems due to the high particle energies,various possibilities are discussed to complement them. Recently different neutral atom beam techniques withthermal beams have been investigated for lithography. In neutral beams no space charge effects make the beam

We describe two experiments that use neutral atomic beam techniques to write nanostructures. In the chromium experiment, we have used neutral chromium atoms to write one- and two-dimensional periodic nanometer-scale structures in a direct way. The periodic structure is given to the atomic beam by a laser light mask. In a second experiment, we have used a self-assembling monolayer as a resist for metastable helium atoms in a proximity printing experiment.

Within the ELIPS program of ESA, the “Space Optical Clocks” (SOC) project aims to install and to operate an optical lattice clock on the ISS towards the end of this decade. In this project two accurate transportable lattice optical clock demonstrators having relative frequency instability below 1×10-15 at 1 s integration time and relative inaccuracy below 5×10-17 are under development. Crucial requirements are moderate volume, electrical power consumption and mass, and robustness. Furthermore, a modular concept is favourable.

We present a novel industrial-grade prototype version of a continuous-wave 193 nm laser system entirely based on solid state pump laser technology. Deep-ultraviolet emission is realized by frequency-quadrupling an amplified diode laser and up to 20 mW of optical power were generated using the nonlinear crystal KBBF. We demonstrate the lifetime of the laser system for different output power levels and environmental conditions. The high stability of our setup was proven in > 500 h measurements on a single spot, a crystal shifter multiplies the lifetime to match industrial requirements. This laser improves the relative intensity noise, brilliance, wall-plug efficiency and maintenance cost significantly. We discuss first lithographic experiments making use of this improvement in photon efficiency.

The Matter-Wave laser Interferometer Gravitation Antenna, MIGA, will be a hybrid instrument composed of a network of atom interferometers horizontally aligned and interrogated by the resonant field of an optical cavity. This detector will provide measurements of sub Hertz variations of the gravitational strain tensor. MIGA will bring new methods for geophysics for the characterization of spatial and temporal variations of the local gravity field and will also be a demonstrator for future low frequency Gravitational Wave (GW) detections. MIGA will enable a better understanding of the coupling at low frequency between these different signals. The detector will be installed underground in Rustrel (FR), at the "Laboratoire Souterrain Bas Bruit" (LSBB), a facility with exceptionally low environmental noise and located far away from major sources of anthropogenic disturbances. We give in this paper an overview of the operating mode and status of the instrument before detailing simulations of the gravitational background noise at the MIGA installation site., Proceedings of SPIE Photonics Europe conference, Brussels (Belgium), 3-7 April 2016