Efficient guidance of physical experiments involving many control parameters presents a challenging optimization problem. In this work, we investigate how machine learning methods can be utilized to dramatically speed up the parameter tuning process pertinent to cold-atom sources with applications in quantum memories and atom interferometry. We compare the capabilities of several machine learning strategies in controlling the experimental process and report on the superior performance of the scalable Bayesian optimization algorithm, specifically tailored for this task.
Within the DLR project COMPASSO, optical clock and link technologies will be evaluated in space on the Bartolomeo platform attached to the Columbus module of the ISS. The system utilizes two iodine-based frequency references, a frequency comb, an optical laser communication and ranging terminal and a GNSS disciplined microwave reference. While COMPASSO is specifically dedicated to test optical technologies relevant for future satellite navigation (i.e. Galileo), the technologies are also crucial for future missions related to Earth observation and science. The optical frequency reference is based on modulation transfer spectroscopy (MTS) of molecular iodine near a wavelength of 532 nm. An extended cavity diode laser (ECDL) at a wavelength of 1064 nm is used as light source, together with fiber-optical components for beam preparation and manipulation. The laser light is frequency-doubled and sent to a mechanically and thermally highly stable free-beam spectroscopy board which includes a 20 cm long iodine cell in four-pass configuration. The iodine reference development is lead by the DLR-Institute of Quantum Technologies and includes further DLR institutes, space industry and research institutions. Phase B of the project will be finalized soon and an Engineering Model of the iodine reference, which represents the flight models in form, fit and function, will be realized by mid 2023. The launch of the COMPASSO payload is planned for 2025. Additional presentation content can be accessed on the supplemental content page.
Cold atom based quantum sensors require robust and miniaturized optical systems for applications on mobile platforms. A micro-integrated optical system (volume ∼25 mL) for trapping and manipulation of neutral atoms is presented. This setup focuses and precisely overlaps two high power laser beams (1064 nm, up to 2W total, wR = 34 µm) launched via a single-mode, polarization maintaining optical fiber, thereby realizing a crossed beam optical dipole trap (ODT). Adhesive bonding is qualified in application relevant geometries and material systems of micro-integrated optical systems for application on mobile platforms or space. Fused silica test blocks (bond area 2 × 4 mm2 ) are bonded with four different adhesives on silicon wafers. Theses samples are aged by thermal cycling (up to −55 °C to 150 °C) and/or gamma-radiation (10 000 mSv) and subsequently the bond strength is evaluated by die shear testing according to MIL-STD-883L. The influence of the environmental aging on the bond strength is presented, the failure mode and the influence of fillets discussed. In addition, the effects of plasma cleaning on the bond strength in this geometry is presented.
Manual optimization of experimental parameters can quickly become too complex and time-consuming if more than a few correlated parameters need to be adjusted. We discuss automating this process using Bayesian optimization. This machine learning-based method is particularly suitable because it can handle noisy measurements, performs a global search and requires relatively few experimental runs. We discuss the efficient, scalable implementation of Bayesian optimization, present practical applications for tuning experimental parameters, and compare it with other local and global heuristic methods to show its application range.
We report on our latest progress on the ongoing development of a compact optical frequency reference for CubeSat missions in LEO. This reference will be based on Doppler free laser spectroscopy of rubidium vapor. Our simplified solution is based on frequency modulation spectroscopy using a customized, shielded 5 mm long vapor cell and a monolithic distributed feedback (DFB) laser diode on a mesoscopic breadboard setup. The electro-optical system features miniaturized optics as well as a polarization maintaining fiber coupling inside a housing with dimensions of 70 mm × 26 mm × 19 mm (38 cm³). The latter will be installed on a 90 mm × 80mm electronics board for full functionality of the system. This way, our reference constitutes a key technology for future compact, simple and robust atomic quantum technologies for nanosatellite applications.
Employing compact quantum sensors in field or in space (e.g., small satellites) implies demanding requirements on components and integration technologies. Within our work on integrated sensors, we develop miniaturized, ultra-stable optical setups for optical cooling and trapping of cold atomic gases. Besides challenging demands on alignment precision, and thermo-mechanical durability, we specifically address ultra-high vacuum (UHV) compatibility of our integration technologies and optical components. A prototype design of an UHV-compatible, crossed beam optical dipole trap setup and its application within a cold atomic quantum sensor is described.
First qualification efforts on adhesive micro-integration technologies are presented. These tests are conducted in application-relevant geometries and material combinations common for micro-integrated optical setups. Adhesive aging will be investigated by thermal cycling or gamma radiation exposure. For vacuum compatibility testing, a versatile UHV testing system is currently being set up, enabling residual gas analysis and measurement of total gas rates down to 5•10-10mbar l/s at a base pressure of 10-11 mbar, exceeding the common ASTM E595 test.
Within the European Space Agency (ESA) activity “Gravitational Wave Observatory Metrology Laser” we designed a laser head to fulfill the LISA laser requirements using a non-NPRO seed laser technology: an external cavity diode laser (ECDL) with resonant optical feedback from an external cavity as master oscillator for further linewidth narrowing. Furthermore, our design features a single-stage fiber amplifier with an amplification factor of about 20 dB. This paper covers the requirements on the laser source for LISA, the design and first results of performance characterization of the laser head breadboard.
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