NEXCERA has emerged as a ceramic-based material for spacers in ultra-stable optical cavities, with a coefficient of thermal expansion that crosses zero near room temperature. In such cavities, frequency stability is ultimately limited by Brownian thermal noise in the cavity components. A key parameter in this context is the mechanical loss, which has remained unknown for NEXCERA. In this work, we investigate the mechanical loss of NEXCERA N117B at room temperature for various resonances using the gentle nodal suspension technique. We measure a promising minimum mechanical loss of phi = 1.89 x 10-5, indicating the suitability of NEXCERA for low-noise optical cavities. Using this value, we calculate the thermal noise of a cavity with a NEXCERA spacer and compare its performance to established materials such as ULE and Zerodur, taking into account different mirror substrate options. Our analysis shows that NEXCERA is a strong candidate for ultra-stable cavities due to its low thermal noise. Combined with its previously reported low linear drift, it offers a highly attractive option for long-term stable optical frequency references. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

In this work, we introduce a new bispectral optical cavity concept for which we design twin pairs of highly reflective, ultra-low noise metamirrors. Metasurfaces, artificial structures composed of periodic or quasi-periodic arrays of nanostructures, offer unprecedented control over light properties, paving the way for new applications in areas from high-precision optical metrology to quantum science. Custom phase and an ultra-high reflection coefficient make these metasurfaces an ideal candidate to surpass traditional multilayer mirrors as metamirrors in precision interferometry, particularly by also minimizing thermal noise. The focusing metamirrors designed in this study expect to reflect 99.95% and 99.96% of the incoming light at both, 1064 nm and 1550 nm wavelength. Their planar counterparts even reach theoretical reflectivities of 99.9999% (1064 nm) and 99.9995% (1550 nm). These specialized metamirrors enable bispectral low-noise optical cavities, which would reduce the number of cavities in optical experiments or could be used as a versatile transfer cavity for frequency locking.

Interferometric sensors, renowned for their exceptional accuracy, leverage the wave properties of coherent electromagnetic radiation. The periodicity of the measurement signal often critically limits the measurement range of sensors utilizing interferometry. Here we introduce a cavity-based interferometry concept that capitalizes on a laser with moderate coherence, thereby combining ultra-high accuracy with ultra-high measurement bandwidth and range. To this end mid-fringe detection is combined with measurements of the interferometric visibility. We present experimental results that demonstrate the effectiveness of our approach exemplarily for length sensing. Notably, our system achieves an accuracy of 1 nm with a measurement range of 120 μm (relative uncertainty of 0.00083 %) and a bandwidth ranging from 0 Hz to 20 kHz. These findings support advancements in high-precision sensing applications that demand simultaneous accuracy, measurement range and bandwidth.

The precision of many applications in high-precision metrology involving optical cavities is limited by the Brownian thermal noise of mirror coatings. Meta-mirrors are promising to overcome current noise limitations. In this contribution, we demonstrate a meta-etalon combining a meta-mirror with a conventional multilayer mirror to enhance the maximum reflectivity of the meta-mirror while maintaining low thermal noise. By this, we achieve a cavity finesse of 11.500, more than a factor of 10 larger than the maximum achieved with standalone meta-mirrors.

Interferometric experiments are often limited in sensitivity by the thermal noise of the mirrors. In particular, interferometric gravitational wave detectors and laser stabilization resonators can benefit from reduced mirror noise. We present results of experimental investigations on micro-structured mirrors (meta-mirrors) and hybrid etalon mirrors (meta-etalons) promising particularly low thermal noise. We show the first characterization of meta-etalons scattering and absorption losses, demonstrating optical losses below 500 ppm. This level of optical losses is sufficient for planning direct thermal noise measurement in dedicated optical cavity experiments. These measurements would be very important for validating the thermal noise predictions. We present our development toward the integration of meta-etalons in ultra-stable optical cavities.

In order to accomplish more functional and efficient light routing on a chip, photonic integration is necessary. Particularly in quantum technologies, which require a high precision of operation, avoiding bulky optical arrangements is in high demand. Scalable and robust photonic components open up a plethora of possibilities. The light guiding systems have to be able to cover a wide range of operational wavelengths and different light polarization states. In this work, we present the first numerical results for our approach of a PIC producing NIR circularly polarized light based on a Si3N4 material platform. This concept includes waveguides and metasurfaces that are easily integrable on the chip surface of many trapped-ion quantum computer architectures.

The most precise measurement tools of humankind are equipped with ultra-stable lasers. State-of-the-art laser stabilization techniques are based on external cavities, that are limited by noise originated in the coatings of the cavity mirrors. Microstructured mirror coatings (so-called meta-mirrors) are a promising technology to overcome the limitations of coating noise and therewith pave the way towards next-generation ultra-stable lasers. We present experimental realization of a 12,000-finesse optical cavity based on one low-noise meta-mirror. The use of the mirrors studied here in cryogenic silicon cavities represents an order of magnitude reduction in the current limiting mirror noise, such that the stability limit due to fundamental noise can be reduced to 5 × 10 −18 .

We present theoretical and experimental results of low-noise microstructured mirrors based on silicon on silica for applications in ultrastable lasers. In particular, we show the experimental realization of a hybrid etalon containing microstructured and conventional mirrors. We address the measurement of reflectivity with cavity ringdown spectroscopy, the calculation of noise contributions, and scattered light measurements on the mirror.

Integrated optics are a vital approach toward scalable trapped-ion quantum computers. We present numerical results for controlling linearly polarized light with various focusing features of a µm-beam via grating structures. Furthermore, we discover a multi-wavelength addressing by optimizing the design of the structure and manipulating the beam's overlap

Ion traps are a promising platform for the realisation of high-performance quantum computers. To enable the future scalability of these systems, integrated photonic solutions for guiding and manipulating the laser light at chip level are a major step. Such passive optical components offer the great advantage of providing beam radii in the μm range at the location of the ions without increasing the number of bulk optics. Different wavelengths, from UV to NIR, as well as laser beam properties, such as angle or polarisation, are required for different cooling and readout processes of ions. We present simulation results for different optical photonic components, such as grating outcouplers or waveguide splitters and their applications on ion trap chips. Furthermore, we will introduce the experimental setup for the optical characterisation of the fabricated structures.

We present the progress towards the first realization of an optical lattice clock based on the Bosonic 24 Mg 1 S 0 – 3 P 0 optical transition. We achieve the highest Q-factor for Mg with linewidths below 50 Hz which allows a precise determination of the systematic shifts.

We present a magnesium optical lattice clock with the highest Q value of 1.6 × 10 -13 and an evaluation of its accuracy limitations for an upcoming frequency measurement.