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Aluminum oxide (Al 2 O 3 ) is an emerging material in integrated photonics. It exhibits a very broad transparency window from the UV to the mid-IR, very low propagation losses and a high solubility for rare-earth ions leading to optical gain in different spectral ranges. Al 2 O 3 can be deposited by different wafer-level deposition techniques, including atomic layer deposition and reactive magnetron sputtering, being compatible with the monolithic integration onto passive integrated photonics platforms, such as Si 3 N 4 , to which it provides optical amplification and lasing. When deposited at low temperatures, it is also compatible with integration onto CMOS chips. In this review, the state-of-the-art on the deposition, integration and device development in this photonic platform is described.

Optical clocks based on trapped ions are highly stable frequency standards with applications in navigation, fundamental physics tests, and chronometric geodesy. Hence, ion traps are a key component for ion-based quantum technology applications. To achieve greater scalability and laser pointing stability, it is crucial to integrate nanophotonics monolithically into ion trap architectures. Addressing and manipulating the ions requires wavelengths ranging from ultraviolet (UV) to near-infrared (NIR). In this contribution, we report on the design and characterization of a photonic integrating circuit for the optical addressing of Yb+ ions using a foundry-fabricated single-layer Al2O3 nanophotonic platform.

Optical clocks based on trapped ions are highly stable frequency standards with applications in navigation, fundamental physics tests, and chronometric geodesy. Hence, ion traps are a key component for ion-based quantum technology applications. To achieve greater scalability and laser pointing stability, it is crucial to integrate nanophotonics monolithically into ion trap architectures. Addressing and manipulating the ions requires wavelengths ranging from ultraviolet (UV) to near-infrared (NIR). In this contribution, we report on the design and characterization of a photonic integrating circuit for the optical addressing of Yb + ions using a foundry-fabricated single-layer Al 2 O 3 nanophotonic platform.

Integrated photonics is an essential technology for optical quantum computing. Universal, phase-stable, reconfigurable multimode interferometers (quantum photonic processors) enable manipulation of photonic quantum states and are one of the main components of photonic quantum computers in various architectures. In this paper, we report the realization of the largest quantum photonic processor to date. The processor enables arbitrary unitary transformations on its 20 input modes with an amplitude fidelity of \\(F_{\\text{Haar}} = 97.4\\%\\) and \\(F_{\\text{Perm}} = 99.5\\%\\) for Haar-random and permutation matrices, respectively, an optical loss of 2.9 dB averaged over all modes, and high-visibility quantum interference with \\(V_{\\text{HOM}}=98\\%\\). The processor is realized in \\(\\mathrm{Si_3N_4}\\) waveguides and is actively cooled by a Peltier element.

Photonic processors are pivotal for both quantum and classical information processing tasks using light. In particular, linear optical quantum information processing requires both largescale and low-loss programmable photonic processors. In this paper, we report the demonstration of the largest universal quantum photonic processor to date: a low-loss, 12-mode fully tunable linear interferometer with all-to-all coupling based on stoichiometric silicon nitride waveguides.

Reconfigurable quantum photonic processors are an essential technology for photonic quantum computing. Although most large-scale reconfigurable quantum photonic processors were demonstrated at the telecommunications C band around 1550 nm, high-performance single photon light sources utilizing quantum dots that are well-suited for photonic quantum computing operate at a variety of wavelengths. Thus, a demand exists for the compatibility of quantum photonic processors with a larger wavelength range. Silicon nitride (SiN) has a high confinement and wide transparency window, enabling compact, low-loss quantum photonic processors at wavelengths outside the C band. Here, we report a SiN universal 12-mode quantum photonic processor with optimal operation at a wavelength of 940 nm, which is compatible with InGaAs quantum dot light sources that emit light in the 900 nm to 970 nm wavelength range. The processor can implement arbitrary unitary transformations on its 12 input modes with a fidelity of 98.6 %, with a mean optical loss of 3.4 dB/mode.

The existence of fully transmissive eigenchannels (\"open channels\") in a random scattering medium is a counterintuitive and unresolved prediction of random matrix theory. The smoking gun of such open channels, namely a bimodal distribution of the transmission efficiencies of the scattering channels, has so far eluded experimental observation. We observe an experimental distribution of transmission efficiencies that obeys the predicted bimodal Dorokhov-Mello-Pereyra-Kumar distribution. Thereby we show the existence of open channels in a linear optical scattering system. The characterization of the scattering system is carried out by a quantum-optical readout method. We find that missing a single channel in the measurement already prevents detection of the open channels, illustrating why their observation has proven so elusive until now. Our work confirms a long-standing prediction of random matrix theory underlying wave transport through disordered systems.

Efficient and reliable measurements of photonic indistinguishability are crucial to solidify claims of a quantum advantage in photonics. Existing indistinguishability witnesses may be vulnerable to implementation loopholes, showing the need for a measurement which depends on as few assumptions as possible. Here, we introduce a semi-device-independent witness of photonic indistinguishability and measure it on an integrated photonic processor, certifying three-photon indistinguishability in a way that is insensitive to implementation errors in our processor.

The ecosystem services that humans obtain from the soil are strongly linked to the soil's biota. There is ample evidence that intensive agriculture has a negative effect on the soil's biological diversity. While in other ecosystems, habitat specialists are at a higher risk of extinction due to human impacts than generalists, we have no evidence of whether this holds true for soil biota. We calculated the realized niche width for soil nematodes using co‐occurrence data. We compared these with ecological traits. We then calculated an index of community specialization and tested whether land use intensity leads to decreases in the index of community specialization, taxon richness, diversity and to changes in nematode abundance. The resulting realized niche widths did not correlate with ecological traits such as feeding group, body mass or c‐p class. While it is possible that there are no relationships between these traits and the realized niche width, it is likelier that food availability, pH tolerance, or host breadth are more important factors in explaining niche width. Contrary to our expectations, the lowest community specialization levels were found in soils with the lowest human intervention (shrubland–woodland ecosystems), while grasslands, dairy farms and arable farms had an overall higher level of specialization. Weather variables and land use intensity explained 66% of the variation in the index of community specialization in sandy soils. We found highest richness and diversity at intermediate levels of disturbance (grasslands and dairy farms). The lowest abundances were found on shrubland–woodland systems. Dairy farms on sand and clay had similar indices of community specialization, whereas peaty soils fostered a higher proportion of habitat specialists. We argue that farmland supposes a stable environment for organisms with shorter life spans. Agricultural management strives to lower disturbances, allowing shorter lived organisms to escape pressures otherwise present in nature, such as drought or nutrient deficiencies during the growing season. In very disturbed systems, however, specialists may also suffer from negative effects of land use intensity. This co‐occurrence method to assess niche width opens the door to estimating the soil community's niche breadth, for which resource‐based methods are difficult to implement. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.