@article{21765, abstract = {Dielectric particles of the same material exchange electrical charge during collisions or sliding contacts, yet the underlying charge-exchange mechanism is still not understood. The fact that particles can become highly charged as a result of this effect has significant consequences for many settings, both in nature and industry, such as thunderstorms, volcanic eruptions, particle aggregation during meteorite and planet formation, and the clogging of industrial granular systems. Toward understanding these systems, great efforts have been made to develop precise in situ measurements for particle charge, e.g., to determine ensemble charge distributions or measure exchange during individual contacts. Here, we present experimental results concerning the particle size scaling of the stationary-state charge distributions of oxide particles in the sub-millimeter range. We measure the charge distributions for large ensembles of monodisperse ZrO2:SiO2 composite spheres, ranging from 172 to 545µ⁢m in diameter. These distributions are non-Gaussian and collapse to a single master curve when plotted as functions of the surface charge density Σ=𝑞/4⁢𝜋⁢𝑅2. X-ray fluorescence and atomic force microscopy measurements show that the differences in the measured charge distributions are not due to variations in chemical composition or surface roughness, but rather to size alone. Our findings provide constraints on microscopic models for charge exchange, namely that they should lead to steady-state distributions that are non-Gaussian and scale in a specific way with particle size.}, author = {Lara, Macarena and Flores, Marcos and Castillo, Gustavo and Tassara, Santiago and Waitukaitis, Scott R and Mujica, Nicolás}, issn = {2475-9953}, journal = {Physical Review Materials}, number = {4}, publisher = {American Physical Society}, title = {{Particle size scaling of non-Gaussian granular charge distributions}}, doi = {10.1103/qw6t-xqdw}, volume = {10}, year = {2026}, } @article{21766, abstract = {We provide a new characterisation of the decades old open problem of extending bilipschitz mappings given on a Euclidean separated net. In particular, this allows for the complete positive solution of the open problem in dimension two. Along the way, we develop a set of tools for bilipschitz extensions of mappings between subsets of Euclidean spaces.}, author = {Dymond, Michael and Kaluza, Vojtech}, issn = {2737-114X}, journal = {Annales Fennici Mathematici}, keywords = {Lipschitz, bilipschitz, extension, separated net.}, number = {1}, pages = {237--260}, publisher = {Finnish Mathematical Society}, title = {{Extending bilipschitz mappings between separated nets}}, doi = {10.54330/afm.181562}, volume = {51}, year = {2026}, } @article{21776, abstract = {Pyridyl motifs equipped with N-substituents can be powerful ligands for catalysis, yet their broader adoption is limited by the lack of a practical method to prepare these scaffolds. We report a modular, robust, and versatile Buchwald–Hartwig amination protocol that enables the rapid synthesis of bipyridine, phenanthroline, terpyridine, and pybox ligands bearing dialkylamine, diarylamine, and heteroaromatic N-substituents. These conditions streamline ligand library synthesis and will facilitate systematic studies in catalysis and related applications.}, author = {Petrik, Adam and Bena, Aleksander and Baunis, Haralds and Kelch, Riley M. and Yoon, Tehshik P. and Pieber, Bartholomäus}, issn = {1615-4169}, journal = {Advanced Synthesis & Catalysis}, number = {9}, publisher = {Wiley}, title = {{Facile access to N-substituted pyridyl ligands}}, doi = {10.1002/adsc.70417}, volume = {368}, year = {2026}, } @article{21778, abstract = {We prove that every 𝐿-bilipschitz mapping ℤ 2 → ℝ2 canbe extended to a 𝐶(𝐿)-bilipschitz mapping ℝ2 → ℝ2,and we provide a polynomial upper bound for 𝐶(𝐿).Moreover, we extend the result to every separated netin ℝ2 instead of ℤ 2, with the upper bound gaininga polynomial dependence on the separation and netconstants associated to the given separated net. Thisanswers an Oberwolfach question of Navas from 2015and is also a positive solution of the two-dimensionalform of a decades old open (in all dimensions at leasttwo) problem due to Alestalo Trotsenko and Väisälä.}, author = {Dymond, Michael and Kaluza, Vojtech}, issn = {1469-7750}, journal = {Journal of the London Mathematical Society}, number = {4}, publisher = {Wiley}, title = {{Planar bilipschitz extension from separated nets}}, doi = {10.1112/jlms.70540}, volume = {113}, year = {2026}, } @article{21780, abstract = {It is predicted that half or more of all cataclysmic variables (CVs) should have evolved past the period minimum and now exist as so-called period bouncers where a white dwarf should be accreting from a Roche lobe filling substellar companion. However, this prediction stands in stark contrast to observations, where only a few per cent of CVs are found in this evolutionary phase. A potential solution to this discrepancy is that a magnetic field emerges from within the white dwarf after the system has reached the period minimum. The transfer of angular momentum from the spin of the white dwarf into the orbit then pushes the two stars apart, detaching them for potentially billions of years. Here we present the discovery of ZTF J021804.16+071152.93, a detached 0.69 +- 0.01 M⁠, 19 MG magnetic white dwarf plus 37 +- 5MJup brown dwarf binary with an orbital period of 1.7 h. The kinematics of the system indicate that it is a high probability member of the Galactic thick disc. However, this strongly disagrees with the much younger age of the system obtained from the white dwarf parameters, implying that the system may have been accreting in the past. This system is therefore consistent with having detached as a result of the emergence of the magnetic field of the white dwarf when the system was still mass transferring, and may represent the ultimate fate for many (perhaps even most) CVs.}, author = {Parsons, S. G. and Brown, A. J. and Casewell, S. L. and Littlefair, S. P. and van Roestel, Joannes C and Rebassa-Mansergas, A. and Murillo-Ojeda, R. and Zorotovic, M. and Schreiber, M. R. and Bagnulo, S. and Stroet, M. A. and Castro Segura, N. and Dhillon, V. S. and Dyer, M. J. and Garbutt, J. A. and Green, M. J. and Jarvis, D. and Kennedy, M. R. and Kerry, P. and Mccormac, J. and Munday, J. and Pelisoli, I. and Pike, E. and Sahman, D. I. and Yates, A.}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, publisher = {Oxford University Press}, title = {{ZTF J021804.16+071152.93: A dead cataclysmic variable and potential solution to the missing period bouncer cataclysmic variables}}, doi = {10.1093/mnras/stag521}, volume = {547}, year = {2026}, } @article{21781, abstract = {Given a set A of n points (vertices) in general position in the plane, the complete geometric graph Kn[A] consists of all (n2) segments (edges) between the elements of A. It is known that the edge set of every complete geometric graph on n vertices can be partitioned into O(n3∕2) crossing-free paths (or matchings). We strengthen this result under various additional assumptions on the point set. In particular, we prove that for a set A of n randomly selected points, uniformly distributed in [0,1]2, with probability tending to 1 as n→∞, the edge set of Kn[A] can be covered by O(nlogn) crossing-free paths and by O(n√logn) crossing-free matchings. On the other hand, we construct n-element point sets such that covering the edge set of Kn[A] requires a quadratic number of monotone paths.}, author = {Dumitrescu, Adrian and Pach, János and Saghafian, Morteza and Scott, Alex}, issn = {2996-220X}, journal = {Combinatorics and Number Theory}, number = {1}, pages = {73--82}, publisher = {Mathematical Sciences Publishers}, title = {{Covering complete geometric graphs by monotone paths}}, doi = {10.2140/cnt.2026.15.73}, volume = {15}, year = {2026}, } @misc{21800, abstract = {LAMMPS input scripts to simulate toroidal vesicles composed of pure bolalipid membranes and archaeal mixture membranes for the following publication: "Cracking donuts and sorting lipids: geometry controls archaeal membrane stability and lipid organization" by Felix Frey, Miguel Amaral, and Andela Saric.}, author = {Frey, Felix F and Santana de Freitas Amaral, Miguel and Šarić, Anđela}, publisher = {Zenodo}, title = {{Cracking donuts and sorting lipids: Geometry controls archaeal membrane stability and lipid organization}}, doi = {10.5281/ZENODO.18772086}, year = {2026}, } @article{21837, abstract = {In a warming world of glacier changes, the scientific community has dedicated increasing attention to debris-covered glaciers and their response to climate. A variety of models with distinct complexity and data requirements have been developed and widely used to simulate melt under debris at different sites and scales, but their skills have never been compared. As part of the activities of the International Association of Cryospheric Sciences (IACS) Debris Covered Glacier Working Group, we present an intercomparison exercise aimed at advancing our understanding of model skills in simulating ice melt under a debris layer. We compare 15 models with different complexity at nine sites in the European Alps, Caucasus, Chilean Andes, Nepalese Himalaya and the Southern Alps of New Zealand, over one melt season. We run the models with measured meteorological data from automatic weather stations and estimated or measured debris properties. We consider four main model categories: (i) energy balance models that calculate melt by solving the physics of heat transfer to the debris layer, but require a high amount of input data; (ii) a simplified energy balance model; (iii) enhanced temperature-index models; and (iv) simple empirical temperature-index models that have been extensively used given their low data requirement but require calibration of their empirical parameters. Model performance is evaluated using on-site measurements of sub-debris melt (for all models) and surface temperature (for models based on the surface energy balance). Our results show that physically-based energy balance models and empirical temperature-index models perform in a distinct manner. At one end of the spectrum, simple temperature-index models are accurate when recalibrated or when using site-specific literature parameters, and show poor results when parameters are uncalibrated. At the other end, energy balance models show a range of performance: the most accurate energy balance models are those with the highest degree of complexity at the atmosphere-debris interface. An important data gap emerged from our experiment: the poor performance of all models at three sites was related to the poor knowledge of debris properties, and specifically of thermal conductivity. Future work should focus on both: (i) consistent data acquisition to evaluate existing models and support new model developments; (ii) advancing models by accounting for processes such as debris-snow interactions, moisture in the debris and refreezing. We suggest that a systematic effort of model development using a common model framework could be carried out in phase II of the Working Group.}, author = {Pellicciotti, Francesca and Fontrodona-Bach, Adrià and Rounce, David R. and Fyffe, Catriona Louise and Anderson, Leif S. and Ayala, Álvaro and Brock, Ben W. and Buri, Pascal and Fugger, Stefan and Fujita, Koji and GANTAYAT, PRATEEK and Groos, Alexander R. and Immerzeel, Walter and Kneib, Marin and Mayer, Christoph and MacDonell, Shelley and McCarthy, Michael and McPhee, James and Miles, Evan and Purdie, Heather and Rets, Ekaterina and Sakai, Akiko and Shaw, Thomas and Steiner, Jakob and Wagnon, Patrick and Winter-Billington, Alex}, issn = {1994-0424}, journal = {The Cryosphere}, number = {3}, pages = {1895--1928}, publisher = {Copernicus Publications}, title = {{DCG-MIP: The debris-covered glacier melt model intercomparison experiment}}, doi = {10.5194/tc-20-1895-2026}, volume = {20}, year = {2026}, } @article{21838, abstract = {We explore the use of a photoacid in a chemical reaction cycle, which allows for the controlled sol‐to‐gel transition of a saccharide aldehyde‐based self‐assembling system. The modulation of the pH with light enables to generate chemical fuels in situ, thus triggering monomer activation and gelation. Our efforts represent a promising step toward dissipative self‐assembled systems with a higher degree of spatiotemporal control.}, author = {Lopez‐Acosta, Alvaro and Valera, Jorge S. and Klajn, Rafal and Hermans, Thomas M.}, issn = {2570-4206}, journal = {ChemSystemsChem}, number = {3}, publisher = {Wiley}, title = {{Photoacid‐mediated controllable gelation in a chemical reaction cycle}}, doi = {10.1002/syst.70037}, volume = {8}, year = {2026}, } @article{21840, abstract = {The transport properties of nanofluidic channels are usually studied under constant (DC) voltage or pressure driving. However, the frequency response under sinusoidal (AC) drivings offers rich insights into the time-dependent transport mechanisms. Inspired by recent electrochemical approaches, we investigate the couplings between ionic and electronic transport under AC driving. We show that conduction electrons of the channel walls participate in ionic current via capacitive electrochemical coupling, defining a critical frequency and length scale where electron-dominated conductivity emerges. We further analyze how electron–ion coupling modifies electro-osmotic flows and demonstrate that fluctuation-induced momentum transfer between the electrolyte and wall electrons produces distinct AC transport signatures, depending on the charge carrier polarity. Altogether, we establish a frequency-dependent transport matrix that couples ionic, electronic, and hydrodynamic flows. These findings establish AC nanofluidic transport as a powerful probe of interfacial phenomena under confinement and suggest new directions for engineering nanofluidic functionalities through electron–electrolyte coupling.}, author = {Coquinot, Baptiste and Lizée, Mathieu and Bocquet, Lydéric and Kavokine, Nikita}, issn = {1089-7690}, journal = {The Journal of Chemical Physics}, number = {13}, publisher = {AIP Publishing}, title = {{Electron–electrolyte coupling in AC transport through nanofluidic channels}}, doi = {10.1063/5.0313352}, volume = {164}, year = {2026}, } @article{21841, abstract = {The long-standing notion that genotypes map to phenotypes through simple one gene–one trait relationships continues to shape both research in the life sciences and public understanding, with implications for policy and funding priorities. Yet this paradigm is increasingly recognized as inadequate for explaining continuous phenotypic variation and the complex genetic architectures of the genotype–phenotype map. Modern genetics emerged from the early 20th-century synthesis of Mendelian and biometric schools of heredity, with R.A. Fisher demonstrating early on how multiple discrete loci could collectively produce continuous variation. Despite this fundamental insight, Mendelism—with its focus on single genes and standardized genetic backgrounds—became the dominant framework, shaping current genetics research and molecular biology as well as science education. The advent of large-scale genomic data has revealed yet again the limitations of this reductionist approach. Evidence from quantitative genetics now shows that most phenotypes arise from complex networks of many interdependent genes and their dynamic responses to environmental perturbations. Here we trace the historical roots of how Mendelian classical genetics departed from the biometric school to create the current predominant paradigm in genetics, despite fundamentally unresolved issues. Moving on from this one-sided paradigm will require systematic development of integrative, evolutionarily grounded experimental approaches that better capture the multigenic and context-dependent nature of inheritance. Achieving such an extended perspective will require methodological innovation, including advances in large-scale (e.g. automated) phenotyping. Dedicated research programs will be necessary to advance a new era of genetic research into the complex mechanisms underlying phenotypic variation.}, author = {Tautz, Diethard and Pallares, Luisa F and Andersson, Leif and Barghi, Neda and Barton, Nicholas H and Bay, Rachael and Chan, Yingguang Frank and Hancock, Angela and Kaiser, Tobias S and Koenig, Daniel and Kontarakis, Zacharias and Liedvogel, Miriam and de Meaux, Juliette and Nordborg, Magnus and Palmer, Abraham A and Purugganan, Michael and Schlötterer, Christian and Schmid, Karl and Stainier, Didier Y R and Weigel, Detlef and Wolf, Jochen B W and Ebert, Dieter and Gibson, Greg}, issn = {1943-2631}, journal = {Genetics}, keywords = {classic genetics, quantitative genetics, genotype–phenotype map}, number = {4}, publisher = {Oxford University Press}, title = {{Beyond Mendel: A call to revisit the genotype–phenotype map through new experimental paradigms}}, doi = {10.1093/genetics/iyag024}, volume = {232}, year = {2026}, } @article{21842, abstract = {AM CVn stars are ultra-compact semi-detached binaries consisting of a white dwarf primary and a hydrogen-depleted secondary. In this paper, we present spectroscopic and photometric results of 15 transient sources pre-classified as AM CVn candidates. Our analysis confirms 9 systems of the type AM CVn, 3 hydrogen-rich cataclysmic variables (accreting white dwarfs with near-main-sequence stars for donors), and 3 systems that could be evolved cataclysmic variables. Eight of the AM CVn stars are analysed spectroscopically for the first time, which increases the number of spectroscopically confirmed AM CVns by about 10%. TESS data revealed the orbital period of the AM CVn star ASASSN-20pv to be Porb =27.282 min, which helps to constrain the possible values of its mass ratio. TESS also helped to determine the superhump periods of one AM CVn star (ASASSN-19ct, Psh =30.94 min) and two cataclysmic variables we classify as WZ Sge stars (Psh =90.77 min for ZTF18aaaasnn and Psh =91.6min for ASASSN-15na).We identified very different abundances in the spectra of theAM CVns binaries ASASSN-15kf and ASASSN-20pv (both Porb ∼27.5min), suggesting different type of donors. Six of the studied AMCVns are X-ray sources, which helped to determine their mass accretion rates. Photometry shows that the duration of all the superoutbursts detected in the AM CVns is consistent with expectations from the disc instability model. Finally, we provide refined criteria for the identification of new systems using all-sky surveys such as LSST.}, author = {Kára, Jan and Rivera Sandoval, Liliana and Mendoza, Wendy and Maccarone, Thomas and Pichardo Marcano, Manuel and Salazar Manzano, Luis E. and Oelkers, Ryan J. and van Roestel, Joannes C}, issn = {1448-6083}, journal = {Publications of the Astronomical Society of Australia}, publisher = {Cambridge University Press}, title = {{A study of transients from ground-based surveys reveals new ultra-compact accreting white dwarf binaries}}, doi = {10.1017/pasa.2026.10184}, volume = {43}, year = {2026}, } @article{21844, abstract = {Little red dots (LRDs) are a newly identified class of broad-line active galactic nuclei (AGNs) with a distinctive V-shaped spectrum characterized by red optical and blue UV continuum emission. Their high abundance at redshifts of z ∼ 6–8 and decline at lower redshifts suggest a transient origin. We propose that the spectral shape of LRDs originates from compact binary black hole systems, in which each black hole is surrounded by a mini-disk and embedded within a larger circumbinary disk. With a binary separation of ≲103 Schwarzschild radii, the Wien tail of a T ≃ 5000 K blackbody spectrum at the inner edge of the circumbinary disk produces the red optical emission, while the mini-disks power the UV continuum. Binary torques carve out a gap between the circumbinary disk and the mini-disks, setting the turnover wavelength of the V-shaped spectrum around the Balmer limit. This scenario naturally reproduces LRD spectra requiring only modest dust attenuation (AV ≲ 1 mag), resolving overestimated luminosities for LRDs in previous studies and alleviating a tension with the so-called Sołtan argument. This model predicts distinct spectral evolution as the binary orbit decays through binary disk interactions and gravitational-wave (GW) emission, linking early-stage “proto-LRD” binaries to the broader AGN population and late-stage “LRD descendants” to coalescing binaries detectable in GW experiments.}, author = {Inayoshi, Kohei and Shangguan, Jinyi and Chen, Xian and Ho, Luis C. and Haiman, Zoltán}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {1}, publisher = {IOP Publishing}, title = {{The emergence of Little Red Dots from binary massive black holes}}, doi = {10.3847/1538-4357/ae548d}, volume = {1002}, year = {2026}, } @article{21845, abstract = {UTe2 exhibits the remarkable phenomenon of re-entrant superconductivity, whereby the zero-resistance state reappears above 40 tesla after being suppressed with a field of around 10 tesla. One potential pairing mechanism, invoked in the related re-entrant superconductors UCoGe and URhGe, involves transverse fluctuations of a ferromagnetic order parameter. However, the requisite ferromagnetic order—present in both UCoGe and URhGe—is absent in UTe2, and neutron scattering shows instead that the magnetic susceptibility is peaked at an antiferromagnetic wavevector. Here, we measure the magnetotropic susceptibility of UTe2 across two field-angle planes. This quantity is sensitive to the magnetic susceptibility in a direction transverse to the applied magnetic field—a quantity that is not accessed in conventional magnetization measurements. We observe a very large decrease in the magnetotropic susceptibility over a broad range of field orientations, indicating a large increase in the transverse magnetic susceptibility. Because our technique probes the magnetic susceptibility in the long wavelength (q = 0) limit, this suggests that the strong transverse susceptibility arises from ferromagnetic spin fluctuations. These ferromagnetic fluctuations are likely important for understanding the pairing mechanism in UTe2, as all three superconducting phases of UTe2 surround this region of enhanced susceptibility in the field-angle phase diagram.}, author = {Zambra, Valeska and Nathwani, Amit and Nauman, Muhammad and Lewin, Sylvia K. and Frank, Corey E. and Butch, Nicholas P. and Shekhter, Arkady and Ramshaw, B. J. and Modic, Kimberly A}, issn = {2041-1723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Giant transverse magnetic fluctuations at the edge of re-entrant superconductivity in UTe2}}, doi = {10.1038/s41467-026-71899-7}, volume = {17}, year = {2026}, } @article{21846, abstract = {We compile a sample of 83 little red dots (LRDs) with JWST imaging and find that a substantial fraction (∼43%, rising to ≳80% for the most luminous LRDs) host one or more spatially offset, UV-bright companions at projected separations of 0.5 kpc ≲ d ≲ 5 kpc, with median 〈d〉 = 1.0 kpc. This fraction is even higher when smaller spatial scales are probed at high signal-to-noise ratio: the two most strongly lensed LRDs, A383-LRD1 and the newly discovered A68-LRD1, both have UV-bright companions at separations of only d ∼ 0.3 kpc, below the resolution limit of most unlensed JWST samples. We explore whether these ubiquitous red/blue configurations may be physically linked to the formation of LRDs, in analogy with the “synchronized pair” scenario originally proposed for direct-collapse black hole formation. In this picture, UV radiation from the companions, with typically modest stellar masses (M∗ ∼ 108−109 M⊙), suppresses molecular hydrogen cooling in nearby gas, allowing nearly isothermal collapse and the formation of extremely compact objects, such as massive black holes, supermassive stars, or quasi-stars. Using component-resolved photometry and spectral energy distribution modeling, we infer Lyman–Werner radiation fields of J21,LW ∼ 102.5–105 at the locations of the red components, comparable to those required in direct-collapse models, suggesting that the necessary photodissociation conditions are realized in many LRD systems. This framework provides a simple and self-consistent explanation for the extreme compactness and distinctive spectral properties of LRDs and links long-standing theoretical models for early compact object formation directly to a population now observed with JWST in the early Universe.}, author = {Baggen, Josephine F.W. and Scoggins, Matthew T. and Van Dokkum, Pieter and Haiman, Zoltán and Torralba Torregrosa, Alberto and Matthee, Jorryt J}, issn = {2041-8213}, journal = {The Astrophysical Journal Letters}, number = {1}, publisher = {IOP Publishing}, title = {{Connecting the dots: UV-bright companions of Little Red Dots as Lyman–Werner sources enabling direct-collapse Black Hole formation}}, doi = {10.3847/2041-8213/ae58a5}, volume = {1002}, year = {2026}, } @article{21847, abstract = {Analog quantum simulators provide access to many-body dynamics beyond the reach of classical computation. However, extracting physical insights from experimental data is often hindered by measurement noise, limited observables, and incomplete knowledge of the underlying microscopic model. Here, we develop a machine learning approach based on a variational autoencoder (VAE) to analyze interference measurements of tunnel-coupled one-dimensional Bose gases, which realize the sine-Gordon quantum field theory. Trained in an unsupervised manner, the VAE learns a minimal latent representation that strongly correlates with the equilibrium control parameter of the system. Applied to nonequilibrium protocols, the latent space uncovers signatures of frozen-in solitons following rapid cooling, and reveals anomalous postquench dynamics not captured by conventional correlation-based methods. These results demonstrate that generative models can extract physically interpretable variables directly from noisy and sparse experimental data, providing complementary probes of equilibrium and nonequilibrium physics in quantum simulators. More broadly, our work highlights how machine learning can supplement established field-theoretical techniques, paving the way for scalable, data-driven discovery in quantum many-body systems.}, author = {Moller, Frederik Skovbo and Fernández-Fernández, Gabriel and Schweigler, Thomas and De Schoulepnikoff, Paulin and Schmiedmayer, Jörg and Muñoz-Gil, Gorka}, issn = {2643-1564}, journal = {Physical Review Research}, number = {2}, publisher = {American Physical Society}, title = {{Learning minimal representations of many-body physics from snapshots of a quantum simulator}}, doi = {10.1103/r7pj-gl7r}, volume = {8}, year = {2026}, } @phdthesis{21863, abstract = {Atoms and photons, two things so different but yet so alike. The former, the building block of matter, something we learn about in school and imagine it as some tiny marbles encircled by other tinier marbles. The latter, an electromagnetic wave, a light particle or an excitation of the electromagnetic field. Quantum mechanics tells us about the properties of these two entities. And even if it sounds, looks and writes counter-intuitive, it has proven right for over a century now. In this work, I elaborate on how we tested the laws of quantum mechanics and how we used them learn more about the tiny building blocks of nature and the fields they use to talk to each other. The atoms we use, are artificial. Superconducting qubits, small electrical circuits with quantized energy levels behave like electrons that transition between different orbitals in an atom. One of the qubits' advantages, is also a big disadvantage. We design the circuits' energy levels and fabricate them in a cleanroom. This allows for arbitrary spaced energy levels but in contrast to real atoms, prevents two superconducting qubits from being alike. Still, this qubit platform is one of the frontrunners for future quantum computing technology and testing fundamental physics due to their scalability. We interface superconducting qubits, which operate in the GHz regime, with microwave photons. We use 3D aluminum cavities as mediators between qubits and photons. The cavities allow for non-destructive readout of the qubit state, they shield the qubits from noise at the qubit frequency and they give us an easy way to frequency-tune these joint systems. We need to operate superconducting qubits and their cavities at millikelvin temperatures in dilution refrigerators. At higher temperatures, superconductivity suffers and even worse, the environment is filled with thermal noise photons. This poses a fundamental limitation on the scalability of superconducting qubit devices. Also connecting multiple devices in different fridges does not work over room temperature links because the microwave photons used for this purpose will be covered in noise and the quantum information they carry, will be unusable. Infrared photons do not suffer from this noise problem since there are close to zero thermal noise photons at their frequencies at room temperature. We cannot simply interface superconducting devices with optical photons due their frequency mismatch and the destructive effect of optical photons on superconductors. Therefore, we use microwave-to-optics transducers that allow to convert microwave photons into optical ones and vice-versa. The transducers that we use are macroscopic electro-optic transducers using the Pockels effect in a disk-shaped Lithium Niobate whispering gallery mode resonator. By using a strong optical pump, photons from the two frequency domains experience a beam-splitter interaction and get converted from one to the other. We measure the generated optical photons using elaborate optical setups, optical heterodyning and single photon detectors to gain knowledge about the qubit state or the converted microwave photons. Bridging the microwave and the optical world allows us to take advantage of both of their strengths but it also requires deep knowledge about both of their working principles. In this work, we describe two experiments that our group conducted to showcase the opportunities that arise from interfacing superconducting qubits with optical photons but also the pitfalls, one may encounter on the way. In the first experiment, we managed to all-optically read out a superconducting qubit. We show that the assignment fidelity, the probability that a measurement of the qubit state matches the prepared state, is close to equal for all-optical, microwave-to-optics and conventional microwave readout. We show T1 and T2 measurements for all three readout types and give an analysis of the noise caused by the optics. Finally, we show that the infrared light does not affect the qubit performance in a negative way but that the heating it causes does. This is an important insight that we used in the next experiment. The second experiment is the upconversion of itinerant single microwave photons to the optical domain. We show that we can generate single microwave photons from a qubit-cavity system. We upconvert these single photons, measure them with a single photon detector and reconstruct their shape. By conducting a single photon Rabi measurement, we show correlations between the microwave and the optical domain. And by thorough signal-to-noise measurements and noise analysis, we find that we can generate single infrared photons with high signal-to-noise ratio 5.1 and low transducer added noise (<0.012 quanta). We show that this measurement creates a path towards entanglement of a superconducting qubit and an optical photon and what parameters need to be improved to achieve it. Additionally, this experiment is a proof of principle for an on-demand infrared single photon source. More generally, it allows to link microwave quantum technology in general to the optical domain.}, author = {Werner, Thomas}, issn = {2663-337X}, keywords = {Superconducting qubits, Quantum optics, Single photons and quantum effects, Nonlinear optics}, pages = {97}, publisher = {Institute of Science and Technology Austria}, title = {{Interfacing superconducting qubits with optical photons}}, doi = {10.15479/AT-ISTA-21863}, year = {2026}, } @unpublished{21870, abstract = {Superconducting qubits are a leading candidate for utility-scale quantum computing due to their fast gate speeds and steadily decreasing error rates. The requirement for millikelvin operating temperatures, however, creates a significant scaling bottleneck. Modular architectures using optical fiber links could bridge separate cryogenic nodes, but superconducting circuits do not have coherent optical transitions and microwave-to-optical conversion has not been shown for any non-classical photon state. In this work, we demonstrate the on-demand generation and tomographic reconstruction of itinerant single microwave photons at 8.9 GHz from a superconducting qubit. We upconvert this non-Gaussian state with a transducer added noise below 0.012 quanta and count the converted telecom photons at 193.4 THz with a signal-to-noise ratio of up to 5.1$\pm$1.1. We characterize the trade-offs between throughput and noise, and establish a viable path toward heralded entanglement distribution and gate teleportation. Looking ahead, these results empower existing superconducting devices to take a key role in distributed quantum technologies and heterogeneous quantum systems.}, author = {Werner, Thomas and Riyazi, Erfan and Hawaldar, Samarth and Sahu, Rishabh and Arnold, Georg M and Paul Falthansl-Scheinecker, Paul Falthansl-Scheinecker and Naranjo, Jennifer A. Sánchez and Loi, Dante and Kapoor, Lucky N. and Zemlicka, Martin and Qiu, Liu and Militaru, Andrei and Fink, Johannes M}, booktitle = {arXiv}, title = {{Electro-optic conversion of itinerant Fock states}}, doi = {10.48550/arXiv.2602.00928}, year = {2026}, } @article{21881, abstract = {I review recent contributions on nonlinear Dirichlet forms. Then, I specialise to the case of 2- homogeneous and local forms. Inspired by the theory of Finsler manifolds and metric measure spaces, I establish new properties of such nonlinear Dirichlet forms, which are reminiscent of differential calculus formulae.}, author = {Brigati, Giovanni}, issn = {2730-9657}, journal = {La Matematica}, number = {2}, publisher = {Springer Nature}, title = {{Nonlinear Dirichlet forms, energy spaces, and calculus rules}}, doi = {10.1007/s44007-026-00217-w}, volume = {5}, year = {2026}, } @article{21882, abstract = {The nature of little red dots (LRDs) has largely been investigated through their continuum emission, with lines assumed to arise from a broad-line region. In this paper, we instead use recombination lines to infer the intrinsic properties of the central engine. Our analysis first reveals a tension between the ionizing properties implied from Hα and He ii λ4686. The high Hα EWs require copious H-ionizing photons, more than the bluest active galactic nucleus (AGN) ionizing spectra can provide. In contrast, He ii emission is marginally detected, and its low EW is, at most, consistent with the softest AGN spectra. The low He ii/Hβ (∼10−2, <20× local AGN median) further points to an unusually soft ionizing spectrum. We extend our analysis to dense gas envelopes (quasi-star/black-hole star) and find that hydrogen recombination lines become optically thick and lose diagnostic power, but He ii remains optically thin and a robust tracer. Photoionization modeling with Cloudy rules out standard AGN accretion disk spectra. Alternative explanations include exotic AGN with red rest-optical emission, high average optical depth (>10) from gas/dust, and soft ionizing spectra with abundant H-ionizing photons, consistent with, e.g., a cold accretion disk or a composite of AGN and stars. The latter is an intriguing scenario since high hydrogen densities are highly conducive for star formation, and nuclear star clusters are found in the vicinity of local massive black holes. While previous studies have mostly focused on features dominated by the absorbing hydrogen cloud, the He ii-based diagnostic proposed here represents a crucial step toward understanding the central engine of LRDs.}, author = {Wang, Bingjie and Leja, Joel and Katz, Harley and Inayoshi, Kohei and Cleri, Nikko J. and De Graaff, Anna and Hviding, Raphael E. and Van Dokkum, Pieter and Greene, Jenny E. and Labbé, Ivo and Matthee, Jorryt J and Mcconachie, Ian and Naidu, Rohan P. and Nelson, Erica J.}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {1}, publisher = {IOP Publishing}, title = {{The missing hard photons of Little Red Dots: Their incident ionizing spectra resemble massive stars}}, doi = {10.3847/1538-4357/ae5bab}, volume = {1003}, year = {2026}, }