Papers

These proceedings summarise a lecture on Digital Signal Processing (DSP) delivered at the CERN Accelerator School (CAS) on Beam Instrumentation (BI). In this context, a signal is any measurable quantity conveying information about the beam. A digital signal is obtained by discretising a continuous-time signal in both time (sampling) and amplitude (quantisation). Digital signal processing refers to the set of techniques used to analyse and manipulate such signals. Given the breadth of the field, this contribution focuses on fundamental DSP concepts and on techniques most commonly encountered in beam instrumentation applications.

We investigate whether a Hayward regular black hole can be observationally distinguished from a Schwarzschild black hole through strong gravitational lensing when effective field theory (EFT) corrections to photon propagation are taken into account. We derive the modified photon propagation law induced by non-minimal couplings between the electromagnetic field and spacetime curvature, and analyze the resulting photon trajectories in the Hayward spacetime. Using the strong deflection limit, we derive the corrections to the photon sphere and the logarithmically divergent part of the deflection angle. Although the EFT corrections are parametrically small, their effects can be enhanced near the critical propagation region, where the deflection angle exhibits a logarithmic divergence. We evaluate the strong-deflection observables for representative values of the Hayward parameter and compare them with the Schwarzschild case. We find that EFT corrections to photon propagation can leave characteristic imprints on strong-lensing observables. Furthermore, the contribution of the EFT corrections becomes more pronounced as the Hayward parameter $g^3$ approaches its critical value, indicating that curvature-dependent corrections to photon propagation can become particularly relevant in the near-critical regime. These results suggest that strong gravitational lensing may provide a means of distinguishing Hayward regular black holes from Schwarzschild black holes.

Circular states of strontium are promising platforms for quantum technologies. They exhibit much longer lifetimes than laser-accessible Rydberg states and possess an optically active ionic core that can be manipulated with laser light. Here we trap circular states in optical tweezers by exploiting the dynamical polarizability of the ionic core. We measure the decay of the orbital component of a n=51 circular state and observe singlet-triplet spin oscillations arising from the interplay of vector light shifts induced by the optical tweezers, spin-orbit coupling associated with the Rydberg electron, and the difference in Landé $g$-factor between the ionic core and the Rydberg electrons. By observing the two electron spin dynamics, we measure the spin-orbit interaction and the correction $\delta g \sim$ 10^(-5) of the Landé $g$-factor of the Sr$^+$ 5s$_{1/2}$ ionic core electron with respect to that of a free electron. This provides a first high-precision measurement of $g_{\textrm{Sr}^+, 5s_{1/2}}$ = 2.002290(1).

We use a large database of direct numerical simulations to investigate the transition of the Rayleigh–Taylor instability to turbulence and its evolution toward a late-time self-similar regime. In addition to tracking the growth of the mixing layer through the mean heavy-fluid concentration profile, we analyze one-dimensional profiles of turbulent kinetic energy and dissipation, two key quantities in classical turbulent-mixing models. We consider two reduced-order modeling strategies that differ in where nonlinearity is introduced: either in the construction of the latent space or in the description of its temporal evolution. The first method uses a linear encoder–decoder obtained using Proper Orthogonal Decomposition (POD), with nonlinear reduced dynamics learned by a physics-informed neural network (PINN). The second uses a nonlinear encoder–decoder learned by an autoencoder, while constraining the latent dynamics to remain linear and satisfy physical constraints. Both approaches achieve satisfactory performance in reconstructing, interpolating, and extrapolating the dynamics of the Rayleigh–Taylor instability.

Two-band superconductors maintain a relative interband phase which can carry winding soliton excitations in a superconducting ring, supported by independent winding numbers in the two bands. In rings of superconductors obeying the inversion symmetry the interband phase solitons are metastable states, separated from the uniform ground state by the energy of screening currents. In this work we find that, breaking the inversion symmetry strongly enough, one can make the soliton a true ground state. In that case, a magneto-electric coupling, absent in centrosymmetric materials, contributes critically above a certain threshold, a relevant, free-energy term, odd with respect to the winding number, which biases the energy balance in favor of a particular winding sign. Once the bias outweighs the energy cost that originally made the soliton metastable, a phase soliton with a finite winding number becomes the ground state, with chirality set by the applied field. In current–flux measurements performed in equilibrium states, the effect is demonstrated by field-odd soliton branches, that replace the metastable ones existing in mesoscopic rings, built by two-component superconductors, realizing a magneto-electric analog of the Little–Parks fluxoid-branch physics in the interband relative-phase sector.

For unitary transformations, the quantum Fisher information (QFI) of a pure state is given by the uncertainty of the generator in that state. In post-selected metrology, the QFI is given by a modified expression describing conditional quantum statistics of the generator. Here, we show that the conditional generator uncertainties defined by post-selected QFI correspond to Ozawa-Hall uncertainties known from the theoretical analysis of quantum measurements. The post-selected measurement outcome updates the generator uncertainty according to the quantum statistics of that outcome. Enhancements of QFI beyond the maximal uncertainties of the generator eigenvalues are possible because post-selection tends to concentrate the largest part of the initial generator uncertainty in low probability outcomes of the post-selection measurement. Anomalous conditional uncertainties thus explain the extreme sensitivities that can be achieved in post-selected metrology.

While the standard interpretation of quantum mechanics does not assign definite trajectories to particles, the Bohmian interpretation does. Only recently has an operational method for reconciling Bohmian mechanics with relativity been proposed. Here, we experimentally reconstruct relativistic Bohmian trajectories of a single photon in a Michelson-Sagnac interferometer, where counter-propagating probability amplitudes interfere head-on at the speed of light. As predicted by the relativistic Bohmian theory, we observe subluminal and superluminal features of the Bohmian trajectories of the photon traversing through the fringes. Our work provides experimental access to relativistic Bohmian mechanics and enables exploration of its unusual and counterintuitive properties.

We develop a perturbative framework for constructing the fields of electromagnetic beams beyond the paraxial approximation, in which the vectorial correction is shared symmetrically between the electric and magnetic fields and separated from the isotropic scalar correction. The method is based on a direct iterative derivation from Maxwell equations and combines complementary electric-first and magnetic-first constructions, thereby removing the construction-dependent assignment of the vectorial correction to either the electric or magnetic field. In addition, the scalar envelope correction is obtained independently from the isotropic co-polar contribution to the solutions of the higher-order Helmholtz equation. The resulting corrected fields apply to an arbitrary paraxial envelope and input Jones polarization.

We perform a model independent reconstruction of the cosmic expansion history using Gaussian Process regression, investigating how the smoothness properties of covariance kernels influence the inferred Hubble parameter. Using 32 cosmic chronometer measurements, we reconstruct $H(z)$ with the Matérn $3/2$, $5/2$, $7/2$, $9/2$, and Squared Exponential kernels, which form a well-defined hierarchy of differentiability. Across this hierarchy, we observe a systematic and monotonic trend in which increasing kernel smoothness is associated with progressively lower reconstructed values of the present-day Hubble constant $H_0$, accompanied by reduced statistical uncertainties. Rather than indicating a statistical preference for a specific kernel, this behaviour reflects the sensitivity of non-parametric reconstructions to the assumed smoothness prior encoded in the covariance function. The same ordering is reflected in descriptive goodness-of-fit statistics and remains stable when incorporating recent DESI DR2 BAO measurements and performing jackknife resampling tests, demonstrating robustness against individual data points and dataset variations. Additional analysis of derivative reconstructions shows that differences in kernel differentiability propagate into the local slope of the expansion history, providing a consistent interpretation of the observed ordering in $H_0$. Our results highlight that kernel smoothness plays an important role in Gaussian Process reconstructions and should be carefully accounted for when interpreting non-parametric cosmological inferences.

In Brownian yet non-Gaussian diffusion (BnGD) the mean squared displacement grows linearly in time. However, the displacement statistics do not follow a normal distribution throughout. Typically, they are non-Gaussian at intermediate times, before they cross over to Gaussian in the long-time regime. We demonstrate that nonlinear friction under correctly applied stochastic equilibrium conditions provides an explanation of this phenomenon also for homogeneous environments.

The propagation of sustained Boussinesq gravity-current fronts along a heated wall is examined through laboratory experiments. The gravity currents are generated by continuously supplying a mixture of air and carbon dioxide at the inlet of a rectangular channel, while uniform wall heating is provided by resistive fabrics. In addition to the Froude number, defined either at the source (Fr_s) or at the current front (Fr), we show that the front velocity is governed by \Lambda_s, the ratio of the two buoyancy fluxes per unit area driving the flow: that generated by wall heating and that supplied at the inlet. As wall heating increases (i.e., as \Lambda_s increases), the current front propagates more slowly. This slowdown results from the direct heating of the current, which reduces the buoyancy of its head, and from the interaction between the front and the thermal plumes generated by natural convection downstream. In the most strongly heated experiments, the front eventually stops at a distance from the source that is inversely proportional to \Lambda_s. In these cases, the buoyancy of the head changes sign, and the head evolves into a positively buoyant plume whose vertical extent continues to increase. The experimental results are compared with predictions from a lumped analytical model describing the propagation and eventual arrest of the current.

We investigate the thermal structure of the Venusian middle atmosphere between 45 and 80 km using radio occultation (RO) measurements from Venus Express and Akatsuki spanning 2006-2024. Retrieved temperature profiles are compared with climatological predictions from the Venus-GRAM and the Venus Climate Database (VCD). Systematic deviations exceeding 10 K are observed between the RO temperatures and model climatologies, particularly at high latitudes in both hemispheres. The long-term dataset further reveals a possible decadal-scale temporal variability in temperatures across the low-to-mid latitude regions. This variability becomes less coherent at higher altitudes. A combination of post-stratification and bootstrap analysis on the temperature anomalies indicates that the observed temporal variability at low-to-mid and polar latitudes is not readily explained by the latitudinal sampling bias quantified using the adopted analysis, while the trends at mid-to-high latitudes are affected by sparse and uneven RO sounding. Sensitivity tests using modified cloud albedo inputs in VCD simulations show that adjusting cloud radiative forcing partially reconciles the discrepancies, especially at the lower altitudes, below 60 km. However, above the cloud top, at the lower latitudes, the divergence from the observations increases significantly, thereby failing to provide a general reconciliation between VCD and RO. These results highlight the need for updated empirical climatologies incorporating recent RO measurements and for improved physical parameterizations in Venus general circulation models to better capture the global variability in the planet's middle atmosphere.

We use perfect-model, large-ensemble nonlinear Recharge Oscillator (RO) simulations to quantify ENSO internal variability and the detectability of forced changes in ENSO characteristics. Fixed-parameter simulations show that linear trends in ENSO standard deviation, period, and skewness as large as those observed since 1955 can arise from internal variability in 10% of simulations. RO parameters estimated from single realizations exhibit spurious drifts even without forcing, underscoring the need for ensembles. Using 100-member ensembles, comparable to the largest climate-model ensembles, we identify detectable parameter trends. For ENSO amplitude, the detectability thresholds for forced changes in underlying processes are 15% per century for stochastic forcing, 25% per century for basin adjustment, and 50% per century for the Bjerknes feedback. For ENSO period, the detectability threshold for forced changes in the underlying recharge–discharge processes and delayed oceanic feedback is 15% per century. These results provide a testbed for interpreting RO-diagnosed ENSO changes in climate-model ensembles.

Machine learning offers a possible route to data-driven real-space renormalization when the relevant observables are nonlocal and difficult to prescribe explicitly. We explore this idea for two-dimensional site percolation developping a supervised, scale-shared neural architecture. The model recursively applies the same learned coarse-graining rule across scales, producing a latent field from which the crossing probability is predicted, while a corresponding fine-graining decoder reconstructs the largest-cluster mask. Trained only on small lattices, the model extrapolates to substantially larger systems, recovers the spanning cluster with high fidelity, and produces observables obeying the expected finite-size scaling near the critical point. We observe that to get such performance it is key that the learned latent representation exhibits critical fluctuations and scale-dependent flows consistent with the renormalization-group structure of percolation.

Classical Cepheids are fundamental distance indicators that anchor the cosmic distance ladder through their Period-Luminosity, Period-Luminosity-Color, and Period-Wesenheit relations, while also providing valuable constraints on young stellar populations. Recent advances in space-based near-infrared observations highlight the need for theoretical calibrations of Classical Cepheid observables in modern photometric systems optimized for precision distance-scale applications. This work provides a homogeneous theoretical framework for Classical Cepheids in the JWST/NIRCam and Roman/WFI systems and explores their use as standard candles in the near-infrared. We exploit an extensive grid of nonlinear convective pulsation models spanning a broad range of masses, effective temperatures, periods, metallicities, convective efficiencies, and mass-luminosity relations. We derive mean magnitudes, colors, pulsation amplitudes, amplitude ratios, and new theoretical Period-Luminosity-Color, Period-Wesenheit, and metal-dependent Period-Wesenheit relations. The theoretical Wesenheit relations are compared with recent JWST observations of Classical Cepheids in six SN Ia host galaxies from the SH0ES collaboration. We find excellent agreement between predictions and observations, with the largest systematic effects arising from the adopted mass-luminosity relation. Theoretical distance moduli are fully consistent with empirical JWST determinations when a mildly overluminous mass-luminosity relation is adopted instead of the canonical one. These results provide a self-consistent pulsation-based calibration for JWST and Roman observations and a theoretical framework for future precision studies of the local distance scale.

Charge orders in the kagome metals AV$_3$Sb$_5$ sit at the center of a rich phase diagram that also includes superconductivity, nematicity, and signatures of time-reversal-symmetry breaking. Yet even the basic question of which charge ordering wave vectors are intrinsic, and which are selected by dimensionality and lattice coupling, remains unsettled. Importantly, the microscopic origin of different charge orders and, in particular, the relationship between the robust bulk $2 \times 2$ charge order and the controversial $4 \times 1$ modulation, which is primarily resolved by surface probes, remains unresolved. Here, we use first-principles calculations to study the role of interlayer coupling in CsV$_3$Sb$_5$ by tuning the interlayer separation from the monolayer limit to the bulk limit. In the monolayer AV$_3$Sb$_5$ (A = Rb, Cs), the phonon spectrum exhibits no instability at the M point; instead, the dominant lattice instability occurs at q = (1/4, 0, 0), consistent with a $4 \times 1$ modulation. As interlayer coupling increases in CsV$_3$Sb$_5$, an M-point phonon progressively softens and becomes unstable already near c = 12.24 Å, evolving into the strong $2 \times 2$ instability characteristic of the bulk. These results identify interlayer coupling as a control parameter at a fixed stoichiometry that links competing $4 \times 1$ and $2 \times 2$ tendencies, providing a unified framework for understanding why multiple charge-order wave vectors coexist and compete in kagome metals.

We study moderate deviations for the largest eigenvalue of the randomly deformed Gaussian unitary ensemble introduced by Johansson (Probab. Theory Relat. Fields, 138: 75–112, 2007). In the fixed-coupling regime, the rescaled largest eigenvalue converges to the convolution of the Tracy–Widom law and a Gaussian law arising from the random displacement of the spectral edge. We derive sharp logarithmic asymptotics for the right and left tails on growing Airy scales and obtain the corresponding phase diagram. The two tails have different transition scales. At criticality, the rate functions are nontrivial infimal convolutions of the Tracy–Widom and Gaussian rate functions. We establish a trace-norm Airy approximation that is uniform over typical diagonal configurations on a logarithmic window. A conditional convolution argument then combines the resulting tail estimates with the Gaussian moderate deviations of the edge displacement.

We demonstrate a physical mechanism for causal information filtering in a physical reservoir computing (PRC) by exploiting asymmetric coupling anisotropy. Using a network of coupled Duffing oscillators, we show that the directionality of internal coupling induces a spatial gradient in the effective potential, establishing a deterministic upstream-to-downstream information flow. This anisotropy allows for the selective amplification of semantic drifts, triggering a macroscopic saddle-node bifurcation as a physical interlock before global computational failure. Through spatiotemporal analysis of a 50-node system under traveling wave inputs, we confirm that local phase transitions effectively purge anomalous information while preserving the computational integrity of the remaining nodes. The results suggest that the intrinsic causality of the reservoir's topology provides a robust framework for autonomous reliability and fault-tolerant physical intelligence.

Altermagnets (AMs) are collinear compensated magnets that exhibit momentum-dependent spin splitting without requiring a net magnetization. Since local magnetic moments and exchange-driven order do not rely on relativistic effects, altermagnetism can be naturally formulated in a nonrelativistic spin-group framework. This raises a basic question: can two-dimensional altermagnetic order be stabilized by purely exchange interactions in the absence of spin-orbit-induced anisotropy? We address this question by applying Bogoliubov's inequality to a minimal $d$-wave altermagnetic spin model. We show that the anisotropic exchange pattern responsible for altermagnetism still contributes only a quadratic long-wavelength term to the Bogoliubov denominator. Consequently, short-ranged exchange interactions alone cannot stabilize long-range altermagnetic order in two dimensions when continuous spin-rotation symmetry is preserved. In contrast, the corresponding three-dimensional system has a finite small-momentum contribution and is not ruled out by the Mermin-Wagner argument.

Aims. We revisit the carbon abundance in the primitive iron-poor star J0815+4729 ([Fe/H] = -5.49). J0815+4729 is so carbon-enhanced and oxygen-rich that, in addition to CH and C2 molecular lines, weaker neutral atomic transitions are measurable in its spectrum, providing a unique opportunity to explore the line formation of C I and O I transitions in such an extremely iron-deficient star. Methods. Based on high-resolution spectroscopy and newly constructed atomic models for carbon and oxygen, we present the first investigation to derive carbon and oxygen abundances of this hyper iron-poor star from neutral atomic transitions under non-local thermodynamic equilibrium (NLTE) conditions. Results. The carbon abundance derived from C I lines is A(C)NLTE = 8.08+-0.07, consistent with that inferred from C2 lines (A(C)LTE =7.96 +- 0.08), but around 0.6 dex higher than the value from CH lines (A(C)LTE = 7.47 +- 0.17). Since CH lines are the most commonly-used carbon abundance indicator for extremely metal-poor stars, this result casts doubt on the quantitative interpretation of CH absorption in the most primitive stars. We confirm that J0815+4729 is one of the most carbon-enhanced stars with [Fe/H] <= -4.5 known to date. We have also determined A(O)NLTE as 7.25 +- 0.11, with NLTE corrections of around -0.11 dex. The carbon-to-oxygen ratio of the star is [C/O] = 1.06 +- 0.1.

Thermodynamic significance of near-horizon symmetries remains an important open question in black hole physics, particularly in the context of black hole evaporation and information recovery. In this work, we investigate the role of horizon-adapted Bondi-van der Burg-Metzner-Sachs (BMS)-like supertranslations in the thermodynamic description of a dynamical Schwarzschild black hole. Working in a near-horizon Rindler coordinate system, we construct a class of diffeomorphisms that preserve the horizon structure and promote the associated supertranslation parameter to a Goldstone-like mode arising from the breaking of horizon symmetry. By expanding the Einstein-Hilbert action around the background geometry, we obtain the effective action for the Goldstone mode and identify the corresponding conserved horizon charge from the surface contribution of the action. The relevant horizon is defined at the future outer trapping horizon, while the surface gravity is computed using the Kodama-vector construction appropriate for dynamical spacetimes. We show that the horizon supertranslation mode contributes non-trivially to the surface gravity and modifies the thermodynamic description of the black hole beyond the stationary limit. Using the associated Noether charge, we derive the entropy of the horizon-BMS transformed geometry and find that the Bekenstein-Hawking area law is recovered at leading order, while subleading corrections depend explicitly on the supertranslation sector and the dynamical evolution of the black hole.

Molecular aggregates are at the basis of a broad range of functional systems, including photosynthetic light-harvesting complexes, organic photovoltaics, optoelectronic devices, and molecular sensors. Their structural organization, however, is often difficult to resolve because intrinsic heterogeneity. In this context, circular dichroism (CD) spectroscopy is particularly powerful because of its sensitivity to the three-dimensional organization of molecular building blocks. Extending CD measurements from ensembles to individual objects therefore offers a unique approach to probing supramolecular architecture in heterogeneous, non-crystallizable systems. However, without spatial and orientational averaging, measurements are highly sensitive to imbalances between left- and right-circularly polarized excitation, deviations from ideal circular polarization, and polarization imperfections coupled to linear dichroism, which creates spurious CD signals. Here, we present a systematic theoretical and experimental framework for understanding, quantifying, and controlling artifacts in single-object CD spectroscopy. We develop a mathematical description of the principal artifact mechanisms, identify their origins in practical implementations, including Pockels-cell-based polarization modulation, and establish strategies for their minimization. We validate this framework using an experimental implementation capable of acquiring CD spectra from individual molecular aggregates over 690-785 nm. Our results demonstrate that reliable single-object CD measurements are achievable when polarization-related artifacts are rigorously characterized and controlled. This Tutorial Review provides a unified theoretical framework and practical guide for single-object CD spectroscopy and its application to single-particle chirality, supramolecular photonics, and biophotonics.

Reconstructing pressure and turbulence quantities from experimental velocity measurements is challenging, especially without time-resolved data. Furthermore, limitations such as low seeding density, finite resolution, and measurement noise severely hinder the reconstruction of accurate flow fields. We introduce SnapPINN, a two-stage physics-informed neural network (PINN) that successfully reconstructs 3D velocity, their spatial gradients, pressure fields and estimates turbulent kinetic energy dissipation from a single snapshot of sparse, noisy velocity data. Evaluated here on 3D DNS turbulent pipe flow data, SnapPINN uses a sine-activated architecture with sequentially trained, decoupled velocity and pressure sub-networks. In stage 1, the velocity network fits particle data while enforcing incompressibility, serving as a physically consistent smoothing operator that regularises velocity gradients against noise. In stage 2, the velocity network is frozen, and the pressure network is trained using the pressure Poisson equation and the pretrained velocity gradients. We systematically map reconstruction performance of SnapPINN across 100 test cases to mimic challenging experimental, such as adding significant position noise, linearization of velocity field and seeding sparsity as low as $0.07\%$ of the fully resolved DNS grid. Quantitatively, bulk velocity was reconstructed within $0.5\%$, while errors remained below $50\%$ for the gradient-sensitive energy dissipation rate and within $4$–$24\%$ for the a~posteriori inferred $\mathrm{Re}_{\tau}$, even under extremely sparse and noisy conditions. Finally, we establish a practical reliability map that shows which experimental conditions are likely to yield reliable SnapPINN reconstructions in the absence of ground truth.

For a relativistically decoupled thermal relic, the dark-matter energy-to-entropy ratio scales as $\rho_{\rm DM}/s\sim 10^{-3}m_{\rm DM}$. This is the familiar hot-dark-matter abundance relation. Immediately after weak-sphaleron freeze-out, the baryon asymmetry can be parametrized as $\rho_{\rm baryon}/s\sim 10^{-4}|\mu_B|$. Here $\mu_B$ is the baryon-number chemical potential. We propose a new class of models, called chemical-potential-matched dark matter ($\mu$DM), in which $|\mu_B|\sim m_{\rm DM}$, thereby providing a new route to the baryon-dark matter coincidence. As a concrete example of $\mu$DM, we consider an Affleck-Dine field whose excitations constitute dark matter. We also briefly discuss spontaneous electroweak baryogenesis associated with axion-like-particle walls. In the absence of entropy dilution, this coincidence mechanism generically points to dark matter in the eV-keV mass range. Its momentum distribution can nevertheless be cold if thermal production is dominated by Bose-enhanced stimulated emission. Alternatively, entropy dilution after both the dark-matter and baryon yields are fixed allows masses up to the MeV scale.

We present an analysis of ALMA high-frequency observations of nine bright Lyman-break galaxies at $5.8<z_{\rm spec}<8.3$. Our sample consists of five galaxies at $z\sim6$ newly observed in Band-9 and/or 10, allowing us to better constrain the dust temperature ($T_{\rm dust}$) in a statistical sample of $z\gtrsim6$ galaxies. Our measurements of the dust temperature at $z\sim6-9$ suggest most of the star-forming galaxies show $T_{\rm dust}\sim40\,{\rm K}$ on average, whereas three galaxies show significantly higher $T_{\rm dust}$ ($\gtrsim60\,{\rm K}$). We find a potential negative correlation between $T_{\rm dust}$ and gas-phase metallicity with $T_{\rm dust}\propto Z^{-0.50\pm0.19}$, implying decreased dust shielding and efficient dust heating in low-metallicity environments. Given the systematic offset of $T_{\rm dust}$ between $z\sim0$ and $z\sim6-9$ at fixed metallicity, we find $T_{\rm dust}$ is well described by sSFR as well as $Z$ with $\log T_{\rm dust}=-0.25^{+0.03}_{-0.04}\times(\log Z-0.57\times\log {\rm sSFR})+4.88^{+0.47}_{-0.43}$ across $z\sim0$ to $z\sim6-9$. Simultaneously with the dust continuum, these observations cover the [OI]63$\mu$m emission line for five galaxies, which traces dense neutral gas. We find a lower [CII]/[OI] ratio in $z\gtrsim6$ galaxies than in local samples, suggesting that [CII] becomes fainter due to collisional de-excitation at high gas density. Combining the [OI], [OIII], and [CII] lines and cloudy modeling, our results imply $\log U_{\rm ion}\sim-2$ and $\log n_{\rm H}\,[{\rm cm}^{-3}]\sim2.5$ in $z\gtrsim6$ galaxies, which is $\sim3-10\times$ higher $U_{\rm ion}$ and $\sim2-3\times$ higher $n_{\rm H}$ than the local samples. The combination of these enhanced $U_{\rm ion}$ and $n_{\rm H}$ naturally explains the high [OIII]/[CII] ratio at $z\gtrsim6$.

We show that long-range radiative coupling in a passive chiral medium produces an unusual non-Hermitian skin effect in a chain of dipoles. The skin-mode profile consists of a long-range light-line branch-cut contribution, a non-exponential factor $1/[n(\ln n)^2]$ with $n$ being the site number. Finite-chain calculations show that part of the open-boundary spectrum contracts toward the Bloch spectrum, whereas the number of boundary-localized modes remains extensive. The retarded radiative coupling makes both the real-space profile and the finite-size spectral signatures of boundary localization depart from standard finite-range and pure exponential coupling theory.

Direct magnetic field sensors can address integration drift commonly observed in conventional inductive magnetic diagnostics used in fusion systems. In this work, an AlGaN/GaN Hall-effect sensor was fabricated, packaged, and deployed inside the Helically Symmetric eXperiment (HSX)—the first quasi-helically symmetric stellarator, operating with a 1 T on-axis magnetic field and up to 200 kW of launched electron cyclotron resonance heating (ECRH) power—for in-situ magnetic field monitoring near the plasma edge. The sensor leverages the high-mobility two-dimensional electron gas (2DEG) formed in the AlGaN/GaN heterostructure for sensitive magnetic field measurement, while the wide-bandgap GaN material system provides thermal robustness for harsh-environment operation. During 68 consecutive plasma discharge shots, the sensor remained functional and produced clear transient responses associated with plasma ignition and discharge dynamics. Comparisons between biased and unbiased operation, as well as plasma-discharge and coil-only shots, confirmed that the response originated from the biased Hall-effect sensor element. Furthermore, the sensor output exhibited temporal correlation with the plasma stored energy measured by the HSX diamagnetic loop across high-energy, late-breakdown, and failed-breakdown discharges.

Generating non-locally entangled electron pairs via Cooper-pair splitting is vital for solid-state quantum information processing. However, isolating the underlying crossed Andreev reflection (CAR) is challenging due to competing transport processes like electron tunneling (ET) and local Andreev reflection (AR). Here, we propose a flux-tunable four-terminal normal metal-superconductor junction that achieves deterministic, 100% efficient CAR. We demonstrate that at exactly half a magnetic flux quantum ($\phi=\pi$), exact destructive Aharonov-Bohm and Peierls interferences structurally forbid ET and AR respectively. By tuning the central junction hopping, electron reflection is also suppressed to zero. Using the Cauchy argument principle, we prove that this suppression manifests as a quantized topological winding number, guaranteeing a topologically protected unit CAR probability. We establish that this regime is characterized by a strictly positive cross-correlation shot noise, providing an unambiguous experimental signature of Cooper-pair splitting. Furthermore, this perfect CAR is nearly broadband within the superconducting gap and remarkably robust against structural disorder, offering a highly resilient architecture for deterministic nonlocal entanglement generation.

Whispering gallery mode (WGM) resonators with broken rotational symmetry exhibit phenomena that are generally absent in conventional symmetric cavities, including directional emission. While such effects have been extensively investigated in solid and planar resonators, they remain largely unexplored in hollow, three-dimensional cavities, where optical confinement is fundamentally altered by the thin wall geometry. Here, we demonstrate controlled fabrication of asymmetric silica microbubble resonators through anisotropic expansion during the microbubble formation process. X-ray tomography confirms the resulting three-dimensional geometry and allows us to quantitatively characterize the cavity deformation. Despite the broken rotational symmetry, the resonators maintain whispering gallery modes with high loaded Q-factors exceeding $10^5$ for moderate deformations. Optical characterization reveals that only certain resonances exhibit directional emission, whereas neighboring modes retain conventional isotropic behavior. Two-dimensional numerical simulations reproduce the observed emission characteristics and indicate that deformation-induced leakage of higher-order modes provides a plausible mechanism for the directional radiation. These results establish asymmetric hollow microbubble resonators as a platform for investigating light transport in three-dimensional asymmetric whispering gallery cavities while preserving the high-Q performance required for photonics applications.

We show a finite-time Otto-like quantum thermodynamic cycle that preserves the adiabatic population structure of a time-dependent harmonic oscillator in the non-quasi-static regime. In the conventional energy representation, finite-rate driving induces non-adiabatic population redistribution and leaves residual excitations after the Hamiltonian has returned to its initial value. We show that this difficulty can be avoided by formulating the dynamics in the Lewis-Riesenfeld invariant representation, without modifying the physical Hamiltonian through auxiliary counterdiabatic driving. For a parametric Mathieu protocol, quantum inertia produces a mismatch between the spatial width of the working mode and its transient dressed energy scale. We propose an experimental implementation of this scheme in a trapped-ion Paul trap using stimulated Raman interactions, with independent control of the laser detuning and beam intersection angle. This provides a finite-time implementation in which the invariant population structure is preserved while the physical trap frequency evolves non-quasi-statically. Our results establish a clear distinction between adiabatic operation and quasi-static driving, providing a route toward finite-time quantum thermal cycles that retain the adiabatic energy structure without requiring the quasi-static limit.