Plasma Physics
Study of low-frequency core-edge coupling in a tokamak: III. Core-localized MHD continuum pulsations & distant forced reconnection
Andreas Bierwage, Panith Adulsiriswad, Gyungjin Choi et al. (+2 more)
Slow magnetoacoustic pulsations (SMAPs) are found in MHD simulations of a tokamak
plasma whose safety factor $q$ near the center is flat and slightly above unity ($q \gtrsim 1$). SMAPs are located on the central plateau of the slow magnetoacoustic continuum $\omega_{\rm S} = k_\parallel c_{\rm S}$, where $c_{\rm S}$ is the speed of sound and $k_\parallel$ the wavenumber parallel to the
magnetic field. In our model, SMAPs exist when the ion viscosity and thermal diffusivity are sufficiently low. They can be driven unstable by a pressure gradient in the $q \sim 1$ region when the electric resistivity is sufficiently high. Exponentially growing SMAPs consist of standing slow waves on
magnetic surfaces that are radially synchronized into a quasi-interchange structure with poloidal/toroidal mode numbers $m/n=1/1$. After free energy depletion, saturated quasi-linear pulsations (alternating $n=1$ and $0$) in the central $q\sim 1$ region couple to distant $q\geq 2$ rational surfaces that undergo "reversible"
magnetic reconnection: as the
magnetic islands wax and wane with period $2\pi/\omega_{\rm S}$, their X- and O-points alternate. These results show how the MHD model facilitates non-local coupling of slow waves, pressure-driven resistive interchange and tearing. This motivates further study in kinetic models, where collisionless mechanisms for fast reversible reconnection exist and proper treatment of parallel dynamics will allow to assess the role of Landau damping as well as the question whether the ${\mathbf B}$ field's weak ergodicity in the $q\sim 1$ region allows the waves to outpace the ion's parallel streaming to maintain the thermal misbalance underlying SMAPs. Also of interest are pulsations closer to the Alfvénic branch, satisfying $\omega \approx k_\parallel v_{\rm A}$ with Alfvén speed $v_{\rm A}$, which require no resistivity and are less dependent on thermal misbalance.
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All authors Andreas Bierwage, Panith Adulsiriswad, Gyungjin Choi, Young-chul Ghim, Masatoshi Yagi
Applied Physics · Cross-listed from cond-mat.mes-hall
Spin-Polarized Magnetic Metal Electrodes for Magnetic Tunnel Junctions
Zhiyuan Duan, Peixin Qin, Li Liu et al. (+7 more)
Magnetic tunnel junctions are foundational components of spintronic
memory, sensing, and computing, and their performance depends critically on the
magnetic metallic electrodes. This Perspective examines electrode materials through the lens of
magnetic order and the distinct microscopic mechanisms that generate
spin-selective tunneling. Conventional ferromagnets, including CoFeB and half-metallic Heusler
alloys, support exchange-split electronic states and
symmetry-filtered tunneling, whereas compensated collinear and noncollinear antiferromagnets exploit sublattice selectivity,
spin-orbit anisotropy, vector
spin textures, and
magnetic multipoles. Altermagnets provide a collinear, zero-net-moment route based on
symmetry-allowed momentum-dependent
spin splitting. Across these material classes, we compare the origins of tunneling polarization, the roles of barrier evanescent states and interface termination, and strategies for electrically writing and reading the relevant
magnetic order. This comparison reveals a broader design principle: effective electrode polarization is not a scalar bulk quantity, but a momentum-, orbital-,
symmetry-, and interface-resolved transport property. Beyond the pursuit of ever larger tunneling magnetoresistance, future progress will depend on converting the unconventional
spin polarization of emerging
magnetic metals into electrically addressable, thermally robust, and reproducible tunneling functionality at realistic interfaces.
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All authors Zhiyuan Duan, Peixin Qin, Li Liu, Guojian Zhao, Sixu Jiang, Xiaoyang Tan, Jingyu Li, Xiaoning Wang, Ziang Meng, Zhiqi Liu
Plasma Physics
Quasi-symmetric error field correction and applications to ITER
Gwang-Geun Seo, Jong-Kyu Park, S. J. Han et al. (+1 more)
Reliable correction of nonaxisymmetric error fields (EFs) is essential to the safety and performance of tokamak operation. Although resonant error field correction (EFC) is well established, supported by an improved understanding of 3D
plasma response, the residual fields left after resonant EFC remain an open question: they are expected to be predominantly nonresonant, yet can still degrade both confinement and stability. Here we introduce a systematic EFC scheme that minimizes resonant and nonresonant EF effects simultaneously, based on neoclassical torque response computed from self-consistent perturbed
equilibria. The scheme extends the method developed for designing quasi-symmetric
magnetic perturbations to the case where actual error fields are present. Application to standard ITER target
plasmas with a range of intrinsic EF scenarios demonstrates the advantages of this quasi-symmetric (QS) EFC scheme for controlling residual EFs. QS EFC consistently yields low-torque solutions while strongly suppressing resonant response, outperforming single-mode resonant overlap EFC in most cases and approaching the performance of
multimodal resonant EFC. We also show that the QS EFC solution varies only tolerably between half- and full-$I_p$ ITER scenarios, despite the greater sensitivity expected from its higher-order nature.
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All authors Gwang-Geun Seo, Jong-Kyu Park, S. J. Han, M. Dubrov
Optics
Fiber-based scanning levitated nanoparticle force sensor near a metalized membrane
Andrew M. Dana, Samuel J. Borden, Nia Burrell et al. (+10 more)
We describe a fiber-based dual-beam trap for dielectric nanospheres with the ability to transfer the trapped particles into a retro-reflective standing-wave trap within micron-range distances of a metallic mirror surface. We illustrate its capability for three dimensional scanning force sensing over a several square micron area of an ultra-thin gold-coated silicon nitride mirror-membrane with a total thickness of approximately 370~nm. We also demonstrate three-dimensional
laser feedback cooling and zeptonewton force resolution in high-
vacuum at micron range from the membrane, showing promise for future improved tests of
gravity at short distances and other surface force investigations. By using charged nanospheres, we expect the method may be useful for studying fluctuating patch potentials and electric field noise in the vicinity of a surface in the $\sim$ kHz to $\sim 100$ kHz frequency regime.
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All authors Andrew M. Dana, Samuel J. Borden, Nia Burrell, Chethn Galla, Alexey Grinin, Mark Nguyen, Kristina Menon, Shafaq Elahi, Katarina Boskovic Guy, Andrew Laeuger, Evan Weisman, Gambhir Ranjit, Andrew A. Geraci
History and Philosophy of Physics
$\delta$-flatness and its natural extension
Henrique Gomes
What, if anything, makes Minkowski spacetime a privileged local reference geometry in General Relativity? Recent work by \cite{WeatherallFletcher} argues: nothing. In response, I proposed a criterion of “$\delta$-flatness”, which bounds the magnitude of tidal acceleration within a tubular neighborhood by $\delta$, and showed that Minkowski uniquely saturates the bound. Here I ask how $\delta$-flatness generalises, and distinguish two kinds of extension. Reference-metric generalisations compare physical tidal acceleration with a reference tidal-force term constructed from another metric. Lorentzian signature obstructs every such comparison in which the reference fails to share the lightcones of the physical metric. Criterion modifications instead build the criterion from the physical geometry alone. The space of such modifications is wide, and I focus on those closest to $\delta$-flatness, where one bounds the deviation of tidal acceleration from a non-zero target. The minimal candidate, which I call $\delta$-MSS, has a singular limit that picks out the maximally symmetric spacetimes (Minkowski, de Sitter, Anti-de Sitter) via Schur's
theorem. A restricted variant, which compares $g$ with a conformal rescaling of itself, either collapses to $\delta$-MSS or fails to pick out a unique geometry. The chief result is that $\delta$-flatness distinguishes Minkowski with no free parameter. $\delta$-MSS, a weaker variant, picks out the maximally symmetric family at the cost of an externally supplied scalar.
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History and Philosophy of Physics
Piezoelectricity: A Brief History of its Discovery and Physical Principles Using the Example of Low Quartz
Ruediger G. Ballas and Nataliya Koev
Piezoelectricity is a key phenomenon in solid-state physics and has significant technological relevance. In teaching, however, it is often treated either without a historical context or an explicit link to the microscopic
crystal structure, meaning that a crucial level of understanding remains untapped. This study combines the history of the discovery of piezoelectricity with its physical description within a didactically coherent framework. Building on the work of the brothers, Jacques and Pierre Curie (1880 - 1882), it demonstrated how investigations into pyroelectricity led to the identification of polarization induced by mechanical compression in hemihedral
crystals such as tourmaline and quartz. The development from early qualitative experiments towards the first quantitative determination of piezoelectric constants is traced in a structured manner. Using low quartz as an example, the microscopic cause of piezoelectricity was attributed to the asymmetric displacements of silicon and oxygen ions within the orthosilicate ion tetrahedral network. This leads to the formation of macroscopic polarization owing to uncompensated dipole moments in the
crystal lattice. The direct and reciprocal piezoelectric effects are qualitatively distinguished and discussed in the context of mechanical-electrical coupling. The article is aimed at students in physics and engineering as well as lecturers. It was conceived as a didactic review article (tutorial article) and serves as a structured introduction to the physical and historical foundations of piezoelectricity.
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Atomic Physics · Cross-listed from cond-mat.quant-gas
Microscopic theory of the collective optical response of dilute atomic clouds at finite temperature
Tanja Schoger, Romain Pierrat and Nicolas Cherroret
At low temperature, collective light-induced dipole-dipole interactions are known to strongly reshape the optical response of atomic clouds, revealing the breakdown of the independent-scattering picture as the density increases. While thermal motion is generally believed to progressively suppress these interactions, the microscopic mechanisms behind this suppression remain largely unexplored. Here, we develop a microscopic theory of the optical response of a dilute atomic gas at finite temperature, explicitly accounting for atomic ballistic motion during the recurrent-scattering events associated with the collective corrections. Using a diagrammatic approach for scalar light, we derive the collective contribution to the optical permittivity and characterize its behavior across the full temperature range. We find that thermal corrections scale as $\sim T$ at low temperature, while recurrent-scattering contributions are suppressed as $\sim T^{-3/2}$ at high temperature. Our predictions are confirmed by extensive coupled-dipole simulations that explicitly account for atomic motion. These simulations also reveal the inaccuracy of the modified frozen-dipole approximation commonly used to treat thermal effects. Finally, extending our theory to vector light, we provide a complete picture of how the resonance shift continuously evolves from the collective Lamb shift at low temperatures to the classical Lorentz-Lorenz shift at high temperatures.
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Optics
Real-Time Event-Based Optical Camera Communication at 80 kbit/s over a 320 m Outdoor Link with 120{\deg} Field-of-View
Francesco Nardo, Peter Krötz, Ricardo Barrios et al. (+1 more)
We demonstrate an event-based optical camera communication system using a 120{\deg} field-of-view sensor. In daylight, three transmitting nodes achieve an aggregate 240 kbit/s, with individual links reaching 106 kbit/s at 1 m and 80 kbit/s at 320 m. Our results, establish a new baseline for event-OCC.
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All authors Francesco Nardo, Peter Krötz, Ricardo Barrios, Sebastian Randel
Optics
Non-Hermitian multimode interferometry
Subhajyoti Bid and Henning Schomerus
Interferometers form a cornerstone of precision measurement, leveraging wave superposition and phase coherence to convert minute physical perturbations into measurable intensity variations. Here, we establish how paradigmatic interferometric architectures, the canonical Michelson and Mach-Zehnder interferometers, can be endowed with entirely new operating principles by replacing conventional beam splitters with judiciously designed non-Hermitian resonators. To uncover how non-Hermitian physics can assist in interferometry, we subject these canonical interferometers to a modern non-Hermitian
symmetry analysis. A fundamentally transformed interference landscape then arises when the resonators and interference pathways collectively induce partially deficient spectral degeneracies, mathematically characterized as multimode versions of exceptional points. Key characteristics of these exceptional interferometers are nonanalytic destructive interference conditions, resulting in distinct bright-fringe and dark-fringe operating regimes organized by non-Hermitian winding and braiding
topology. By revealing how exceptional-point-assisted interference reshapes the canonical geometries, our findings transfer central paradigms of non-Hermitian spectroscopy into the interferometric setting, and establish exceptional-point interferometry as a new platform-independent paradigm for general-purpose precision sensing, applicable from on-chip photonics to macroscopic observatories.
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Optics · Cross-listed from quant-ph
100 million photons per second from a single organic molecule
Siwei Luo, Tim Hebenstreit, Alexey Shkarin et al. (+3 more)
At cryogenic temperatures, organic single-
photon sources (SPSs) offer
Fourier-limited emission, virtually unlimited photostability, and emission wavelengths selectable by molecular design, making them attractive for
quantum metrology, secure communication, and photonic
quantum information processing. However, their efficient integration with photonic microstructures has remained challenging, limiting
photon collection from single organic emitters under cryogenic operation. Here, we demonstrate a cryogenic planar metallo-dielectric
antenna that efficiently directs the emission of a single dibenzoterrylene (DBT) molecule towards the collection optics. The device reaches a collection efficiency of 97% and delivers 100 million
photons per second into the first lens. We measure a
photon indistinguishability for the
Fourier-limited transition of 91.2% while maintaining a high single-
photon purity of 97.7% under strong continuous-wave (CW) and pulsed excitation. These results establish organic molecules as a high-performance platform for single-
photon generation and represent an important step towards scalable organic
quantum photonic technologies.
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All authors Siwei Luo, Tim Hebenstreit, Alexey Shkarin, Jan Renger, Tobias Utikal, Stephan Goetzinger
Biological Physics · Cross-listed from nlin.AO
Higher-Order Competition as a Minimal Mechanism for Spatial Pattern Diversity in Population Dynamics
David Pinto-Ramos, Anudeep Surendran and Ricardo Martinez-Garcia
We show that negative feedback alone generates the diversity of self-organized shapes usually attributed to scale-dependent activation-inhibition. For a broad class of kernels, pairwise competition models only generate hexagonal spot arrays. Higher-order terms eliminate this restriction and promote stripes and gaps. Combining individual-based simulations and nonlinear analysis, we derive the pattern-selection thresholds and construct the full state diagram, including an unusual spots-stripes-spots sequence. Spot patterns are thus not a reliable indicator of proximity to a tipping point.
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Applied Physics · Cross-listed from cond-mat.mes-hall
Cavity-waveguide coupling in phononic crystals
Jakub Rosiński, Benjamin Mayer, Hubert J. Krenner et al. (+1 more)
Phononic
crystal platforms provide a promising route toward scalable on-chip
quantum networks, where mechanical excitations mediate interactions between solid-state
qubits. A key building block of such architectures is the cavity-waveguide system, in which localized mechanical modes couple to propagating phononic modes. However, a quantitative understanding of the mechanisms governing this coupling remains incomplete. In this work, we investigate the interaction between localized modes of snowflake-type phononic
crystal cavities and a phononic
crystal waveguide using finite-element simulations and experimental measurements. We show that the coupling strength is primarily governed by the spatial overlap between the displacement fields of the corresponding isolated cavity and waveguide modes. After accounting for the effective-mass dependence of the normalized cavity displacement amplitude, we establish a strong correlation between the spatial overlap and the interaction strength across a wide range of mode combinations. Deviations from this leading-order behavior are associated with Bloch-phase effects, variations in waveguide group velocity, and intrinsic hybridization of waveguide modes. Furthermore, we provide experimental evidence for cavity-waveguide coupling in a GaAs phononic
crystal membrane by observing a clear resonance in the spectral broadening of the photoluminescence emission from an embedded
quantum dot, which serves as a local probe of the mechanical field. The observed resonance at approximately 398 MHz is in good agreement with the corresponding cavity resonance near 395 MHz predicted by finite-element simulations. Our results identify spatial mode overlap as a leading-order design parameter for cavity-waveguide coupling and provide practical guidelines for controlling interactions between localized and propagating modes in phononic
crystal structures.
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All authors Jakub Rosiński, Benjamin Mayer, Hubert J. Krenner, Paweł Machnikowski
Applied Physics · Cross-listed from cond-mat.soft
Microscopic origin of the Baumgärtel-Schausberger-Winter Relaxation Spectrum in Polymer Melts and Particle Rafts
Dario Nichetti, H. Henning Winter and Alessio Zaccone
Entangled
polymer melts exhibit the robust two-branch Baumgärtel-Schausberger-Winter (BSW) relaxation spectrum, while related spectra occur in nonpolymeric monodisperse disordered systems. In spite of the successful application of BSW to many different materials, a molecular derivation of these spectra is lacking. We construct a molecular theory in which a chain segment moves relative to a screened, dynamically responding multichain environment. Gaussian-chain preaveraging gives $M_{\rm seg}(\Delta m)\sim(\Delta m)^{-1/2}$, hence $\lambda_p\sim p^{3/2}$ and, after stress projection, $H(\tau)\sim\tau^{-2/3}$. Independently, longitudinal primitive-path
diffusion gives contour-length fluctuations with $H(\tau)\sim\tau^{1/4}$. A molecular-weight-constrained implementation is tested simultaneously against experimental $G'(\omega)$ and $G''(\omega)$ data for four monodisperse polybutadiene (PBD) melts, without fitting spectral exponents or individual modal weights. The resulting BSW spectrum exhibits a continuous transfer from the fast cooperative to the slow constraint-renewal cascade before a finite-chain terminal edge. A common two-sector caged dynamics then connects
polymers to particle rafts without assuming identical microscopic mechanisms.
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Applied Physics
Dynamical Diversity for Reservoir Computing in Reconfigurable Nanomechanics
Humayun Ahmed, Inês S. Garcia, Filipa C. Mota et al. (+7 more)
Physical reservoir computing uses nonlinear dynamics and a trained linear readout to process information. Nanoelectromechanical (NEMS) resonators combine
geometric Duffing nonlinearity with fading
memory, but most electromechanical implementations use a single resonance mode. Here, we demonstrate reservoir computing with two interacting modes of a single NEMS resonator measured through one readout port. We introduce dynamical diversity through complementary modal drive settings: the same input sequence is replayed under different allocations of drive amplitude between the modes, and the responses are concatenated into a single feature
matrix. This multiplexing expands the representation available to the readout without additional devices or training of internal parameters. On NARMA-2, it reduces variance-normalized test error more than 28-fold relative to single-mode operation and more than threefold relative to the best individual two-mode setting. Linear
memory-capacity measurements show that accessible recall spans only a few symbols at the tested symbol duration. Its rapid decline with delay, consistent with mechanical dissipation, accompanies rising NARMA error and the eventual loss of multiplexing gains at higher orders. We also use electrical feedthrough as an internal reference for assessing the computational contribution of the NEMS response. Separate linear readouts are trained on feedthrough features and features derived from the measured NEMS response, using the same recordings and matched drive settings and processing. On challenging nonlinear mapping tasks, the multiplexed NEMS features yield substantially lower errors than the feedthrough features. These results demonstrate how dynamical diversity through variations in modal drive amplitudes expands the computational capability of a single multimode NEMS resonator.
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All authors Humayun Ahmed, Inês S. Garcia, Filipa C. Mota, Muhammad Asim, Ghaith Mahook, Suleyman Celik, Yunus Selcuk, Filipe S. Alves, Alper Demir, M. Selim Hanay
Plasma Physics
Equation of state and transport coefficients of warm dense aluminum from mixed deterministic-stochastic density functional theory
Zi Li, Weijie Li, Cong Wang et al. (+2 more)
Aluminum is a reference standard in high-energy-density research and serves as a liner material in megampere Z-pinch facilities. Using mixed deterministic-
stochastic finite-temperature density functional theory, we compute the equation of state and transport coefficients of
liquid aluminum up to temperatures of 1000 eV and compare the results with model-based approaches. We find that for T<200 eV the density-functional results differ from the models by more than 10% at high density, with a maximum deviation of over 30% (at T = 10 eV), leading to significant discrepancies in the Hugoniot curve at high compression; the calculated electrical and thermal conductivities deviate from model predictions by 26% to 63% at T~100 eV. We further employ the Drude model and the Epperlein-Haines framework to examine the
magnetic-field dependence of the conductivities. These results can provide valuable input data for radiation-hydrodynamics codes.
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All authors Zi Li, Weijie Li, Cong Wang, Ping Zhang, Xianjue Peng
Optics
Fully passive monolithic silicon quantum photonic circuit for entangled photon-pair generation
David E. Medina, Paul J. Robin, Romain Dalidet et al. (+8 more)
Integrated
quantum photonic
circuits are a key enabling technology for the scalability of
quantum information systems. Among the available platforms, silicon photonics offers an unrivalled capability for the large-scale integration of photonic components within compact footprints. However, the strong index contrast that enables ultra-compact silicon devices also makes them highly sensitive to fabrication imperfections. As
circuit complexity increases, active tuning is generally required to maintain spectral
alignment among the different components, leading to significant power consumption that ultimately limit scalability. Here, we demonstrate a fully integrated silicon
quantum photon-pair source operating without active tuning of any component. The
circuit combines
photon-pair generation in a micro-ring resonator, pump rejection using Bragg filters, and signal/idler demultiplexing through modal add-drop filters with building blocks engineered to minimize sensitivity to fabrication variations. The resulting
circuit achieves excellent experimental
quantum performance. Coincidence rates up to 4000 counts s^-1 with coincidence-to-accidental ratios as high as 100 are obtained across the generated spectrum, while separate two-
photon interference measurements yield raw visibilities exceeding 93% for individually selected ITU wavelength-channel pairs. By eliminating the need for active spectral tuning while maintaining high
quantum performance, this work addresses a major bottleneck in the scaling of complex silicon
quantum photonic
circuits.
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All authors David E. Medina, Paul J. Robin, Romain Dalidet, Sébastien Tanzilli, Anthony Martin, Segolene Olivier, Quentin Wilmart, Laurent Vivien, Laurent Labonte, Carlos Alonso-Ramos, Eric Cassan
Optics
Vertical microcavities with optical Kerr materials
Riya Varghese, Ali Panahpour, Marco Ornigotti et al. (+1 more)
Optical Kerr nonlinearity is central to optical bistability in high-Q microcavities. Here, we show that optical Kerr nonlinearities in Fabry Perot resonators can also result in self-focusing effects, that can substantially modify the Q-factors of the resonators. For the studied cavities, up to five-fold increase in Q-factors is predicted, attributed to reduction of sidewall leakage, confirmed via simulations performed on curved cavities. We also show that for high Q-factor cavities, the higher-order Kerr effect can become relevant already at modest input intensities scaling inversely with Q-factor for a particular n2/n4 ratio. We investigate numerically the role of higher-order Kerr effect on optical bistability responses and find that its inclusion can shift the bistability threshold to higher input intensities than predicted by the standard n2-only model.
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All authors Riya Varghese, Ali Panahpour, Marco Ornigotti, Mikko J Huttunen
Accelerator Physics
Production of a Titanium Ion Beam Using Fluorides and Fluorine-Forming Precursors in an ECR Ion Source
D.K. Pugachev, K.I. Berestov, A.E. Bondarchenko et al. (+7 more)
The production of multiply charged titanium ions is of significant interest for accelerator-based experiments, surface modification technologies, and applications in nuclear physics. Due to the low saturated vapor pressure of titanium at temperatures below 1000 {\deg}C, the generation of titanium ion beams from an electron cyclotron resonance ion source (ECRIS) remains a challenging task. The choice of titanium vapor injection methods into the ECR
plasma plays a key role in achieving high ionization efficiency,
plasma stability, and reliable long-term source operation. In this work, alternative approaches for the injection of neutral titanium atoms into the ECR
plasma are investigated, focusing on the use of fluorine-containing compounds. Titanium fluorides (TiF3, TiF4) possess a relatively high saturated vapor pressure at moderate temperatures, allowing to use standard resistively heated ovens operating up to 1000 {\deg}C. Another method involves the in-situ formation of titanium fluorides inside the
plasma chamber via chemical reactions between metal titanium and the dissociation products of sulfur hexafluoride (SF6). These approaches enable controlled and efficient titanium injection into the ECRIS
plasma with satisfactory extracted ion beam stability.
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All authors D.K. Pugachev, K.I. Berestov, A.E. Bondarchenko, V.N. Loginov, A.N. Lebedev, E.Yu. Kidanova, K.I. Kuzmenkov, V.E. Mironov, D.S. Podoinikov, D.S. Yakovlev
Plasma Physics
Frequency-inference method for reduced modeling of energetic particle modes (EPM) utilizing resonant auto-optimization remnants of imperfect time-scale separation
Andreas Bierwage, Vinícius N. Duarte, Pablo Oyola et al. (+2 more)
Integrated codes simulating interactions between Alfvén waves and fast ions in tokamak
plasmas use perturbative models for the relatively slow processes of instability growth, saturation, chirping and bursting, and transport. Faster processes by which an Alfvén mode's spatiotemporal structure forms are assumed to have been completed within the mode's oscillation period, $\tau_0 \equiv 2\pi/\omega_0$. This separation of time scales underlies the computational efficiency of perturbative models, where the Alfvén mode's time-dependence is reduced to that of a scalar signal $s(t) = A(t)\sin(-\omega_0 t - \phi(t))$ with variable amplitude $A(t)$ and phase $\phi(t)$. For this, accurate input data in the form of a mode's spatial structure $\delta\Phi({\mathbf x})$, damping rate $\gamma_{\rm d}$, and initial frequency $\omega_0$ are required. For modes residing in dense or continuous spectra, $\delta\Phi$ and $\gamma_{\rm d}$ could be estimated from the form of the continua and fast ion orbits, but it is difficult to guess the seed frequency $\omega_0$. Here, we report results of numerical experiments showing that it is possible to find $\omega_0$ using a
prompt frequency shift that occurs during the first few $100$ time steps of a simulation. Restarts with the shifted frequency iteratively converge to a value of $\omega_0$ that seems to maximize the resonant drive, suggesting an auto-optimization process. The need for iteration is attributed to the fact that the terms required for rapid frequency adjustments were truncated when deriving the perturbative model. Meanwhile, the fact that partial auto-optimization is possible at all is attributed to the fact that series truncation alone (without filter) does not strictly enforce slowness. Remnants of and cross-talk with faster dynamics still occur in numerical implementations. This entails potential for both uncertainty and utility.
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All authors Andreas Bierwage, Vinícius N. Duarte, Pablo Oyola, Kouji Shinohara, Roscoe B. White
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Combining physical models with dynamically acquired experimental information for the optimization of multicomponent NASICON fast ionic conductors in a self-driving laboratory
Bernardus Rendy, Yuxing Fei, Tanjin He et al. (+9 more)
Elemental substitution within existing structural frameworks is a widely applied strategy for developing advanced materials. Yet, optimizing target properties while maintaining phase purity usually demands extensive trial-and-error, which becomes substantially inefficient when navigating a complex design space. Here, we introduce a strategy that simultaneously and dynamically assesses composition-dependent synthetic accessibility and target properties via aggregated cost functions that guide autonomous experimentation in a truly self-driving and self-learning mode. Specifically, we developed a cost-guided autonomous solid-state synthesis (CASS) framework and demonstrate its application in the discovery of Na superionic conductor (NASICON) solid electrolytes. CASS successfully optimizes ionic conductivity and phase purity, leading to the identification of 18 promising compositions in 78 trials conducted in an autonomous laboratory, the A-Lab. Among these, we identified two fast-conducting NASICONs yielding total (bulk) ionic conductivity of 0.7 (3.96) and 0.3 (3.17) mS/cm. The successful deployment of CASS reinforces the potential of coupling self-driving autonomous laboratories with physics-informed generative models to accelerate materials discovery. Moreover, the interpretability of the design factors, informed by outcomes from both successful and failed syntheses, enables model refinement and generation of new chemical insights.
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All authors Bernardus Rendy, Yuxing Fei, Tanjin He, Xiaochen Yang, Andrea Giunto, Lauren N. Walters, David Milsted, Hao Qiu, Matthew J. McDermott, Bin Ouyang, Yan Zeng, Gerbrand Ceder
Plasma Physics
PQLS: A Quasilinear Gyrokinetic Transport Solver with a Bayesian Saturation-Rule Closure
F. Wilms, A. Agrawal, J. J. Freigang et al. (+3 more)
Quasilinear models make gyrokinetic turbulent-transport predictions sufficiently fast for integrated modelling, but their predictive capability is limited by two factors: the physical and geometrical applicability of the linear solver, and the validity of the saturation rule used to close the model. We present the Predictive Quasilinear Solver (PQLS), a quasi- linear gyrokinetic transport solver formulated in general
magnetic geometry. Its implementation as an
eigenvalue solver retains electromagnetic and collisional effects, provides access to dominant and subdominant modes and is differen- tiable with respect to all
plasma parameters. Linear
benchmarks against GENE reproduce the growth rates, frequencies, and eigenfunctions. We additionally formulate the saturation-rule closure as a
Bayesian inference problem that distin- guishes uncertainty in its fitted coefficients from the residual model-form uncertainty. The approach is demonstrated by calibrating the SAT3 rule on PQLS quasilinear weights against published nonlinear CGYRO cases. In addition to improving the robustness of the calibration, the new method also quantifies the uncertainty in each of the fit coefficients. Such uncertainty is propagated through transport calculations to produce error-aware profiles that are compared to the ones obtained from the full gyrokinetic simulation, showing excellent agreement.
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All authors F. Wilms, A. Agrawal, J. J. Freigang, T. F. Neiser, B. J. Frei, O. Meneghini
Computational Physics
Monte Carlo sampling of first-order QED processes in laser and pulsar plasmas
Verneri Sarjomaa and Joonas Nättilä
Monte Carlo sampling of strong-field
quantum electrodynamics processes underpins simulations of high-intensity
laser experiments and of astrophysical compact-object magnetospheres. Sampling an event requires the total rate of the process together with the cumulative probability that determines how energy is partitioned between the produced particles. Simulations typically tabulate both in advance and invert the tabulated probability numerically. Here we replace this procedure with elementary-function approximations for synchrotron radiation and the nonlinear Breit–Wheeler process. For each process, we approximate the auxiliary function that sets the total rate, as well as the cumulative probability, with Padé approximants chosen so that the inversion reduces to a quartic equation. This yields the sampled
quantum parameter—electron $\chi_e$ or
photon $\chi_\gamma$—in closed form. The approximations and the particle spectra sampled from them agree with the exact results to within $1\%$. The procedure requires no lookup tables, no interpolation, and no numerical root finding, and can be inserted directly into radiative particle-in-
cell codes.
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Applied Physics · Cross-listed from quant-ph
A low-temperature entropy source for on-chip true random number generation: universal robustness beyond device quality
Y. Q. Chai, M. Y. Wang, X. N. Feng et al. (+1 more)
True random number generation is a critical capability for fault-tolerant
quantum computing at millikelvin temperatures. Yet existing Josephson-junction-based TRNGs all rest on a widely accepted but untested assumption: that reliable
entropy extraction requires precisely controlled device parameters. Here we show that this assumption does not always hold. We demonstrate a counterintuitive finding: a single current-biased Josephson junction, regardless of its parameter quality, can serve as a cryptographic-grade true random number generator. To establish the universality of this conclusion, we deliberately selected the most extremely deviated devices from fabrication, with critical currents three orders of magnitude away from theoretical predictions and $I_cR$ products an order of magnitude above conventional values, as the ultimate stress test. Even under these extreme conditions, the raw Shannon
entropy reaches 0.9981~bit (99.8% of the theoretical maximum), with a min-
entropy of 0.9271~bit. Using a square-wave pulsed-bias scheme, we tune the switching probability to $P\approx0.5$. After SHA-256 post-processing, the bitstreams pass all 15 NIST SP 800-22 tests under a conservative $m=3$ criterion that is more demanding than the standard recommendation, and this certification holds across the entire 100-700~mK operating window of a dilution refrigerator.
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All authors Y. Q. Chai, M. Y. Wang, X. N. Feng, L. F. Wei
Optics
Zero-forward Kerker scattering via synthesized complex-frequency excitation
Jianfei Liu{\dag}, Zheng Gong{\dag}, Ao Li et al. (+3 more)
All objects illuminated with light inevitably cast a shadow – a universal phenomenon encapsulated in the fundamental property that all passive systems with plane-wave illumination feature a non-zero forward scattering amplitude. Since Kerker's landmark 1983 paper, considerable effort has been devoted to overcoming this limitation and achieving the elimination of forward scattering – an objective now widely known as the zero-forward Kerker scattering. However, this objective is fundamentally restricted to active systems, requiring either physical gain in materials or virtual gain in the excitation source. Despite advances in active materials science and non-Hermitian photonics, the experimental realization of zero-forward Kerker scattering still remains an open challenge. Here, we show, both theoretically and experimentally, how zero-forward Kerker scattering can be effectively synthesized by a weighted superposition of readily accessible real-frequency responses. Our synthetic recipe builds on creating an artificial pole at a complex frequency that prevails over inherent scattering poles. These findings not only unlock a realistic experimental framework for non-Hermitian light-matter interactions, but also hold technological relevance for non-invasive sensing and imaging.
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All authors Jianfei Liu{\dag}, Zheng Gong{\dag}, Ao Li, Hongsheng Chen, Stefan Rotter, Xiao Lin
Chemical Physics
Strong-Field-Driven Non-Linear Electron Dynamics in Thiophene Oligomers
Mustapha Driouech, Caterina Cocchi and Michele Guerrini
The interaction between conjugated molecules and intense electric field pulses drives a plethora of intriguing nonlinear phenomena, including optical limiting. While excited-state absorption was recently identified as the primary mechanism for this effect in thiophene oligomers, open questions remain regarding field-dependent population dynamics under intense
laser driving. Using real-time time-dependent density functional theory combined with a determinant-overlap population framework, we track the intensity-dependent nonlinear response of a single thiophene ring (1T) and quaterthiophene (4T) as prototypical members of the oligothiophene family with different length and
symmetry. We demonstrate that extended $\pi$-conjugation in 4T lowers nonlinear excitation thresholds by orders of magnitude compared to 1T. State-resolved population dynamics reveal complete ground-state depletion accompanied by sequential excited-state absorption channels under intense driving. High-harmonic generation spectra explicitly reflect molecular
symmetry constraints, while energy-resolved occupation densities confirm continuous orbital redistribution across the $\pi^*$-
manifold. This work provides dynamic physical insights for engineering organic materials with tailored nonlinear optical properties.
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Computational Physics
A Physics-Driven Framework for Parametric Periodic-Flow Modeling and Finite-Amplitude Aeroelastic Response Analysis
Daiwei Dong, Wenbo Cao and Weiwei Zhang
Periodic unsteady flows are common in forced-motion and fluid-structure interaction problems. Their parametric analysis typically requires repeated high-fidelity simulations, whereas existing reduced-order and surrogate models generally rely on pre-generated flow-field or aerodynamic data. This study proposes a purely physics-driven framework for solving parametric periodic flows and finite-amplitude aeroelastic responses. First, a Periodic Physics-Informed Neural Network (P-PINN) is developed to directly solve periodic flows by imposing temporal periodicity over a single motion cycle, thereby avoiding the need to resolve the long transient
evolution preceding the establishment of the periodic state. The flow conditions and motion parameters are further incorporated as network inputs to construct continuous parametric representations of the periodic flow field and aerodynamic forces. On this basis, the parametric aerodynamic model is coupled with the structural dynamic equation through first-order harmonic balance to solve the response amplitude and frequency of a single-degree-of-freedom aeroelastic system. This framework is validated using forced-motion cases of a circular cylinder and an airfoil, demonstrating accurate reproduction of periodic aerodynamic forces, surface load distributions, and instantaneous flow fields under different flow and motion parameters compared with time-marching results. Furthermore, aeroelastic analysis is conducted for an elastically mounted circular cylinder at subcritical Reynolds numbers, and the resulting aeroelastic response agrees well with fully coupled CFD/CSD results. Once trained offline, the parametric model can be repeatedly evaluated for different structural parameter states, enabling the complete aeroelastic response curve to be obtained online within seconds, without repeated long-time fluid-structure interaction time marching.
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Plasma Physics
Prediction of Re-Ignition Times in Dielectric Barrier Discharges
Cristian Flores, Hans Höft, Tomáš Hoder et al. (+3 more)
Discharge ignition events in dielectric barrier discharges (DBDs) self-organise into spatio-temporal patterns with varying degrees of order. The complex dynamics of a DBD and intricate structure of occurring patterns complicate the formulation of predictive, mechanistic descriptions. We present the formulation of a reduced-order model that describes the re-ignition dynamics between consecutive discharges appearing at the same position inside a DBD arrangement. The model is derived from an equivalent electric
circuit and validated against fluid-Poisson simulations and experiments performed with a multi-filament arrangement in air-like gas mixtures at atmospheric pressure driven by sinusoidal high-voltage waveforms. The experimental scenarios include a highly ordered regime where discharges ignite at regular time and space intervals generating a pattern stable over several periods, and an unstable regime with discharges appearing at seemingly random positions and times. The model accuracy is assessed in both regimes and it is found that the associated prediction uncertainty provides a quantitative measure of the spatial order of the discharge pattern.
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All authors Cristian Flores, Hans Höft, Tomáš Hoder, Franz X. Bronold, Klaus-Dieter Weltmann, Markus M. Becker
Atomic Physics
Second-Order Rayleigh-Schrödinger Perturbation Theory for the Grasp
G. Gaigalas, P. Rynkun and L. Kitovienė
A developed method, based on the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form, allows us to determine the most important core-valence, core, core-core, and valence-valence correlations for any atom or ion with an arbitrary number of valence and core electrons. This paper presents the Feynman diagrams that describe these correlations. Additionally, it provides the rules for obtaining algebraic expressions in an irreducible tensorial form for any Feynman diagram coming from second-order many-body perturbation theory. Whereas some types of the valence-valence and core-valence correlations are described by the three-particle Feynman diagrams, additional developments to calculate the
spin-angular parts of these diagrams have been made to the program library librang of the Grasp2018. As an example of the application of the developed method, the atomic calculations of the energy level structure and transition data for Ar II are presented.
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Chemical Physics
Full-frequency GW from Cayley-transformed self-energy moments
Marcus K. Allen and George H. Booth
The dynamical GW self-energy approximation is a key computational tool to provide the fundamental spectrum of electronic systems. We reformulate this approximation, representing the particle and hole parts of the GW self-energy through a highly compact set of Cayley-transformed moment constraints. The Cayley transformation maps real frequencies to the unit circle, keeping the moments bounded as their order increases, ensuring numerical stability and allowing resolution to be focused on an energy range of interest. We calculate these Cayley-transformed moments via an efficient O[N$^4$] scaling contour integration, and from them, construct a Hermitian upfolded
Hamiltonian with a linearly scaling dimensionality with system size. A single-shot diagonalization of this effective
Hamiltonian gives an explicit full-frequency G0W0 Green's function with manifestly real poles and non-negative spectral weights. This enables quasiparticle energies, satellite features, and their spectral weights to be obtained across the full G0W0 spectrum. Comparisons with exact G0W0 calculations and convergence across the GW100 test set and the larger Chlorophyll A molecule demonstrate substantially faster and more reliable convergence with moment order than an earlier monomial-moment approach. These Cayley moment representations therefore provide a stable, compact, and systematically improvable route to the complete spectral information of zero-temperature GW, without explicit frequency grids, plasmon-pole models and other common approximations, or analytic continuation.
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Plasma Physics
The quadratic density response function for non-interacting fermions at arbitrary temperature
Pontus Svensson, Jan Vorberger, Zhandos A. Moldabekov et al. (+5 more)
We develop and implement the quadratic density response function of non-interacting
fermions at arbitrary temperature, frequencies, and wave vectors. Starting from a Green's function formulation, we derive the quadratic response and demonstrate its equivalence to the result obtained from the Wigner equation. We further derive the classical limit through a perturbative expansion of the Vlasov equation and demonstrate that the
quantum and classical formulations agree in the high-temperature limit. We analyse the limiting behaviour with respect to wavenumber and derive the zeroth harmonic response. Two independent implementations are provided and extensively benchmarked against density-functional theory, canonical path integral Monte Carlo (PIMC), and grand canonical PIMC simulations. As the density response of the interacting electron gas is commonly modelled through the ideal response functions and approximate models for the local field correction, the presented formulation will also allow for more complete explorations of interacting systems. Especially, our efficient implementation, which evaluates the ideal static and dynamic quadratic response functions in less than 0.5 ms on a 1.3 GHz processor, will enable evaluation of quadratic corrections to integrated quantities such as interaction potentials and stopping powers in warm dense matter.
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All authors Pontus Svensson, Jan Vorberger, Zhandos A. Moldabekov, Panagiotis Tolias, Paul Hamann, Xuecheng Shao, Cheng Ma, Tobias Dornheim