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We present a laser-based neutron source that produces $1.8 \times 10^5$ neutrons/s with a conversion rate of $7.8 \times 10^5$ neutrons/J. Laser pulses of 12 fs and 23 mJ were focused onto a 430-nm-thick heavy water liquid sheet at a 10 Hz repetition rate. The resulting peak intensity of $4 \times 10^{18}$ W/cm$^2$ accelerated deuterium ions from the target rear side to a kinetic energy of 1 MeV. This deuteron beam induced $^{2}$H(d,n)$^{3}$He fusion reactions in a deuterated polyethylene target, producing fast neutrons. The neutron yield was measured using two independent detection systems: the LILITH time-of-flight spectrometer, consisting of eight plastic scintillators covering nearly $180^\circ$, and a calibrated bubble detector spectrometer. The neutron yield per laser shot is 35 times higher than that recently achieved by lasers with comparable pulse energies, while the conversion rate is the highest ever achieved by continuously operating, sub-100 fs lasers. The generated neutrons are emitted from an area of 0.65 cm$^2$ corresponding to the deuteron beam spot on the catcher. Their angular distribution is peaked in forward and backward directions in agreement with the literature data on the angular distribution of $^{2}$H(d,n)$^{3}$He reaction. The system operated continuously for several hours per day with an unprecedented stability of 5%.

To realize braiding of vortex lines and understand the basic properties of the energy landscape for vortex motion, precise manipulation of superconducting vortices on the nanoscale is required. Here, we reveal that a localized trapping potential powerful enough to pull in the vortex line can be created with nanoscale precision on the surface of an FeSe superconductor using the tip of a scanning tunneling microscope. The mechanism of tip-induced force is traced to local modification of electronic properties and reduction of the superconducting gap, most likely due to tip-induced strain. Intriguingly, the tip-induced trapping potential is much less pronounced along the twin boundaries, dramatically reducing the vortice's degree of motion relative to the surrounding lattice. By enabling nanoscale manipulation of single vortices in Fe-based superconductors, and likely similar materials with strong strain-susceptibility of the superconducting gap, our findings provide an important step toward further development of vortex-based quantum information processing.

The coupling of matter to the quantized electromagnetic field of a plasmonic or optical cavity can be harnessed to modify and control chemical and physical properties of molecules. In optical cavities, a term known as the dipole self-energy (DSE) appears in the Hamiltonian to assure gauge invariance. The aim of this work is twofold. First, we introduce a method, which has its own merits and complements existing methods, to compute the DSE. Second, we study the impact of the DSE on cavity-induced nonadiabatic dynamics in a realistic system. For that purpose, various matrix elements of the DSE are computed as functions of the nuclear coordinates and the dynamics of the system after laser excitation is investigated. The cavity is known to induce conical intersections between polaritons, which gives rise to substantial nonadiabatic effects. The DSE is shown to slightly affect these light-induced conical intersections and, in particular, break their symmetry.

Topological quantum computation relies on control of non-Abelian anyons for inherently fault-tolerant storage and processing of quantum information. By now, blueprints for topological qubits are well developed for electrically active topological superconductor and fractional quantum Hall platforms. We leverage recent insights into the creation and detection of non-Abelian anyons in electrically insulating spin systems to propose topological qubit architectures based on quantum spin liquids. We present two types of prototype designs that enable the requisite control in a potentially scalable framework: one invokes spin liquids integrated into magnetic tunnel junction arrays, the other uses semiconductor-spin liquid hybrids. We further identify various protocols for interrogating spin-liquid-based topological qubits, both to validate the underlying principles of topological quantum computation and to establish gates required for universal quantum computation. These results provide long-term direction for experimental investigation of Kitaev materials and potentially other solid-state spin liquid hosts.

Silicon isotopic ratios measured in meteoritic presolar grains can provide useful information about the nucleosynthesis origin of these isotopes if the rates of nuclear reactions responsible for their production are known. One of the key reactions determining the Si isotopic abundances is 29Si(p,gamma)30P. Its reaction rate is not known with sufficient precision due in part to some ambiguous resonance strength values. In the present work, the strength of the E_p = 416.9 keV resonance has been measured with high precision using the activation technique. The new strength of omega_gamma = 219 +- 16 meV can be used in updated reaction rate estimations and astrophysical models., Comment: Accepted for publication in European Physical Journal A

Identifying experimental probes capable of diagnosing extreme quantum behavior is widely regarded as one of the foremost challenges in modern condensed matter physics. Here, we propose a novel approach for detecting chiral Kitaev spin liquid states through measurements of the local dynamical spin structure factor on the boundary using scanning tunneling microscopy (STM). We specifically focus on unpaired ("dangling") Majorana fermions, which naturally emerge along boundaries of Kitaev spin liquids, and can serve as indicators of chiral boundary modes under broad conditions, thereby offering a clear signature of these exotic quantum states.

Recent experimental work indicates that the Kitaev spin liquid may be realizable close to zero magnetic field in exfoliated $\alpha$-RuCl$_3$ flakes, thus providing a more versatile setting for studying non-Abelian anyons. Here, we propose a robust nanoscale signature of the Kitaev spin liquid that results from its edge states and manifests in the low-energy spin dynamics. In particular, we highlight a singular peak in the dynamical spin structure factor of a zigzag edge whose energy scales linearly with only one component of the magnetic field. This sharp feature in the local spin dynamics directly reflects the bond-directional Kitaev spin interactions and, more generally, the projective symmetries of the Kitaev spin liquid. We demonstrate that our proposed signature survives in the presence of edge disorder as well as non-Kitaev interactions, and provide detailed guidelines for experimentally observing it using inelastic electron tunneling spectroscopy and color-center relaxometry., Comment: 6+2 pages, 4 figures

Thermally driven transitions between ferromagnetic and paramagnetic phases are characterized by critical behavior with divergent susceptibilities, long-range correlations, and spin dynamics that can span kHz to GHz scales as the material approaches the critical temperature $\mathrm{T_c}$, but it has proven technically challenging to probe the relevant length and time scales with most conventional measurement techniques. In this study, we employ scanning nitrogen-vacancy center based magnetometry and relaxometry to reveal the critical behavior of a high-$\mathrm{T_c}$ ferromagnetic oxide near its Curie temperature. Cluster analysis of the measured temperature-dependent nanoscale magnetic textures points to a 3D universality class with a correlation length that diverges near $\mathrm{T_c}$. Meanwhile, the temperature-dependent spin dynamics, measured through all optical relaxometry suggest that the phase transition is in the XY universality class. Our results capture both static and dynamic aspects of critical behavior, providing insights into universal properties that govern phase transitions in magnetic materials.

Placing an atom and a molecule in a cavity opens the door to initialize molecular dynamics by exciting a level of the atom. This approach enlarges the range of choosing the light source to trigger molecular dynamics substantially. The interplay of the atomic, molecular and photonic populations gives rise to rich dynamics. The cavity photon plays the role of a mediator between the atom and the molecule and it is found that the photonic population is rather low throughout and its evolution follows that of the molecule. Cavities are known to be subject to losses. In spite of the losses it is demonstrated that the presence of the atom gives rise to a long-lived dynamics which should be of relevance for experimental investigations. The presence of more atoms and molecules is expected to further enrich the dynamics.

We study the impact of hole-doping on the Kitaev-Heisenberg model on the honeycomb lattice. We investigate the pairing tendencies and correlation functions in the framework of a $t-J-K$ model using density matrix renormalization group calculations on three-leg cylinders. In the case of the pure Kitaev model, which realizes a quantum spin-liquid phase at half-filling, we find that binding of two holes only occurs at low values of the hopping, where the holes are slow. We have theoretically verified that pair formation occurs in the limit of immobile holes, where the pure Kitaev model remains exactly solvable. When we instead fix the hopping at an intermediate, more realistic, value, and vary the Heisenberg and Kitaev interaction strengths, we find pairing tendencies only in the N\'eel phase. This is in contrast to prior mean-field calculations, highlighting the importance of accounting for the kinetic energy of dopants in generalized Kitaev models. Interestingly, we also find signatures of pair-density wave formation over the studied range of model parameters, namely a periodic modulation of the charge density as well as the spin-spin and pair-pair correlations in real space. Moreover, we present a comparative study of the different correlations as a function of doping. We finally discuss the potential for experimentally observing the studied physics in quantum materials and heterostructures., Comment: Main text: 11 pages, 7 figures. Supplemental material: 5 pages, 1 figure

We study quasiparticle interference (QPI) in the Kitaev quantum spin liquid (QSL) for electrons tunneling into the QSL. The local tunneling conductance around a spin vacancy or localized vison reveals unique features associated with fractionalized Majorana fermions, chargons, and visons. In certain parameter regimes, the single-spinon density of states and momentum dispersion can both be directly extracted from the tunneling conductance. Our results suggest that QPI is a promising tool for identifying the Kitaev QSL and its fractionalized excitations.

In several processes of stellar nucleosynthesis, like the astrophysical gamma-process, nuclear reactions involving alpha particles play an important role. The description of these reactions necessitates the knowledge of the alpha-nucleus optical model potential (AOMP) which is highly ambiguous at low, astrophysical energies. This ambiguity introduces a substantial uncertainty in the stellar models for predicting elemental and isotopic abundances. The experimental study of the AOMP is thus necessary which can be implemented by measuring the cross section of alpha-induced nuclear reactions. At low energies, (a,n) reactions are suitable for such a purpose. Therefore, in the present work, the (a,n) cross sections of four Te isotopes have been measured, mostly for the first time, and compared with theoretical predictions. The (a,n) cross sections of 120,122,124,130Te have been measured in the energy range between about 10 and 17 MeV using the activation method. The detection of the gamma radiation following the decay of the radioactive reaction products were used to determine the cross sections. The measured cross sections are compared with statistical model calculations obtained from the widely used TALYS nuclear reaction simulation code. Predictions using various available AOMPs are investigated. It is found that the recently developed Atomki-V2 AOMP provides the best description for all studied reactions and this potential also reproduces well the total reaction cross sections from elastic scattering experiments, when they are available in literature. We recommend therefore to use the astrophysical reaction rates based on this potential for nucleosynthesis models of heavy elements., Comment: Accepted for publication in Phys. Rev. C

The 2024 Brain Tumor Segmentation Meningioma Radiotherapy (BraTS-MEN-RT) challenge aims to advance automated segmentation algorithms using the largest known multi-institutional dataset of radiotherapy planning brain MRIs with expert-annotated target labels for patients with intact or postoperative meningioma that underwent either conventional external beam radiotherapy or stereotactic radiosurgery. Each case includes a defaced 3D post-contrast T1-weighted radiotherapy planning MRI in its native acquisition space, accompanied by a single-label "target volume" representing the gross tumor volume (GTV) and any at-risk postoperative site. Target volume annotations adhere to established radiotherapy planning protocols, ensuring consistency across cases and institutions. For preoperative meningiomas, the target volume encompasses the entire GTV and associated nodular dural tail, while for postoperative cases, it includes at-risk resection cavity margins as determined by the treating institution. Case annotations were reviewed and approved by expert neuroradiologists and radiation oncologists. Participating teams will develop, containerize, and evaluate automated segmentation models using this comprehensive dataset. Model performance will be assessed using an adapted lesion-wise Dice Similarity Coefficient and the 95% Hausdorff distance. The top-performing teams will be recognized at the Medical Image Computing and Computer Assisted Intervention Conference in October 2024. BraTS-MEN-RT is expected to significantly advance automated radiotherapy planning by enabling precise tumor segmentation and facilitating tailored treatment, ultimately improving patient outcomes., Comment: 14 pages, 9 figures, 1 table

Using the framework of semi-classical Landau-Lifshitz dynamics (LLD), we conduct a systematic investigation of the temperature-dependent spin dynamics in the S = 1/2 Heisenberg square-lattice antiferromagnet (SqAF). By performing inelastic neutron scattering measurements on Zn2VO(PO4)2 (ZVPO) and corresponding finite-temperature spin dynamics simulations based on LLD, we present a comprehensive analysis that bridges quantum and classical spin dynamics over a broad temperature range. First, a remarkable agreement between experimental data and LLD simulations is found in the paramagnetic phase of ZVPO, demonstrating the capability of LLD in accurately determining the spin Hamiltonian of S = 1/2 systems and capturing the quantum-to-classical crossover of their spin dynamics. Second, by analyzing the discrepancies between the experimental data and the LLD simulations at lower temperatures, we determine the experimental temperature dependence of the quantum effects in the excitation spectrum of the S = 1/2 SqAF: the quantum renormalization factor for the magnon energies and the quantum continuum above the one-magnon bands. Notably, the emergence of each quantum effect is found to correlate with the formation of three-dimensional long-range order. This work demonstrates the utility of LLD in gaining experimental insights into the temperature-induced modifications of quantum spin dynamics and their convergence towards classical expectations at higher temperatures. This motivates further applications to more challenging quantum antiferromagnets dominated by stronger quantum fluctuations., Comment: 8 pages, 4 figures, Supplemental Material can be found on the journal's website

Non-adiabatic molecular phenomena, arising from the breakdown of the Born-Oppenheimer approximation, govern the fate of virtually all photo-physical and photochemical processes and limit the quantum efficiency of molecules and other solid-state embedded quantum emitters. A simple and elegant description, the energy gap law, was derived five decades ago, predicting that the non-adiabatic coupling between the excited and ground potential landscapes lead to non-radiative decay with a quasi-exponential dependence on the energy gap. We revisit and extend this theory to account for crucial aspects such as vibrational relaxation, dephasing, and radiative loss. We find a closed analytical solution with general validity which indicates a direct proportionality of the non-radiative rate with the vibrational relaxation rate at low temperatures, and with the dephasing rate of the electronic transition at high temperatures. Our work establishes a connection between nanoscale quantum optics, open quantum system dynamics and non-adiabatic molecular physics., Comment: 18 pages and 5 figures

We propose a deep learning based novel prediction framework for enhanced bandwidth reduction in motion transfer enabled video applications such as video conferencing, virtual reality gaming and privacy preservation for patient health monitoring. To model complex motion, we use the First Order Motion Model (FOMM) that represents dynamic objects using learned keypoints along with their local affine transformations. Keypoints are extracted by a self-supervised keypoint detector and organized in a time series corresponding to the video frames. Prediction of keypoints, to enable transmission using lower frames per second on the source device, is performed using a Variational Recurrent Neural Network (VRNN). The predicted keypoints are then synthesized to video frames using an optical flow estimator and a generator network. This efficacy of leveraging keypoint based representations in conjunction with VRNN based prediction for both video animation and reconstruction is demonstrated on three diverse datasets. For real-time applications, our results show the effectiveness of our proposed architecture by enabling up to 2x additional bandwidth reduction over existing keypoint based video motion transfer frameworks without significantly compromising video quality.

The exchange of energy between electronic and nuclear motion is the origin of non-adiabaticity and plays an important role in many molecular phenomena and processes. Conical intersections (CIs) of different electronic potential energy surfaces lead to the most singular non-adiabaticity and have been intensely investigated. The coupling of light and matter induces conical intersections which are termed light-induced conical intersections (LICIs). There are two kinds of LICIs, those induced by classical (laser) light and those by quantum light like that provided by a cavity. The present work reviews the subject of LICIs, discussing the achievements made so far. Particular attention is paid to comparing classical and quantum LICIs, their similarities and differences and their relationship to naturally occurring CIs. In contrast to natural CIs, the properties of which are dictated by nature, the properties of their light-induced counterparts are controllable by choosing the frequency and intensity (or coupling to the cavity) of the external light source. This opens the door to inducing and manipulating various kinds of non-adiabatic effects. Several examples of diatomic and polyatomic molecules are presented covering both dynamics and spectroscopy. The computational methods employed are discussed as well. To our opinion, the young field of LICIs and their impact show much future potential.

The S = 1/2 triangular lattice antiferromagnet (TLAF) is a paradigmatic example of frustrated quantum magnetism. An ongoing challenge involves understanding the influence of exchange anisotropy on the collective behavior within such systems. Using inelastic neutron scattering (INS) and advanced calculation techniques, we have studied the low and high-temperature spin dynamics of Ba2La2CoTe2O12 (BLCTO): a Co2+-based Jeff = 1/2 TLAF that exhibits 120{\deg} order below TN = 3.26 K. We determined the spin Hamiltonian by fitting the energy-resolved paramagnetic excitations measured at T > TN, revealing exceptionally strong easy-plane XXZ anisotropy. Below TN, the excitation spectrum exhibits a high energy continuum having a larger spectral weight than the single-magnon modes, suggesting a scenario characterized by a spinon confinement length that markedly exceeds the lattice spacing. We conjecture that this phenomenon arises from the proximity to a quantum melting point, even under strong easy-plane XXZ anisotropy. Finally, we highlight characteristic flat features in the excitation spectrum, which are connected to higher-order van Hove singularities in the magnon dispersion directly induced by easy-plane XXZ anisotropy. Our results provide a rare experimental insight into the nature of highly anisotropic S = 1/2 TLAFs between the Heisenberg and XY limits., Comment: 5 figures, Supplementary Information can be found on the journal's website

The use of cavities to impact molecular structure and dynamics has become popular. As cavities, in particular plasmonic nanocavities, are lossy and the lifetime of their modes can be very short, their lossy nature must be incorporated into the calculations. The Lindblad master equation is commonly considered as an appropriate tool to describe this lossy nature. This approach requires the dynamics of the density operator and is thus substantially more costly than approaches employing the Schr\"odinger equation for the quantum wave function when several or many nuclear degrees of freedom are involved. In this work we compare numerically the Lindblad and Schr\"odinger descriptions discussed in the literature for a molecular example where the cavity is pumped by a laser. The laser and cavity properties are varied over a range of parameters. It is found that the Schr\"odinger description adequately describes the dynamics of the polaritons and emission signal as long as the laser intensity is moderate and the pump time is not much longer than the lifetime of the cavity mode. Otherwise, it is demonstrated that the Schr\"odinger description gradually fails. We also show that the failure of the Schr\"odinger description can often be remedied by renormalizing the wave function at every step of the time propagation. The results are discussed and analyzed.

It has been known that electronic conical intersections in a molecular system can also be created by laser light even in diatomics. The direct consequence of these light-induced degeneracies is the appearance of a strong mixing between the electronic and vibrational motions, which has a strong fingerprint on the ultrafast nuclear dynamics. In the present work, pump and probe numerical simulations have been performed with the NaH molecule involving the first three singlet electronic states (X1{\Sigma}+(X), A1{\Sigma}+(A) and B1{\Pi}(B)) and several light-induced degeneracies in the numerical description. To demonstrate the impact of the multiple light-induced non-adiabatic effects together with the molecular rotation on the dynamical properties of the molecule, the dissociation probabilities, kinetic energy release spectra (KER) and the angular distributions of the photofragments were calculated by discussing the role of the permanent dipole moment as well.

We study the dynamical response of vacancy-induced quasiparticle excitations in the site-diluted Kitaev spin liquid with a magnetic field. Due to the flux-binding effect and the emergence of dangling Majorana fermions around each spin vacancy, the low-energy physics is governed by a set of vacancy-induced quasi-zero-energy modes. These localized modes result in unique characteristics of the dynamical spin correlation functions, which intriguingly mimic the single-quasiparticle density of states and further exhibit a quasi-zero-frequency peak. By recognizing the potential observability of these local correlation functions via scanning tunneling microscopy (STM), we show how the STM response is sensitive to the local flux configuration, the magnetic field strength, and the vacancy concentration. Constructing a simple model of the localized modes, we also elucidate how the local correlation functions can be interpreted in terms of the hybridization between these modes., Comment: 14 pages, 8 figures

Ionization phenomena are widely studied for decades. With the advent of cavity technology, the question arises how quantum light affects molecular ionization. As the ionization spectrum is recorded from the neutral ground state, it is usually possible to choose cavities which exert negligible effect on the neutral ground state, but have significant impact on the ion and the ionization spectrum. Particularly interesting are cases where the ion exhibits conical intersections between close-lying electronic states, which gives rise to substantial nonadiabatic effects. Assuming single-molecule strong coupling, we demonstrate that vibrational modes irrelevant in the absence of cavity play a decisive role when the molecule is in the cavity. Here, dynamical symmetry breaking is responsible for the ion-cavity coupling and high symmetry enables control of the coupling via molecular orientation relative to the cavity field polarization. Significant impact on the spectrum by the cavity is found and shown to even substantially increase for less symmetric molecules.

Reliable manipulation of non-Abelian Ising anyons supported by Kitaev spin liquids may enable intrinsically fault-tolerant quantum computation. Here, we introduce a standalone scheme for both generating and detecting individual Ising anyons using tunable gate voltages in a heterostructure containing a non-Abelian Kitaev spin liquid and a monolayer semiconductor. The key ingredients of our setup are a Kondo coupling to stabilize an Ising anyon in the spin liquid around each electron in the semiconductor, and a large charging energy to allow control over the electron numbers in distinct gate-defined regions of the semiconductor. In particular, a single Ising anyon can be generated at a disk-shaped region by gate tuning its electron number to one, while it can be interferometrically detected by measuring the electrical conductance of a ring-shaped region around it whose electron number is allowed to fluctuate between zero and one. We provide concrete experimental guidelines for implementing our proposal in promising candidate materials like $\alpha$-RuCl$_3$., Comment: 6+2 pages, 2+2 figures

The current challenge to realizing continuously tunable magnetism lies in our inability to systematically change properties such as valence, spin, and orbital degrees of freedom as well as crystallographic geometry. Here, we demonstrate that ferromagnetism can be externally turned on with the application of low-energy helium implantation and subsequently erased and returned to the pristine state via annealing. This high level of continuous control is made possible by targeting magnetic metastability in the ultra-high conductivity, non-magnetic layered oxide PdCoO2 where local lattice distortions generated by helium implantation induce emergence of a net moment on the surrounding transition metal octahedral sites. These highly-localized moments communicate through the itinerant metal states which triggers the onset of percolated long-range ferromagnetism. The ability to continuously tune competing interactions enables tailoring precise magnetic and magnetotransport responses in an ultra-high conductivity film and will be critical to applications across spintronics., Comment: https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.3c01065

Spin vacancies in the non-Abelian Kitaev spin liquid are known to harbor Majorana zero modes, potentially enabling topological quantum computing at elevated temperatures. Here, we study the spectroscopic signatures of such Majorana zero modes in a scanning tunneling setup where a non-Abelian Kitaev spin liquid with a finite density of spin vacancies forms a tunneling barrier between a tip and a substrate. Our key result is a well-defined peak close to zero bias voltage in the derivative of the tunneling conductance whose voltage and intensity both increase with the density of vacancies. This ''quasi-zero-voltage peak'' is identified as the closest analog of the zero-voltage peak observed in topological superconductors that additionally reflects the fractionalized nature of spin-liquid-based Majorana zero modes. We further highlight a single-fermion Van Hove singularity at a higher voltage that reveals the energy scale of the emergent Majorana fermions in the Kitaev spin liquid. Our proposed signatures are within reach of current experiments on the candidate material $\alpha$-RuCl$_3$., Comment: 6+4 pages, 2+1 figures

The $^3$He($\alpha$,$\gamma$)$^7$Be reaction plays a major role both in the BBN producing the majority of the primordial $^7$Li, and in the pp-chain, where it is the branching point. As a few-nucleon system, this reaction is often used to validate ab-initio theoretical calculations and/or test R-matrix theory and code implementations. For the latter, experimental data in an extended energy range is of crucial importance to test the fit and extrapolation capabilities of the different codes. The $^3$He($\alpha$,$\gamma$)$^7$Be reaction cross section has been measured by several groups up to the first resonance ($E_{c.m.} \approx 3$ MeV) in the reaction. However, only one dataset exists above the $^7$Be proton separation threshold measured in a narrow energy range ($E_{c.m.} = 4.0-4.4$ MeV). In this work we extend the available experimental capture cross section database to the energy range of known $^7$Be levels. The activation method was used. The experiment was performed using a thin-window gas cell with two high-purity Al foils as entrance and exit windows. The activity of the $^7$Be nuclei implanted in the exit/catcher foil was measured by detecting the yield of the emitted $\gamma$~rays using shielded high-purity germanium detectors. New experimental $^3$He($\alpha$,$\gamma$)$^7$Be reaction cross section data were obtained for the first time in the $E_{c.m.}=4.3-8.3$ MeV energy region. The new dataset with about 0.2 MeV step covers the energy range of known levels and particle separation thresholds. No prominent structures are observer around the $^7$Be levels. The reaction cross section is slowly increasing with increasing energy. Above the $^6$Li$+p_1$ threshold, a decrease starts in the cross section trend. The overall structure of the cross section suggest a broad resonance peaking around $E_x=7.5$ MeV $^7$Be excitation energy, with a width of 8 MeV., Comment: Typos are corrected, mainly in Table II., second column where the numerical values were incorrectly entered before

This work describes a silicon tracker system developed for experiments with proton-rich radioactive ion beams at the SAMURAI superconducting spectrometer of RIBF at RIKEN. The system is designed for accurate angular reconstruction and atomic number identification of relativistic heavy ions and protons which are simultaneously produced in reactions motivated by studies of proton capture reactions of interest for nuclear astrophysics. The technical characteristics of the tracking array are described in detail as are its performance in two pilot experiments. The physics justification for such a system is also presented.

The CNO cycle is one of the fundamental processes of hydrogen burning in stars. The first reaction of the cycle is the radiative proton capture on 12C and the rate of this 12C(p,gamma)13N reaction is related to the 12C/13C ratio observed e.g. in the Solar System. The low-energy cross section of this reaction was measured several times in the past, however, the experimental data are scarce in a wide energy range especially around the resonance at 1.7 MeV. In the present work the 12C(p,gamma)13N cross section was measured between 300 and 1900 keV using the activation method. This method was only used several decades ago in the low-energy region. As the activation method provides the total cross section and has uncertainties different from those of the in-beam gamma-spectroscopy technique, the present results provide a largely independent data set for future low-energy extrapolations and thus for astrophysical reaction rate calculations., Comment: Accepted for publication in European Physical Journal A

Nuclear reactions involving alpha particles play an important role in various astrophysical processes such as the gamma-process of heavy element nucleosynthesis. The poorly known low-energy alpha-nucleus optical (AOMP) potential is a key parameter to estimate the rates of these reactions. The AOMP can be tested by measuring the cross section of alpha-scattering as well as alpha-induced reactions. Low energy elastic alpha-scattering on 144Sm has recently been measured with high precision. The aim of the present work was to complement that work by measuring the (a,n) cross sections on 144Sm at low energies. The experimental data shall be used to constrain the AOMP. From this potential the 144Sm(a,g)148Gd reaction rate can be derived with reduced uncertainties. The 144Sm(a,n)147Gd reaction was studied by bombarding Sm targets with alpha-beams provided by the cyclotron accelerator of Atomki. The cross section was determined using the activation method. The gamma-radiation following the decay of the 147Gd reaction product was measured with a HPGe detector. The experimental data are analyzed within the statistical model. The cross section was measured in the alpha-energy range between 13 and 20 MeV in 1 MeV steps, i.e., from close above the (a,n) threshold. The results were compared with statistical model calculations using various approaches and parametrizations for the AOMP, and excellent agreement was obtained for two recent potentials. However, these potentials cannot reproduce literature data for the 144Sm(a,g)148Gd reaction with the same accuracy. Constraints for the AOMP were derived from an analysis of the new 144Sm(a,n)147Gd data and literature data for 144Sm(a,g)148Gd. These constraints enable a determination of the reaction rate of the 144Sm(a,g)148Gd reaction with significantly reduced uncertainties of less than a factor of two., Comment: Accepted for publication in Phys. Rev. C

The celebrated Little-Parks effect in mesoscopic superconducting rings has recently gained great attention due to its potential to probe half-quantum vortices in spin-triplet superconductors. However, despite the large number of works reporting anomalous Little-Parks measurements attributed to unconventional superconductivity, the general signatures of spin-triplet pairing in the Little-Parks effect have not yet been systematically investigated. Here we use Ginzburg-Landau theory to study the Little-Parks effect in a spin-triplet superconducting ring that supports half-quantum vortices; we calculate the field-induced Little-Parks oscillations of both the critical temperature itself and the residual resistance resulting from thermal vortex tunneling below the critical temperature. We observe two separate critical temperatures with a single-spin superconducting state in between and find that, due to the existence of half-quantum vortices, each minimum in the upper critical temperature splits into two minima for the lower critical temperature. From a rigorous calculation of the residual resistance, we confirm that these two minima in the lower critical temperature translate into two maxima in the residual resistance below and establish the general conditions under which the two maxima can be practically resolved. In particular, we identify a fundamental trade-off between sharpening each maximum and keeping the overall magnitude of the resistance large. Our results will guide experimental efforts in designing mesoscopic ring geometries for probing half-quantum vortices in spin-triplet candidate materials on the device scale.

A random 2-cell embedding of a connected graph $G$ in some orientable surface is obtained by choosing a random local rotation around each vertex. Under this setup, the number of faces or the genus of the corresponding 2-cell embedding becomes a random variable. Random embeddings of two particular graph classes, those of a bouquet of $n$ loops and those of $n$ parallel edges connecting two vertices, have been extensively studied and are well-understood. However, little is known about more general graphs. The results of this paper explain why Monte Carlo methods cannot work for approximating the minimum genus of graphs. In his breakthrough work [Permutation-partition pairs, JCTB 1991], Stahl developed the foundation of "random topological graph theory". Most of his results have been unsurpassed until today. In our work, we analyze the expected number of faces of random embeddings (equivalently, the average genus) of a graph $G$. It was very recently shown that for any graph $G$, the expected number of faces is at most linear. We show that the actual expected number of faces $F(G)$ is almost always much smaller. In particular, we prove: 1) $\frac{1}{2}\ln n - 2 < \mathbb{E}[F(K_n)] \le 3.65 \ln n +o(1)$. 2) For random graphs $G(n,p)$ ($p=p(n)$), we have $\mathbb{E}[F(G(n,p))] \le \ln^2 n+\frac{1}{p}$. 3) For random models $B(n,\Delta)$ containing only graphs, whose maximum degree is at most $\Delta$, we get stronger bounds $\mathbb{E}[F(B(n,\Delta))]=\Theta(\ln n)$., Comment: Accepted at the 35th ACM-SIAM Symposium on Discrete Algorithms (SODA 2024). 55 pages, 10 figures