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At least 793 records · Page 44

Enhancing strontium clock atom interferometry using quantum optimal control

Strontium clock atom interferometry is a promising new technology, with multiple experiments under development around the world to explore its potential for dark matter and gravitational wave detection. In these detectors, large momentum transfer using sequences of many laser pulses is necessary, and thus high-fidelity pulses are important since small errors become magnified. Quantum optimal control (QOC) is a framework for developing control pulse waveforms that achieve high fidelity and are robust against experimental imperfections. Resonant single-photon transitions using the narrow clock transition of strontium involve significantly different quantum dynamics than more established atom interferometry methods based on far-detuned two-photon Raman or Bragg transitions, which leads to new opportunities and challenges when applying QOC. Here, we study in simulation QOC pulses for strontium clock interferometry and demonstrate their advantage over basic square pulses (primitive pulses) and composite pulses in terms of robustness against multiple noise channels. In conclusion, this could improve the scale of large momentum transfer in Sr clock interferometers, paving the way to achieving these scientific goals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Novel thermal energy storage component: Development, performance, and phase transition diagnosis

Thermal energy storage (TES) using phase change materials (PCMs) is a promising technology for capturing and storing excess thermal energy for later use. However, challenges such as poor heat transfer efficiency and a lack of modular, scalable designs have limited widespread adoption of TES in real-world applications. This study developed and evaluated modular brick-type and blade-type TES prototypes featuring an aluminum housing, an embedded serpentine coil for active or passive thermal exchange, and a cost-effective metal mesh to enhance PCM thermal conductivity. The blade-type TES achieved notable geometric efficiency, with a thickness-to-length ratio of 0.03 and a thickness-to-width ratio of 0.08, enabling highly compact and modular thermal storage suitable for space-constrained applications. The paper presents a detailed evaluation of the TES prototypes’ performance. The comparative analysis indicated that the TES prototypes provide a highly cost-effective, thermally optimized alternative for compact energy storage and load shifting. A novel diagnostic technique was also introduced: using a portable endoscope to capture real-time visualizations of PCM phase transitions inside the TES. This method provides critical insights into internal heat transfer mechanisms, identifies potential issues, and offers valuable support for optimizing the TES design and developing the control algorithm. Overall, the modular brick-type and blade-type TES designs demonstrated in this work provide a scalable, efficient, and economically viable solution for advancing TES across residential, commercial, and industrial sectors. The designs’ compact structure, enhanced thermal performance, and integrated diagnostic capabilities make them strong candidates for future deployment in energy-efficient systems.

Gao, Zhiming [ORNL] (ORCID:0000000271397995)↗

Synthesis of Sandwich-α-Diimine Ligands via Copper-Mediated Stille Coupling

While sandwich diimines have found use in transition metal catalysis, the general method for their preparation has been lacking. Here, this approach utilizes a copper-mediated Stille-type coupling between aryl stannanes and α-diimines bearing 8-bromonaphthylimino group in commercial-grade N,N-dimethylformamide solvent and employs CuI or thiophene-2-carboxylate to promote the reactions. No other additives or bases are required. Electron-poor, electron-rich, heterocyclic, and hindered aryl stannanes can be employed as coupling reagents. Ligand scaffolds derived from structurally diverse α-diketones can be used.

Catalysts↗

Initiation reactions in acetylene pyrolysis

In gas-phase combustion systems the interest in acetylene stems largely from its role in molecular weight growth processes. The consensus is that above 1500 K acetylene pyrolysis starts mainly with the homolytic fission of the C–H bond creating an ethynyl radical and an H atom. However, below ~1500 K this reaction is too slow to initiate the chain reaction. It has been hypothesized that instead of dissociation, self-reaction initiates this process. Nevertheless, rigorous theoretical or direct experimental evidence is lacking, to an extent that even the molecular mechanism is debated in the literature. In this work we use rigorous ab initio transition-state theory master equation methods to calculate pressure- and temperature-dependent rate coefficients for the association of two acetylene molecules and related reactions. We establish the role of vinylidene, the high-energy isomer of acetylene in this process, compare our results with available experimental data, and assess the competition between the first-order and second-order initiation steps. As a result, we also show the effect of the rapid isomerization among the participating wells and highlight the need for time-scale analysis when phenomenological rate coefficients are compared to observed time scales in certain experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Interference of interchromophoric energy-transfer pathways in π-conjugated macrocycles

The interchromophoric energy-transfer pathways between weakly coupled units in a π-conjugated phenylene–ethynylene macrocycle and its half-ring analogue have been investigated using the nonadiabatic excited-state molecular dynamics approach. To track the flow of electronic transition density between macrocycle units, we formulate a transition density flux analysis adapted from the statistical minimum flow method previously developed to investigate vibrational energy flow. Following photoexcitation, transition density is primarily delocalized on two chromophore units and the system undergoes ultrafast energy transfer, creating a localized excited state on a single unit. In the macrocycle, distinct chromophore units donate transition density to a single acceptor unit but do not interchange transition density among each other. We find that energy transfer in the macrocycle is slower than in the corresponding half ring because of the presence of multiple interfering energy-transfer pathways. Finally, simulation results are validated by modeling the fluorescence anisotropy decay.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Manipulation of the magnetic monopole injection for topological transition

Abstract Manipulating the topological properties of spin textures in magnetic materials is of great interest due to the rich physics and promising technological applications of these materials in advanced electronic devices. A spin texture with desired topological properties can be created by magnetic monopole injection, resulting in topological transitions involving changes in the topological charge. Therefore, controlling magnetic monopole injection has paramount importance for obtaining the desired spin textures but has not yet been reported. Here, we report the use of reliably manipulated magnetic monopole injection in the topological transition from stripe domains to skyrmions in an Fe/Gd multilayer. An easily tunable in-plane magnetic field applied to an Fe/Gd multilayer plays a key role in the magnetic monopole injection by modulating the local exchange energy. Our findings facilitate the efficient management of topological transitions by providing an important method for controlling magnetic monopole injection.

36 MATERIALS SCIENCE↗

Field trials results of guided wave tomography

Corrosion is one of the industries major issues regarding the integrity of assets. Guided wave travel time tomography is a method capable of providing an absolute wall thickness map. This method is currently making the transition from the laboratory to the field. For this purpose a dedicated data acquisition system and special purpose EMAT sensor rings have been developed. The system can be deployed for permanent monitoring and inspections. Field trials have been conducted on various pipes with different diameters, containing either liquid or gas. The main focus has been on pipe supports. The results demonstrate the successful operation of the technology in the field. Expected corrosion damage was clearly visible on the produced results enabling asset owner to make calculated decisions on the pipelines safety, maintenance and operations.

42 ENGINEERING↗

Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension

Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Importance sampling large deviations in nonequilibrium steady states. I

Large deviation functions hold information on the stability and response of systems driven into nonequilibrium steady states and in such a way are similar to free energies for systems at equilibrium. As with equilibrium free energies, evaluating large deviation functions numerically for all but the simplest systems is difficult because by construction they depend on exponentially rare events. In this first paper of a series, we assess different trajectory-based sampling methods capable of computing large deviation functions of time integrated observables within nonequilibrium steady states. We highlight some convergence criteria and best practices using a number of different models, including a biased Brownian walker, a driven lattice gas, and a model of self-assembly. We show how two popular methods for sampling trajectory ensembles, transition path sampling and diffusion Monte Carlo, suffer from exponentially diverging correlations in trajectory space as a function of the bias parameter when estimating large deviation functions. Improving the efficiencies of these algorithms requires introducing guiding functions for the trajectories.

74 ATOMIC AND MOLECULAR PHYSICS↗

Argon metastable and resonant level densities in Ar and Ar/Cl 2 discharges used for the processing of bulk niobium

In this work, a comparative analysis of two popular spectroscopy techniques is conducted in a coaxial cylindrical capacitively coupled discharge designed for the plasma processing of superconducting radio frequency (SRF) cavities. The density of the metastable and resonant levels in Ar is measured in both Ar and Ar/Cl 2 discharges to properly characterize the unique discharge system and aid in the development of a cavity etching routine. The first method, deemed the “branching fraction method,” utilizes the sensitivity of photon reabsorption of radiative decay to measure the lower state (metastable and resonant) densities by taking ratios of spectral lines with a common upper level. This method has been gaining popularity as it does not require any a priori knowledge about the electron energy distribution. The second method is a tunable diode laser absorption spectroscopy technique that measures the thermal Doppler broadening of spectral lines, from which the neutral gas temperature and lower state density of the transition can be evaluated. The two methods were conducted in tandem, while external parameters that were empirically determined to be important to the etching mechanism of SRF cavities are varied. Relationships between the excited state densities and the external parameters are presented for both spectroscopy methods and conclusions about the effects of these parameters on the discharge are stated when appropriate.

Plasma properties and parameters↗

Enhancement to the conductivity of surface transfer-doped (111) diamond through thermochemical surface etching

The use of a transition metal catalyzed thermochemical etching method for improving the carrier transport properties of the near-surface two-dimensional (2D) hole gas in surface transfer-doped hydrogen-terminated (111) diamond is demonstrated. Using Ni 0.8 Cr 0.2 films deposited and annealed to a temperature of 900 °C, with up to three etch cycles, preferential (111) surface etching produces large terraces exceeding 10 μm in size with a surface microroughness, σ 2 RMS λ, that is two orders of magnitude lower than for the pre-etched (111) surface. Magnetotransport measurements on hydrogen-terminated Hall bars engineered on the pre- and post-etched surfaces and rendered conductive by the adsorbed water layer formed on exposure to ambient conditions demonstrate that this etching causes an improvement in the hole mobility by an order of magnitude, resulting in a measured sheet resistivity of 1.04 kΩ/sq at a temperature of 4.2 K without gating.

42 ENGINEERING↗

Spin-forbidden and spin-allowed cyclopropenone (c-H{sub 2}C{sub 3}O) formation in interstellar medium

Three proposed mechanisms of cyclopropenone (c-H{sub 2}C{sub 3}O) formation from neutral species are studied using high-level electronic structure methods in combination with nonadiabatic transition state and collision theories to deduce the likelihood of each reaction mechanism under interstellar conditions. The spin-forbidden reaction involving the singlet electronic state of cyclopenylidene (c-C{sub 3}H{sub 2}) and the triplet state of atomic oxygen is studied using nonadiabatic transition state theory to predict the rate constant for c-H{sub 2}C{sub 3}O formation. The spin-allowed reactions of c-C{sub 3}H{sub 2} with molecular oxygen and acetylene with carbon monoxide were also investigated. The reaction involving the ground electronic states of acetylene and carbon monoxide has a very large reaction barrier and is unlikely to contribute to c-H{sub 2}C{sub 3}O formation in interstellar medium. The spin-forbidden reaction of c-C{sub 3}H{sub 2} with atomic oxygen, despite the high probability of nonadiabatic transition between the triplet and singlet states, was found to have a very small rate constant due to the presence of a small (3.8 kcal mol{sup –1}) reaction barrier. In contrast, the spin-allowed reaction between c-C{sub 3}H{sub 2} and molecular oxygen is found to be barrierless, and therefore can be an important path to the formation of c-H{sub 2}C{sub 3}O molecule in interstellar environment.

79 ASTRONOMY AND ASTROPHYSICS↗

NEXT GENERATION OF TELESCOPES OR DYNAMICS REQUIRED TO DETERMINE IF EXO-MOONS HAVE PROGRADE OR RETROGRADE ORBITS

We survey the methods proposed in the literature for detecting moons of extrasolar planets in terms of their ability to distinguish between prograde and retrograde moon orbits, an important tracer of the moon formation channel. We find that most moon detection methods, in particular, sensitive methods for detecting moons of transiting planets, cannot observationally distinguishing prograde and retrograde moon orbits. The prograde and retrograde cases can only be distinguished where the dynamical evolution of the orbit due to, e.g., three body effects is detectable, where one of the two cases is dynamically unstable, or where new observational facilities, which can implement a technique capable of differentiating the two cases, come online. In particular, directly imaged planets are promising targets because repeated spectral and photometric measurements, which are required to determine moon orbit direction, could also be conducted with the primary interest of characterizing the planet itself.

79 ASTRONOMY AND ASTROPHYSICS↗

Probing Excited-State Dynamics of Transmon Ionization

The fidelity and quantum nondemolition character of the dispersive readout in circuit QED are limited by unwanted transitions to highly excited states at specific photon numbers in the readout resonator. This observation can be explained by multiphoton resonances between computational states and highly excited states in strongly driven nonlinear systems, analogous to multiphoton ionization in atoms and molecules. In this work, we utilize the multilevel nature of high-𝐸 𝐽 /𝐸 𝐶 transmons to probe the excited-state dynamics induced by strong drives during readout. With up to ten resolvable states, we quantify the critical photon number of ionization, the resulting state after ionization, and the fraction of the population transferred to highly excited states. Moreover, using pulse shaping to control the photon number in the readout resonator in the high-power regime, we tune the adiabaticity of the transition and verify that transmon ionization is a Landau-Zener-type transition. We further extend these methods to a typical transmon with 𝐸 𝐽 /𝐸 𝐶 ≈ 55 and probe the offset-charge dependence of ionization dynamics in a timed-resolved manner. Our experimental results agree well with the theoretical prediction from a semiclassical driven transmon model and may guide future exploration of strongly driven nonlinear oscillators.

cavity quantum electrodynamics↗

Topological and magnetic properties of the interacting Bernevig-Hughes-Zhang model

We investigate the effects of electronic correlations on the Bernevig-Hughes-Zhang model using the real-space density matrix renormalization group (DMRG) algorithm. We introduce a method to probe topological phase transitions in systems with strong correlations using DMRG, substantiated by an unsupervised machine learning methodology that analyzes the orbital structure of the real-space edges. Including the full multi-orbital Hubbard interaction term, we construct a phase diagram as a function of a gap parameter (m) and the Hubbard interaction strength (U) via exact DMRG simulations on N×4 cylinders. Our analysis confirms that the topological phase persists in the presence of interactions, consistent with previous studies, but it also reveals an intriguing phase transition from a paramagnetic to a stripey antiferromagnetic topological insulator. The combination of the magnetic structure factor, strength of magnetic moments, and the orbitally resolved density, provides real-space information on both topology and magnetism in a strongly correlated system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Isotensor Axial Polarizability and Lattice QCD Input for Nuclear Double- β Decay Phenomenology

The potential importance of short-distance nuclear effects in double-$\beta$ decay is assessed using a lattice QCD calculation of the $nn\rightarrow pp$ transition and effective field theory methods. At the unphysical quark masses used in the numerical computation, these effects, encoded in the isotensor axial polarisability, are found to be of similar magnitude to the nuclear modification of the single axial current, which phenomenologically is the quenching of the axial charge used in nuclear many-body calculations. This finding suggests that nuclear models for neutrinoful and neutrinoless double-$\beta$ decays should incorporate this previously neglected contribution if they are to provide reliable guidance for next-generation neutrinoless double-$\beta$ decay searches. The prospects of constraining the isotensor axial polarisabilities of nuclei using lattice QCD input into nuclear many-body calculations are discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Nanosecond Freezing of Water at High Pressures: Nucleation and Growth near the Metastability Limit

The fundamental study of phase transition kinetics has motivated experimental methods toward achieving the largest degree of undercooling possible, more recently culminating in the technique of rapid, quasi-isentropic compression. This approach has been demonstrated to freeze water into the high-pressure ice VII phase on nanosecond timescales, with some experiments undergoing heterogeneous nucleation while others, in apparent contradiction, suggest a homogeneous nucleation mode. We show through a combination of theory, simulation, and analysis of experiments that these seemingly contradictory results are in agreement when viewed from the perspective of classical nucleation theory. We find that, perhaps surprisingly, classical nucleation theory is capable of accurately predicting the solidification kinetics of ice VII formation under an extremely high driving force ( | Δ μ / k B T | ≈ 1 ) but only if amended by two important considerations: (i) transient nucleation and (ii) separate liquid and solid temperatures. Finally, this is the first demonstration of a model that is able to reproduce the experimentally observed rapid freezing kinetics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Breaking the curse of dimensionality: Solving configurational integrals for crystalline solids by tensor networks

Accurately evaluating configurational integrals for dense solids remains a central and difficult challenge in the statistical mechanics of condensed systems. Here, we present a tensor network approach that reformulates the high-dimensional configurational integral for identical-particle crystals into a sequence of computationally efficient summations. We represent the integrand as a high-dimensional tensor and apply tensor-train (TT) decomposition together with a custom TT-cross interpolation. This approach circumvents the need to explicitly construct the full tensor. We introduce tailored rank-1 and rank-2 schemes optimized for sharply peaked Boltzmann probability densities, typical for identical-particle crystals. When applied to the calculation of internal energy and pressure-temperature curves for crystalline Cu and Ar at high (GPa) pressures, as well as the alpha-to-beta phase transition diagram of Sn, our method accurately reproduces molecular dynamics simulation results using tight-binding, machine learning, hierarchical interacting particle–neural network, and modified embedded atom method potentials,all within seconds of computation time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗