Optics
Topologically enhanced optical helicity density in the thermal near field of twisted bilayer van der Waals materials
Xiaohong Zhang, Chiyu Yang, Wenshan Cai et al. (+1 more)
Twisted van der Waals (vdW)
bilayers can support tunable surface/
hyperbolic phonon polariton (S/HPhP) depending on the interlayer twist angle. S/HPhPs can be thermally excited and significantly modify the thermal near field. A photonic topological phase transition occurs at a critical twist angle where the polariton dispersion switches from
hyperbolic to elliptical. Because the twist angle governs the polariton modes, it is intrinsically linked to the optical helicity density (OHD) of the near-field thermal emission. In this work, a relationship between the OHD of near-field emission and the twist angle of
bilayer twisted vdW materials is discovered and investigated. To evaluate the OHD, a 3$\times$3 coherence
matrix method is obtained from the fluctuation-dissipation
theorem (FDT), which provides a complete description of the thermal electromagnetic field of the twisted
bilayer, and a formalism for OHD based on the polarization
matrix is employed. The topological transition angle (TTA) is determined by calculating the polariton dispersion relation of the vdW
bilayer at different twist angles. A strong correlation between OHD and TTA is observed, which can be attributed to polariton canalization and confined group velocity, leading to enhanced polariton directionality. This study provides new insights into the analysis of angular momentum in near-field thermal radiation from twisted vdW structures.
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All authors Xiaohong Zhang, Chiyu Yang, Wenshan Cai, Zhuomin M. Zhang
Chemical Physics · Cross-listed from quant-ph
Parallel iQCC Enables 200 Qubit Scale Quantum Chemistry on Accelerated Computing Platforms Surpassing Classical Benchmarks in Ruthenium Catalysts
Seyyed Mehdi Hosseini Jenab, Brandon Henderson and Scott N. Genin
We introduce a parallel, GPU-accelerated implementation of the iterative
qubit coupled cluster (iQCC) method that overcomes the exponential growth of the transformed
Hamiltonian – the principal bottleneck for classical emulation of
quantum chemistry
circuits. By distributing
Hamiltonian terms across compute nodes via bit-wise partitioning and offloading Pauli contractions to GPUs, we achieve speedups exceeding two orders of magnitude over the serial CPU approach. Crucially, iQCC confines the variational
evolution to a classically simulable operator subspace by selecting entanglers exclusively from the Direct Interaction Space, which guarantees non-vanishing energy gradients at every iteration and thereby naturally avoids the barren-plateau phenomenon that renders highly expressive
quantum circuits untrainable. Leveraging these algorithmic and hardware advances, we simulate electronic-structure
Hamiltonians for industrially relevant ruthenium catalysts in the 100–124
qubit regime, completing full ground-state calculations on NVIDIA GPUs in the ranges of 1.2 - 45 hrs and surpassing the accuracy of Density
Matrix Renormalization Group. These results effectively de-quantize a significant portion of the NISQ roadmap:
quantum advantage for chemistry is often assumed to emerge beyond ${\sim}50$
qubits, yet our work demonstrates that this frontier lies significantly further – potentially past 200
qubits – reshaping expectations for where genuine
quantum advantage may first appear.
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Fluid Dynamics
Improving boundary-layer separation prediction by an IDDES turbulence model using a pressure-gradient sensor
Benjamin S. Savino, Kevin Patrick Griffin, Bumseok Lee et al. (+3 more)
This work extends a pressure-gradient sensor for boundary-layer separation originally developed for the $k-\omega$ shear-stress transport Reynolds-averaged Navier-Stokes (RANS) model (Griffin et al., 2025, J. Turb.) to the Improved Delayed Detached Eddy Simulation (IDDES)
turbulence model of Gritskevich et al. (2012, Flow Turbul. Combust.). The pressure-gradient sensor identifies local regions of strong adverse pressure-gradient where the eddy-viscosity is reduced, as in the original RANS model. Additionally, to promote separation in the IDDES model, the elevation term in the IDDES length scale, designed to augment the RANS-mode Reynolds stress in attached flow regions, is turned off where the pressure-gradient sensor is active. The model is applied on various airfoils representative of both wind energy and aerospace applications, and is used in fully turbulent and transitional IDDES model variants. The proposed model improves the prediction of stall onset and post-stall regimes relative to the baseline IDDES model without significant degradation of attached-flow regimes relative to state-of-the-art RANS models or deep-stall regimes relative to state-of-the-art IDDES models. Significant overall improvements are observed in predictions of lift and drag polars across 90 degrees of angle of attack, yielding a unified model able to predict various (two- and three-dimensional) flow regimes. Shortcomings are identified to be related to the underlying RANS pressure-gradient sensor rather than the extension of the sensor to the IDDES model, which is the focus of this work.
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All authors Benjamin S. Savino, Kevin Patrick Griffin, Bumseok Lee, Ganesh Vijayakumar, Wen Wu, Michael A. Sprague
Optics · Cross-listed from quant-ph
Quantum Sensing of Birefringence Beyond the Classical Limit with a Hyper-Squeezed SU(1,1) Interferometer
Samata Gokhale, Netanel P. Yaish, Michal Natan et al. (+3 more)
Quantum interferometric sensing plays a crucial role in a wide range of applications, including
quantum metrology,
quantum imaging, and
quantum lithography, where minute phase shifts carry valuable physical information. The strength of
quantum sensing lies in surpassing classical sensitivity limits, particularly through the use of
quantum correlations and squeezing to suppress optical shot noise. Birefringence sensing is crucial for various applications, as it provides detailed information about the material's structure, stress, composition, and environmental conditions. We present an interferometric scheme for detecting unknown small birefringence beyond the shot-noise limit of sensitivity that leverages the hyper-squeezing (squeezed in both number-phase and polarization correlations) within a pair of polarized nonlinear SU(1,1) interferometers, coupled by the birefringence. Specifically, two pairs of crossed-polarization nonlinear media, both generate and measure two-mode
quantum light that is squeezed and polarization-entangled. We present a complete theoretical analysis of the interferometer's sensitivity to small birefringence under realistic conditions of gain and internal loss, illuminating the potential for enhancement of the sensitivity by 3-15dB in practical, real-world experiments (the exact achievable enhancement is governed solely by the loss).
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All authors Samata Gokhale, Netanel P. Yaish, Michal Natan, Saar Levin, Yogesh Dandekar, Avi Pe'er
Atomic Physics · Cross-listed from hep-ph
The ultrafine splitting of heavy quarkonium with next-to-next-to-next-to-next-to-leading-order accuracy
Jose M. Escario, Andreas Maier, Clara Peset et al. (+1 more)
We compute the hyperfine splitting of P-wave heavy quarkonium states with next-to-next-to-next-to-next-to-leading-order accuracy. The resummation of logarithms with next-to-next-to-next-to-next-to-leading-logarithmic accuracy is also addressed. A phenomenological analysis of these results is performed for bottomonium, charmonium and the $B_c$ system. We also apply these results to positronium, muonium, hydrogen and muonic hydrogen.
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All authors Jose M. Escario, Andreas Maier, Clara Peset, Antonio Pineda
Atomic Physics · Cross-listed from cond-mat.quant-gas
Analog Simulation of Massive Relativistic Quantum Fields in 2 + 1 Dimensions
Yansheng Zhang, Feiyang Wang, Paul H. C. Wong et al. (+8 more)
Quantum field theories provide fundamental models of complex interacting systems, from high-energy physics and cosmology to condensed matter. However, solving these models in non-perturbative and dynamical regimes is often challenging, particularly in more than one spatial dimension. Analog simulation using tunable synthetic
quantum systems can both verify existing theoretical predictions and lead to new physical insights. Here, we realize analog simulation of massive relativistic
quantum fields in $2+1$ dimensions (two spatial dimensions and time), using two coherently coupled
spin components in a uniform two-dimensional atomic Bose–Einstein condensate. Specifically, we encode the paradigmatic sine-Gordon model in the long-wavelength modes of the field describing the relative phase, $\phi$, of the two components. In the perturbative regime, collective field excitations exhibit a relativistic dispersion with a tunable mass gap. We also observe explicitly non-perturbative phenomena, including the existence of topological domain walls across which $\phi$ rapidly winds by $2\pi$. Our work opens possibilities for studies of cosmologically relevant phenomena including preheating, dynamics of topological defects, and relativistic false-
vacuum decay.
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All authors Yansheng Zhang, Feiyang Wang, Paul H. C. Wong, Alexander C. Jenkins, Yi Jiang, Konstantinos Konstantinou, Gehrig Carlse, Nishant Dogra, Joseph H. Thywissen, Christoph Eigen, Zoran Hadzibabic
Medical Physics
Feasibility of Concurrent 1H MRS & 31P MRSI at 7T: Brain Energy Metabolism Responses to Hyperglycemia
Mark Widmaier, Brooke C. Matson, Uzay Emir et al. (+1 more)
How the human
brain adjusts fuel handling and its bioenergetic state during changing glucose levels remains difficult to assess noninvasively. In this study, we established an interleaved multinuclear 7 T MR spectroscopy protocol to track a glucose-related 1H signal alongside 31P measures of high-energy phosphate metabolism during a hyperglycemic clamp. Five healthy adults completed a morning, fasted infusion experiment consisting of baseline, ramp-up, and hyperglycemic stages over approx. 120 min. Short-block, short-TE 1H single-voxel spectroscopy (STEAM, TE = 11 ms; mean block duration 5.71 (SD:0.62 min)) was acquired in frontal cortex and quantified using the composite Glucose+Taurine (Glc+Tau) measure. 31P was acquired with rapid 3D PETALUTE MRSI using an ultrashort echo time (UTE; TE = 65 micros; 381 s per block), and high-energy phosphate ratios were derived from a posterior cortical region of interest. Across participants, 1H Glc+Tau increased with blood glucose and showed significant elevations from baseline into hyperglycemia. In parallel, 31P ratios exhibited smaller but significant glycemia-linked responses: both PCr/Pi and gamma-ATP/Pi increased with blood glucose and differed across glucose clamp stages. These findings show that 1H and 31P MRS(I) can be interleaved at 7 T to measure energy metabolism within a single session
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All authors Mark Widmaier, Brooke C. Matson, Uzay Emir, Janice J. Hwang
Fluid Dynamics
Experimental Challenges in Determining Heat Transfer Efficiency Scaling in Highly Turbulent Cryogenic Rayleigh-Benard Convection
P. Urban, V. Musilova, P. Hanzelka et al. (+3 more)
Cryogenic Rayleigh-Benard convection (RBC) at very high Rayleigh numbers (Ra) serves as a key system for understanding buoyancy-driven industrial and large scale natural flows and for testing theories of turbulent convective heat transport. Cryogenic helium experiments allow one to reach extremely high Ra under well-controlled laboratory conditions; however, interpretation of the resulting heat-transfer scalings remains sensitive to non-Oberbeck-Boussinesq (NOB) effects, experimental uncertainties, as well as a number of corrections that ought to be applied to raw data, including corrections for the adiabatic temperature gradient, parasitic heat leaks, or finite thermal conductivity of plates and sidewalls of RBC
cells. We present an analysis of experimental uncertainties and data corrections procedures applicable to cryogenic RBC experiments, specifically to those performed in cylindrical RBC
cells in Brno: measurement uncertainties, parasitic effects, choice of 4He working points in the p-T diagram and evaluation of relevant properties of the particular working fluid in connection with the available thermophysical property databases. In particular, our study highlights the necessity of rigorous uncertainty analysis for assessing experimental evidence suggesting either transition to the ultimate regime of RBC due to intrinsic ultimate-regime dynamics or as a manifestation of NOB effects and experimental imperfections.
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All authors P. Urban, V. Musilova, P. Hanzelka, T. Kralik, M. Macek, L. Skrbek
Computational Physics · Cross-listed from astro-ph.IM
unxt: A Python package for unit-aware computing with JAX
Nathaniel Starkman, Adrian Price-Whelan and Jake Nibauer
unxt is a Python package for unit-aware computing with JAX. unxt is built on top of quax, which provides a framework for building array-like objects that can be used with JAX. unxt extends quax to provide support for unit-aware computing using the astropy.units package as a units backend. unxt provides seamless integration of physical units into high performance numerical computations, significantly enhancing the capabilities of JAX for scientific applications.
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Atomic Physics · Cross-listed from cond-mat.quant-gas
Fermi-pressure-assisted superradiant transition with a mesoscopic Fermi gas in a cavity
Francesca Orsi, Ekaterina Fedotova, Rohit Prasad Bhatt et al. (+3 more)
We study the superradiant phase transition of a mesoscopic
Fermi gas comprising between a few tens and a few thousand $^6$Li atoms in a high-finesse cavity across a wide range of densities. We observe a non-monotonic variation of the superradiant threshold as a function of density, with a minimum reached when the
Fermi and
recoil wavevectors are comparable. The minimum corresponds to a crossover between
Fermi pressure-assisted ordering and Pauli blocking of
photon scattering, in good agreement with theory. This interpretation is confirmed by a study of the atom-number dependence of the ordering threshold and
photon number scaling. Our system opens the perspective of studying few-
fermion systems with strong and coherent light-matter coupling.
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All authors Francesca Orsi, Ekaterina Fedotova, Rohit Prasad Bhatt, Mae Eichenberger, Léa Dubois, Jean-Philippe Brantut
Applied Physics · Cross-listed from cond-mat.mes-hall
Nonlinear Mode Coupling in Silicon Nitride Membrane Resonators
Soumya Kanti Das, Nishta Arora, Hridhay A S et al. (+2 more)
Nonlinear interactions between vibrational modes play a crucial role in understanding the dynamical response of nanomechanical resonators. Here, we report the experimental observation and theoretical modeling of nonlinear mode coupling in a high-stress square silicon nitride membrane resonator. We quantify frequency shifts of the fundamental mode arising from tension-mediated
geometric nonlinearity by increasing the amplitude of the fundamental mode and higher-order flexural modes. A quantitative theoretical framework based on Kirchhoff-Love plate theory is developed, which incorporates both intrinsic Duffing nonlinearity and nonlinear intermodal coupling and shows good agreement with experimental measurements for the (1,1)-(2,1) and (1,1)-(2,2) mode pairs. We further compute the nonlinear coupling
matrix across mode families, revealing the role of mode
symmetry and spatial overlap in governing intermodal interactions. These results establish nonlinear mode coupling as a controllable resource for multimode frequency tuning and mechanical transduction.
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All authors Soumya Kanti Das, Nishta Arora, Hridhay A S, Akshay Naik, Chandan Samanta
Atomic Physics
Electromagnetically induced transparency and population repump readout of Rydberg states of Cs atoms in a J-scheme
Noah Schlossberger, Christopher L. Holloway, Erik McKee et al. (+2 more)
Rydberg atom electrometry offers traceable electric field measurements over many decades of
radio frequencies in a single device. Miniaturization of these sensors is primarily limited by requirements of the
lasers used. Here we demonstrate a three-
photon sensing scheme using a J-shaped energy level coupling that can be achieved using external cavity diode
lasers, without the need for a doubling
crystal or tapered amplifier. In the low
laser power regime, we demonstrate a full-width at half-maximum linewidth of 1.3 MHz. We demonstrate that for RF field electrometry using conventional heterodyne techniques, we can detect 4.7 GHz at a sensitivity of 27 {\mu}V m-1 Hz-1/2, comparable to that of two-
photon detection schemes which require the use of a tapered amplifier. We also investigate a modified scheme where the probe
laser is locked to a different hyperfine state, thus measuring the two-
photon electromagnetically induced transparency in the other two
lasers via the change in population of this separate state due to repumping. In this scheme we find the sensitivity for a 4.7 GHz field to be 39 {\mu}V m-1 Hz-1/2, and demonstrate that the amplitude scaling with probe power offers a different saturation profile than the linked J-scheme counterpart.
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All authors Noah Schlossberger, Christopher L. Holloway, Erik McKee, Michael A. Highman, Nikunjkumar Prajapati1
Computational Physics
NATPS: Nonadiabatic Transition Path Sampling Using Time-Reversible MASH Dynamics
Xiran Yang, Madlen Maria Reiner, Brigitta Bachmair et al. (+3 more)
Rare nonadiabatic events play a central role in photochemistry but remain difficult to simulate because excited-state dynamics is computationally demanding and often
stochastic. Here we introduce a deterministic and time-reversible implementation of nonadiabatic dynamics that enables the application of transition path sampling (TPS) to excited-state processes. Our approach builds on the Mapping Approach to Surface Hopping (MASH) and establishes the conditions required for path ensemble sampling, in particular time reversibility and detailed balance. Combining this dynamics with the TPS framework yields a new method, termed nonadiabatic transition path sampling (NATPS). Using a model system of electronically coupled potential energy surfaces, we demonstrate that NATPS efficiently generates ensembles of reactive trajectories and provides mechanistic insight into nonadiabatic pathways. Compared with brute-force trajectory simulations and forward-flux sampling approaches, NATPS substantially reduces the computational effort required to obtain reactive trajectories.
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All authors Xiran Yang, Madlen Maria Reiner, Brigitta Bachmair, Leticia González, Johannes C. B. Dietschreit, Christoph Dellago
Optics
Low Reflectance All-Glass Metasurface Lenses Based on Laser Self-generated Nanoparticles
Jae Hyuck Yoo, Nathan J. Ray, Mike A. Johnson et al. (+2 more)
Optical metasurfaces, comprised of subwavelength nanostructures, hold a great promise to high-power
laser optics but also a limited pertinence due to their currently limited aperture size, throughput and durability. Here, an alternative approach is presented, reliant on
laser-controlled self-organizing mask formation followed by ion etching which results in an all-fused-silica-glass metasurface. Two 1 mm diameter optical elements (an axicon lens and a shadower) are fabricated and their optical performance is validated at 532 nm wavelength with an extremely low broadband reflection (<0.15%) - a result of the unique metasurface elements shape. The self-organizing working principle enables producing large amounts of nano-elements at-once, thus a path for aperture scaleup. It also enables generation of sub-100 nm nanoelements, thus a path to short wavelengths operation. Two key advancements towards viability are presented: a
laser scan with in-situ transmission feedback enables patterning the etching mask to a prescribed nanoparticle distribution, and a crafted beyond-mask-erosion-point etching of the mask enables increasing the metasurface phase difference to at least pi, while keeping extremely low reflection across it. This paves a path to high-power
lasers optics, requiring large aperture, high throughput and
laser light durability.
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All authors Jae Hyuck Yoo, Nathan J. Ray, Mike A. Johnson, Hoang T. Nguyen, Eyal Feigenbaum
Plasma Physics
3D Dynamics of a Premagnetized Gas-puff Z-pinch implosion
P. Phillips, M. Escalona, P. Retamales et al. (+3 more)
We present the first simultaneous, spatially-resolved measurement of all three velocity components (radial, azimuthal, and axial) in an annular magnetized argon gas-puff Z-pinch, performed using Collective Thomson Scattering along three orthogonal lines of sight from the same scattering volume at each time step. Measurements were carried out on the Llampüdkeñ pulse-power generator (400 kA peak, 200 ns rise time), for applied axial fields ranging from 0.04 to 0.26 T using two coil configurations: a double coil with negligible initial radial field at the probed plane ($z = 8$ mm), and a single coil that imposes a finite initial radial field. Three principal results are reported. First, the axial velocity component, which had not previously been measured experimentally in this configuration, reaches 60–70~km\,s$^{-1}$ near the axis at low applied fields ($B_{z0} < 0.1$ T) and is suppressed to within $\pm 20$~km\,s$^{-1}$ for stronger applied fields, in correlation with the reduction of the zippering angle, with direct implications for the implosion energy balance. Second, the self-generated rotation extends across the full
plasma diameter, not only at the periphery, and the diametrical profile of the azimuthal velocity decreases toward the axis with an exponential-like shape consistent with the underlying current density distribution; this feature was not visible in previous edge-localized measurements. Third, rotation persists in the double-coil case ($B_{r0} \approx 0$) and is enhanced in the single-coil case (finite $B_{r0}$), supporting the interpretation that $B_r$ develops self-consistently during the implosion and drives the rotation through a $J_z \times B_r$ torque. These results constrain the role of each
magnetic-field component and motivate direct measurement of $B_r$ and the current density distribution as the next step.
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All authors P. Phillips, M. Escalona, P. Retamales, M. Ribeiro, F. Veloso, J. C. Valenzuela
Optics
Experimental investigation of Lévy flights for step-length distributions with a length-dependent local power exponent
Isaac C. Nunes, Jesús P. López and Thierry Passerat de Silans
We experimentally investigate the transmission of light by dense atomic vapor. The light propagating in dense atomic vapor can be modeled as a Lévy flight random walk. For such system, the step-length distribution can be modeled as $P(\ell)\sim \ell^{-1-\alpha(\ell)}$, with the Lévy index $\alpha(\ell)$ varying smoothly with the step length. Moreover, the walkers alternate between two distinct distributions depending on the occurrence of collisions between atoms in the light scattering. We obtain the Lévy index from transmission measurements for different system sizes and atomic densities. The measured Lévy index is determined by the system size $\alpha=\alpha(\ell=L)$. Simulations are made for walkers alternating between two Lévy like step-length
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Atomic Physics · Cross-listed from astro-ph.GA
An Alternate Pathway for H$_2$ Formation in the Early Universe: A physical process to account for the presence and coevolution of the luminous galaxies and supermassive black holes at the high redshifts
Amrendra Pandey, Olivier Dulieu and Nadia Bouloufa-Maafa
Molecular hydrogen (H$_2$) and hydrogen deuteride (HD) are key coolants in
primordial gas and regulate the formation of the first
stars and proto-
galaxies. Recent results from the James Webb Space
Telescope provide striking insights into
galaxies detected at high
redshifts, which are found to be significantly more abundant and luminous than expected from
galaxy formation models, thus suggesting a gap in our understanding of the early Universe. Standard pathways for H$_2$ formation in the early Universe proceed through the H$^-$ and H$_2^+$ intermediates, both of which are strongly suppressed at high
redshift by the
cosmic microwave background. We propose an additional pathway for H2 and HD formation that could be active as early as the end of the epoch of recombination and could enable the formation of the first
stars earlier than the current prediction at
redshift z ~ 30 - 20. The proposed pathway relies on the manifestation of Jahn-Teller dynamical coupling between electronic states of H$_3^+$. This coupling induces transient three-body recombination in H$^+$, H and H, and charge exchange within the charged atom-dimer complex that directly creates ground-state H$_2$ (and HD), bypassing the fragile intermediates that limit the standard
primordial pathways. Our analysis shows that this mechanism could occur under the thermodynamic conditions of the post-recombination epoch, also suggesting that it might be playing a role in the active
galactic nuclei feedback processes, regulating the formation rates of the first
stars and the
accretion rates of the first black holes. Though the global impact on
galaxy formation and black-hole growth is not yet determined and will require quantitative assessment in future modeling, the mechanism offers an additional chemical route for H$_2$ and HD formation, with substantial cosmological relevance for
primordial chemistry and early structure formation.
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Chemical Physics · Cross-listed from quant-ph
Symmetry-based perturbation theory for electronic structure calculations
Hiromichi Nishimura, Nam Nguyen, Tanvi Gujarati et al. (+1 more)
We develop a multi-reference perturbation theory for electronic structure calculations based on
symmetries of the
Hamiltonian. The reference
Hamiltonian in the
symmetry-based perturbation theory (SBPT) is chosen such that it possesses more
symmetries than the original
Hamiltonian, leading to a larger reduction of computational resources in terms of both the number of configurations in the configuration interaction expansion and the number of required
qubits in
quantum computing applications. We provide approximate, scalable solutions for the second-order correction, as well as an application to selected configuration interaction. We show that SBPT is an extension of other existing multi-reference perturbation theories and that it can give better results for some molecular systems in a robust way.
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All authors Hiromichi Nishimura, Nam Nguyen, Tanvi Gujarati, Mario Motta
Computational Physics · Cross-listed from cs.LG
Integral Formulas for Vector Signal Tensor Products
Valentin Heyraud, Zachary Weller-Davies and Jules Tilly
We derive integral formulas that simplify the Vector Signal Tensor Product recently introduced by Xie et al., which generalizes the Gaunt tensor product to anti-symmetric couplings. In particular, we obtain explicit closed-form expressions for the anti-symmetric analogues of the Gaunt coefficients. This enables us to simulate the Clebsch-Gordan tensor product using a single Vector Signal Tensor Product, yielding up to a $9\times$ reduction in the required tensor product evaluations. Our results enable efficient and practical implementations of the Vector Signal Tensor Product, paving the way for applications of this generalization of Gaunt Tensor Products in $\mathrm{SO}(3)$-equivariant neural networks. Moreover, we discuss how the Gaunt and the Vector Signal Tensor Products allow to control the expressivity-runtime tradeoff associated with the usual Clebsch-Gordan Tensor Products. Finally, we investigate low rank decompositions of the normalizations of the considered tensor products in view of their use in equivariant neural networks.
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Chemical Physics
Improved SABRE hyperpolarisation using pulse sequences to reduce effective coupling
Vitaly P. Kozinenko, Bogdan A. Rodin, James Eills et al. (+3 more)
Hyperpolarisation using Signal Amplification By Reversible Exchange (SABRE) is a convenient method for high repeatability studies. The core of this technique is polarisation transfer to the target substrate during an on-going chemical exchange process. Typically, polarisation transfer is achieved as fast as possible. In this study we employ NMR sequences that on contrary slow down the polarisation transfer and yet demonstrate improved performance. Simulations confirm that such methods can lead to high polarisation yield in SABRE system that exhibit higher
magnetic inequivalence and lower chemical exchange rate.
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All authors Vitaly P. Kozinenko, Bogdan A. Rodin, James Eills, Ilai Schwartz, Stephan Knecht, Laurynas Dagys
Geophysics
The direct spectral element method for the calculation of synthetic seismograms in self-gravitating, spherically symmetric planets
Alex D.C. Myhill and David Al-Attar
This paper describes the implementation of the direct solution method (DSM) using radial spectral elements for the calculation of synthetic seismograms in self-gravitating, spherically symmetric, non-rotating, anelastic, and transversely isotropic Earth models. In contrast to previous implementations of the DSM that used a potential formulation within fluid regions, we use a displacement formulation throughout. It is this feature that allows us to extend the DSM to account fully for self-gravitation along with arbitrary fluid stratification. Our code, $\texttt{DSpecM1D}$, is benchmarked against the normal mode summation code $\texttt{MINEOS}$ as well as the direct radial integration code $\texttt{YSpec}$. Agreement between the codes is excellent for both elastic and anelastic models.
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Optics
Heterogeneously Integrated Diamond-on-Lithium Niobate Quantum Photonic Platform
Sophie W. Ding, Chang Jin, Zixi Li et al. (+9 more)
Diamond photonics has enabled efficient interfaces for
quantum memories and is predicted to be a critical component of
quantum networks. However, scalable network architectures require spatial, temporal, and spectral control of
photons, which relies on nonlinear and electro-optic functionalities that diamond alone cannot provide. Here, we demonstrate heterogeneous integration of a thin-film lithium niobate (TFLN) platform, which has strong chi-2 nonlinearity and electro-optic effects, with thin diamond films. We demonstrate high-Q diamond photonic
crystal cavities (Q factors exceeding 5x10^4 at 735 nm) that are lithographically aligned with TFLN photonic backbone and critically coupled to it. This allows us to realize low-loss diamond-TFLN "escalators" (loss ~1 dB/coupler) that support efficient light transfer between them. At cryogenic temperatures (5K), we can collect
photons emitted from silicon vacancies (SiVs) embedded within the diamond structure via the TFLN photonic
circuit. This approach establishes a scalable route toward integrated photonic
circuits for practical
quantum networking and other technologies.
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All authors Sophie W. Ding, Chang Jin, Zixi Li, Nicholas Achuthan, Kazuhiro Kuruma, Xinghan Guo, Brandon Grinkemeyer, David D. Awschalom, Nazar Delegan, F. Joseph Heremans, Alexander A. High, Marko Loncar
Atomic Physics
Accurate Vector Magnetometer via Zeeman Rabi Oscillations
Thanmay S. Menon, Dawson P. Hewatt, Christopher Kiehl et al. (+3 more)
Accurate
magnetic field direction sensing in compact platforms is critical in applications spanning
magnetic navigation, space science, and biomedical imaging. We demonstrate a single-optical-axis vector optically pumped magnetometer based on Rabi oscillations between Zeeman sublevels driven by a series of resonant radiofrequency (RF) polarization ellipses (PEs). A calibration protocol based on controlled rotations of the DC
magnetic field determines the spatial orientation of each PE. We develop a detailed theoretical model describing the angular dependence of the Rabi frequencies, incorporating key systematics including RF Stark shifts and Bloch-Siegert shifts. We also account for an RF-based heading-error systematic affecting Rabi-frequency measurements arising from the nonlinear Zeeman effect. Simultaneous Larmor measurements yield the magnitude of the
magnetic field, enabling integrated vector-scalar measurements. The magnetometer achieves deadzone-free vector operation with 80 $\mu$rad mean angular accuracy and angular noise densities as low as 8 $\mu$rad$/\sqrt{\mathrm{Hz}}$, offering a pathway towards miniaturized sensors without requiring 3D optical access or sensor rotations.
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All authors Thanmay S. Menon, Dawson P. Hewatt, Christopher Kiehl, Michaela Ellmeier, Svenja Knappe, Cindy A. Regal
Fluid Dynamics
Glassy phase transition in immiscible steady-state two-phase flow in porous media
Santanu Sinha, Humberto Carmona, José S. Andrade Jr. et al. (+1 more)
Two-phase flow in porous media is a ubiquitous phenomenon that has been studied for well over a century. However, we still lack a successful theory that predicts flow on a macroscopic length scale (the so-called Darcy scale) on the basis of a "microscopic" model. Here we show that the characteristic features of two-phase flow on the Darcy scale can be predicted by mapping the distribution of droplets in 2-phase flow onto the distribution of
spins in a
spin-glass model. The success of this approach is surprising, as two-phase flow is a non-
equilibrium phenomenon, whereas the properties of the
spin glass are obtained using
equilibrium statistical mechanics. To obtain this mapping, we follow the approach of Meshulam and Bialek (Rev. Mod. Phys. 97, 045002 (2025)) and use the Jaynes maximum
entropy principle to derive the
spin-glass
Hamiltonian using machine learning trained on many realizations of the two-phase flow pattern in a dynamic pore network model. With this mapping, we can construct a "phase diagram" for the 2-phase flow system. We find that the critical line separating the paramagnetic phase from a
spin glass phase coincides with the transition where the dependence of the rate of two-phase flow on the imposed pressure gradient changes from linear to non-linear. The glassy phase of the
spin model coincides with a flow regime characterized by hysteresis and strong fluctuations over a wide range of time scales. It is tempting to identify this flow regime as a dynamic glass state.
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All authors Santanu Sinha, Humberto Carmona, José S. Andrade Jr., Alex Hansen
Atmospheric and Oceanic Physics
Emergence of an Advective Boundary Layer in Monsoon Cross-Equatorial Flow: Scaling, Dynamics, and Idealized Models
Rajat Masiwal, Ashwin K Seshadri and Vishal Dixit
The conventional Ekman model of the tropical boundary layer neglects nonlinear momentum advection and breaks down near the equator, where Coriolis effects are weak. During South Asian monsoon onset, we identify a dynamical regime transition to an advective boundary layer (ABL). Reanalysis links this transition to a shift in the zonal momentum balance from frictional to meridional-advection control as cross-equatorial flow intensifies, accompanied by increasing local Rossby number and vanishing absolute vorticity, signaling the breakdown of Ekman balance. A scaling analysis shows that this transition occurs when the meridional length scales of geopotential and zonal wind contract such that their product approaches $\phi/f^2$. In the resulting ABL regime, kinetic energy is governed by a balance between its generation and advection, yielding a linear diagnostic relation between meridional geopotential gradient and meridional wind. A simple theoretical model predicts that the sensitivity of this relation is controlled by an advective timescale that equals the inertial timescale ($1/f$) at the transition latitude, where zonal and meridional wind speeds become comparable. Testing this framework in idealized aquaplanet experiments confirms that stronger cross-equatorial pressure gradients and slower planetary rotation rates amplify advective effects and shift the transition latitude poleward. Across experiments, the sensitivity of meridional winds to the geopotential gradient remains tightly linked to $1/f$ at the transition latitude. Together, these results establish the ABL as a distinct dynamical regime, with important implications for monsoon onset, intraseasonal variability, and the representation of tropical boundary layer processes in
climate models.
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Optics
Recent advances in spatial light modulator-based three-dimensional optical imaging (Invited)
Joseph Rosen
Phase-only spatial light modulators (SLMs) are used in optical systems for several purposes. In this article, the main landmarks of SLM-based imaging systems are surveyed. In addition to conventional two-dimensional imaging, these systems are useful for multidimensional imaging, axial sectioning, field-of-view expansion, improved image resolution, imaging through scatterers, and depth-of-field control. The SLMs in this review are positioned in the system aperture and modulate the input light in various ways to achieve different imaging goals. This review begins with the nearly 20-year-old Fresnel incoherent correlation holography system, continues with coded-aperture holography, and progresses to the most recent versions of interferenceless coded-aperture holography systems.
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Plasma Physics
Spatiotemporal Properties of Compressible Magnetohydrodynamic Turbulence from Space Plasma
Siqi Zhao, Huirong Yan, Terry Z. Liu et al. (+2 more)
Previous studies have established that a weak-to-strong transition occurs in Alfvenic magnetohydrodynamic (MHD)
turbulence as energy cascades from large to small scales. However, the spatiotemporal (frequency-wavenumber) properties of compressible MHD
turbulence involving all eigenmodes, which encode the strength of nonlinear interactions, remain difficult to characterize observationally. Consequently, whether a similar weak-to-strong transition occurs in compressible
turbulence remains elusive. Using a novel multi-spacecraft, polarization-based mode-decomposition technique with measurements from the Cluster spacecraft in Earth's magnetosheath, we obtain spatiotemporal power spectra of all MHD eigenmodes and present the first quantitative assessment of nonlinear frequency broadening. Our results show that slow modes exhibit a weak-to-strong transition, evolving from wave-like peaks to frequency-broadened spectra as nonlinearity increases, whereas fast modes remain weakly turbulent with narrow peaks near their eigenfrequencies. Both Alfvenic and compressible fluctuations contribute significantly to low-frequency, large-scale quasi-two-dimensional structures. These findings provide a comprehensive observational characterization of compressible
turbulence across mode composition, spatiotemporal scales, and weak-strong
turbulence regimes, with implications for energetic particle transport, turbulent dynamos,
plasma heating, and
solar wind-magnetosphere coupling.
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All authors Siqi Zhao, Huirong Yan, Terry Z. Liu, Chuanpeng Hou, Ka Ho Yuen
Fluid Dynamics · Cross-listed from astro-ph.SR
Nonlinear evolution of unstable solar inertial modes: The case of viscous modes on a differentially rotating sphere
Muneeb Mushtaq, Damien Fournier, Rama Ayoub et al. (+2 more)
On the Sun, the inertial mode with the largest observed amplitude (rms velocity exceeding $10$ m/s) is the high-latitude mode with longitudinal wavenumber $m=1$. In two dimensions, on the sphere, linear theory predicts that this mode is unstable due to a shear instability associated with latitudinal differential rotation (fast equator, slower polar regions). We investigate the
evolution of this instability numerically and theoretically. The nonlinear vorticity equation is solved using direct numerical simulations in the time domain. The only control parameter is the Ekman number $E$. For $10^{-3}\lesssim E< E_c \approx 1.5\times10^{-3}$, only the high-latitude $m=1$ mode is unstable. We extract its saturation amplitude as a function of $E$ and compare the results with predictions from two perturbative approaches in nonlinear stability theory. The simulations reveal a supercritical
Hopf bifurcation. Near onset, the mode amplitude is well described by the Landau equation $d|A|/dt=\sigma_I |A|+\beta_I |A|^3$, with a positive linear growth rate $\sigma_I$ and a negative nonlinear coefficient $\beta_I$. The coefficient $\beta_I$ depends weakly on $E$, implying that the saturated amplitude scales approximately as $|A|\propto\sigma_I^{1/2}$. The
equilibrium mode contains the $m=1$ fundamental and harmonics $m=2$ and $m=3$, whose amplitudes scale as $\sigma_I^{m/2}$. Saturation results from Reynolds stresses that smooth the latitudinal differential rotation. For $E=4\times10^{-4}$, consistent with
solar-like turbulent viscosity, the saturated velocity reaches $28$ m/s, comparable to
solar observations. These results should be interpreted cautiously, since in three dimensions the instability is baroclinic and involves different physics.
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All authors Muneeb Mushtaq, Damien Fournier, Rama Ayoub, Peter J. Schmid, Laurent Gizon
Atomic Physics
The robustness of composite pulses elucidated by classical mechanics. II. The role of initial state imperfection
Jonathan Berkheim and David J. Tannor
In
nuclear magnetic resonance (NMR), Composite Pulses (CPs) are widely used to correct for pulse imperfections, e.g., RF field inhomogeneity and resonance offset. Although robust pulse sequences have been developed throughout the years, the imperfection of the initial state has not been widely discussed in the literature as an additional systematic error. In previous work, we developed a classical canonical framework to perform stability analysis and used this as a measure of CP robustness. In that work, a single initial condition was allowed to evolve under various pulse imperfections. The current work extends this approach to $2D$ distributions of initial conditions on the Bloch Sphere; the objective is to minimize the area in order to preserve coherence, while maximizing population inversion of the entire distribution. As a case study, we investigate Levitt's $90(x)180(y)90(x)$ pulse sequence, when there is a spread in initial conditions. The canonical framework enables us to assess the robustness of Levitt's pulse sequence, and we find that it is maintained to a great extent even when considering a spread of initial conditions. Nevertheless, by conducting a numerical optimization, we have identified several variants of Levitt's pulse sequence that produce a larger coherent population inversion when there is a spread in initial conditions.
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General Physics
An implicit restriction in the Dirac quantization
Han Geurdes
A restriction was found in the mathematics of the Dirac equation for a free
neutrino type of particle. The basic assumption here is the equivalence of the four variables of spacetime. A perspective is defined as a metric tensor format. We asked what happens when we add a perspective where a time variable, $\sim ct$ unit [meter], becomes a space variable, unit [meter], and vice versa. A Lorentz invariant mixed metric tensor equation can be set up in an attempt to describe the
neutrino in the cross-hairs of two different perspectives. Despite the equivalence of variables, and despite the fact that no single perspective is likely to be preferred, we find that the
neutrino is "internally" changed in the cross-hairs of two different perspectives. Of course, if the two perspectives do not go together this conclusion collapses.
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