Quantum Physics
Trading Circuit Depth for Pulse Sparsity in Chromatic Dynamical Decoupling
Amy F. Brown and Daniel A. Lidar
Suppressing decoherence and crosstalk systematically across large networks of
qubits is a pressing concern as
qubit counts increase rapidly. General multi-
qubit dynamical decoupling (DD) has historically been based on Hadamard
matrices and orthogonal arrays, with instantaneous-pulse sequences whose
circuit depth scales linearly with the number of
qubits. Chromatic-Hadamard DD (CHaDD) improves upon these methods by properly coloring the hardware graph and assigning to each color a row of a Hadamard
matrix, resulting in a
circuit depth that scales linearly with the number of colors $C$, which can be as low as the chromatic number of the graph. Here, we explore the tradeoff between
circuit depth and the pulse repetition rate (PRR), the average fraction of time steps in which a
qubit is pulsed, i.e., a measure of pulse density. We introduce two single-axis sequences based on binary and Gray
matrices, Chromatic-Binary DD (CBDD) and Chromatic-Gray DD (CGDD), which, for $C>2$, are special cases of non-minimum-depth CHaDD and achieve PRR $<2/C$ and PRR $=1/C$, respectively, compared with a PRR above $1/4$ for CHaDD, at the price of a
circuit depth of $2^C$. In state preservation experiments on a $127$-
qubit IBM processor with $C=3$, the less dense sequences outperform CHaDD at short times when the pulses are not robust; this advantage is largely eliminated by robust versions designed to compensate for coherent pulse errors, and among the robust sequences, CGDD uses the fewest pulses over a fixed protection time. Across non-robust $C=3$ and $C=5$ schedules, equal PRR on a fixed
qubit subset is empirically associated with similar state preservation. Thus, the PRR serves as a practical figure of merit for chromatic DD whenever coherent pulse errors dominate.
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Quantum Physics
Optimal spectrum estimation
Ainesh Bakshi, Apoorv Vikram Singh and Xinyu Tan
We prove that the spectrum of an unknown $d$-dimensional
quantum state can be estimated to error $\varepsilon$ in total variation distance using \[ O\!\left(d^2\min\left\{ \frac{1}{(\varepsilon\log d)^4},\; \frac{1}{(\varepsilon\log d)^2} \right\}\right) \] copies. This matches the recent lower bound of Wang. When restricted to unentangled measurements, we give an
algorithm with an additional factor of $d$ in copy complexity, which we
conjecture to be optimal. We develop a framework for recovering the small
eigenvalues of a
quantum state by matching Chebyshev moments. We bound the variance of each Chebyshev moment estimate in terms of scalar derivatives of the corresponding
polynomial, using classical and
quantum Efron–Stein decompositions. Different rescalings of the Chebyshev
polynomials balance approximation error and variance, yielding two regimes in our copy complexity bound.
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General Relativity and Quantum Cosmology
The third law of black hole thermodynamics and the mass-to-charge ratio of scalar fields
Shahar Hod and Tsvi Piran
Kehle and Unger have recently shown that self-gravitating charged classical scalar fields can collapse to form extremal Reissner-Nordström (eRN) black holes in finite time, thus violating the third law of thermodynamics (TLT). Reall has subsequently proved that the formation of an eRN black hole in gravitational collapse is impossible if the mass-to-charge ratio of the field exceeds unity, $m/e\geq1$. In the present compact paper we
conjecture, using
quantum considerations, that the Reall bound is not sharp. In particular, we point out that the electric field of a charged system with charge $Q$ will spontaneously polarize the
vacuum in the regime $(eQ/\hbar)^2>(mQ/\hbar)^2+1/4$, thereby creating pairs of charged particles that discharge the black hole and ensure the
quantum validity of the TLT in this regime. Motivated by the TLT, we
conjecture that the classical Reall bound can be strengthened such that classical considerations would prevent eRN black holes from forming dynamically in the regime $m/e\geq\sqrt{1-\big({{\hbar}/{2eQ}}\big)^2}$, where
quantum polarization effects are unable to protect the TLT.
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Medical Physics
Cone-beam artifact reduction in Gamma Knife CBCT images using a line-arc-line scan trajectory
Alexandra Alain-Beaudoin, Håkan Nordström, Luc Beaulieu et al. (+1 more)
Objective. Gamma Knife cone-beam computed
tomography (CBCT) images suffer from distinct cone-beam artifacts for some patients, due to the conical X-ray beam which is oriented to intersect the detector perpendicularly at its inferior edge. The use of an exotic scan trajectory which provides more complete sampling across the field of view than the current arc can reduce cone-beam artifacts. In this study, the feasibility of a line-arc-line scan trajectory for the Gamma Knife CBCT is assessed through a proof of concept. Approach. Using a customized research Gamma Knife, a Catphan 503 and an anthropomorphic head phantom are imaged for different exotic scan trajectories, consisting of combinations of arcs and lines. The CBCT images for each trajectory are then reconstructed with an iterative
algorithm. Main results. A line-arc-line trajectory provides the largest image quality improvement among the investigated trajectories, with no noticeable cone-beam artifacts in the CBCT images: the axial interfaces between modules of the Catphan are well defined, and the superior edge of the phantom on the axial axis is sharper by 92%, compared with the current arc trajectory. For the head CBCT images, the proposed trajectory removes most of the cone-beam artifact on the superior side of the skull, characteristic of the current Gamma Knife CBCT images. The artifact reduction also leads to a visual improvement in terms of uniformity in both phantoms. Significance. A line-arc-line CBCT scan trajectory would be feasible on the Gamma Knife with limited changes to the current configuration, and could produce images with improved image quality.
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All authors Alexandra Alain-Beaudoin, Håkan Nordström, Luc Beaulieu, Joakim da Silva
High Energy Physics (Experiment)
Separating coherent and incoherent photoproduction at an Electron-Ion Collider: Comparing lead, gold and silver beams
Spencer R. Klein and Mathias C. Labonte
Exclusive photoproduction is an important probe of
nuclear parton distributions at low Bjorken-$x$. The Good-Walker paradigm relates coherent photoproduction to the average
nuclear configuration, giving access to the transverse distribution of
gluons in a target, while incoherent photoproduction is sensitive to fluctuations such as gluonic hotspots. Efficiently separating coherent and incoherent interactions is a key challenge for experiments at the future Electron-Ion
Collider (EIC). In this article, we study
nuclear de-excitation via
photon emission, and see how the finite
photon detection efficiency leads to misidentification of incoherent emission. We compare the detection efficiency for incoherent $J/\psi$ production using the BeAGLE event generator for Ag-107, Au-197, and Pb-208 targets, for two different forward
photon energy thresholds: 50 MeV and 200 MeV. The shell structures of the three species exhibit different incoherent tagging efficiencies due to differences in the lifetimes and energy levels of their excited states. Some of the low-lying states live long enough so that they decay outside the EIC detectors. Especially for the lower
photon energy threshold, lead allows a higher tagging efficiency than gold, due to its lack of low-lying and/or long-lived excited states.
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Computational Physics
CTrex: A Research-Oriented Framework for Kernel- and Projection-Level Algorithm Development in CT Reconstruction
Karel Desplenter, Wannes Goethals, Thomas De Schryver et al. (+3 more)
Micro-computed
tomography (micro-CT) is increasingly applied to imaging scenarios in which object motion, deformation, truncated fields of view, continuous rotation, or unconventional scanning protocols violate assumptions underlying classical reconstruction pipelines. Existing reconstruction frameworks efficiently support standard geometries and workflows but offer limited control over how projection operators are discretized and evaluated. This restricts methodological exploration when accuracy depends on ray sampling, interpolation, or operator coupling. We introduce CTrex, a research-oriented, GPU-accelerated iterative reconstruction framework that exposes the projection-correction-backprojection pipeline down to the kernel level. Rather than treating these operators as fixed black boxes, CTrex represents them as editable computational building blocks within a unified iterative structure. This allows non-ideal acquisition effects to be incorporated directly into the numerical operators rather than treated as external corrections. CTrex combines GPU-level accessibility with an extensible geometry formulation based on homogeneous-coordinate view
matrices, allowing rigid and affine transformations, detector misalignments, and time-varying geometries to be expressed consistently. It supports circular, helical, offset, and conveyor-belt trajectories while keeping GPU kernels agnostic to the trajectory definition. Applications in motion- and deformation-aware reconstruction, event-based 4D imaging, cylindrical-coordinate reconstruction, and extended-field-of-view CT illustrate how operator-level adaptations enable strategies difficult to realize in conventional frameworks. CTrex provides a flexible platform for CT reconstruction research under realistic and unconventional imaging conditions.
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All authors Karel Desplenter, Wannes Goethals, Thomas De Schryver, Marjolein Heyndrickx, Jan Aelterman, Matthieu N. Boone
Solar and Stellar Astrophysics
Coronal Green-Line Emission During a Solar Prominence Eruption: Spectroscopic Evidence of Its Correspondence with the EUV Late Phase
P. Vemareddy, R. Ramesh and V. Muttu Priyal
We report spectroscopic observations during a prominence eruption on 9 October 2025 from the Sun's west limb, associated with an M2.0
flare that commenced at 12:11 UT. The event was captured in sit-and-stare mode by the Visible Emission Line Coronagraph (VELC) onboard Aditya-L1, providing continuous observations of the Fe XIV 5303 Åcoronal greenline. The spatially averaged green-line emission exhibits a clear correspondence with the EUV late-phase (ELP) emission observed in multiple SDO/AIA channels. In particular, an enhanced 5303 Åemission peak at 15:24 UT coincides with secondary peaks in the AIA 211, 171, 193, and 335 Åpassbands, occurring $\sim173$ minutes after the X-ray peak. The 5303 Åline-width information provides important constraints on the mechanism responsible for the ELP. The line-width decreases progressively by about 28% toward the ELP peak, broadly consistent with the cooling of post-
flare coronal loops. This behavior suggests that the ELP is predominantly associated with
plasma cooling, with relatively weak additional energy input from
magnetic reconnection, which does not produce a significant enhancement in line-widths. The estimated non-thermal velocity decreases from $\sim$36 km s$^{-1}$ during the impulsive phase to $\sim$21 km s$^{-1}$ during the gradual phase, indicating a reduction in turbulent
plasma motions. And doppler velocities evolve from predominantly positive values during the eruptive rise phase to negative values during the later gradual phase, implying upward and subsequent downward
plasma motions. To our knowledge, this study provides the first space-based spectroscopic evidence linking coronal green-line emission with the ELP and its origin during a
solar flare.
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Strongly Correlated Electrons
From dimensional reduction to tetramerization in mixed ferro-antiferro breathing pyrochlores
Sourin Chatterjee, Kelvin Salou-Smith, Benedikt Schneider et al. (+8 more)
We study the
spin-1/2 nearest-neighbor Heisenberg model on the breathing pyrochlore
lattice in the mixed ferro-
antiferromagnetic regime, where one tetrahedral sublattice is
antiferromagnetic and the other
ferromagnetic. The classical ground-state
manifold is then that of the nearest-neighbor face-centered-cubic (fcc) antiferromagnet built from composite tetrahedral moments. Classical Monte Carlo simulations and the self-consistent Gaussian approximation show that thermal order-by-disorder lifts its subextensive degeneracy and selects the collinear Type-I state with wave vector $X=(1,0,0)$ through a strongly first-order transition. Pseudofermion functional renormalization group calculations for $S=1/2$ and $S=1$ reveal a nonmagnetic window adjacent to the decoupled
antiferromagnetic-tetrahedron limit, beyond which $X$ order reappears. Density
matrix renormalization group calculations show that this window is not featureless: the
antiferromagnetic tetrahedra develop nearly ideal tetramer correlations, with four bonds carrying $\langle\mathbf{S}_i\cdot\mathbf{S}_j\rangle\simeq-1/2$ and the two opposite bonds $\simeq+1/4$, while the structure factor retains broad maxima at $X$. A third-order effective
Hamiltonian in the tetrahedral-singlet
manifold explains this: reversing the sign of the inter-tetrahedron coupling converts Tsunetsugu's dimer selection into a uniform tetramer selection, as confirmed by exact diagonalization. A dynamic high-temperature expansion traces how local tetrahedral excitations give way to low-energy $X$-centered spectral weight. Finally, we place density-functional parameters for eight structures of
spin-3/2 breathing chromium thiospinels in the classical phase diagram. The mapping reproduces the $\mathbf{k}=(1,0,0)$ order of CuInCr$_4$S$_8$, accounts for the absence of order in LiGaCr$_4$S$_8$, and predicts Type-I order for LiInCr$_4$S$_8$.
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All authors Sourin Chatterjee, Kelvin Salou-Smith, Benedikt Schneider, Imre Hagymási, Arnaud Ralko, Johannes Reuther, Jeffrey G. Rau, Karlo Penc, Harald O. Jeschke, Ludovic D. C. Jaubert, Yasir Iqbal
Quantum Physics
Non-Abelian sheaf quantum LDPC codes: good and magical
Zimu Li, Fuchuan Wei, Zhengyi Han et al. (+1 more)
Non-Abelian
quantum codes connect
quantum error correction, phases of matter, and computational resources. In this work, we develop a general framework for constructing non-Abelian
quantum low-density parity-check (qLDPC) codes by gauging sheaf codes via cup products and use it to establish code families with constant encoding rate and linear distance, simultaneously achieving optimal asymptotic scaling in both parameters. In particular, we characterize explicit logical representatives of the full gauged code space, and provide a fundamental treatment of non-Abelian code distance in the sense of Knill–Laflamme based on combining expansion with cleaning to establish protection against arbitrary errors. We further construct an almost-good family with entire code spaces exhibiting long-range magic. Moreover, we use linearly addressable cup product to directly generate linearly many encoded magic states from gauging measurements of Clifford operators. These results extend good qLDPC codes beyond the Pauli stabilizer setting, lay the foundation for pursuing the no low-energy trivial magic
conjecture and shed light on non-Abelian
quantum phases and orders beyond
geometric locality.
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All authors Zimu Li, Fuchuan Wei, Zhengyi Han, Zi-Wen Liu
Quantum Physics
Learning and interpreting policies for simultaneous entanglement requests in quantum networks
Leon Rode, Sumeet Khatri and Supartha Podder
Future
quantum networks will make use of
entanglement to perform numerous tasks, such as sending
quantum information over long distances, distributed
quantum computing, and
quantum sensing. In general, these tasks will need to be performed simultaneously in various regions of a network, while minimizing resources and latency. We will thus require policies for scheduling link-level
entanglement resources, and using the link-level
entanglement to create various forms of multipartite
entanglement required for every task. In this work, we address this problem using reinforcement learning. We formulate a Markov Decision Process for the problem and use double deep Q-networks (DQN) with Message Passing Neural Networks (MPNNs), experience replay buffers, and curriculum training to obtain policies. The key physical parameter is the probability of link-level
entanglement generation, i.e., the link activation probability. We show that our policies maintain 100% success for up to 71% lower link activation probability than the baseline heuristics for a set of physically relevant network
topologies. We then examine an additional constraint where experiment (task) placements are restricted to specific hardware types and demonstrate a similar advantage in performance over heuristics, with our policy maintaining at least an 80% success rate for up to a 59% lower link activation probability. Finally, we explore methods to interpret the learned policy by defining metrics enabling conclusions to be drawn about the model's behavior and by tasking a large
language model (LLM) to derive a novel heuristic given example actions taken by the DQN-trained policy. We find that the LLM heuristic performs similarly to the DQN-trained policy in performance, indicating a promising method for interpretable policy extraction for large
quantum networks, where direct training becomes computationally expensive.
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Plasma Physics
Singularities of the cold plasma theory: Modeling challenges for ICRF operation in low-density edge plasma
Wouter Tierens, Chris Klepper, Raymond Diab et al. (+1 more)
Sustained ICRF operation in a fusion power plant may require low edge densities to mitigate
plasma-wall interactions, a regime which was recently achieved in WEST with very little
impurity sputtering. Cold
plasma theory, however, predicts singular radiofrequency electric fields in this regime, both at the lower hybrid resonance and along the resonance cones, raising the question of whether standard collisional cold
plasma models suffice to describe low-density edge ICRF at all. Collisions in principle remove these singularities, replacing them with finite but sharply peaked fields. We derive these peak length scales analytically and confirm them with a 2D finite-element simulation using exponential mesh refinement, achieving micrometer resolution where needed. We conclude that edge collisions in cold
plasma do not remove the need to resolve length scales ordinarily associated with hot-
plasma and Bernstein-wave physics.
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All authors Wouter Tierens, Chris Klepper, Raymond Diab, Guillaume Urbanczyk
Statistical Mechanics · Cross-listed from q-bio.PE
Consistent determination of stability regimes in natural ecological communities from abundance time series
Alberto Megías, Vicente J. Ontiveros, David Alonso et al. (+1 more)
The stability of an ecological community is conventionally defined through species interactions, which quantify how species affect one another. Interaction strengths are notoriously difficult to measure in species-rich assemblages. Long-term monitoring of species-rich communities, however, provides species abundance time series, increasingly available across habitats and taxa but not yet connected to the stability properties of the communities they describe. Here we develop a statistical framework that infers stability regimes in large ecological communities directly from abundance time series. We study
stochastic Generalized Lotka–Volterra dynamics with random interactions and environmental fluctuations using dynamical mean-field theory, reducing the multispecies system to an effective
stochastic process for a representative species. The theory predicts three stability regimes (stable coexistence, intermittent dynamics close to extinction, and unbounded growth) separated by analytical boundaries, and shows that environmental stochasticity systematically destabilizes coexistence by promoting intermittent low-abundance dynamics. The resulting steady-state species abundance distribution is a Gamma law that ties the dynamical phases to the variability-based stability metrics used in empirical studies. Recasting the effective dynamics as a multivariate regression model, we infer interaction statistics, environmental variability and the characteristic timescale of the dynamics from community data, without reconstructing the interaction network. Applied to natural communities spanning a broad range of habitats and taxa, the method resolves contrasting stability regimes and yields quantitative estimates of species extinction risk.
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All authors Alberto Megías, Vicente J. Ontiveros, David Alonso, José A. Capitán
Quantum Physics
Bobak T. Kiani
We determine the exact universal high-temperature separability threshold for Pauli
Hamiltonians of bounded degree $\Delta\ge2$. If every coefficient in the
Hamiltonian has magnitude at most one and each term has overlapping support with at most $\Delta$ other terms, the Gibbs state is a mixture of product Pauli eigenstates whenever \[ \beta \le z_\Delta := \operatorname{arctanh}\left[\max_{0\le x \le 1}x\left(\frac{1-x}{1+x}\right)^{\Delta-1} \right]. \] For every $\beta>z_\Delta$, a finite commuting
Hamiltonian with maximum overlap degree at most $\Delta$ has an entangled Gibbs state. At any fixed $\beta<z_\Delta$ strictly below the threshold, a classical
polynomial-time
algorithm produces samples from a distribution over product Pauli eigenstates approximating the Gibbs state in trace distance.
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Quantum Physics
Proper Agnostic Learning of Matrix Product States and Tree Tensor Networks
Constantin Cedillo Vayson de Pradenne and Jordan Cotler
We establish proper agnostic learning of
matrix product states and tree tensor networks. Given copies of an arbitrary
quantum state $\rho$, our
algorithms return a state $|\psi\rangle$ of chosen bond dimension such that $\langle\psi| \rho |\psi\rangle$ is within $\varepsilon$ of the optimum over the model class, without assuming that $\rho$ itself belongs to or is well approximated by that class. The main idea is to use improper learning to compress the mixed-state objective, reducing proper agnostic learning to optimization against a finite collection of explicitly specified pure states. We then introduce a comparator-dual compression procedure that reduces the bond dimension of these targets while uniformly preserving their overlaps with all bounded-bond comparators, with an error independent of system size. For
matrix product states, this gives
polynomial copy complexity in the system size, local dimension, bond dimension, and $1/\varepsilon$, together with
polynomial runtime in the system size for fixed local dimension, bond dimension, and accuracy. The same framework yields proper agnostic learning of tree tensor networks on bounded-degree trees, with both copy complexity and runtime
polynomial in the system size when the remaining parameters are fixed.
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Astrophysics of Galaxies
CERIDWEN: Fast and Flexible GPU-Accelerated Stellar Population Inference
Amanda Stoffers, Sandro Tacchella and Benjamin D. Johnson
JWST has increased both the number of high-
redshift galaxies with high-quality spectral energy distributions (SEDs) and their information content. In parallel, wide-area surveys from Euclid, Rubin's LSST, and Roman will increase
galaxy samples by orders of magnitude. Analysing these
datasets requires
stellar-population models that are both flexible and computationally efficient. We present CERIDWEN, a GPU-native SED fitting framework written in JAX, with an end-to-end differentiable forward model spanning
stellar populations, nebular emission,
dust attenuation and emission, and projection into the observer frame. Its vectorised, compiled architecture lets nested sampling replace a batch of live points in parallel on the GPU, which makes flexible
stellar-population models tractable under full
Bayesian inference. Automatic differentiation also provides exact gradients for the gradient-based samplers in the package. We jointly infer time-dependent chemical-enrichment histories instead of a single
stellar metallicity, and demonstrate non-parametric
star-formation histories (SFHs) with $\sim$120 age bins. Using $\alpha$-enhanced
stellar libraries from FSPS, CERIDWEN can sample
stellar [$\alpha$/Fe] jointly with [Fe/H], mass, and SFH, so that the joint posterior represents the [Fe/H]-[$\alpha$/Fe] degeneracy explicitly. In controlled mocks, CERIDWEN recovers parameters with well-calibrated posterior uncertainties, while fits to real JWST observations reproduce posteriors from the established Prospector framework: on a single GPU, CERIDWEN completes a fit in a median sampling time of $\sim$4 min, $\sim$134$\times$ faster per fit than equivalent CPU-based Prospector runs. CERIDWEN therefore makes full
Bayesian inference practical for larger
galaxy samples and more flexible
stellar-population models, reducing computational constraints on the physical complexity explored in SED fitting.
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General Relativity and Quantum Cosmology
Stiffness corrections for f-mode neutron star universal relations
Isaac G. Chu and Carolyn A. Raithel
Excitations of the
neutron star (NS) fundamental mode (f-mode) during a binary NS inspiral or from a glitching
pulsar can produce gravitational waves (GWs) that will be detectable with the next generation of detectors, opening the door to GW asteroseismology of
neutron stars. There exist approximately equation-of-state (EOS)-insensitive, or "universal," relations that relate the f-mode to other NS properties. These universal relations have typically been identified with relatively small, selective EOS samples. To more thoroughly explore the parameter space, we examine the f-modes for a large sample of piecewise-parametric EOSs by solving the linearized fluid perturbation equations for the f-mode frequency and damping time in full general relativity. We utilize our sample to evaluate the EOS-sensitivity of previously-proposed universal relations (URs) for both the f-mode frequency and damping time. We find that URs that depend on combinations of only NS mass and radius have significant residuals, as previously reported; but that these residuals are strongly correlated with the overall stiffness of the EOS. We account for this residual dependence on the EOS by introducing linear correction terms that depend on the characteristic radius predicted by the EOS and the slope of the mass-radius curve at intermediate masses. To assess the impact of our new correction terms on observables, we consider the case of GW emission due to a glitch in a Vela-like
pulsar and demonstrate that the predicted signal-to-noise ratio for such an event is over/under-estimated by up to ~10% when using an existing, single-parameter UR, but is recovered nearly exactly with our improved 3-parameter UR. In contrast, we find that URs between the f-mode and
tidal deformability exhibit only minimal EOS-dependent correlations in their residuals and overall remain highly EOS-insensitive.
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Quantum Physics
Disorder-induced quantum Fisher information in topological quantum systems
Advay Burte, Keshav Das Agarwal, Leela Ganesh Chandra Lakkaraju et al. (+1 more)
The topological order of the Kitaev toric code is insensitive to disorder in its couplings since all
star and plaquette operators commute; consequently, the stabilizer ground-state
manifold is independent of the individual coupling strengths, and the phase remains stable against weak local perturbations. This insensitivity, however, is a property of the eigenstates and not of the dynamics they generate, and we show that the disorder sensitivity of a probe prepared outside that eigenbasis can be a metrological resource. In particular, we investigate the estimation of the strength of three topological-order-breaking perturbations, the nonlinear Castelnovo-Chamon deformation, nearest-neighbor Ising interactions, and a
magnetic field along horizontal edges, encoded on an initially separable probe through
unitary evolution under the disordered toric code
Hamiltonian. We demonstrate that the quenched average
quantum Fisher information (QFI), a figure of merit for metrological precision, exceeds that of its ordered counterpart in suitable regimes of perturbation strength and encoding time. For the ordered case, we further identify optimal product probes, for which the quadratic and cubic terms of the short-time expansion vanish identically, leaving a transient quartic scaling of QFI. Interestingly, this window persists as long as the multipartite
entanglement generated by the encoding continues to increase, and it survives under local dephasing, bit-flip, and amplitude damping noise acting independently on each site, with the non-unital channel being the least detrimental.
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All authors Advay Burte, Keshav Das Agarwal, Leela Ganesh Chandra Lakkaraju, Aditi Sen De
Quantum Physics
Optimal Two-Qubit Gate-Cutting Cost and Measures of Nonlocality
Michael Hart
Circuit cutting enables
quantum computations to be decomposed into smaller subcircuits at the cost of additional sampling overhead. Gate-cutting provides one such approach by replacing nonlocal gates with quasiprobability decompositions of local operations. Starting from the known optimal two-
qubit gate-cutting formula, we derive complete sharp lower and upper envelopes relating the quasiprobability extent $\gamma$ to five established descriptors: entangling power, gate typicality, operator
entanglement, Schmidt strength, and maximum product-input concurrence. We recast $\gamma$ as a Rényi-$1/2$ functional of the operator-Schmidt spectrum and show how the physical constraints on two-
qubit spectra sharpen generic
entropy bounds and select a small set of recurring extremal Cartan families. None of the five descriptors generically determines $\gamma$ alone, but each imposes exact constraints, revealing how substantially the optimal gate-cutting cost can vary between gates with similar nonlocal characteristics.
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Quantum Physics · Cross-listed from cs.CC
A General Composition Theorem for Approximate Degree
Samruddhi Pednekar and Supartha Podder
A longstanding open question in Boolean function complexity asks whether approximate degree composes multiplicatively under block composition. Although a general multiplicative upper bound is known, matching lower bounds have previously been established only for restricted classes of functions. We resolve this question for all total Boolean functions by proving the matching lower bound. Together with Sherstov's upper bound, our result shows that, for every pair of total Boolean functions $f:\{0,1\}^n\to\{0,1\}$ and $g:\{0,1\}^m\to\{0,1\}$, \[ \widetilde{deg}(f\circ g) = \Theta\!\left( \widetilde{deg}(f)\,\widetilde{deg}(g) \right), \] where $\widetilde{deg}$ denotes constant-error approximate degree. We also consider the analogous question for exact
quantum query complexity and give a counterexample showing that multiplicative composition fails in this setting.
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Computational Physics · Cross-listed from math.NA
High-dimensional extreme eigenvalue problems: low-rank tensor parametrization and optimization
Pengfei Hao, Renfeng Peng, Yang Kuang et al. (+1 more)
High-dimensional extreme
eigenvalue problems often arise from molecular vibrational models, electronic structure calculations, and
quantum mechanics. Directly solving these problems suffers from the curse of dimensionality. Instead of tackling the problem in high-dimensional ambient space, we reformulate the problem through low-rank tensor formats, which can significantly reduce the computational cost and storage. Specifically, we consider the Rayleigh–Ritz problem on bounded-rank tensors in the tensor train format, which enables a more flexible choice of rank parameters. Moreover, we consider a smooth parametrization for bounded-rank tensors by introducing slack variables, leading to a smooth
manifold structure. The original Rayleigh–Ritz problem is therefore transferred to an optimization problem on the
manifold. We develop the Riemannian geometry and propose optimization methods for solving extreme
eigenvalue problems. In practice, the Kronecker-product structure in
Hamiltonian and PDE operators is employed to simplify the computation. Numerical experiments on the harmonic oscillator, the Laplace operator, the Schrödinger equation, the layered cluster problem, and the Bose–Einstein model demonstrate that the proposed method achieves accuracy comparable to full-space eigensolvers with reduced computation time and avoids storing full vectors. The results also show numerical rank reduction during iteration and robustness when the rank parameter is over-estimated. In addition, the fixed-point iterations illustrate that the proposed methods are able to serve as an inner eigensolver for solving nonlinear
eigenvalue problems.
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All authors Pengfei Hao, Renfeng Peng, Yang Kuang, Bin Gao
High Energy Physics (Phenomenology)
High-quality axion from chain seesaw
Pei-Hong Gu
We propose a chain seesaw mechanism to generate not only the masses of neutral
neutrinos but also the masses of charged
fermions, by supplementing the standard model $SU(3)_c^{}\times SU(2)_L^{}\times U(1)_Y^{}$ gauge
symmetries with an additional $U(1)_{Y'}^{}$ gauge
symmetry. The chains for the down-type and up-type
quarks contain different numbers of links, because the corresponding mediator vector-like
fermions and new
Higgs scalars carry different $U(1)_{Y'}^{}$ charges. The Peccei-Quinn global
symmetry is automatically embedded in this $U(1)_{Y'}^{} $ gauge
symmetry which is sufficient to guarantee the high quality of
axion.
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Materials Science
AI-guided high-throughput discovery of iridium- and ruthenium-free palladium-oxide catalysts for durable acidic oxygen evolution
Ken J. Jenewein, Faezeh Habib Zadeh, Xiaoxiao Wang et al. (+19 more)
Catalyzing acidic oxygen
evolution at the
proton-exchange-membrane water electrolysis (PEMWE) anode relies almost entirely on iridium or ruthenium, drawn from concentrated supply chains that constrain gigawatt-scale deployment. We report an artificial intelligence (AI)-guided, human-supervised closed-loop platform (>90% automation) integrating combinatorial sputter synthesis, high-throughput screening, machine-learning composition-property models, adaptive multi-objective optimization, and context-aware large-
language-model
reasoning, where lead catalysts advanced to long-term validation in 1 M H2SO4 at 10 mA cm-2. Navigating a combinatorial metal
oxide space, the platform iteratively evaluated the activity-stability trade-off of 2,942 catalysts across 53 material systems and 26 elements, surfacing Ir- and Ru-free complex
oxides such as InMnPdOx and NiTaPdOx that conventional design logic, and off-the-shelf
language models, would not predict. In retrospective benchmarking, our sequential learning
agent advanced the activity-stability frontier faster than fixed-policy
Bayesian optimization or in-context
language-model selection. During long-term testing, NiTaPdOx operated at lower overpotential than PdOx, but both eventually exceeded 0.5 V: PdOx at ~200 h and NiTaPdOx at ~470 h. InMnPdOx showed a similar overpotential improvement in addition to a dramatic increase in operational stability, retaining overpotential below 0.5 V over 1,000 h of operation. The additive elements promote the formation of a nanostructure that is associated with catalytic activity while stabilizing Pd against corrosion. The results highlight the power of AI-driven science in addressing long-standing challenges in materials chemistry, and the greater availability of Pd relative to incumbent Ir and Ru offers a near-term option to ease supply constraints on scaled electrochemical H2 generation.
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All authors Ken J. Jenewein, Faezeh Habib Zadeh, Xiaoxiao Wang, Gustavo Malkomes, Huafan Zhang, Natalie Page, Jae Jin Bang, Peter J. Santiago, Karla V. Contreras, Katherine K. Li, Allison Perna, Lorena M. Britton, Fahrettin Kilic, Kevin J. Cruse, Armin Taheri, Krishnanand Mallayya, Harley Quinn, Rebecca A. Durr, Peter A. Beaucage, Santiago Miret, John M. Gregoire, Rafael Gómez-Bombarelli
Quantum Physics
Collective thermalization, work reliability, and resource bounds in a population-inverted Dicke Otto engine
Cler T. Garcez, Gabriella G. Damas, Norton G. de Almeida et al. (+1 more)
Population inversion and collective relaxation can both enhance the performance of a
quantum heat engine, but through distinct mechanisms. We study a
quantum Otto engine whose working medium is a symmetric collective
spin of $N$ two-level constituents. For commuting work strokes and collective reservoir coupling, the dynamics reduces exactly to a finite birth–death process on the Dicke ladder, allowing a unified treatment of stationary operation, work fluctuations, and finite-time relaxation. In the complete-reset limit, passive work per cycle saturates with system size, whereas population inversion yields work that grows linearly with $N$. The work reliability shows the same linear scaling, exceeding the square-root behavior of $N$ independent engines. This enhancement originates from a macroscopic polarization displacement between hot and cold states, while collective coupling instead accelerates the finite-time dynamics through Dicke transition rates. For matched passive and inverted hot states, the extra gross work equals the Otto efficiency times the ergotropy of the inverted state. Charging the corresponding reversible excess state-formation cost removes this advantage, showing that the enhanced output converts a pre-existing active-state resource rather than generating a free thermodynamic gain. Exact finite-contact trajectory statistics further quantify how collective kinetics, fluctuations, correlations, and resource accounting remain linked away from complete reset.
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All authors Cler T. Garcez, Gabriella G. Damas, Norton G. de Almeida, G. D. de Moraes Neto
Mesoscale and Nanoscale Physics
Pomeranchuk-like electronic localization above 100 K in twisted MoS$_{2}$
Zhiren Xiong, Jianqi Huang, Ruyue Han et al. (+8 more)
Twisted transition-metal dichalcogenides (TMDs) have manifested a rich variety of emerging physical phenomena, yet experimental studies have so far been largely limited in their valence bands (p-doped). Here, we show correlated electronic states in the conduction bands (n-doped) of near-AA-twisted
bilayer MoS$_2$ with twist angles ranging from $\sim2.3^\circ$ to $\sim3.5^\circ$, down to the mK temperature regime. A strongly reconstructed correlated phase diagram as a function of twist-angle has been observed - correlated gaps persist to temperatures approaching $160$ K at small twist angles, but collapse to only $\sim20$ K at intermediate angles, where a richer landscape of interaction-driven states emerges. At the largest twist-angle $\sim 3.5\,^{\circ}$, correlated resistance at 1 electron per moiré unit
cell is enhanced upon heating, consistent with thermally assisted localization, or, a Pomeranchuk-like behaviour. Its
magnetic-field response, however, is highly anisotropic, which differs markedly from that of canonical isospin moiré Pomeranchuk effect in
graphene systems. Strikingly, such signature can persist even above 100 K around a filling of 2 electrons per moiré, despite of its weak resistive nature. Our results establish the twisted MoS$_2$ as a platform for studying the complexity of charge localization, internal flavour degrees of freedom, and band
topology in conduction bands of semiconducting moiré systems.
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All authors Zhiren Xiong, Jianqi Huang, Ruyue Han, Hanwen Wang, Hui Ding, Jianming Lu, Jianpeng Liu, Zheng Vitto Han, Xingdan Sun, Siwen Zhao, Baojuan Dong
Solar and Stellar Astrophysics
Formation of adducts of C$_6$H with Na$^+$, Mg$^+$ and Al$^+$ metal cations by radiative association
Niyazi Bulut, Octavio Roncero, Maria Mallo et al. (+6 more)
The Mg-bearing cations MgC$_4$H$^+$, MgC$_6$H$^+$, MgC$_3$N$^+$, and MgC$_5$N$^+$ have been recently observed in the carbon-rich envelope IRC\,+10216. These species are thought to form upon radiative association between Mg$^+$ and the corresponding neutral radical. This work aims to determine the radiative association rate coefficients for the cations Al$^+$, Mg$^+$, and Na$^+$ reacting with carbon chain radicals to estimate the relative importance of metal-bearing carbon cations for each of these metals. For this purpose we use statistical methods in combination with highly accurate ab initio calculations to obtain the radiative association rate coefficient. Moreover, anisotropic effects beyond mono-dimensional capture model are considered, providing a more reliable description of the simulated processes.} The radiative association rate coefficients to form Mg-, Al- and Na-C$_6$H$^+$, as well as MgC$_4$H$^+$, MgC$_3$N$^+$, and MgC$_5$N$^+$, are calculated with the new restrictions considered in this work. These new rate coefficients are included in a chemical model of the C-rich AGB envelope IRC\,+10216. The abundances of MgC$_4$H$^+$, MgC$_6$H$^+$, and MgC$_5$N$^+$ are consistent with observations, with differences no greater than one order of magnitude, corroborating radiative association as a plausible formation mechanism for these adducts. However, the calculated abundance of MgC$_3$N$^+$ is about two orders of magnitude lower than observed, which indicates that either the chemistry of this species is significantly different from the others or the calculated rate coefficient is too low. The abundances obtained for Na-C$_6$H$^+$ and Al-C$_6$H$^+$ are around two orders of magnitude lower than for Mg, making very difficult to detect the analogous metal-bearing cations in IRC\,+10216.
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All authors Niyazi Bulut, Octavio Roncero, Maria Mallo, German Molpeceres, Marcelino Agundez, Maysa Yusef-Buey, Jose Cernicharo, Carlos Cabezas, Piotr Zuchowski
Quantum Physics
Transport and Channel Normal Forms for Clifford Interactions
Xiong Chunhe, Kim Sunho, Zhang Qing-Hua et al. (+2 more)
We study how Clifford interactions with a fixed environment determine
quantum transmission, in a setting that extends positive discrete
quantum convolution . We characterize when Clifford operations on the environment can be replaced by operations on the signal input and the two outputs, and classify the interactions under local Clifford transformations . For pure stabilizer environments, we determine the noiseless, dephasing, and completely depolarizing parts of the channel directly from the interaction and environmental stabilizers, obtaining its
quantum and private capacities . This reveals a distinction between interactions: those locally equivalent to positive convolution produce
entanglement-breaking channels for every pure stabilizer environment, whereas every other interaction in the class admits noiseless
quantum transmission with a suitable pure stabilizer environment . For positive convolution, environmental Clifford transport also allows us to separate the stabilized coordinates of an arbitrary mixed environment . These coordinates carry only a classical label shared by the receiver and environment, so removing them preserves
quantum and private capacities . The resulting channel reduction yields a private-capacity bound by the modified relative
entropy of magic of the environmental state .
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All authors Xiong Chunhe, Kim Sunho, Zhang Qing-Hua, Fei Shao-Ming, Wu Junde
Quantum Gases
Characterizing quasiparticles in strongly correlated systems using nonlinear spectroscopy in quantum simulators
Luka Skolc, Utso Bhattacharya, Jonathan B. Curtis et al. (+2 more)
Characterizing carrier type in strongly correlated
quantum systems conventionally relies on the
Hall effect. In cold-atom
quantum simulators, implementing
Hall transport measurements typically requires synthetic gauge fields, which introduces significant heating. Here, we present nonlinear spectroscopic and fluctuation-based protocols that establish an alternative route to identifying the sign of quasiparticle charge. We demonstrate that second-order density and current responses to finite-momentum quenches and drives-as well as
equilibrium third-order density cumulants-distinguish electron- from hole-like quasiparticles. For a
Fermi-Hubbard multi-leg ladder on a square
lattice, numerical simulations reveal a crossover from hole- to electron-like carriers upon hole-doping away from half-filling, matching the sign change in the
Hall coefficient. To demonstrate the applicability of our protocols beyond fermionic systems, we show that the nonlinear density response to a finite-momentum, finite-frequency drive reveals the sign of charge carriers in a hard-core
boson ladder, and that the nonlinear signal can be significantly enhanced when driving near resonance with a nonlinear collective mode. Our results establish nonlinear density and current response and
equilibrium non-Gaussian fluctuations as complementary probes, offering
quantum simulators a direct route to characterize the carrier sign, without the experimental hurdles of conventional transport setups.
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All authors Luka Skolc, Utso Bhattacharya, Jonathan B. Curtis, Immanuel Bloch, Eugene Demler
Medical Physics
Melanin- and linewidth-corrected pulse-oximetry
Giles Blaney, Jodee Frias, Ravi Durbha et al. (+2 more)
Current pulse oximeters tend to overestimate arterial saturation in darkly pigmented patients, increasing occult hypoxemia rates. One proposed mechanism is spectral coloring: melanin contributes to reshaping the detected spectrum of a broad-linewidth source, making the wavelength-dependent parameters behind calibration skin-tone-dependent. Diffuse optics theory allows for a melanin- and linewidth-corrected calibration equation, which to our knowledge has never been tested in vivo. In this work, we fit the empirical linear equation, the diffuse optics theoretical equation, and its corrected form to the public OpenOximetry Repository—considering 98 patients with paired arterial blood-draws, raw photoplethysmograms, and skin reflectance spectra. Accuracy is practically indistinguishable between the three approaches, yet the saturation error's dependence on melanin falls from +2.8 to +1.2 to +0.1 percentage points per unit melanin volume fraction—consistent with the spectral-coloring theory. None of these dependencies on melanin are statistically resolved here—a cohort roughly ten times larger is needed—so the correction is backed by theory and its expected direction. All three calibration approaches carry two degrees of freedom: the theoretical equation drops into existing calibration procedures, and its melanin-aware form needs a per-patient skin-tone measurement. This work demonstrates how the theoretical pulse oximetry model can be applied in calibration.
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All authors Giles Blaney, Jodee Frias, Ravi Durbha, Sergio Fantini, Valencia Koomson
General Relativity and Quantum Cosmology
Binary black hole scattering in the extreme-mass-ratio limit: time-domain waveform
Andrea Geralico
The time-domain gravitational waveform emitted during the scattering of two nonspinning compact bodies is computed in the extreme-mass-ratio limit. It provides a time-domain description of the gravitational radiation emitted during the encounter and complements previous first-order self-force calculations, which have primarily been formulated in the frequency domain. In this way, the present results provide a complementary representation of the radiative dynamics and facilitate a direct comparison between time-domain and frequency-domain approaches to the gravitational-wave signal. The waveform is accurate to the fifth post-Minkowskian (three-loop) level and seventh post-Newtonian order, and will serve as a
benchmark for future calculations by other methods, to first order in the mass ratio. The results have been already tested in a previous work by constructing the energy and angular momentum fluxes, thereby computing the corresponding radiative losses at the 5PM and 4PM level, respectively, with the same PN accuracy, which are in agreement with recent amplitude-based calculations.
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Fluid Dynamics
Magneto-coalescence phenomena in colliding ferrofluid droplets
Neeladri Sekhar Bera, Abhishek Kumar Jaiswal, Devranjan Samanta et al. (+1 more)
We explore the collision hydrodynamics of a ferrofluid droplet falling freely onto a sessile droplet of the same
liquid, in the presence of a horizontal
magnetic field; a configuration that couples droplet-on-droplet coalescence with concomitant field-governed wetting and spreading. Using high-speed imaging, we track the events through crown formation, radial spreading, and rim detachment (under specific conditions), across three ferrofluid concentrations, two substrates of different wettability (glass and PET), and a range of impact velocities and
magnetic field strengths. The maximum crown height is noted to scale as $H_{c,\max}/D_t\sim Fr^{0.5}$ ($Fr:$ Froude number); well below the ballistic upper bound of $H_{c,\max}/D_t\sim Fr$. At zero-field, the maximum spreading collapses onto the boundary-layer scaling $\beta_{0,\max}\sim (We_0/Oh)^{1/6}$ ($We_0$: Weber number, $Oh:$ Ohnesorge number) when expressed in terms of the merged impact velocity, and coalesced-drop size . With the field applied, a bulk-dissipation energy balance predicts $\beta_{\max}\sim Z^{1/5}$, where $Z$ combines the
magnetic-driving, and inertial-capillary-viscous terms, but the observations instead follow a markedly weaker $\sim Z^{1/11}$, a deficit traced to enhanced dissipation from the magnetoviscous effects, and manifested via an effective Ohnesorge number. Finally, rim detachment occurs beyond a field- and height-dependent threshold, described by a size-independent criterion $Fr^2Bo\approx 3550$ ($Bo:$ Bond number), above which the rim may fragment into daughter droplets. These scalings provide predictive tools for magnetically assisted printing, droplet-on-demand systems, and coating processes, where repeated droplet collisions occur on the residual
liquid droplet or layer.
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All authors Neeladri Sekhar Bera, Abhishek Kumar Jaiswal, Devranjan Samanta, Purbarun Dhar