Papers

We present the Quantum Accelerator (QuAcc), an open-source workflow library for atomistic simulations with an emphasis on quantum-mechanical calculations. QuAcc provides predefined workflow recipes spanning first-principles electronic-structure methods, semiempirical and tight-binding approaches, classical potentials, and foundation machine-learned interatomic potentials (MLIPs). A central design feature of QuAcc is its separation of domain-specific scientific logic from the workflow engine used to orchestrate and execute calculations. Workflows are written as ordinary Python functions and can be executed with multiple supported workflow engines without modifying the underlying source code, lowering the barrier to developing and contributing new workflows. QuAcc also streamlines the evaluation of foundation MLIPs by providing a unified platform for generating ab initio reference calculations consistent with the model of interest, mitigating methodological drift when assessing model performance. Together, these features make QuAcc a flexible and accessible framework for atomistic simulation workflows that have become central to the current era of machine learning and artificial intelligence.

We formulate the low-energy theory of superconducting pairing in the geometric algebra $Cl_{3,0}$. Conventional BCS mean-field theory and its extensions ($s$-, $p$-, $d$-wave, etc.) have algebraic counterparts in an eight-dimensional real multivector space. The construction is a two-level projection: matrix blocks are represented as Clifford multivectors, and their grade-0 projected geometric products extract the scalar blocks from which Hamiltonians are built. The result is an algebraic reconstruction, physically equivalent to the standard complex-matrix formulation. In this reconstruction, the dichotomy of pairing channels acquires an algebraic root: it follows from the fermionic identity $B^\dagger(V)=-B^\dagger(V^{\mathsf T})$, and the Fierz rearrangement is realized by the map $\Phi:G\mapsto Ge_{31}$ (with $e_{31}^2=-1$). This yields a kernel/matrix dictionary: at the effective-kernel level grades $0\oplus3$ correspond to spin singlets and grades $1\oplus2$ to triplets; at the pairing-matrix level the singlet plane is $\mathrm{span}\{e_2,e_{31}\}$. The BCS limit has a double grade identity: kernel grade 0 (scalar glue) and vertex grade 2, a bivector ($i\sigma_2\leftrightarrow e_{31}$). We state three algebraic results: (i) a decomposition theorem for BdG quantum geometry with a null-texture criterion, applied to the chiral-state controversy in CsV$_3$Sb$_5$; (ii) a Fierz sign duality in the four-dimensional Minkowski algebra, with a chirality-reversal extension to two-node Weyl-semimetal models; (iii) an error bound and condition-number structure for tomographic reconstruction under a linear-response probe model. Illustrations include a glue-generation mechanism, a one-loop algebraic renormalization flow whose feeding constant coincides in magnitude with the $\mathfrak{su}(2)$ Casimir, closed-form $\mu=0$ inter-node spectra, and a UTe$_2$ two-phase analysis.

Understanding quantum phases of matter has long relied on physicists' intuition and mathematical tools such as symmetry and topology. Remarkably successful as these approaches have been, they provide no universal way to explore a Hamiltonian space whose organizing principle is not known in advance. In this work, we introduce a fully autonomous system combining differentiable programming and unsupervised learning for quantum phase discovery. The search evaluates ground-state data along an adaptive trajectory rather than on a predetermined parameter grid. We demonstrate the system with three different solvers and benchmark it against random sampling at equal ground-state-evaluation budgets. On a generalized cluster chain hosting up to $200$ distinct phases, the search finds up to $25$ more phases at the same budget, and matches random sampling given thirty times its budget. On a $50$-parameter Chern insulator, it reaches sectors not obtained by the simple harmonic constructions considered here, in a family whose inverse problem remains open, while recovering all sectors found by sampling. Our results establish autonomous, gradient-driven exploration of Hamiltonian space as a practical route to discovering quantum phases without phase labels or a prescribed target phase.

Electrolytes under an external magnetic field exhibit a Hall conductivity, much like metals and semiconductors. However, existing theories fail to quantitatively account for their measured Hall conductivities. To make progress toward such a theory, we develop a stochastic density functional framework for electrolytes in a magnetic field. This framework, which we dub odd SDFT, extends the celebrated stochastic density functional theory (SDFT) to incorporate transverse mobilities and chiral time-correlated noise. Using this framework, we calculate the Hall conductivity in the absence of hydrodynamic solvent effects through three approaches: (i) direct response, (ii) Green-Kubo relation, and (iii) a hybrid fluctuation-dissipation relation. We further show that odd SDFT applies more broadly to fluids with broken time-reversal and mirror symmetry, including odd-diffusive fluids and chiral active matter. Our results generalize the relaxation correction of Debye-Hückel-Onsager theory to magnetized electrolytes and provide a foundation for incorporating additional effects mediated by the solvent that could quantitatively reconcile theory and experiments.

Charge regulation refers to the ability of ionizable biomolecules and their counterparts to adjust their ionization state in response to external perturbations, including changes in pH, ionic strength, or electrostatic interactions with neighboring charged species. Here, we use explicit-ion molecular dynamics / charge-regulation Monte Carlo simulations to compute the interaction force between two spherical, charge-regulated nanoparticles as a function of separation, and compare symmetric (chemically identical) and asymmetric (chemically complementary) surface configurations against the constant charge approximation. We find that charge regulation produces up to an order-of-magnitude stronger short-range attraction than constant charge for asymmetric nanoparticle pairs, particularly at low electrolyte concentration, and that charge regulation qualitatively alters the interaction between symmetric, chemically identical nanoparticles, driving a crossover from net repulsion to net weak-attraction as ionic strength decreases. This transition is not observed under the constant charge assumption which shows that charge regulation is not a minor correction but can change both the strength and the sign of nanoscale electrostatic interactions, with implications for the assembly and stability of charge-regulated colloidal systems

Structural observations in polymer chemistry are often rationalized through underlying mechanistic insights. The study of families of mechanisms - and the phenomenology and lawlike behavior that can accompany them - is less common. Here we construct a theory that links a mechanistic feature - the number of nearest neighbors $k$ that influence monomer incorporation - with the accessible copolymer sequence space. We find that the reaction mechanisms can be mapped 1-to-1 to a regular de Bruijn graph of degree $k$. We calculate the periodic copolymer sequences as function of neighbor index $k$, and number of monomers $s$. We show that the number of periodic sequences grows explosively with $s,k$, bounded from below by $s!^{s^{k-1}}/s^k$. We find that periodic k-polymerization is governed by several simple laws describing allowed sequences, number of specific reactions, repeating unit length and the allowed and disallowed sequence coexistence in block copolymers. We formulate Simple Assembly Rules (SAR) that capture commonly observed behavior and design of literature systems, and characterize the possible k-polymerizations they are allowed to access ($k\leq2$) as function of symmetries and illustrate our findings with reported examples from the coordination chemistry and supramolecular chemistry literature. We discuss chemical-structural contributions by which nontrivial ($k>1$) sequences are formed, highlighting the importance steric hindrance, long-range interactions and degrees of freedom.

Phase diagrams and energy surfaces require low-energy states across a family of Hamiltonians, but solving each parameter point independently is prohibitively expensive. An important question is not how a single labeled eigenstate behaves under parameter variation, but how much information about the low-energy sector is contained in a small set of reference wavefunctions. We show that the physically relevant object is the isolated low-energy subspace itself: it remains well defined through degeneracies and level crossings, and it can be learned efficiently from nearby sampled states. Working in this subspace, we prove that a sampling pattern cancelling the first $q$ nonconstant response orders yields an energy-density error bounded by $d^{2(q+1)}$ for every retained level, where $d$ is the parameter-space sampling distance. For a gapped local ground state on $n$ sites, locality sharpens this to $d^2(nd^2)^q$, identifying $nd^2$ as the natural scaling variable governing the effectiveness of higher-order information from sampled wavefunctions. In a local analytic regime this gives a sampling cost $K=\mathcal{O}([\log(1/\varepsilon)]^D)$ at fixed parameter dimension $D$. Numerical results on Heisenberg and transverse-field Ising chains confirm the distance scaling law and the $nd^2$ collapse. Beyond characterizing learnability, the scaling behavior further provides a finite-size probe of phase transitions near criticality.

X-ray absorption spectroscopy (XAS) is a powerful, element-specific probe for investigating the local structural and electronic properties of materials. However, quantitative analysis remains challenging, necessitating accurate first-principles spectral simulations. In this study, we benchmark first-principles simulations of Ti K-edge X-ray absorption near-edge structure (XANES) against experimental data for nine common titanium compounds. We systematically investigate key physical effects, including quadrupole excitations, thermal disorder, and many-body shake-up. Our results demonstrate that quadrupole excitations and thermal disorder are essential for capturing accurate pre-edge features, while many-body shake-up effects significantly influence the spectral shape of the main- and post-edge regions. By incorporating these effects alongside a band-theory treatment of the core-hole final state, our simulated spectra achieve excellent agreement with experimental data for most of the systems, as evidenced by high similarity scores. The shoulder peak in BaTiO$_3$ at 4980 eV in the experiment is largely missing in simulation. Further analysis shows that more accurate electronic structure theory than semi-local density functional theory is required to capture the correlation effects of the Ba $4f$ orbitals and that defects, such as oxygen vacancies, may also contribute to the shoulder. Beyond tackling specific titanium material systems, this work establishes a robust workflow for generating high-fidelity Ti K-edge XANES databases for titanium compounds, providing a framework that can be generalized to a broad range of materials.

We investigate the positional statistics and thermodynamic properties of a Brownian particle confined in a Harmonic trap. The stiffness of the particle fluctuates in time as the square of the Brownian process. First, in the absence of a thermal bath, we investigate the probability density function of the position of the particle at time $t$. Then, we provide an expression to compute the $n$th positional moment. We evaluate the first four positional moments and discuss their asymptotic behavior in the long-time limit. In contrast to previously studied models of fluctuating stiffness, the current model describes a non-stationary process. Furthermore, we provide the exact expression for the average work performed on the system and the average heat exchanged by the particle with the bath. Their long time behavior again reflects the non-stationary nature of the process. Our theoretical predictions are supported by numerical simulations.

We investigate the dynamics of full counting statistics (FCS) of the growth of the total number of fermions in a one-dimensional non-interacting lattice subjected to a localized particle gain (source) at one edge. The dynamics of the setup is modeled by the Gorini–Kossakowski–Sudarshan–Lindblad (GKSL) quantum master equation. We recast the counting problem that involves counting particle number at every lattice site to a problem where only the local injected site is involved. We employ the Schwinger-Keldysh path integral formalism within the GKSL framework and derive an analytical expression for the cumulant generating function at arbitrary times and obtain a Levitov-Lesovik type formula in the long-time limit, earlier derived for boundary driven setups in the steady-state. For clean lattices with either short- or long-range hopping, supporting single-particle delocalized eigenstates, we show that all cumulants grow linearly with time in the asymptotic regime. Our analytical results are in excellent agreement with direct numerical simulations. These findings establish a general framework for characterizing FCS and quantum fluctuations in driven open fermionic systems with localized particle injection.

The negatively charged boron vacancy is an optically addressable spin centre in hexagonal boron nitride (hBN), but bringing two vacancies together introduces electronic interactions absent from the isolated-defect picture. Here we use density-functional theory at total charge q = -2 to show that atomic-scale placement reverses the preferred collinear spin alignment in monolayer hBN. Among seven configurations, the closest pair, separated by 4.3 angstrom, favours parallel alignment by 27.6 meV within the semilocal approximation. Moving one vacancy by a single lattice vector reverses the preference, and a 7.5 angstrom pair favours antiparallel alignment by 50.7 meV. Numerical controls change these two reference splittings by less than 1 meV; hybrid-functional calculations retain their signs while substantially changing their magnitudes. Local distortions connect the antiparallel preference at 7.5 angstrom to changes in vacancy-state hybridization along an intervening atomic chain. The closest pair instead exhibits a contact-localized spin-density contrast and constrained angular energies that depart from the bilinear Heisenberg form. These results identify a placement-sensitive regime of interacting defects and provide a microscopic foundation for investigating coupled spin centres in atomically thin materials.

Predicting the full spin Hall conductivity tensor of a magnetic crystal is difficult because crystallographic and magnetic symmetries do not constrain all parts of the response in the same way. Here, we separate the spin Hall conductivity of altermagnets into time-reversal-even and time-reversal-odd channels and combine symmetry analysis with first-principles calculations for six representative compounds spanning distinct crystallographic classes. The even channel follows crystallographic selection rules consistent with its Berry-curvature Fermi-sea origin. The odd channel is set by magnetic symmetry and can be reshaped by antiunitary operations whose spatial parts originate from screw or glide symmetries. Momentum-resolved analysis further links the even response to spin-orbit-driven avoided crossings and the odd response to anisotropic near-Fermi-level spin-current response textures. By converting crystallographic and magnetic symmetry operations into linear constraints on the full 27-component SHC tensor, this framework provides a computational prescreening route for identifying symmetry-allowed spin Hall channels before dense first-principles transport calculations. Extending the same analysis to 62 spin-split collinear antiferromagnets yields a magnetic-point-group tensor atlas, identifying design limits such as the complete 13/14tensor partition in CuF2 and the one-parameter time-odd tensor compression in MnSe.

Reduced descriptions of unresolved fluctuations are commonly based on Gaussian processes, although many realistic forcings have finite correlation times and a renewal structure. For memoryless step (Kubo–Anderson) noise, we show that the reduced dynamics admit two exact and complementary descriptions: a kernel representation governed by the Boolean cumulants of the jump distribution, and a frozen-noise representation adapted to stationary probability densities. For exponentially distributed waiting times, the totally time-ordered $G$-cumulants coincide with the Boolean cumulants of the jump law, and the memory kernel is resummed exactly as the Boolean generator $\eta$ evaluated on a resolvent operator. Second-order closure is exact if and only if the jump law is symmetric Bernoulli; otherwise, the leading closure error is controlled by $(b_4/b_2)\lambda^2$. The Boolean hierarchy, however, acts on the kernel, not on the stationary measure. Stationary densities are approximated by replacing the jump law with its $N$-point Gauss quadrature: each surrogate preserves all multi-time correlations up to order $2N-1$ for any waiting-time law, its kernel is a Padé resummation of the Boolean one, and it is itself an exactly solvable renewal problem. For the linear system with linear multiplicative interaction (LIMI/CAM), the frozen-noise representation reduces the dynamics to a random affine recursion and yields exact support boundaries, singularity exponents and Kesten tail indices, confirmed numerically. Rates, moments and closure errors are governed by the Boolean hierarchy, whereas stationary densities are determined by the geometry of the jump distribution. For memoryless renewal noise, the combinatorial structure controlling finite-correlation reductions is Boolean.

Quantum computing offers a promising route for electronic-structure calculations, but practical condensed-matter applications often require solving large families of related Hamiltonians arising from $\mathbf{k}$-point sampling, compositional variation, defects, and changes in system size. Here, we develop strategies for transferring variational information between related Hamiltonians to accelerate quantum simulations. For Hamiltonians of the same embedded size, optimized variational parameters are transferred between related calculations. For different sizes, we introduce Augmented Ansatz Reuse for Target Initialization (AARTI), which transfers compatible Pauli-generator structure and optimized source parameters, then augments the ansatz with target-specific generators. Our workflow combines density functional theory, Wannier downfolding, embedded tight-binding Hamiltonians, variational quantum algorithms, and neural-network quantum states, with quantum-circuit simulations implemented using NVIDIA's CUDA-Q platform. Using Li$_x$CoO$_2$ as a representative battery cathode material, we study Hamiltonian families spanning multiple delithiation levels, dense $\mathbf{k}$-point meshes, and increasing sizes. Parameter and ansatz transfer substantially reduce the optimization steps required to solve these related Hamiltonians while maintaining the common target accuracy, with lower terminal errors in several cases. The calculated electronic-structure evolution with delithiation exhibits pronounced non-rigid-band behavior consistent with experiment. These results establish a framework for exploiting similarity among related Hamiltonians to improve the efficiency and scalability of quantum workflows for realistic condensed-matter systems.

We study three particles on the square lattice with contact interactions of infinite strength, for all total quasimomenta, for three statistics: three identical bosons, two identical fermions plus a third particle, and two identical bosons plus a third particle. Previous work treated only the trimer and zero quasimomentum. Here the atom-dimer sector is analyzed on the whole Brillouin zone. A Feshbach-Schur reduction onto the infinitely degenerate eigenvalue 1 of the pair-contact operator gives explicit effective Hamiltonians with proved first-order error. The threshold problem reduces to a 4x4 Hermitian matrix criterion built from the two-point resistances of the square lattice, and hence to a quartic polynomial. This yields the complete atom-dimer zone and the critical mass ratio on the Brillouin zone, with bound between 1 and pi/(pi-2), and closed forms at all symmetry points. We prove: the zones in closed form; the critical mass ratio with exact value pi/(pi-2) at zero quasimomentum, reproducing a numerical value; at most two atom-dimer states for every quasimomentum and mass ratio; the onset laws, an essential singularity on the zone boundary and a linear-over-logarithm onset in the pure p-wave; two exact dualities showing that a change of statistics is equivalent to a shift of quasimomentum by pi; and the global range of the second fermionic threshold. The onset laws admit a renormalization-group reading: the inverse lattice Green function is a marginal s-wave coupling, binding energies arise by dimensional transmutation with lattice scale 16, and the zone boundary is of marginal (BCS/Kondo) type rather than of Berezinskii-Kosterlitz-Thouless type. All constants are verified independently by lattice quadrature, computer algebra, exact diagonalisation, and infinite-lattice solvers.

We show that stronger interactions protect periodically driven time-crystal order against dephasing but destabilise order under random multipolar drives, and that coordination matters beyond the total interaction strength. We studied a disordered kicked Ising model of $N=12$ and $16$ spins with imperfect $\pi$ pulses and per-site dephasing by exact diagonalisation, comparing a periodic drive, random multipolar drives of order $n=0,1,2$ and the Thue-Morse sequence, and separated coupling strength from coordination by comparing a grid with a ring at equal total interaction strength $zJ$. For the periodic drive the coherence time scales approximately as $1/\gamma$, and stronger coupling reduces the transverse tilt on which dephasing acts. For multipolar drives of order $n\ge1$, doubling the coupling on a ring shortens the coherence time to $0.54$ ($n=1$), $0.37$ ($n=2$) and $0.44$ (Thue-Morse) at $N=16$, while random signs ($n=0$) are unaffected. A disorder scan supports a toggling-frame picture in which interactions spoil the block cancellation of the pulse error. At equal $zJ$ the grid outlives the ring by $2.15$ ($N=12$) and $2.78$ ($N=16$) for the periodic drive despite an identical transverse tilt, a coordination effect beyond this picture. All ratios hold under three definitions of the coherence time.

We investigate three-component Hubbard models on a bipartite lattice in the presence of a trans?verse field. Unlike the two-component Hubbard model, where the {\eta}-pairing symmetry survives the transverse field, the three-component model possesses neither {\eta}-pairing symmetry nor conservation of the particle number of each component. We introduce a generalized {\eta}-pairing operator, formed as a hybridization of three types of two-component pairing operators, and employ the restricted spectrum-generating algebra to construct a family of exact eigenstates. These eigenstates exhibit off-diagonal long-range order. Furthermore, we construct an exact tensor-product state whose co?herent periodic dynamics provide an exact realization of quantum many-body scar dynamics while simultaneously exhibiting long-range magnetic order. We also propose three protocols for preparing this state via quench dynamics, and verify their effectiveness through numerical simulations.

Point defects in wide-bandgap semiconductors offer spin and photonic qubits in a solid-state platform, making them important building blocks for quantum information processing, communication, and sensing. While these systems have the strong advantage of room-temperature operation, intrinsic electron-phonon interaction induces broad phonon-sideband emission and weak zero-phonon-line transitions, limiting efficient spin-photon interfaces and scalable photon-mediated interaction. Here, we introduce a controlled heterophase interface based on the remote epitaxy technique as a crystal heterogeneity-engineering strategy. While stacking faults are treated as imperfections to be eliminated, our results instead show that crystal-phase interfaces can provide an additional degree of freedom to engineer defect-phonon interaction beyond the intrinsic properties of a single crystal. In comparison with single-phase 4H-silicon carbide (SiC) membranes, Vsi in 3C/4H heterointerface SiC exhibits a drastic enhancement of zero-phonon optical transitions, with a substantially narrower zero-phonon linewidth of 4.71 meV even at room temperature. These results establish heterophase-interface engineering as an effective route for tailoring defect-phonon interactions and realizing bright room-temperature quantum emitters with enhanced zero-phonon optical transitions.

A reproducible method for sustained catalyst-mediated growth of diamond and cubic boron nitride (cBN) wires has yet to be established. Catalyst-assisted growth has produced carbon and boron nitride nanotubes and a wide range of elemental, compound and alloy nanowires. Diamond and cBN wires could combine high specific stiffness and strength with heat conduction and electrical insulation. I propose vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) routes in which temperature, feed, catalyst or starting contact changes between formation of the first diamond or cBN segment and its continued growth. The approaches include switching from carbide or boron-rich starter wires, depositing catalyst on selected facets of existing crystals, and using local solid feedstock to supply the catalyst during initial growth. Historical diamond-whisker reports motivate renewed tests of diamond-metal contacts. The proposed experiments ask whether these contacts can favor tetrahedral bonding while maintaining a supply of atoms to the growing wire. Both single-crystal and polycrystalline products, from nanometer to micrometer and larger diameters, are of interest.

Semiconductor electronic devices are increasingly constrained by fundamental quantum tunneling effects and charge-based mechanisms, which severely limit further miniaturization, write-speed scaling, and environmental robustness of silicon-based technologies. These limitations are particularly prohibitive for deep-space exploration, where extreme temperatures, ultra-strong magnetic fields, and intense radiation rapidly incapacitate conventional electronics without massive shielding. Here, we present an intrinsically resilient, strain-mediated antiferromagnetic MnIr/PMN-PT edge processor that operates reliably as a bare die under temperatures up to 500 K, magnetic fields of 55 T, and radiation doses of 1.5 Mrad. By exploiting an input-modulated in situ self-refreshing encoding mechanism, the device performs nonlinear feature extraction and classification directly from raw analog signals, enabling an analog computing architecture that requires no time-frequency transformation. This architecture achieves 99.8% accuracy in speech recognition without digital preprocessing and 100% accuracy in astronaut visual object recognition. Furthermore, an all-hardware integrated drone vision system demonstrates real-time in situ command execution and autonomous navigation, delivering a terahertz-level response frequency and an ultra-low energy consumption of approximately 0.2 fJ per operation. This work expands the functional scope of antiferromagnetic devices beyond memory and logic, establishing them as a promising materials platform for energy-efficient physical computing and autonomous intelligence in extreme environments.

We study the spin-$1/2$ Kitaev-Heisenberg model on the square-hexagon-dodecagon lattice with a symmetry-preserving tri-coloring of the Kitaev exchanges. We focus on two cases: (i) the pure Kitaev model with anisotropic exchanges and (ii) the Kitaev-Heisenberg model with isotropic Kitaev exchange. In the absence of Heisenberg interactions, we use the standard mapping of the Kitaev model onto a quadratic Majorana-fermion problem in a $\mathbb{Z}_2$ gauge field. We find a gapped energy spectrum throughout the positive-coupling phase diagram, except at a single point where the twofold-degenerate energy bands form a Dirac cone. This unique gapped region corresponds to a toric code phase. However, depending on the couplings, vortex excitations on square, hexagonal, and dodecagonal plaquettes realize three distinct relative assignments to the $e$ and $m$ anyons. We determine these relative assignments from the physical fermion parity of the vortex sectors and locate their boundaries by tracking zero crossings of vortex-bound Majorana levels. For the isotropic Kitaev-Heisenberg model, we combine graph-based projected entangled-pair-state calculations, exact diagonalizations, and linear spin-wave theory to study the entire phase diagram. Apart from the toric code topological phases that are robust around the Kitaev limits, we obtain four collinear magnetically ordered phases that can be characterized by their local and relative orderings of hexagonal plaquettes. We also identify a special point at which the ground state is a product state.

Thermoelectric heat harvesting provides in principle a flexible, reliable way to convert heat into electric energy, thus recovering waste heat and powering off-net devices. However, thermoelectricity conversion efficiency is still low, despite the major efforts deployed over the last two decades to improve materials performances. A largely unexplored opportunity to increase harvesting efficiency is offered by converting heat flux dynamically. It was shown [D. Narducci et al., Mater. Today Phys. 54, 101713 (2025)] that when the temperature of the heat source is sinusoidally modulated, this leads to an increase of the maximum power by up to 50 %. In this paper we show how this approach can be further and significantly enhanced. We found that sinusoidal modulation can be outperformed by a different periodic modulation, leading to an increase of the power output by up to 100 % compared to the stationary case. Furthermore, we extended our analyses beyond the constant-property approximation, showing that the power output enhancement is robust, applying to any real material where the temperature dependence of all phenomenological coefficients is accounted for. This major power output enhancement offers a novel, immediately applicable pathway to overcome the efficiency limits of thermoelectric devices.

De novo crystal generation (DNG) models decide where to search in composition space and how to generate structures with one set of weights. We argue that discovery is better served by separating the two. A crystal structure prediction (CSP) model is a physical prior that should be improved by likelihood training, while rewards, including novelty measured against the search's own history, should act on a search over compositions. We introduce ANCHOR, a GRPO composition policy trained with multi-objective rewards around a frozen CSP model, and continuous adaptive novelty (CAN), a graded novelty score against known structures and a growing discovery history. Using the frozen CSP model as a fixed ruler under one evaluator, we test where adaptation should act. Replacing DNG compositions with ANCHOR's policy on the same CSP backbone raises MSUN from 11.4% to 47.6% and SUN from 1.1% to 22.1% at 99.9% formula uniqueness. Fine-tuning DNG models directly on the same rewards instead moves their composition marginal without raising their on-hull fraction. We show that KL-regularized fine-tuning of a DNG model can only reweight chemistry the pretrained model already supports by a bounded factor, while unregularized DNG fine-tunes move toward known or less stable chemistry. Even a stability-only reward routed into ANCHOR's CSP backbone roughly halves SUN relative to the frozen backbone, whereas likelihood training on structures found during search can improve a CSP backbone. Under MatterGen's evaluation pipeline, ANCHOR raises state-of-the-art MSUN from 29.2% to 41.3%, transfers without retraining to two further CSP backbones, and reaches 47.1% after distillation into Crystalite-CSP. As with any model optimised against a potential, its on-hull rate depends on that potential.

Strong coupling generally drives a subsystem away from the Gibbs state of its bare Hamiltonian at the bath temperature. We formulate a temperature–Hamiltonian ambiguity: the reduced equilibrium state fixes the dimensionless Gibbs generator, but does not by itself uniquely determine the local Hamiltonian and temperature entering a Gibbs representation. We propose an operational resolution in which the local Hamiltonian is identified from physical information independent of the stationary Gibbs parametrization. Whenever the exact reduced state is compatible with the Gibbs family generated by that independently identified Hamiltonian, it then determines a unique local temperature. An exactly solvable two-level-system–oscillator model makes the ambiguity explicit through state-equivalent descriptions based on temperature renormalization relative to a specified local Hamiltonian and Hamiltonian-of-mean-force level renormalization at the bath temperature. An exact bosonic model provides the complementary case in which retarded dynamics independently fixes a renormalized local excitation scale and thereby specifies the local Hamiltonian before the stationary populations determine the temperature. These results distinguish state representation from thermodynamic assignment and provide an operational framework for local thermodynamics beyond weak coupling.

Criticality in the Ising model is conventionally generated by Hamiltonian dynamics and controlled by temperature. Here we show that critical like behavior can emerge in an Ising system whose dynamics is completely independent of the Ising Hamiltonian and contains no temperature like parameter. We introduce an adaptive cluster dynamics in which spin connectivity is controlled by a local quiet time variable, the time elapsed since a spin was last updated. The Ising Hamiltonian enters only as an observable characterizing the resulting configurations. As the parameter $\alpha$, controlling the connectivity strength, is varied, the system undergoes spontaneous symmetry breaking accompanied by strong collective fluctuations. The cluster size distribution develops an extended power law regime, terminated by a small finite size hump at the largest scales, while the Ising energy exhibits a singular response to the variation of $\alpha$. These results show that memory dependent connectivity alone can generate collective critical behavior, revealing a route to nonequilibrium criticality without energy based dynamics.

We investigated the low-temperature thermal expansion of the $\alpha$ phase and the $\omega$ phase, a high-pressure polymorph of titanium, by X-ray diffraction measurements from approximately 5 to 300 K, together with first-principles calculations. Single-phase bulk polycrystalline $\omega$-Ti was synthesized at 7.7 GPa and 500 $^\circ$C and recovered to ambient pressure. Although the two phases exhibit very similar volumetric thermal expansion, their axial responses are markedly different. In $\alpha$-Ti, the $c$-axis thermal expansion coefficient becomes negative below approximately 50 K and reaches a minimum of $-0.71 \times 10^{-6}$ K$^{-1}$ at 20 K. Both experiment and theory indicate substantially smaller $c$-axis negative thermal expansion than previously reported from single-crystal length measurements. In contrast, $\omega$-Ti expands nearly isotropically along the $a$ and $c$ axes, and its $c/a$ ratio remains nearly temperature independent and close to the ideal bcc-derived value. The $c$/$a$ ratio of $\alpha$-Ti decreases with increasing temperature. Debye-Grüneisen analysis yielded Debye temperatures of $427 \pm 5$ K and $409 \pm 12$ K and effective Grüneisen parameters of $1.33 \pm 0.04$ and $1.23 \pm 0.04$ for $\alpha$-Ti and $\omega$-Ti, respectively. The first-principles calculations reproduce the volumetric thermal expansion of both phases and capture the overall trends of their axial responses.

We investigate the dynamics of a clean mobile impurity coupled to a bath subjected to a linear Stark potential as well as asymmetric hopping in one dimension. The impurity mediates resonant tunnelling in the bath whenever the interaction strength matches the Stark potential and leads to loss in the memory of the initial state of the bath particles. The non-Hermitian asymmetry does not shift these resonances but reshapes them directionally, and it destroys the bath's Stark-induced memory through the non-Hermitian skin effect. On the other hand, we find that the impurity is localised only within an intermediate range of Stark potential. At very weak tilt strengths the bath offers no potential to trap the impurity, while at strong tilt the bath freezes into a nearly periodic charge density wave that pushes the impurity towards partial localisation. Counterintuitively, the impurity localises in the intermediate regime where the bath's initial-state memory is strongly suppressed, yet a spatially inhomogeneous density profile persists. The interaction amplifies these density fluctuations, dressing the impurity with an effective disordered potential that traps it. Since the skin effect degrades this intermediate density distribution, the impurity localisation window shifts toward stronger tilt in the non-Hermitian regime.

Achieving high-fidelity and robust qubit manipulations is a crucial requirement for realizing faulttolerant quantum computation. Here, we demonstrate a single-hole spin qubit in a germanium quantum dot and characterize its control fidelity using gate set tomography. The maximum control fidelities reach 97.48%, 99.81%, 99.88% for the I, X/2 and Y /2 gate, respectively. These results reveal that off-resonance noise during consecutive I gates in gate set tomography sequences severely limits qubit performance. Therefore, we introduce geometric quantum computation to realize noiseresilient qubit manipulation. The geometric gate control fidelities remain above 99% across a wide range of Rabi frequencies. The maximum fidelity surpasses 99.9%. Furthermore, the fidelities of geometric X/2 and Y /2 (I) gates exceed 99% even when detuning the microwave frequency by +-2.5 MHz (+-1.2 MHz), highlighting the noise-resilient feature. These results demonstrate that geometric quantum computation is a potential method for achieving high-fidelity qubit manipulation reproducibly in semiconductor quantum computation.

It remains an open question whether the modular data $(S,T)$ together with the Whitehead-link matrix $W$ determine a modular tensor category up to ribbon equivalence. We answer negatively by constructing two braided-inequivalent Dijkgraaf–Witten modular categories for $(\mathbb Z/p\mathbb Z)^3$ for prime $p\ge5$ with identical $(S,T,W)$ and, more generally, identical Reshetikhin–Turaev invariants of all framed oriented links with at most two components under a single bijection of simple objects. The construction varies an alternating $3$-cocycle while fixing a quadratic cohomology class, using restriction to subgroups of rank at most two to match link invariants and the quadratic and alternating classes together to obstruct braided equivalence. A complete classification of modular tensor categories up to ribbon equivalence therefore requires invariants beyond those of colored framed links with at most two components. We also analytically evaluate an uncolored partition function on a closed oriented three-manifold that separates all $(p-1)/2$ equivalence classes in the family.

Hole spin qubits based on semiconductor quantum dots are promising for building future large-scale quantum computers owing to their all-electrical manipulation. However, abundant physical mechanisms of valence band holes lead to anisotropic qubit properties. There is an opportunity to prolong the coherence time and achieve high-fidelity qubit manipulations. Here, we report a single-hole spin qubit in a planar germanium quantum dot and investigate its anisotropic susceptibility to charge noise under an in-plane magnetic field. By correlating the longitudinal spin-electric susceptibility with qubit coherence and control performance, we identify an optimal operating point where the sensitivity to charge noise is minimized. We find that optimizing the magnetic-field orientation reduces the spin-electric susceptibility, resulting in a five-fold enhancement of the Hahn-echo coherence time and a nearly tenfold suppression of control infidelity. At the optimal operating point, gate set tomography demonstrates the maximum gate fidelity of 99.82 %. Our finding enhances the prospects of hole spin qubits for scalable quantum information processing.