A quantum mechanical Maxwell demon is proposed in a quantum dot setting. The demon avoids continuous-measurement-induced decoherence by exploiting an undetailed charge detector. The control of coherent tunneling via Landau-Zener-Stückelberg-Majorana driving allows for efficient feedback operations with no work invested. The local violation of the second law achieves simultaneous power generation and cooling. We discuss the response current fluctuations, and the demon backaction derived from failures, finding optimal performance in the nonadiabatic regime.

We study near-field radiative transfer of energy, angular momentum, and linear momentum between a nanoparticle and a plate consisting of magnetic Weyl semimetals, and demonstrate that these can be efficiently tuned by a relative angle between the Weyl node separations. This tunability originates from the coupling between the particle-induced rotational Poynting vector and the nonreciprocal surface plasmon polaritons supported by the plate. Remarkably, we uncover a counterintuitive regime in which both energy and angular momentum transfer are maximized when the Weyl node separations are antiparallel rather than parallel. This arises from optimal mode matching between the rotation direction of the particle's circular heat flux and the propagation direction of the surface plasmon polaritons in the antiparallel configuration.

Non-Markovian $1/f$ noise is a major source of decoherence in superconducting qubits, yet its low-frequency nature poses a significant challenge for accurate simulation. Here, we develop a hierarchical equations of motion (HEOM) framework that enables efficient and reliable modeling of qubit dynamics and gate operations under $1/f$ noise. Using this approach, we first show that perturbative quantum master equations fail to reproduce the correct dephasing dynamics of a qubit coupled to $1/f$ noise. We then analyze dynamical decoupling using the Carr-Purcell-Meiboom-Gill (CPMG) protocol with finite-duration pulses. The results reveal that errors accumulate linearly with parity effects in $X$-CPMG, quadratically in $Y$-CPMG, and are strongly suppressed in alternating $\mathit{XY}$ sequences. Finally, we extend the framework to simulate a two qubit cross-resonance gate and reconstruct the Pauli transfer matrix to characterize the error channels induced by $1/f$ noise. Together, these results establish HEOM as a robust and accurate method for simulating the slow non-Markovian $1/f$ noise in superconducting qubits and provide insights into error mechanisms in both single and two qubit gates.

We investigate the low-energy electronic properties of a two-dimensional topological semimetal hosted by a nonsymmorphic system with checkerboard antiferromagnetic order. Such a topological semimetallic state emerges only when the local magnetic moments align along the crystallographic direction, where the hopping is restricted to nearest neighbors and spin-orbit coupling acts between the next-nearest neighbors. We find that the quasiparticle states near Dirac or Weyl points exhibit pronounced anisotropy. Interplay of the spin-orbit coupling and magnetic moment orientation breaks the fourfold rotation symmetry, resulting in a strong directional dependence of the optical response. Using the $T$-matrix formalism, we further analyze quasiparticle interference for magnetic and nonmagnetic impurities exhibiting distinct sublattice- and spin-dependent features. The results highlight how the interplay between magnetic order and spin-orbit coupling governs anisotropic charge dynamics and impurity-induced interference, offering measurable signatures in optical and scanning tunneling spectroscopies.

Two-dimensional ferroelectric materials are widely used in advanced technologies and devices due to their unique physical properties. One of the device design strategies is the lateral heterostructures (LHS) which are easy to synthesize and precisely control. To tackle the challenge of large-scale LHS simulations, the Machine Learning Interatomic Potential (MLIP) can be utilized. Here we train the potential model specifically for monolayer GeTe and (Ge,Pb)Te LHS, which can respond to external electric fields. We investigate the thermal hysteresis and the dynamic properties including domain evolution during the ferroelectric phase transition of GeTe. According to the hysteresis loop under different temperatures and electric field frequencies, GeTe shows stable ferroelectric performance and tunability by electric fields. Additionally, we simulate and regulate multiple phases of the (Ge,Pb)Te LHS. With corrections for dipole interactions, the results show the relationship among the different states. Our research demonstrates that GeTe possesses good ferroelectric properties and highlights the application value of MLIP in the design and study of ferroelectric materials.

Recent neutron scattering and thermodynamic measurements suggest that Weyl electrons in the emergent Weyl semimetal SmAlSi mediate unconventional magnetic interactions and induce spiral magnetic order. In this work, we investigate the nature of these interactions by modeling long-range $f-f$ exchange mediated by itinerant $d$ electrons via the Ruderman-Kittel-Kasuya-Yosida mechanism, employing a material-specific tight-binding Hamiltonian obtained from first-principles calculations. The magnetic susceptibility is derived from the spin-spin correlation function based on the random phase approximation. Our results demonstrate that Fermi-surface nesting alone cannot account for the experimentally observed magnetic modulation at the wave vector (1/3, 1/3, 0); however, incorporating appropriate antiferromagnetic exchange interactions among the $d$ electrons yields the correct propagation vector. The spin-texture analysis reveals a configuration that is close to a cycloidal spin structure, preserving combined glide and time-reversal symmetry, and reflecting an intricate competition between inter- and intrasublattice interactions in SmAlSi.

We report inelastic neutron scattering (INS) measurements on the magnetically frustrated $S=\frac{1}{2}$ sawtooth-chain compound atacamite ${\mathrm{Cu}}_2\mathrm{Cl}{\left(\mathrm{OH}\right)}_3$ featuring inequivalent Cu(1) and Cu(2) sites. Transverse to the sawtooth chains, INS reveals two dispersive spin-wave modes and a gap of at least 0.75 meV. This behavior is rationalized within a zigzag-chain model of Cu(2) spins in an effective magnetic field of Cu(1) spins. The model is compatible with first-principles calculations and accounts for INS dispersions within linear spin-wave theory calculations. Our results reveal a unique case of an effective separation of energy scales between two differently oriented one-dimensional chains, with the zigzag-chain model being essential to fully characterize the low-energy magnetism of atacamite.

${\mathrm{GdCo}}_2{\mathrm{B}}_2$ is a member of the ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ family of compounds which exhibits good magnetocaloric properties associated with antiferromagnetic orderings in the temperature range for hydrogen liquefaction applications. As antiferromagnetic compounds typically do not exhibit a large magnetocaloric effect, understanding the magnetic orderings in ${\mathrm{GdCo}}_2{\mathrm{B}}_2$ could help uncover more magnetocaloric compounds that rely on antiferromagnetic ordering. ${\mathrm{GdCo}}_2{\mathrm{B}}_2$ exhibits four antiferromagnetic phase transitions at 22 K, 18.5 K, 13 K, and 7 K. Due to the difficulty of conducting neutron diffraction measurements on compounds containing affordable natural Gd, the microscopic magnetic structures have so far not been investigated. In this study, by using high energy neutrons and devising special sample preparations for lower energy neutrons, powder neutron diffraction patterns of ${\mathrm{GdCo}}_2{\mathrm{B}}_2$ have successfully been measured. A long-period incommensurate magnetic ordering with ${\mathit{k}}_1=\left(0.053100\right)$ was seen at 20 K. The propagation vector of the incommensurate structure shifted to ${\mathit{k}}_1=\left(0.07100\right)$ at 16 K, and an additional $\mathit{k}=\left(000\right)$ ferromagnetic component was observed. At 10 K, two incommensurate propagation vectors of ${\mathit{k}}_1=\left(0.073100\right)$ and ${\mathit{k}}_2=\left(0.07310.07310\right)$, which shifted to ${\mathit{k}}_1=\left(0.074100\right)$ and ${\mathit{k}}_2=\left(0.07410.07410\right)$ at 6 K, were observed to coexist. By considering only the ${\mathit{k}}_1$-modulation, two possible magnetic structures below 10 K are reported to describe the data, either $\mathit{ac}$-cycloid structure with constant moment at each Gd site or ellipsoidal $\mathit{ab}$-cycloid structure. Exchange interaction energy calculations indicated that the long-period antiferromagnetic ordering in ${\mathrm{GdCo}}_2{\mathrm{B}}_2$ is energetically close to the ferromagnetic state due to the strong competition between ferromagnetic and antiferromagnetic exchange interactions, which plays an essential role for the emergence of the large magnetocaloric effect in ${\mathrm{GdCo}}_2{\mathrm{B}}_2$.

The recent discovery of high-pressure hydrides has revealed superconducting critical temperatures ($T_{\mathrm{c}}$) surpassing 200 K above 150 GPa, advancing the pursuit of room-temperature superconductivity. Although ongoing research aims to elevate the $T_{\mathrm{c}}$ in these systems further, addressing the challenges associated with their high-pressure synthesis remains an essential task. Inspired by the recent prediction of high-temperature superconductivity in $\mathrm{La}{\mathrm{Sc}}_2{\mathrm{H}}_{24}$, we explore its isostructural counterparts $\mathrm{Ce}{\mathrm{Sc}}_2{\mathrm{H}}_{24}$ and $\mathrm{Th}{\mathrm{Sc}}_2{\mathrm{H}}_{24}$ using ab initio methods. Our calculations reveal that chemical substitution of La with Ce or Th substantially lowers the stabilization pressure. Specifically, the Ce and Th variants are found to be thermodynamically stable above 185 and 200 GPa, respectively, compared to 242 GPa for $\mathrm{La}{\mathrm{Sc}}_2{\mathrm{H}}_{24}$. Harmonic calculations yield $T_{\mathrm{c}}$ values of 204 K at 200 GPa for $\mathrm{Ce}{\mathrm{Sc}}_2{\mathrm{H}}_{24}$ and 230 K at 210 GPa for $\mathrm{Th}{\mathrm{Sc}}_2{\mathrm{H}}_{24}$. Notably, when anharmonic effects are included for $\mathrm{Ce}{\mathrm{Sc}}_2{\mathrm{H}}_{24}$, it reduces its dynamic stability pressure to 100 GPa while retaining a high $T_{\mathrm{c}}$ of 216 K. The crucial synergy between chemical precompression mediated by delocalized $f$ electrons, which substantially reduces the stabilization pressure, and the inclusion of anharmonic quantum nuclear effects, which provides a more precise physical description leading to a further dramatic reduction of the dynamic stability pressure, is essential for accurately predicting the high-$T_{\mathrm{c}}$ superconductivity in these hydrides at experimentally relevant pressures. Our results establish a foundation for targeted exploration of high-$T_{\mathrm{c}}$ superconductors under milder experimental conditions.

The cooperative effect of Rashba spin-orbit coupling (SOC) and Coulomb attraction in stabilizing topological spin-triplet excitonic condensates (ECs) in two-dimensional electron-hole systems in external magnetic field is investigated by using an unrestricted Hartree-Fock approach combined with the random-phase approximation. At weak electron-hole Coulomb interaction, the intraband Rashba SOC induces spin-momentum locking and topological semimetal behavior, while stronger interaction stabilizes spin-triplet ECs. Increasing the valence-band SOC drives a transition from a topologically trivial EC with coexisting spin-up and spin-down components to a topological spin-up EC only with quantized Chern number $C=2$. The dynamical excitonic susceptibility reveals a soft spin-up triplet mode acting as the precursor of the condensate. These results establish a microscopic mechanism for Rashba SOC-induced topological ECs and suggest realistic situations for their realization in noncentrosymmetric Janus transition-metal dichalcogenides and twisted van der Waals heterostructures.

The low-temperature metallic phase of $1\mathrm{T}\text{−}{\mathrm{TaS}}_2$ may originate from the current- and voltage-driven destabilization of the commensurate charge density wave in a strongly correlated Mott-insulator, alongside the robust yet rarely realized influence of intrinsic electronic distortions. Electrical pulse-driven transport, combined with the second harmonic response, reveals abrupt switching, negative differential resistance, and multiscale domain-wall reorganization. The free-energy analysis identifies a critical order parameter threshold for the Mott-metal transition, with scaling exponents ($\beta \approx 1.3$) consistent with two-dimensional percolation. The sparse limit fractal dimension $D_f\approx 0.3$ at 10 K, rising to $\approx 0.9$ at 300 K, reflects the hierarchical evolution of the conductive pathways throughout the temperature. These findings establish a direct connection between fractal percolation, pulse-induced instabilities, and correlated electron transport, offering a framework for controlled access to nonequilibrium phase transitions in low-dimensional quantum materials.

In this work, we investigate the physical origin of ferroelectricity in monolayer ${\mathrm{Bi}}_2{\mathrm{TeO}}_5$ using first-principles theoretical approaches. It is revealed that the room-temperature ferroelectric order arises from the cooperative interplay between strong individual dipoles and moderate interdipole interactions. Based on the first-principles energy landscape, a phenomenological model is constructed to predict the temperature-dependent phase transition behavior via Monte Carlo simulations, in agreement with experimental observations. The finite-temperature results further indicate a small ferroelectric domain size, consistent with the moderate strength and relatively localized effective range of the interdipole interactions. Additionally, the experimentally observed antiferroelectriclike order induced by intercalated buffer layers is demonstrated to be a robustly pinned ${180}^{\circ }$ ferroelectric domain wall rather than a genuine antiferroelectric phase.

Motivated by the order fractionalization in the Kitaev-Kondo model, we propose an exactly solvable spin-charge ladder model to study order fractionalization with discrete symmetry. The spin-charge ladder is composed of a spin chain and a superconducting wire coupled via an Ising-type interaction, and we obtain the exact solution in the flat band limit. The exact solution reveals the ${\mathbb{Z}}_2$ order fractionalization with dual symmetry breaking and intertwined order parameters. We investigate the topological phase transition of the spin-charge ladder via the spectral chiral index, and we identify the correlated topological superconductor phase with gapped ${\mathbb{Z}}_2$ Kondo flux excitations. We demonstrate that Majorana spinons generate odd frequency pairing in the superconducting wire. We also discuss the order fractionalization from the perspective of ${\mathbb{Z}}_2$ lattice gauge theory.

We revisit gradient-based optimization for infinite projected entangled-pair states, a tensor network ansatz for simulating many-body quantum systems. This approach is hindered by two major challenges: the high computational cost of evaluating energies and gradients, and an ill-conditioned optimization landscape that slows convergence. To reduce the number of optimization steps, we introduce an efficient preconditioner derived from the leading term of the metric tensor. We benchmark our method against standard optimization techniques on the Heisenberg and Kitaev models, demonstrating substantial improvements in overall computational efficiency. Our approach is broadly applicable across various contraction schemes, unit-cell sizes, and Hamiltonians, highlighting the potential of preconditioned optimization to advance tensor network algorithms for strongly correlated systems.

Quantum chemistry is envisioned as an early and disruptive application for quantum computers. Yet, closer scrutiny of the proposed algorithms shows that there are considerable difficulties along the way. Here, we propose two criteria for evaluating two leading quantum approaches for finding the ground state of molecules. The first criterion applies to the variational quantum eigensolver (VQE) algorithm. It sets an upper bound to the level of imprecision/decoherence that can be tolerated in quantum hardware as a function of the targeted precision, the number of gates and the typical energy contribution from states populated by decoherence processes. We find that decoherence is highly detrimental to the accuracy of VQE and performing relevant chemistry calculations would require performances that are expected for fault-tolerant quantum computers, not mere noisy hardware, even with advanced error mitigation techniques. Physically, the sensitivity of VQE to decoherence originates from the fact that, in VQE, the spectrum of the studied molecule has no correlation with the spectrum of the quantum hardware used to perform the computation. The second criterion applies to the quantum phase estimation (QPE) algorithm, which is often presented as the go-to replacement of VQE upon availability of (noiseless) fault-tolerant quantum computers. QPE requires an input state with a large enough overlap with the sought-after ground state. We provide a criterion to estimate quantitatively this overlap based on the energy and the energy variance of said input state. Using input states from a variety of state-of-the-art classical methods, we show that the scaling of this overlap with system size does display the standard orthogonality catastrophe, namely an exponential suppression with system size. This in turns leads to an exponentially reduced QPE success probability.

We report quantum oscillations in magnetoresistance that are periodic in magnetic field ($B$), observed at the interface between (${\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7}$)(${\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}$)${\mathrm{O}}_3$ and ${\mathrm{SrTiO}}_3$. Unlike Shubnikov–de Haas oscillations, which appear at magnetic fields $>7\mathrm{T}$ and diminish quickly as the temperature rises, these $B$-periodic oscillations emerge at low fields and persist up to 10 K. Their amplitude decays exponentially with both temperature and field, specifying dephasing of quantum interference. Increasing the carrier density through electrostatic gating results in a systematic reduction in both the amplitude and frequency of the oscillations, with complete suppression beyond a certain gate voltage. We attribute these oscillations to the Altshuler-Aronov-Spivak effect, likely arising from naturally formed closed-loop paths due to the interconnected quasi-one-dimensional conduction channels along ${\mathrm{SrTiO}}_3$ domain walls. The relatively long phase coherence length ($\simeq 1.8\mu \mathrm{m}$ at 0.1 K), estimated from the oscillation amplitude, highlights the potential of complex oxide interfaces as a promising platform for exploring quantum interference effects and advancing device concepts in quantum technologies, such as mesoscopic interferometers and quantum sensors.

The magnon orbital Hall effect in two-dimensional (2D) honeycomb antiferromagnets driven by pseudogauge fields induced by surface acoustic waves (SAWs) has been investigated. Unlike previous studies where the orbital Hall response of magnons was primarily driven by temperature gradients, we demonstrate that strain-induced pseudoelectric fields generated by Rayleigh-type SAWs can also induce a finite magnon orbital Hall current. In the absence of Dzyaloshinskii-Moriya (DM) interaction, the contribution originates solely from the valley-independent pseudoelectric field ${\mathbf{E}}_1^s$, whereas the valley-contrasting field ${\mathbf{E}}_2^s$ gives no net contribution. When the DM interaction is introduced, the valley degeneracy in the magnon bands is lifted, leading to a population imbalance between the $K$ and $K^{\prime }$ valleys, which activates additional contributions from ${\mathbf{E}}_2^s$, and consequently modifies the anomalous orbital Hall conductivity of magnons. Our results reveal a distinct mechanistic pathway to control magnon orbital transport using SAWs, offering opportunities for valley-orbitronics and magnonic device functionalities in 2D magnetic systems.

The recent surge of interest in magnetism in van der Waals (vdW) crystals has opened opportunities for exploring antiferromagnetic order and spin dynamics in the two-dimensional limit. Here, we present a comprehensive study of the layered antiferromagnetic ${\mathrm{NiCl}}_2$, combining static magnetization, broadband microwave absorption spectroscopy, and tunneling transport measurements. Despite early studies of bulk ${\mathrm{NiCl}}_2$, our systematic approach provides a modern reexamination of its magnetic properties with several new insights. We find nearly identical in-plane and out-of-plane saturation fields once demagnetization corrections are applied, as well as a pronounced spin-flop transition at low fields. The Néel transition temperature ($T_{\mathrm{N}}$) shows minimal anisotropy at low fields but undergoes a distinct crossover between in-plane and out-of-plane field orientations at high fields. Spin resonance experiments reveal strongly anisotropic behavior: robust in-plane antiferromagnetic resonance modes are observed over a broad gigahertz frequency and temperature range, while out-of-plane measurements show suppressed response near $T_{\mathrm{N}}$. This enables the extraction of the effective $g$ factor across a wide temperature window. Furthermore, tunneling magnetoconductance through a thin ${\mathrm{NiCl}}_2$ flake barrier exhibits field-enhanced transmission with clear signatures of the spin-flop and saturation fields. Our findings establish ${\mathrm{NiCl}}_2$ as a model vdW antiferromagnet for studying the interplay of static order, spin dynamics, and tunneling transport, highlighting its potential for future applications in two-dimensional spintronics.