Donor-based spin qubit offers a promising silicon quantum computing route for building large-scale qubit arrays, attributed to its long coherence time and advancements in nanoscale donor placement. However, the state-of-the-art device designs face scalability challenges, notably in achieving tunable two-qubit coupling and ensuring qubit addressability. Here, we propose a surface-code-compatible architecture, where each module has both tunable two-qubit gates and addressable single-qubit gates by introducing only a single extra donor in a pair of donors. We found that to compromise between the requirement of tunability and that of addressability, an asymmetric scheme is necessary. In this scheme, the introduced extra donor is strongly tunnel-coupled to one of the donor spin qubits for addressable single-qubit operation, while being more weakly coupled to the other to ensure the turning on and off of the two-qubit operation. The fidelity of single-qubit and two-qubit gates can exceed the fault-tolerance threshold in our design. Additionally, the asymmetric scheme effectively mitigates valley oscillations, allowing for engineering precision tolerances up to a few nanometers. Thus, our proposed scheme presents a promising prototype for large-scale donor-based spin quantum processors.

We propose various tight-binding models with arbitrary Chern number $n$, constructed from one-dimensional (1D) tight-binding models with winding number $m$, where $n$ is divisible by $m$. Our approach relies on the Thouless adiabatic charge pumping mechanism applied to 1D insulators, where the cyclic time parameter is reinterpreted as an additional momentum dimension. Equivalently, this yields protocols for adiabatically pumping $n$ charges per cycle in a 1D lattice with winding number $m$. As a concrete example, we use an extended Su-Schrieffer-Heeger (SSH) model with long-range hoppings, which allows for arbitrary winding numbers. By promoting the cyclic parameter to a momentum coordinate, we generalize this 1D model to two dimensions (2D), producing a square-lattice model with an arbitrary Chern number. Furthermore, we derive the full real-space Hamiltonians for other lattice geometries, including hexagonal and triangular lattices, by deforming the square lattice. We analyze the role of lattice geometry and identify the simplest Chern insulator models with rotational symmetry—both with and without spin degrees of freedom. This provides alternatives to the Haldane model for realizing Chern insulators and generalizes the construction to arbitrary Chern numbers.

In easy-plane magnets, the spin superfluid phase was predicted to facilitate coherent spin transport. So far, experimental evidence remains elusive. In this Letter, we propose an indirect way to sense this effect via the spin superfluid quantum interference device (spin SQUID), inspired by its superconducting counterpart (rf SQUID). The spin SQUID is constructed as a quasi-one-dimensional (1D) magnetic ring with a single Josephson weak link, functioning as an isolated device with a microwave response. The spin current is controlled by an in-plane electric field through Dzyaloshinskii-Moriya interaction. This interaction can be interpreted as a gauge field that couples to the spin supercurrent through the Aharonov-Casher effect. By investigating the static and dynamic properties of the device, we show that the spin current and the harmonic frequencies of the spin superfluid are periodic with respect to the accumulated Aharonov-Casher phase and are, therefore, sensitive to the radial electric flux through the ring in units of an electric flux quantum, suggesting a potential electric-field sensing functionality. For readout, we propose to apply spectroscopic analysis to detect the frequency shift of the harmonic modes induced by this magnonic Stark effect.

The broken inversion symmetry of the magnetic lattice is normally described by Lifshitz invariants in a micromagnetic energy functional. Three exceptions are the lattices with $T_d, C_{3h}$, and $D_{3h}$ point group symmetries. For such lattices all Lifshitz invariants are forbidden despite broken inversion symmetry. In these cases the inversion symmetry breaking of the corresponding magnets is reflected by four-spin chiral invariants that are not related to the Dzyaloshinskii-Moriya interaction. The experimental detection of four-spin chiral interactions is an important task that has yet to be performed. We propose that the four-spin chiral interaction can be probed by energy-selective magnon relaxation in the two-dimensional ferromagnet ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ that possesses $D_{3h}$ point group symmetry.

We present the results of recent experiments conducted on the Sandia Z machine and a new tabular equation of state for ${\mathrm{B}}_4\mathrm{C}$. The equation of state was calibrated to a combination of density functional calculations reported here and fits to preexisting data. It was constructed partly to recover the effects of a shock-driven, polymorphic phase transition of unknown character beginning at particle velocities of just under 3 km/s (shock pressures of 95 GPa). Some of the Z experiments included sound speeds determined by the overtaking rarefaction method, from which we calculate the Grüneisen parameter and compare with previous experiments conducted at the OMEGA laser [Fratanduono et al., Phys. Rev. B 94, 184107 (2016)], our own first principles calculations, and another recent tabular equation of state [Zhang et al., Phys. Rev. E 102, 053203 (2020)]. We also compare our results with previous static compression, thermophysical, and melt studies, finding mixed consistency. We predict the onset and completion of shock melting at 225 and 265 GPa, respectively, and predict a melt curve that is largely flat to pressures of several hundred GPa.

Oxide materials, particularly ternary and quaternary oxides, typically exhibit low thermal conductivities. However, a recent experiment revealed that the trirutile compound ${\mathrm{Ga}}_2{\mathrm{TeO}}_6$ possesses a relatively high lattice thermal conductivity of approximately $20{\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$ at 323 K, significantly exceeding that of most ternary oxides. Here, we systematically investigate the lattice thermal conductivities of six trirutile materials using first-principles three-phonon calculations. For ${\mathrm{Ga}}_2{\mathrm{TeO}}_6$, the calculated room-temperature lattice thermal conductivities are 22.6 and $25.8{\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$ along the $a$ and $c$ directions, respectively, in good agreement with the experimental data. By substituting lighter elements into ${\mathrm{Ga}}_2{\mathrm{TeO}}_6$, we predict that their lattice thermal conductivity can be further enhanced, potentially reaching $40{\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$ at room temperatures. We show that the trirutile materials consistently exhibit higher lattice thermal conductivities than most other ternary oxides, despite their complex structures and the presence of heavy elements, primarily attributed to their high bulk moduli, reaching up to 240 GPa. This work provides valuable insights into the thermal and mechanical behavior of trirutile oxides, which may stimulate further theoretical and experimental investigations.

We present an effective two-band model for infinite-layer nickelates ${\mathrm{NdNiO}}_2$ that consists of a $d$ band centered at the Ni site and an interstitial $s$-like band centered at the Nd site. To the large extent of the wave functions, we find intersite Coulomb interactions to be substantial. We then use the variational cluster approach together with mean-field theory to investigate magnetic and charge ordering. While tendencies towards charge modulation are found, they are weak and might be due to finite-size effects. Magnetic order is determined mostly by the filling of the $d$ band and hardly affected by including longer-ranged interactions. For a $d$-band density consistent with density-functional theory, magnetic ordering vanishes once quantum fluctuations are included to a sufficient spatial extent. Apart from self-doping, $d$ and $s$ bands remain largely uncoupled despite the presence of interorbital Coulomb interaction and (small) interorbital hopping.

We investigate the terahertz conductivity of conventional superconductors in Voigt and Faraday magneto-optical configurations. First, we review theoretical approaches describing the fundamental processes of suppression of superconductivity in magnetic field and how the in-gap states are filled. In the Voigt geometry, thin superconducting films are fully penetrated by the magnetic field which interacts with the spin, thus modifying the magnitudes of the optical gap and of the density of the condensate. In this configuration, we provide an alternative description of the recent experiments showing the gapless conductivity of a Nb film measured by Lee et al. [Nat. Commun. 14, 2737 (2023)], which better fits their data for magnetic fields above 1 T. In the Faraday geometry, we measured and analyzed the terahertz conductivity of three NbN films with varying thicknesses using the Maxwell-Garnett model, treating vortices as normal-state inclusions within a superconducting matrix. In both geometries, the optical conductivity can be comprehensively described by the model of Herman and Hlubina [Phys. Rev. B 96, 014509 (2017)] involving pair-conserving and magnetic-field-dependent pair-breaking disorder scattering processes.

Lee-Yang phase transition theory is a milestone in statistical physics. Its applications in realistic systems, however, had been substantially hindered by availability of practical schemes to calculate the Lee-Yang zeros. In this manuscript, we extend the scheme we have designed earlier [Phys. Rev. E 109, 024118 (2024)] and report simulation results for the melting temperature $\left(T\right)$ of ice Ih under ambient pressure $\left(p\right)$. The enhanced sampling technique is shown to be crucial for accessing Lee-Yang zeros accurately. The real and imaginary parts of the Lee-Yang edges exhibit linear finite-size scaling, yielding an extrapolated melting $T$ of 274.70 K for the mW water potential in the thermodynamic limit. This result agrees quantitatively with prior coexistence simulations, while offering a significant reduction in computational cost: the phase boundary can be determined from a single simulation even when performed distant from actual transition conditions, unlike conventional methods that require multiple simulations scanning $T$ or $p$. With these, we demonstrate the applicability of Lee-Yang phase transition theory in realistic molecular systems and provide a feasible scheme for high-throughput calculations in determining the phase transition temperature.

Periodically driven systems often exhibit behavior distinct from static systems. In single-particle, static systems, any amount of disorder generically localizes all eigenstates in one dimension. In contrast, we show that in topologically nontrivial, single-particle Floquet loop drives with chiral symmetry in one dimension, a localization-delocalization transition occurs as the time $t$ is varied within the driving period ($0\le t\le T_{\text{drive}}$). We find that the time-dependent localization length $L_{\mathrm{loc}}\left(t\right)$ diverges with a universal exponent as $t$ approaches the midpoint of the drive: $L_{\mathrm{loc}}\left(t\right)\sim {(t-T_{\text{drive}}/2)}^{-\nu }$ with $\nu =2$. We provide analytical and numerical evidence for the universality of this exponent within the AIII symmetry class.

Quantum computing offers the potential for computational abilities that can go beyond classical machines. However, they are still limited by several challenges such as noise, decoherence, and gate errors. As a result, efficient classical simulation of quantum circuits is vital not only for validating and benchmarking quantum hardware but also for gaining deeper insights into the behavior of quantum algorithms. A promising framework for classical simulation is provided by tensor networks. Recently, the density-matrix renormalization group (DMRG) algorithm was developed for simulating quantum circuits using matrix product states (MPS). Although MPS are efficient for representing quantum states with one-dimensional correlation structures, the fixed linear geometry restricts the expressive power of the MPS. In this work, we extend the DMRG algorithm for simulating quantum circuits to tree tensor networks (TTNs). The framework employs a variational compression scheme that optimizes the TTN to approximate the evolved quantum state. To benchmark the method, we simulate random circuits and the quantum approximate optimization algorithm (QAOA) with various two-qubit gate connectivities. For the random circuits, we devise treelike gate layouts that are suitable for TTN and show that TTN requires less memory than MPS for the simulations. For the QAOA circuits, a naive TTN construction that exploits graph structure significantly improves the simulation fidelities. Our findings show that the DMRG algorithm with TTNs provides a promising framework for simulating quantum circuits, particularly when gate connectivities exhibit clustering or a hierarchical structure.

The symmetry of chaotic systems plays a pivotal role in determining the universality class of spectral statistics and dynamical behaviors, which can be described within the framework of random matrix theory. Understanding the influence of system symmetry on these behaviors is crucial for characterizing universal properties in quantum chaotic systems. In this work, we explore the universality of out-of-time-ordered correlator (OTOC) dynamics in quantum chaotic systems, focusing on the kicked rotor and the kicked Harper model. By modulating the periodically kicked potential, we control system symmetry to examine its impact on OTOC dynamics and level spacing distributions. Our results show that ensemble-averaged OTOC dynamics exhibit distinct universal behaviors depending on system symmetry, enabling classification through random matrix theory. These distinctions become evident after the localization time in localized regimes and emerge at specific time scales corresponding to the translational period of the Floquet operator in momentum space under quantum resonance conditions. Our findings provide a rigorous understanding of the relationship between symmetry and quantum chaotic dynamics, contributing to a deeper comprehension of universal behaviors in these systems.

Magnetoelectric responses are related, in general, to magnetic multipoles and, in particular, the off-diagonal linear response is proportional to the toroidization order parameter. In multiferroics with three order parameters (polarization, magnetization, and toroidization), such response turns out to also be proportional to the trilinear coupling between the order parameters. Here we explore this scenario, discussing the effects of such trilinear coupling within a Landau theory framework, and using ab initio calculations to discuss a specific model system for this effect, namely, the recently predicted three-order-parameter multiferroic metal ${\mathrm{Bi}}_5{\mathrm{Mn}}_5{\mathrm{O}}_{17}$.

The emergence of ferro- and ferrimagnetic behavior in insulating materials is uncommon, largely due to Hund's rules. Utilizing symmetry analysis, first-principles methods, and classical Monte Carlo simulations, we report technologically important insulating ferro- and ferrimagnetic double-double perovskite oxides. Our study predicts ${\text{La}A}^{\prime }{\mathrm{MnNiO}}_6$ ($A^{\prime }=\mathrm{V}$, Cr, Mn, Co, and Ni) as promising candidates for spintronic and optical applications exhibiting band gaps between 1.3 and 1.9 eV. We explain the mechanisms driving band-gap openings and magnetic exchange interactions in these ferro- and ferrimagnetic compounds. Monte Carlo simulations together with state-of-the-art orbital-decomposed exchange parameter analysis reveal intriguing variations in magnetic transition temperatures (up to 242 K) and the corresponding exchange mechanisms in all ${\text{La}A}^{\prime }{\mathrm{MnNiO}}_6$ compounds. In addition, we assess the thermodynamic and dynamic stability of these compounds to comment on the feasibility of these systems.

There are now many examples of gapped fracton models which are defined by the presence of restricted-mobility excitations above the quantum ground state. However, the theory of fracton orders remains in its early stages, and the complex landscape of examples is far from being mapped out. Here we introduce the class of planon-modular ($p$-modular) fracton orders, a relatively simple yet still rich class of quantum orders that encompasses several well-known examples of type I fracton order. The defining property is that any nontrivial pointlike excitation can be detected by braiding with planons. From this definition, we uncover a significant amount of general structure, including the assignment of a natural number (dubbed the weight) to each excitation of a $p$-modular fracton order. We identify simple new phase invariants, some of which are based on weight, which can easily be used to compare and distinguish different fracton orders. We also study entanglement renormalization group (RG) flows of $p$-modular fracton orders, establishing a close connection with foliated RG. We illustrate our general results with an analysis of several exactly solvable fracton models that we show to realize $p$-modular fracton orders, including ${\mathbb{Z}}_n$ versions of the X-cube, anisotropic, checkerboard, 4-planar X-cube, and four color cube (FCC) models. We show that each of these models is $p$-modular and compute its phase invariants. We also show that each example admits a foliated RG at the level of its nontrivial excitations, which is a new result for the 4-planar X-cube and FCC models. We show that the ${\mathbb{Z}}_2$ FCC model is not a stack of other better-studied models but predict that the ${\mathbb{Z}}_n$ FCC model with $n$ odd is a stack of ten 4-planar X-cubes, possibly plus decoupled layers of two-dimensional toric code. We also show that the ${\mathbb{Z}}_n$ checkerboard model for $n$ odd is a stack of three anisotropic models.

The theory of purified pseudomodes (arXiv:2412.04264) was recently developed to provide a numerical tool for the analysis of the properties of a quantum system and the environment it couples to via linear system-bath interactions. Here we extend this theory to allow for the description of general nonlinear system-bath interactions. We demonstrate the validity of our method by considering the spontaneous decay of a two-level atom placed inside a single-mode lossy cavity, and furthermore, its potential application to nanophotonics by calculating the resonance fluorescence spectrum of a quantum dot in the presence of a phonon environment. Our method provides a useful tool for the study of phonon-assisted emission in quantum dots and holds the promise for broad applications in fields like quantum biology, nonlinear phononics, and nanophotonics.

Odd-parity pairings offer a natural pathway for realizing topological superconductivity. When two identical even-parity superconductors form a $\pi$-junction, the metallic material sandwiched between them experiences an effective odd-parity pairing, facilitating the emergence of topological superconductivity in the intermediate region. In this work, we consider the intermediate material to be a two-dimensional spin-orbit-coupled Dirac semimetal. When the two superconductors are conventional $s$-wave superconductors, we find that a helical topological superconductor can be realized. This phase is characterized by the presence of a pair of helical Majorana edge states. Interestingly, when the superconductors are $s_{\pm }$-wave superconductors, we observe not only the helical topological superconductor but also an unconventional topological superconductor. The latter is distinguished by the existence of two pairs of helical Majorana edge states, despite the fact that the global topological invariants for this system take trivial values. By further applying an in-plane magnetic field, we demonstrate that second-order topological superconductors can be achieved. These phases host isolated Majorana corner modes as well as twofold Majorana corner modes. Our findings reveal that two-dimensional $\pi$-junction Dirac semimetals can support a rich variety of topological superconducting phases, offering a versatile platform for exploring exotic topological phenomena.