Particles in a crowded environment exhibit slow anomalous diffusion, and their efficient manipulation is important in controlling transport phenomena in complex materials. Skyrmions and half-skyrmions, spatially localized quasiparticles observed in magnetic systems and liquid crystals, also exhibit diffusive motion. They exhibit normal diffusion in dilute conditions. However, the cooperative dynamics and diffusion of skyrmions and half-skyrmions in their condensed liquid, hexatic, and crystalline phases are elusive. Here we show in the half-skyrmion condensed phases that the fusion and fission of half-skyrmions, not their diffusion, are responsible for the primary structural relaxation. The fusion and fission occur due to the nonconserved nature of the quasiparticle number density. The diffusion, which contributes to the secondary structural relaxation, is suppressed by cages formed by surrounding half-skyrmions, whereas enhanced by Mermin-Wagner fluctuation characteristic to two-dimensional systems, leading to subdiffusive motion. Large displacement of half-skyrmions is locally excited by fusion-fission and bond breaking between adjacent half-skyrmions via heterogeneous elastic fields. Furthermore, the motion of half-skyrmions couples with transverse and longitudinal sound wave excitation differently, where the transverse sound wave is more attenuated than the longitudinal one due to the coupling between transverse sound wave and half-skyrmion deformation. We also discuss the relationship between half-skyrmion diffusion in our system and skyrmion diffusion in magnetic systems. Our result provides a qualitative difference in dynamical properties between half-skyrmion gaseous and condensed phases, suggesting the efficient manipulation of high-density half-skyrmions and skyrmions.

The performance of quantum key distribution protocols is evaluated based on the ease of implementation and key generation rate. Among major protocols, the differential-phase-shift (DPS) protocol has the advantage of simple implementation using a train of coherent pulses and a passive detection unit. Unfortunately, however, its key rate is known to be at least proportional to ${\eta }^2$ with respect to channel transmission $\eta \to 0$. If one can only prove the rate proportional to ${\eta }^2$ and cannot improve the analysis beyond that, then the DPS protocol will be deemed inferior to other major protocols, such as the decoy BB84 protocol. In this paper, we consider a type of DPS protocol in which the phase of each emitted block comprising $n$ pulses is randomized and significantly improves the analysis of its key rate. Specifically, we reveal that the key rate is proportional to ${\eta }^{1+\frac{1}{n-2}}$ and this scaling is tight. This implies that the DPS protocol can achieve a key rate proportional to $\eta$ for a large number of $n$, which is the same scaling as the decoy BB84 protocol. Our result suggests that the DPS protocol can achieve a combination of both advantages of ease of implementation and a high key generation rate.

Inertial waves in convective regions of stars exhibit topological properties linked to a Chern number of 1. The first of these is a unique, unidirectional, prograde oscillation mode within the cavity, which propagates at arbitrarily low frequencies for moderate azimuthal wave numbers. The second are phase singularities around which the phase winds in Fourier space, with winding numbers $\nu =\pm 1$ depending on the hemisphere. Phase winding is a collective effect over waves propagating in all directions that is strongly robust to noise. This suggests a topology-based method for wave detection in noisy observational data.

The occurrence of a second-order superradiant quantum phase transition is brought to light in a quantum system consisting of two interacting qubits coupled to the same quantized field mode. We introduce an appropriate thermodynamic limit for the integrable two-qubit quantum Rabi model with spin-spin interaction. Namely, this limit is determined by the infinite ratios of the spin-spin and the spin-mode couplings to the mode frequency, regardless of the spin-to-mode frequency ratios.

Quasiparticle poisoning errors in Majorana-based qubits are not suppressed by the underlying topological properties, which undermines the usefulness of this proposed platform. This work tackles the errors originating from intrinsically excited quasiparticles by developing an erasure conversion scheme based on local quasiparticle detection. To model such measurements, we begin by constructing the quasiparticle position operator for the Kitaev chain. A measurement probe coupling to this operator is shown to allow projective measurements in the Wannier quasiparticle basis. Detection of quasiparticles in a region of width $d$ adjacent to each Majorana zero-energy mode allows implementation of an error-detecting Majorana stabilizer code ${\mathcal{C}}_d$ based on microscopic fermionic (nontopological) physical degrees of freedom. The implementation of ${\mathcal{C}}_d$ converts a large fraction of Pauli errors to erasure errors, thus achieving “erasure conversion” in Majorana qubits. We show that the fraction of Pauli errors escaping conversion to erasure errors is exponentially small in $d$, a result tied to the exponential localization of Wannier functions which we prove rigorously. The suppression in Pauli error rate comes at the cost of the erasure rate increasing sublinearly with $d$, but this can be readily compensated for by a suitable outer code, with the net effect being a higher threshold rate of quasiparticle poisoning. The framework developed here serves as a basis for understanding how realistic measurements, such as conductance measurements, could be utilized for achieving fault tolerance in these systems.

We demonstrate a simple and versatile resonator design based on a short strip of a typical coplanar waveguide shorted at one end to the ground and shunted at the other end with a large parallel-plate capacitor. Due to the shape of the structure, we coin it the tadpole resonator. The design allows tailoring the characteristic impedance of the resonator to especially suit applications requiring low values. We demonstrate characteristic impedances ranging from $Z_{\mathrm{c}}=2$ to $10\mathrm{\Omega }$ and a frequency range from $f_{\mathrm{r}}=290\mathrm{MHz}$ to $1.1\mathrm{GHz}$ while reaching internal quality factors of order $Q_{\mathrm{int}}=8.5\times {10}^3$ translating into a loss tangent of $tan\left(\delta \right)=1.2\times {10}^{-4}$ for the aluminum oxide used as the dielectric in the parallel-plate capacitor. We conclude that these tadpole resonators are well suited for applications requiring low frequency and low characteristic impedance while maintaining a small footprint on chip. The low characteristic impedance of the tadpole resonator renders it a promising candidate for achieving strong inductive coupling to other microwave components.

The combination of structural chirality and magnetism leads to the formation of spin chirality through noncoplanar magnetic structures, resulting in unusual electronic transport properties. The spin chirality generates nonzero Berry curvature in real space, acting as an emergent magnetic field and contributing to the unconventional anomalous Hall effect, known as the geometrical or topological Hall effect (THE). This study unveils the remarkable occurrence of THE in a chiral antiferromagnetic (AFM) semiconductor $\mathrm{Eu}{\mathrm{Ir}}_2{\mathrm{P}}_2$ in the hopping regime. It exhibits a complex incommensurately spiral AFM ground state due to its chiral crystalline structure, providing fertile ground for the emergence of topologically nontrivial spin textures such as skyrmions. A substantial THE is observed under finite magnetic fields, making $\mathrm{Eu}{\mathrm{Ir}}_2{\mathrm{P}}_2$ an exceptional case within the ultralow-conductivity hopping regime for investigating the interplay between topologically nontrivial magnetic structures and hopping carriers. Owing to its semiconducting nature, we have formulated a theoretical model based on Mott's variable range-hopping mechanism, effectively elucidating the temperature and magnetic field-dependent behavior of THE. $\mathrm{Eu}{\mathrm{Ir}}_2{\mathrm{P}}_2$ thus serves as an ideal candidate for comprehending transport properties in the hopping regime and offers a unique opportunity for the implementation of AFM semiconductor-based spintronic devices.

Traditional small angle X-ray scattering (SAXS) techniques utilize a focused microbeam for spatial scanning to achieve spatially resolved imaging of the nanostructures of nonuniform materials. However, this method is notably inefficient regarding information acquisition, and its spatial resolution is constrained by the beam's focusing capabilities. We propose a proof-of-concept experiment using structured illumination to demonstrate a SAXS method capable of achieving high spatial resolution. This method leverages the experimental setup of real-space ghost imaging in intensity correlation measurements. It maps reciprocal space signals—specifically, small angle scattering signals—to real space, enabling small angle scattering imaging with enhanced spatial resolution without needing beam-focusing elements. Due to its inherent compatibility with compressed sensing, this method can significantly reduce the number of measurements. Successfully validated using synchrotron radiation X-rays, this approach theoretically applies to scattering imaging of photons and high-energy particles across various wavelength bands. It holds broad application prospects in the fields of nanomaterials and biomedicine.

Quantum circuits with gates (local unitaries) respecting a global symmetry have broad applications in quantum information science and related fields, such as condensed-matter theory and quantum thermodynamics. However, despite their widespread use, fundamental properties of such circuits are not well understood. Recently, it was found that generic unitaries respecting a global symmetry cannot be realized, even approximately, using gates that respect the same symmetry. This observation raises important open questions: What unitary transformations can be realized with $k$-local gates that respect a global symmetry? In other words, in the presence of a global symmetry, how does the locality of interactions constrain the possible time evolution of a composite system? In this work, we address these questions for the case of Abelian (commutative) symmetries and develop constructive methods for synthesizing circuits with such symmetries. Remarkably, as a corollary, we find that, while the locality of interactions still imposes additional constraints on realizable unitaries, certain restrictions observed in the case of non-Abelian symmetries do not apply to circuits with Abelian symmetries. For instance, in circuits with a general non-Abelian symmetry such as $\mathrm{SU}\left(d\right)$, the unitary realized in a subspace with one irreducible representation (charge) of the symmetry dictates the realized unitaries in multiple other sectors with inequivalent representations of the symmetry. Furthermore, in certain sectors, rather than all unitaries respecting the symmetry, the realizable unitaries are the symplectic or orthogonal subgroups of this group. We prove that none of these restrictions appears in the case of Abelian symmetries. This result suggests that global non-Abelian symmetries may affect the thermalization of quantum systems in ways not possible under Abelian symmetries.

Magnetic kagome metals have attracted tremendous research interests recently, because they represent an ideal playground for exploring the fascinating interplay between their intrinsically inherited topologically nontrivial electron band structures, magnetism and electronic correlation effects, and the resultant novel electronic/magnetic states and emergent excitations. In this work, we report a comprehensive single-crystal neutron diffraction investigation of the ground-state magnetic structures of the recently discovered V-based topological kagome metals $R{\mathrm{V}}_6{\mathrm{Sn}}_6$ (R = Tb, Dy, Ho, Er). Furthermore, the sample synthesis details and our systematic studies of crystal structure, low-temperature magnetic and thermodynamic properties of these compounds via various in-house characterization techniques are also reported. Our single-crystal neutron diffraction measurements confirm that the long-range magnetic order forms below 4.3 K for $R=\mathrm{Tb}$, 3.0 K for $R=\mathrm{Dy}$, 2.4 K for $R=\mathrm{Ho}$, and 0.6 K for $R=\mathrm{Er}$, respectively. The ground-state magnetic structures of the studied compounds are comprehensively determined via the magnetic crystallography approaches. It can be revealed that $R{\mathrm{V}}_6{\mathrm{Sn}}_6$ ($R$ = Tb, Dy, Ho) have a collinear ferromagnetic order in the ground state, with the ordered magnetic moment aligned along the $c$ axis for $R$ = Tb, Ho, while approximately $20{}^{\circ }$ tilted off from the $c$ axis for $R$ = Dy. In contrast, ${\mathrm{ErV}}_6{\mathrm{Sn}}_6$ shows an A-type antiferromagnetic structure with a magnetic propagation vector k = (0, 0, 0.5), and with the ordered magnetic moment aligned in the $ab$ plane. The ordered magnetic moments are determined as 9.4(2) ${\mu }_B$, 6.6(2) ${\mu }_B$, 6.4(2) ${\mu }_B$, and 6.1(2) ${\mu }_B$ for $R$ = Tb, Dy, Ho, and Er, respectively. A comparison of the low-temperature magnetic structures for both the extensively investigated topological kagome metal series of $R{\mathrm{V}}_6{\mathrm{Sn}}_6$ and $R{\mathrm{Mn}}_6{\mathrm{Sn}}_6$ is given in detail. This allows to gain new insights into the complex magnetic interactions, diverse single-ion magnetic anisotropies and spin dynamics in these compounds. The reported ground-state magnetic structures in $R{\mathrm{V}}_6{\mathrm{Sn}}_6$ ($R$ = Tb, Dy, Ho, Er) can pave the way for further explorations of the possible interplay between magnetism and topologically nontrivial electron band structures in the magnetically ordered phase regime.

We show that various nonmonotonic ratchet effects can arise when mesophase pattern-forming systems, which exhibit anisotropic crystal, stripe, and bubble regimes, are coupled to one-dimensional asymmetric substrates under ac driving. The patterns emerge in the absence of a substrate when the ratio of attraction to repulsion is varied for particles with competing short-range attraction and long-range repulsion potentials. In the presence of the substrate, we find that the ratchet efficiency varies nonmonotonically with increasing attraction, depending upon how well the mesophase morphology matches the substrate spacing and periodicity. For strong repulsion, there is a weak but finite ratchet effect, while at intermediate attraction, there is a robust ratchet effect in which the system forms stripes aligned with the substrate symmetry direction. For strong attraction, large bubbles appear that have weak or no ratchet effects when the bubble width exceeds the substrate lattice spacing, causing the bubble to be only weakly coupled to the substrate. For very strong attraction, small bubbles form and undergo a strong ratchet effect with an efficiency that oscillates as a function of ac drive amplitude. Although the small bubble regime is a strongly correlated regime in which each bubble contains many particles, the system behaves as if it is in a single-particle regime since the bubble width is much smaller than the substrate lattice spacing. We map out the different rectification phases as a function of the pattern morphology, substrate strength, and ac drive amplitude. The pronounced ratchet effects that we observe in some regimes can be exploited for pattern sorting in hard and soft matter systems.

Generalized noncontextuality is a well-studied notion of classicality that is applicable to a single system, as opposed to Bell locality. It relies on representing operationally indistinguishable procedures identically in an ontological model. However, operational indistinguishability depends on the set of operations that one may use to distinguish two procedures: we refer to this set as the reference of indistinguishability. Thus, whether or not a given experiment is noncontextual depends on the choice of reference. The choices of references appearing in the literature are seldom discussed, but typically relate to an implicit notion of a system underlying the experiment. This shift in perspective then begs the question: how should one define the extent of the system underlying an experiment? This question depends in part on one's beliefs in the universe being fundamentally continuous or fundamentally composite. To draw a coherent picture of the possible approaches one may use, we start by formulating a notion of noncontextuality for prepare-and-measure scenarios with respect to an explicit reference of indistinguishability. We investigate how verdicts of noncontextuality depend on this choice of reference, and in the process we introduce the concept of the noncontextuality graph of a prepare-and-measure scenario. We then discuss several proposals that one may appeal to in order to fix the reference to a specific choice, and we relate these proposals to different conceptions of what a system really is. With this discussion, we advocate that whether or not an experiment is noncontextual is not as absolute as often perceived.

Quantum algorithms provide a potential strategy for solving computational problems that are intractable by classical means. Computing the topological invariants of topological matter is one central problem in research on quantum materials, and a variety of numerical approaches for this purpose have been developed. However, the complexity of quantum many-body Hamiltonians makes calculations of topological invariants challenging for interacting systems. Here, we present two quantum circuits for calculating Chern numbers of two-dimensional quantum matter on quantum computers. Both circuits combine a gate-based adiabatic time evolution over the discretized Brillouin zone with particular phase estimation techniques. The first algorithm uses many qubits, and we analyze it using a tensor-network simulator of quantum circuits. The second circuit uses fewer qubits, and we implement it experimentally on a quantum computer based on superconducting qubits. Our results establish a method for computing topological invariants with quantum circuits, taking a step towards characterizing interacting topological quantum matter using quantum computers.

Accurately describing properties of challenging problems in physical sciences often requires complex mathematical models that are unmanageable to tackle head on. Therefore, developing reduced-dimensionality representations that encapsulate complex correlation effects in many-body systems is crucial to advance the understanding of these complicated problems. However, a numerical evaluation of these predictive models can still be associated with a significant computational overhead. To address this challenge, in this paper we discuss a combined framework that integrates recent advances in the development of active-space representations of coupled cluster (CC) downfolded Hamiltonians with neural network approaches. The primary objective of this effort is to train neural networks to eliminate the computationally expensive steps required for evaluating hundreds or thousands of Hugenholtz diagrams, which correspond to multidimensional tensor contractions necessary for evaluating a many-body form of downfolded effective Hamiltonians. Using small molecular systems (the ${\mathrm{H}}_2\mathrm{O}$ and HF molecules) as examples, we demonstrate that training neural networks employing effective Hamiltonians for a few nuclear geometries of molecules can accurately interpolate or extrapolate their forms to other geometrical configurations characterized by different intensities of correlation effects. We also discuss differences between effective interactions that define CC downfolded Hamiltonians with those of bare Hamiltonians defined by Coulomb interactions in the active spaces.

Metamaterials engineered to host topological states of matter in controllable quantum systems hold promise for the advancement of quantum simulations and quantum computing technologies. In this context, the Su-Schrieffer-Heeger (SSH) model has gained prominence due to its simplicity and practical applications. Here we present the implementation of a gate-tunable, five-unit-cell resonator-based SSH chain on a one-dimensional lattice of superconducting resonators. We achieve electrostatic control over the inductive intracell coupling using semiconductor nanowire junctions, which enables the spectroscopic observation of a transition from a trivial to a topological phase in the engineered metamaterial. In contrast to prior work, our approach offers precise and independent in situ tuning of the coupling parameters, which is critical to directly approximate ideal tight-binding Hamiltonians via the control over local variables. Our results supplement efforts towards gate-controlled superconducting electronics and large controllable resonator-based lattices to enable quantum simulations.

We present a mesoscale field theory unifying the modeling of growth, elasticity, and dislocations in quasicrystals. The theory is based on the amplitudes entering their density-wave representation. We introduce a free energy functional for complex amplitudes and assume nonconserved dissipative dynamics to describe their evolution. Elasticity, including phononic and phasonic deformations, along with defect nucleation and motion, emerges self-consistently by prescribing only the symmetry of quasicrystals. Predictions on the formation of semicoherent interfaces and dislocation kinematics are given.

Quantum field theories (QFTs) as relevant for condensed-matter or high-energy physics are formulated in continuous space and time, and typically emerge as effective low-energy descriptions. In atomic physics, an example is given by tunnel-coupled superfluids, which realize the paradigmatic sine-Gordon model, and can act as quantum simulators of continuous QFTs. To quantitatively characterize QFT simulators, or to discover the Hamiltonian governing the dynamics of a continuous many-body quantum system, we discuss Hamiltonian learning as a method to systematically extract the operator content and the coupling constants of Hamiltonians from experimental data. In contrast to Hamiltonian learning for lattice models with a given lattice scale, we learn QFT Hamiltonians on a resolution scale set by the experiment. Varying the resolution scale gives access to QFTs at different energy scales, and allows to learn a flow of Hamiltonians reminiscent of the renormalization group. Applying these techniques to available experimental data from a tunnel-coupled quantum gas experiment allows a definite distinction between a free quadratic theory from an interacting sine-Gordon model, as the underlying QFT description of the system.

Taking advantage of the anomalous Hall effect, we electrically probe low-frequency magnetization fluctuations at room temperature in a thin ferromagnetic $\mathrm{Pt}/\mathrm{Co}/{\mathrm{AlO}}_x$ layer stack with perpendicular magnetic anisotropy. We observe a strong enhancement of the Hall voltage fluctuations within the hysteretic region of the magnetization loop. Analyzing both the temporal evolution of the anomalous Hall voltage and its frequency-dependent noise power density, we identify two types of magnetic noise: abrupt changes in the magnetic domain configuration, evident as Barkhausen-like steps in the Hall voltage time trace, yield a noise power density spectrum scaling with frequency as $1/f^{\beta }$ with $\beta \approx 2.0$. In contrast, quasistationary magnetization configurations are connected with a magnetic noise power density with an exponent $\beta \approx 1.0$. The observation of Barkhausen steps and relaxation effects shows that the magnetic system is in a nonstationary state in the hysteresis region, such that the fluctuation-dissipation theorem cannot be expected to hold. However, the time-dependent change in the Hall voltage for constant magnetic field strength resembles the integrated noise power.