The realization of magnetic skyrmions in two-dimensional (2D) magnets offers significant potential for both fundamental research and device applications. Despite recent progress, the 2D skyrmion hosts remain limited, largely due to the fact that most 2D magnets are centrosymmetric and therefore lack Dzyaloshinskii-Moriya interaction (DMI). In this work, inspired by experimental works, we systematically explore the magnetic properties of a series of 2D magnetic materials, i.e., $\mathrm{C}{\mathrm{r}}_2\left(X,Y\right)\mathrm{T}{\mathrm{e}}_6$ $(X,Y=\mathrm{C},\mathrm{Si},\mathrm{Ge},\mathrm{Sn},X\ne Y)$, by using first-principles calculations and Monte Carlo simulations. The introduction of different $X$ and $Y$ atoms breaks inversion symmetry, thereby inducing DMI. Interestingly, the ground states of $\mathrm{C}{\mathrm{r}}_2\mathrm{CSi}\mathrm{T}{\mathrm{e}}_6, \mathrm{C}{\mathrm{r}}_2\mathrm{CGe}\mathrm{T}{\mathrm{e}}_6, \mathrm{C}{\mathrm{r}}_2\mathrm{CSn}\mathrm{T}{\mathrm{e}}_6$, and $\mathrm{C}{\mathrm{r}}_2\mathrm{SiSn}\mathrm{T}{\mathrm{e}}_6$ monolayers are determined to be noncollinear spin structure, and skyrmions can be successfully generated by applying a moderate magnetic field. We further introduce a dimensionless parameter κ to elucidate the relationship between skyrmion physics and magnetic parameters governing these materials.

Superconductivity in few-layer semiconducting transition-metal dichalcogenides (TMDs) can be induced by field-effect doping through ionic-liquid gating. While several experimental observations have been collected over the years, a fully consistent theoretical picture is still missing. Here we develop a realistic framework that combines the predictive power of first-principles simulations with the versatility and insight of Bardeen-Cooper-Schrieffer gap equations to rationalize such experiments. The multivalley nature of semiconducting TMDs is taken into account, together with the doping- and momentum-dependent electron-phonon and Coulomb interactions. Consistently with experiments, we find that superconductivity occurs when the electron density is large enough that the $Q$ valleys get occupied, as a result of a large enhancement of electron-phonon interactions. Despite being phonon driven, the superconducting state is predicted to be sensitive to Coulomb interactions, which can lead to the appearance of a relative sign difference between valleys and thus to a $s_{+-}$ character. We discuss qualitatively how such scenario may account for many of the observed physical phenomena for which no microscopic explanation has been found so far, including in particular the presence of a large subgap density of states, and the sample-dependent dome-shaped dependence of $T_c$ on accumulated electron density. Our results provide a comprehensive analysis of gate-induced superconductivity in semiconducting TMDs, and introduce an approach that will likely be valuable for other multivalley electronic systems, in which superconductivity occurs at relatively low electron density.

Several methods have been developed to improve the predictions of density functional theory (DFT) in the case of strongly correlated electron systems. Out of these approaches, $\mathrm{DFT}+U$, which corresponds to a static treatment of the local interaction, and DFT combined with dynamical mean field theory ($\mathrm{DFT}+\mathrm{DMFT}$), which considers local fluctuations, have both proven incredibly valuable in tackling the description of materials with strong local electron-electron interactions. While it is in principle known that the Hartree-Fock (HF) limit of the $\mathrm{DFT}+\mathrm{DMFT}$ approach should recover $\mathrm{DFT}+U$, demonstrating this equivalence in practice is challenging, due to the very different ways in which the two approaches are generally implemented. In this work, we introduce a way to perform $\mathrm{DFT}+U$ calculations in quantum espresso using Wannier functions as calculated by wannier90, which allows us to use the same Hubbard projector functions both in $\mathrm{DFT}+U$ and in $\mathrm{DFT}+\mathrm{DMFT}$. We benchmark these $\mathrm{DFT}+U$ calculations against $\mathrm{DFT}+\mathrm{DMFT}$ calculations where the DMFT impurity problem is solved within the HF approximation. Considering a number of prototypical materials including NiO, MnO, ${\mathrm{LaMnO}}_3$, and ${\mathrm{LuNiO}}_3$, we establish the sameness of the two approaches. Finally, we showcase the versatility of our approach by going beyond the commonly used atomic orbital-like projectors by performing $\mathrm{DFT}+U$ calculations for ${\mathrm{VO}}_2$ using a special set of bond-centered Wannier functions.

A robust quantum protocol has been developed that achieves highly efficient entanglement transfer from a three-atom Rydberg system, initially in a W-state $\left(\right|rrg\rangle +|rgr\rangle +|grr\rangle )/\sqrt{3}$, to an equivalent photonic W-state $\left(\right|101\rangle +|110\rangle +|011\rangle )/\sqrt{3}$. The entanglement transfer is achieved by dynamically adjusting the cavity mode frequencies and modulating the coupling rates, simplifying the complex transfer process into a sequence of processes involving two-level avoided crossings. We demonstrate that entanglement transfer can be achieved using either a fully adiabatic protocol or a quasi-adiabatic one with controlled nonadiabatic transitions at avoided crossings, generated by continuously chirping the cavity modes. Our adiabatic protocol uses the fractional stimulated Raman adiabatic passage method to facilitate the partial population transfer required for generation of the photonic W-state. In comparison, the quasi-adiabatic protocol uses nonadiabatic transitions to achieve the required partial population transfer. Furthermore, we propose two strategies for experimental implementation of our protocols.

Dynamically reconfigurable metasurfaces, offering real-time wavefront control, promise the realization of unprecedented components for the future information and communication technologies. The current reconfiguration approaches, though, suffer from certain inefficiencies, such as small tunability range and depth, slow response, complex implementation, etc. Plasma discharges promise to face some of those inefficiencies, as they exhibit a wide tunable range of electric permittivity, via simple control of the plasma source in the implementation. Here, exploiting these unique tunability properties of plasma, we design and numerically demonstrate dynamically reconfigurable metasurfaces formed as arrays of plasma cylinders. Analytical results for single-cylinder scattering properties provide initial guidelines for the realization of a generalized Kerker condition below the plasma frequency of the plasma cylinder, where both the electric dipole and quadrupole moments are excited and balanced, and Huygens response for the cylinders array is expected. This is verified by numerical investigation of arrays of identical cylinders, demonstrating tunable high transmission and a wide phase coverage. Based on those results, a phase gradient metasurface made of tunable plasma cylinders is designed, optimized, and demonstrated. The analysis is extended to practically realizable coated plasma cylinders, where both frequency tunability and dynamically controllable beam steering capabilities are demonstrated.

The ability of groups to make accurate collective decisions depends on a complex interplay of various factors, such as prior information, biases, social influence, and the structure of the interaction network. Here, we investigate a spin model that accounts for heterogeneous preferences and enables control over the nonlinearity of social interactions. Building on previous results for complete graphs and regular two-dimensional lattices, we investigate how the modification of network topology towards (sparse) random graphs can affect collective decision-making. We use two different measures of susceptibility to assess the responsiveness of the system to internal and external perturbations. In particular, we investigate how the maximum of susceptibility depends on network connectivity. Based on our findings, we discuss how collective systems might adapt to changes in environmental fluctuations by adjusting their network structure or the nature of their social interactions in order to remain in the region of maximal susceptibility.

We present a quantum heat engine based on a quantum Otto cycle whose working substance reproduces the same outcomes as an $\mathrm{SU}(1,1)$ interference process at the end of each adiabatic transformation. This device takes advantage of the extraordinary quantum metrological features of the $\mathrm{SU}(1,1)$ interferometer to better discriminate the sources of uncertainty of relevant observables during each adiabatic stroke of the cycle. In particular, the $\mathrm{SU}(1,1)$ adiabatic transformations enable high-precision estimations of the energy extracted from the adiabatic stroke, despite the presence of thermal fluctuations. Applications to circuit QED platforms are also discussed.

The simulation of various properties of quantum field theories is rapidly becoming a testing ground for demonstrating the prowess of quantum algorithms. Some examples include the preparation of ground states, as well as the investigation of various simple wave packets relevant for scattering phenomena. In this paper, we study the ability of quantum algorithms to prepare ground states in a matter-free non-Abelian $SO\left(3\right)$ lattice gauge theory in $2+1\mathrm{D}$ in a phase where the global charge conjugation symmetry is spontaneously broken. This is challenging for two reasons: the necessity of dealing with a large Hilbert space for gauge theories compared to that of quantum spin models, and the closing of the gap between the two ground states, which becomes exponentially small as a function of the volume. To deal with the large Hilbert space of gauge fields, we demonstrate how the exact imposition of the non-Abelian Gauss law in the rishon representation of the quantum link operator significantly reduces the degrees of freedom. Further, to resolve the gap, we introduce symmetry-guided ansätze in the Gauss-law-resolved basis for trial states as the starting point for the quantum algorithms to prepare the two lowest-energy states. In addition to simulation results for a range of two-dimensional system sizes, we also provide experimental results from the trapped-ion-based quantum hardware, IonQ, when working on systems with four quantum links. The experimental/simulation results derived from our theoretical developments indicate the role of metrics—such as the energy and the infidelity—to assess the obtained results.

Neuron spiking constitutes the central information node in neural networks. Nanoscale fluidic pores with rectification and hysteresis provide the opportunity to induce voltage oscillations with the same physical principles as in living neurons. We establish the conditions that enable self-sustained limit-cycle oscillations in a single artificial pore channel by a Hopf bifurcation, thus providing the minimal model for the elementary neuron. On a fluidic nanochannel that contains the necessary ingredients as the capacitive and inductive response and a stationary negative resistance, we identify the range of physical parameters where oscillations occur. These results provide crucial guidelines for identifying the conditions to build the oscillating nanopore according to the system's geometrical, electrical, fluidic, and chemical variables, which otherwise could be overlooked, since the relevant parameter region producing oscillations can be narrow.

We present the RF Quantum Upconverter (RQU) and describe its application to quantum metrology of electromagnetic modes between dc and the very high frequency band (VHF) ($\lesssim 300$ MHz). The RQU uses a Josephson interferometer made up of superconducting loops and Josephson junctions to implement a parametric interaction between a low-frequency electromagnetic mode (between dc and VHF) and a mode in the microwave C Band ($\sim 5$ GHz), analogous to the radiation pressure interaction between electromagnetic and mechanical modes in cavity optomechanics. We analyze RQU performance with quantum amplifier theory and show that the RQU can operate as a quantum-limited op-amp in this frequency range. It can also use nonclassical measurement protocols equivalent to those used in cavity optomechanics, including back-action evading (BAE) measurements, sideband cooling, and two-mode squeezing. These protocols enable experiments using dc VHF electromagnetic modes as quantum sensors with sensitivity better than the standard quantum limit (SQL). We demonstrate signal upconversion from low frequencies to the microwave C band using an RQU and show a phase-sensitive gain (extinction ratio) of $46.9\mathrm{dB}$, which is a necessary step towards the realization of full BAE.

Rare-earth magnets with parent cubic symmetry exhibit unique topological properties. However, the origin of these behaviors presently remains unclear. Here, we develop minimal models for Dirac semimetals (DSMs) with accidental band crossings and higher-order topology in cubic systems, incorporating candidate magnetic order to analyze bulk, surface, and hinge state characteristics. In certain cubic-symmetric DSMs, we identify an effective ${\mathbb{Z}}_2$ chiral symmetry which significantly impacts surface and hinge-localized states. Our results highlight distinct features in surface-state dispersions, Fermi arcs, polarization dependence, and band splitting that correlate with photoemission data in rare-earth monopnictides. We also suggest candidate materials and experimental tests for further validation. These findings advance our understanding of surface states in rare-earth magnets with parent cubic symmetries and illuminate the role of DSM physics in these systems.

The negatively charged nitrogen-vacancy (NV) center is one of the most significant and widely studied defects in diamond that plays a prominent role in quantum technologies. The precise engineering of the location and concentration of NV centers is of great importance in quantum technology applications. To this end, irradiation techniques such as nitrogen-molecule ion implantation are applied. Recent studies have reported enhanced NV center creation and activation efficiencies introduced by nitrogen molecule ion implantation in doped diamond layers, where the maximum creation efficiency at $\sim 75\%$ has been achieved in sulfur-doped layers. However, the microscopic mechanisms behind these observations and the limits of the efficiencies are far from understood. In this study, we employ hybrid density-functional-theory calculations to compute the formation energies, charge transition levels, and the magneto-optical properties of various sulfur defects in diamond where we also consider the interaction of sulfur and hydrogen in chemical vapor-deposited diamond layers. Our results imply that the competition between the donor substitutional sulfur and the hyperdeep acceptor sulfur-vacancy complex is an important limiting factor on the creation efficiency of the NV center in diamond. However, both species are able to trap interstitial hydrogen from diamond, which favorably mediates the creation of NV centers in chemical vapor-deposited diamond layers.

Rare-earth elements containing aperiodic quasicrystals and their related periodic approximant crystals can exhibit nontrivial physical properties at low temperatures. Here, we investigate the 1/1 and 2/1 approximant crystal phases of the Ce-Au-Al system by studying the ac susceptibility and specific heat at low temperatures and in magnetic fields up to 12 T. We find that these systems display signs of quantum criticality similar to the observations in other claimed quantum critical systems, including the related Yb-Au-Al quasicrystal. In particular, the ac-susceptibility at low temperatures shows a diverging behavior $\chi \propto 1/T$ as the temperature decreases as well as cutoff behavior in magnetic field. Notably, the field dependence of $\chi$ closely resembles that of quantum critical systems. However, the ac susceptibility both in zero and nonzero magnetic fields can be understood from the splitting of a ground state Kramers doublet of ${\mathrm{Ce}}^{3+}$. The high-temperature Curie-Weiss fit yields an effective magnetic moment of approximately $2.54{\mu }_{\mathrm{B}}$ per Ce for both approximant systems, which is reduced to $\sim 2.0{\mu }_{\mathrm{B}}$ at temperatures below 10 K. The low-temperature specific heat is dominated by the Schottky anomaly originating from the splitting of the ${\mathrm{Ce}}^{3+}$ Kramers doublet, resulting in an entropy of $Rln2$ at around 10 K.

We define quantum chaos and integrability in open quantum many-body systems as a dynamical property of single stochastic realizations, referred to as quantum trajectories. This definition relies on the predictions of random matrix theory applied to the subset of the Liouvillian eigenspectrum involved in each quantum trajectory. Our approach, which we name spectral statistics of quantum trajectories (SSQT), enables a natural distinction between transient and steady-state quantum chaos as general phenomena in open setups. We test the generality and reliability of the SSQT criterion on several dissipative systems, further showing that an open system with a chaotic structure can evolve towards either a chaotic or integrable steady state. We apply our theoretical framework to two driven-dissipative bosonic systems. First, we study the driven-dissipative Bose-Hubbard model, a paradigmatic example of a quantum simulator, clarifying the interplay of integrability, transient, and steady-state chaos across its phase diagram. Our analysis shows the existence of an emergent dissipative quantum chaotic phase, whereas the classical and semiclassical limits display an integrable behavior. In this regime, chaos arises from the quantum and classical fluctuations associated with the dissipation mechanisms. Second, we investigate dissipative quantum chaos in the dispersive readout of a transmon qubit: a measurement technique ubiquitous in superconducting-based quantum hardware. Through the SSQT, we distinguish several regimes where the performance of the measurement instrument can be connected to the integrable or chaotic nature of the underlying driven-dissipative bosonic system. Our work offers a general understanding of the integrable and chaotic dynamics of open quantum systems and paves the way for the investigation of dissipative quantum chaos and its consequences on state-of-the-art noisy intermediate-scale quantum devices.

The onset and growth of rigid clusters in a two-dimensional (2D) suspension in shear flow are studied by numerical simulations. The suspension exhibits the lubricated-to-frictional rheology transition, but the key results here are for stresses above the levels that cause extreme shear thickening. At large solid fraction, $\varphi$, but below the stress-dependent jamming fraction, we find a critical ${\varphi }_c(\sigma ,\mu )$ where $\sigma$ is a dimensionless shear stress and $\mu$ is the interparticle friction coefficient. For $\varphi >{\varphi }_c$, the proportion of particles in rigid clusters grows sharply, as $f_{\mathrm{rig}}\sim {|\varphi -{\varphi }_c|}^{\beta }$ with $\beta =1/8$. The fluctuations in the fraction of particles in rigid clusters yield a susceptibility measure ${\chi }_{\mathrm{rig}}\sim {|\varphi -{\varphi }_c|}^{-\gamma }$ with $\gamma =7/4$. The system is thus found to exhibit criticality. The results are shown to depend on an effective field $h\left(\mu \right)$, which provides data collapse near ${\varphi }_c$ for both $f_{\mathrm{rig}}$ and ${\chi }_{\mathrm{rig}}$. This behavior occurs over a range of stresses, with ${\varphi }_c(\sigma ,\mu )$ increasing as the stress decreases.