As a rare topological phonon material, $\beta \text{−}{\mathrm{MoB}}_2$ exhibits superconductivity (SC) and undergoes structural transitions when subjected to pressure or doping. This unique property makes it an intriguing platform for investigating the interplay of diverse quantum order. However, the current understanding of phonons in this material remains limited. Therefore, in this study, we employ a combination of Raman scattering and first-principle calculations to investigate the phonon properties of $\beta \text{−}{\mathrm{MoB}}_2$. Several noteworthy observations were made during the study. (1) We identified five Raman-active modes ($3A_{1g}+2E_g$) and two abnormal modes in $\beta \text{−}{\mathrm{MoB}}_2$. The authenticity of the five Raman-active modes was further confirmed through angle-resolved polarized Raman spectra (ARPRS) measurements and theoretical calculations. (2) We found that all Raman spectra obtained at various temperatures exhibited symmetric Lorentzian profiles. This finding implies a weak electron-phonon coupling (EPC) strength in $\beta \text{−}{\mathrm{MoB}}_2$. We calculated the EPC strength $\lambda$ of bulk $\beta \text{−}{\mathrm{MoB}}_2$ to be 0.37, which is significantly lower than 1.71 of superconducting $\alpha \text{−}{\mathrm{MoB}}_2$. (3) Based on ARPRS measurements and the phonon dispersion, we attributed the origin of the two abnormal modes to structural distortions with regard to B atom layers of $\beta \text{−}{\mathrm{MoB}}_2$. This research provides a foundation for exploring the relationship between defect structures and various intriguing physical phenomena observed in $\beta \text{−}{\mathrm{MoB}}_2$.

The coherent energy transfer between two quantum devices (a quantum charger and a quantum battery) mediated by a photonic cavity is investigated, in presence of dissipative environments, with particular focus on the ultrastrong coupling regime. Here, very short transfer times and high charging power can be achieved in comparison with the usually addressed weak coupling case. Such phenomenology is further magnified by the presence of level crossings appearing in the energy spectrum and which reveal very robust against dissipative environmental effects. Moreover, by carefully controlling the physical parameters of the model, e.g., the matter-radiation coupling and the frequencies of the system, it is possible to tune these crossings making this device more flexible and experimentally feasible. Finally to broaden our analysis, we assume the possibility of choosing between a Fock and a coherent initial state of the cavity, with the latter showing better energetic performances.

Motivated by recent experimental observations carried out in superconducting transmon circuits, we compare two different charging protocols for three-level quantum batteries based on time-dependent classical pulses. In the first case, the complete charging is achieved through the application of two sequential pulses, while in the second the charging occurs in a unique step applying the two pulses simultaneously. The latter approach is characterized by a shorter charging time, and consequently by a greater charging power. Moreover, both protocols are analytically solvable, leading to a complete control on the dynamics of the quantum system and opening unique perspectives in the manipulation of the so-called qutrits. To support this analysis, we have tested both protocols on IBM quantum devices based on superconducting circuits in the transmon regime. The minimum achieved charging time represents one of the fastest stable charging reported so far in solid-state quantum batteries.

Incompatibility is a feature of quantum theory that sets it apart from classical theory, and the inability to clone an unknown quantum state is one of the most fundamental instances. The no-hiding theorem is another such instance that arises in the context of the black-hole information paradox, and can be viewed as being dual to no-cloning. Here, we formulate both of these fundamental features of quantum theory in a single form that is amenable to efficient verification, and that is robust to errors arising in state preparation and measurements. We extend the notion of unitarity—an average figure of merit that for quantum theory captures the coherence of a quantum channel—to general physical theories. Then, we introduce the notion of compatible unitarity pair (CUP) sets, that correspond to the allowed values of unitarities for compatible channels in the theory. We show that a CUP set constitutes a simple “fingerprint” of a physical theory, and that incompatibility can be studied through them. We derive information-disturbance constraints on quantum CUP sets that encode both the no-cloning/broadcasting and no-hiding theorems of quantum theory. We then develop randomized benchmarking protocols that efficiently estimate quantum CUP sets and provide simulations using IBMQ of the simplest instance. Finally, we discuss ways in which CUP sets and quantum no-go theorems could provide additional information to benchmark quantum devices.

We provide a systemic theory to entangle excitons with microcavity photons. This is realized by adopting an exciton-optomechanics system and introducing a nonlinear dispersive interaction with a mechanical oscillator. We show that when either the exciton and cavity modes in the weak-coupling regime, or the two exciton-polariton modes in the strong-coupling regime are, respectively, resonant with the optomechanical Stokes and anti-Stokes sidebands, entanglement between excitons and cavity photons, or between two exciton polaritons, can be established. The entanglement is in the steady state and can potentially be achievable at room temperature. In both cases, genuine tripartite entanglement is shown to be present.

Competitors in an intransitive loop of dominance can form a defensive alliance against an external species. The vitality of this superstructure, however, is jeopardized if we modify the original rock-scissors-paper-like rule and allow that the vicinity of a predator blocks stochastically the invasion success of its neighboring prey towards a third actor. To explore the potential consequences of this multipoint interaction we introduce a minimal model where two three-member alliances are fighting but one of them suffers from this inner blocking mechanism. We demonstrate that this weakness can be compensated by a faster inner rotation which is in agreement with previous findings. This broadly valid principle, however, is not always true here because the increase of rotation speed could be harmful and results in a series of reentrant phase transitions on the parameter plane. This unexpected behavior can be explained by the relation of the blocked triplet and a neutral pair formed by a triplet member with an external species. Our results provide novel aspects to the fundamental laws which determine the evolutionary process in multistrategy ecological systems.

While entanglement between distant parties has been extensively studied, entangled measurements have received relatively little attention despite their significance in understanding nonlocality and their central role in quantum computation and networks. We present a systematic study of entangled measurements, providing a complete classification of all equivalence classes of iso-entangled bases for projective joint measurements on two qubits. The application of this classification to the triangular network reveals that the elegant joint measurement, along with white noise, is the only measurement resulting in output permutation invariant probability distributions when the nodes are connected by Werner states. The paper concludes with a discussion of partial results in higher dimensions.

We consider a system of classical hard rods or billiard balls in one dimension, initially prepared in a Bragg-pulse state at a given temperature and subjected to external periodic fields. We show that at late times the system thermalizes in the thermodynamic limit via a three-stages process characterized by: an early phase where the dynamics is well described by Euler hydrodynamics, a subsequent phase where a (weak) turbulent phase is observed and where hydrodynamic gradient expansion can be broken, and a final one where the gas thermalizes according to viscous hydrodynamics. As the hard rod gas shares the same large-scale hydrodynamics as other quantum and classical integrable systems, we expect these features to universally characterize all many-body integrable systems in generic external potentials.

We determine the ground states and excitation spectra of the paradigmatic four-flavor Heisenberg model with nearest- and next-nearest-neighbor exchange couplings on the triangular lattice in a field controlling the population imbalance of flavor pairs. Such a system arises in the strongly correlated limit of moiré bilayers of transition metal dichalcogenides in an electric displacement field or in-plane magnetic field, and can be simulated via ultracold alkaline-earth atoms. We argue that the field tunes between effective SU(4) and SU(2) symmetries in the balanced and fully polarized limits and employ a combination of mean-field calculations, flavor-wave theory, and exact diagonalization to analyze the intermediate, imbalanced regime. We find different symmetry-broken phases with simultaneous spin and excitonic order depending on the field and next-nearest-neighbor coupling. Furthermore, we demonstrate that there is a strongly fluctuating regime without long-range order that connects candidate spin liquids of the SU(2) and SU(4) limit. The strong fluctuations are facilitated by an extensive classical degeneracy of the model, and we argue that they are also responsible for a strong polarizability at 1/3 polarization that survives from the mean-field level to the exact spectrum.

The competition between unitary time evolution and quantum measurements could induce phase transitions in the entanglement characteristics of quantum many-body dynamics. In this work, we reveal such entanglement transitions in the context of non-Hermitian Floquet systems. Focusing on noninteracting fermions in a representative bipartite lattice with balanced gain/loss and under time-periodic quenches, we uncover rich patterns of entanglement transitions due to the interplay between driving and non-Hermitian effects. Specially, we find that the monotonic increase of quenched hopping amplitude could flip the system between volume-law and area-law entangled Floquet phases, yielding alternated entanglement transitions. Meanwhile, the increase of gain/loss strength could trigger area-law to volume-law reentrant transitions in the scaling behavior of steady-state entanglement entropy, which are abnormal and highly unexpected in nondriven systems. Connections between entanglement transitions and parity-time-reversal (PT) transitions in Floquet spectra are further established. Our findings not only build a foundation for exploring entanglement phase transitions in Floquet non-Hermitian setups, but also provide efficient means to engineer and control such transitions by driving fields.

Recent experiments observed a phase transition within the superconducting regime of the heavy-fermion system ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ when subjected to a $c$-axis magnetic field. This phase transition has been interpreted as a parity switching from even to odd parity as the field is increased, and is believed to be of first order. If correct, this scenario provides a unique opportunity to study the phenomenon of local nucleation around inhomogeneities in a superconducting context. Here, we study such nucleation in the form of sharp domain walls emerging on a background of spatially varying material properties and hence, critical magnetic field. To this end, we construct a spatially inhomogeneous Ginzburg-Landau functional and apply numerical minimization to demonstrate the existence of localized domain-wall solutions and study their physical properties. Furthermore, we propose ultrasound attenuation as an experimental bulk probe of domain-wall physics in the system. In particular, we predict the appearance of an absorption peak due to domain-wall percolation upon tuning the magnetic field across the first-order transition line. We argue that the temperature dependence of this peak could help identify the nature of the phase transition.

Optical fields can exert forces of chiral nature on molecules and nanoparticles, which would prove extremely valuable in the separation of enantiomers with pharmaceutical applications, yet it is inherently complex, and the varied frameworks used in the literature further complicate the theoretical understanding. This paper unifies existing approaches used to describe dipolar optical forces and introduces a symmetry-based “force basis” consisting of twelve vector fields, each weighted by particle-specific coefficients, for a streamlined description of force patterns. The approach is rigorously applied to evanescent waves and dielectric nanofibers, yielding concise analytical expressions for optical forces. Through this, we identify optimal strategies for enantiomer separation, offering invaluable guidance for future experiments.

Temperature-dependent nitrogen-vacancy (NV)-center relaxometry is an established tool to characterize paramagnetic molecules near a sensing diamond, gaining momentum in different fields of science. However, recent results indicate that conversion between NV-center charge states impedes these measurements and influences the results for the $T_1$ time. While the temperature dependence of NV centers' $T_1$ time is well studied, additional contributions from temperature-dependent charge conversion during the dark time may further affect the measurement results. We combine temperature-dependent relaxometry and fluorescence spectroscopy at varying laser powers to unravel the temperature dependence of charge conversion in nanodiamond for biologically relevant temperatures. While we observe a decrease of the $T_1$ time with increasing temperatures, charge conversion remains unaffected by the temperature change. These results allow the temperature-dependent performance of $T_1$ relaxometry without further consideration of temperature dependence of charge conversion.

In the field of quantum information science and technology, the representation and visualization of quantum states and related processes are essential for both research and education. In this context, a focus lies especially on ensembles of few qubits. There exist many powerful representations for single-qubit and multiqubit systems, such as the famous Bloch sphere and generalizations. Here, we utilize the dimensional circle notation as a representation of such ensembles, adapting the so-called circle notation of qubits and the idea of representing the $n$-particle system in an $n$-dimensional space. We show that the mathematical conditions for separability lead to symmetry conditions of the quantum state visualized, offering a new perspective on entanglement in few-qubit systems and therefore on various quantum algorithms. In this way, dimensional notations promise significant potential for conveying nontrivial quantum entanglement properties and processes in few-qubit systems to a broader audience, and could enhance understanding of these concepts as a bridge between intuitive quantum insight and formal mathematical descriptions.

We demonstrate the use of quantum annealing for the selection of multiple martensite variants in a microstructure with long-range coherency stresses and external mechanical load. The general approach is illustrated for martensites with four different variants based on the minimization of the linear elastic energy. The equilibrium variant distribution is then analyzed under application of tensile and shear strains and for different values of the considered shear and tetragonal contributions of the different martensite variants. The interface orientations between different domains of variants can be explained using the perspective of the elastic energy anisotropy for regular stripe patterns. For random grain orientations, the response to an external elastic strain is weaker and variant changes can be interpreted based on the rotated eigenstrain tensor.

Generating entanglement between distributed network nodes is a prerequisite for the quantum internet. Entanglement distribution protocols based on high-dimensional photonic qudits enable the simultaneous generation of multiple entangled pairs, which can significantly reduce the required coherence time of the qubit registers. However, current schemes require fast optical switching, which is experimentally challenging. In addition, the higher degree of error correlation between the generated entangled pairs in qudit protocols compared to qubit protocols has not been widely studied in detail. We propose a qudit-mediated entangling protocol that completely circumvents the need for optical switches at the expense of a lower success probability of the scheme. Furthermore, we quantify the amount of error correlation between the simultaneously generated entangled pairs and analyze the effect on entanglement purification algorithms and teleportation-based quantum error correction. We find that optimized purification schemes can efficiently correct the correlated errors, while the quantum error correction codes studied here perform worse than for uncorrelated error models.

Strontium titanate (${\mathrm{SrTiO}}_3$) two-dimensional electron gases (2DEGs) have broken spatial inversion symmetry and possess a finite Rashba spin-orbit coupling. This enables the interconversion of charge and spin currents through the direct and inverse Edelstein effects, with record efficiencies at low temperature but more modest effects at room temperature. Here, we show that making these 2DEGs ferromagnetic enhances the conversion efficiency by nearly one order of magnitude. Starting from the experimental band structure of nonmagnetic ${\mathrm{SrTiO}}_3$ 2DEGs, we mimic magnetic exchange coupling by introducing an out-of-plane Zeeman term in a tight-binding model. We then calculate the band structure and spin textures for increasing internal magnetic fields and compute the Edelstein effect using a semiclassical Boltzmann approach. We find that the conversion efficiency first increases strongly with increasing magnetic field, then shows a maximum, and finally decreases. This field dependence is caused by the competition of the exchange coupling with the effective Rashba interaction. While the magnetic field enhances the splitting of band pairs (both in momentum and in spin expectation value), it also weakens the in-plane Rashba-type spin texture. The former mechanism increases the Edelstein effect, and the latter reduces it.