Nodal semimetals (e.g., Dirac, Weyl, and nodal-line semimetals, graphene, etc.) and systems of pinned particles with power-law interactions (trapped ultracold ions, nitrogen defects in diamonds, spins in solids, etc.) are presently at the center of attention of large communities of researchers working in condensed-matter and atomic, molecular, and optical physics. Although seemingly unrelated, both classes of systems are abundant with novel fundamental thermodynamic and transport phenomena. In this Rapid Communication, we demonstrate that low-energy field theories of quasiparticles in semimetals may be mapped exactly onto those of pinned particles with power-law hopping excitations. The duality between the two classes of systems, which we establish, trades strong disorder in one class for weak disorder in the other, and allows one to describe the transport and thermodynamics of each class of systems using the results established for the other class. In particular, using the duality mapping, we establish the existence of another class of disorder-driven transition in systems with the power-law hopping $\propto 1/r^{\gamma }$ of excitations with $d/2<\gamma <d$, different from the conventional Anderson-localization transition. Non-Anderson disorder-driven transitions have been studied broadly for nodal semimetals. Our work extends the class of systems exhibiting such transitions to systems with long-range hopping (interactions) with $\gamma <d$.

The impact of collisionality and the range of the interparticle interaction on the bump-on-tail instability is examined both computationally and theoretically. Using three-dimensional, nonequilibrium molecular dynamics with a force law that varies continuously from long range (pure $1/r$ Coulomb limit) to short range and across coupling regimes from weakly to strongly collisional, we examine properties of the instability; unlike other computational methods, molecular dynamics includes large-angle scattering, including the extreme limit of caging, and dynamical nonlinear screening across length scales as small as the interparticle spacing. A simpler theoretical model is also developed for comparison to the molecular dynamics results; we find that the two methods agree well in the appropriate limit, revealing that molecular dynamics is an accurate tool for the exploration of plasma instabilities. Our results reveal that the bump-on-tail instability exists only for long-range interactions.

Exploitation of time-frequency properties of spontaneous parametric down conversion photon pairs has recently found application in many endeavors. Complete characterization and control over the states in this degree of freedom is of paramount importance for the development of optical quantum technologies. This is achieved by accessing information both on the joint spectral amplitude and the joint spectral phase. Here we propose a scheme based on the MICE algorithm, which aims at reconstructing the joint spectral phase by adopting a multishear approach, making the technique suitable for noisy environments. We report on simulations for the phase reconstruction and propose an experiment using a Franson-modified interferometer.

Coevolutionary arms races form between interacting populations that constitute each other's environment and respond to mutual changes. This inherently far-from-equilibrium process finds striking manifestations in the adaptive immune system, where highly variable antigens and a finite repertoire of immune receptors coevolve on comparable timescales. This unique challenge to the immune system motivates general questions: How do ecological and evolutionary processes interplay to shape diversity? What determines the endurance and fate of coevolution? Here, we take the perspective of responsive environments and develop a phenotypic model of coevolution between receptors and antigens that both exhibit cross reactivity (one-to-many responses). The theory predicts that the extent of asymmetry in cross reactivity is a key determinant of repertoire composition: small asymmetry supports persistent large diversity, whereas strong asymmetry yields long-lived transients of quasispecies in both populations. The latter represents a different type of Turing mechanism. More surprisingly, patterning in the trait space feeds back on population dynamics: spatial resonance between the Turing modes breaks the dynamic balance, leading to antigen extinction or unrestrained growth. Model predictions can be tested via combined genomic and phenotypic measurements. Our work identifies cross reactivity as an important regulator of diversity and coevolutionary outcome, and reveals the remarkable effect of ecological feedback in pattern-forming systems, which drives evolution toward nonsteady states different than the Red Queen persistent cycles.

We analyze charge fluctuations in a parasitic state strongly coupled to a superconducting Josephson-junction-based charge detector. The charge dynamics of the state resembles that of electron transport in a quantum dot with two charge states, and hence we refer to it as a two-level fluctuator. By constructing the distribution of waiting times from the measured detector signal and comparing it with a waiting time theory, we extract the electron in- and out-tunneling rates for the two-level fluctuator, which are severely asymmetric.

In metal-anode batteries such as zinc, the concentration of metal ions in the electrolyte usually plays a significant role in the metal electrodeposition upon charging. This study aims to clarify the concentration of zincate ions near the zinc anode. After preliminary experiments in a minichannel were conducted to identify the system parameters, galvanostatic charging experiments in a zinc battery cell were conducted at current densities of 20 and $40\mathrm{mA}{\mathrm{cm}}^{-2}$. The bulk concentrations of zincate ions were set to 0.49 and $0.98\mathrm{mol}{\mathrm{L}}^{-1}$. Images near the zinc anode were captured using an optical microscope to calculate the zincate ion concentration distribution through the background-oriented Schlieren (BOS) technique. They were taken at an equal time intervals to investigate the transition of the concentration diffusion layer. It was confirmed that the BOS technique enables us to quantitatively measure the zincate ion concentration in zinc anode batteries. The results are consistent with the theoretical expectation. The applied current density basically determines the concentration gradient near the anode surface, although it takes time to reach a steady state. The spatial variance in the zincate ion concentration at the anode surface increases with the distance from equilibrium.

In this paper, we propose a scheme for generating genuine tripartite steering nonlocality in a cavity magnomechanical system composed of an yttrium iron garnet (YIG) sphere with a diameter of a few hundred micrometers inside a microwave cavity. In the system, the magnons, i.e., collective spin excitations in the sphere, are coupled to the cavity photons via magnetic-dipole interaction and at the same time coupled to phonons, the quanta of vibration of the sphere, by magnetostrictive interaction. We consider that the output field of the driven microwave cavity is subject to a time-continuous homodyne detection. We find that without the continuous measurement, only weak bipartite steering among the photons, magnons, and phonons can be obtained and the genuine tripartite steering is unachievable, although there exists weak genuine tripartite entanglement; when the continuous measurement is present, the bipartite steering is enhanced considerably and furthermore the genuine photon-magnon-phonon tripartite steering can be generated in the steady-state regime. It is shown that the generated tripartite steering is robust against thermal fluctuations for realistic parameters. Our scheme opens a promising route for exploring and exploiting macroscopic quantum effects in such a macroscopic quantum interface of photons, magnons, and phonons.

Interface-driven magnetic properties such as exchange bias and inverted hysteresis are highly sought after in modern functional materials, where at least two magnetically active layers are required. The ability to achieve these functionalities in a single-layer thin film (monolithic) reduces the dimensionality while enriching the magnetism. Here we uncover a previously unseen part of the phase diagram of a monolithic epitaxial thin film of $\mathrm{L}{\mathrm{a}}_{0.67}\mathrm{S}{\mathrm{r}}_{0.33}\mathrm{Mn}{\mathrm{O}}_3$ on $\mathrm{SrTi}{\mathrm{O}}_3$ which exhibits inverted hysteresis, spontaneous magnetic reversal, and exchange bias due to a structural gradient in the oxygen-octahedral network. Varying the growth conditions, we have mapped the phase diagram of this material and discovered that at a specific oxygen pressure and above a critical thickness, a complex magnetic behavior appears. Atomic-scale characterization shows that this peculiar magnetism is closely linked to a continuous structural gradient that creates three distinct regions within the monolithic film, each with a different magnetism onset. Extracting oxygen-octahedral geometry by electron microscopy, we found that the Curie temperature is directly correlated with the metal-oxygen bond angle. This study illustrates the importance of octahedral geometry in shaping the physical properties of the materials.

The kernel mean embedding of probability distributions is commonly used in machine learning as an injective mapping from distributions to functions in an infinite-dimensional Hilbert space. It allows us, for example, to define a distance measure between probability distributions, called the maximum mean discrepancy. In this work, we propose to represent probability distributions in a pure quantum state of a system that is described by an infinite-dimensional Hilbert space and prove that the representation is unique if the corresponding kernel function is $c_0$ universal. This enables us to work with an explicit representation of the mean embedding, whereas classically one can only work implicitly with an infinite-dimensional Hilbert space through the use of the kernel trick. We show how this explicit representation can speed up methods that rely on inner products of mean embeddings and discuss the theoretical and experimental challenges that need to be solved in order to achieve these speedups.

We present electric deflection results for the fullerenes ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ obtained with a long-baseline matter-wave interferometer. The second grating of the interferometer is interchangeable between a material grating for fast atom beams and an optical phase grating for polarizable molecules. This allows us to use cesium as a calibration particle and thus measure molecular susceptibilities with improved systematic uncertainty. The static polarizabilities of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ are measured as $4\pi {\varepsilon }_0\times 87.4\pm 0.4\pm 2.5{\AA }^3$ and $4\pi {\varepsilon }_0\times 106.4\pm 0.2\pm 1.1{\AA }^3$, respectively, in excellent agreement with previous deflection experiments, but with improved uncertainties.

Employing a combination of first-principles density functional theory and a solution of a generalized spin Hamiltonian, we predict finite-temperature ferromagnetism in a yet-to-be synthesized two-dimensional monolayer of Cu spins, derived out of the layered structure of inorganic-organic hybrid perovskites. The computed cleavage energies are found to be a factor of 2–3 smaller than that of graphite, thereby making the synthesis of such monolayers by exfoliation of their bulk counterparts probable. The ferromagnetic exchanges, together with in-plane magnetic anisotropy, give rise to the possibility of a finite-temperature long-range ordering of Cu spins, as established through the solution of a generalized model Hamiltonian. Our study should motivate future experiments in this exciting class of compounds.

We propose to use the complex quantum dynamics of a massive particle in a nonquadratic potential to reconstruct an initial unknown motional quantum state. We theoretically show that the reconstruction can be efficiently done by measuring the mean value and the variance of the position quantum operator at different instances of time in a quartic potential. We train a neural network to successfully solve this hard regression problem. We discuss the experimental feasibility of the method by analyzing the impact of decoherence and uncertainties in the potential.

Quantum response theory is a cornerstone of statistical physics. However, the standard Kubo formalism is restricted to isolated equilibrium systems. We here generalize Kubo's results to open quantum systems in nonequilibrium steady states. We derive three different, but equivalent, forms of the quantum response function. We discuss for each of them the role of the noncommutativity of quantum operators and introduce a steady-state extension of the Kubo transformation. We show in particular that the equilibrium response vanishes for perturbations that commute with the unperturbed Hamiltonian, while the steady-state response does not, highlighting the profound difference between the two linear response theories.

We report on the formation of heteronuclear quantum droplets in an attractive bosonic mixture of ${}^{41}\mathrm{K}$ and ${}^{87}\mathrm{Rb}$. We observe long-lived self-bound states, both in free space and in an optical waveguide. In the latter case, the dynamics under the effect of a species-dependent force confirms their bound nature. By tuning the interactions from the weakly to the strongly attractive regime, we study the transition from expanding to localized states, in both geometries. We compare the experimental results with beyond-mean-field theory and we find good agreement in the full range of explored interactions. Our findings provide access to the production of long-lived droplets with important implications for further research.

We have systematically studied the effects of in-plane uniaxial pressure $p$ on the superconducting transition temperature $T_c$ in many iron-based superconductors. The change of $T_c$ with $p$ is composed of linear and nonlinear components. The latter can be described as a quadratic term plus a much smaller fourth-order term. In contrast to the linear component, the nonlinear $p$ dependence of $T_c$ displays a pronounced in-plane anisotropy, which is similar to the anisotropic response of the resistivity to $p$. As a result, it can be attributed to the coupling between the superconducting and nematic orders, in accordance with the expectations of a phenomenological Landau theory. Our results provide direct evidences for the interplay between nematic fluctuations and superconductivity, which may be a common behavior in iron-based superconductors.

Rutile $\mathrm{Ti}{\mathrm{O}}_2$ is a paradigmatic transition-metal oxide with applications in optics, electronics, photocatalysis, etc., that are subject to pervasive electron-phonon interaction. To understand how energies of its electronic bands, and in general semiconductors or metals where the frontier orbitals have a strong $d$-band character, depend on temperature, we perform a comprehensive theoretical and experimental study of the effects of electron-phonon $\left(e-p\right)$ interactions. In a two-photon photoemission (2PP) spectroscopy study we observe an unusual temperature dependence of electronic band energies within the conduction band of reduced rutile $\mathrm{Ti}{\mathrm{O}}_2$, which is contrary to the well-understood $sp$-band semiconductors and points to a so far unexplained dichotomy in how the $e-p$ interactions affect differently the materials where the frontier orbitals are derived from the $sp$- and $d$ orbitals. To develop a broadly applicable model, we employ state-of-the-art first-principles calculations that explain how phonons promote interactions between the $\mathrm{Ti}-3d$ orbitals of the conduction band within the octahedral crystal field. The characteristic difference in $e-p$ interactions experienced by the $\mathrm{Ti}-3d$ orbitals of rutile $\mathrm{Ti}{\mathrm{O}}_2$ crystal lattice are contrasted with the more familiar behavior of the $\mathrm{Si}-2s$ orbitals of stishovite $\mathrm{Si}{\mathrm{O}}_2$ polymorph, in which the frontier $2s$ orbital experiences a similar crystal field with the opposite effect. The findings of this analysis of how $e-p$ interactions affect the $d$- and $sp$-orbital derived bands can be generally applied to related materials in a crystal field. The calculated temperature dependence of $d$-orbital derived band energies agrees well with and explains the temperature-dependent inter-$d$-band transitions recorded in 2PP spectroscopy of $\mathrm{Ti}{\mathrm{O}}_2$. The general understanding of how $e-p$ interactions affect $d$-orbital derived bands is likely to impact the understanding of temperature-dependent properties of highly correlated materials.

We experimentally investigate laser-induced dissociative recombination of ${\mathrm{CO}}_2$ in linearly polarized strong laser fields with coincidence measurements. Our results show laser-induced dissociative processes with electron recombination after laser-induced double ionization. After double ionization, one electron can recombine to one of the two ionic fragments during laser-induced molecular dissociation. Our measurements reveal that the recombination probability of the second ionized electron is three times as high as that of the first ionized electron.

An equilibrium system which is perturbed by an external potential relaxes to a new equilibrium state, a process obeying the fluctuation-dissipation theorem. In contrast, perturbing by nonconservative forces yields a nonequilibrium steady state, and the fluctuation-dissipation theorem can in general not be applied. Here we exploit a freedom inherent to linear response theory: Force fields which perform work that does not couple statistically to the considered observable can be added without changing the response. Using this freedom, we demonstrate that the fluctuation-dissipation theorem can be applied for certain nonconservative forces. We discuss the case of a nonconservative force field linear in particle coordinates, where the mentioned freedom can be formulated in terms of symmetries. In particular, for the case of shear, this yields a response formula, which we find advantageous over the known Green-Kubo relation in terms of statistical accuracy.

Recent studies of scalar and gravitational waveforms from high-eccentricity, extreme mass-ratio black-hole binaries show the presence of quasinormal bursts (QNBs), lingering high-frequency decaying oscillations (also known as “wiggles”), soon after each periapsis passage. One puzzle associated with these QNBs is that in the case of a nearly extreme rotating central black hole the frequency of the QNBs has been found to be in a range which is lower than the corresponding range of relevant quasinormal modes. We reproduce these results using a different approach and perform a detailed analysis to find evidence for the resolution of the puzzle and for the origin of the QNBs. We find that the QNB frequency as measured at future null infinity evolves in (retarded) time and approaches the dominant quasinormal frequency exponentially in time. We also show that the QNB amplitude decays inversely in (retarded) time. We discuss the time dependence of both the QNB waveform frequency and its amplitude and argue that this behavior arises as a result of the excitation of many quasinormal overtones and the summation thereof.

Here we show how time-resolved broadband optical spectroscopy can be used to quantify, with femtometer resolution, the oscillation amplitudes of coherent phonons through a displacive model without free tuning parameters, except an overall scaling factor determined by comparison between experimental data and density functional theory calculations. ${\mathrm{WTe}}_2$ is used to benchmark this approach. In this semimetal, the response is anisotropic and provides the spectral fingerprints of two ${\mathrm{A}}_1$ optical phonons at $\approx 8$ and $\approx 80{\mathrm{cm}}^{-1}$. In principle, this methodology can be extended to any material in which an ultrafast excitation triggers coherent lattice modes modulating the high-energy optical properties.