There is considerable research interest in discovering new permanent magnetic materials that perform equally as champion neomagnets, with the minimal use of critical rare-earth elements. Recently ${\mathrm{ThMn}}_{12}$-type (1:12) rare-earth iron (Ce-Fe) intermetallic materials have been on the frontline of research as Ce is naturally abundant that drastically lowers the cost of permanent magnets. Here, we investigate the lattice stability and electronic and magnetic properties of Ti- or Zr-substituted ${\mathrm{CeFe}}_{12}$ and ${\mathrm{CeFe}}_{12}\mathrm{N}$ using density functional theory. We find negative formation energy for all compositions in the bulk structure with respect to unaries except for ${\mathrm{CeFe}}_{12}$. The inclusion of nitrogen in the interstitial sites of ${\mathrm{CeFe}}_{12}$ improves its chemical stability by reducing the formation energy. The first time successfully calculated phonon frequencies including $4f$ electrons indicate that all compositions are dynamically stable. With the help of electronic structure calculations, we demonstrate that cerium exhibits the mixed-valence character in 1:12 materials. The mixed-valency sensibly affects the magnetocrystalline anisotropy (MCA) and magnetic moment. Nitrogen improves the net magnetic moment by influencing the spin polarization with extra electrons, although it has the opposite effect in the MCA constant, $K_1$. The predicted value of $K_1$ confirms all compounds uniaxial along the crystalline $c$ axis. Especially for ${\mathrm{CeZrFe}}_{11}$, $K_1$ is the largest in which Ce exhibits ${\mathrm{Ce}}^{3+}$ $(S=1/2)$, and $\mathrm{Ce}\left(4f\right)$ spin-density contour is elongated towards the uniaxial direction. The substantially large values of the MCA and magnetic moments suggest that these critical element-free materials qualify for high-performance permanent magnets.

It is well known that qubits immersed in a squeezed vacuum environment exhibit many exotic phenomena, including dissipative entanglement stabilization. Here we show that these effects only require interference between excitation and decay processes, and can be faithfully mimicked without nonclassical light using a simple classical temporal modulation. We present schemes that harness this idea to stabilize entanglement between two remote qubits coupled via a transmission line or waveguide, where either the qubit-waveguide coupling is modulated, or the qubits are directly driven. We analyze the resilience of these approaches against various imperfections and also characterize the trade-off between the speed and quality of entanglement stabilization. Our protocols are compatible with state-of-the-art cavity QED systems.

In this paper, we study the topological properties of non-Hermitian Su-Schrieffer-Heeger (SSH) lattices by periodically introducing onsite imaginary potentials in the manner of ($i{\gamma }_1$, $-i{\gamma }_2$, $-i{\gamma }_1$, $i{\gamma }_2$), where ${\gamma }_1$ and ${\gamma }_2$ are the imaginary-potential strengths. Results show that by changing the lattice to a tetratomic non-Hermitian system, such imaginary potentials induce the nontrivial transition of the topological properties of the SSH system. First, the topologically nontrivial region is extended, followed by the non-Hermitian spontaneous breaking of the anti-$\mathcal{P}T$ symmetry. In addition, a new edge state appears, but its locality is different from the state induced by the Hermitian SSH lattice. If such potentials are strong enough, the bulk states of this system can become purely imaginary states. We believe that these imaginary potentials play special roles in modulating the topological properties of the non-Hermitian SSH lattice.

The layered perovskite ${\mathrm{YBaCuFeO}}_5$ is a rare example of a cycloidal spiral magnet whose ordering temperature $T_{\text{spiral}}$ can be tuned far beyond room temperature by adjusting the degree of ${\mathrm{Cu}}^{2+}/{\mathrm{Fe}}^{3+}$ chemical disorder in the structure. This unusual property qualifies this material as one of the most promising spin-driven multiferroic candidates. However, very little is known about the response of the spiral to magnetic fields, crucial for magnetoelectric cross-control applications. Using bulk magnetization and neutron powder diffraction measurements under magnetic fields up to 9 T, we report here a temperature-magnetic field phase diagram of this material. Besides revealing a strong stability of the spiral state, our data uncover the presence of weak ferromagnetism coexisting with the spiral modulation. Since ferromagnets can be easily manipulated with magnetic fields, this observation opens new perspectives for the control of the spiral orientation, directly linked to the polarization direction, as well as for a possible future use of this material in technological applications.

Understanding ultrafast magnetization dynamics on the microscopic level is of strong current interest due to the potential for applications in information storage. In recent years, spin-lattice coupling has been recognized as essential for ultrafast magnetization dynamics. Magnetoelectric multiferroics of type II possess intrinsic correlations among magnetic sublattices and electric polarization $\left(P\right)$ through spin-lattice coupling, enabling fundamentally coupled dynamics between spins and lattice. Here, we report on ultrafast magnetization dynamics in a room-temperature multiferroic hexaferrite possessing ferrimagnetic (FM) and antiferromagnetic sublattices, revealed by time-resolved resonant x-ray diffraction. A femtosecond above-bandgap excitation triggers a coherent magnon in which the two magnetic sublattices entangle and give rise to a transient modulation of $P$. A microscopic mechanism for triggering the coherent magnon in this FM insulator based on the spin-lattice coupling is proposed. Our finding opens a general pathway for ultrafast control of magnetism.

Quantum computational devices currently under development have the potential to accelerate data analysis techniques beyond the ability of any classical algorithm. We propose the application of a quantum algorithm for the detection of unknown signals in noisy data. We apply Grover's algorithm to matched filtering, a signal processing technique that compares data to a number of candidate signal templates. In comparison to the classical method, this provides a speedup proportional to the square root of the number of templates, which would make possible otherwise intractable searches. We demonstrate both a proof-of-principle quantum circuit implementation and a simulation of the algorithm's application to the detection of the gravitational wave signal GW150914. We discuss the time complexity and space requirements of our algorithm as well as its implications for the currently computationally limited searches for continuous gravitational waves.

The XY model on a spherical surface, inspired by recently realized atomic gases trapped in a spherical shell, is analyzed here. Instead of a traditional latitude-longitude lattice, we introduce the much more homogeneous Fibonacci lattice and use classical Monte Carlo (MC) simulations to generate spin configurations. The results clearly show that topological defects, in the form of vortices, must exist in the stable configuration on a sphere but vanish in a plane due to a mathematical theorem. Using these spin configurations as training samples, a graph-convolutional network-based method is implemented to recognize different phases and successfully predict the phase-transition temperature. We also apply the density-based spatial clustering of applications with noise, a powerful machine-learning algorithm, to monitor the path of two vortices with topological charges on the sphere during MC simulations. Our results provide reliable predictions for quantum simulators using polaritons or future space-based experiments on ultracold atoms in microgravity.

This paper reports the findings of the late time behavior of the out-of-time-ordered correlators (OTOCs) via quantum kicked rotor and kicked top models with $\mathcal{PT}$-symmetric driving potential. An analytical expression of the OTOCs' power-law growth with time is yielded as $C\left(t\right)=G\left(K\right)t^{\gamma }$, with $\gamma$ being system dependent. Interestingly, the growth rate $G$ features a quantized response to the increase of the kick strength $K$. The physics behind this is the quantized absorption of energy from the non-Hermitian driving potential. This discovery and the ensuing establishment of the quantization mechanism in the dynamics of quantum chaos with non-Hermiticity will provide insights in chaotic dynamics, promising unprecedented observations in updated experiments.

One of the fundamental limits of classical optical microscopy is the diffraction limit of optical resolution. It results from the finite bandwidth of the optical transfer function (or OTF) of an optical microscope, which restricts the maximum spatial frequencies that are transmitted by a microscope. However, given the frequency support of the OTF, which is fully determined by the used optical hardware, an open and unsolved question is what is the optimal amplitude and phase distribution of spatial frequencies across this support that delivers the “sharpest” possible image. In this paper, we will answer this question and present a general rule how to find the optimal OTF for any given imaging system. We discuss our result in the context of optical microscopy, by considering in particular the cases of wide-field microscopy, confocal image scanning microscopy (ISM), 4pi microscopy, and structured illumination microscopy (SIM). Our results are important for finding optimal deconvolution algorithms for microscopy images, and we demonstrate this experimentally on the example of ISM. They can also serve as a guideline for designing optical systems that deliver best possible images, and can be easily generalized to nonoptical imaging such as telescopic imaging, ultrasound imaging, or magnetic resonance imaging.

The scattering between light and individual saturable quantum emitters can induce strong optical nonlinearities and correlations between individual light quanta. Typically, this leads to an effective attraction that can generate exotic bound states of photons, which form quantum mechanical precursors of optical solitons, as found in many optical media. Here, we study the propagation of light through an optical waveguide that is chirally coupled to three-level quantum emitters. We show that the additional laser coupling to a third emitter state not only enables control of the properties of the bound state but can even eliminate it entirely. This makes it possible to turn an otherwise focusing nonlinearity into a repulsive photon-photon interaction. We demonstrate this emerging photon-photon repulsion by analyzing the quantum dynamics of multiple photons in large emitter arrays and reveal a dynamical fragmentation of incident uncorrelated light fields and self-ordering into regular trains of single photons. These striking effects expand the rich physics of waveguide quantum electrodynamics into the domain of repulsive photons and establish a conceptually simple platform to explore optical self-organization phenomena at the quantum level. We discuss implementations of this setting in cold-atom experiments and propose an approach based on arrays of mesoscopic Rydberg-atom ensembles.

We develop a general framework for studying the equilibrium and non-equilibrium properties of arbitrary networks of Sachdev-Ye-Kitaev clusters coupled to thermal baths. We proceed to apply this technique to the problem of energy transport, which is known to be diffusive due to the strange metal behavior of these models. We use the external baths to impose a temperature gradient in the system and study the emerging non-equilibrium steady state using the Schwinger-Keldysh formalism. We consider two different configurations for the baths, implementing either a boundary or bulk driving, and show that the latter leads to a significantly faster convergence to the steady state. This setup allows us to compute both the temperature and frequency dependence of the diffusion constant. At low temperatures, our results agree perfectly with the previously known values for diffusivity in the conformal limit. We also establish a relationship between energy transport and quantum chaos by showing that the diffusion constant is upper bounded by the chaos propagation rate at all temperatures. Moreover, we find a simple analytical form for the non-equilibrium Green's functions in the linear response regime and use it to derive exact closed-form expressions for the diffusion constant in various limits. We mostly focus on uniform one-dimensional chains, but we also discuss higher-dimensional generalizations.

We investigate two separate notions of dynamical phase transitions in the two-dimensional nearest-neighbor transverse-field Ising model on a square lattice using matrix product states and a hybrid infinite time-evolving block decimation algorithm, where the model is implemented on an infinitely long cylinder with a finite diameter along which periodic boundary conditions are employed. Starting in an ordered initial state, our numerical results suggest that quenches below the dynamical critical point give rise to a ferromagnetic long-time steady state with the Loschmidt return rate exhibiting anomalous cusps even when the order parameter never crosses zero. Within the accessible timescales of our numerics, quenches above the dynamical critical point suggest a paramagnetic long-time steady state with the return rate exhibiting regular cusps connected to zero crossings of the order parameter. Additionally, our simulations indicate that quenching slightly above the dynamical critical point leads to a coexistence region where both anomalous and regular cusps appear in the return rate. Quenches from the disordered phase further confirm our main conclusions. Our work supports the recent finding that anomalous cusps arise only when local spin excitations are the energetically dominant quasiparticles. Our results are accessible in modern Rydberg experiments.

Given a set of local dynamics, are they compatible with a global dynamics? We systematically formulate these questions as quantum channel marginal problems. These problems are strongly connected to the generalization of the no-signaling conditions to quantized inputs and outputs and can be understood as a general toolkit to study notions of quantum incompatibility. In fact, they include as special cases channel broadcasting, channel extendibility, measurement compatibility, and state marginal problems. After defining the notion of compatibility between global and local dynamics, we provide a solution to the channel marginal problem that takes the form of a semidefinite program. Using this formulation, we construct channel incompatibility witnesses, discuss their operational interpretation in terms of an advantage for a state-discrimination task, prove a gap between classical and quantum dynamical marginal problems, and show that the latter is irreducible to state marginal problems.

Hydrogen-rich superhydrides are believed to be very promising high critical temperature (high $T_c$) superconductors, with experimentally observed critical temperatures near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g., ${\mathrm{LaH}}_{10}$ at 170 GPa and ${\mathrm{CeH}}_9$ at 150 GPa. With the motivation of discovering new hydrogen-rich high $T_c$ superconductors at the lowest possible pressure, quantitative theoretical predictions are needed. In these promising compounds, superconductivity is mediated by the highly energetic lattice vibrations associated with hydrogen and their interplay with the electronic structure, requiring fine descriptions of the electronic properties, notoriously challenging for correlated $f$ systems. In this paper, we propose a first-principles calculation platform with the inclusion of many-body corrections to evaluate the detailed physical properties of the Ce-H system and to understand the structure, stability, and superconductivity of ${\mathrm{CeH}}_9$ at high pressure. We report how the calculation of $T_c$ is affected by the hierarchy of many-body corrections and obtain a compelling increase in $T_c$ at the highest level of theory, which goes in the direction of experimental observations. Our findings shed significant light on the search for superhydrides in close similarity with atomic hydrogen within a feasible pressure range. We provide a practical platform to further investigate and understand conventional superconductivity in hydrogen-rich superhydrides.

Space-borne gravitational wave detectors like TianQin are expected to detect gravitational wave signals emitted by the mergers of massive black hole binaries. Luminosity distance information can be obtained from gravitational wave observations, and one can perform cosmological inference if redshift information can also be extracted, which would be straightforward if an electromagnetic counterpart exists. In this paper, we concentrate on the conservative scenario where the electromagnetic counterparts are not available, and comprehensively study if cosmological parameters can be inferred through a statistical approach, utilizing the nonuniform distribution of galaxies as well as the black hole mass-host galaxy bulge luminosity relationship. By adopting different massive black hole binary merger models, and assuming different detector configurations, we conclude that the statistical inference of cosmological parameters is indeed possible. TianQin is expected to constrain the Hubble constant to a relative error of about 4%–7%, depending on the underlying model. The multidetector network of TianQin and LISA can significantly improve the precision of cosmological parameters. In the most favorable model, it is possible to achieve a level of 1.7% with a network of TianQin and LISA. We find that without electromagnetic counterparts, constraints on all other parameters need a larger number of events or more precise sky localization of gravitational wave sources, which can be achieved by the multidetector network or under a favorable model for massive black hole mergers. However, in the optimistic case, where electromagnetic counterparts are available, one can obtain useful constraints on all cosmological parameters in the Lambda cold dark matter cosmology, regardless of the population model. Moreover, we can also constrain the equation of state of the dark energy without the electromagnetic counterparts, and it is even possible to study the evolution of equation of state of the dark energy when the electromagnetic counterparts are observed.

We show that, in the pure-quartic systems, modulation instability (MI) undergoes heteroclinic-structure transitions (HSTs) at two critical frequencies of ${\omega }_{c1}$ and ${\omega }_{c2}$ $({\omega }_{c2}>{\omega }_{c1})$, which indicates that there are significant changes of the spatiotemporal behavior in the system. The complicated heteroclinic structure of instability obtained by the mode truncation method reveals all possible dynamic trajectories of nonlinear waves, which allows us to discover the various types of Fermi-Pasta-Ulam (FPU) recurrences and Akhmediev breathers (ABs). When the modulational frequency satisfies $\omega <{\omega }_{c2}$, the heteroclinic structure encompasses two separatrixes corresponding to the ABs and the nonlinear wave with a modulated final state, which individually separate FPU recurrences into three different regions. Remarkably, crossing critical frequency ${\omega }_{c1}$, both the staggered FPU recurrences and ABs essentially switch their patterns. These HST behaviors will give vitality to the study of MI.

Ultrasound injection effect on a magnetic Bragg peak of yttrium iron garnet has been studied by quasielastic neutron scattering. The magnetic Bragg peak is vastly enhanced with decreasing temperature. The energy width increases proportionally to the square root of the sample temperature increase induced by the ultrasound injection. Based on a liquid model, the estimated effective mass becomes light when magnetic domain walls are removed under a magnetic field. Because the magnetic Bragg peak is enhanced by the lattice vibration, the enhancement is expected to closely relate to the spin-lattice coupling. The sharp drop is observed above 100 K for the longitudinal mode, indicating the degradation of the spin-lattice coupling. It is consistent with the suppression of the spin Seebeck effect when the temperature rises above 100 K, demonstrating the spin-lattice coupling as the degradation mechanism.