Non-Hermitian skin effect (NHSE), which is a localization phenomenon in non-Hermitian systems, has recently been of great interest. Most previous works in various systems studied periodic systems. However, electromagnetic waves do not feel the periodicity of a system if the wavelength is sufficiently long, and it has not been clear that electromagnetic waves exhibit the localization caused by the non-Hermiticity itself even in uniform systems without the periodicity. Here, we establish the theory of the optical NHSE in non-Hermitian uniform media and show that the optical NHSE occurs even in uniform media. We apply our theory to subwavelength metamaterials and demonstrate the existence of a non-Hermitian skin mode in a multilayer metamaterial. Finally, we propose a concept of a stationarily excited skin mode to describe a lossy system under stationary excitation with real excitation frequency.

The switching mechanisms in artificial spin ice systems are investigated with focus on shakti and vertex-modified shakti lattices. Minimum energy paths are calculated using the geodesic nudged elastic band method implemented with a micromagnetic description of the system, including the internal magnetic structure of the islands and edge deviations. Two switching mechanisms, uniform magnetization rotation and domain wall formation, are found to have comparable activation energies. The preference for one over the other depends strongly on the saturation magnetization and the magnetic ordering of neighboring islands. Surprisingly, these mechanisms can coexist, leading to an enhanced probability of magnetization reversal. These results provide valuable insight that can help control internal magnetization switching processes in spin ice systems and help predict their thermodynamic properties.

We show that magnons in two-dimensional altermagnets can spontaneously decay at zero temperature. The decay rate is determined by quantum fluctuations and scattering processes involving the decay of a single magnon into three. These processes are kinematically allowed due to the convexity of the altermagnetic magnon dispersion. For small wave vectors $k$, the decay rate is proportional to $k^5$ with a direction-dependent prefactor, which is maximal along the diagonals of the Brillouin zone. Moreover, for a given momentum only magnons with one specific chirality can spontaneously decay.

Suppressing Floquet thermalization is an important goal in the field of Floquet engineering. Here, we propose a driving transparency mechanism to suppress the Floquet thermalization in periodically driven tilted lattices of interacting spinless fermions. By leveraging the interplay between the tilting and interaction, the system can be engineered to prevent direct energy absorption from the driving at particular frequencies. We analytically determine these driving transparency frequencies through the Floquet time-dependent perturbation theory. The system is near-integrable at the driving transparency frequencies. The suppression of thermalization by the driving transparency is demonstrated numerically by the violation of the Floquet eigenstate thermalization hypothesis, the retention of the initial state, and the logarithmic growth of entanglement entropy. Our work provides an intuitive way to suppress Floquet thermalization and offers an opportunity to engineer exotic nonequilibrium Floquet states in tilted lattice systems.

Networks of coupled Kerr parametric oscillators (KPOs) hold promise for the realization of neuromorphic and quantum computation. Yet, their rich bifurcation structure remains poorly understood. Here, we employ secular perturbation theory to map the stability regions of these networks and identify the regime where the system can be mapped to an Ising model. Starting with two coupled KPOs, we show how the bifurcations arise from the competition between the global parametric drive and linear coupling between the KPOs. We then extend this framework to larger networks with all-to-all equal coupling, deriving analytical expressions for the full cascade of bifurcation transitions. In the thermodynamic limit, we find that these transitions become uniformly spaced, leading to a highly regular structure. Our results reveal the precise bounds under which KPO networks have an Ising-like solution space, and thus provide crucial guidance for their experimental implementation.

In this paper we derive the Landau-Fokker-Planck (LFP) equation for the energy distribution function of a nondegenerate hot electrons in bulk semiconductors with strong electron-electron (e-e) interaction by the screened Coulomb potential described by a static dielectric function (the effect of dynamic screening is also analyzed qualitatively). The e-e scattering rates are calculated quantum-mechanically using the first Born approximation. The LFP equation was derived employing two different approaches: (i) a direct general transformation of the integral Boltzmann scattering operator; (ii) using the Chapman-Kolmogorov integral equation (CKE) for conditional transition probability densities. The screened potential allows to avoid any ad hoc cutoff procedures for tackling the problem of the Coulomb divergence of the matrix element in the scattering probability rates. However, the screening at the same time brings to the theory another problem, namely, that increase of the screening strength changes the character of the e-e scattering when it eventually becomes strongly inelastic. This corresponds to large energy transfer between the scattering electrons, which in turn, prohibits in principle considering the electron scattering process as a diffusion in the energy space (the necessary condition for the LFP approximation). We show that the screening effect must be explicitly included into the kinetic theory to correctly address the above two problems, and the cases of a weak and a strong screening need to be analyzed in detail. The LFP approximation is physically justified only for a weak screening. The obtained screening function coincides with the Brooks-Herring screening function. We have established general relationships between the kinetic coefficients in the LFP operator obtained by the above two approaches. The explicit expressions for the dynamic friction and the diffusion coefficients in the energy space are also obtained. Although, both approaches lead to the same solutions, we demonstrate that the CKE method is more universal approach, and the obtained here general relationships can be applied for any other scattering mechanism, provided that the required conditions are satisfied. We discuss the necessary validity conditions for the LFP equation, and show that for typical physical situations, e.g., for high-energy photoexcitation of the carriers, the LFP equation can be used up to the densities $\sim {10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$. However, for higher densities the screening energy becomes too large, which results in an increase of the minimum energy transfer in the scattering events, and the required for the LFP conditions are violated. In this case, one must use the integral e-e scattering operator, which we obtained in the form suitable for numerical solution. Dynamic screening extends the LFP validity range. As an example of the application of the LFP equation, we discuss the perovskite solar cells, which are characterized by relatively low and comparable energies of the optical and acoustic phonons, and the generated carrier densities of the order of ${10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$. In this case, the LFP equation can be applied for each of these interactions (electron-phonon and the e-e scattering). This allows to find correct distribution function of the hot electrons, and calculate the electron power loss, to which the e-e scattering makes the direct contribution through the corresponding energy relaxation channel in the kinetic equation.

We present a quantum repeater protocol for distributing entanglement over long distances, where a dedicated communication stage enables trial rates not limited by the travel time between repeater nodes. To accomplish this, each node contains several qubits that can couple to one single-photon emitter. Photons from the emitters in neighboring nodes generate heralded entanglement between qubits in these nodes. The protocol leaves the emitters disentangled from the rest of the system immediately after emitting the photons, thus allowing them to be reused to entangle other qubits without waiting for the repeater link round-trip time. This time multiplexing increases the protocol trial rate by up to an order of magnitude. The protocol is then combined with conventional deterministic entanglement swapping and heralded entanglement purification to extend the entanglement distance and reduce the entanglement error, respectively. We perform a complete protocol analysis by considering all relevant error sources, such as initialization, two-qubit gate, and qubit measurement errors, as well as the exponential decoherence of the qubits with time. The latter is particularly important since we analyze the protocol performance for a broad range of experimental parameters and obtain secret key rates ranging from 1 to $1000\mathrm{Hz}$ at a distance of 1000 km. Our results suggest that it is important to reach a qubit memory coherence time of around 1 s, and two-qubit gate and measurement errors on the order of ${10}^{-3}$ to obtain reasonable secret key rates over distances longer than achievable with direct transmission. While this work focuses on optimizing secret key rates, the protocol can also be used for Einstein-Podolsky-Rosen pair generation and is thus also relevant for, e.g., distributed quantum computing.

Physical quantities with long lifetimes have both theoretical significance in the study of quantum many-body systems and practical implications for quantum technologies. In this manuscript, we investigate the roles played by topological defects in the construction of quasiconserved quantities, using as a prototypical example the Kramers-Wannier duality defect in a deformed one-dimensional quantum transverse-field Ising model. We construct the duality defect Hamiltonian in three different ways: half-chain Kramers-Wannier transformation, utilization of techniques in the Ising fusion category, and defect-modified weak integrability breaking deformation. The third method is also applicable for the study of generic integrable defects under weak integrability breaking deformations. We also work out the deformation of defect-modified higher charges in the model and study their slower decay behavior. Furthermore, we consider the corresponding duality defect twisted deformed Floquet transverse-field Ising model and investigate the stability of the isolated zero mode associated with the duality defect in the integrable Floquet Ising model, under such weak integrability breaking deformation.

We investigate the quantum Hall effect in bilayer dice lattices with AA-BB-CC and AB-BC-CA stacking configurations, focusing on the interplay between flat band stability and band topology. For the aligned AA-BB-CC stacking, the system exhibits a narrow zero Hall conductivity plateau at the Dirac point and hybrid integer quantum Hall states $(n=\pm 2,\pm 4)$ in some energy regions, originating from the coexistence of spin, valley, and layer degeneracies. Additionally, the flat band generated by AA-BB-CC stacking is more easily destroyed. In contrast, the cyclic AB-BC-CA stacking displays irregular Hall conductivity due to complex band structures lacking complete flat bands. By tuning interlayer coupling strength $t_{\perp }$ and hopping parameter $\alpha$, the corresponding results show that the position of the Dirac point relative to the high-symmetry point in the Brillouin zone determines the appearance of the conductivity transitions. A mixed integer quantum Hall effect with $n$ = 2 and  = 4 appears for specific values of $\alpha$.

For several decades it has been known that divergences arise in the ground-state energy and chemical potential of unitary superfluids, where the scattering length diverges, due to particle-hole scattering. Leading textbooks and research articles recognize that there are serious issues but ignore them due to the lack of an approach that can regularize these divergences. We find a solution to this difficulty by proposing a general method, called the weighted Hartree-Fock-Bogoliubov theory, to handle multiple decomposition channels originating from the same interaction. We distribute the interaction in weighted channels determined by minimization of the action, and we apply this idea to unpolarized Fermi superfluids. Using our method, we solve a long-standing difficulty in the partitioning of the interaction into Hartree, Fock, and Bogoliubov channels for Fermi superfluids, and we obtain a phase diagram at the saddle-point level, which contains multichannel nonperturbative corrections. In particular, we find a previously overlooked superfluid phase for weak interactions, which is dominated by particle-hole processes, in addition to the usual superfluid phase only containing particle-particle physics.

The coupling between magnetism and topological states at a topological insulator (TI)-magnetic insulator interface can induce exchange gap opening and spin texture change, resulting in many emergent transport phenomena, including anisotropic magnetoresistance (AMR) and planar Hall effect (PHE). While AMR/PHE have been reported in several ferromagnetic insulator-TI heterostructures so far, such effects in antiferromagnetic insulator-TI heterostructure remain elusive. Here, we observe unique features of AMR and PHE in an antiferromagnetic insulator-TI heterostructure $\mathrm{MnSe}\text{/}{\left(\mathrm{Bi},\mathrm{Sb}\right)}_2\mathrm{T}{\mathrm{e}}_3$. Specifically, at low magnetic fields ($H$), the in-plane AMR exhibits dips under $H$ applied parallel to the current ($H\text{//}I$) but peaks under the perpendicular geometry ($H\text{⊥}I$), opposite to the zero AMR features in ferromagnetic insulator-TI heterostructures. The low-field PHE is most striking at $H\text{//}I$, but gradually suppressed when $H$ deviates from parallel direction. At high magnetic fields, both AMR and PHE show prominent π-period oscillation. Gate-tuning and temperature-dependence measurements demonstrate that the observed AMR/PHE originate from the interplay between the topological surface state of TI with the spin canting and magnetic phase transition of MnSe. These results not only differentiate the AMR/PHE in TI-based magnetic heterostructure from the pristine TI, but also offer a feasible way to distinguish spin Hall effect and AMR in TI-based heterostructures.

As has been known for almost 20 years, topological characteristics of polygonal proliferative epithelial cells of various animal and plant species are universal. Here, we address the question of whether this universality paradigm is applicable to the level of colonial organisms, i.e., at a significantly higher level of life organization than cell populations. By comparing the cellular structure of the epithelium with the arrangement of individual polyps in coral colonies, we discover common topological patterns at distinct levels of life structuring. We hypothesize that the mechanism behind this universality is a repulsion between structural units limited by a certain critical distance. By minimizing the corresponding repulsive energy, we produce packings, which are similar to the epithelial and colonial systems in the distribution of structural units by both the number of their neighbors and their area. The surprising analogies between the systems together with the developed theoretical approach could provide an efficient tool for further studies on morphogenesis, development, and evolution of living systems.

It is well known that the time-dependent response of a correlated system can be inferred from its spectral correlation functions. As a textbook example, the zero-sound collective modes of a Fermi liquid appear as poles of its particle-hole susceptibilities. However, the Fermi liquid’s interactions endow these response functions with a complex analytic structure, so that this time-frequency relationship is no longer straightforward. We study how the geometry of this structure is modified by a nontrivial band geometry, via a calculation of the zero-sound spectrum of a Dirac cone in two dimensions. We find that the chiral wave functions, which encode the band geometry, fundamentally change the analytic structure of the response functions, which encode its Riemannian geometry. As a result, isotropic interactions can give rise to a variety of unconventional zero-sound modes, which, due to the geometry of the functions in frequency space, can only be identified via time-resolved probes. These modes are absent in a conventional Fermi liquid with similar interactions, so that these modes can be used as a sensitive probe for the existence of Dirac points in a band structure.

Superconducting circuit quantization conventionally starts from classical Euler-Lagrange circuit equations of motion. Invoking the correspondence principle yields a canonically quantized description of circuit dynamics over a bosonic Hilbert space. This approach has been very successful for describing experiments, but implicitly starts from the classical Ginsberg-Landau mean-field theory for the circuit. Here, we employ a different approach that starts from a microscopic fermionic Hamiltonian for interacting electrons, whose ground space is described by the Bardeen-Cooper-Schrieffer (BCS) many-body wave function that underpins conventional superconductivity. We introduce the BCS ground space as a subspace of the full fermionic Hilbert space, and show that projecting the electronic Hamiltonian onto this subspace yields the standard Hamiltonian terms for Josephson junctions, capacitors, and inductors, from which standard quantized circuit models follow. This approach does not impose a spontaneously broken symmetry so that it consistently describes quantized circuits that support superpositions of phases, and the canonical commutation relations between phase and charge are derived from the underlying fermionic commutation properties, rather than imposed. By expanding the projective subspace, this approach can be extended to describe phenomena outside the BCS ground space, including quasiparticle excitations.