Artificially fabricated $3d/5d$ superlattices (SLs) involve both strong electron correlation and spin-orbit coupling in one material by means of interfacial $3d\text{−}5d$ coupling, whose mechanism remains mostly unexplored. In this work we investigated the mechanism of interfacial coupling in ${\mathrm{LaMnO}}_3\text{/}{\mathrm{SrIrO}}_3$ SLs by several spectroscopic approaches. Hard x-ray absorption, magnetic circular dichroism and photoemission spectra evidence the systematic modulation of the Ir ferromagnetism and the electronic structure with the change of the SL repetition period. First-principles calculations further reveal the mechanism of the SL-period dependence of the interfacial electronic structure and the local properties of the Ir moments, confirming that the formation of Ir-Mn molecular orbital is responsible for the interfacial coupling effects. The SL-period dependence of the ratio between orbital and spin components of the Ir magnetic moments can be attributed to the realignment of electron spin during the formation of the interfacial molecular orbital. Our results clarify the nature of interfacial coupling in this prototypical $3d/5d$ SL system and the conclusion will shed light on the study of other strongly correlated and spin-orbit coupled oxide heterointerfaces.

Higher-order topological materials with topologically protected states at the boundaries of their boundaries (hinges or corners) have attracted attention in recent years. In this paper, we utilize time-periodic driving to generate second-order topological superconductors out of systems which otherwise do not even allow second-order topological characterization. This is made possible by the design of periodic drives which inherently exhibit nontrivial winding in the time domain. Through the interplay of topology in both spatial and temporal dimensions, nonchiral Majorana modes may emerge at the systems' corners and sometimes even coexist with chiral Majorana modes. Our proposal thus presents an opportunity for Floquet engineering with minimal system complexity and its application in quantum information processing.

Motivated by the recent experimental realization of twisted double bilayer graphene (TDBG) samples, we study, both analytically and numerically, the effects of circularly polarized light propagating in free space and confined in a waveguide on the band structure and topological properties of these systems. These two complementary Floquet protocols allow us to selectively tune different parameters of the system by varying the intensity and light frequency. For the drive protocol in free space, in the high-frequency regime, we find that in TDBG with $AB/BA$ stacking, we can selectively close the zone-center quasienergy gaps around one valley while increasing the gaps near the opposite valley by tuning the parameters of the drive. In TDBG with $AB/AB$ stacking, a similar effect can be obtained upon the application of a perpendicular static electric field. Furthermore, we study the topological properties of the driven system in different settings, provide accurate effective Floquet Hamiltonians, and show that relatively strong drives can generate flat bands. On the other hand, longitudinal light confined in a waveguide couples to the components of the interlayer hopping that are perpendicular to the TDBG sheet, allowing for selective engineering of the bandwidth of Floquet zone-center quasienergy bands without breaking the symmetries of the static system.

We show that the microwave (MW) spectra in semiconductor-nanowire-based transmon qubits provide a strong signature of the presence of Majorana bound states in the junction. This occurs as an external magnetic field tunes the wire into the topological regime and the energy splitting of the emergent Majorana modes oscillates around zero energy owing to their wave function spatial overlap in finite-length wires. In particular, we discuss how these Majorana oscillations, and the concomitant fermion parity switches in the ground state of the junction, result in distinct spectroscopic features—in the form of an intermittent visibility of absorption lines—that strongly deviate from standard transmon behavior. In contrast, nonoscillating zero modes, such as topologically trivial Andreev bound states resulting from sufficiently smooth potentials, exhibit an overall standard transmon response. These differences in the MW response could help determine whether the junction contains topological Majoranas or not.

A solution to the quantum Zermelo problem for control Hamiltonians with general energy resource bounds is provided. Interestingly, the energy resource of the control Hamiltonian and the control time define a pair of conjugate variables that minimize the energy-time uncertainty relation. The resulting control protocol is applied to a single qubit as well as to a two-interacting qubit system represented by a Heisenberg spin dimer. For these low-dimensional systems, it is found that physically realizable control Hamiltonians exist only for certain quantized energy resources.

Skyrmion crystals support chiral magnonic edge states akin to electronic quantum Hall edge states. However, magnonic topology relies on the harmonic approximation, neglecting ubiquitous magnon-magnon interactions that yield a finite zero-temperature quantum damping. We demonstrate that spontaneous quasiparticle decay in two-dimensional ferromagnetic skyrmion crystals is a delicate issue, with the quantum damping ranging over several orders of magnitude. Flat magnon bands cause exceptionally strong spontaneous decay at twice their energy. The resulting externally controllable energy-selective magnon breakdown is measurable not only by scattering but also by magnetic resonance experiments, probing the magnetically active anticlockwise, breathing, and clockwise modes. They exhibit distinct decay behavior, with the clockwise (anticlockwise) mode being the least (most) stable mode out of the three. The quantum damping of the topologically nontrivial anticlockwise mode is negligible, establishing the harmonic theory as a trustworthy approximation at low energies, implying excellent prospects of topological magnonics in skyrmion crystals.

Turning a pristine Mott insulator into a correlated metal by chemical doping is a common procedure in strongly correlated materials physics, e.g., underlying the phenomenology of high-$T_c$ cuprates. The ruthenate bilayer compound ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ is a prominent example of a reversed case, namely, a correlated metal at stoichiometry that realizes a transition into an insulating state via Ti doping. We here investigate this puzzling metal-insulator transition (MIT) by first-principles many-body theory and elucidate a challenging interplay between electronic correlations and symmetry breaking on the Ru sublattice. While average effects on the ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ crystal structure are still relevant, the key to the MIT is the cooperation of electronic correlations with the spatial inhomogeneity in the defect regime. Together they give rise to the emergence of site-selective Mott criticality and competing orbital-ordering tendencies.

The on-demand preparation of higher-order Fock states is of fundamental importance in quantum information sciences. We propose and compare different protocols to generate higher-order Fock states in solid state quantum-dot–cavity systems. The protocols make use of a series of laser pulses to excite the quantum dot exciton and off-resonant pulses to control the detuning between dot and cavity. Our theoretical studies include dot and cavity loss processes as well as the pure-dephasing type coupling to longitudinal acoustic phonons in a numerically complete fashion. By going beyond the two-level approximation for quantum dots, we study the impact of a finite exchange splitting, the impact of a higher energetic exciton state, and an excitation with linearly polarized laser pulses leading to detrimental occupations of the biexciton state. We predict that under realistic conditions, a protocol which keeps the cavity at resonance with the quantum dot until the desired target state is reached is able to deliver fidelities to the Fock state $|5\rangle$ well above $40\%$.

Motivated by emergent SU(2) symmetry in the spin-orbit-coupled system, we study the spin-helix-driven insulating phase in a two-dimensional lattice. When both Rashba and Dresselhaus spin-orbit couplings are present, the perfect Fermi-surface nesting occurs at a special condition depending on the lattice geometry. In this case, the energies of spin up at any wave vector $\vec{k}$ are equivalent to the ones of spin down at $\vec{k}+\vec{Q}$ with the shifting wave vector $\vec{Q}$. Thus, the system stabilizes the magnetic insulator with spiral-like magnetic ordering even in the presence of tiny electron-electron interaction where the magnetic ordering wave vector is proportional to $\vec{Q}$. We first show the condition for the existence of the shifting wave vector in a general lattice model and emergent SU(2) symmetry in the spin-orbit-coupled system. Then, we exemplify this in a square lattice at half filling and discuss the insulating phase with (non)coplanar spin density wave and charge order. Our study emphasizes different possible types of two-dimensional magnetic materials that can be applicable to various van der Waals materials and their heterostructures with the control of electric field, strain, and pressure.

We perform a detailed analysis of the phase transition between the uniform superfluid and normal phases in spin- and mass-imbalanced Fermi mixtures. At mean-field level we demonstrate that at temperature $T\to 0$ the gradient term in the effective action can be tuned to zero for experimentally relevant sets of parameters, thus providing an avenue to realize a quantum Lifshitz point. We subsequently analyze damping processes affecting the order-parameter field across the phase transition. We show that in the low-energy limit, Landau damping occurs only in the symmetry-broken phase and affects exclusively the longitudinal component of the order-parameter field. It is however unavoidably present in the immediate vicinity of the phase transition at temperature $T=0$. We subsequently perform a renormalization group analysis of the system in a situation, where, at mean-field level, the quantum phase transition is second order (and not multicritical). We find that, at $T$ sufficiently low, including the Landau-damping term in a form derived from the microscopic action destabilizes the renormalization group flow toward the Wilson-Fisher fixed point. This signals a possible tendency to drive the transition weakly first order by the coupling between the order-parameter fluctuations and fermionic excitations effectively captured by the Landau-damping contribution to the order-parameter action.

Increasing the number of delays in nonlinear dynamical systems is generally assumed to lead to higher complexity, but “distributed delay” systems with an infinite number of delays to lesser complexity. This paradox is studied here using the Lang-Kobayashi laser model by first extending a recent method for Lyapunov exponent estimation from single to multiple delays. The Kolmogorov-Sinai entropy, permutation entropy, and time delay signature suppression initially increase with number of delays as the dynamics become more hyperchaotic. At a large number of delays that depends on the feedback strength, this trend reverses, leading to simpler dynamics. The phenomenon is also found in other delay equations, such as the Mackey-Glass system. A similar collapse is uncovered in the distributed delay case with broadening delay kernel.

Stochastic effects in the spin (de)polarization of an ultrarelativistic electron beam during photon emissions in a counterpropagating ultrastrong focused laser pulse in the quantum radiation reaction regime are investigated. We employ a Monte Carlo method to describe the electron dynamics semiclassically and photon emission and electron radiative polarization quantum mechanically. While in the latter the photon emission is inherently stochastic, we are able to identify its imprints in comparison with the semiclassical stochasticity-free method of radiative polarization applicable in the quantum regime. With an initially-spin-polarized electron beam, the impact of stochastic effects of photon emissions on the spin observable is demonstrated in the dependence of the depolarization degree on the electron scattering angle and the final electron energy (spin stochastic diffusion). With an initially unpolarized electron beam, the stochastic effects on the spin are exhibited in enhancing the known effect of splitting of the electron beam along the propagation direction into two oppositely polarized parts by an elliptically polarized laser pulse. The considered stochastic effects for the spin are observable with currently achievable laser and electron-beam parameters.

The characteristics of the photon channels in the collinear two-color high-order harmonic generation (HHG) are investigated with the vortices. It is found that the yields of the photon channels sensitively depend on ratio of the intensities $I_{2\omega }/I_{\omega }$. This sensitive dependence exhibits unique characteristics such as the suppression of the $n\text{−}\omega$ fundamental channel and the photon localization in the high-order channel. Therefore, one can adjust $I_{2\omega }/I_{\omega }$ to select one dominant channel to generate and tune the harmonic vortices with well-defined orbital angular momentum (OAM). Our findings provide an effective way to generate extreme ultraviolet vortices or helical attosecond pulses with well-defined and controllable OAM.

We investigate pattern formation in an inclined layer of liquid water with poorly conducting boundaries. We show that above the threshold for convection the presence of an inclination larger than 14 mrad determines a transition from a square pattern to longitudinal rolls, a behavior remarkably different than the one reported in the presence of inclined conducting boundaries, where transitions between convective planforms occur at inclination angles of the order of several degrees. The longitudinal rolls are characterized by a dimensionless wave vector $k\approx 1.8$, significantly smaller than $k\approx 3.117$ reported for conducting boundaries at large Prandtl number. The transition can be triggered by changing dynamically the inclination of the layer of fluid, and does not occur symmetrically in the two directions. By starting in the horizontal configuration, it develops slowly through the demolition of the square structure to form longitudinal rolls, while it develops rapidly in the other direction, through the formation of a cross-roll structure perpendicular to the longitudinal rolls.

We explore the nonlinear dynamics of a cavity optomechanical system. Our realization consisting of a drumhead nanoelectromechanical resonator (NEMS) coupled to a microwave cavity allows for a nearly ideal platform to study the nonlinearities arising purely due to radiation-pressure physics. Experiments are performed under a strong microwave Stokes pumping which triggers mechanical self-sustained oscillations. We analyze the results in the framework of an extended nonlinear optomechanical theory and demonstrate that quadratic and cubic coupling terms in the opto-mechanical Hamiltonian have to be considered. Quantitative agreement with the measurements is obtained considering only genuine geometrical nonlinearities: no thermo-optical instabilities are observed, in contrast with laser-driven systems. Based on these results, we describe a method to quantify nonlinear properties of microwave optomechanical devices. Such a technique, now available in the quantum electromechanics toolbox, but completely generic, is mandatory for the development of schemes where higher-order coupling terms are proposed as a resource, like quantum nondemolition measurements or in the search for new fundamental quantum signatures, like quantum gravity. We also find that the motion imprints a wide comb of extremely narrow peaks in the microwave output field, which could also be exploited in specific microwave-based measurements, potentially limited only by the quantum noise of the optical and the mechanical fields for a ground-state-cooled NEMS device.

The Coulomb interaction among massless chiral particles harbors unusual emergent phenomena in solids beyond the conventional realm of correlated electron physics. An example of such an effect is excitonic condensation of interacting massless Dirac fermions, which drives spontaneous mass acquisition and whose exact nature remains actively debated. Its precursor fluctuations growing prior to the condensate have been suggested by a recent nuclear magnetic resonance study in an organic material, hosting a pair of two-dimensional (2D) tilted Dirac cones at charge neutrality. Here, we theoretically study the excitonic transition in 2D tilted cones to understand the electron-hole pairing instability as functions of temperature ($T$), chemical potential ($\mu$), and in-plane magnetic field ($H$). By solving a gap equation within a weak-coupling treatment and incorporating self-energy effects due to the Coulomb interaction through a renormalization-group technique, we calculate excitonic instability in a $T\text{−}\mu \text{−}H$ parameter space, and find that the pairing is promoted as $H$ is increased but suppressed as $\mu$ moves away from the charge-neutrality point. We show that these findings are explained by enhanced or degraded Fermi-surface nesting between the Zeeman-induced pockets connecting the two tilted cones. Furthermore, to evaluate the precursor excitonic fluctuations in relation to this diagram, we consider the Coulomb interaction via a ladder-type approximation and calculate the nuclear spin-lattice relaxation rate, which provides rational ways to understand otherwise puzzling experimental results in the organic material by the μ and $H$ dependence of the instability.

We compare the exact evolution of an expanding three-dimensional Bose-Einstein condensate with that obtained from the effective scaling approach introduced in D. Guéry-Odelin [Phys. Rev. A 66, 033613 (2002)]. This approach, which consists in looking for self-similar solutions to be satisfied on average, is tested here in different geometries and configurations. We find that, in case of almost isotropic traps, the effective scaling reproduces with high accuracy the exact evolution dictated by the Gross-Pitaevskii equation for arbitrary values of the interactions, in agreement with the proof-of-concept of M. Modugno, G. Pagnini, and M. A. Valle-Basagoiti [Phys. Rev. A 97, 043604 (2018)]. Conversely, it is shown that the hypothesis of universal self-similarity breaks down in case of strong anisotropies and trapped geometries.

Genetic sequences are known to possess nontrivial composition together with symmetries in the frequencies of their components. Recently, it has been shown that symmetry and structure are hierarchically intertwined in DNA, suggesting a common origin for both features. However, the mechanism leading to this relationship is unknown. Here we investigate a biologically motivated dynamics for the evolution of genetic sequences. We show that a metastable (long-lived) regime emerges in which sequences have symmetry and structure interlaced in a way that matches that of extant genomes.

We revisit the cellular dynamical mean-field theory (CDMFT) for the single-band Hubbard model on the square lattice at half filling, reaching real-space cluster sizes of up to $9\times 9$ sites. Using benchmarks against direct lattice diagrammatic Monte Carlo at high temperature, we show that the self-energy obtained from a cluster center-focused extrapolation converges faster with the cluster size than the periodization schemes previously introduced in the literature. The same benchmark also shows that the cluster spin susceptibility can be extrapolated to the exact result at large cluster size, even though its spatial extension is larger than the cluster size.

We suggest a method for fast and robust quantum-state transfer in a Su-Schrieffer-Heeger (SSH) chain, which exploits the use of next-to-nearest-neighbor (NNN) interactions. The proposed quantum protocol combines a rapid change in the topological edge state, induced by a modulation of nearest-neighbor interactions, with a fine-tuning of NNN interactions operating a counterdiabatic driving which cancels nonadiabatic excitations. We use this shortcut technique on the edge states in order to obtain a quantum state transfer on a single dimerized chain and also through an interface that connects two dimerized Su-Schrieffer-Heeger chains with different topological order. We investigate the robustness of this protocol against both uncorrelated and correlated disorder and demonstrate its strong resilience to the former. We show that introducing spatial correlations in the disorder increases the robustness of the protocol, widening the range of its applicability. In comparison to traditional adiabatic methods, the short transfer time enabled by the NNN protocol in the SSH chains drastically improves the fidelity of the quantum state transfer.