Papers

Floquet theory describes quantum systems governed by time-periodic Hamiltonians, much as Bloch theory describes spatially periodic solids. In voltage-biased multiterminal Josephson junctions, the Josephson relation causes superconducting phase differences to evolve periodically in time, thereby providing an intrinsic Floquet drive. In this Letter, we consider three-terminal Josephson junctions formed on a ballistic two-dimensional normal conductor with a continuum of electronic states. We show that the quartet and higher-order multipair processes yield characteristic Floquet-multiple Andreev reflection (Floquet-MAR) finite-bias conductance and noise resonances that are parameterized by the bias voltage and electrochemical potential. This microscopic picture opens a route toward implementing and probing Floquet-MAR physics in ballistic multiterminal Josephson junctions.

In non-diffusive conduction regimes of strongly correlated quantum electron systems, electromagnetic perturbations simultaneously probe the electronic dynamics in time and space: the exchanged energy $\hbar \omega$ excites retarded, i.e., frequency-dependent, many-body interactions, while the probing spatial modulation renders the response spatially nonlocal, i.e., dependent on the external wave vector $\vec{q}$. This work derives the nonlocal electrodynamic response of such dynamical quantum fluids assuming local but frequency-dependent self-energies and particle-hole irreducible two-particle vertex functions, and preserving charge/mass conservation. The latter is ensured by Bethe-Salpeter equations for renormalized interaction vertices, entering the Kubo formalism for two-particle correlation functions (e.g., for density, currents, momentum, stress). Within such a framework, exact symmetry criteria for the absence of vertex corrections are inferred. In particular, vertex corrections vanish at $q=0$ for single-particle dispersions that are even and bare interaction vertices that are odd with respect to specific momentum-space point group transformations, including inversion for vector vertices, and mirror reflections or two- or higher-fold rotations for tensor vertices. If the dispersion is isotropic, vertex corrections vanish from the transverse part ($\perp\vec{q}$) of vectorial vertices (such as for electric/particle current) at any finite $\hbar \omega$ and $\vec{q}$. These cancellations extend to the full current-current correlation function for quadratic isotropic dispersion. Further symmetry breaking, multiband effects, and the additional imposition of momentum conservation, are discussed, with application to the Hall viscosity of Landau levels. Explicit expressions for generic nonlocal correlation functions are derived for Fermi liquids and non-Fermi liquids.

The electron pairing mechanism by the interfacial charge-induced adsorption mode of high-temperature superconductors is revealed. For the YBCO superconductors, the coupling of electrons and valence-flexible state of oxygen ions forms a charge-regulated interfacial layer induced by the adsorption potential, and electrons are paired by sharing the optimized interfacial structure and exchanging the adsorption mode, generating strong attraction to form Cooper pairs. Then the effective interaction potential between electrons is exactly derived in details, as well as the electron-adsorption-mode coupling strength, in which the adsorption coupling constant is up to 43.4. Furthermore, we verify that d-wave come from the anisotropy of interfacial adsorption forces, and explain the pseudo-energy gap behavior. By using the one-dimensional Ginzburg-Landau equation in the absence of a magnetic field, we obtain the coherence length expression, and the coherence length calculated is very close to the literature results. By establishing the energy gap equation, we obtain the superconducting gap , which is very close to the measured result of 17meV by Scanning Tunneling Microscopy/Spectroscopy. These quantitative predictions close to the known results could verify our theoretical framework.

Nonequilibrium Green's functions provide a powerful framework for studying quantum many-body dynamics including the laser-induced dynamics in solids. The Non-Equilibrium Systems Simulation package (NESSi) offers an efficient platform for such simulations, ranging from perturbative approaches like nonequilibrium $GW$ to nonequilibrium dynamical mean-field theory. However, simulations based on nonequilibrium Green's functions become computationally demanding when the dynamics span a large temporal range, such as from sub-femtosecond electron dynamics to the picosecond dynamics of collective modes. Due to the memory integral in the Kadanoff-Baym equations, which serve as equations of motion for nonequilibrium Green's functions, the computational cost scales as $\mathcal{O}(N_t^3)$ with the number of timesteps $N_t$, and the memory requirement scales as $\mathcal{O}(N_t^2)$. In this work, we extend NESSi by incorporating techniques that aim to overcome this bottleneck: (i) By truncating the memory integrals in the KBE to a maximum of $N_c$ timesteps, the computational complexity is reduced to $\mathcal{O}(N_tN_c^2)$, and the memory requirement to $\mathcal{O}(N_c^2)$. Provided that the results converge with respect to the cutoff $N_c$, memory truncation allows to extend the simulations to significantly longer times. (ii) We introduce functionalities to describe nonequilibrium steady states, i.e. time-translationally invariant nonequilibrium states. Such states are relevant for transport settings, and they provide an approximate description of slowly evolving (prethermal) nonequilibrium states.

Shape anisotropy of individual building blocks plays a crucial role in creating exotic structures and controlling phase behavior in equilibrium systems. We present a combined experimental and simulation study in which we used light-driven self-propelled rods to investigate when and how shape-induced alignment and steric and hydrodynamic interactions govern self-organization. Varying rod aspect ratio and area fraction causes the system to evolve from active Brownian motion to swarming, active turbulence, flocking, large clusters, and jamming. A state diagram summarizes emergent behaviors, and spatiotemporal analyses reveal distinct giant-number fluctuations across states. This minimal model offers insight into the self-organization of biological rodlike microswimmers, enabling the decoupling of physical from biological mechanisms. Our results provide design rules for programmable synthetic active materials and highlight parallels with bacterial swarms and other biological assemblies.

The von Neumann entanglement entropy of exact valence-bond ground states is studied in two frustrated one-dimensional spin chains: the spin-1/2 Majumdar-Ghosh (MG) model and the spin-3/2 J1-J2-J3 chain in its fully dimerized (FD) and partially dimerized (PD) phases. Using matrix-product-state representations, the entropy is computed as a function of system size for three complementary bipartitions - half-chain, single-site, and pairwise - under both open and periodic boundary conditions. In all cases, the entropy saturates to a finite constant in the thermodynamic limit, confirming area-law behavior. The saturation values, extracted via finite-size scaling, are directly related to the underlying virtual-spin bond structure. The MG model and FD phase exhibit similar entanglement behavior, differing primarily in saturation magnitude determined by spin value and bond multiplicity, and both display even-odd oscillations and exponential convergence with system size. In contrast, the PD phase shows qualitatively distinct signatures, including multiple half-chain saturation values depending on the bond type at the cut, asymmetric edge contributions in the single-site entropy, and a multi-band structure in the pairwise entropy reflecting the coexistence of single- and double-singlet bonds. These results establish entanglement entropy as a robust signature of frustrated bond architecture, enabling clear distinction among dimerized phases with different spin magnitude, bond multiplicity, and dimerization patterns.

This work presents a general thermodynamic approach to describe particle diffusion on a lattice, a model used to study transport processes in solids and on surfaces. By treating each lattice site as an open thermodynamic system, the effects of microscopic particle interactions are represented through the chemical potential. A fundamental relationship between the Onsager matrix ($L$) and its ideal-system counterpart ($L_\text{id}$, where interactions are neglected) using the determinant of the covariance matrix is demonstrated. This framework allows for the calculation of transport coefficients using the combination of their ideal values and thermodynamic properties. The general result is successfully applied to reproduce the Darken equation for substitutional diffusion in solids and to derive the non-diagonal diffusion matrix of the Zhdanov model for surface diffusion of Langmuir particles. In the last case, analytical predictions are further validated through numerical simulations across various interaction potentials.

The effective mass approximation is widely used across models of carrier transport, optical response, and excitons in semiconductors and insulators, but its validity hinges on the assumption that the band dispersion $E_n(\mathbf{k})$ at the relevant extremum is analytic. We prove that analyticity holds at any non-degenerate extremum for Kohn-Sham density functional theory (DFT) with local or hybrid exchange-correlation functionals, for Hartree-Fock, and for band-edge $G_0 W_0$ quasiparticle energies in gapped systems. Band non-analyticity (or warping) in these settings is therefore intrinsically tied to degeneracy. We then use group theory to determine the symmetry-allowed form of the effective mass tensor for each of the 32 crystallographic point groups, providing a stringent consistency check on first-principles calculations. As a representative application, we show that the electron and hole effective masses at the $K$ point of monolayer MoS$_2$ must be strictly isotropic at the DFT and $G_0W_0$ levels.

We use quantum mechanical scattering calculations implemented in a basis of tight-binding muffin-tin orbitals to calculate nonequilibrium spin and orbital currents in transition metals with a view to understanding the length scale on which they decay. In the case of spin currents, the relaxation length, called the spin-flip diffusion length, is reasonably well understood. We apply our experience with spin currents to study orbitally-polarized currents and find that they behave qualitatively differently. Upon injection from a lead, orbital currents decay within a few atomic layers contradicting the current interpretation of experimental results which appear to show exponential decay on the length scale of the spin-flip diffusion length and longer. When spin-orbit coupling is included, the injected orbital current is partially converted into a spin current within a few atomic layers. This insight provides a new perspective on the physics of the orbital Hall effect.

We report a significant enhancement of room-temperature photoluminescence from trivalent erbium-doped (Er3+) silicon nitride (Si3N4) metasurfaces at the telecommunication wavelength prepared via ion implantation. The metasurfaces, consisting of periodic nanocylinder arrays, are designed to support Mie-type resonances that tailor the local density of optical states. By systematically optimizing the nanocylinder radii, we achieve a photoluminescence (PL) enhancement factor of ~18 at a radius of 390 nm after thermal annealing, which is in excellent agreement with our simulations. Time-resolved PL measurements reveal a nearly ten-fold reduction in luminescence lifetime, confirming that the enhancement is primarily driven by the Purcell effect. Furthermore, we demonstrate that the PL intensity is strongly dependent on the Er3+ ion implantation depth, with a four-fold increase in emission observed from 20 nm to 80 nm ion range. These results provide a robust pathway for integrating efficient, active light sources into CMOS-compatible photonic device.

Following the Fukushima Daiichi disaster, an increasing number of studies concentrate on the development of Accident Tolerant Fuel (ATF) cladding materials for nuclear fuel, aiming to prevent the oxidation of zirconium during incidents such as Loss of Coolant Accident (LOCA) and to effectively lower the amount of heat and hydrogen released during emergency core cooling (ECC). Zirconium alloy cladding with a protective chromium (Cr) coating is considered one of the promising candidates, largely due to its relatively short timeline for deployment in nuclear power plants. In this study, Cr-coated and uncoated Zircaloy-4 claddings were evaluated using high temperature X-ray diffraction (HT-XRD) in vacuum over a temperature range from RT to 1100oC. The temperatures corresponding to the formation of oxide phases are >200oC and >600oC for the uncoated and Cr-coated samples, respectively. SEM and TEM characterisation of the sub-surface in Cr-coated specimen after HT-XRD revealed Fe segregation, formation of Zr(Fe,Cr)2 Laves phase and nano-bubbles at the former Cr / Z4 interface.

One of the most powerful strategies to address properties of real many-body systems is to incorporate data obtained for models, for example, to use data of the homogeneous electron gas in order to build the Local Density Approximation for the Kohn-Sham exchange-correlation potential. In the present work, we examine to what extent we can use model data to design functionals directly for observables of materials. In particular, we study different approximations for the charge density of real inhomogeneous materials expressed as a simple, explicit functional of a given Kohn-Sham potential, using as central building block the Lindhard density-density response function of the homogeneous electron gas. Our increasingly realistic set of approximations includes a fully nearsighted expression equivalent to the Thomas-Fermi approximation, functional Taylor expansions, and different approximations to the Connector Theory developed in [Aouina et al., npj Computational Materials 11, 242 (2025)]. In all cases, the charge density is obtained without ever solving the Kohn-Sham Schrödinger equation. Results for cubic helium, a prototypical strongly inhomogeneous material, as well as the covalent semiconductor silicon and metallic aluminum, systematically improve with higher levels of approximation. At the present stage, the results may be used for qualitative discussions or as optimized starting point for a self-consistent Kohn-Sham cycle. More generally, their quality indicates that this is a promising route to obtain functional expressions for observables that are relatively simple to calculate and to analyze.

In this report, a unified description of the loss of saturation magnetization in the presence of a distribution of finite-size effects is provided for weakly disordered spin-1/2 ferromagnets. This description allows us to derive a unified form of the Bloch equation for these systems. We further extend this approach to obtain a unified expression for spin transport in such systems.

In this PhD thesis, we study topological defects in two-dimensional non-equilibrium systems, focusing on active extensions of the XY model, including activity, mobility and non-reciprocity. In a noisy Kuramoto lattice with short-range coupling, intrinsic frequency heterogeneity destroys quasi-long-range order and fragments the system into finite domains. Defects unbind at all temperatures and exhibit superdiffusive random walks, advected by evolving domain boundaries. By contrast, when oscillators are allowed to move in space, the system undergoes a Berezinskii-Kosterlitz-Thouless transition and regains quasi-long-range order, revealing the fundamental role of motility in sustaining coherence. We also analyse a non-reciprocal O(2) model with vision-cone couplings and derive a continuum theory that captures the same large-scale physics. Non-reciprocity selects defect shapes, enriches the annihilation process, and reshapes patterns through advection. Together, these results elucidate the fundamental role of activity and non-reciprocity in shaping topological defects and ordering in non-equilibrium systems. Keywords: Topological defects, XY model, Steep XY model, Kuramoto model, Non-reciprocal interactions, Active matter, Phase transitions, Berezinskii-Kosterlitz-Thouless transition, Non-equilibrium statistical mechanics

Single-event burnout (SEB) in silicon carbide (SiC) power MOSFETs is often characterized by deterministic threshold quantities. Near the boundary between recovery and runaway, stochastic variability can make this threshold description probabilistic rather than sharp. This work introduces a first-passage perspective for stochastic threshold broadening in burnout. The process is described by a reduced electrothermal feedback-relaxation model with an absorbing boundary. The model combines carrier multiplication, avalanche feedback, localized heating, carrier loss, and thermal relaxation. Stochastic carrier and thermal terms represent unresolved event-level variability. The main finding is that finite fluctuations broaden the deterministic burnout threshold into a probabilistic transition band. Noise-induced subthreshold runaway also emerges, where nominally recoverable conditions can still fail through rare stochastic excursions. First-passage-time distributions resolve the time scale of burnout and survival probabilities further distinguish rapid feedback-dominated runaway from delayed stochastic failure. A feedback-relaxation phase diagram organizes recoverable, probabilistic, and rapidly unstable regimes. This framework provides a statistical-physics interpretation of threshold dispersion in single-event burnout of SiC power MOSFETs by linking coarse-grained electrothermal dynamics to probabilistic and time-resolved failure observables.

The nonconservative elastic responses of active solids have driven a recent explosion of interest in two-dimensional "odd" elasticity: small, linear deformations of these Cauchy elastic solids enable new behaviour absent from classical, passive elasticity. Here, we establish the description of large, nonlinear deformations of isotropic two-dimensional Cauchy elastic solids. We apply our framework to the Rivlin problem, perhaps the simplest problem of elasticity lacking a linear analogue: a square deforms under dead load tractions. Surprisingly, we find that oddness suppresses the bifurcations of a passive Rivlin square. By contrast, we discover that the bifurcations of a three-dimensional Rivlin cube survive oddness even though there is no isotropic, odd linear elasticity in three dimensions. Our results thus form the basis for describing large deformations of active, biological solids while revealing their unexpected nonlinear behaviour that arises even in minimal problems.

Frequency locking between coupled laser systems provides a powerful mechanism for stabilizing and controlling coherent emission, yet its implementation and applicability down to the nanoscale remains unknown and unexplored. Here, we demonstrate optical coupling and frequency locking in closely spaced ZnO nanowire lasers operating in the extreme near field (gap < 10 nm). We observe both full and partial frequency locking, manifested as the alignment of all or a subset of the lasing modes, by spatially controlling the optical excitation. We also observe single-mode lasing in a coupled nanowire pair where the multi-mode lasing of individual nanowires is suppressed. In contrast to previously reported coupled-cavity nanowire lasers, where spectral control arises from static filtering mechanisms such as the Vernier effect, our results indicate a dynamically established relationship between actively lasing nanowires. These findings establish frequency locking as a robust and tunable mechanism in nanowire lasers, opening new routes toward stabilized and controllable nanoscale light sources for integrated nanophotonic systems.

The record age tau_k, defined as the time between the k-th and k+1-st record-breaking events, is a central observable of extreme-value statistics. In Markovian processes, the absence of memory makes tau_k independent of k. How memory breaks this invariance and induces aging, meaning a dependence of tau_k on k, remains a fundamental question, closely connected to widely observed aging phenomena in non-Markovian dynamics. In this Letter, we derive the exact asymptotic distribution of tau_k for saturating self-interacting random walks, a broad class of non-Markovian processes. We uncover two asymptotic regimes, in agreement with recent scaling predictions: at short times (tau much smaller than k squared), record statistics are governed by the geometry of the explored region, while at long times (tau much larger than k squared), memory effects become subdominant and reduce to nontrivial prefactor corrections. Our exact result provides a rare analytic window beyond scaling theory and extends to a framework that fully quantifies aging dynamics in the presence of saturating self-interaction.

Cation-based Ag/Cu filaments formed in an insulating $\alpha$-Si matrix are widely used as memristors in crossbar arrays for efficient in-memory computing. However, the stochastic nature of filament formation and rupture gives rise to device-to-device and cycle-to-cycle variation. Despite successful implementation of large-scale memristor arrays, systematic studies of filament parameters and their spatial distribution in the memristors are scarce. In this work, we use conductive atomic force microscopy (c-AFM) to probe the spatial distribution of conductive filaments in $\alpha$-Si memristors. The charge transport is dominated by a limited number of discrete filaments rather than by uniform conduction across the device area. The systematic analysis of the experiment gives the mean surface density of the conductive filaments $\sim$3200 per $\mu\text{m}^2$. Both volatile and non-volatile filaments can be found within one memristor. The experimental data and the nature of volatile and non-volatile filaments may be explained within the model of multiple trap assisted tunnelling. The model yields reasonable estimates for physical properties for both types of filaments.

We revisit the effect of surface roughness on midgap Andreev edge states (MAES) in p- and d- wave superconductors. For a perfectly specular surface, MAES form a flat band at the Fermi energy, which manifests as a sharp midgap peak in the surface density of states (SDOS). Previous theoretical studies have shown that MAES in p- and d-wave superconductors respond markedly differently to surface roughness. In the d-wave state, diffuse surface scattering significantly broadens the midgap peak in the SDOS, accompanied by the emergence of a V-shaped structure centered at the Fermi energy. In contrast, the midgap peak in the p-wave state remains robust against diffuse scattering. In this work, we clarify the physical origin of this contrasting behavior. A key aspect of our analysis is that the flat band in the d-wave state consists of two distinct types of MAES modes. We show that inter-mode diffuse scattering leads to substantial broadening of the midgap peak and to the formation of the V-shaped structure. By contrast, the robustness of MAES in the p-wave state arises from the presence of a single MAES mode in the flat band. These results provide new insight into the response of MAES to surface roughness.

In this chapter, I will enter into the roots of entropically-driven transport with a focus on diffusio-osmotic transport in nanochannels. Diffusio-osmosis is a subtle surface transport, originating in entropic driving forces occuring within the diffuse layers at solid boundaries. Specifying diffusio-osmosis to nanochannels may first look like a marginal refinement, yet it reveals that osmotic drivings can arise in channels and membranes without the prerequisite of semi-permeability, so that diffusio-osmosis extends the domain of existence of entropically driven transport. Osmosis and diffusio-osmosis are two faces of the same phenomenon, naturally embedded in an Onsager framework and quantified by local and global force balances. This perspective clarifies why nanochannels are privileged arenas where diffusio-osmosis and its consequence do flourish. Throughout the chapter, I discuss a set of conceptually relevant examples to show how diffusio-osmosis "pops up" in various situations: as enhanced diffusion, mechano-sensitivity, rectified osmotic flows and, ultimately, as a lever for osmotic energy conversion from single nanopores to membrane modules approaching industrial reality.

The optical control of domain structures in ferroelectrics is of great interest. In the present work, we demonstrate the reliable creation of charged domain walls - conductive channels in otherwise insulating barium titanate - by a combined effect of light and electric field. We propose a scenario for the documented process, in which the bulk photovoltaic effect plays the key role, providing charge screening at the walls. Our scenario is supported by the results of phase-field simulations. The results are of interest for future reconfigurable electronic and opto-electronic devices.

Universal scaling near phase transitions is one of the central ideas of physics, linking the growth of spatial correlations to the slowing down of dynamics. So far, direct experimental access to this critical behavior has remained largely confined to equilibrium many-body systems, and especially to static critical behavior. Here we probe how universality emerges in a driven quantum fluid of light formed by exciton–polaritons in a semiconductor microcavity. By probing the fluctuation-dominated disordered phase below the condensation threshold, we directly measure both the static growth of the correlation length $\xi$ and the dynamical slowing down of the relaxation time $\tau$. We find that these quantities obey the universal relation $\tau \propto \xi^{z}$ with dynamical exponent $z \approx 2$, revealing diffusive dynamics of a non-conserved order parameter. Our results extend the physics of critical dynamics from equilibrium matter to driven optical systems, bridging quantum condensates and lasers.

Graphene has been one of the most investigated materials in the last decade. Its unique optoelectronic properties have indeed raised it to an ideal and revolutionary candidate for the development of entirely novel technologies across the whole electromagnetic spectrum, from the microwaves to the x-rays, even crossing domain of intense application relevance, as terahertz (THz) frequencies. Owing to its exceptionally high tensile strength, electrical conductivity, transparency, ultra-fast carrier dynamics, non-linear optical response to intense fields, electrical tunability and ease of integration with semiconductor materials, graphene is a key disruptor for the engineering of generation, manipulation, and detection technologies with ad-hoc properties, conceived from scratch. In this review, we elucidate the fundamental properties of graphene, with an emphasis on its transport, electronic, ultrafast and non-linear interactions, and explore its enormous technological potential of integration with a diverse array of material platforms. We start with a concise introduction to graphene physics, followed by the most remarkable technological developments of graphene-based photodetectors, modulators, and sources in the 1-10 THz frequency range. As such, this review aims to serve as a valuable resource for a broad audience, ranging from novices to experts, who are keen to explore graphene physics for conceiving and realizing micro- and nano-scale devices and systems in the far infrared. This would allow addressing the present challenging application needs in quantum science, wireless communications, ultrafast science, plasmonics and nanophotonics.

A systematic investigation of the structural, electronic, and spin-orbital transport properties of the AgI (110) surface is presented using first-principles calculations combined with analytical modelling. The non-centrosymmetric and nonsymmorphic nature of the system gives rise to a robust persistent spin texture (PST), characterized by a unidirectional spin configuration and suppressed spin relaxation, enabling an effectively infinite spin lifetime. Unlike previously reported PST materials, which are predominantly based on chalcogen compounds, this work demonstrates that a halide semiconductor can host PST, thereby significantly expanding the materials platform for spintronic applications. The underlying mechanism is captured using an effective spin-orbit coupled Hamiltonian, which reproduces the anisotropic spin splitting and momentum shift observed in the band structure. This work introduces two new analytical models describing PST and compares them with existing models, offering new perspectives on PST arising from spin-orbit interaction. In addition, the system exhibits sizable intrinsic spin Hall conductivity (SHC) and orbital Hall conductivity (OHC), highlighting its potential for efficient charge-to-spin and charge-to-orbital conversion. The PST is found to be robust against biaxial strain, structural distortion, and multilayer formation, while a vertical electric field breaks the symmetry protection and drives a transition to a Rashba-type spin texture. These findings establish AgI (110) as a promising platform for realizing long-lived spin transport and tunable spin-orbit functionalities in the low-dimensional halide systems.

Deterministic and bright quantum light sources based on scalable semiconductor technologies are a crucial building block for future quantum communication networks. While circular Bragg gratings (CBGs) are highly effective for extracting light from solid-state quantum emitters, conventional architectures rely on complex multi-layer processing or flip-chip bonding, which introduce detrimental strain and limit scalability. Here, we present a fabrication-minimal approach to realize monolithic, free-standing CBG cavities with deterministically positioned single GaAs quantum dots (QDs). By utilizing aspect-ratio-dependent etching (ARDE) in a single-step top-down process, we achieve the necessary vertical structural asymmetry for directional emission without requiring bottom reflectors. Finite-difference time-domain (FDTD) simulations validate this geometry, predicting free-space extraction efficiencies up to $68 \, \%$ and coupling efficiencies of $40 \, \%$ into a lensed single-mode fiber ($\text{NA} = 0.6$). Experimentally, the deterministically coupled QD-CBG devices yield a photoluminescence intensity enhancement of up to $\times 700$ compared to unprocessed planar QDs, reaching integrated count rates of $45 \, MHz$. Furthermore, the suspended membrane architecture effectively relaxes residual strain, significantly reducing the average exciton fine-structure splitting from $7.3 \, \mu eV$ in planar QDs to $1.3 \, \mu eV$ in the CBGs. Interferometric measurements confirm that the fabrication process preserves the optical quality of the emitters, with average coherence times of $70 \, ps$. By bridging optimized FDTD design with precise nanofabrication and robust optical performance, these results establish free-standing GaAs CBGs as a highly scalable platform for bright and coherent entangled photon pair sources.

We study the quadrupolar Kitaev model, an $S=1$ honeycomb-lattice model with frustrated bond-dependent quadrupolar interactions. Using complementary methods and expanding around controlled limits, we uncover several intertwined structures. First, a semiclassical variational analysis based on $\mathrm{SU}(3)$ flavor theory reveals an extensively degenerate manifold of classical mean-field ground states, suggesting that quantum fluctuations may stabilize a quantum-disordered phase. Second, in the bond-anisotropic limit, perturbation theory is used to derive effective low-energy Hamiltonians, which crucially depend on the presence (or absence) of a residual symmetry $\mathcal{M}$ of combined lattice reflection and discrete spin rotation. A Majorana parton construction uncovers an exact $\mathbb Z_2$ gauge structure and motivates possible confined and deconfined phases driven by gauge-charge condensation, consistent with the effective theories obtained in anisotropic limit. Further, within the same parton formalism, different Majorana mean-field ansätze produce both gapless and gapped candidate quantum-disordered states, distinguished by linear versus projective implementations of $\mathcal M$. Our results highlight frustrated quadrupolar interactions as a route to quantum-disordered phases, relevant to $S \geq 1$ Kitaev materials and Rydberg-array quantum simulators.

We propose to generate heat pulses in mesoscopic conductors using light fields. In contrast to single-electron excitations such as levitons, which are created by accurate voltage drives, our approach relies on modulating the temperature of an electronic reservoir. To this end, we show that the interactions with a light field can induce a controllable time-dependent temperature in an electrode. The temperature modulations generate charge-neutral heat pulses that can be emitted into a mesoscopic conductor and detected in the outputs. We illustrate our approach by evaluating the time-dependent currents and their fluctuations using a tight-binding model of two electronic reservoirs connected by a quantum point contact. Our work establishes a route towards on-demand caloritronics, where energy rather than charge carries quantum information, and it paves the way for probing time-resolved heat transport and quantum coherence in thermally driven conductors.

We develop a nonequilibrium Green's function theory for dispersion interactions between two nanostructures, each an open quantum system driven into a nonequilibrium steady state by an applied bias voltage. Starting from the two-particle nonequilibrium Green's function, we derive a general expression for the interaction energy in terms of the polarisation propagators of the individual systems. The interaction energy admits a physically transparent decomposition into charge noise and charge dissipation contributions, providing a fluctuation-dissipation interpretation that generalises the equilibrium London picture. Model calculations for coupled molecular junctions demonstrate that the applied voltage can enhance the attractive dispersion interaction by nearly an order of magnitude relative to equilibrium. In thermal equilibrium, the dispersion interaction is universally attractive, irrespective of the specific form of the nanostructure Hamiltonians or their coupling to reservoirs. Out of equilibrium, we introduce a generalised Kubo-Martin-Schwinger ratio that parametrises the departure from detailed balance. We show that, in contrast to equilibrium, nonequilibrium conditions can lead to a repulsive dispersion interaction. Finally, we discuss the conditions under which population inversion in the electronic leads can drive a sign reversal of the dispersion interaction.

Macroscopic assemblies of one- and two-dimensional materials promise to translate nanoscale electronic properties into device-scale performance, yet the microscopic principles governing charge transport in such networks remain unresolved. In these systems, conductivity is often interpreted using phenomenological models that do not explicitly connect electronic structure to macroscopic magnetotransport. Here we develop a unified atomistic framework that links quantum-coherent transport, thermal disorder and magnetic-field effects, and combine it with ultrahigh-field magnetotransport measurements up to 60 T over a broad temperature range on carbon nanotube fibres. We show that positive magnetoresistance is controlled by junction overlap length, whereas negative magnetoresistance arises predominantly from lattice-mismatched heterojunctions rather than weak localisation alone. Statistical analysis of a large-scale numerical dataset reveals that the experimentally observed positive quadratic magnetoresistance originates from junction transport. These results show that macroscopic transport in disordered low-dimensional networks is governed primarily by junction-level quantum interference rather than solely by defects or doping.