Probing shift-current responses in noncentrosymmetric materials using quantum algorithms
Accessing the geometric origin of shift current in noncentrosymmetric quantum materials is essential for understanding nonlinear photoresponses governed by band geometry and Berry connections. We present a quantum-algorithmic approach, implemented on a classical simulator of quantum circuits, to compute the shift current in a phase-coherent and gauge-consistent manner. By expressing the geometric ingredients of the bulk photovoltaic effect as observables accessible within a quantum-circuit framework, the method enables the evaluation of the second-order dc photocurrent without explicit gauge fixing. Using the one-dimensional Rice–Mele model as a benchmark, we obtain shift-current spectra in quantitative agreement with classical calculations and exhibiting smooth behavior across the Brillouin zone. These results position quantum algorithms as a promising framework for addressing shift-current responses and, more broadly, nonlinear optical phenomena in quantum materials.
Highly Stretchable Eu3+ – Doped PEBAX Elastomers With Complementary Optical Readouts of Strain and Temperature
Soft photonic materials capable of maintaining optical functionality under large mechanical deformation are highly desirable for wearable photonics, flexible sensors, optical and mechanically adaptive photonic systems. Here, we report highly stretchable luminescent elastomers based on the thermoplastic copolymer PEBAX 2533 incorporating a europium β-diketonate complex. The transparent films combine intense europium emission with exceptional mechanical flexibility, displaying elongation at break exceeding 1200%, while maintaining high optical transparency in the visible range. The elastomers exhibit intense red luminescence with absolute quantum yields of 0.61. Under mechanical deformation, the 5D0 → 7F0 transition shows a strain-dependent spectral shift and intensity modulation, enabling optical strain readout with sensitivities of –1.6 ± 0.2 cm−1·ε−1 and −0.44 ± 0.04 ε−1, respectively. The luminescence spectra also display a thermal dependence, characterized by a blue shift and intensity decrease of the Eu3+ emission with a temperature sensitivity of 0.08 ± 0.01 cm−1·°C−1 over the investigated temperature range. The coexistence of large deformability, high transparency, efficient Eu3+ emission, and two independently calibrated optical responses establishes Eu-doped elastomers as a versatile soft photonic platform for multimodal optical transduction, highlighting their potential for flexible sensing technologies in which mechanical and thermal perturbations are optically encoded within the same material platform.
Enabling the bulk photovoltaic effect in centrosymmetric materials through an external electric field
We develop a practical approach to electrically tuning the nonlinear photoresponse of two-dimensional semiconductors by explicitly incorporating a static out-of-plane electric field into the electronic ground state prior to optical excitation, as a gate bias. The method is implemented by dressing a Wannier-interpolated Hamiltonian with the field through its position matrix elements, which allows the gate bias to modify orbital hybridization and band dispersion beyond perturbative treatments. Within the independent-particle approximation, the resulting second-order (shift) conductivity is evaluated for both centrosymmetric and noncentrosymmetric layered systems. Applied to MoS2, the approach captures the emergence of a finite shift current in centrosymmetric bilayers and the tunability of intrinsic responses in polar structures. The shift conductivity rises linearly at small fields and saturates at higher intensities, reflecting the competition between the growing shift vector and the weakening interband coupling as resonant transitions move away from high-symmetry valleys. A Taylor expansion of the field-dressed conductivity connects this behavior to the third-order optical response, revealing a unified picture of field-induced nonlinearities. These results establish field dressing of Wannier Hamiltonians as a practical route to model and predict nonlinear photocurrents in layered materials.
Post consumer expanded polystyrene as an optical-grade host for lanthanide-doped luminescent solar concentrators
The transition toward net-zero buildings has increased interest in building-integrated photovoltaics (BIPV). Luminescent solar concentrators (LSCs) are particularly attractive due to their transparency, colour tunability, and seamless architectural integration. Yet most LSCs rely on virgin polymers, including polystyrene (PS), a fossil-derived polymer. Expanded polystyrene (EPS) waste is difficult to recycle because of degradation, contamination, and low material value. This study addresses this challenge by converting post-consumer EPS into an optical-grade matrix for LSCs, giving a second life to a hard-to-recycle plastic. Recycled PS (r-PS) was doped with two lanthanide complexes — Eu(TFNB)3Phen and Tb(4BBA)3Phen — and analysed structurally and photophysically. The r-PS retained high transparency and achieved quantum yields of 0.53 ± 0.05 (Eu) and 0.40 ± 0.04 (Tb). Its mechanical properties were preserved, enabling fabrication of functional LSCs with power conversion and optical efficiencies of (0.013 ± 0.001)% and (1.2 ± 0.1)%, respectively. The devices also exhibited dual-mode thermometric sensitivity up to 3.9 ± 0.6 % °C−1. A life-cycle assessment showed significant reductions in acidification, terrestrial eutrophication, and resource use when virgin PS is replaced with r-PS.
Design and fabrication of 3D-printed Y-branch power splitters based on the conjugated polymer PFeF8
Conjugated polymers are essential materials employed in organic optoelectronics. Their application in photonic circuits is a subject of increasing relevance and study. In this work, we present the design, numerical simulation, fabrication, and experimental characterization of a Y-branch optical power splitter based on the PFeF8 conjugated polymer, a basic building block used in such circuits. The blend with PMMA enables the control and reduction of the refractive index and offers a large transparency region above 550 nm, which is useful for the design of waveguide structures based on materials with a low extinction coefficient. Measurements in samples of the PFeF8/PMMA blend at concentrations of 5% and 10% revealed propagation losses of 0.022 dB/mm (R2 = 0.96) and 0.025 dB/mm (R2 = 0.90), respectively. The splitters fabricated with the DLP 3D printing technique show excess loss from 4.78 dB to 6.36 dB, most of it due to scattering on the guiding structure. An average 0.16 dB power imbalance between the two arms indicates the uniformity of the splitting ratio.
Security-aware non-uniform multipath traffic partitioning for QKD networks: A MILP-based squeezing protection approach
Quantum Key Distribution (QKD) enables information-theoretic secure key exchange, but the deployment of large-scale QKD networks introduces new challenges related to routing, resource allocation, and security exposure in trusted-node-based architectures. In multipath QKD networks, the secret key rate can be partitioned and transmitted over multiple link-disjoint paths, so that an adversary must simultaneously compromise all paths to reconstruct the complete secret key. However, traffic is often equally distributed across the available disjoint paths, although such uniform partitioning may be suboptimal when candidate paths exhibit heterogeneous vulnerability levels. This paper proposes a security-aware optimization framework for QKD-enabled optical networks that determines a non-uniform multipath traffic partitioning strategy aimed at minimizing the expected amount of eavesdropped traffic. The proposed approach is formulated as a Mixed-Integer Linear Programming (MILP) model that integrates probabilistic secrecy metrics derived from trusted node compromise probabilities, a traffic vulnerability threshold that limits partial information exposure, and adaptive bandwidth squeezing protection to ensure service continuity under failure scenarios. The model jointly optimizes traffic allocation and excess key capacity, allowing the protection overhead to be dynamically determined according to security and resilience requirements. Numerical evaluations conducted on both a toy topology and the Pan-European network demonstrate that the proposed exposure-aware partitioning strategy significantly reduces the expected eavesdropped traffic compared to conventional equal-splitting approaches while maintaining resilience guarantees. These results highlight the potential of security-driven traffic engineering for the design of resilient and efficient multipath QKD networks.
Universal BPS structure of scalar kinks in static geometries
We present a geometric extension of the Bogomolny-Prasad-Sommerfield (BPS) construction for scalar kinks in (1+1) dimensions embedded in static curved spacetimes. By introducing a nonminimal coupling between the scalar prepotential and the extrinsic curvature of the static foliation, the flat-space first-order Bogomolny equation remains exactly valid for arbitrary static backgrounds. As a consequence, the kink profile is unchanged, while the effective potential and vacuum structure acquire a controlled geometric dependence. We show that these curved-space BPS kinks are always linearly stable. However, the existence of the translational zero mode is not guaranteed: its normalizability depends on the competition between the intrinsic length scale of the kink and the asymptotic curvature scale of the geometry. When the geometric scale dominates, the zero mode is removed and the soliton becomes geometrically pinned, despite remaining an exact BPS solution. Explicit realizations in AdS2 demonstrate how different static slicings of the same spacetime lead to qualitatively distinct physical outcomes, ranging from preserved translational invariance to its complete removal by horizons. These results establish geometry as a precise mechanism for controlling solitonic moduli without compromising linear stability.
Asymmetric CNN-based equalization for clipping distortion compensation in LED-based VLC systems
Visible Light Communication (VLC) systems utilizing Direct Current-biased Optical Orthogonal Frequency Division Multiplexing (DCO-OFDM) are inherently limited by a high Peak-to-Average Power Ratio (PAPR), which leads to non-linear distortions due to the restricted dynamic range of LEDs. Conventional PAPR reduction techniques often impose significant computational overhead on the transmitter or severely degrade the Error Vector Magnitude (EVM). This paper proposes an asymmetric deep learning-based framework to mitigate clipping noise. We introduce a low-complexity clipping approach at the transmitter ((𝑁)) and shift the compensation burden to a Convolutional Neural Network (CNN) at the receiver. Two clipping ratios were evaluated: CR = 0.9 (moderate, 2.9 dB PAPR reduction) and CR = 0.7 (aggressive, 5.8 dB PAPR reduction). Experimental results from 20 spatial positions within a 2.0 × 1.0 m2 test area demonstrate that the proposed CNN effectively recovers the signal under both clipping conditions. For 64-QAM modulation with CR = 0.7,
the CNN achieves a mean EVM of 7.07%, below the 8% reference threshold defined by 3GPP standards, and a mean BER of 8.98 × 10−4, while the conventional MMSE equalizer reaches 15.05% EVM and 5.37 × 10−2 BER. The architecture shows consistent generalization and spatial robustness compared to standard Deep Neural Networks (DNNs), suggesting its potential for LED-based lighting applications.
RVFL-Based Nonlinearity Compensation for MISO VLC Systems: Experimental Validation and Performance Analysis
Visible Light Communication (VLC) systems employing multiple Light-Emitting Diode (LED) transmitters face significant challenges from aggregate nonlinear distortions that degrade signal quality and limit practical deployment. This work presents experimental validation of Random Vector Functional Link (RVFL) networks for post-distortion compensation in Multiple-Input Single-Output (MISO) VLC systems. RVFL’s closed-form training and memoryless architecture offer distinct computational advantages over iterative methods. Comprehensive experimental validation across variable drive amplitude (300-900 mV) and bias current (50-350 mA) in a 2×1 dual-luminaire testbed demonstrates that RVFL achieves EVM of 7.81% for 16-QAM and 3.97% for 64-QAM at 200 cm distance, enabling reliable transmission where uncompensated signals exceed thresholds. Comparative analysis reveals superior computational efficiency: RVFL inference requires 45.5 ms versus 502.5 ms for Artificial Neural Networks (ANN) and 338.5 ms for Volterra, achieving 11× faster inference than ANN. These results position RVFL as an attractive candidate for practical VLC receivers where computational efficiency is critical.
Influence of vertical X-ray beam angulation and receptor-holders on the radiographic detection of implant abutment–prosthesis misfit
Periapical radiographs have been the primary adjunctive diagnostic method of evaluating abutment-prosthesis misfit. However, whether different radiographic receptor‑holders interfere with diagnostic accuracy depending on the vertical X-ray beam angulation remains unclear.