The capability of anisotropic media to exert an optical torque on electromagnetic fields is crucial for polarization control. Here we investigate twisted layered stacks of uniaxial anisotropic media to engineer chiral mirrors for the manipulation of circularly polarized light by adjusting the layer number, thicknesses, and orientation. To this aim, we undertake a comprehensive theoretical analysis devising a multilayered twisted anisotropic photonic crystal enabling highly efficient circular polarization manipulation functionalities, i.e., showing concurring close-to-unitary helicity-preserving reflectance of one circular polarization and transmittance of the opposite one. Owing to the angular-momentum manipulation concept enabled by our proposed devices, we envisage that such chiral mirrors are promising candidates for an alternative class of integrated circular polarizers, holding great potential for applications in quantum technologies, polarization-sensitive optical detectors, and electro-optical information processing.

Silicon carbide is a promising material platform for hosting various color centers that are suitable for quantum information processing. Here, we report the design and demonstration of an integrated electro-optic modulator that can directly interface silicon-vacancy centers in the 4H-silicon-carbide-on-insulator platform. Despite a relatively low electro-optic coefficient ($0.22$ pm/V), the optimized silicon carbide modulator is able to work in the 920-nm range with a propagation loss of less than $0.5$ dB/cm, featuring a 3-dB bandwidth of around 500 MHz, an extinction ratio of 8–12 dB for an operating peak-to-peak voltage of 10 V, and a footprint of less than $0.1{\mathrm{mm}}^2$. With such modulation performance, this approach described provides a cost-effective solution for the chip-scale implementation of the electro-optic modulation technology required for interfacing with color centers in the silicon carbide platform.

Efficient verification of entangled states is crucial to many applications in quantum information processing. However, the effectiveness of standard quantum state verification (QSV) is based on the condition of independent and identical distribution (IID), which impedes its applications in many practical scenarios. Here we demonstrate a defensive QSV protocol, which is effective in all kinds of non-IID scenarios, including the extremely challenging adversarial scenario. To this end, we build a high-speed preparation-and-measurement apparatus controlled by quantum random-number generators. Our experiments clearly show that standard QSV protocols often provide unreliable fidelity certificates in non-IID scenarios. In sharp contrast, the defensive QSV protocol based on a homogeneous strategy can provide reliable and nearly tight fidelity certificates at comparable high efficiency, even under malicious attacks. Moreover, our scheme is tolerant of the imperfections in a realistic experiment, which is very appealing to practical applications.

We study the single-photon purity of a resonantly driven single-photon source in the realistic scenario where the excitation laser pulse can leak into the detection path. We find that the duration of the excitation pulse strongly influences the quality of the single-photon source. We calculate the influence of this on the effective parameters describing the most relevant properties, including the two-photon component and Hong-Ou-Mandel visibility. Furthermore, we analyze how these properties can be strongly affected by frequency filtering of the outgoing field. Our results highlight that the relation between the two-photon component of the emission and the Hong-Ou-Mandel visibility is more complicated than typically assumed in the literature, and depends on the specific details of the source.

Topological physics in electromagnetics has enabled topological edge-state waveguides, yet traditional propagation path designs of topological photonics are restricted by the geometry of the underlying periodic lattice. Here, we propose a topological waveguide scheme based on Voronoi diagrams, allowing for arbitrary propagation paths and offering greater flexibility beyond the constraints of conventional periodic structures. Focusing on gyromagnetic photonic topological insulators and valley topological insulators, we detail the construction and implementation process. Our method ensures smooth connections between unit cells and efficient wave transmission, which are validated through both simulations and experiments. The proposed scheme greatly expands the flexibility for topological transport and enables more applications for complex topological devices and systems.

This work develops the thermal spectrum field theory in the dynamic steady state for photothermal fields under arbitrary optical excitation, utilizing a combined Fourier-Laplace formalism subject to generalized conductive and radiative boundary (surface) conditions. The theory represents a generalization of the thermal field spectral theory of opaque solids to photothermal spectroscopy of optically nonopaque media. The developed formalism introduces infrared thermophotonic emission as the spectrally resolved response of condensed media while eliminating signal background variations caused by incoherent (“decoherent”) leaky degrees of freedom inherent to diffusion physics. The theory is applied to ink-water mixtures with varying optical absorption coefficients. The Fourier-Laplace approach to photothermal spectroscopy demonstrates the absence of decoherent thermal energy superposition in the photothermal field, validates the dynamic steady-state nature of the recorded transient thermal waves, and enables accurate measurements of optical absorption, thermophotonic emission, and surface heat transfer coefficients.

Compact localized states (CLSs) associated with flat bands (FBs) exhibit significant potential for wave localization and enhanced wave-matter interactions. The Lieb lattice, characterized by its unique bipartite and chiral symmetries, features a dispersionless FB cutting through the Dirac points, distinguishing it from other lattices and providing substantial flexibility for controlling CLS configurations. Herein, we investigate theoretically the generation and manipulation of CLSs in a two-dimensional dielectric photonic crystal (PC) with a Lieb lattice. Particularly, to address the inevitable non-nearest-neighboring interactions of the lattice sites, we propose an optimized strategy by embedding perfect electric conductors between dielectric sites, enabling the first observation of an ideal FB in Lieb PCs; this closely matches the tight-binding model that considers only the nearest-neighbor coupling. Furthermore, by leveraging the robust CLS in Lieb PCs, we demonstrate the on-demand design of diverse localized mode patterns through CLS engineering and showcase their selective optical excitation. These advancements offer promising applications in on-chip optical routing and switching, as well as in the design of high-performance cavity-based photonic devices.

Unidirectional guided resonances (UGRs), which are eigenstates that radiate exclusively in a single channel, are promising for advancing diverse photonic devices. However, existing approaches face an inherent trade-off between achieving high-Q factors and maximizing the radiation-asymmetry ratios. To address this challenge, we propose a scheme that exploits both out-of-plane and in-plane couplings to generate bound states in the continuum with precise radial and rotational control in momentum space. This approach effectively decouples the Q factors of UGRs from their radiation-asymmetry ratios. As a result, we achieve UGRs with Q factors exceeding ${10}^4$, which is 1–2 orders of magnitude higher than traditional UGRs. Furthermore, we demonstrate the ability to reverse the emission direction of these UGRs, leading to a broad range of radiation-asymmetry ratios from −53 to 55 dB. We further validate the practical realization of high-Q UGRs using a silicon-on-silica system. Our findings provide a versatile method for generating high-Q UGRs, offering alternative pathways for innovations in nonlinear optics, light-matter interactions, and advanced optoelectronic applications.

Dual-band second-order photonic topological insulators (SPTIs), characterized by multiple corner states, offer exceptional potential for robust multiband manipulation of electromagnetic waves in lower dimensions. However, previous theoretical implementations of dual-band SPTIs have been constrained by limited flexibility, hindering their adaptability for diverse applications. Additionally, experimental validation of these dual-band SPTIs has been lacking. In this study, we introduce a topology optimization method to design SPTIs with customizable dual-band corner states tailored for specific multiband applications. Dual-band SPTIs with customized corner states for manipulating electromagnetic waves of transverse magnetic and electric modes are created. Furthermore, multiple corner states within dual bandgaps are experimentally confirmed. This work opens new avenues for creating customizable photonic devices with dual-band topological features, enabling versatile multiband applications.

The control of flying qubits carried by itinerant photons is ubiquitous in quantum networks. In addition to their logical states, the shapes of flying qubits must also be tailored for high-efficiency information transmission. In this paper, we introduce quantum optimal control theory to the shaping of flying qubits. Building on the flying-qubit control model established in our previous work, we design objective functionals for the generation of shaped flying qubits under practical constraints on the emitters and couplers. Numerical simulations employing gradient-descent algorithms demonstrate that the optimized control can effectively mitigate unwanted level and photon leakage caused by these nonidealities. Notably, while coherent control offers limited shaping capacity with a fixed coupler, it can significantly enhance the shaping performance when combined with a tunable coupler that has restricted tunability. The proposed optimal control framework provides a systematic approach to achieving high-quality control of flying qubits using realistic quantum devices.

The generation of electro-optic (EO) combs has recently attracted broad interest in photonics due to their great original characteristics of reconfigurability, high comb power, and recent breakthroughs in bandwidth and conversion efficiency. This work explores the connection between EO-comb generation and the synthetic frequency dimension, presenting a theoretical framework that leverages the underlying dynamics in the synthetic frequency lattice to predict and potentially control comb spectra. Specifically, we study non-Hermitian mechanisms with physical factors such as group velocity dispersion and modulation detuning, as well as concepts involving effective gauge flux and Su-Schrieffer-Heeger lattice in the synthetic frequency dimension; and we explore their influence on the dynamics and spectral characteristics of EO combs. Using the concept of non-Hermitian dynamics in a synthetic frequency lattice, we provide physical insights into key phenomena, such as bandwidth limitations and anomalous non-Hermitian skin effect, that arise in comb generation. Our work offers a complementary perspective that may inspire comb generation applications.

We introduce iQSync, a clock-offset recovery method designed for implementation on low-level hardware, such as field-programmable gate arrays or microcontrollers, for quantum key distribution (QKD). iQSync requires minimal memory, only a simple instruction set (e.g., no floating-point operations), and can be evaluated with sublinear time complexity, typically involving no more than a few thousand iterations of a simple loop. Furthermore, iQSync allows for a precise clock-offset recovery within a few seconds, even for large offsets, and is well suited for scenarios with high channel loss and low signal-to-noise ratio, irrespective of the prepare-and-measure QKD protocol used. We implemented the method on our QKD platform, demonstrating its performance and conformity with analytically derived success probabilities for channel attenuations exceeding $70\mathrm{dB}$.

This study investigates the performance of a binarized neuromorphic network leveraging polariton dyads, optically excited pairs of interfering polariton condensates within a microcavity to function as binary logic gate neurons. Employing numerical simulations, we explore various neuron configurations, both linear (nand, nor) and nonlinear (xnor), to assess their effectiveness in image classification tasks. We demonstrate that structural nonlinearity, derived from the network’s layout, plays a crucial role in facilitating complex computational tasks, effectively reducing the reliance on the inherent nonlinearity of individual neurons. Our findings suggest that the network’s configuration and the interaction among its elements can emulate the benefits of nonlinearity, thus potentially simplifying the design and manufacturing of neuromorphic systems and enhancing their scalability. This shift in focus from individual neuron properties to network architecture could lead to significant advancements in the efficiency and applicability of neuromorphic computing.

We demonstrate efficient in-plane optical fiber collection of single-photon emission from a quantum dot embedded in a photonic-crystal cavity. This was achieved via adiabatic coupling between a tapered optical fiber and a tapered on-chip photonic waveguide coupled to a modified high-$Q$ L3 photonic cavity, with a theoretical in-plane fiber-collection efficiency of 47%. Experimentally, this efficiency is measured by comparing the luminescence intensities collected by the fiber and by a NA 0.65 microscope objective placed above the cavity and reaches half of the theoretically expected value. Simulations show that the in-plane collection efficiency can be further increased to 77% by improving the dot-cavity coupling and by increasing the overlap length between the tapered fiber and waveguide. Near-unity adiabatic coupling is predicted for an overlap length of $5\text{μ}\mathrm{m}$. The single-photon source was characterized by second-order correlation measurements giving $g^{(2)}(0)=0.17$ under nonresonant excitation.

Generation and control of entanglement are fundamental tasks in quantum information. In this paper, we propose a novel approach to generating controllable frequency-entangled photons using the concept of synthetic frequency dimension in an optical system. This system consists of a ring resonator made of tailored third-order nonlinear media to induce photon-photon interactions and a periodic modulator to manipulate coupling between different frequency modes. We show that this system provides a unique platform for the exploration of distinct few- or many-body quantum phases including chaos, localization, and integrability in a highly integrable photonics platform. In particular, we develop a proposal to calculate the spectral form factor, which characterizes the degree of chaos in the system and differentiates between these phases based on observable measurements. Then, the switching of the quench dynamics from an intermediate phase between integrable and chaotic to the Stark many-body phase can generate and sustain stable frequency-entangled multiphoton states. This work is the first to explore rich and controllable quantum phases beyond single-particle physics in a synthetic dimension.

Pure dephasing and spontaneous emission are two nonunitary processes of atoms or spins interacting with fluctuating electromagnetic (EM) modes. The dissipative collective emission processes (e.g., superradiance) originate from interactions with EM modes in resonance with atoms and have received considerable attention. Meanwhile, the analogous nondissipative collective dephasing phenomena mediated by EM environments remain poorly understood. Here, we introduce the nano-EM superdephasing phenomenon arising in the photonic environments near materials. We show that collective dephasing in this nano-EM environment is enhanced by over 10 orders of magnitude compared to free space or cavities. This giant enhancement originates from long-range correlations in off-resonant, low-frequency evanescent EM fluctuations, which lead to collectively accelerated (super) or suppressed (sub) dephasing in many-body entangled states. We further unravel that nano-EM collective dephasing exhibits universal interaction ranges near materials with different anisotropies that can be reciprocal or nonreciprocal. This nano-EM interaction range, which is not present in free space and cavities, leads to unique scaling laws of superdephasing in Greenberger-Horne-Zeilinger states different from the conventional $N^2$ scaling of superradiance. Finally, we discuss how to experimentally isolate and control superdephasing to open interesting frontiers for scalable quantum systems.