Broadband optical waveguiding in an optical nanofiber can give great versatility to nanofiber-optic technology. To date, high-transmittance single-mode waveguiding in a single optical nanofiber in the full visible spectral range remains challenging. Here, by using a commercially available silica fiber with a single-mode cut-off wavelength smaller than 400 nm (Nufern, 405-HP) as the fiber preform, and taper-drawing the fiber into a nanofiber with a standard fabrication technique, we show that the nanofiber can support broadband single-mode waveguiding with high optical transmittance in the full visible spectral range. Quantitatively, a silica nanofiber with a uniform diameter between 210 and 270 nm can support single-mode optical waveguiding with transmittance higher than 96% (i.e., less than 0.18 dB in loss) from 400 to 800-nm wavelength. Such a broadband single-mode nanofiber may find applications including near-field optical coupling, optical interconnection, optical sensing, atom optics and fiber lasers in the broad visible spectral range.

ABSTRACT Chiral photonic metasurfaces provide unique capabilities for tailoring light–matter interactions, which are essential for next‐generation photonic devices. Here, we report an advanced optimization framework that combines deep learning and evolutionary algorithms to significantly improve both the design and performance of chiral photonic nanostructures. Building on previous work utilizing a three‐layer perceptron, reinforced learning, and a stochastic evolutionary algorithm with decaying changes and mass extinction for chiral photonic optimization, our study introduces a refined pipeline featuring a two‐output neural network architecture to reduce the trade‐off between high chiral dichroism (CD) and reflectivity. Additionally, we use an improved fitness function and efficient data augmentation techniques. A comparative analysis between a neural network (NN)‐based approach and a genetic algorithm (GA) is presented for structures of different interface pattern depth, material combinations, and geometric complexity. We demonstrate a twice‐higher CD and the impact of both the corner number and the refractive index contrast in the example of a GaP/air and PMMA/air metasurface as a result of superior optimization performance. Additionally, a substantial increase in the number of structures explored within limited computational resources is highlighted, with tailored spectral reflectivity suggested by our electromagnetic simulations, paving the way for chiral mirrors applicable to polarization‐selective light–matter interaction studies.

The number resolution of solid-state artificial atoms is of fundamental interest for the study of quantum few-body systems, yet remains experimentally challenging. Quantum optical experiments offer a non-invasive approach which links up macroscopic measurements with the quantity of quantum emitters. In this work, we propose a time-domain quantum optical methodology for the strict numbering of colloidal CdSe/CdS/ZnS quantum dots (QDs) confined in subwavelength-size polystyrene capsules. The non-polarized, homogeneously broadened emission of colloidal QDs in the subwavelength volume satisfies the description of Dicke's superradiance of identical quantum emitters. An analytic relation describes the numerical dependence of the second-order photon correlation on the number and the collective lifetime of emitters, yielding an experimental counting range of colloidal QDs from one to ten. This work provides a robust pathway for the non-invasive numbering of artificial atoms and the investigation of collective light-matter interactions at the nanoscale.

This study investigates multipartite entanglement in quantum emitter (QE) systems coupled to a two-dimensional hyperbolic surface (TDHS). Within the master equation framework, which distinguishes the contributions of surface plasmon field (SPF) with different spatial modes, we demonstrate that both the collective decay coefficients and the in-plane emission pattern of the emitters are strongly governed by the polarization of the transition dipole. Numerical analysis further reveals that the TDHS functions as a planar plasmonic waveguide supporting both reciprocal and nonreciprocal inter-emitter interactions. Building on these intriguing properties, we analyze the dynamics of spontaneously generated entanglement (SGE) in tripartite and quadripartite systems under various interaction configurations. Our results show that in certain two-dimensional geometries, strong nonreciprocal interactions enhance global entanglement compared with one-dimensional arrangements. Notably, the rhombic configuration supports destructive interference that suppresses on-site decay and drives the system into dark states with steady entanglement. Moreover, for systems initialized in mixed states, entanglement generation relies mainly on reciprocal interactions and shows only weak dependence on the interaction geometry. These findings provide a versatile route for engineering multipartite entanglement in TDHS-based plasmonic architectures, with promising applications in quantum information processing and integrated photonic devices.

We propose a genuine two-dimensional chiral waveguide platform based on the hyperbolic surfaces to engineer nonreciprocal interactions and entanglement between quantum emitters. Tuning the dipole polarization allows for maximally chiral coupling between each emitter and the surface plasmon field, resulting in highly directional energy transfer. By employing a master equation approach, we show that the chiral environment not only enables nonreciprocal dipole interactions but also significantly enhances both transient and steady-state entanglement compared with reciprocal systems. The degree of steady-state entanglement is further tunable through dipole polarization, emitter separation, and external driving. Unlike prior implementations constrained by one-dimensional geometries, our fully planar and highly reconfigurable platform provides a scalable route toward integrated quantum photonic networks and on-chip multipartite entanglement.

Colloidal quantum dots (cQD) are heralded for their tunable bandgaps, solution-processibility, and cost-effectiveness, making them ideal candidates for lasing applications. However, previous cQD lasing demonstrations have largely depended on close-packed solid-state films, which are deemed essential to counteract the rapid decay of material gain. In this study, a novel approach is introduced utilizing "entropic ligands and solvent" to enhance the solubility of cQDs in solution. By achieving the necessary critical volume fraction for lasing, this strategy leads to the groundbreaking development of the first liquid-state vertical-cavity surface-emitting lasers (VCSELs) based on cQDs across the blue and green spectrum, encompassing diverse material systems such as CdSe-based and InP-based cQDs. Furthermore, by integrating the liquid-state VCSEL with a microfluidic channel, it is demonstrated that heat dissipation during intense excitation is pivotal for cQD lasing likely across various excitation modes-whether pulsed or continuous-wave, optically or electrically-pumped-and different media, including liquid and solid states. The research will lay the foundation for a new era of liquid-state cQD lasers for specific occasions, distinguished by their customizable and largely-variable wavelengths, compact form factors, diverse materials basis, and dependable performance.

Polarization-entangled photon pairs are essential sources for photonic quantum information processing. However, generating entangled photon pairs with large detuning via spontaneous parametric down-conversion (SPDC) often requires complex configurations to compensate for phase matching. Here, we propose a simple and efficient scheme to generate polarization-entangled photon pairs based on type-0 SPDC in a thin-film lithium niobate waveguide with a single poling period. By utilizing the strong dispersion engineering capabilities of thin-film waveguides, we can achieve both degenerate and highly detuned entangled photon pairs. Furthermore, we demonstrate on-chip temporal compensation using an integrated waveguide structure. Our approach offers a compact and scalable solution for integrated quantum photonic circuits.

We investigate the population dynamics and Casimir-Polder (CP) force experienced by an atom placed near a two-dimensional anisotropic surface (TDAS) supporting surface plasmon polaritons (SPPs). Within the non-Markovian macroscopic quantum electrodynamics framework, we first analyze how atom-SPP coupling influences the evolution of the atomic population and the temporal behavior of the CP force. Our results show that variations in the atomic dipole moment, atom-surface distance, transition frequency, and carrier concentration can selectively modulate the coupling strength between the atom and the SPP modes. In the strong coupling regime, the system shows oscillatory behavior in both the population and CP force dynamics, with an enhanced force amplitude and periodic directional changes. By contrast, in the weak coupling regime, the dynamics are dominated by exponential decay. Additionally, when a coherent driving field is introduced, we adopt the Markovian approximation and demonstrate that the system can reach a steady state with a finite excited-state population, resulting in a persistent CP force that is highly sensitive to the driving frequency and strength. These findings indicate that dispersion forces can be precisely tailored through the combined influence of anisotropic plasmonic platforms and external coherent driving, which paves the way for new opportunities in nanoscale atomic control and manipulation within plasmonic systems.

We propose a control system based on an optical link utilizing a silicon-on-insulator (SOI) technology fabricated MRR. Experiments demonstrate the system's capability to achieve wavelength selection and stable wavelength locking within 1.35 seconds for four C-band light waves with arbitrary wavelength spacing exceeding 1 nm.

This study proposes a nanophotonic structure that supports the generation and enhancement of the lateral Casimir-Polder (CP) force acting on atoms. By applying the two-dimensional anisotropic material, we demonstrate that both the spontaneous decay rate and the emission pattern of the atom exhibit distinct features by manipulating the parameters of the system. In particular, the exact numerical solutions of population dynamics reveal the occurrence of Rabi oscillations in the strong atom-field coupling case, where the Markovian results fail to describe this phenomenon. We also show that the asymmetric spatial distribution of the in-plane dipole radiation into surface plasmon modes is achievable for the system under consideration. Based on these intriguing properties, we predict the generation of the lateral CP force, where the transient evolution of the force indicates the periodical variation in both the direction and the amplitude under strong light-atom interaction conditions. Our findings have potential applications for novel optical nanotechnologies and devices, which provide a method for atom manipulation and trapping.

Owing to their consistently emerging applications in modern photonics, highly sensitive and rapid mid-infrared (MIR) photodetectors, operating at high temperatures, are of great significance. Herein, a novel PbTe/Ge heterostructure is introduced. Notably, the discovery of a 2D electron gas (2DEG) system on the surface of the PbTe layer is experimentally identified for the first time. A high-performance PbTe/Ge heterostructure MIR photodetector utilizing a plasmonic photovoltaic effect is developed by employing asymmetric electrodes. The photodetecting device demonstrates an exceptionally high detectivity of 1.1 x 1011 Jones along with a short response time of 15 ns at room temperature. Additionally, the proposed plasmonic photovoltaic mechanism of the device is investigated and mainly ascribed to the propagating plasmons, generated by the coupling of the 2DEG with incident MIR photons. Moreover, a linear detector array (LDA) of PbTe/Ge is demonstrated for a thermal imaging application, which exhibits promising high-quality real-time imaging via the 2D photodetector arrays on Ge-based integrated circuits. This work opens up a new way for the development of next-generation, advanced MIR photonic devices and integrated photonic systems. A 2D electron gas system (2DEG) in the newly synthesized PbTe/Ge heterostructure is discovered. A plasmonic photovoltaic MIR photodetector is developed using the 2DEG characteristics, operating at high temperatures with high detectivity and fast response speed. Thermal imaging application of the plasmonic photovoltaic MIR photodetector is demonstrated by further developing PbTe/Ge 2DEG linear detector array. image

AbstractThe construction of a large-scale quantum internet requires quantum repeaters containing multiple entangled photon sources with identical wavelengths. Semiconductor quantum dots can generate entangled photon pairs deterministically with high fidelity. However, realizing wavelength-matched quantum-dot entangled photon sources faces two difficulties: the non-uniformity of emission wavelength and exciton fine-structure splitting induced fidelity reduction. Typically, these two factors are not independently tunable, making it challenging to achieve simultaneous improvement. In this work, we demonstrate wavelength-tunable entangled photon sources based on droplet-etched GaAs quantum dots through the combined use of AC and quantum-confined Stark effects. The emission wavelength can be tuned by ~1 meV while preserving an entanglement fidelity f exceeding 0.955(1) in the entire tuning range. Based on this hybrid tuning scheme, we finally demonstrate multiple wavelength-matched entangled photon sources with f > 0.919(3), paving the way towards robust and scalable on-demand entangled photon sources for quantum internet and integrated quantum optical circuits.

Complete quantum control of a stationary quantum bit embedded in a quantum emitter is crucial for photonic quantum information technologies. Recently, the orbital degree of freedom in optically active quantum dots has emerged as a promising candidate. However, the essential ability to perform arbitrary rotations on orbital qubits remains elusive. Here, we demonstrate arbitrary rotation of a hole orbital qubit with direct phase control using picosecond optical pulses. This is achieved by inducing stimulated Raman transitions within Λ systems coupled via radiative Auger processes. This new capability enables direct control of polar and azimuth angles of the Bloch vector without requiring timed precession. Our results establish orbital states in solid-state quantum emitters as a viable resource for applications in high-speed quantum information processing.

Colloidal semiconductor nanocrystals are promising candidates for quantum light sources, yet their application has been impeded by photoluminescence instability due to blinking and spectral diffusion. This study introduces a new category of cube-shaped CdSe/CdS core/shell nanocrystals with exceptionally stable photoluminescence characteristics. Under continuous excitation, the emissive quantum state remained consistent without alterations of the charge state for 4000 s, and the average photon energy variation stayed within the bounds of spectral resolution throughout this extended duration. Systematic examination of single-nanocrystal photoluminescence, upon variation of the core and shell dimensions, revealed that a thicker CdS shell and increased core edge length significantly curtail spectral diffusion, considering that the nanocrystals possess well-controlled CdSe-CdS and facet-ligand interfaces. This study advances the optimization of colloidal semiconductor nanocrystals as high-performance quantum light sources.

In general, a high-Q microresonator can accommodate abundant whispering gallery modes (WGMs) with the mode number increasing with the dimensional sizes of the microresonator. Removing the unnecessary modes while reorganizing the remaining modes is of vital importance, which, however, has been proved challenging and usually results in a tradeoff with the Q of the microresonator. Here, we reveal an effective and controllable mode trimming and clustering mechanism underlying the generation of polygon and star modes in weakly perturbed tapered fiber-coupled lithium niobate whispering gallery microresonators. Experimentally, various polygon and star modes are observed in sequence within a single microresonator by tuning the excitation wavelength or varying the coupling position between a tapered fiber and the circular microresonator, which can be well reproduced with our theoretical model. The finding offers a ubiquitous solution for a broad range of applications requiring elaborate selection and organization of the high-Q WGMs.

量子随机数因为其不可预测性和真随机性,在信息安全方面发挥着越来越重要的作用.现有的随机数生成协议大都假定光源服从一定确知的分布概率,然后通过测量值估算可提取随机数的最小熵.但是由于实际光源器件的不完美,其光强分布存在一定波动,倘若在计算最小熵过程中忽略该强度波动,将导致计算最小熵数值偏大,影响安全性;倘若使用传统的方法考虑光强波动,则导致估算结果过差,降低可获取随机性的大小.针对该问题,本文提出了一种具有光源监控功能的量子随机数发生器方案,并且以基于维度目击值的自检测量子随机数发生器协议为例进行介绍.仿真结果显示通过在源端添加光源监控模块的方法,能够对单光子贡献的上下界给出更紧致的估计,与传统方法相比,能够获得更高的最小熵和随机性.该方案为量子随机数发生器的实用化提供了一个有用的工具.

As miniature fibre-optic platforms, micro/nanofibres (MNFs) taper-drawn from silica fibres have been widely studied for applications from optical sensing, nonlinear optics to optomechanics and atom optics. While continuous-wave (CW) optical waveguiding is frequently adopted, so far almost all MNFs are operated in low-power region (e.g., <0.1 W). Here, we demonstrate high-power low-loss CW optical waveguiding in MNFs around 1550-nm wavelength. We show that a pristine MNF, even with a diameter down to 410 nm, can waveguide an optical power higher than 10 W, which is about 30 times higher than demonstrated previously. Also, we predict an optical damage threshold of 70 W. In high-power CW waveguiding MNFs, we demonstrate high-speed optomechanical driving of microparticles in air, and second harmonic generation efficiency higher than those pumped by short pulses. Our results may pave a way towards high-power MNF optics, for both scientific research and technological applications.

The nonlinear optical radiation of an integrated lithium niobate microcavity is demonstrated, which has been neglected in previous studies of nonlinear photonic devices. We find that the nonlinear coupling between confined optical modes on the chip and continuum modes in free space can be greatly enhanced on the platform of integrated microcavity, with feasible relaxation of the phase-matching condition. With an infrared pump laser, we observe the vertical radiation of second-harmonic wave at the visible band, which indicates a robust phase-matching-free chip-to-free-space frequency converter and also unveils an extra energy dissipation channel for integrated devices. Such an unexpected coherent nonlinear interaction between the free-space beam and the confined mode is also validated by the different frequency generation. Furthermore, based on the phase-matching-free nature of the nonlinear radiation, we build an integrated atomic gas sensor to characterize Rb isotopes with a single telecom laser. The unveiled mechanism of nonlinear optical radiation is universal for all dielectric photonic integrated devices, and provides a simple and robust chip-to-free-space as well as visible-to-telecom interface.

Atoms are ideal quantum sensors and quantum light emitters. Interfacing atoms with nanophotonic devices promises novel nanoscale sensing and quantum optical functionalities. But precise optical control of atomic states in these devices is challenged by the spatially varying light-atom coupling strength, generic to nanophotonic. We demonstrate numerically that despite the inhomogenuity, composite picosecond optical pulses with optimally tailored phases are able to evanescently control the atomic electric dipole transitions nearly perfectly, with $f>99\%$ fidelity across large enough volumes for {\it e.g.} controlling cold atoms confined in near-field optical lattices. Our proposal is followed by a proof-of-principle demonstration with a $^{85}$Rb vapor -- optical nanofiber interface, where the excitation by an $N=3$ sequence of guided picosecond D1 control reduces the absorption of a co-guided nanosecond D2 probe by up to $\sim70\%$. The close-to-ideal performance is corroborated by comparing the absorption data across the parameter space with first-principle modeling of the mesoscopic atomic vapor response. Extension of the composite technique to $N\geq 5$ appears highly feasible to support arbitrary local control of atomic dipoles with exquisite precision. This unprecedented ability would allow error-resilient atomic spectroscopy and open up novel nonlinear quantum optical research with atom-nanophotonic interfaces.