Huapeng Ye

Multipartite entanglement is a fundamental resource for quantum communication networks, and scaling it up is essential for advancing quantum information processing. However, flexible manipulation and reconfiguration of multipartite entangled states generally require complex optical systems, restricting scalability. Here, we propose a tunable four‐mode continuous‐variable (CV) entanglement scheme via multiple nonlinear processes, including cascaded spontaneous parametric four‐wave mixing (SP‐FWM) and sum‐frequency four‐wave mixing (SF‐FWM). Our results reveal that the properties of four‐mode CV entanglement, in terms of entanglement degree and correlation range, can be dynamically modulated via nonlinear susceptibility and photon detuning engineering. This allows diverse quadripartite entanglement configurations—linear, square, rhombus, and pyramid—to be efficiently constructed by manipulating the entanglement distribution across the four modes. In this system, we also demonstrate the generation of 13 sets of orbital angular momentum (OAM) multiplexed quadripartite entanglement under resonance condition, with entanglement structures across different OAM channels flexibly reconfigurable via photon detunings. Notably, appropriate adjustment of photon detunings significantly expands the accessible parameter range for genuine quadripartite entanglement of high‐order OAM modes, thereby enhancing experimental robustness. Such a scheme enables the redistribution of entanglement configurations among OAM channels, offering a scalable platform for constructing reconfigurable quantum networks and realizing flexible quantum information processing.

Vortex beams carrying orbital angular momentum have attracted increasing attention due to the helical wavefront, extensive high-dimensional state space, and cross-disciplinary applicability in fields such as high-capacity optical communication, optical manipulation, and super-resolution optical imaging. However, the intensity profile of vortex beams exhibits a topological charge-dependent annular structure, which imposes fundamental constraints on wavefront modulation flexibility, particularly in multi-mode coupling systems. In this study, we report a switchable perfect vortex beam (PVB) generator with high efficiency in the visible by combining spatially patterned photoalignment of nematic liquid crystal (LC) with multiplexed geometric phase profiles. Comprehensive simulations and experimental characterization demonstrate that the LC geometric-phase-based PVB generator produces high-quality vortex beams with spatially invariant intensity profiles across topological charges ranging from l = − 8 to + 8 and with an average conversion efficiency up to 86%. Moreover, we reveal that the PVB generator is switchable between left- and right-handed circularly polarized beams. This study demonstrates the feasibility of generating high-quality PVB through highly integrated flat LC photonic device, and may find applications in OAM multiplexing in quantum communication networks and ultrahigh-capacity photonic interconnects.

Bulk Dirac semimetals are becoming the potential candidates for the photonic spin Hall investigations because of its three dimensional bulk characteristics and controllable optical properties. Here, we realize an enhanced reflected photonic spin Hall effect in three dimensional Dirac semimetal material-based grating structure, whose magnitude reaches the theoretical upper limit under the horizontal polarization because of its large reflectance contrast under horizontal and vertical polarizations. In particular, due to the contributions of the controllability in the optical parameters of the Dirac semimetal materials, we demonstrate that the reflected spin shift in this grating structure can be engineered by the Fermi energy of the Dirac semimetal. Our work directly highlight the vital role of grating structure in enhancing the spin shifts and provide a promising approach to achieve its manipulation via the property of the Dirac semimetal material, paving the way toward realizing the functional and switchable spin-photonics applications.

Orbital angular momentum (OAM) mode multiplexing holography holds significant potential for high-capacity optical display and high-security data encryption. However, current mode multiplexing holography faces challenges in the expanding and switching of holographic channels due to the finite dimensionality of optical multiplexing parameters and the fixed mode-to-hologram mappings. To overcome these limitations, we present a dual-parameter encoded OAM mode multiplexing holography approach, which introduces rotation states as an extrinsic modulation degree of freedom via rotatable diffractive neural networks (R-DNNs) beyond intrinsic OAM modes. This framework enables a one-to-many mapping between a single OAM mode and multiple distinct holograms, allowing for information encoding across multi-dimensional spaces and extending holographic channel capacity. By combining 4 OAM modes with a three-layer R-DNN supporting 4 rotation states, we achieved a 16-channel multiplexed holographic system. Additionally, we demonstrated an optical image encryption scheme utilizing segmentation mapping, achieving high-fidelity encryption of a floral pattern by exploiting the diverse mappings between modes and rotation states. This work introduces a novel method for enhancing OAM holography capacity, confirming the feasibility of non-optical parametric encoding for multiplexing holography.

Nonreciprocal photonic spin Hall effect manifests it as the different spin dependent reflected/transmitted transverse splittings of linearly polarized incident waves at two opposite wave propagation directions. However, its realization remains obscure. Here, we report the discovery of the prominent nonreciprocal photonic spin Hall effect in a bulk Dirac semimetal based on quasiperiodic Tribonacci photonic crystal, which is evidenced by the significantly large reflected spin shift along one propagation direction but the trivial spin shift along the opposite propagation direction due to its asymmetrical geometrical structure and electromagnetic field distribution. In addition, the Fermi energy of the bulk Dirac semimetal can be continuously modified by the external stimulus, which enables the effective control of the nonreciprocal photonic spin Hall effect in the Dirac semimetal based Tribonacci photonic crystal. Our results open up the alternative platform to generate the controllably nonreciprocal photonic spin Hall effect in the quasiperiodic systems via the combination of the bulk Dirac semimetals and Tribonacci photonic crystal. PACS: 78.67.-n, 73.20.Mf, 73.43.-f

Valley-topological photonic crystals have emerged as a promising solution for on-chip mode multiplexing communication, attributable to their unique advantages in device integration. However, the inherent fixed waveguide width associated with the topological valley-kink state leads to significant challenges, including severe mode field leakage and distortion, which obstruct mode compatibility and result in untargeted radiation modes during coupling and separation processes. These issues render them currently unsuitable for effective mode (de)multiplexing. To address these limitations, we propose a photonic crystal waveguide with a sandwich structure, incorporating a tunable number of Dirac photonic crystal layers as interlayers. This design allows for the adjustment of the valley-topological edge waveguide width. The tunable waveguide width, in conjunction with strong optical-matter interaction modulation, facilitates adiabatic mode evolution among width-dependent mode fields via evanescent wave coupling. As a proof-of-concept, we have designed and fabricated a bi-mode valley-topological photonic crystal mode (de)multiplexer with a compact footprint of 55.08 × 10.9 μm2. This device exhibits minimal mode field leakage, with crosstalk levels below −18.52 dB. Furthermore, the (de)multiplexer demonstrates effective mode field compatibility, successfully transmitting 1.875 Tbit/s QPSK-OFDM signals with bit error rates below the forward error correction threshold. By leveraging topological protection and unidirectional excitation, this approach not only advances on-chip mode division multiplexing but also enhances stable channel connectivity, thereby improving the resilience of integrated optical communication networks.

Magnetooptical effects, manifesting the interactions between the light and magnetic materials, enable a wide range of the potential applications in sensing, optical isolators, switches as well as data storages. The emergence of monolayer transition metal dichalcogenides allows the alternative chances to unravel their magnetooptical effects under the application of the magnetic field. Here, without relying on the magnetic field, we demonstrate the generation of the magnetooptical effect in monolayer transition metal dichalcogenides driven by the irradiation of an off-resonant circularly polarized light, which breaks the limitation of the absence of the magnetooptical effect in the pristine ones. We find that the induced optical Hall conductivity of monolayer transition metal dichalcogenides can be engineered by the effective energy term depending on the amplitude and frequency of the circularly polarized light. Furthermore, we also present the efficient control of the optical Hall conductivity in monolayer transition metal dichalcogenides by its chemical potential. Our results establish an effective way to produce the remarkable magnetooptical effects in monolayer transition metal dichalcogenides and the avenue for next-generation applications via two-dimensional layered materials.

Multi-singularity structured beams carrying SU(2) modes offer significant potential for expanding communication capacity by leveraging their three orthogonal mode degrees of freedom (DoFs): central orbital angular momentum (OAM), sub-beam OAM, and coherent-state phase. Despite considerable advancements in the recognition of SU(2) modes, challenges remain in the sorting of these modes for signal demultiplexing, including multi-mode conversion and mode separation. In this work, we propose a novel, to the best of our knowledge, SU(2) mode sorting strategy based on off-axis phase modulation, which converts SU(2) modes into quasi-Gaussian modes with customized diffraction angles by combining conjugate phase and gradient phase modulation, thus sorting coaxially transmitted SU(2) modes to distinct spatial positions. We demonstrate the simultaneous sorting of 18 SU(2) modes (including three central OAM, three sub-beam OAM, and two coherent-state phases) with minimal cross talk, achieving levels below −13.8 dB. As a proof of concept, we have developed an SU(2) mode multiplexing communication link that successfully transmits 100 Gbit/s quadrature phase-shift keying (QPSK) signals with bit error rates (BERs) below 10⁻⁵. Our approach provides flexibility in the spatial reallocation of SU(2) modes and holds promise for advancing multidimensional multiplexing communication and high-efficiency shift-keying (SK) communication.

Two dimensional layered van der Waals (vdW) ferromagnetic (FM) and anti FM materials enable the alternative candidates for establishing the next-generation magnetooptical (MO) devices. However, the explorations of the MO effects are primarily focused on the layered FM materials and their nanostructures. How the MO responses behave in the structures with vdW layered anti FM materials remain largely unknown. Here, we identify that a layered collinear antiferromagnet supports the nontrivial MO Faraday rotation (FR) angle in the presence of the electric field instead of magnetic field due to its lifted spin degeneracy and asymmetric band structure at different valleys, whose value is comparable with those of vdW layered ferromagnets and closely correlates with the size of the electric field. Specifically, the FR angle of the layered collinear antiferromagnet can be substantially enhanced via integrating it into a cavity structure, which promises the chance of improving their MO performance. Our result highlights the fundamental opportunities of utilizing the collinear antiferromagnets for various MO applications ranging from magnetometry to high density holographic data storage.