We propose a self-optimizing photonic neural network based on multiplane light conversion (MPLC) for quantum parameter estimation. Unlike static mode sorters, our system adaptively learns measurement strategies by maximizing Classical Fisher Information (CFI) employing a minimal number of detectors using a simultaneous perturbation stochastic approximation algorithm. We demonstrate this on the two-point source separation problem. Our approach achieves near-optimal precision and maintains robustness against centroid misalignment, outperforming standard direct imaging and spatial mode demultiplexing methods.

ABSTRACT Programmable metasurfaces enable dynamic electromagnetic (EM) wave control, but many remain limited to single‐polarization operation or duplicated wavefront‐control functions. Here, we report a polarization‐decoupled 1‐bit reflective programmable metasurface that combines PIN‐diode‐loaded meta‐elements with a dual‐bias per‐element control network, enabling independent programming of two orthogonal linear polarizations on a shared aperture. The x‐polarization channel realizes wide‐angle beam steering, experimentally verified at six discrete frequencies from 10.0 to 10.5 GHz using 10.5 GHz‐designed phase codes. The y‐polarization channel demonstrates proof‐of‐concept EM illusion at 11 GHz by matching normalized angular scattering profiles in a selected observation plane under y‐polarized normal and 15° oblique illumination. A differential‐evolution‐assisted inverse‐programming workflow maps target scattering signatures to deployable low‐bit phase codes. Full‐wave simulations, microwave measurements, a 45° linearly polarized oblique‐incidence simulation, and co‐loaded cross‐interference tests validate the hardware‐algorithm co‐design and confirm weakly coupled functional coexistence between the two channels. This work provides a low‐complexity shared‐aperture route for integrating polarization‐selective communication/sensing and EM camouflage functions.

The bosonic Kitaev chain is known to have extraordinary properties distinct from its fermionic counterpart. For example, it exhibits the non-Hermitian skin effect-its eigenmodes are exponentially localized to the edges of the chain-even when the system is Hermitian. Such non-Hermitian effects originate from the fact that the dynamics of bosonic quadratic Hamiltonians is governed by a non-Hermitian matrix. In the topological phase of the model, the modes conspire to lead to phase-dependent and directional exponential amplification of a classical drive. In this work, we study the robustness of this topological amplification to on-site dissipations. We examine the effect of uniform and nonuniform losses under various configurations. We find a remarkable resilience to dissipation in some configurations, while in others the dissipation causes a topological phase transition which eliminates the exponential amplification. In particular, when the dissipation is placed on every other site, the system remains topological and the exponential amplification persists even for very large loss rates which exceed the system's non-Hermitian gap. On the other hand, we find that dividing the chain into unit cells of an odd number of sites and placing dissipation on the first site leads to a topological phase transition at a certain critical value of the dissipation. Our work thus provides insights into the robustness against losses of the topological amplification of non-Hermitian systems and sets explicit limits on the bosonic Kitaev chain's ability to act as a multimode quantum sensor in realistic lossy scenarios.

We demonstrate the potential of inversely designed optical metasurfaces as ultra-thin and scalable elements for quantum state discrimination of single-photon polarization states. By integrating metasurface design with positive operator-valued measure (POVM)-based measurement strategies, we achieve high discrimination success probabilities under practical constraints.

We experimentally create non-Abelian lattice gauge fields for photons in the synthetic frequency dimension using polarization as the pseudo-spin degree of freedom. The presence of non-Abelian lattice gauge fields is confirmed by experimental signatures.

We present inversely designed metasurfaces for reconstructing the density matrix (including amplitude, phase, coherence, and entanglement) of multidimensional spatial states of entangled photons with simple correlation imaging achieving high fidelity.

Reconstructing the density matrix of the quantum state of photons through a tomographically complete set of measurements, known as quantum state tomography, is an essential task in nearly all applications of quantum science and technology, from quantum sensing to quantum communications. Recent advances in optical metasurfaces enable the design of ultrathin nanostructured optical elements performing such state tomography tasks, promising greater simplicity, miniaturization, and scalability. However, reported metasurfaces on this goal were limited to a small Hilbert dimension, e.g., polarization qubits or spatial qudits with only a few states. When scaling up to higher-dimensional qudit tomography problems, especially those involving spatial qudits, a natural question arises: whether a metasurface with randomized nanostructures is sufficient to perform such qudit tomography, achieving optimal conditions. In this work, we attempt to answer this question through a set of numerical experiments with random metasurfaces, utilizing large-scale simulations of over 16,000 distinct metasurfaces each exceeding 200 wavelengths in size. We show that with sufficient redundancy in the number of detectors, random metasurfaces perform reasonably well in quantum photonic spatial qudit tomography encoded in Hermite-Gaussian states for up to approximately 10 states. Furthermore, we discuss additional considerations for optimizing metasurfaces in multiphoton cases. Our work opens a pathway toward computationally efficient, miniaturized, and error-tolerant quantum measurement platforms.

Non-Hermitian systems with nonreciprocal hopping may display the non-Hermitian skin effect, where states under open boundary conditions localize exponentially at one edge of the system. This localization has been linked to spectral winding and topological gain, forming a bulk-boundary correspondence akin to the one relating edge modes to bulk topological invariants in topological insulators and superconductors. In this work, we establish a bulk-boundary correspondence for disordered Hatano-Nelson models. We relate the localization of states to spectral winding using the Lyapunov exponent and the Thouless formula. We identify two kinds of phase transitions and relate them to transport properties. Our framework is relevant to a broad class of 1D non-Hermitian models, opening alternative directions for disorder-resilient transport and quantum-enhanced sensing in photonic, optomechanical, and superconducting platforms.

Non-Abelian gauge fields provide a conceptual framework for the description of particles having spins. The theoretical importance of non-Abelian gauge fields motivates their experimental synthesis and explorations. Here, we demonstrate non-Abelian lattice gauge fields for photons. In the study of gauge fields, lattice models are essential for the understanding of their implications in extended systems. We utilize the platform of synthetic frequency dimensions, which enables the study of lattice physics in a scalable and programmable way. We observe Dirac cones at time-reversal-invariant momenta as well as the direction reversal of eigenstate trajectories associated with such Dirac cones. Both of them are unique signatures of non-Abelian gauge fields in our lattice system. Our results highlight the implications of non-Abelian gauge field in the study of topological physics and suggest opportunities for the control of photon spins and pseudospins.

We report inverse-designed nonlocal metasurfaces for transforming multidimensional states of light represented in the Hermite-Gaussian basis into optimally designed spatial states, where a simple imaging can accurately extract the full multidimensional state including amplitude, phase, and coherence.

We develop a scalable photonic neural network utilizing the discrete frequency degree of freedom of light with the ability to train itself based on an in-situ backpropagation method with minimal reliance on external computers.

We experimentally demonstrate a method to fully measure multi-dimensional band structures in synthetic frequency dimensions by introducing a gauge potential into the lattice Hamiltonian. We use this method to study non-Hermitian topology in high dimensions.

Studying quantum correlations in the presence of loss is of critical importance for the physical modeling of real quantum systems. Here, we demonstrate the control of spatial correlations between entangled photons in a photonic chip, designed and modeled using the singular value decomposition approach. We show that engineered loss, using an auxiliary waveguide, allows one to invert the spatial statistics from bunching to antibunching. Furthermore, we study the photon statistics within the loss-emulating channel and observe photon coincidences, which may provide insights into the design of quantum photonic integrated chips.

We formulate a new conceptual approach for one-shot complete polarization state measurement with nanostructured metasurfaces applicable to classical light and multiphoton quantum states by drawing on the principles of generalized quantum measurements based on positive operator-valued measures. Accurate polarization reconstruction from a combination of photon counts or correlations from several diffraction orders is robust with respect to even strong fabrication inaccuracies, requiring only a single classical calibration of the metasurface transmission. Furthermore, this approach operates with a single metagrating without interleaving, allowing for a reduction in metasurface size while preserving high transmission efficiency and output beam quality. We theoretically obtained original metasurface designs, fabricated the metasurface from amorphous silicon nanostructures deposited on glass, and experimentally confirmed accurate polarization reconstruction of laser beams. We also anticipate robust operation under changes in environmental conditions, opening new possibilities for space-based imaging and satellite optics.

Non-Abelian gauge fields give rise to nontrivial topological physics. Here we develop a scheme to create an arbitrary SU(2) lattice gauge field for photons in the synthetic frequency dimension using an array of dynamically modulated ring resonators. The photon polarization is taken as the spin basis to implement the matrix-valued gauge fields. Using a non-Abelian generalization of the Harper-Hofstadter Hamiltonian as a specific example, we show that the measurement of the steady-state photon amplitudes inside the resonators can reveal the band structures of the Hamiltonian, which show signatures of the underlying non-Abelian gauge field. These results provide opportunities to explore novel topological phenomena associated with non-Abelian lattice gauge fields in photonic systems.

We propose and experimentally demonstrate a dielectric metasurface that allows monitoring of polarization deviations from an arbitrary elliptical input anchor state simply by tracking in real-time the output ratio between the powers of horizontal and vertical components after the metasurface. Importantly, this ratio can be enhanced corresponding to increased responsivity. Such nontrivial functionality is achieved by designing binary metasurfaces that realize tailored nonunitary and chiral polarization transformation. We experimentally demonstrate the operation at telecommunication wavelengths with enhanced responsivity up to 25 for various anchor states, including the strongly elliptical and circular. We also achieve the uncertainty of deviation measurement that is significantly better than the fundamental limit for nonchiral metasurfaces.

We demonstrate that time reflection and refraction can be observed in a two-band model centered around a non-zero reference energy. Our model can be physically implemented as a system of two coupled dynamically-modulated ring resonators.

Convolution is an essential operation in signal and image processing and consumes most of the computing power in convolutional neural networks. Photonic convolution has the promise of addressing computational bottlenecks and outperforming electronic implementations. Performing photonic convolution in the synthetic frequency dimension, which harnesses the dynamics of light in the spectral degrees of freedom for photons, can lead to highly compact devices. Here we experimentally realize convolution operations in the synthetic frequency dimension. Using a modulated ring resonator, we synthesize arbitrary convolution kernels using a pre-determined modulation waveform with high accuracy. We demonstrate the convolution computation between input frequency combs and synthesized kernels. We also introduce the idea of an additive offset to broaden the kinds of kernels that can be implemented experimentally when the modulation strength is limited. Our work demonstrate the use of synthetic frequency dimension to efficiently encode data and implement computation tasks, leading to a compact and scalable photonic computation architecture.