3890138.pdf

Supplement

Single-photon embedded eigenstates in coupled cavity-atom systems

Confining light in open structures is a long-sought goal in nanophotonics and cavity quantum electrodynamics. Embedded eigenstates provide infinite lifetime despite the presence of available leakage channels, but in linear time-invariant systems they cannot be excited from the outside, due to reciprocity. Here, we investigate how atomic nonlinearities may support single-photon embedded eigenstates, which can be populated by a multi-photon excitation followed by internal relaxation. We calculate the system dynamics and show that photon trapping, as well as the reverse release process, can be achieved with arbitrarily high efficiencies. We also discuss the impact of loss, and a path towards the experimental verification of these concepts

Nonreciprocal total cross section of quantum metasurfaces

Nonreciprocity originating from classical interactions among nonlinear scatterers has been attracting increasing attention in the quantum community, offering a promising tool to control excitation transfer for quantum information processing and quantum computing. In this work, we explore the possibility of realizing largely nonreciprocal total cross sections for a pair of quantum metasurfaces formed by two parallel periodic arrays of two-level atoms. We show that large nonreciprocal responses can be obtained in such nonlinear systems by controlling the position of the atoms and their transition frequencies, without requiring that the environment in which the atoms are placed is nonreciprocal. We demonstrate the connection of this effect with the population of a slowly-decaying dark state, which is critical to obtain large nonreciprocal responses

Space-Time Nonlocal Metasurfaces for Event-Based Image Processing

Analog computation with passive optical components can enhance processing speeds and reduce power consumption, recently attracting renewed interest thanks to the opportunities enabled by metasurfaces. Basic image processing tasks, such as spatial differentiation, have been recently demonstrated based on engineered nonlocalities in metasurfaces, but next-generation computational schemes require more advanced capabilities. Here, we tailor nonlocalities in space and time to design a metasurface that can perform mixed spatio-temporal differentiation of an input image, realizing event-based edge detection with a passive ultrathin silicon-based structured film compatible with standard fabrication techniques. The metasurface detects the object edges only when the object moves, and its design can be tailored to selectively enhance objects moving at desired speeds. Our results point towards fully-passive processing of spatio-temporal signals, for highly compact neuromorphic cameras

Spin-Dependent Emission from Arrays of Planar Chiral Nanoantennas Due to Lattice and Localized Plasmon Resonances

Chiral plasmonic nanoantennas manifest a strong asymmetric response to circularly polarized light. Particularly, the geometric handedness of a plasmonic structure can alter the circular polarization state of light emitted from nearby sources, leading to a spin-dependent emission direction. In past experiments, these effects have been attributed entirely to the localized plasmonic resonances of single antennas. In this work, we demonstrate that, when chiral nanoparticles are arranged in diffractive arrays, lattice resonances play a primary role in determining the spin-dependent emission of light. We fabricate 2D diffractive arrays of planar chiral metallic nanoparticles embedded in a light-emitting dye-doped slab. By measuring the polarized photoluminescence enhancement, we show that the geometric chirality of the array’s unit cell induces a preferential circular polarization, and that both the localized surface plasmon resonance and the delocalized hybrid plasmonic–photonic mode contribute to this phenomenon. By further mapping the angle-resolved degree of circular polarization, we demonstrate that strong chiral dissymmetries are mainly localized at the narrow emission directions of the surface lattice resonances. We validate these results against a coupled dipole model calculation, which correctly reproduces the main features. Our findings demonstrate that, in diffractive arrays, lattice resonances play a primary role into the light spin–orbit effect, introducing a highly nontrivial behavior in the angular spectra

Temporal Signal Processing with Nonlocal Optical Metasurfaces

Nonlocal metasurfaces have recently enabled an ultra-compact, low-power and high-speed platform to perform analog image processing. While several computational tasks have been demonstrated based on this platform, most of the previous studies have focused only on spatial operations, such as spatial differentiation and edge detection. Here, we demonstrate that metasurfaces with temporal nonlocalities – that is, with a tailored dispersive response – can be used to implement time-domain signal processing in deeply subwavelength footprints. In particular, we show a passive metasurface performing first-order differentiation of input signals with high-fidelity and high-efficiency. We also demonstrate that this approach is prone to scalability and cascaded computation. Our work paves the way to a new generation of ultra-compact, passive devices for all-optical computation, with applications in neural networks and neuromorphic computing

Dispersion Engineered Metasurfaces for Broadband, High-NA, High-Efficiency, Dual-Polarization Analog Image Processing

Analog computing and image processing with optical metasurfaces holds a great potential for increasing processing speeds and reducing power consumption. Among different functionalities, spatial differentiation and edge detection have recently attracted much interest in this context. While a few demonstrations have achieved analog edge detection, current approaches often suffer from trade-offs in terms of spatial resolution, overall throughput, polarization asymmetry, operational bandwidth and isotropy. Here, we exploit dispersion engineering to design and realize metasurfaces capable of performing isotropic 2D edge detection over a broad operational bandwidth and for any input polarization, while simultaneously maintaining high numerical aperture and large efficiency. Remarkably, we show that this performance can be achieved within a single-layer metasurface consisting of a silicon photonic crystal on glass. We demonstrate metasurfaces performing isotropic dual-polarization edge-detection with numerical apertures up to 0.35, and operating within a spectral bandwidth of 35 nm (5 THz) around 1500 nm. Moreover, we introduce quantitative metrics to properly assess the efficiency of the analog image processing. Thanks to the low insertion loss and the dual-polarization response, our metasurface provides edge-enhanced images with high efficiency and contrast across a broad operational bandwidth and for arbitrary input polarization. Our results pave the way for the application of metasurfaces for low-loss, high-efficiency and broadband optical computing and image processing

Temporal Signal Processing with Nonlocal Optical Metasurfaces

Nonlocal metasurfaces have recently enabled an ultra-compact, low-power and high-speed platform to perform analog image processing. While several computational tasks have been demonstrated based on this platform, most of the previous studies have focused only on spatial operations, such as spatial differentiation and edge detection. Here, we demonstrate that metasurfaces with temporal nonlocalities - that is, with a tailored dispersive response - can be used to implement time-domain signal processing in deeply subwavelength footprints. In particular, we show a passive metasurface performing first-order differentiation of an input signal with high-fidelity and high-efficiency. We also demonstrate that this approach is prone to scalability and cascaded computation. Our work paves the way to a new generation of ultra-compact, passive devices for all-optical computation, with applications in neural networks and neuromorphic computing

Supplementary document for Polarization Imaging and Edge Detection with Image-Processing Metasurfaces - 6605867.pdf

Supplementary Material

Arbitrarily polarized and unidirectional emission from thermal metasurfaces

Thermal emission from a hot body is ubiquitous, yet its properties remain inherently challenging to control due to its incoherent nature. Recent advances in thermal emission manipulation have been unveiling exciting phenomena and new opportunities for applications. In particular, judiciously patterned nanoscale features over their surface have been shown to channel emission sources into partially coherent beams with tailored directionality and frequency selectivity. Yet, more sophisticated forms of control, such as spin-selective and unidirectional thermal emission have remained elusive. Here, we experimentally demonstrate single-layer metasurfaces emitting unidirectional, narrowband thermal light in the infrared with arbitrary polarization states - an operation enabled by photonic bound states in the continuum locally tailored by a geometric phase controlling the temporal and spatial coherence of emitted light. The demonstrated platform paves the way to a compactification paradigm for metasurface optics, in which thermal emission or photoluminescence can feed arbitrarily patterned beams without the need of external coherent sources