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Synergistic control of the frequency and orbital angular momentum (OAM) of light offers new opportunities for the generation of spatio-temporal optical waveforms and optical metrology. However, their physical realizations are typically bulky and complex owing to challenges in creating, manipulating and detecting mutually coherent, high-dimensional OAM states. Here we achieve combined control over the frequency and the OAM of a comb structure on a photonic chip. Dissipative optical solitons are formed in a nonlinear ring microresonator and emitted owing to engraved angular gratings, with each comb line carrying a distinct OAM. The beam of such a vortex soliton microcomb manifests dynamically revolving, double-helical intensity profiles. The one-to-one correspondence between the OAM and frequencies features a high extinction ratio of over 18.5 dB, enabling precision spectroscopy of optical vortices. Our work provides an integrated solution for realizing coherent light sources that are multiplexed in the spatial and frequency domains, with the potential to establish a new approach to the generation of high-dimensional structured light. Nonlinear microring resonators can generate a vortex soliton microcomb, that is, a frequency comb with each comb line carrying a distinct orbital angular momentum. [ABSTRACT FROM AUTHOR]

The topological photonics plays an important role in the fields of fundamental physics and photonic devices. The traditional method of designing topological system is based on the momentum space, which is not a direct and convenient way to grasp the topological properties, especially for the perturbative structures or coupled systems. Here, we propose an interdisciplinary approach to study the topological systems in real space through combining the information entropy and topological photonics. As a proof of concept, the Kagome model has been analyzed with information entropy. We reveal that the bandgap closing does not correspond to the topological edge state disappearing. This method can be used to identify the topological phase conveniently and directly, even the systems with perturbations or couplings. As a promotional validation, Su–Schrieffer–Heeger model and the valley-Hall photonic crystal have also been studied based on the information entropy method. This work provides a method to study topological photonic phase based on information theory, and brings inspiration to analyze the physical properties by taking advantage of interdisciplinarity. [ABSTRACT FROM AUTHOR]

Complex entangled states are the key resources for measurement-based quantum computations, which is realised by performing a sequence of measurements on initially entangled qubits. Executable quantum algorithms in the graph-state quantum computing model are determined by the entanglement structure and the connectivity of entangled qubits. By generalisation from graph-type entanglement in which only the nearest qubits interact to a new type of hypergraph entanglement in which any subset of qubits can be arbitrarily entangled via hyperedges, hypergraph states represent more general resource states that allow arbitrary quantum computation with Pauli universality. Here we report experimental preparation, certification and processing of complete categories of four-qubit hypergraph states under the principle of local unitary equivalence, on a fully reprogrammable silicon-photonic quantum chip. Genuine multipartite entanglement for hypergraph states is certificated by the characterisation of entanglement witness, and the observation of violations of Mermin inequalities without any closure of distance or detection loopholes. A basic measurement-based protocol and an efficient resource state verification by color-encoding stabilizers are implemented with local Pauli measurement to benchmark the building blocks for hypergraph-state quantum computation. Our work prototypes hypergraph entanglement as a general resource for quantum information processing. [ABSTRACT FROM AUTHOR]

Modulation of topological phase transition has been pursued by researchers in both condensed matter and optics research fields, and has been realized in Euclidean systems, such as topological photonic crystals, topological metamaterials, and coupled resonator arrays. However, the spin-controlled topological phase transition in non-Euclidean space has not yet been explored. Here, we propose a non-Euclidean configuration based on Möbius rings, and we demonstrate the spin-controlled transition between the topological edge state and the bulk state. The Möbius ring, which is designed to have an 8π period, has a square cross section at the twist beginning and the length/width evolves adiabatically along the loop, accompanied by conversion from transverse electric to transverse magnetic modes resulting from the spin-locked effect. The 8π period Möbius rings are used to construct Su–Schrieffer–Heeger configuration, and the configuration can support the topological edge states excited by circularly polarized light, and meanwhile a transition from the topological edge state to the bulk state can be realized by controlling circular polarization. In addition, the spin-controlled topological phase transition in non-Euclidean space is feasible for both Hermitian and non-Hermitian cases in 2D systems. This work provides a new degree of polarization to control topological photonic states based on the spin of Möbius rings and opens a way to tune the topological phase in non-Euclidean space. [ABSTRACT FROM AUTHOR]

Electrons detached from atoms by photoionization carry valuable information about light-atom interactions. Characterizing and shaping the electron wave function on its natural timescale is of paramount importance for understanding and controlling ultrafast electron dynamics in atoms, molecules and condensed matter. Here we propose a novel attoclock interferometry to shape and image the electron wave function in atomic photoionization. Using a combination of a strong circularly polarized second harmonic and a weak linearly polarized fundamental field, we spatiotemporally modulate the atomic potential barrier and shape the electron wave functions, which are mapped into a temporal interferometry. By analyzing the two-color phase-resolved and angle-resolved photoelectron interference, we are able to reconstruct the spatiotemporal evolution of the shaping on the amplitude and phase of electron wave function in momentum space within the optical cycle, from which we identify the quantum nature of strong-field ionization and reveal the effect of the spatiotemporal properties of atomic potential on the departing electron. This study provides a new approach for spatiotemporal shaping and imaging of electron wave function in intense light-matter interactions and holds great potential for resolving ultrafast electronic dynamics in molecules, solids, and liquids. Electrons detached from atoms by photoionization carry valuable information about light-atom interactions. Here, authors propose a novel attoclock interferometry to spatiotemporally shape and image the electron wave function, from which the quantum nature of strong-field ionization is identified. [ABSTRACT FROM AUTHOR]

Non-orthogonal eigenstates are a fundamental feature of non-Hermitian systems and are accompanied by the emergence of nontrivial features. However, the platforms to explore non-Hermitian mode couplings mainly measure near-field effects, and the far-field behaviours remain mostly unexplored. Here, we study how a microcavity with non-Hermitian mode coupling exhibits eigenstate non-orthogonality by investigating the spatial field and the far-field polarization of cavity modes. The non-Hermiticity arises from asymmetric backscattering, which is controlled by integrating two scatterers of different size and location into a microdisk. We observe that the spatial field overlap of two modes increases abruptly to its maximum value, whilst different far-field elliptical polarizations of two modes coalesce when approaching an exceptional point. We demonstrate such features experimentally by measuring the far-field polarization from the fabricated microdisks. Our work reveals the non-orthogonality in the far-field degree of freedom, and the integrability of the microdisks paves a way to integrate more non-Hermitian optical properties into nanophotonic systems. Whispering gallery mode microcavities with asymmetric backscattering provide a platform to characterise non-orthogonal Hermitian features, but the majority of the studies focus on near-field measurements. The authors realize a non-Hermitian platform and characterise its far-field features in terms of polarization via confocal micro-photoluminescence. [ABSTRACT FROM AUTHOR]

Parity-time (PT) symmetry and broken in micro-/nanophotonic structures have been investigated extensively as they bring new opportunities to control the flow of light based on non-Hermitian optics. Previous studies have focused on the situations of PT-symmetry broken in loss-loss or gain-loss coupling systems. Here, we theoretically predict the gain-gain and gain-lossless PT-broken from the phase diagram, where the boundaries between PT-symmetry and PT-broken can be clearly defined in the full-parameter space including gain, lossless and loss. For specific micro-/nanophotonic structures, such as coupled waveguides, we give the transmission matrices of each phase space, which can be used for beam splitting. Taking coupled waveguides as example, we obtain periodic energy exchange in the PT-symmetry phase and exponential gain or loss in the PT-broken phase, which are consistent with the phase diagram. The scenario giving a full view of PT-symmetry or broken, will not only deepen the understanding of fundamental physics, but also will promote the breakthrough of photonic applications like optical routers and beam splitters. [ABSTRACT FROM AUTHOR]

Nonreciprocal interlayer coupling is difficult to practically implement in bilayer non-Hermitian topological photonic systems. In this work, we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss. The similarity transformation is widely applicable, and we show its application in one- and two-dimensional bilayer topological systems as examples. The bilayer non-Hermitian system with nonreciprocal interlayer coupling, whose topological number can be defined using the gauge-smoothed Wilson loop, is topologically equivalent to the bilayer system with on-site gain/loss. We also show that the topological number of bilayer non-Hermitian C6v-typed domain-induced topological interface states can be defined in the same way as in the case of the bilayer non-Hermitian Su–Schrieffer–Heeger model. Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems. This scheme is useful for observation of non-Hermitian skin effect in three-dimensional systems. [ABSTRACT FROM AUTHOR]

Vibrational spectroscopy is a ubiquitous technology that derives the species, constituents and morphology of an object from its natural vibrations. However, natural vibrations of mesoscopic particles—including most biological cells—have remained hidden from existing technologies. These particles are expected to vibrate faintly at megahertz to gigahertz rates, requiring a sensitivity and resolution that are impractical for current optical and piezoelectric spectroscopies. Here we demonstrate the real-time measurement of natural vibrations of single mesoscopic particles using an optical microresonator, extending the reach of vibrational spectroscopy to a different spectral window. Conceptually, a spectrum of vibrational modes of the particles is stimulated photoacoustically by the absorption of laser pulses and acoustically coupled to a high-quality-factor optical resonance for ultrasensitive readout. Experimentally, this scheme is verified by measuring mesoscopic particles with different constituents, sizes and internal structures, showing an unprecedented signal-to-noise ratio of 50 dB and detection bandwidth of over 1 GHz. This technology is further applied for the biomechanical fingerprinting of the species and living states of microorganisms at the single-cell level. This work opens up new avenues to study single-particle mechanical properties in vibrational degrees of freedom and may find applications in photoacoustic sensing and imaging, cavity optomechanics and biomechanics. Natural vibrations of mesoscopic particles, such as living cells, are typically faint; occurring at megahertz to gigahertz frequencies also makes detection challenging. Now, researchers demonstrate real-time measurement of natural vibrations of single mesoscopic particles by using photoacoustic excitation and acoustic coupling to an optical microresonator for readout. [ABSTRACT FROM AUTHOR]

Low-loss dielectric modes are important features and functional bases of fundamental optical components in on-chip optical devices. However, dielectric near-field modes are challenging to reveal with high spatiotemporal resolution and fast direct imaging. Herein, we present a method to address this issue by applying time-resolved photoemission electron microscopy to a low-dimensional wide-bandgap semiconductor, hexagonal boron nitride (hBN). Taking a low-loss dielectric planar waveguide as a fundamental structure, static vector near-field vortices with different topological charges and the spatiotemporal evolution of waveguide modes are directly revealed. With the lowest-order vortex structure, strong nanofocusing in real space is realized, while near-vertical photoemission in momentum space and narrow spread in energy space are simultaneously observed due to the atomically flat surface of hBN and the small photoemission horizon set by the limited photon energies. Our approach provides a strategy for the realization of flat photoemission emitters. The application of time-resolved photoemission electron microscopy (TR-PEEM) to non-conducting materials is challenging. Here, the authors report the TR-PEEM characterization of near-field dielectric modes and photoemission properties of insulating hexagonal boron nitride structures on indium tin oxide/glass substrates. [ABSTRACT FROM AUTHOR]

This study reviews the recent progress of high-dimensional quantum information processing with photons. We first introduce the basic language of high-dimensional quantum information, including the representation of quantum dits (qudits), unitary operations of qudit states, and the general format of quantum algorithms with qudits. We discuss experimental implementations of high-dimensional quantum information processing and quantum computing in photonic systems, particularly in integrated quantum photonic platforms. We also discuss how qudit-based quantum photonic devices and systems can be adopted for further improving qubit-based quantum computation and quantum simulation. [ABSTRACT FROM AUTHOR]

Single photon emission of quantum emitters (QEs) carrying internal degrees of freedom such as spin and angular momentum plays an important role in quantum optics. Recently, QEs in two-dimensional semiconductors have attracted great interest as promising quantum light sources. However, whether those QEs are characterized by the same valley physics as delocalized valley excitons is still under debate. Moreover, the potential applications of such QEs still need to be explored. Here we show experimental evidence of valley symmetry breaking for neutral QEs in WSe2 monolayer by interacting with chiral plasmonic nanocavities. The anomalous magneto-optical behaviour of the coupled QEs suggests that the polarization state of emitted photon is modulated by the chiral nanocavity instead of the valley-dependent optical selection rules. Calculations of cavity quantum electrodynamics further show the absence of intrinsic valley polarization. The cavity-dependent circularly polarized single-photon output also offers a strategy for future applications in chiral quantum optics. The microscopic origin and valley physics of quantum emitters (QEs) in 2D semiconductors are still not fully understood. Here, the authors report an anomalous magneto-optical behaviour of QEs in WSe2 monolayers coupled to chiral plasmonic nanocavities, suggesting the absence of intrinsic valley symmetry of the emitters. [ABSTRACT FROM AUTHOR]

Air lasing is a simple and promising technique to efficiently produce coherent light in the atmosphere. Yet, its capability to obtain structured light like optical vortices or vector beams is still unexplored. Here, we demonstrate the generation of vortex superfluorescent radiation with the same orbital angular momentum as the pump beam, obtained via N2+ lasing by focusing a vortex pump beam on N2 gas. The vortex superfluorescence is amplified without altering the vorticity when seeded by a Gaussian beam, in which the vortex pump beam transfers the spatial spiral phase into the N2+ gain medium and the N2+ lasing obtains the phase information. The same mechanism is applied for a vector pump beam, turning the Gaussian seed into an amplified cylindrical vector beam. We corroborate our mechanism for generating vectorially structured light via air lasing with numerical calculations. This work provides a promising approach to generating structured light via superfluorescence. Air lasing is a cavity-free lasing action that is generated in air owing to the plasma filamentation process of high-power femtosecond laser pulses. The authors demonstrate that air lasing can be used to generate structured light, obtaining optical vortex beams and optical vector beams via superfluorescence from N2+. [ABSTRACT FROM AUTHOR]

Over the past few decades, exciton-polaritons have attracted substantial research interest due to their half-light-half-matter bosonic nature. Coupling exciton-polaritons with magnetic orders grants access to rich many-body phenomena, but has been limited by the availability of material systems that exhibit simultaneous exciton resonances and magnetic ordering. Here we report magnetically-dressed microcavity exciton-polaritons in the van der Waals antiferromagnetic (AFM) semiconductor CrSBr coupled to a Tamm plasmon microcavity. Using angle-resolved spectroscopy, we reveal an exceptionally high exciton-photon coupling strength, up to 169 meV, demonstrating ultrastrong coupling that persists up to room temperature. By performing temperature-dependent spectroscopy, we show the magnetic nature of the exciton-polaritons in CrSBr microcavity as the magnetic order changes from AFM to paramagnetic. By applying an out-of-plane magnetic field, we achieve effective tuning of the polariton energy while maintaining the ultrastrong exciton-photon coupling strength. We attribute this to the spin canting process that modulates the interlayer exciton interaction.Exciton-polaritons are hybrid light matter quasi-particles, which can occur in systems exhibiting strong light-matter coupling. Here, Wang et al study exciton-polaritons in the van der Waals antiferromagnetic material, CrSBr, coupled to a Tamm plasmon microcavity and find the exciton-polaritons are sensitive to and can be tuned by the magnetic order of CrSBr. [ABSTRACT FROM AUTHOR]

Characterization and categorization of quantum correlations are both fundamentally and practically important in quantum information science. Although quantum correlations such as non-separability, steerability, and non-locality can be characterized by different theoretical models in different scenarios with either known (trusted) or unknown (untrusted) knowledge of the associated systems, such characterization sometimes lacks unambiguous to experimentalist. In this work, we propose the physical interpretation of nonlocal quantum correlation between two systems. In the absence of complete local description of one of the subsystems quantified by the local uncertainty relation, the correlation between subsystems becomes nonlocal. Remarkably, different nonlocal quantum correlations can be discriminated from a single uncertainty relation derived under local hidden state (LHS)–LHS model only. We experimentally characterize the two-qubit Werner state in different scenarios. [ABSTRACT FROM AUTHOR]

Wigner negativity, as a well-known indicator of nonclassicality, plays an essential role in quantum computing and simulation using continuous-variable systems. The conditional preparation of Wigner-negative states through appropriate non-Gaussian operations on an auxiliary mode is common procedure in quantum optics experiments. Motivated by the demand of real-world quantum network, here we investigate the remote creation and distribution of Wigner negativity in the multipartite scenario from a quantitative perspective. By establishing a monogamy relation akin to the generalized Coffman-Kundu-Wootters inequality, we show that the amount of Wigner negativity cannot be freely distributed among different modes. Moreover, for photon subtraction—one of the main experimentally realized non-Gaussian operations—we provide an intuitive method to quantify remotely generated Wigner negativity. Our results pave the way for exploiting Wigner negativity as a valuable resource for numerous quantum information protocols based on non-Gaussian scenario. [ABSTRACT FROM AUTHOR]

Entanglement and topology portray nature at the fundamental level but differently. Entangled states of particles are intrinsically sensitive to the environment, whereas the topological phases of matter are naturally robust against environmental perturbations. Harnessing topology to protect entanglement has great potential for reliable quantum applications. Generating topologically protected entanglement, however, remains a significant challenge, requiring the operation of complex quantum devices in extreme conditions. Here we report topologically protected entanglement emitters that emit a topological Einstein–Podolsky–Rosen state and a multiphoton entangled state from a monolithically integrated plug-and-play silicon photonic chip in ambient conditions. The device emulating a photonic anomalous Floquet insulator allows the generation of four-photon topological entangled states at non-trivial edge modes, verified by the observation of a reduced de Broglie wavelength. Remarkably, we show that the Einstein–Podolsky–Rosen entanglement can be topologically protected against artificial structure defects by comparing the state fidelities of 0.968 ± 0.004 and 0.951 ± 0.010 for perfect and defected emitters, respectively. Our topologically protected devices may find applications in quantum computation and in the study of quantum topological physics. A photonic anomalous Floquet insulator is emulated in a silicon photonic chip. Up to four-photon topologically protected entangled states are generated in a monolithically integrated emitter in ambient conditions through four-wave mixing on top of the edge modes of the insulator. [ABSTRACT FROM AUTHOR]

Laser-induced electron tunnelling—which triggers a broad range of ultrafast phenomena such as the generation of attosecond light pulses, photoelectron diffraction and holography—has laid the foundation for strong-field physics and attosecond science. Using the attoclock constructed by single-colour elliptically polarized laser fields, previous experiments have measured the tunnelling rates, exit positions, exit velocities and delay times for some specific electron trajectories, which are mostly created at the field peak instant, that is, when the laser electric field and the formed potential barrier are stationary in terms of the derivative versus time. From the view of wave-particle dualism, the electron phase under a classically forbidden, tunnelling barrier has not been measured, which is at the heart of quantum tunnelling physics. Here we present a robust measurement of tunnelling dynamics including the electron sub-barrier phase and amplitude. We combine the attoclock technique with two-colour phase-of-phase (POP) spectroscopy to accurately calibrate the angular streaking relation and to probe the non-stationary tunnelling dynamics by manipulating a rapidly changing potential barrier. This POP attoclock directly links the measured phase of the two-colour relative phase with the ionization instant for the photoelectron with any final momentum on the detector, allowing us to reconstruct the imaginary tunnelling time and the accumulated phase under the barrier. The POP attoclock provides a general time-resolved approach to accessing the underlying quantum dynamics in intense light–matter interactions. Electron non-stationary tunnelling dynamics is probed by the attoclock with the two-colour phase-of-phase photoelectron spectroscopy. Contrary to the case of static tunnelling, angle-to-time mapping in attoclock is found to be not angularly uniform. [ABSTRACT FROM AUTHOR]

The spatial features of a light field, such as in the form of the optical singularities, provide a new degree of freedom for the application of light fields in different areas of science and technology. However, although the exploration of structured light is growing rapidly, the investigation of strong-field photoionization using such light fields is noticeably lagging behind. Here, we present an experimental study that reveals the signatures of intense, structured light fields with controlled optical singularities in strong-field photoionization. The different types of optical singularities can be identified through photoionization observables, i.e., photoelectron momentum distributions (PMDs). By concurrently shifting the locations of the phase and polarization singularities, the focal electric field features can be designated, and subsequently, the photoionization appearances can be manipulated. In this process, the behaviors of the different intense optical singularities are clearly visualized by the PMDs. This work will advance both the strong-field science and singularity optics. [ABSTRACT FROM AUTHOR]

Dissipative Kerr soliton (DKS) featuring broadband coherent frequency comb with compact size and low power consumption, provides an unparalleled tool for nonlinear physics investigation and precise measurement applications. However, the complex nonlinear dynamics generally leads to stochastic soliton formation process and makes it highly challenging to manipulate soliton number and temporal distribution in the microcavity. Here, synthesized and reconfigurable soliton crystals (SCs) are demonstrated by constructing a periodic intra-cavity potential field, which allows deterministic SCs synthesis with soliton numbers from 1 to 32 in a monolithic integrated microcavity. The ordered temporal distribution coherently enhanced the soliton crystal comb lines power up to 3 orders of magnitude in comparison to the single-soliton state. The interaction between the traveling potential field and the soliton crystals creates periodic forces on soliton and results in forced soliton oscillation. Our work paves the way to effectively manipulate cavity solitons. The demonstrated synthesized SCs offer reconfigurable temporal and spectral profiles, which provide compelling advantages for practical applications such as photonic radar, satellite communication and radio-frequency filter. Here the authors demonstrate an on-demand generation of perfect soliton crystal using synthesized potential field. The individual solitons can also be controlled, for example oscillate around their equilibrium position, by the external field. [ABSTRACT FROM AUTHOR]

Bohr's complementarity is one central tenet of quantum physics. The paradoxical wave-particle duality of quantum matters and photons has been tested in Young's double-slit (double-path) interferometers. The object exclusively exhibits wave and particle nature, depending measurement apparatus that can be delayed chosen to rule out too-naive interpretations of quantum complementarity. All experiments to date have been implemented in the double-path framework, while it is of fundamental interest to study complementarity in multipath interferometric systems. Here, we demonstrate generalized multipath wave-particle duality in a quantum delayed-choice experiment, implemented by large-scale silicon-integrated multipath interferometers. Single-photon displays sophisticated transitions between wave and particle characters, determined by the choice of quantum-controlled generalized Hadamard operations. We characterise particle-nature by multimode which-path information and wave-nature by multipath coherence of interference, and demonstrate the generalisation of Bohr's multipath duality relation. Our work provides deep insights into multidimensional quantum physics and benchmarks controllability of integrated photonic quantum technology. Wave-particle duality and delayed choice are keys to our understanding of quantum mechanics. Here, leveraging the capabilities of silicon nanophotonics, the authors probe the extension of wave-particle duality from dual-path to multipath case. [ABSTRACT FROM AUTHOR]

The performance of perovskite photovoltaics is fundamentally impeded by the presence of undesirable defects that contribute to non-radiative losses within the devices. Although mitigating these losses has been extensively reported by numerous passivation strategies, a detailed understanding of loss origins within the devices remains elusive. Here, we demonstrate that the defect capturing probability estimated by the capture cross-section is decreased by varying the dielectric response, producing the dielectric screening effect in the perovskite. The resulting perovskites also show reduced surface recombination and a weaker electron-phonon coupling. All of these boost the power conversion efficiency to 22.3% for an inverted perovskite photovoltaic device with a high open-circuit voltage of 1.25 V and a low voltage deficit of 0.37 V (a bandgap ~1.62 eV). Our results provide not only an in-depth understanding of the carrier capture processes in perovskites, but also a promising pathway for realizing highly efficient devices via dielectric regulation. Performance of perovskite photovoltaics is greatly affected by undesirable defects that contribute to non-radiative losses. Here, the authors mitigate these losses by doping perovskite with KI to alter the dielectric response, thus defect capturing probability, resulting in inverted device with PCE of 22.3% and low voltage loss. [ABSTRACT FROM AUTHOR]

Optical evanescent sensors can non-invasively detect unlabeled nanoscale objects in real time with unprecedented sensitivity, enabling a variety of advances in fundamental physics and biological applications. However, the intrinsic low-frequency noise therein with an approximately 1/f-shaped spectral density imposes an ultimate detection limit for monitoring many paramount processes, such as antigen-antibody reactions, cell motions and DNA hybridizations. Here, we propose and demonstrate a 1/f-noise-free optical sensor through an up-converted detection system. Experimentally, in a CMOS-compatible heterodyne interferometer, the sampling noise amplitude is suppressed by two orders of magnitude. It pushes the label-free single-nanoparticle detection limit down to the attogram level without exploiting cavity resonances, plasmonic effects, or surface charges on the analytes. Single polystyrene nanobeads and HIV-1 virus-like particles are detected as a proof-of-concept demonstration for airborne biosensing. Based on integrated waveguide arrays, our devices hold great potentials for multiplexed and rapid sensing of diverse viruses or molecules. Suppressing 1/f-shaped low-frequency noise is critical but fundamentally challenging to both electrical and optical transducers. Here, the authors demonstrate a 1/f-noise-free optical sensor with integrated CMOS-compatible heterodyne interferometer and an upconversion amplifying technique, which suppresses the noise by two orders of magnitude. [ABSTRACT FROM AUTHOR]

The interaction between a quantum particle's spin angular momentum1 and its orbital angular momentum2 is ubiquitous in nature. In optics, the spin–orbit optical phenomenon is closely related with the light–matter interaction3 and has been of great interest4,5. With the development of laser technology6, the high-power and ultrafast light sources now serve as a crucial tool in revealing the behaviour of matter under extreme conditions. A comprehensive knowledge of the spin–orbit interaction for intense light is of utmost importance. Here, we report the in situ modulation and visualization of the optical orbital-to-spin conversion in the strong-field regime. We show that, through manipulating the morphology of femtosecond cylindrical vector vortex pulses7 by a slit, the photon's orbital angular momentum can be controllably transformed into spin after focusing. By employing a strong-field ionization experiment, the orbital-to-spin conversion can be imaged and measured through the photoelectron momentum distributions. Such detection and consequent control of the spin–orbit dynamics of intense laser fields has implications for controlling photoelectron holography and coherent extreme-ultraviolet radiation8. Sculpting and focusing femtosecond cylindrical vector vortex pulses by a slit allows the controllable transformation of the photon's orbital angular momentum into spin angular momentum, which can be characterized in situ by a strong-field ionization experiment. [ABSTRACT FROM AUTHOR]

Since its invention, optical frequency comb has revolutionized a broad range of subjects from metrology to spectroscopy. The recent development of microresonator-based frequency combs (microcombs) provides a unique pathway to create frequency comb systems on a chip. Indeed, microcomb-based spectroscopy, ranging, optical synthesizer, telecommunications and astronomical calibrations have been reported recently. Critical to many of the integrated comb systems is the broad coverage of comb spectra. Here, microcombs of more than two-octave span (450 nm to 2,008 nm) is demonstrated through χ(2) and χ(3) nonlinearities in a deformed silica microcavity. The deformation lifts the circular symmetry and creates chaotic tunneling channels that enable broadband collection of intracavity emission with a single waveguide. Our demonstration introduces a new degree of freedom, cavity deformation, to the microcomb studies, and our microcomb spectral range is useful for applications in optical clock, astronomical calibration and biological imaging. Here, the authors demonstrate the use of chaos to obtain 2-octave comb generation. The deformation lifts the circular symmetry and creates chaotic tunneling channels that enable broadband collection of intracavity emission with a single waveguide, introducing a new degree of freedom to microcomb studies. [ABSTRACT FROM AUTHOR]

Optical cavity polaritons, originated from strong coupling between the excitons in materials and photons in the confined cavities field, have recently emerged as their applications in the high-speed lowpower polaritons devices, low-threshold lasing and so on. However, the traditional exciton polaritons based on metal plasmonic structures or Fabry-Perot cavities suffer from the disadvantages of large intrinsic losses or hard to integrate and nanofabricate. This greatly limits the applications of exciton poalritons. Thus, here we implement a compact low-loss dielectric photonic — organic nanostructure by placing a 2-nm-thick PVA doped with TDBC film on top of a planar Si asymmetric nanogratings to reveal the exciton polaritons modes. We find a distinct anti-crossing dispersion behavior appears with a 117.16 meV Rabi splitting when varying the period of Si nanogratings. Polaritons dispersion and mode anti-crossing behaviors are also observed when considering the independence of the height of Si, width of Si nanowire B, and distance between the two Si nanowires in one period. This work offers an opportunity to realize low-loss novel polaritons applications. [ABSTRACT FROM AUTHOR]

Second-order nonlinear optical processes lie at the heart of many applications in both classical and quantum regimes1-3. Inversion symmetry, however, rules out the second-order nonlinear electric-dipole response1,4,5 in materials widely adopted in integrated photonics (for example, SiO2, Si and Si3N4). Here, we report nonlinear optics induced by symmetry breaking6-10 at the surface of an ultrahigh-Q silica microcavity under a sub-milliwatt continuous-wave pump. By dynamically coordinating the double-resonance phase matching, a second harmonic is achieved with an unprecedented conversion efficiency of 0.049% W−1, 14 orders of magnitude higher than that of the non-enhancement case11. In addition, the nonlinear effect from the intrinsic symmetry breaking at the surface8,12 can be identified unambiguously, with guided control of the pump polarization and the recognition of the second-harmonic mode distribution. This work not only extends the emission frequency range of silica photonic devices, but also lays the groundwork for applications in ultra-sensitive surface analysis. A second harmonic with a conversion efficiency of 0.049% W−1, originating from surface nonlinearity and bulk multipole response in a silica whispering-gallery microcavity, is observed with a continuous-wave pump power below 1 mW. [ABSTRACT FROM AUTHOR]

Efficiency is an important criterion in developing a practical surface-plasmon-polariton (SPP) unidirectional launcher. In this paper, we show that multi-groove structures can efficiently launch SPPs by numerically optimizing structural parameters and normal incident light. Experimentally, a high efficiency of 58.4 % is demonstrated in a six-groove structure with a lateral dimension of 3.9 μm. For a three-groove structure with even smaller lateral dimension of 1.35 μm, the efficiency presents a broadband response, which remains higher than 42 % from 720 to 860 nm. The proposed multi-groove structures with high SPP launching efficiency and small size exhibit potential in highly integrated plasmonic circuits. [ABSTRACT FROM AUTHOR]

We demonstrate that Young's modulus of polymerized microstructures in both air and liquid can be controlled by changing the writing velocity of the femtosecond laser two-photon polymerization, which is crucial for many practical applications. For the zirconium/silicon inorganic/organic hybrid sol-gel, the Young's modulus for dry polymerized micro-cantilevers in air can be adjusted from 5.5 to 9.4 GPa by varying writing velocity from 600 to 200 μm/s, and it also can be controlled in liquid, which is four orders smaller than in air. To characterize the Young's modulus in liquid, we propose a simple method by measuring non-adhered lengths of the arc-shaped or s-shaped polymerized micro-cantilevers after drying in air. [ABSTRACT FROM AUTHOR]

Einstein, Podolsky and Rosen (EPR) pointed out in their famous paradox that two quantum-entangled particles can have perfectly correlated positions and momenta. Such correlations give evidence for the nonlocality of quantum mechanics and form the basis for quantum cryptography and teleportation. EPR steering is the nonlocality associated with the EPR paradox and has traditionally been investigated between only two parties. Using optical networks and efficient detection, we present experimental observations of multiparty EPR steering and of the genuine entanglement of three intense optical beams. We entangle the quadrature phase amplitudes of distinct fields, in analogy to the position-momentum entanglement of the original paradox. Our experiments complement tests of quantum mechanics that have entangled small systems or have demonstrated tripartite inseparability. Our methods establish principles for the development of multiparty quantum communication protocols with asymmetric observers, and can be extended to qubits, whether photonic, atomic, superconducting, or otherwise. [ABSTRACT FROM AUTHOR]

Single gold nanoshell with mutilpolar plasmon resonances is proposed to enhance two-photon fluorescence efficiently. The single emitter single nanoshell configuration is studied systematically by employing the finite-difference time-domain method. The emitter located inside or outside the nanoshell at various positions leads to a significantly different enhancement effect. The fluorescent emitter placed outside the nanoshell can achieve large fluorescence intensity given that both the position and orientation of the emission dipole are optimally controlled. In contrast, for the case of the emitter placed inside the nanoshell, it can experience substantial two-photon fluorescence enhancement without strict requirements upon the position and dipole orientations. Metallic nanoshell encapsulating many fluorescent emitters should be a promising nanocomposite configuration for bright two-photon fluorescence label. The results provide a comprehensive understanding about the plasmonic-enhanced two-photon fluorescence behaviors, and the nanocomposite configuration has great potential for optical detecting, imaging and sensing in biological applications. [ABSTRACT FROM AUTHOR]

Fano resonances are numerically predicted in an ultracompact plasmonic structure, comprising a metal-isolator-metal (MIM) waveguide side-coupled with two identical stub resonators. This phenomenon can be well explained by the analytic model and the relative phase analysis based on the scattering matrix theory. In sensing applications, the sensitivity of the proposed structure is about 1.1 × 10 3 nm/RIU and its figure of merit is as high as 2 × 10 5 at λ = 980 nm, which is due to the sharp asymmetric Fano line-shape with an ultra-low transmittance at this wavelength. This plasmonic structure with such high figure of merits and footprints of only about 0.2 μm 2 may find important applications in the on-chip nano-sensors. [ABSTRACT FROM AUTHOR]

The coupling between optical and mechanical degrees of freedom has been of broad interest for a long time. However, it is only until recently, with the rapid development of optical microcavity research, that we are able to manipulate and utilize this coupling process. When a high Q microcavity couples to a mechanical resonator, they can consolidate into an optomechanical system. Benefitting from the unique characteristics offered by optomechanical coupling, this hybrid system has become a promising platform for ultrasensitive sensors to detect displacement, mass, force and acceleration. In this review, we introduce the basic physical concepts of cavity optomechanics, and describe some of the most typical experimental cavity optomechanical systems for sensing applications. Finally, we discuss the noise arising from various sources and show the potentiality of optomechanical sensing towards quantum-noise-limited detection. [ABSTRACT FROM AUTHOR]

A compact plasmonic coupled-resonator system, consisting of a stub resonator and baffles in the metal-insulator-metal waveguide, is numerically investigated with the finite element method. Simulations show that sharp and asymmetric response line-shapes can occur in the system. The asymmetric line-shapes in the transmission spectra depend on the relative positions of the resonant wavelengths between the single-stub resonator and the inner resonator constructed by the baffle and the stub resonator, while the other part of the transmission spectra (except the asymmetric part) maintains the spectral features of the structure constructed by the baffles. An analytic model and a relative phase analysis based on the scattering matrix theory are used to describe and explain this phenomenon. These sharp and asymmetric response line-shapes are important for improving the nano-plasmonic devices' performances. [ABSTRACT FROM AUTHOR]

In this study, we theoretically investigated the single-molecule fluorescence enhancement in a slit-groove structure. The excitation field enhancement, modified quantum efficiency, collection efficiency, and position dependence of a single-molecule spontaneous emission coupled to a plasmonic antenna are explored together. Simulation results revealed that the metal gratings play a crucial role in strengthening the local electromagnetic field enhancement in the excitation process and beaming the radiation light into a tiny angular volume in the emission process, whereas the total radiative decay rate and quantum efficiency are mainly determined by the slit cavity. Our findings provide an intuitive guideline to further optimize the plasmonic antenna for single-molecule detection and the results make a promising route to the development of photonic devices for the manipulation of single-molecule spontaneous emission. [ABSTRACT FROM AUTHOR]

Efficient all-optical molecule-plasmon modulation is experimentally demonstrated by employing a compact T-shape single slit on a metal film coated with an azopolymer film, in which the azobenzene molecules can be reoriented by a pump beam. In the T-shape single slit, the transmission spectra exhibit periodic behaviors and are quite sensitive to variations of the refractive index of the azopolymer in the groove. Under a pump beam, the azobenzene molecules are reoriented, so the SPPs in the groove feel a refractive index quite different from that of the originally isotropic azopolymer with randomly orientations. This leads to a high modulation depth of about 53 % (3.3 dB) and a phase variation of > π experimentally. [ABSTRACT FROM AUTHOR]

The effects of highly anisotropic dielectric on surface plasmon polaritons (SPPs) are investigated in several three-layer plasmonic nanostructures. Dispersion relations of SPPs in anisotropic-dielectric-metal (ADM), dielectric-anisotropic-metal (DAM), and metal-anisotropic-metal (MAM) structures are analytically derived. The numerical results in the visible indicate that, in ADM, the propagation length of a conductor-gap-dielectric mode is changed from 5.9 to 91 μm and its cutoff thickness from 83 to 7 nm with varying the optical axis, while in DAM, the influences of anisotropic dielectric are reversed on propagation length and cutoff thickness. In MAM, by tuning the optical axis, the light confinement of symmetry SPPs mode varies about 10 %. Further numerical calculations show that the above results induced by the anisotropy of dielectric can be extended to the telecommunication frequency. The improved mode properties may be used in plasmonic-based nanodevices and tunable single surface plasmon sources. [ABSTRACT FROM AUTHOR]

A ferroelectric hybrid plasmonic waveguide, made of a polycrystal lithium niobate waveguide separated from a gold film by a silicon dioxide isolation layer, is fabricated by use of laser molecular beam epitaxy growth, electron beam evaporation, and focused ion beam etching. Strong subwavelength mode confinement and excellent long-range propagation are achieved simultaneously for the hybrid plasmonic mode. An all-optical logic OR gate is also realized based on the ferroelectric hybrid plasmonic waveguide. This may provide a way for the study of all-optical logic gates and integrated photonic circuits. [ABSTRACT FROM AUTHOR]

An all-optical tunable nanoscale wavelength-division multiplexing device is realized theoretically based on a plasmonic microstructure, which is composed of a silver film coated with a monolayer colloidal crystal made of cholesteryl iodide-doped polystyrene. The physical mechanism is attributed to the variation of surface plasmon polariton modes and guided modes caused by pump-laser-induced refractive index change of cholesteryl iodide. An up to 90-nm shift in the resonant wavelength of optical channels can be reached under excitation of a 500 mJ/cm pump laser. The number of optical channels can be tuned by adjusting the structure parameters of the monolayer colloidal crystal. This may open a new way for the study of integrated photonic devices. [ABSTRACT FROM AUTHOR]

The electrocatalytic properties of nanoparticles depend on their size, shape and composition. These properties are typically probed by measuring the total electrocatalytic reaction current of a large number of nanoparticles, but this approach is time-consuming and can only measure the average catalytic activity of the nanoparticles under study. However, the identification of new catalysts requires the ability to rapidly measure the properties of nanoparticles synthesized under various conditions and, ideally, to measure the electrocatalytic activity of individual nanoparticles. Here, we show that a plasmonic-based electrochemical current-imaging technique can simultaneously image and quantify the electrocatalytic reactions of an array of 1.6 × 105 platinum nanoparticles printed on an electrode surface, which could facilitate high-throughput screening of the catalytic activities of nanoparticles. We also show that the approach can be used to image the electrocatalytic reaction current and measure the cyclic voltammograms of single nanoparticles. [ABSTRACT FROM AUTHOR]

Based on the strongly coupled-resonator effects, a high wavelength-resolution plasmonic Y-splitter, consisting of a Y-branch metal-insulator-metal waveguide with a baffle in each channel, is numerically investigated using the finite element method. Due to the coupling of different resonators (with nearly equal bandwidths) in the Y-splitter, sharp and asymmetric transmission spectra occur. This greatly increases the wavelength resolution of the Y-splitter to be Δ λ ≈ 15 nm, which is significantly narrower than the bandwidth of the single resonator (Δ λ ≈ 110 nm). An analytic model based on the scattering matrix theory is provided to describe and explain this phenomenon. [ABSTRACT FROM AUTHOR]