Mirror symmetry is among the most fundamental concepts of physics, and its spontaneous breaking at the molecular level allows chiral molecules to exist in two enantiomers that are mirror images of each other. The majority of the chiro-optical effects routinely used to detect enantiomers in mixtures, such as circular dichroism, rely on chiral sensitivity to photon circular polarization, and thus do not harness the full potential of mirror-symmetry breaking, which also involves the spatial profile of the radiation. Here we show that the parity indefiniteness of an electromagnetic field interacting with chiral matter supports mirror optical activity, a chiro-optical effect where a chiral film, when it is probed by the mirror-symmetric field of a nanoemitter, produces a near field whose spatial profile has broken mirror symmetry. The detection of near-field dissymmetry can provide an efficient chiral sensing technique. We specialize the discussion to nanofilms with infrared chirality by using a swift electron in an aloof configuration as the nanoemitter and an off-axis transparent conducting nanoparticle as the near-field probe; the spatial dissymmetry factor of the nanoparticle cathodoluminescence is 1 order of magnitude larger than the dimensionless circular dichroism, and is further enhanced to 2 orders of magnitude if an additional graphene sheet is deposited on the film interface.

We describe and operate a spin-magnetometer based on the phase modulation of cavity magnon polaritons. In this scheme a rf magnetic field is detected through the sidebands it induces on a pump, and the experimental configuration allows for a negligible pump noise and a high-frequency readout. The demonstrator setup, based on a copper cavity coupled to an yttrium iron garnet sphere hybrid system, reached a sensitivity of $2.0\mathrm{pT}/\sqrt{\mathrm{Hz}}$ at 220 MHz, evading the pump noise and matching the theoretical predictions. An optimized setup can attain a rf magnetic field sensitivity of about $8\mathrm{fT}/\sqrt{\mathrm{Hz}}$ at room temperature. An orders of magnitude improvement is expected at lower temperatures, making this instrument one of the few magnetometers accessing the subfemtotesla limit.

When a liquid film lies on a nonwettable substrate, the configuration is unstable, and the film spontaneously ruptures to form droplets. This phenomenon, known as dewetting, commonly leads to undesirable morphological changes. Nevertheless, recent works, combining spontaneous dewetting triggered by thermal annealing and topographic pattern-directed dewetting, demonstrate the possibility of harnessing dewetting with a degree of precision on par with that of advanced lithographic processes for high-performance nanophotonic applications. Since resonant behavior is highly sensitive to geometrical changes, predicting quantitatively dewetting dynamics is of high interest. Here, we develop a continuum model that predicts the evolution of a thin film on a patterned substrate, from the initial reflow to the nucleation and growth of holes. We provide an operative framework based on macroscopic measurements to model the intermolecular interactions at the origin of the dewetting process, involving length scales that span from sub-nanometer to micrometer. A comparison of experimental and simulated results shows that the model can accurately predict the final distributions, thereby offering predictive tools to tailor the optical response of dewetted nanostructures.

Characterizing the input-output photon-number distribution of an unknown optical quantum channel is a worthwhile task for many applications in quantum information processing. Ideally, this would require deterministic photon-number sources and photon-number-resolving detectors, but these technologies are still work in progress. In this work, we propose a general method to rigorously bound the input-output photon-number distribution of an unknown optical channel using standard optical devices such as coherent light sources and non-photon-number-resolving detectors and homodyne detectors. To demonstrate the broad utility of our method, we consider the security analysis of practical quantum key distribution systems based on calibrated single-photon detectors and an experimental proposal to implement time-correlated single-photon counting technology using homodyne detectors instead of single-photon detectors.

A natural choice for quantum communication is to use the relative phase between two paths of a single photon for information encoding. This method was nevertheless quickly identified as impractical over long distances, and thus a modification based on single-photon time bins has become widely adopted. It, however, introduces a fundamental loss, which increases with the dimension and limits its application over long distances. Here solve this long-standing hurdle by using a few-mode-fiber space-division-multiplexing platform working with orbital-angular-momentum modes. In our scheme, we maintain the practicability provided by the time-bin scheme, while the quantum states are transmitted through a few-mode fiber in a configuration that does not introduce postselection losses. We experimentally demonstrate our proposal by successfully transmitting phase-encoded single-photon states for quantum cryptography over 500 m of few-mode fiber, showing the feasibility of our scheme.

We demonstrate that a triangular cavity can operate as an efficient discriminator for Hermite-Gaussian optical modes. The process is applied to distinct fields produced by a spatial light modulator, decomposing the generated paraxial field onto a basis of modes defined by the resonant optical cavity. We also present a proposal for the realization of a mode sorter based on a sequence of these cavities, without the need for optical isolation. We discuss its possible applications in sensitive measurements and distribution of information in optical systems. The high purity of the process should enable its use at the level of quantum information sharing.

Erbium-implanted silicon is promising for both photonic and quantum-technology platforms, since it possesses both telecommunications and integrated-circuit processing compatibility. However, several different $\mathrm{Er}$ centers are generated during the implantation and annealing process, the presence of which could hinder the development of these applications. When $\mathrm{Si}$ is coimplanted with ${10}^{17}{\mathrm{cm}}^{-3}$ $\mathrm{Er}$ and ${10}^{20}{\mathrm{cm}}^{-3}$ $\mathrm{O}$ ions, and the appropriate annealing process is used, one of these centers, which is present at higher $\mathrm{Er}$ concentrations, can be eliminated. Characterization of samples with $\mathrm{Er}$ concentrations of <${10}^{17}{\mathrm{cm}}^{-3}$ is limited by the sensitivity of standard electron paramagnetic resonance (EPR) instruments. The collective coupling strength between a superconducting (SC) $\mathrm{Nb}\mathrm{N}$ lumped-element resonator and a ${10}^{17}{\mathrm{cm}}^{-3}$ $\mathrm{Er}$-implanted $\mathrm{Si}$ sample at 20 mK is measured to be about 1 MHz, which provides a basis for the characterization of low-concentration $\mathrm{Er}$-implanted $\mathrm{Si}$ and for future networks of hybrid quantum systems that exchange quantum information over the telecommunication network. Of six known $\mathrm{Er}$-related EPR centers, only one trigonal center couples to the SC resonator.

Expanding bound states in the continuum (BIC) beyond photonic crystal systems may enable broader applications benefiting from the unique properties of BIC states. We use photonic integrated circuit to realize a Fabry-Pérot BIC on a silicon chip. The devices consist of cascaded ring resonators with tunable resonance frequencies and phase delays. As a result, the BIC state is dynamically tuned with electrical I/O. We analyze the mechanism of the formation of BIC states in this waveguide system and point out the fundamental differences between the BIC states and electromagnetically induced transparency states in integrated photonics. The high transmission protected by the BIC state enables versatile optical filters, which are capable of independent control over switching, peak position, and quality factor. We also demonstrate the scalability of this platform. This integrated silicon photonic platform brings opportunities for practical BIC applications.

The inherent narrow bandwidth and wavelength-transparent nature of the stimulated Brillouin scattering (SBS) process make it a potential candidate for high-resolution wideband microwave photonic notch filters (MPNFs). The simplest way to realize a SBS-based MPNF is to use the narrowband Brillouin loss resonance with single-sideband modulation, where the modulation sideband is at the anti-Stokes frequency. However, using Brillouin loss with single-sideband modulation is highly inefficient because a large notch extinction requires large Brillouin loss, and thus, a large pump power. Here, we exploit an analogue of electromagnetically induced absorption (EIA) in the microwave domain to enhance MPNF rejection, at a fixed Brillouin pump power, by more than 6 orders of magnitude. We use this analogue of EIA to realize a MPNF with $>75$-dB rejection up to 40 GHz, using a Brillouin loss of about 15 dB. We harness a coherent Brillouin interaction between the orthogonally polarized components of a probe, which is comprised of a laser carrier and a single-modulation sideband. Stimulated Brillouin scattering and other components used in our demonstration have recently been demonstrated on integrated platforms. The proposed scheme, therefore, has the potential for realizing efficient integrated microwave photonic notch filters with ultrahigh rejection.

Masking of quantum information is a way of hiding information in correlations such that no information is accessible to any local observer. Although the set of all quantum states as a whole cannot be masked into bipartite correlations according to the no-masking theorem, the set of real states is maskable and is a maximal maskable set. In this work, we experimentally realize a masking protocol of the real ququart by virtue of a photonic quantum walk. Our experiment clearly demonstrates that quantum information of the real ququart can be completely hidden in bipartite correlations of two-qubit hybrid entangled states, which are encoded in two different degrees of freedom of a single photon. The hidden information is not accessible from each qubit alone, but can be faithfully retrieved with a fidelity of about 99% from correlation measurements. By contrast, any superset of the set of real density matrices cannot be masked.

We experimentally study the free-space electromagnetic field emitted from a multimode rectangular waveguide equipped with a diagonal-horn antenna. Using the frequency range of 215–580 GHz, a photomixer is used to launch a free-space circularly polarized electromagnetic field, exciting multiple modes at the input of the rectangular waveguide via an input diagonal-horn antenna. A second photomixer is used, together with a silicon mirror Fresnel scatterer, to act as a polarization-sensitive coherent detector to characterize the emitted field. We find that the radiated field, excited by the fundamental waveguide mode, is characterized by a linear polarization. In addition, we find that the polarization of the radiated field rotates by ${45}^{\circ }$ if selectively exciting higher-order modes in the waveguide. Despite the higher-order modes, the radiated field appears to maintain a predominant Gaussian beam character, since an unidirectional coupling to a detector was possible, whereas the unidirectionality is independent of the frequency. We discuss a possible application of this finding.

We propose all-optical neural networks characterized by very high energy efficiency and performance density of inference. We argue that the use of microcavity exciton polaritons allows one to take advantage of the properties of both photons and electrons in a seamless manner. This results in strong optical nonlinearity without the use of optoelectronic conversion. We propose a design of a realistic neural network and estimate energy cost to be at the level of attojoules per bit, also when including the optoelectronic conversion at the input and output of the network, several orders of magnitude below state-of-the-art hardware implementations. We propose two kinds of nonlinear binarized nodes based either on optical phase shifts and interferometry or on polariton spin rotations.

In this paper, we show that the Gouy phase shift plays a key role in the far-field waveform evolution of the reflected harmonic radiations from plasma surfaces driven by a relativistic Gaussian laser. With a proper adjustment of laser focal position away from the plasma surface, the inherent separations between the peaks of different harmonic carrier waves as well as the fundamental wave due to different wavelengths can be cleared away when they propagate from near to far field, since they experience the same Gouy phase shift of $\pi /2$. Using this method, intense attosecond pulses can be obtained in the far field with no need of any spectral filters. Three-dimensional particle-in-cell simulations show that far-field attosecond pulses with intensity of $4\times {10}^{15}\mathrm{W}/{\mathrm{cm}}^2$ ($2.56\times {10}^{17}\mathrm{W/sr}$; 65 times increase) and duration of $76\mathrm{as}$ (50% decrease) can be obtained by lasers at intensities of ${10}^{21}\mathrm{W}/{\mathrm{cm}}^2$. Such brilliant pulses with fully reserved spectra significantly benefit applications in attosecond science.

Metamaterials with near-zero permittivity exhibit extraordinary total transmission of waves within the length-independent conduit. However, such an ε-near-zero (ENZ) transmission mode demonstrates an intrinsic narrow-band property using low-loss metastructures, e.g., extremely narrow waveguide transition at the cutoff frequency. As the counterpart to the ENZ mode, the Fabry-Perot (FP) mode also has near-zero reflection but depends on the channel length. For application considerations, the phenomenon of superpositioning ENZ and FP modes is analyzed theoretically and numerically to enhance the bandwidth of near-zero reflection within extreme mismatching waveguide transitions. The achieved bandwidth of the ENZ and FP mode cooperation is larger than the sum of two single modes, exhibiting feasible applications in the integrated waveguide structures, such as integrated transmission lines, circuits, and antennas. As an application example of this physical property, a waveguide crossover is proposed and experimentally verified to achieve wideband dual-narrow-channel total transmission within only one dielectric layer with an extremely low profile.

Recently discovered photonic higher-order topological insulators enable unprecedented flexibility in the robust localization of light in structures of different dimensionality. While the potential of the two-dimensional systems is currently under active investigation, only a few studies explore the physics of the three-dimensional higher-order topological insulators. Here we propose a three-dimensional structure with cubic symmetry exhibiting vanishing bulk polarization but nonzero corner charge and hosting a zero-dimensional corner state mediated by the long-range interactions. We trace the evolution of the corner state with the next-nearest-neighbor coupling strength and prove the topological origin of the corner mode, calculating the associated topological invariants. Our results thus reveal the potential of long-range couplings for the formation of three-dimensional higher-order topological phases.

A simple way of implementing a scalable laser-driven nanophotonic electron accelerator on a chip is presented. The design requires only a single incident laser pulse and can be fabricated straightforwardly on commercial silicon-on-insulator wafers. We investigate the low-energy regime of tabletop electron microscopes where the silicon structures safely allow peak gradients of about 150 MeV/m. By means of a three-dimensional alternating-phase-focusing scheme, we obtain about half of the peak gradient as the average gradient with six-dimensional confinement and full-length scalability. The structures are completely designed within the device layer of the wafer and can be arranged in stages. We choose the stages as energy doublers and outline how errors in the handshake between the stages can be corrected by on-chip steerers. Since the electron pulse length in the attosecond realm is preserved, our chip is the ideal energy booster for ultrafast-electron-diffraction machines, opening the megaelectronvolt scale on tabletop setups.