We experimentally demonstrate a transverse magnetic (TM) mode laser in a photonic crystal (PhC) slab structure at room temperature. This study proposes a PhC nanobeam (NB) cavity to support a high-quality-factor ($Q$-factor) TM mode. For a large and complete photonic band gap, the PhC NB structures consist of large air holes in a thick dielectric slab. The PhC NB cavity is optimized numerically for a high-$Q$-factor TM mode of over 1 000 000 by reducing the radii of the air holes quadratically from the center to the edge of the PhC NB. A single-TM-mode lasing action is observed in an In-Ga-As-P quantum well (QW)-embedded optimized PhC NB cavity structure at room temperature via optical pulse pumping, where the QW layer is lightly etched. We believe that the TM mode lasers in PhC NB cavities with a lightly etched QW can be good candidates for a surface plasmon excitation source or a highly sensitive optical sensor.

Exciton polaritons in metallic nanocavities and transition-metal dichalcogenide monolayers has led to striking discoveries, ranging from Bose-Einstein condensation to slowing light. Although plasmonic nanocavities offer small mode volumes, the intrinsic losses of plasmonic nanocavities remain an open challenge in exciton-polariton devices. Consequently, dielectric nanocavities are used as an alternative candidate due to their low intrinsic losses. However, large mode volumes are a central bottleneck in dielectric nanocavities. Here, we theoretically propose to use a hybrid dielectric-metallic nanocavity to enhance light-matter interactions between the excitons of the ${\mathrm{WS}}_2$ monolayer and the hybrid nanocavity. Such a hybrid nanoresonator inherits the advantages of both dielectric and metallic nanocavities, including ultrasmall mode volume, ultralow losses, and reasonably-high-Q factor. It is demonstrated that the thickness and material of the central gap film together with the thickness of the metallic substrate play vital roles in governing the coupling strength between 1L-${\mathrm{WS}}_2$ excitons and the cavity. After optimizing the geometry and material parameters, the Rabi splitting is increased to 113 meV, almost twice that in dielectric metasystems. The significant improvement can be attributed to the greatly enhanced near field and the ultrasmall mode volume. Furthermore, we show that Rabi splitting can be further boosted to 151 meV by increasing the number of layers of ${\mathrm{WS}}_2$ and h-$\mathrm{BN}$ film in the nanocavity.

Quantum entanglement has become an essential resource in quantum information processing. Existing works employ entangled quantum states to perform various tasks, while little attention is paid to the control of the resource. In this work, we propose a simple protocol to upgrade an entanglement source with access control through phase randomization at the optical pump. The enhanced source can effectively control all users in utilizing the entanglement resource to implement quantum cryptography. In addition, we show this control can act as a practical countermeasure against memory attack on device-independent quantum key distribution at a negligible cost. To demonstrate the feasibility of our protocol, we implement an experimental setup using just off-the-shelf components and characterize its performance accordingly.

${\mathrm{Cr}}^{2+}$ - and ${\mathrm{Fe}}^{2+}$ -doped $\mathrm{Zn}\mathrm{Se}$ crystals are laser materials with phonon-broadened absorption and emission spectra, which provide broadband laser gain in the 2- to 5-$\text{μ}\mathrm{m}$ wavelength range. While ${\mathrm{Cr}}^{2+}\text{:ZnSe}$ can be directly pumped with high-power Er, Ho, or Tm lasers, no such possibility exists for ${\mathrm{Fe}}^{2+}\text{:ZnSe}$. To this end, electronic excitation transfer between ${\mathrm{Cr}}^{2+}$ and ${\mathrm{Fe}}^{2+}$ ions in codoped ZnSe is investigated as an alternative excitation process in photo luminescence (PL) experiments with sub-10-ns temporal resolution. For a wide range of ion concentrations, we observe nonexponential decays of ${\mathrm{Cr}}^{2+}$ PL on a microsecond time scale, a 60-ns rise time of ${\mathrm{Fe}}^{2+}$ PL at high doping densities, and a prolonged decay of ${\mathrm{Fe}}^{2+}$ PL due to the temporal characteristics of excitation transfer over a range of interionic distances. Using a multirate equation model, the transfer process is analyzed on length scales up to 30 nm and compared to the established continuum model approach. The analysis reveals an unexpectedly efficient excitation transfer from ${\mathrm{Cr}}^{2+}$ to ${\mathrm{Fe}}^{2+}$ ions with an enhancement of the excitation transfer rates by up to a factor of 5 in comparison to resonant dipole-dipole coupling. The enhancement is assigned to (multi)phonon-assisted excitation transfer, in analogy to the phonon-mediated efficient radiationless decay of the excited ${\mathrm{Fe}}^{2+}$ state. As nonradiative losses and excitation transfer show different temperature scaling, a cryogenic temperature regime is found that promises overall efficiencies above 50%, making ${\mathrm{Fe}}^{2+}:{\mathrm{Cr}}^{2+}\text{:ZnSe}$ a much more viable alternative to parametric conversion schemes in the midinfrared range.

Heralded single-photon sources are a fundamental building block for optical quantum technologies. These sources need to be unfiltered and integrated to have good scalability and avoid unnecessary losses. To attain this goal, it is necessary to control the effective nonlinearity seen by the fields as they mix and propagate in a waveguide source. In this paper, we introduce a method to design nonlinear waveguides with arbitrarily shaped effective nonlinearity profiles. The method takes advantage of the fact that the second-order nonlinear response is a tensor quantity and thus the local effective nonlinearity of a material depends on the propagation direction of the fields participating in the interaction. Thus, by locally changing the propagation direction of the fields we can modulate the wave-mixing process. Our method allows for the waveguide fabrication process to be significantly simplified. The material structure of the waveguide is made by a single crystal, no longer needing oriented patterning or periodic poling. We use our method to design waveguides with a nonlinearity profile that is Gaussian in the propagation length, allowing the generation of perfectly pure heralded single photons.

We propose a scheme for optical entanglement distribution in quantum networks based on a quasideterministic entangled photon-pair source. By combining heralded photonic Bell-pair generation with spectral mode conversion to interface with quantum memories, the scheme eliminates switching losses due to multiplexing in the source. We analyze this “zero-added-loss multiplexing” (ZALM) Bell-pair source for the particularly challenging problem of long-baseline entanglement distribution via satellites and ground-based memories, where it unlocks additional advantages: (i) the substantially higher channel efficiency $\eta$ of downlinks versus uplinks with realistic adaptive optics, and (ii) photon loss occurring before interaction with the quantum memory—i.e., Alice and Bob receiving rather than transmitting—improve entanglement generation rate scaling by $\mathcal{O}(\sqrt{\eta })$. Based on numerical analyses, we estimate our protocol to achieve $>10\text{ebit/s}$ at memory multiplexing of ${10}^2$ spin qubits for ground distance $>{10}^2\text{km}$, with the spin-spin Bell-state fidelity exceeding 99%. Our architecture presents a blueprint for realizing global-scale quantum networks in the near term.

An optical lattice is a platform that is used in studies in multiple branches of physics, e.g., ultracold atoms and microfluidic sorting. Unlike traditional complex optical systems, surface plasmon polaritons enable the generation of optical lattices on a chip. Here, we propose an on-chip scheme to transform five topological optical lattices using tunable polarization and a phase vortex. Using the dipolar approximation and numerical simulations, we demonstrate that the spin density force is the main force for sorting chiral particles in the out-of-plane direction when their radius is more than 100 nm. A microflow system is proposed to trap particles with electric optical lattices and sort chiral particles with spin optical lattices. Our findings offer possible routes toward realization of on-chip optical lattices and enable their potential application in both biology and chemistry, e.g., in simultaneous trapping or excitation of multiple objects and identification and sorting of chiral objects.

Programmable unitary photonic devices are emerging as promising tools to implement unitary transformation for quantum information processing, machine learning, and optical communication. These devices typically use a rectangular mesh of Mach-Zehnder interferometers, which has a clear mathematical structure and can be configured deterministically. However, this mesh architecture is sensitive to fabrication errors, and the correction techniques are still under investigation. In contrast, the multiplane light-conversion (MPLC) architecture is more robust against fabrication errors, but a deterministic method for configuring the converter has not yet been developed due to its complex mathematical structure. In this work, we propose a fast iterative configuration method for MPLC, following the mathematical review of the matrix distance and proposal of an alternative norm. We show through numerical simulations that adding a few redundant layers significantly improves the convergence of the MPLC architecture, making it a practical and attractive option. We also consider the effects of finite resolution and cross-talk in phase shifters in our simulations. In addition, we propose a phase-insensitive distance suited for applications using only intensity detections. Our method demonstrates orders of magnitude better accuracy and a 20-fold speedup compared to previous approaches.

We study permeability ($\mu$) variation of a lithographically prepared magnetic meta-atom consisting of $\mathrm{Ta}$/Py/$\mathrm{Pt}$ trilayers by means of spin-torque ferromagnetic resonance (ST FMR). With an injection of a direct current up to $\pm 20\mathrm{mA}$ together with an alternating current in GHz frequencies, the meta-atom under external magnetic fields shows significant changes in position and width of ST FMR signals due to a massive spin-current injection. This leads to the spin-current-driven $\mu$ variation, which is verified by analytical calculation based upon the experimentally obtained resonance field and Gilbert-damping parameter. The present study paves a way to time-varying spintronic metamaterials with a high modulation frequency for realizing microwave sources toward the post-fifth-generation mobile-communication system.

Restricted by pulse dispersion, dephasing, and bunch deflection, it has been a challenging task to realize high-gain particle acceleration and bunch focusing by using an ultrashort-pulse laser to drive an integrable acceleration structure, which is necessary to develop an on-chip particle accelerator for practical applications. Here we propose a laser-driven traveling-wave linac (linear accelerator), which uses the cascade reflection and refraction of an ultrashort laser pulse on a microscale dielectric structure to achieve long-range laser-particle interaction, avoiding waveguide dispersion, and enhancing sustainable acceleration gradient. It is scalable and extensible, and can realize full-course particle acceleration by using a single laser source via the inverse Cherenkov effect. With this accelerator scheme, we further propose a dynamic synchronization and focusing method, which not only counteracts dephasing but also restrains the bunch spread and deflection caused by space-charge and emittance effects, realizing stable bunch transport and acceleration in a tiny-size bunch channel without resorting to the need for external focusing equipment. This accelerator scheme paves the way toward a high-efficiency laser-driven all-dielectric on-chip particle accelerator for practical applications.

The rotational Doppler effect (RDE) is of fundamental importance in the detection of rotating systems, ranging from molecules to macroscopic bodies. Metasurfaces, which are potential substitutes for traditional optical devices, have been reported to induce a RDE. However, the mechanism of the interaction between an electromagnetic wave and a spinning artificial meta-atom is not yet fully understood. Here, we report a multiple RDE based on a time-varying generalized Pancharatnam-Berry phase, obtained from a single spinning meta-atom placed in a rectangular waveguide. Twofold and sixfold rotational Doppler shifts with respect to the rotational velocity are obtained from meta-atoms with C2 and C3 rotational symmetry, respectively. In contrast to full-size devices, a single meta-atom has minimal rotational inertia and size, enabling its application in integrated systems. This work represents the interaction of an electromagnetic wave with a single spinning meta-atom, which may have potential applications in rotation-detection systems, frequency-gradient metasurfaces, and frequency modulators.

Multiplexing techniques combine multiple signals into one channel, in order to increase the channel capacity and speed. Here we propose a correlation-based imaging method to efficiently measure the quantum states of orbital-angular-momentum (OAM)-multiplexed Gaussian light. The covariance matrices for all OAM components of the multiplexed Gaussian light can be efficiently reconstructed by one homodyne measurement on each beam. We also show that the proposed scheme can be simplified and implemented with only two charge coupled device detectors.

In recent years, twisted bilayer graphene has become a hot topic and inspired the upsurge of research on the photonic moiré lattice. Here, we design a photonic moiré superlattice with two synthetic twist angles and construct a synthetic moiré sphere based on these two angles. Thus, we have more degrees of freedom to design the band structure flexibly. A type of transition photonic band (TPB) is obtained in such a moiré superlattice. We investigate the influence of two twist angles on TPBs and find a series of magic angle pairs with optimal band compression of the TPB. Interesting optical properties of TPBs are experimentally demonstrated, including pulse delay, nonlinear optical enhancement, and pulse-width compression. Our work introduces an alternative path to explore multitwist-angle moiré superlattices and reveals that the designed photonic moiré superlattice based on moiré spheres has broad application prospects, including optical signal processing, nonlinear optic processes, and other light-matter interactions.

Low-electron-density Drude (LEDD) materials such as indium tin oxide (ITO) are receiving considerable attention for their combination of CMOS compatibility, unique epsilon-near-zero (ENZ) behavior, and giant ultrafast nonlinear thermo-optic response. However, current understanding of the electronic and optical response of LEDD materials is limited due to the simplistic modeling that extends only the known models of noble metals without considering the interplay among the lower electron density, relatively high Debye energy, and the nonparabolic band structure. We bridge this knowledge gap and provide a complete understanding of the nonlinear electronic-thermal-optical response of LEDD materials. In particular, we rely on state-of-the-art electron dynamics modeling, as well as a time-dependent permittivity model for LEDD materials under optical pumping within the adiabatic approximation. We find the electron temperature may reach values much higher than realized before, even exceeding the Fermi temperature, in which case the effective chemical potential dramatically decreases and even becomes negative, thus, transient giving the material some characteristics of a semiconductor. We further show that the nonlinear optical response of LEDD materials originating from the changes to the real part of the permittivity is associated with changes of the population. This resolves the argument about the rise time of the permittivity, showing that it is instantaneous. In this vein, we show that referring to the LEDD permittivity as having a Kerr or “saturable” nonlinearity is unsuitable since its permittivity dynamics is absorptive rather than nonresonant and does not originate from population inversion. Finally, we analyze the probe-pulse dynamics and unlike previous work, we obtain a quantitative agreement with the results of recent experiments.

Erbium-doped solids are prime candidates for quantum memories in optical quantum networks given their telecom-compatible photon emission. An electron spin of erbium with millisecond coherence time is desirable for generating remote entanglement between adjacent quantum network nodes. Here we report GHz-range electron-spin transitions of ${}^{167}{\mathrm{Er}}^{3+}$ in a yttrium oxide (${\mathrm{Y}}_2{\mathrm{O}}_3$) matrix with coherence times that are consistently longer than a millisecond. By polarizing paramagnetic impurity spins we achieve a spin $T_2$ up to 1.46 ms, and up to 7.1 ms after dynamical decoupling. These coherence lifetimes are among the longest found for erbium in crystalline matrices despite the presence of host nuclear spins. We further enhance the coherence time beyond conventional dynamical decoupling, using customized sequences to simultaneously mitigate spectral diffusion and dipolar interactions. Our study not only establishes ${}^{167}{\mathrm{Er}}^{3+}$: ${\mathrm{Y}}_2{\mathrm{O}}_3$ as a significant quantum memory platform but also provides a guideline for engineering long-lived erbium spins in a variety of host materials for quantum technologies.

A fiber-optic molecular dispersion spectrometer using code-division multiplexing to make simultaneous phase measurements of a hydrogen cyanide (${\mathrm{H}}^{13}{\mathrm{C}}^{14}\mathrm{N}$) $2{\nu }_3$-band P10 rovibrational transition at multiple optical frequencies is demonstrated. A second-derivative anomalous dispersion response is digitally synthesized from sets of these concurrent measurements. The synthesized measurement demonstrates 3 orders of magnitude noise suppression relative to individual measurements, has intrinsic wavelength tuning linearization, and a spectroscopic detection limit of $146\mathrm{ppb}\mathrm{m}/\sqrt{\mathrm{Hz}}$.

Although the field of two-dimensional (2D) materials has democratized materials science by making high-quality samples accessible cheaply, due to the atomically thin nature of these systems, an integration with nanostructures is almost always required to obtain a significant optical response. Traditionally, these nanostructures are fabricated via electron beam lithography or focused ion beam milling, which are expensive, and large-area fabrication can be further time-consuming. In order to overcome this problem, we report the integration of 2D semiconductors on a cost-effective and large-area fabricated nanocone platform. We show that the plasmon modes of our nanocone structures lead to photoluminescence enhancement of monolayer ${\text{WSe}}_2$ by about eight to ten times compared with the nonplasmonic case, consistent with finite-difference time-domain simulations. Excitation power-dependent measurements reveal that our nanocone platform enables a versatile route to engineering the relative exciton trion contributions to the emission.