Optomechanical Anti-lasing with Infinite Group Delay at a Phase Singularity

Singularities that symbolize abrupt changes and exhibit extraordinary behavior are of broad interest. We experimentally study optomechanically induced singularities in a compound system consisting of a three-dimensional aluminum superconducting cavity and a metalized high-coherence silicon nitride membrane resonator. Mechanically-induced coherent perfect absorption and anti-lasing occur simultaneously under a critical optomechanical coupling strength. Meanwhile, the phase around the cavity resonance undergoes an abrupt $\pi$-phase transition, which further flips the phase slope in the frequency dependence. The observed infinite-discontinuity in the phase slope defines a singularity, at which the group velocity is dramatically changed. Around the singularity, an abrupt transition from an infinite group advance to delay is demonstrated by measuring a Gaussian-shaped waveform propagating. Our experiment may broaden the scope of realizing extremely long group delays by taking advantage of singularities

Hybridized Frequency Combs in Multimode Cavity Electromechanical System

The cavity electromechanical devices with radiation-pressure-interaction induced Kerr-like nonlinearity are promising candidates to generate microwave frequency combs. We construct a silicon-nitride-membrane-based superconducting cavity electromechanical device and study two mechanical modes mediated synergistic frequency combs. Around the threshold of intracavity field instability, we firstly show independent frequency combs with tooth spacing equalling to each mechanical mode frequency. At the overlap boundaries of these two individual mechanical mode mediated instability thresholds, we observe hybridization of frequency combs based on the cavity field mediated indirect coupling between these two mechanical modes. The spectrum lines turn to be unequally spaced but can be recognized into combinations of the coexisting frequency combs. Beyond the boundary, the comb reverts to the single-mode case, and which mechanical mode frequency will the tooth spacing depend on the mode competition. Our work demonstrates mechanical mode competition enabled switchability of frequency comb tooth spacing and can be extended to other devices with multiple nonlinearities

Supplementary document for Tailoring permittivity using metasurface: a facile way to enhance extreme-angle transmissions for both TE- and TM-polarizations - 5952809.pdf

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Supplementary document for Polarization-multiplexed full-space metasurface simultaneously with ultrawide-angle antireflection and large-angle retroreflection - 6032530.pdf

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Supplementary document for Polarization-multiplexed full-space metasurface simultaneously with ultrawide-angle antireflection and large-angle retroreflection - 6108639.pdf

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Parity-dependent unidirectional and chiral photon transfer in reversed-dissipation cavity optomechanics

Nonreciprocal elements, such as isolators and circulators, play an important role in classical and quantum information processing. Recently, strong nonreciprocal effects have been experimentally demonstrated in cavity optomechanical systems. In these approaches, the bandwidth of the nonreciprocal photon transmission is limited by the mechanical resonator linewidth, which is arguably much smaller than the linewidths of the cavity modes in most electromechanical or optomechanical devices. In this work, we demonstrate broadband nonreciprocal photon transmission in the \emph{reversed-dissipation} regime, where the mechanical mode with a large decay rate can be adiabatically eliminated while mediating anti-$\mathcal{PT}$-symmetric dissipative coupling with two kinds of phase factors. Adjusting the relative phases allows the observation of \emph{periodic} Riemann-sheet structures with distributed exceptional points (Eps). At the Eps, destructive quantum interference breaks both the $\mathcal{T}$- and $\mathcal{P}$-inversion symmetry, resulting in unidirectional and chiral photon transmissions. In the reversed-dissipation regime, the nonreciprocal bandwidth is no longer limited by the mechanical mode linewidth but is improved to the linewidth of the cavity resonance. Furthermore, we find that the direction of the unidirectional and chiral energy transfer could be reversed by changing the \emph{parity} of the Eps. Extending non-Hermitian couplings to a three-cavity model, the broken anti-$\mathcal{PT}$-symmetry allows us to observe high-order Eps, at which a parity-dependent chiral circulator is demonstrated. The driving-phase controlled periodical Riemann sheets allow observation of the parity-dependent unidirectional and chiral energy transfer and thus provide a useful cell for building up nonreciprocal array and realizing topological, e.g., isolators, circulators, or amplifiers

Selective Hydrodeoxygenation of Furfural to 2‑Methylfuran over Silica-Supported MoP Catalysts under Mild Conditions

In the catalytic conversion of biomass-derived furfural to 2-methylfuran, a concerted combination of hydrogenation and hydrogenolysis is required. Highly dispersed MoP catalysts supported on SiO2 were prepared by incipient impregnation with the aid of citric acid and subsequent temperature-programmed hydrogen reduction. The prepared MoP/SiO2 exhibited a markedly high performance in the selective hydrodeoxygenation of furfural to 2-methylfuran. A full conversion of furfural with 96.3% selectivity to 2-methylfuran under mild reaction conditions (120 °C, 1.0 MPa, WHSV: 0.3 h–1) was obtained with over 20% MoP/SiO2 in a continuous fixed bed reactor. The oxophilicity of Mo species and surface acidity of MoP might enhance the adsorption of furfural and the subsequent cleavage of the C–O bond of the intermediate furfuryl alcohol, leading to considerably high selectivity to 2-methylfuran. The complexion of Mo species with citric acid improved the dispersion of MoP particles due to the controllable decomposition of the complex in the course of preparation. Although the activity of MoP/SiO2 decreased gradually with the reaction time in 50 h, it could be restored by in situ hydrogen reduction

Phase-controlled pathway interferences and switchable fast-slow light in a cavity-magnon polariton system

We study the phase controlled transmission properties in a compound system consisting of a 3D copper cavity and an yttrium iron garnet (YIG) sphere. By tuning the relative phase of the magnon pumping and cavity probe tones, constructive and destructive interferences occur periodically, which strongly modify both the cavity field transmission spectra and the group delay of light. Moreover, the tunable amplitude ratio between pump-probe tones allows us to further improve the signal absorption or amplification, accompanied by either significantly enhanced optical advance or delay. Both the phase and amplitude-ratio can be used to realize in-situ tunable and switchable fast-slow light. The tunable phase and amplitude-ratio lead to the zero reflection of the transmitted light and an abrupt fast-slow light transition. Our results confirm that direct magnon pumping through the coupling loops provides a versatile route to achieve controllable signal transmission, storage, and communication, which can be further expanded to the quantum regime, realizing coherent-state processing or quantum-limited precise measurements

Supplementary document for Polarization-multiplexed full-space metasurface simultaneously with ultrawide-angle antireflection and large-angle retroreflection - 6113034.pdf

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Fabrication of a Monolith Reactor in a Copper Tube by Polymerization of Acetylene for Flow Catalysis

Continuous-flow processing is considered as a disruptive technology in the synthesis of active pharmaceutical ingredients and other fine chemicals. However, it remains extremely challenging to immobilize heterogeneous catalysts in the channels of microreactors in a facile and flexible manner. In the present investigation, a polymer monolith coiled copper reactor was fabricated by Cu-catalyzed polymerization of acetylene at atmospheric pressure in the temperature range of 290–370 °C. The polymerization yielded a cotton-like structure of carbonaceous fibers, which were able to assemble by themselves to form a monolith inside the copper tube. The characterization results revealed that unsaturated CC groups, which are favorable for post-surface modification, were present on the carbonaceous fibers. After air oxidation at 160 °C for 10 h, a fraction of the CC groups were converted to CO groups. By strong interaction with CO groups, Pd was immobilized in the polymer monolith by circulating an ethanol solution of palladium acetate through the copper tube. A 1000 mm-long monolith tube reactor with an inner diameter of 2 mm with a Pd loading of 1.15 wt % was fabricated and used in the continuous Suzuki–Miyaura coupling reaction. An ethanol–water (2:1 in volume) solution of iodobenzene (0.0125 M), phenylboronic acid (0.0188 M), and potassium carbonate (0.0250 M) was used as the feed, and the reaction took place at 100 °C and 1.0 MPa. The selectivity to biphenyl was kept at >99% with complete conversion of iodobenzene in a 100 h run