Dispersion-boosting wideband electromagnetic transparency under extreme angles for TE-polarized waves.

Half-wave wall is the most common method of achieving electromagnetic (EM) transparency. Transmission windows can be formed when reflected waves are out of phase. Due to the interference mechanism, these windows are dependent on the frequency and incident angle of EM waves, leading to limited bandwidth, especially under extreme angles. In this letter, we propose to extend the bandwidth of the transmission window under extreme angles by utilizing dispersion. To this end, long metallic wires are embedded into the half-wave wall matrix, without increasing the physical thickness. Due to the plasma-like behavior of metallic wires under TE-polarization, the effective permittivity of the half-wave wall, rather than keeping constant, increases with frequency nonlinearly. Such a dispersion will boost wideband transparency in two aspects. On one hand, an additional transmission window will be generated where the effective permittivity equals that of the air; on the other hand, the 1st- and 2nd-order half-wave windows will be made quite closer. By tailoring the dispersion, the three windows can be merged to enable wideband transparency under extreme incident angles. A proof-of-principle prototype was designed, fabricated, and measured to verify this strategy. Both simulated and measured results show that the prototype can operate in the whole Ku-band under incident angle [70°, 85°] for TE-polarized waves. This work provides an effective method of achieving wideband EM transparency under extreme angles and may find applications in radar, communications, and others.

Probing the symmetry breaking of a light-matter system by an ancillary qubit.

Hybrid quantum systems in the ultrastrong, and even more in the deep-strong, coupling regimes can exhibit exotic physical phenomena and promise new applications in quantum technologies. In these nonperturbative regimes, a qubit-resonator system has an entangled quantum vacuum with a nonzero average photon number in the resonator, where the photons are virtual and cannot be directly detected. The vacuum field, however, is able to induce the symmetry breaking of a dispersively coupled probe qubit. We experimentally observe the parity symmetry breaking of an ancillary Xmon artificial atom induced by the field of a lumped-element superconducting resonator deep-strongly coupled with a flux qubit. This result opens a way to experimentally explore the novel quantum-vacuum effects emerging in the deep-strong coupling regime.

Polarization-multiplexed full-space metasurface simultaneously merging with an ultrawide-angle antireflection and a large-angle retroreflection.

Multifunctional electromagnetic (EM) metasurfaces are capable of manipulating electromagnetic waves with kaleidoscopic functions flexibly, which will significantly enhance integration and applications of electronic systems. However, most known design schemes only realize the reflection or transmission functions under a specific angle range, which wastes the other half EM space and restricts wider applications of multifunctional metadevices. Herein, an encouraging strategy of broadband and wide-angle EM wavefronts generator is proposed to produce two independent functions, i.e., antireflections for transverse electric (TE) waves and retroreflection for transverse magnetic (TM) waves, which utilizes band-stop and bandpass responses of the metasurface, respectively. As a feasibility verification of this methodology, a three-layer cascaded metasurface, composed of anisotropic crossbar structures patterned on the two surfaces of a dielectric substrate with sandwiched orthogonal metal-gratings, is designed, fabricated, and measured. Both the simulated and experimental results are in good accordance with theoretical analyses. This full-space metasurface opens up a new route to multifunctional metasurfaces and will further promote engineering applications of metasurfaces.

Large-angle broadband transmission of electromagnetic waves through dielectric plates by embedding meta-atoms.

In many practical applications, dielectric electromagnetic (EM) windows are usually under large-angle incidence of EM waves rather than normal incidence. To guarantee normal operation of devices inside, high transmission must be maintained under large incident angles, especially for TE-polarized waves. In this work, we propose a method of achieving broadband transmission of TE-polarized waves under large incident angles by embedding meta-atoms within dielectric plates. To this end, long metallic wires and S-shaped structures are embedded in the original dielectric plate, the former of which will dilute the effective permittivity due to plasma oscillation and the latter will increase the effective permeability due to induced strong current loops under large incident angles. In this way, two consecutive transmission peaks can be generated, forming a broad transmission band under large incident angles. A proof-of-principle Ku-band prototype was designed, fabricated, and measured to verify this strategy. Both simulated and measured results show that the prototype can operate in the whole Ku-band under incident angle [60°, 85°] for TE-polarized waves, with significantly enhanced transmission. This work provides an effective method of enhancing large-angle transmission of EM waves and may find applications in radar, communications and others.

Extremely angle-stable transparent window for TE-polarized waves empowered by anisotropic metasurfaces.

Impedance mismatch generally exists upon interfaces between different media. This is especially true for TE-polarized waves with large incident angles since there is no Brewster effect. As a result, high-efficiency transmission can only be guaranteed within limited incident angle range. It is desirable that transparent windows possess robust angle-stability. In this work, we propose a strategy of realizing transparent windows with extreme angle-stability using anisotropic metasurfaces. Different from traditional isotropic materials, anisotropic metasurfaces require specific three-dimensional permittivity and permeability parameters. Theoretical formulas are derived to realize a highly efficient transmission response without angular dispersion. To validate our design concept, a two-layer cascaded electromagnetic anti-reflector is designed, and it exhibits a characteristic impedance matching for nearly all incidence angles under TE-polarization illumination. As a proof-of-concept, a prototype of extremely angle-stable transparent window is fabricated and measured. Compared with the pure dielectric plate, the reflection coefficients are on average reduced by 40% at 13.5 GHz for TE-polarized waves from 0° to 80°. Therefore, we think, anisotropic cascaded electromagnetic transparent windows are capable of tailoring the electromagnetic parameter tensors as desired, and provide more adjustable degrees of freedom for manipulating electromagnetic wavefronts, which might open up a promising way for electromagnetic antireflection and find applications in radomes, IR windows and others.

Tailoring permittivity using metasurface: a facile way of enhancing extreme-angle transmissions for both TE- and TM-polarizations.

The transmission of electromagnetic (EM) waves through a dielectric plate will be decreased significantly when the incident angle becomes extremely large, regardless of transverse electric (TE)- or transverse magnetic (TM)- polarization. In this regard, we propose a facile way of tailoring the permittivity of the dielectric material using metasurface to enhance the transmissions of both TE- and TM-polarized waves under extremely large incidence angles. Due to parallel or antiparallel electric fields induced by the metasurface, the net electric susceptibility is altered, and hence the effective permittivity can be tailored to improve the impedance matching on the two air-dielectric interfaces, which enhances the wave transmissions significantly under extreme incident angles. As an example, we apply this method to a typical ceramic-matrix composite (CMC) plate. By incorporating orthogonal meta-gratings into the CMC plate, its effective permittivity is reduced for the TE-polarized waves but increased for the TM-polarized waves under the extreme incidence angle, which can reduce the impedance for the TE-polarization and increase the Brewster angle for the TM-polarization. Therefore, the impedance matchings for both TE- and TM-polarizations are improved simultaneously and dual-polarized transmission enhancements are achieved under the extreme angles. Here, the transmission responses have been numerically and investigated using the finite-difference-time-domain (FDTD) method. A proof-of-principle prototype is designed, fabricated, and measured to verify this method. Both numerical simulations and measurement results show that the prototype can operate under extremely large incidence angles θi∈[75°,85°] with significant transmission enhancement for both TE- and TM-polarizations compared to the pure dielectric plate. This work provides a facile way to enhance the transmissions under extreme angles and can be readily extended to terahertz and optical frequencies.

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 synergistic frequency combs. Around the threshold of intracavity field instability, we first show independent frequency combs with tooth spacing equal 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 out to be unequally spaced, but can be recognized in 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 be depends 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.

Transmission enhancement of a half-wave wall under extreme angles by synergy of double lorentz resonances.

The a half-wave wall is usually adopted as the transparent window for electromagnetic (EM) waves ranging from microwave to optical regimes. Due to the interference nature, the bandwidth of the half-wave wall is usually quite narrow, especially under extreme angles for TE-polarized waves. It is usually contradictory to expand the bandwidth and to keep high transmission. To overcome this contradiction, we propose to extend the transmission bandwidth of half-wave walls under extreme angles by introducing Lorentz-type resonances using metasurfaces. The impedance of the half-wave wall is firstly analyzed. To improve the impedance matching, the impedance below and above the half-wave frequency should be increased. To this end, metallic wires and I-shaped structures are incorporated into the half-wave wall as the mid-layer. Due to the Lorentz-type resonance of the metallic wire, effective permittivity below the half-wave frequency can be reduced while that above the half-wave frequency can be increased due to Lorentz-type resonance of the I-shaped structures, both under large incident angles. In this way, the impedance matching, and thus the transmission, can be improved within an extended band. A proof-of-principle prototype was designed, fabricated, and measured to verify this strategy. Both simulated and measured results show that the prototype can operate in 14.0-19.0GHZ under incident angle [70°, 85°] with significant transmission enhancement for TE-polarized waves. This work provides an effective method of enhancing the transmission of EM waves and may find applications in radomes, IR windows, and others.

Near-infrared plasmonic sensing and digital metasurface via double Fano resonances.

Plasmonic sensing that enables the detection of minute events, when the incident light field interacts with the nanostructure interface, has been widely applied to optical and biological detection. Implementation of the controllable plasmonic double Fano resonances (DFRs) offers a flexible and efficient way for plasmonic sensing. However, plasmonic sensing and digital metasurface induced by tailorable plasmonic DFRs require further study. In this work, we numerically and theoretically investigate the near-infrared plasmonic DFRs for plasmonic sensing and digital metasurface in a hybrid metasurface with concentric ϕ-shaped-hole and circular-ring-aperture unit cells. We show that a plasmonic Fano resonance, resulting from the interaction between a narrow and a wide effective dipolar modes, can be realized in the ϕ-shaped hybrid metasurface. In particular, we demonstrate that the tailoring plasmonic DFRs with distinct mechanisms of actions can be accomplished in three different ϕ-shaped hybrid metasurfaces. Moreover, the resonance mode-broadening and mode-shifting plasmonic sensing can be fulfilled by modulating the polarization orientation and the related geometric parameters of the unit cells in the near-infrared waveband, respectively. In addition, the plasmonic switch with a high ON/OFF ratio can not only be achieved but also be exploited to establish a single-bit digital metasurface, even empower to implement two- and three-bit digital metasurface characterized by the plasmonic DFRs in the telecom L-band. Our results offer a new perspective toward realizing polarization-sensitive optical sensing, passive optical switches, and programmable metasurface devices, which also broaden the landscape of subwavelength nanostructures for biosensors and optical communications.

Optomechanical Anti-Lasing with Infinite Group Delay at a Phase Singularity.

Singularities which symbolize abrupt changes and exhibit extraordinary behavior are of a 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 π-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.

Effect of Deep-Defects Excitation on Mechanical Energy Dissipation of Single-Crystal Diamond.

The ultrawide band gap of diamond distinguishes it from other semiconductors, in that all known defects have deep energy levels that are less active at room temperature. Here, we present the effect of deep defects on the mechanical energy dissipation of single-crystal diamond experimentally and theoretically up to 973 K. Energy dissipation is found to increase with temperature and exhibits local maxima due to the interaction between phonons and deep defects activated at specific temperatures. A two-level model with deep energies is proposed to explain well the energy dissipation at elevated temperatures. It is evident that the removal of boron impurities can substantially increase the quality factor of room-temperature diamond mechanical resonators. The deep energy nature of the defects bestows single-crystal diamond with outstanding low intrinsic energy dissipation in mechanical resonators at room temperature or above.

Spectral features of the tunneling-induced transparency and the Autler-Townes doublet and triplet in a triple quantum dot.

We theoretically investigate the spectral features of tunneling-induced transparency (TIT) and Autler-Townes (AT) doublet and triplet in a triple-quantum-dot system. By analyzing the eigenenergy spectrum of the system Hamiltonian, we can discriminate TIT and double TIT from AT doublet and triplet, respectively. For the resonant case, the presence of the TIT does not exhibit distinguishable anticrossing in the eigenenergy spectrum in the weak-tunneling regime, while the occurrence of double anticrossings in the strong-tunneling regime shows that the TIT evolves to the AT doublet. For the off-resonance case, the appearance of a new detuning-dependent dip in the absorption spectrum leads to double TIT behavior in the weak-tunneling regime due to no distinguished anticrossing occurring in the eigenenergy spectrum. However, in the strong-tunneling regime, a new detuning-dependent dip in the absorption spectrum results in AT triplet owing to the presence of triple anticrossings in the eigenenergy spectrum. Our results can be applied to quantum measurement and quantum-optics devices in solid systems.

Bistability of Cavity Magnon Polaritons.

We report the first observation of the magnon-polariton bistability in a cavity magnonics system consisting of cavity photons strongly interacting with the magnons in a small yttrium iron garnet (YIG) sphere. The bistable behaviors emerged as sharp frequency switchings of the cavity magnon polaritons (CMPs) and related to the transition between states with large and small numbers of polaritons. In our experiment, we align, respectively, the [100] and [110] crystallographic axes of the YIG sphere parallel to the static magnetic field and find very different bistable behaviors (e.g., clockwise and counter-clockwise hysteresis loops) in these two cases. The experimental results are well fitted and explained as being due to the Kerr nonlinearity with either a positive or negative coefficient. Moreover, when the magnetic field is tuned away from the anticrossing point of CMPs, we observe simultaneous bistability of both magnons and cavity photons by applying a drive field on the lower branch.

Tunable self-focusing and self-defocusing effects in a triple quantum dot via the tunnel-enhanced cross-Kerr nonlinearity.

Kerr-nonlinearity induced self-focusing or self-defocusing effect provides the opportunity for exploring fundamental phenomena related to the light-matter interactions. Here we show that the linear and nonlinear dispersion responses are significantly sensitive to both the detunings and the tunneling strengths of the indirect-excitonic (IX) states in an asymmetric triple quantum dot system. In particular, the nonlinear dispersion properties are dominated by the tunnel-enhanced cross-Kerr nonlinearity from one of the IX states. Meanwhile, by varying the detunings of other IX states, we reveal that the tunnel-enhanced cross-Kerr nonlinearity gives rise to the realization of the self-focusing and self-defocusing effects. Moreover, by taking into account the effect of the longitudinal-acoustic-phonon induced dephasing of the IX states, it is possible to modulate the height and position of the peak of the self-focusing or self-defocusing effect. Our results may have potential applications in nonlinear-optics and quantum-optics devices based on the tunnel-enhanced nonlinearities in this solid-state system.

Observation of the exceptional point in cavity magnon-polaritons.

Magnon-polaritons are hybrid light-matter quasiparticles originating from the strong coupling between magnons and photons. They have emerged as a potential candidate for implementing quantum transducers and memories. Owing to the dampings of both photons and magnons, the polaritons have limited lifetimes. However, stationary magnon-polariton states can be reached by a dynamical balance between pumping and losses, so the intrinsically nonequilibrium system may be described by a non-Hermitian Hamiltonian. Here we design a tunable cavity quantum electrodynamics system with a small ferromagnetic sphere in a microwave cavity and engineer the dissipations of photons and magnons to create cavity magnon-polaritons which have non-Hermitian spectral degeneracies. By tuning the magnon-photon coupling strength, we observe the polaritonic coherent perfect absorption and demonstrate the phase transition at the exceptional point. Our experiment offers a novel macroscopic quantum platform to explore the non-Hermitian physics of the cavity magnon-polaritons.

Four-junction superconducting circuit.

We develop a theory for the quantum circuit consisting of a superconducting loop interrupted by four Josephson junctions and pierced by a magnetic flux (either static or time-dependent). In addition to the similarity with the typical three-junction flux qubit in the double-well regime, we demonstrate the difference of the four-junction circuit from its three-junction analogue, including its advantages over the latter. Moreover, the four-junction circuit in the single-well regime is also investigated. Our theory provides a tool to explore the physical properties of this four-junction superconducting circuit.

Formulation and characterization of boanmycin-loaded liposomes prepared by pH gradient experimental design.

This study reports the development of a novel liposomal formulation containing boanmycin (BAM) by the pH-gradient, spherical symmetric experimental design. DSC was used to elucidate the thermotropic transition of the soybean egg phosphatidylcholine (EPCS) bilayers. The DSC analysis showed that the incorporation of cholesterol into the EPCS bilayers caused a reduction in the cooperativity of the bilayer phase transition, leading to a dense and more stable structure. To further explore the possibility of the facilitated molecular interaction between BAM and lipids, the effective chemical shift anisotropy (Δδ) of EPCS was measured by (31)P-NMR spectroscopy in the presence and absence of BAM at 25 °C. The results revealed that the amino group of BAM interacted with the hydrophilic head group of EPCS by electrostatic attraction. Effects of the lipid concentration, pH of the outside buffer and incubation temperature on the encapsulation efficiency of the liposomes were investigated by the spherical symmetric design. Multiple nonlinear regression and second-order polynomial model were fitted to the data, and the resulting equations were used to produce the three dimensional response graphs. The actual response values were in good agreement with the predicted values calculated by the visual FoxPro software. To determine the plasma pharmacokinetics and tissue distribution characteristics of BAM, mice were i.v. injected with BAM-loaded liposomes and the commercial injection solution. The BAM-loaded liposomes exhibited significantly different t(1/2), CL and AUC in plasma and tissues. The MTT assay showed that the BAM-loaded liposomes effectively inhibited the cell proliferation by inducing apoptosis of HepG2 cells in a dose- and time-dependent manner. Compared to the control group, the BAM-loaded liposomes induced marked apoptotic morphologic alterations, including cell shrinkage and granular apoptotic bodies.

Preparation of an anhydrous reverse micelle delivery system to enhance oral bioavailability and anti-diabetic efficacy of berberine.

To enhance oral bioavailability and anti-diabetic efficacy of berberine (BER), an anhydrous reverse micelle (ARM) delivery system was prepared through lyophilization of water-in-oil (W/O) emulsions. Using soy phosphatidylcholine as emulsifiers, BER-containing W/O emulsions were prepared and then lyophilized to form dry products which, upon addition of oil, formed clear ARMs containing amorphous BER nanoparticles. BER-loaded ARMs or free BER solutions were administered to streptozocin-induced diabetic mice. In vivo measurements demonstrated that the blood glucose levels (BGLs) of diabetic mice reduced on average to 22% of the initial values 4h after intravenous injection of BER solution at the dose of 2.5mg/kg body weight, while the average BGL reduction was 57% in the group gavaged with ARMs at the dose of 100mg/kg body weight. No significant BGL reduction was noticed in mice orally received BER solutions. Compared to BER solutions, the oral bioavailability of BER-loaded ARMs was enhanced 2.4-fold, and the maximum blood concentration of BER was enhanced 2.1-fold with a 2-h time lag leading to a prolonged efficacy. Thus, this novel ARM delivery system provides a valid method to improve oral bioavailability and anti-diabetic efficacy of BER, offering a promising product alternative to other hypoglycemic drugs for diabetes therapy.

Preparation of submicron liposomes exhibiting efficient entrapment of drugs by freeze-drying water-in-oil emulsions.

A novel liposome preparation method is described as freeze-drying of water-in-oil emulsions containing sucrose in the aqueous phase (W) and phospholipids and poly(ethylene glycol)(1500) (PEG) in the oil phase (O). The water-in-oil emulsions were prepared by sonication and then lyophilized to obtain dry products. Upon rehydration, the dry products formed liposomes with a size smaller than 200 nm and an encapsulation efficiency (EE) higher than 60% for model drugs. The presence of lyoprotectant and PEG was found to be a prerequisite for the formation of liposomes with desirable properties, such as a small particle size and high EE. The lyophilates were stable and could be rehydrated to form liposomes without any change in size or EE even after a storage period of 6 months. Also, the lipophilic drug-containing FWE liposomes were stable and could be stored for at least 6 months although the liposomes containing hydrophilic drugs showed significant leakage. Based on the vesicle size and EEs of the model drugs, as well as the scanning electron micrograph (SEM) and small angle X-ray scattering (SAXS) pattern of the lyophilates, a possible mechanism for the liposome formation is proposed.

Solvent injection-lyophilization of tert-butyl alcohol/water cosolvent systems for the preparation of drug-loaded solid lipid nanoparticles.

A simple procedure involving solvent injection-lyophilization (SIL) was used to prepare solid lipid nanoparticles (SLNs). A tert-butyl alcohol (t-BA) solution containing lipids was injected into a stirred aqueous solution containing lyoprotectants to form SLNs dispersed in a t-BA/water cosolvent system. The t-BA/water cosolvent SLN dispersion was subsequently lyophilized to obtain a dry product which, upon rehydration, formed an aqueous dispersion of spherical SLNs with a size under 200 nm. A lipophilic drug, cinnarizine, was dissolved in t-BA at a drug-to-lipid mass ratio of 1:20 and almost 100% of the drug was entrapped in the formed SLNs following the SIL process. Likewise, hydrophilic 5-fluorouracil, after being solubilized in t-BA through forming anhydrous reverse micelles, could be entrapped in SLNs with an encapsulation efficiency up to 15.6%. Differential scanning calorimetry and small angle X-ray scattering analysis proved that the lipids in the formed SLNs were in a stable beta-form, and there was no recrystallization expulsion of drugs during storage. In contrast to the conventional solvent injection method, the SIL procedure was not time-consuming and no relatively high-temperature evaporation was needed to remove organic solvents. Moreover, the efficiency of the lyophilization was markedly enhanced due to use of the t-BA/water cosolvent system. Thus, the SIL procedure was found to be an efficient method for preparing stable drug-loaded SLNs.