We evaluate the fundamental performance of a fiber-optic gyroscope (FOG) design that is enhanced by the injection of a quantum-optical squeezed vacuum. In the presence of fiber loss, we compute the optimum attainable enhancement below the standard quantum limit in terms of the angular velocity estimator variance from a homodyne measurement. We find that currently realizable amounts of single-mode squeezing are sufficient to access the maximum quantitative improvement, but that this gain in maximum rotation sensitivity is limited to a marginal constant factor. We then propose an entanglement-enhanced FOG design that segments a fixed amount of available fiber into multiple fiber interferometers and feeds this sensor array with a multimode-entangled squeezed vacuum resource. Our design raises the fundamental improvement in sensitivity to an appreciable factor of $e\approx 2.718$.

Rare-earth-transition-metal (RETM) ferrimagnets have received great attention for their small magnetic moments and fast dynamics in the development of next-generation spintronic devices. Here, we study spin Hall magnetoresistance (SMR) in the RETM ferrimagnet and heavy-metal bilayers of ${\mathrm{Co}}_{1\text{−}x}{\mathrm{Tb}}_x/\mathrm{Pt}$. Anomalous temperature dependence of the SMR is observed, where the SMR changes nonmonotonically and has a valley next to the magnetization compensation temperature. Additionally, we find that the SMR varies significantly for different chemical compositions of ${\mathrm{Co}}_{1\text{−}x}{\mathrm{Tb}}_x$ alloys. These anomalous behaviors are interpreted as the dramatically altered spin polarization of the ${\mathrm{Co}}_{1\text{−}x}{\mathrm{Tb}}_x$ layer near the compensation point. By deducing spin polarization from the abnormal temperature dependence of SMR, we provide a convenient way to access spin polarization of the RETM ferrimagnets. These experimental results show implications for tunable spin-current sources of RETM ferrimagnets.

In magnonics, a fast-growing branch of wave physics characterized by low energy consumption, it is highly desirable to create circuit elements useful for wave computing. However, it is crucial to reach the nanoscale so as to be competitive with the electronics, which vastly dominates in computing devices. Here, based on numerical simulations, we demonstrate the functionality of the spin-wave diode and the circulator to steer and manipulate spin waves over a wide range of frequency in the GHz regime. They take advantage of the unidirectional magnetostatic coupling induced by the interfacial Dzyaloshinskii-Moriya interaction, allowing the transfer of the spin wave between thin ferromagnetic layers in only one direction of propagation. Using the multilayered structure consisting of $\mathrm{Py}$ and $\mathrm{Co}$ in direct contact with heavy metal, we obtain submicrometer-size nonreciprocal devices of high efficiency. Thus, our work contributes to the emerging branch of energy-efficient magnonic logic devices, giving rise to the possibility of application as a signal-processing unit in the digital and analog nanoscaled spin-wave circuits.

While there has been tremendous progress in realizing high frequency, tunable, stable, atomically thin microresonators from individual two-dimensional (2D) materials and their combinations, their poor mechanical resonance quality at room temperature is still an open area of research. Taking a multiscale modeling approach and graphene as a representative 2D system, we show that intrinsic dissipation due to flexural mode coupling can explain the room temperature behavior. The inverse quality factor $Q^{-1}$, a nondimensional measure of dissipation, solely due to the coupling with nanometer wavelength flexural modes in the structure is found to be nonlinear in the vibration amplitude, and also dependent on the resonator size, strain, and temperature. At lower amplitudes and submicron to micron sizes, however, $Q^{-1}$ mediated by coupling with the submicro- to micrometer wavelength flexural modes dominates. This $Q^{-1}$ is amplitude independent, and bears a similar implicit dependence on the temperature ($T$) and inverse strain ($1/ϵ$), suggesting that $T/ϵ$ is a better metric to characterize the dissipation.

Using a magneto-optical pump-probe technique with micrometer spatial resolution, we show that magnetization precession can be launched in individual magnetic domains imprinted in a ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$ layer by elastic coupling to ferroelectric domains in a ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ substrate. The dependence of the precession parameters on the strength and orientation of the external magnetic field reveals that laser-induced ultrafast partial quenching of the magnetoelastic coupling parameter of ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$ by approximately 27% along with 10% ultrafast demagnetization triggers the magnetization precession. The relation between the laser-induced reduction of the magnetoelastic coupling and the demagnetization is approximated by an $n(n+1)/2$ law with $n\approx 2$. This correspondence confirms the thermal origin of the laser-induced anisotropy change. Based on analysis and modeling of the excited precession, we find signatures of laser-induced precessional switching, which occurs when the magnetic field is applied along the hard magnetization axis and its value is close to the effective magnetoelastic anisotropy field. The precession-excitation process in an individual magnetoelastic domain is found to be unaffected by neighboring domains. This makes laser-induced changes of magnetoelastic anisotropy a promising tool for driving magnetization dynamics and switching in composite multiferroics with spatial selectivity.

The advent of broadband and tunable acoustic metamaterials, amenable to be fabricated into flat panel geometry, offers broad, emerging possibilities for room acoustics. In particular, the fine tuning of surface acoustic impedance becomes possible to optimize specific room acoustic goals. In this initial simulation study we examine the possibility of minimizing the averaged level of energy density ($L_e$), both globally and locally in an enclosed room. The relationship curve between surface impedance and global $L_e$ shows an optimal value that can reduce $L_e$ by about $15$–$20\mathrm{dB}$ over a wide audible frequency regime. Moreover, partial coverage of the room surface by the optimally tuned acoustic metamaterial already demonstrates considerable effectiveness. We compare and verify our numerical model with the statistical-diffusive acoustics model and find good agreement in the high-frequency regime. In the low-frequency regime, the energy inhomogeneity caused by wave interference can be utilized to create a quiet zone for specific targeted frequency by optimally tuning the surface impedance values at discretized locations on the four walls.

The use of steric hindrance in blue thermally activated delayed fluorophores shows empirically the improvement of operational lifetime for organic light-emitting diodes (OLEDs). Nevertheless, the intrinsic mechanism of this strategy remains unclear and elusive. Here, the steric effects on rate coefficient and degradation probability of bimolecular quenching processes are decoupled by magnetic field effects and quantum-chemical calculation. The respective dependence of magnetoelectroluminescence on triplet density and charge-carrier density indicates that triplet-charge quenching (TCQ) is the dominant degradation mechanism over that of triplet-triplet annihilation, where steric hindrance effectively prevents the occurrence of Dexter-type TCQ and significantly reduces the TCQ rate coefficient. On the contrary, only a slight increase in degradation probability is generated by the steric effect from bulk inert groups. These findings will provide unambiguous guidance for the design of functional materials for OLEDs.

We present an analysis of wave mixing in the recently developed Josephson traveling-wave parametric amplifier (JTWPA). Circuit simulations performed using WRSPICE show the full behavior of the JTWPA, allowing propagation of all tones. The coupled mode equations (CMEs) containing only pump, signal, and idler propagation are shown to be insufficient to completely capture complex mixing behavior in the JTWPA. Extension of the CMEs through additional state vectors in the analytic solutions allows closer agreement with WRSPICE. We consider an ordered framework for the systematic inclusion of extended eigenmodes and make a comparison with WRSPICE at each step. The agreement between the two methods validates both approaches and provides insight into the operation of the JTWPA.

Solids irradiated by energetic photons can be eroded in two modes, depending on the radiation intensity. High average, low-peak power sources, e.g., synchrotron radiation and high-order harmonics, induce desorption of the material at a low etch rate. In contrast, high-peak-power radiation from extreme ultraviolet and x-ray lasers usually causes a massive removal of the material even by a single shot. In this contribution, an effective material erosion is reported in PMMA exposed to multiple accumulated pulses generated by the free-electron x-ray-laser Linac Coherent Light Source (LCLS, tuned at a photon energy of 830 eV in this study, operated in Menlo Park at Stanford, CA, USA) at a fluence below the single-pulse ablation threshold. The effect is caused by polymer-chain scissions initiated by single photons carrying enough energy to break the $\mathrm{C}—\mathrm{C}$ bounds. High efficiency of the erosion is supposed to occur due to a correlation of the single-photon effects. The subthreshold damage exhibits a nonlinear dose dependence resulting from a competition between chain scissions and cross-linking processes. The cross-linking is proven by Raman spectroscopy of the irradiated polymer. Two theoretical models of the x-ray free-electron-laser-induced erosion are suggested, which provide an excellent agreement with the experimental results.

We present the results of an experiment to locally resolve the spin Seebeck effect in a high-quality yttrium iron garnet–Pt sample. We achieve this by using a locally heated scanning thermal probe to generate a highly local nonequilibrium spin current. To support our experimental results, we also present a model based on the nonequilibrium thermodynamic approach that is in a good agreement with the experimental findings. To further corroborate our results, we index the locally resolved spin Seebeck effect with that of the local magnetization texture by magnetic force microscopy and correlate corresponding regions. We hypothesize that this technique allows imaging of magnetization textures within the magnon diffusion length and hence characterization of spin-caloritronic materials at the nanoscale.

We present an acoustic analog of the Landau–Zener-tunneling (LZT) quantum-mechanical effect and apply it for irreversible wave redirection in weakly coupled nonlinear waveguides under impulse excitation. Due to nonlinearity, LZT-induced wave redirection is passively self-tunable with energy, being realized only in a certain energy band, which can be precisely predicted by theoretical models. Apart from the macroscale experimental validation of the classical quantum LZT effect, the findings apply to a broad class of acoustical systems with nonlinearity, disorder, and weak coupling.

The properties and characteristics of thin-film materials strongly depend on their textures and orientations. However, the attainable film morphologies are severely limited by substrates and growth thermodynamics. Metastable films that otherwise cannot be grown by conventional growth methods may overcome these limitations, thus allowing a dramatic expansion of the spectrum of film textures and orientations. Here we present a means to grow metastable platinum layers that are deposited from platinum alloyed with bismuth surfactant material. This is distinct from conventional surfactant-aided growth of films in which surfactants are typically deposited onto the substrate before film deposition, altering the film growth mode but not the film morphology by tuning the surface energy. Surprisingly, we find that almost no bismuth is incorporated into the platinum layer, but rather the structural morphology of this layer is significantly altered. When this metastable platinum layer is applied to spin-orbit-torque technology, a huge increase in the current-driven velocity of chiral domain walls in perpendicularly magnetized wire on top of the metastable platinum layer is observed for otherwise the same current density, while the platinum resistivity is found to barely increase. Our findings show that the metastable film grown from material alloyed with surfactant is promising for the development of devices in various fields, such as spintronics, semiconductors, and quantum materials.

Multiple geometrical conditions for different magnetic vortex states to appear in micrometer-sized magnetic tunnel junctions (MTJs) are investigated in experiment and simulation. Both results match up well, providing clear images of vortex behaviors. We pattern a compact array of single-vortex MTJ elements and perform magnetotransport and noise measurements. This sensor features nonhysteretic behavior, a small size of 0.5 × 0.5 ${\mathrm{mm}}^2$, a low normalized noise of ${10}^{-13}{\mathrm{Hz}}^{-1}$, a detectability of $18nT/\sqrt{Hz}$ at 1 Hz, and a large dynamic range of 100 Oe. Its 115 dB broad dynamic reserve and superior stability against temperature and environmental stray fields are ideally suited for magnetic sensing applications.

It is well known that in organic solids the collision of two excitons can give rise to delayed fluorescence (DF). Revived interest in this topic is stimulated by the current endeavor towards the development of efficient organic optoelectronic devices such as organic light-emitting diodes (OLEDs) and solar cells, or sensitizers used in photodynamic therapy. In such devices, triplet excitations are ubiquitously present but their annihilations can be either detrimental, e.g., giving rise to a roll-off of intensity in an OLED, or mandatory, e.g., if the sensitizer relies on up-conversion of long-lived low-energy triplet excitations. Since the employed materials are usually noncrystalline, optical excitations migrate via incoherent hopping. Here, we employ kinetic Monte Carlo simulations (KMC) to study the complex interplay of triplet-triplet annihilation (TTA) and quenching of the triplet excitations by impurities in a single-component system featuring a Gaussian energy landscape and variable system parameters such as the length of the hopping sites, i.e., a conjugated oligomer, the morphology of the system, the degree of disorder (σ), the concentration of triplet excitations, and temperature. We also explore the effect of polaronic contributions to the hopping rates. A key conclusion is that the DF features a maximum at a temperature that scales with $\sigma /k_{B}T$. This is related to disorder-induced filamentary currents and thus locally enhanced triplet densities. We predict that a maximum for the TTA process near room temperature or above requires typically a disorder parameter of at least 70 meV.

A simple but efficient approach for the synthesis of transmission-type wideband polarization converters is presented. The proposed configuration comprises multilayer metasurfaces including resonant particles that are progressively rotated layer by layer. The progressive rotation of the particles allows for a polarization conversion over a large frequency band. The polarizing structure is efficiently designed and optimized through a transmission-line-model approach handling the cascade of anisotropic impedance layers and dielectrics. An optimized eight-layer design based on gradually rotated dipole resonators is presented as a proof of concept. The results obtained through the efficient transmission-line model are compared with full-wave simulations once the structure is optimized, showing satisfactory agreement. A prototype of the wideband polarization converter is fabricated and measured.

We use Fourier-plane imaging microscopy (FIM) to determine the transition-dipole-moment orientation in doped organic emissive thin films. The use of FIM enables precise, sensitive, and rapid measurement of dipole orientation in the emission layer of an organic light-emitting device (OLED). An optical model of a stratified birefringent multilayer is introduced for interpreting results obtained by FIM. Using the model, we determine the average orientation of transition-dipole-moment vectors of three phosphorescent dopant emitters. The dipole alignment measured by FIM quantitatively explains the difference in OLED efficiencies using these archetype dopant molecules. FIM provides a nondestructive tool to measure and ultimately improve the outcoupling efficiency of OLEDs and other light-emitting devices.

We study current-induced deterministic magnetization switching and domain-wall motion via polar Kerr microscopy in all-amorphous ${\mathrm{W}}_{66}{\mathrm{Hf}}_{34}/\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}(\mathrm{CFB})/{\mathrm{Ta}\mathrm{O}}_x$ with perpendicular magnetic anisotropy and a large spin Hall angle. Investigations of magnetization switching as a function of the in-plane assist field and the current-pulse width yield switching-current densities as low as $3\times {10}^9{\mathrm{A}/\mathrm{m}}^2$. We accredit this low switching-current density to a low depinning-current density, which is obtained from measurements of domain-wall displacements upon current injection. This correlation is verified by investigations of a $\mathrm{Ta}$/$\mathrm{CFB}$/$\mathrm{Mg}\mathrm{O}$/$\mathrm{Ta}$ reference sample, which shows critical-current densities that are at least one order of magnitude larger.

We develop an analytical model for the photocurrent of organic solar cells based on carrier drift and including second-order charge recombination, in which the figure of merit ${\theta }_o$ naturally appears. This approach provides expressions for the fill-factor–${\theta }_o$ and α-${\theta }_o$ relations, where α is the exponent of the function of the short-circuit current versus light intensity ($J_{\mathrm{SC}}$ ∝ $I^{\alpha }$). A correlation between the reduction factor of Langevin recombination and the dissociation probability of charge transfer states (P) is also discussed. Photocurrent curves of a polymer device obtained at different temperatures (100–300 K) are fitted by the model, whose fitting parameters are in agreement with the literature.