Understanding the physical mechanisms governing the response of lipid vesicles under an osmotic imbalance is crucial not only for advancing our knowledge of osmoregulation in living cells but also for guiding the design of biomedical vesicular systems. When placed under osmotic stress, lipid vesicles exhibit a variety of responses, from simple engorgement, to swelling with eventual pore formation, to the only recently observed irreversible explosion triggered by photoreactions. Here, we present a unifying model that incorporates all of these dynamic responses by elucidating the associated energy landscape of vesicle outcomes. We demonstrate the essential, yet previously unrecognized, role of the spontaneous curvature in determining vesicle responses under extreme osmotic stress. We utilize numerical experiments to construct phase diagrams of pore dynamics, which are consistent with the experimental observations, and we further discuss the impacts of compositional lipid properties. Our work not only advances a fundamental understanding of vesicle response in nonequilibrium environments, but also extends the possibility for precise design of vesicle systems regarding controlled release of therapeutic substances in biomedical applications.

Spin-orbit-torque (SOT) symmetry in a heavy-metal–ferromagnet bilayer forbids the deterministic switching of perpendicular magnetization. Traditionally, an external magnetic field-exchange bias-tilted magnetic anisotropy is introduced to break the symmetry, which is not suitable for practical applications. Here, we propose to break the SOT symmetry by introducing a longitudinal composition gradient in $\mathrm{Cu}\text{−}\mathrm{Pt}$ heavy metal. We demonstrate the deterministic switching of a perpendicularly magnetized $\mathrm{Co}/\mathrm{Ni}$ multilayer with good endurance when the electric current flows along the direction of the composition gradient. No field-free switching is observed when the current is applied transverse to the gradient or the gradient is removed. The composition gradient of $\mathrm{Cu}\text{−}\mathrm{Pt}$ leads to a longitudinal gradient of SOT, which results in the field-free switching of perpendicular magnetization. Our work offers a promising approach for lowering the symmetry of the material system for developing spintronic applications.

Using phase-modulation-induced potential gradient whose period is synchronized to a microwave optoelectronic oscillator, dissipative Kerr solitons generated in a crystalline optical microresonator are trapped by the soliton tweezing effect, exhibiting a stabilized soliton repetition rate. In the meantime, side-mode suppression of the microwave signal is enabled by the photodetection of the soliton train. Substantiated both experimentally and theoretically, the hybrid system produces a drift-reduced microcomb and a spectrum-purified optoelectronic oscillator simultaneously, yielding a low-cost toolkit for microwave and optical metrology.

Flat optics has demonstrated great advances in miniaturizing conventional bulky optical elements due to recent developments in metasurface design. Specific applications of such designs include spatial differentiation and the compression of free-space. However, metasurfaces designed for such applications are often polarization-dependent and are designed for a single functionality. In this work, we introduce a polarization-independent metasurface structure by designing guided resonances with degenerate band curvatures in a photonic crystal slab. Our device can perform both free-space compression and spatial differentiation when operated at different frequencies at normal incidence. This work demonstrates the promise of dispersion engineering in metasurface design to create ultrathin devices with polarization-independent functionality.

Electromagnetic environments are becoming increasingly complex and congested, creating a growing challenge for systems that rely on electromagnetic waves for communication, sensing, or imaging, particularly in reverberating environments. The use of programmable metasurfaces provides a potential means of directing waves to optimize wireless channels on demand, ensuring reliable operation and protecting sensitive electronic components. Here we introduce a technique that combines a deep-learning network with a binary programmable metasurface to shape waves in complex reverberant electromagnetic environments, in particular ones where there is no direct line of sight. We apply this technique for wavefront reconstruction and control, and accurately determine metasurface configurations based on measured system scattering responses in a chaotic microwave cavity. The state of the metasurface that realizes desired electromagnetic wave field distribution properties was successfully determined even in cases previously unseen by the deep-learning algorithm. Our technique is enabled by the reverberant nature of the cavity, and is effective with a metasurface that covers only approximately 1.5% of the total cavity surface area.

In order to assess whether quantum resources can provide an advantage over classical computation, it is necessary to characterize and benchmark the nonclassical properties of quantum algorithms in a practical manner. In this paper, we show that using measurements in no more than three out of the possible $3^N$ bases, one can not only reconstruct the single-qubit reduced density matrices and measure the ability to create coherent superpositions, but also possibly verify entanglement across all $N$ qubits participating in the algorithm. We introduce a family of generalized Bell-type observables for which we establish an upper bound to the expectation values in fully separable states by proving a generalization of the Cauchy-Schwarz inequality, which may serve of independent interest. We demonstrate that a subset of such observables can serve as entanglement witnesses for states of the quantum-approximate-optimization algorithm for the MaxCut problem (QAOA MaxCut), and further argue that they are especially well tailored for this purpose by defining and computing an entanglement potency metric on witnesses. A subset of these observables also certifies, in a weaker sense, the entanglement in GHZ states, which share the ${\mathbb{Z}}_2$ symmetry of QAOA MaxCut. The construction of such witnesses follows directly from the cost Hamiltonian to be optimized, and not through the standard technique of using the projector of the state being certified. It may thus provide insights to construct similar witnesses for other variational algorithms prevalent in the noisy intermediate-scale quantum era. We demonstrate our ideas with proof-of-concept experiments on the Rigetti Aspen-9 chip for ansatz containing up to 24 qubits.

Laser interferometers are the core measurement tool in gravitational wave observatories. An important factor that can limit the performance is the relative power instability of the laser, a problem often called relative intensity noise (RIN). But exactly how this influences the interferometer performance is not completely understood. Therefore in this paper we analyze laser RIN coupling into the phase readout in balanced and unbalanced heterodyne interferometers. We describe the coupling theoretically, then simulate and finally measure it. Our results reveal a combination of RIN contributions from the heterodyne frequency and twice the heterodyne frequency in the interferometric phase readout. We also show that when an additional, correlated reference measurement is subtracted the combined coupling factor depends on the differential phase between the two measurements and thus can be minimized. Our results have implications for noise models in future space-based gravitational wave observatories like Laser Interferometer Space Antenna, where RIN-to-phase coupling arises directly and is modulated via spacecraft jitter, testmass position and orientation.

Heterovalent $\mathrm{Bi}$ doping in lead halide perovskites (LHPs) is of particular interest in recent research to improve the electronic and optoelectronic properties. In experiments, the incorporation of $\mathrm{Bi}$ not only converts the conductivity type of crystals from p type to n type, leading to the significant enhancement of charge-carrier concentration, but also results in the appearance of near-infrared photoluminescence (NIR PL) along with the decrease of band-edge PL intensity. However, with a high concentration of $\mathrm{Bi}$ doping, the carrier concentration exhibits a saturated tendency and the intensity of NIR PL decreases abnormally. The origins behind these interesting phenomena are not yet well understood. Herein, based on first-principles calculations, we demonstrate that $\mathrm{Bi}$ dimers form n type and intrinsic LHPs with a high concentration of $\mathrm{Bi}$ doping. They act as effective n-type limiting defects, and hence, cause carrier saturation in experiments. Moreover, the NIR PL arising from the ${\mathrm{Bi}}_{\mathrm{Pb}}$ defect is suppressed due to the density conversion of isolated ${\mathrm{Bi}}_{\mathrm{Pb}}$ defects to $\mathrm{Bi}$ dimers when $\mathrm{Bi}$ is heavily doped. Meanwhile, nonradiative recombination is also promoted due to the deep charge-state transition level introduced by the $\mathrm{Bi}$ dimer. Our work not only reveals the mechanism of highly concentrated $\mathrm{Bi}$ limiting the electronic and optical properties of LHPs, but also suggests the precise control of $\mathrm{Bi}$ doping in electronic and photovoltaic applications.

Phase-gradient metagratings have exhibited unconventional abilities to manipulate electromagnetic waves owing to functionality inherited from metasurface and different physics. In this paper, by integrating homogeneous dielectric materials with gradient thickness into periodical metallic slits, a passive phased metagrating based on mode conversion is designed in which each unit provides nearly perfect broadband transmission. To validate the effectiveness of our scheme, anomalous scattering and planar metalenses with excellent efficiency in a finite band are designed theoretically and proved numerically. Good performance makes the implementation of other metasurface functions possible, providing a platform for functions from holography to caustic engineering. More interestingly, the high fluidity of this structure promises potential application in other physical fields, such as acoustics and water waves.

Semiconductor spin qubits may show significant device-to-device variability in the presence of spin-orbit coupling mechanisms. Interface roughness, charge traps, layout, or process inhomogeneities indeed shape the real-space wave functions, and hence the spin properties. It is, therefore, necessary to understand how reproducible the qubits can be, in order to assess strategies to cope with variability, and to set constraints on the quality of materials and fabrication. Here we model the variability of single-qubit properties (Larmor and Rabi frequencies) due to disorder at the $\mathrm{Si}/{\mathrm{Si}\mathrm{O}}_2$ interface (roughness, charge traps) in metal-oxide-semiconductor devices. We consider both electron qubits (with synthetic spin-orbit coupling fields created by micromagnets) and hole qubits (with intrinsic spin-orbit coupling). We show that charge traps are much more limiting than interface roughness, and can scatter Rabi frequencies over one order of magnitude. We discuss the implications for the design of spin qubits and for the choice of materials.

Parametric amplification—injecting energy into waves via periodic modulation of system parameters—is typically restricted to specific multiples of the modulation frequency. However, broadband parametric amplification can be achieved in active metamaterials which allow local parameters to be modulated both in space and in time. Inspired by the concept of luminal metamaterials in optics, we describe a mechanism for one-way amplification of sound waves across an entire frequency band using spacetime-periodic modulation of local stiffnesses in the form of a traveling wave. When the speed of the modulation wave approaches that of the speed of sound in the metamaterial—a regime called the sonic limit—nearly all modes in the forward-propagating acoustic band are amplified, whereas no amplification occurs in the reverse-propagating band. To eliminate divergences that are inherent to the sonic limit in continuum materials, we use an exact Floquet-Bloch approach to compute the dynamic excitation bands of discrete periodic systems. We find wide ranges of parameters for which the amplification is nearly uniform across the lowest-frequency band, enabling amplification of wave packets while preserving their speed, shape, and spectral content. Our mechanism provides a route to designing acoustic metamaterials which can propagate wave pulses without losses or distortion across a wide range of frequencies.

We investigate the impact of threading dislocations with an edge component ($a$ or $a+c$ type) on carrier recombination and diffusion in $\mathrm{Ga}\mathrm{N}$(0001) layers close to the surface as well as in the bulk. To this end, we utilize cathodoluminescence imaging of the top surface of a $\mathrm{Ga}\mathrm{N}$(0001) layer with a deeply buried (In,$\mathrm{Ga}$)N quantum well. Varying the acceleration voltage of the primary electrons and comparing the signal from the layer and the quantum well enables us to probe carrier recombination at depths ranging from the close vicinity of the surface to the position of the quantum well. Our experiments are accompanied by fully three-dimensional Monte Carlo simulations of carrier drift, diffusion, and recombination in the presence of the surface, the quantum well, and the dislocation, taking into account the dislocation strain field and the resulting piezoelectric field at the dislocation outcrop. Near the surface, this field establishes an exciton dead zone around the dislocation, the extent of which is not related to the carrier diffusion length. However, reliable values of the carrier diffusion length can be extracted from the dipolelike energy shift observed in hyperspectral cathodoluminescence maps recorded around the dislocation outcrop at low acceleration voltages. For high acceleration voltages, allowing us to probe a depth where carrier recombination is unaffected by surface effects, we observe a much stronger contrast than expected from the piezoelectric field alone. This finding provides unambiguous experimental evidence for the strong nonradiative activity of edge threading dislocations in bulk $\mathrm{Ga}\mathrm{N}$ and hence also in buried heterostructures.

We determine the diffusion length of excess carriers in $\mathrm{Ga}\mathrm{N}$ by spatially resolved cathodoluminescence spectroscopy utilizing a single quantum well as a carrier collector or carrier sink. Monochromatic intensity profiles across the quantum well are recorded for temperatures between 10 and 300 K. A classical diffusion model accounts for the profiles acquired between 120 and 300 K, while for temperatures lower than 120 K, a quantum capture process has to be taken into account in addition. Combining the diffusion length extracted from these profiles and the effective carrier lifetime measured by time-resolved photoluminescence experiments, we deduce the carrier diffusivity as a function of temperature. The experimental values are found to be close to theoretical ones for the ambipolar diffusivity of free carriers limited only by intrinsic phonon scattering. This agreement is shown to be fortuitous. The high diffusivity at low temperatures instead originates from an increasing participation of excitons in the diffusion process.

The determination of the carrier diffusion length of semiconductors such as $\mathrm{Ga}\mathrm{N}$ and $\mathrm{Ga}\mathrm{As}$ by cathodoluminescence imaging requires accurate knowledge about the spatial distribution of generated carriers. To obtain the lateral distribution of generated carriers for sample temperatures between 10 and 300 K, we utilize cathodoluminescence intensity profiles measured across single quantum wells embedded in thick $\mathrm{Ga}\mathrm{N}$ and $\mathrm{Ga}\mathrm{As}$ layers. Thin ($\mathrm{Al}$,$\mathrm{Ga}$)$\mathrm{N}$ and ($\mathrm{Al}$,$\mathrm{Ga}$)$\mathrm{As}$ barriers respectively prevent carriers diffusing in the $\mathrm{Ga}\mathrm{N}$ and $\mathrm{Ga}\mathrm{As}$ layers to reach the well, which would broaden the profiles. The experimental cathodoluminescence profiles are found to be systematically wider than the energy loss distributions calculated by means of the Monte Carlo program casino, with the width monotonically increasing with decreasing temperature. This effect is observed for both $\mathrm{Ga}\mathrm{N}$ and $\mathrm{Ga}\mathrm{As}$ and becomes more pronounced for higher acceleration voltages. We discuss this phenomenon in terms of both the electron-phonon interaction controlling the energy relaxation of hot carriers and the shape of the initial carrier distribution. Finally, we present a phenomenological approach to simulate the carrier generation volume that can be used for the investigation of the temperature dependence of carrier diffusion.

We consider the motion of a light sail that is accelerated by a powerful laser beam. We derive the equations of motion for two proof-of-concept sail designs with damped internal degrees of freedom. Using linear stability analysis, we show that perturbations of the sail movement in all lateral degrees of freedom can be damped passively: the sail is asymptotically stable. This analysis also shows complicated behavior akin to that associated with exceptional points in PT-symmetric systems in optics and quantum mechanics. We show that the excess heat that is produced by the damping mechanism is likely to be substantially smaller than the expected heating due to the partial absorption of the incident laser beam by the sail.

The height dependence of Raman light scattering on organic molecules deposited onto thick one-dimensional metal-dielectric gratings is investigated theoretically and experimentally. We observe oscillations of the intensity of Raman light scattering as a function of the height of the metastructure’s strips and demonstrate that these oscillations are explicitly associated with a type of Fabry-Perot effect. We show that the intensity of surface-enhanced Raman scattering can be additionally increased by local field enhancement (by an order of magnitude) at resonances of both pump and Stokes as well as anti-Stokes frequency, due to coupling of the surface plasmon polaritons on the top and bottom metal parts of the gratings via the vertical Fabry-Perot resonances over their middle dielectric part. A semianalytical one-mode model to describe the effect qualitatively is proposed. A significant deviation of the dispersion of Fabry-Perot-coupled plasmon polaritons from the surface-plasmon-polariton dispersion just folded into the first Brillouin zone is demonstrated.

Fewer-qubit quantum logic gate, serving as a basic unit for constructing universal multiqubit gates, has been widely applied in quantum computing and quantum information. However, traditional constructions for fewer-qubit gates often utilize a multipulse protocol, which inevitably suffers from serious intrinsic errors during the gate execution. In this paper, we report an optimal model about universal two- and three-qubit cnot gates mediated by excitation to Rydberg states with easily accessible van der Waals interactions. This gate depends on a global optimization to implement amplitude- and phase-modulated pulses via genetic algorithm, which can facilitate the gate operation with fewer optical pulses. Compared to conventional multipulse piecewise schemes, our gate can be realized by simultaneous excitation of atoms to the Rydberg states, saving the time for multipulse switching at different spatial locations. Our numerical simulations show that a single-pulse two- (three-) qubit cnot gate is possibly achieved with a fidelity of 99.23% (90.39%) for two qubits separated by $7.10\mu \mathrm{m}$ when the fluctuation of Rydberg interactions is excluded. Our work is promising for achieving fast and convenient multiqubit quantum computing in the study of neutral-atom quantum technology.