In this work, we use $\mathrm{N}$-phenylglycine (NPG) molecules as a universal passivant for all typical surface defects of perovskite to improve the photovoltaic performance and stability of perovskite. Our results show that NPG molecules can passivate the organic cation vacancy, $\mathrm{I}$ vacancy, $\mathrm{Pb}$ vacancy, and $\mathrm{Pb}$-$\mathrm{I}$ antisite surface defects of perovskite, through either coordinate and/or hydrogen bonding, or the van der Waals interaction. More interestingly, after the $\mathrm{Pb}$ vacancy on the perovskite surface is passivated by NPG, a transition from metallic to semiconducting properties occurs. The perovskite solar cells (PSCs) passivated by NPG have a high power conversion efficiency (PCE) of 21.16% and retain 91% of the initial efficiency after 700 h in humid air, compared with PSCs without passivation (PCE of 18.29% and maintained efficiency of 75%). Our study proposes one general surface-defect passivant for PSCs that significantly boosts photovoltaic performance and stability.

Optical parametric oscillation in a Kerr nonlinear microresonator can generate coherent laser light with frequencies that are widely separated from the pump frequency, allowing, for example, visible light to be generated using a near-infrared pump. To be practically useful, the pump-to-signal conversion efficiency must be far higher than what has been demonstrated in microresonator-based oscillators with widely separated output frequencies. To address this challenge, here we theoretically and numerically study parametric oscillations in Kerr nonlinear microresonators, revealing an intricate solution space that arises from an interplay of nonlinear processes. As a start, we use a three-mode approximation to derive an efficiency-maximizing relation between pump power and frequency mismatch. However, realistic devices, such as integrated microring resonators, support far more than three modes. Hence, a more accurate model that includes the entire modal landscape is necessary to determine potential inefficiencies arising from unwanted competing nonlinear processes. To this end, we numerically simulate the Lugiato-Lefever equation that accounts for the full spectrum of nonlinearly coupled resonator modes. We observe and characterize two nonlinear phenomena linked to parametric oscillations in multimode resonators: mode competition and cross-phase modulation-induced modulation instability. Both processes may impact conversion efficiency. Finally, we show how to increase the conversion efficiency to approximately 25% by tuning the microresonator loss rates. Our analysis will guide microresonator designs that aim for high conversion efficiency and output power.

We propose an approach for the excitation of polariton Tamm states with a controllable nontrivial topology. The Tamm polaritons emerge at the interface of two binary one-dimensional photonic crystals belonging to a $C_{3v}$ point group, with an exciton resonance within their matching band gaps. The external magnetic field applied in the Faraday geometry endows the dispersion of the Tamm polaritons with the nonreciprocity: it lifts the degeneracy between opposite propagation directions in the interface plane. The phenomenology of Tamm polariton currents closely resembles one of a $Z_2$ topological insulator. The proposed structure acts as an optical spin splitter controlled by the magnetic field magnitude.

Strain engineering is a promising approach for suppressing the off-state conductance in graphene-based devices that arises from Klein tunneling. In this work, we derive a comprehensive tight-binding Hamiltonian for strained graphene that incorporates strain-induced effects that have been neglected hitherto, such as the distortion of the unit cell under strain, the effect of strain on the next-nearest-neighbor coupling, and the second-order contributions of the strain tensor. We derive the corresponding low-energy effective Hamiltonian about the Dirac points and reformulate the boundary conditions at the interfaces between strained and unstrained graphene in light of additional terms in the Hamiltonian. By applying these boundary conditions, we evaluate the transmission across a strained graphene heterostructure consisting of a central segment sandwiched between two unstrained leads. Modulation of the transmitted current can be effected by varying the magnitude and direction of the applied strain, as well as by the application of a gate voltage. Based on realistic parameter values, we predict that high on:off ratios of up to ${10}^{12}$, as well as high current-valley polarization, can be achieved in the strain-modulated device.

We present a portable optically pumped magnetometer instrument for ultrasensitive measurements within the Earth’s magnetic field. The central part of the system is a sensor head operating a MEMS-based Cs vapor cell in the light-shift dispersed $M_z$ mode. It is connected to a compact, battery-driven electronics module by a flexible cable. We briefly review the working principles of the device and detail the realization of both the sensor head and electronics. We show shielded and unshielded measurements within a static magnetic field amplitude of $50\mu \mathrm{T}$, demonstrating a noise level of the sensor system down to $140\mathrm{fT}/\sqrt{\mathrm{Hz}}$ and a sensor bandwidth of several 100 Hz. In a detailed analysis of sensor noise, we reveal the system to be limited by technical sources with straightforward strategies for further improvement toward its fundamental noise limit of $12\mathrm{fT}/\sqrt{\mathrm{Hz}}$. We assess the parameters defining the sensor bandwidth by theoretical modeling based on the Bloch equations. Finally, we compare our sensors’ performance to a commercial superconducting quantum interference device system in a measurement environment typical for geomagnetic observatory practice and geomagnetic prospection.

Accurately measuring the three-dimensional position of an atomic cloud is essential for improving the precision of atom interferometers. In the work presented here, the three-dimensional position of an atomic cloud in an atom interferometer is measured with only one laser beam, generated by a phase modulator. The vertical position is determined from the change in the additional-sideband effect with the time interval $T$ between adjacent Raman pulses in the atom interferometer. Based on this method, the vertical position of the atomic cloud is measured with an uncertainty of 0.2 mm; therefore, the uncertainty in a gravity measurement contributed by the gravity gradient is not limited by the uncertainty in the measurement of the vertical position at the level of $0.1\mu \mathrm{Gal}$. Furthermore, a method of measuring Rabi oscillations at different horizontal positions to determine the horizontal position of the atomic cloud is proposed and is demonstrated experimentally. With this method, the horizontal position can be determined with an uncertainty of less than 0.1 mm, and the horizontal velocity of the atomic cloud can also be deduced. The methods demonstrated in this paper are helpful for evaluating systematic errors in atom interferometers, and also useful in precision measurements based on an atomic fountain.

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.