We demonstrate the detection of broadband intense terahertz electromagnetic pulses by Zeeman-torque sampling (ZTS). Our approach is based on magneto-optic probing of the Zeeman torque that the terahertz magnetic field exerts on the magnetization of a ferromagnet. Using an 8-nm-thick iron film as a sensor, we detect pulses from a silicon-based spintronic terahertz emitter with a bandwidth of 0.1–11 THz and a peak field of >0.1 MV/cm. A simple static magneto-optic calibration measurement provides access to absolute transient terahertz field strengths. We show the relevant added value of ZTS compared to electro-optic sampling (EOS): an echo-free transfer function with simple frequency dependence, linearity even at high terahertz-field amplitudes, the straightforward calibration of EOS response functions, and modulation of the polarization-sensitive direction by an external ac magnetic field. Consequently, ZTS has interesting applications even beyond the accurate characterization of broadband high-field terahertz pulses for nonlinear terahertz spectroscopy.

Superconducting circuits are highly controllable platforms to manipulate quantum states, which make them particularly promising for quantum information processing. We show here how the existence of a distance-independent interaction between microwave resonators coupled capacitively through a qubit offers an alternative control parameter toward this goal. This interaction is able to induce an idling point between resonant resonators, and its state-dependent nature allows one to control the flow of information between the resonators. The advantage of this scheme over the previous one is demonstrated through the generation of high-fidelity NOON states between the resonators, with a lower number of operations than previous schemes. Beyond superconducting circuits, our proposal could also apply to atomic lattices with clock transitions in optical cavities, for example.

The photogalvanic effect in ferroelectric (FE) materials attracts considerable interest in solar cells, polarization-sensitive photodetection, and nonvolatile memory applications. However, narrow-band-gap FE materials that cover the full solar spectrum are currently rare, and there is still room to enhance the light-polarization sensitivity and to improve the switching ratio for FE optoelectronic devices. Here, we investigate the photogalvanic effect induced by elliptically polarized light in the narrow-band-gap ($<1.6$ eV) $\mathrm{In}\mathrm{Se}$/${\mathrm{In}}_2{\mathrm{Se}}_3$ FE heterojunction (HJ) stacked with the $\mathrm{In}\mathrm{Se}$ monolayer and $\alpha$-${\mathrm{In}}_2{\mathrm{Se}}_3$ FE monolayer. The dependence of the photocurrent on the polarization angle, $\varphi$, and on the incidence angle, $\alpha$, is formulated within the nonequilibrium Green’s function formalism, with which the photocurrent is then calculated by using first-principles methods. We find that both the linear photogalvanic effect (LPGE) and circular photogalvanic effect (CPGE) are generated from the infrared to the visible range. The CPGE is only induced at oblique incidence due to $C_{3v}$ symmetry of the HJ and can be ${10}^3$ times larger than the LPGE. The largest photocurrent is achieved when light is irradiated along the zigzag direction, which is dominated by the CPGE. The photocurrent can further be tuned by switching between upward and downward FE polarization, leading to a large switching ratio of 563. The photocurrent also shows an excellent light-polarization sensitivity at normal and oblique incidence, with an impressive extinction ratio of 410. These results shed light on the CPGE of FE materials for applications in low-dimensional FE optoelectronics.

Despite the prospect of next-generation electronic technologies spurring the investigation of the remarkable topological magnetoelectric response, its potential remains largely unexplored in the application of basic electronic devices. In this paper, we undertake this task at the theoretical level by addressing the $\theta$ electrodynamics and examine electromagnetic properties (e.g., tunable inductance, operating frequency range, and power consumption) of three fundamental passive magnetic devices endowed with this effect: the primitive transformer, the bilayer solenoid inductor, and the solenoid actuator. We further exploit the methodology of magnetic circuits to obtain an extended Hopkinson’s law that is valid for both topological and ordinary magnetoelectric responses (provided it is uniform in the bulk). Under low-power conditions, we find out that the functionally passive part of the topological-magnetoelectric transformer, the solenoid inductor as well as the solenoid actuator, is indistinguishable from the conventional situation up to second order in the magnetoelectric susceptibility; we argue that the main benefit of using topological insulators essentially relies on a lower power consumption. Our theoretical framework is also convenient to analyze magnetoelectric inductors endowed with a relatively large magnetoelectric susceptibility, they display a broad inductance tunability of over $200\mathrm{\%}$ up to 100 GHz in the millimeter length scale. Conversely, our treatment predicts that the operating frequency range could be restricted below the ultralow frequency by a significantly strong magnetoelectric response (e.g., retrieved by certain multiferroic heterostructures).

We explore critical field and critical current behavior in inhomogeneous narrow thin-film superconducting strips. Formulations are developed to calculate free energy, critical field, and critical current for strips with inhomogeneous Pearl-length distributions. Our findings show that inhomogeneities, specifically a shorter Pearl length in the middle of the strip, significantly enhance the critical field $B_{c1}$. This has practical implications for achieving complete flux expulsion. While narrow strips have traditionally been considered the most effective approach to improve $B_{c1}$ and eliminate trapped vortices, our results suggest that engineered inhomogeneities offer an alternative method to enhance the critical field and improve flux expulsion without reducing strip width, providing greater design flexibility for superconducting devices. Additionally, we find that for the purpose of increasing the critical current, utilizing an inhomogeneous film with a reduced Pearl length in the middle of the strip is advantageous. The enhancement in critical current arises from the current suppression effect at the edges induced by the inhomogeneous distribution of superfluid density. Furthermore, we demonstrate that an inhomogeneous film with a left-right asymmetric Pearl-length distribution enables control over the nonreciprocity of the critical current, highlighting the potential of engineering inhomogeneous Pearl-length distributions to implement devices exhibiting the superconducting diode effect. Our results provide concrete examples of how manipulating the inhomogeneity of Pearl length can enhance the performance of superconducting devices. Various methods such as doping nonuniform impurities or creating a temperature gradient can be employed to implement an inhomogeneous Pearl-length distribution.

Vertical transistors, with the channel material sandwiched between graphene and metal electrodes, are promising for the development of next-generation electronic devices. However, realizing complementary transport in two-dimensional vertical transistors is challenging due to the significant disorder and severe Fermi-level pinning effects at the metal-semiconductor interface caused by conventional metallization. Here, we report complementary vertical transistors in graphene/${\mathrm{WSe}}_2/$van der Waals metal heterostructures. In this device, the van der Waals metal retains the pristine nature of atomically thin ${\mathrm{WSe}}_2$, minimizing the Fermi-level-pinning effect at the metal-${\mathrm{WSe}}_2$ interface. Thus, the barrier height and the type of majority carrier can be simply controlled by the metal work function. Based on this approach, we achieve n- and p-type ${\mathrm{WSe}}_2$ vertical transistors by laminating $\mathrm{Ag}$ and $\mathrm{Pt}$ as van der Waals contact metals, respectively. Moreover, with highly controllable device polarities, we demonstrate a complementary inverter by integrating two vertical transistors with different polarities. Our work not only enables complementary two-dimensional vertical transistors, but also provides a promising strategy for controlling the polarity of carriers in vertical heterostructures.

Kerr parametric oscillators (KPOs) implemented in the circuit quantum electrodynamic architecture can operate as qubits. Their applications to quantum annealing and universal quantum computation have been studied intensively. For these applications, the readout of the state of KPOs is of practical importance. We develop a scheme of state tomography for KPOs with reflection measurement. Although it is known that the reflection coefficient depends on the state of the KPO, it is unclear whether tomography of a qubit encoded into a KPO can be performed in a practical way mitigating decoherence during the measurement, and how accurate it is. We show that the reflection coefficient has a one-to-one correspondence with a diagonal element of the density matrix of the qubit when a probe frequency is properly chosen and an additional single-photon drive is introduced. Thus, our scheme offers a novel way to read out the qubit along an axis of the Bloch sphere, and therefore the reflection measurement and single-qubit gates can constitute state tomography.

We investigate the magnetic properties of an epitaxial full-Heusler ${\mathrm{Co}}_2\mathrm{Fe}\mathrm{Si}$ film with an atomically controlled multiferroic interface coupled with a ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_3$ substrate. The real-space observation of the magnetic domain structure using a magneto-optical Kerr microscope reveals perfect domain-pattern transfer from the ferroelectric substrate, indicating strong interface magnetoelectric coupling. The unique anisotropic magnetization reversal process was found to be induced by lateral modulation of the magnetic anisotropy constant through the strain-induced magnetoelectric coupling effect. The strong interface coupling yields efficient electrical manipulation of the magnetic property with the appropriate initial ferroelectric domain pattern. Our finding indicates that the interface multiferroic structure based on an epitaxially grown Heusler thin film is a promising approach for efficient electrical manipulation of magnetization.

Topological phases of matter feature exotic edge states. However, the fractional topological numbers at edges, although predicted long ago by Jackiw and Rebbi, remain elusive in topological photonic systems. Here we report on the observation of fractional topological numbers at the topological edges and corners in one- and two-dimensional photonic crystals. The fractional topological numbers are determined via measurements of the photonic local density of states. In one-dimensional photonic crystals, we witness a rapid change of the fractional topological number at the edges rising from 0 to 1/2 when the photonic band gap experiences a topological transition, confirming the well-known prediction of Jackiw and Rebbi. In two-dimensional systems, we discover that the fractional topological number in the corner region varies from 0 to 1/2 and 1/4 in phases with different photonic band gaps. Our study paves the way toward topological manipulation of fractional quantum numbers in photonics.

Josephson traveling-wave parametric amplifiers (TWPAs) enable the amplification of weak microwave signals close to the quantum limit with large bandwidth, which has a broad range of applications in superconducting quantum computing and in the operation of single-photon detectors. While the large bandwidth allows for their use in frequency-multiplexed detection architectures, an increased number of readout tones per amplifier puts more stringent requirements on the dynamic range to avoid saturation. Here, we characterize the undesired mixing processes between the different frequency-multiplexed tones applied to a Josephson TWPA, a phenomenon also known as intermodulation distortion. The effect becomes particularly significant when the amplifier is operated close to its saturation power. Furthermore, we demonstrate that intermodulation distortion can lead to significant crosstalk and reduction of fidelity for multiplexed readout of superconducting qubits. We suggest using large detunings between the pump and signal frequencies to mitigate crosstalk. Our work provides insights into the limitations of current Josephson TWPAs and highlights the importance of performing further research on these devices.

The effect of laser polarization on the laser wakefield acceleration (LWFA) of electrons has been investigated in the bubble regime, in particular when assisted by ionization injection. By utilizing linear and circular laser polarizations, we discover that circular polarization leads to a dramatic increase in the electron reproducibility rate and also increases the electron charge and beam divergence, while linear polarization yields higher electron peak energy and more stable beam pointing. Our experimental findings are also supported by three-dimensional particle-in-cell simulations. Our study highlights the potential of laser polarization as a simple and effective tool in controlling LWFA and electron-beam properties depending on applications.

Frost damage in porous materials is a weathering mechanism that can cause dangerous rockfalls or damage to built cultural heritage. The volume expansion of 9% when water freezes is usually seen as the cause of frost damage. This does not, however, explain why partially saturated porous stones also show damage despite the fact that ice should have room to grow. By performing experiments both at the scale of a single pore and in a real stone, we propose an explanation for the mechanism of frost damage at low water saturations: the meniscus at an air-water interface confines the water in the pores. Because of this confinement, ice that forms will exert a pressure on the pore walls rather than growing into the pore. The amplitude of stress is found to be larger in small pores and when the meniscus has a larger contact angle with the walls. The contact angle is also observed to increase in the case of multiple freeze-thaw cycles, which increases the likelihood of damage. We find that cracks start first in the ice (being weaker than the confining material), followed by damage in the material itself. Remarkably, when multiple air-water interfaces are induced within limestone samples through a hydrophobic surface treatment, the stones are much more susceptible to frost damage than are uncoated stones, with cracks appearing preferentially at the hydrophilic-hydrophobic interface. This shows that indeed the meniscus confining the water during freezing and consequently the wetting properties are the relevant factors for frost damage in partially saturated porous stones.

Chiral halide perovskites are being extensively studied due to their promising spintronic and optoelectronic properties, where the organic chiral ligands introduce chirality into halide perovskites. Right-handed and left-handed chiral materials are mirror images of one another and break the inversion symmetry, which produces ferroelectricity. In this work, we study the dielectric, piezoelectric, and ferroelectric properties of (R)-(−)-1-cyclohexylethylammonium)${\mathrm{Pb}\mathrm{I}}_3$ (R-CYHEA${\mathrm{Pb}\mathrm{I}}_3$), a chiral, one-dimensional perovskite. We performed and analyzed complex impedance spectroscopy; ac conductivity; and the complex electric modulus using the Maxwell-Wagner equivalent circuit model, the universal power law, the Havrilliak-Negami (HN) model, and the Kohlrausch-Williams-Watts (KWW) model to understand the transport and relaxation mechanism in the chiral R-CYHEA${\mathrm{Pb}\mathrm{I}}_3$ perovskite over wide temperature (313–473 K) and frequency (4 Hz–8 MHz) ranges. The dc conductivity is almost constant in the paraelectric-to-ferroelectric phase-transition region (PTR) but increases below and above this region. The activation energy of this region is very low, about 0.09 eV, while below the PTR, the activation energy is about 0.85 eV, and above the PTR, it is about 0.90 eV. We further note that the conduction mechanism changes from overlapped large polaron tunneling to correlated barrier hopping due to the ferroelectric-to-paraelectric phase transition. The activation energy derived from the relaxation time (using HN and KWW models) agrees with that obtained from the dc conductivity. In addition, we measured the saturation polarization of 0.01 µC/${\mathrm{cm}}^2$ at a 4-kV/cm applied electric field and a piezoelectric constant ($d_{33}$) of about 36 pm/V at the maximum applied bias voltage of 10 V. Finally, we fabricated a polyvinylidene fluoride and 3-wt % R-CYHEA${\mathrm{Pb}\mathrm{I}}_3$ chiral perovskite composite film for the development of high-performance energy-harvesting nanogenerators.

By combining the phenomena of voltage-controlled magnetic anisotropy (VCMA) and chiral resonant scattering of spin waves, we demonstrate through micromagnetic simulations that it is possible, by applying a dc voltage, to achieve tunable attenuation of spin waves propagating in an yttrium iron garnet (YIG) film. The resultant device, dubbed as an electrical chiral magnonic resonator (ECMR), provides a solution for implementing the synapse function in a spin-wave-based neuromorphic computational system, which demands that the weight factor be continuously changeable. The voltage-based mechanism ensures the advantages of minimal energy consumption and physical compactness when compared with other tuning strategies, such as a local Oersted field generated by passing current through electrical leads. On the other hand, by applying a rf voltage, it is possible to utilize the same ECMR device design to achieve parametric amplification of spin waves in the same YIG film. This provides a viable solution to apply the concept of voltage-based parametric amplification to YIG materials. An analytical model is developed to describe the scattering characteristics of the ECMR amplifier, which enable fast computation in the case of magnonic circuitry design involving a large number of amplifier devices.

We investigate the effect of coherence on the energy transfer between a donor and an acceptor molecule located on opposite sides of a ${\mathrm{Mo}\mathrm{S}}_2$ nanodisk. We study the energy-transfer efficiency by considering each molecule as a two-level quantum system using the Lindblad master equation, in the limits of fast (within nanoseconds) and slow (within microseconds) free-space relaxation. We incorporate the influence of the ${\mathrm{Mo}\mathrm{S}}_2$ nanodisk via the electromagnetic Green’s-function approach and take into account the donor dissipation and the acceptor charge-separation rate. We compare the energy-transfer efficiency with and without quantum coherence, for various separation distances and dipole orientations of the donor and acceptor. We find that the presence of the ${\mathrm{Mo}\mathrm{S}}_2$ nanodisk enhances the donor and acceptor relaxation rate, as well as the coherent and the incoherent coupling between them. We also find high energy-transfer efficiency between the donor and acceptor in the presence of strong coherence, primarily at a small separation distance from the ${\mathrm{Mo}\mathrm{S}}_2$ nanodisk. Additionally, we observe ultrafast energy transfer in the presence of coherence, which is largely enhanced in comparison to the incoherent coupling, when the donor and acceptor transition energies are off resonant to the excitonic ${\mathrm{Mo}\mathrm{S}}_2$ resonances. These results are important for nanotechnology applications; in particular, the design of novel light-harvesting devices.

The connectivity of self-assembled networks of nanowires and nanoparticles is believed to strongly influence their performance in brainlike (neuromorphic) computing applications. Here we present a new perspective on the connectivity of these networks in which their neuronlike active elements are viewed in the same way as the nodes in artificial and biological neuronal networks. We consider two-dimensional and quasi-three-dimensional networks of nanowires and percolating networks of nanoparticles and show that, from this new perspective, they all have similar small-world characteristics. Other characteristics which may impact the computational performance of the networks are also investigated, including their assortativity and the scalefree nature of the nanoparticle networks. Taken together, these results allow comparison of key network characteristics for a variety of self-assembled nanoscale networks, and provide a basis for detailed investigations of computational performance.

Unlocking the full potential of wavefront manipulation and particle trapping with high spatial precision requires a flexible approach to remotely trigger the desired ultrasonic wave with high central frequency. In this work, we propose a scheme for generating ultrasonic vortices beyond 3 MHz through optoacoustic conversion with the tailored logarithmic spiral absorbing surface. By illuminating the light-absorbing surface with an 8-ns pulsed laser, the laser-generated ultrasonic waves from each loop of the spirals will coherently interfere with each other near their symmetric axis of propagation, and the vortex is then produced, with the common features of a helical wavefront and central null pressure. The generated vortex field with different topological charges is scanned in three dimensions with high spatial resolution using a parabolic focusing detection system. The proposed scheme can produce the desired vortex field at above 3.5 MHz without resorting to elaborate fabrication techniques or distributed arrays, and therefore, has potential in various fields, ranging from particle manipulation to other biomedical applications.

Individually trapped Rydberg atoms show significant promise as a platform for scalable quantum simulation and for the development of programmable quantum computers. In particular, the Rydberg-blockade effect can be used to facilitate both fast qubit-qubit interactions and long coherence times via low-lying electronic states encoding the physical qubits. To bring existing Rydberg-atom-based platforms a step closer to fault-tolerant quantum computation, we demonstrate high-fidelity state and circuit preparation in a system of five atoms. We specifically show that quantum control can be used to reliably generate fully connected cluster states and to simulate the error-correction encoding circuit based on the “Perfect Quantum Error Correcting Code” by Laflamme et al. [Phys. Rev. Lett. 77, 198 (1996)]. Our results make these ideas and their implementation directly accessible to experiments and demonstrate a promising level of noise tolerance with respect to experimental errors. With this approach, we motivate the application of quantum control in small subsystems in combination with the standard gate-based quantum circuits for direct and high-fidelity implementation of few-qubit modules.

Fluorescent nanodiamonds (FNDs) have been exploited as sensitive quantum probes for nanoscale chemical and biological sensing applications, with the majority of demonstrations to date relying on the detection of single FNDs containing either single nitrogen vacancies or nitrogen-vacancy ensembles. This places significant limits on the measurement time, throughput and statistical significance of a measured result as there is usually marked inhomogeneity within FND samples. Here, we have developed a measurement platform that can report the $T_1$ spin relaxation time from a large ensemble of FNDs in solution. We first describe a refined sensing protocol for this modality and then use it to identify the optimal FND size for the detection of paramagnetic targets. Our approach is simple to set up, robust and can be used for rapid material characterization for a variety of in-situ quantum sensing applications.