An ideal third-order nonlinear optical material, which can efficiently absorb and refract light over a broad spectral range, is of both fundamental and technological significance as it enables many helpful functionalities in photonics. However, the optical nonlinearities are rather weak due to their perturbative nature and are limited to electronic resonances, thus restricting the response to a narrow spectral range. A charge-coupled donor-acceptor material pair can enhance the nonlinear optical response and circumvent the narrow spectral range limitation. However, such studies on potential material pairs remain largely unexplored. Here, we report the experimental observation of ultrafast third-order nonlinear optical response spanning the entire visible-to-near-infrared (400–900 nm) region in single-wall-carbon-nanotube (SWCNT)–${\mathrm{VSe}}_2$ nanohybrid in the strong coupling regime, enabled by efficient charge transfer. Compared to control systems, the measured nonlinear absorption and refraction of the nanohybrid show unprecedented or many-fold enhancements. Further, our density-functional theory and Bader-charge analysis show the strong electronic coupling of the nanohybrid in which the electrons are transferred from ${\mathrm{VSe}}_2$ to SWCNT, verified by steady-state and time-resolved photoluminescence measurements. The physics of the ultrafast nonlinear optical response is well captured by our five-level rate-equation model both qualitatively and quantitatively. Using the nanohybrid, we design a liquid cell-based optical limiter with an order of magnitude better device performance parameters, such as the optical limiting onset ($2.5–8.0\mathrm{mJ}{\mathrm{cm}}^{-2}$) and the differential transmittance ($0.42–0.62$), compared to several other benchmark optical limiters in the femtosecond regime.

We study permeability ($\mu$) variation of a lithographically prepared magnetic meta-atom consisting of $\mathrm{Ta}$/Py/$\mathrm{Pt}$ trilayers by means of spin-torque ferromagnetic resonance (ST FMR). With an injection of a direct current up to $\pm 20\mathrm{mA}$ together with an alternating current in GHz frequencies, the meta-atom under external magnetic fields shows significant changes in position and width of ST FMR signals due to a massive spin-current injection. This leads to the spin-current-driven $\mu$ variation, which is verified by analytical calculation based upon the experimentally obtained resonance field and Gilbert-damping parameter. The present study paves a way to time-varying spintronic metamaterials with a high modulation frequency for realizing microwave sources toward the post-fifth-generation mobile-communication system.

Due to the exaggerated properties of highly excited atomic states, a Rydberg-atom-based microwave receiver holds the promise to achieve superior performances in microwave metrology and communication when compared to conventional antennas. However, developing long-distance communication applications based on Rydberg atomic receiver remains challenging, because it requires the simultaneous achievement of low bit error rate (BER), high symbol rate, and weak carrier amplitude. The key to tackle this problem is to encode the information with a proper scheme that maintains high sensitivity and robustness of the Rydberg atomic receiver. Here, we use Rydberg atom-based heterodyne detection for the reception of phase-modulated microwave field, and demonstrate more than one order of magnitude improvement in reception sensitivity compared to the previously investigated amplitude-modulation scheme. Therefore, we achieve low BER communication with high symbol rate of 12 k bit/s and weak carrier amplitude of $13\text{μ}\mathrm{V}{\mathrm{cm}}^{-1}$ simultaneously. Furthermore, we also demonstrate that our scheme is compatible with frequency-division-multiplexing communication.

The strongly correlated material ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{Mn}\mathrm{O}}_3$ ($\mathrm{LSMO}$) exhibits metal-to-insulator and magnetic transition near room temperature. Although the physical properties of $\mathrm{LSMO}$ can be manipulated by strain, chemical doping, temperature, or magnetic field, they often require large external stimuli. To include additional flexibility and tunability, we developed a hybrid optoelectronic heterostructure that uses photocarrier injection from cadmium sulfide ($\mathrm{Cd}\mathrm{S}$) to an $\mathrm{LSMO}$ layer to change its electrical conductivity. $\mathrm{LSMO}$ exhibits no significant optical response; however, the $\mathrm{Cd}\mathrm{S}/\mathrm{LSMO}$ heterostructures show an enhanced conductivity, with a resistance drop of about 37%, at the transition temperature under light stimuli. This enhanced conductivity in response to light is comparable to the effect of a 9 T magnetic field in pure $\mathrm{LSMO}$. Surprisingly, the optical and magnetic responses of $\mathrm{Cd}\mathrm{S}/\mathrm{LSMO}$ heterostructures are decoupled and exhibit different effects when both stimuli are applied. This unexpected behavior shows that heterostructuring strongly correlated oxides may require a new understanding of the coupling of physical properties across the transitions and provide the means to implement new functionalities.

Nonadiabatic geometric quantum computation (NGQC) has attracted a lot of attention for noise-resilient quantum control. However, previous implementations of NGQC require long evolution paths that make them more vulnerable to incoherent errors than their dynamical counterparts. In this work, we experimentally realize a universal short-path nonadiabatic geometric gate set (SP NGQC) with a 2-times shorter evolution path on a superconducting quantum processor. Characterizing with both quantum process tomography and randomized benchmarking methods, we report an average single-qubit gate fidelity of $99.86\mathrm{\%}$ and a two-qubit gate fidelity of $97.9\mathrm{\%}$. Additionally, we demonstrate superior robustness of single-qubit SP NGQC gate to Rabi frequency error in some certain parameter space by comparing their performance to those of the dynamical gates and the former NGQC gates.

Tightly focusing cylindrical vector beams (CVBs) are widely used in diverse applications from particle trapping to high-resolution microscopy. Recently, planar metasurfaces have been proposed as promising alternatives to traditional bulky optical devices for tightly focused CVB generation. However, few metasurfaces allow the generation and independent phase control of different CVBs. In this paper, cascaded dual-channel transmissive metasurfaces that can be used to simultaneously generate different CVBs and independently control their phases are designed. The polarization and phase of the transmitted waves are controlled independently via only two geometric parameters. Under $x$- and $y$-polarized wave incidences, the radially polarized beam (RPB) and azimuthally polarized beam (APB) are generated by a first metasurface. In addition, a second metasurface is used to produce different focal fields in different focal planes under RPB and APB excitations. In such a proposed approach, the phase responses of the RPB and APB are distinct, which is significantly different from existing designs. A regular polygonlike focus and a lateral displacement of the focal spot are, respectively, realized in different focal planes at 7.8 GHz through different channels. Our approach improves the flexibility of focusing, allowing the generation of focal arrays at different locations within the same focal plane. Since the electromagnetic energy can be confined to a small specific zone in the microwave band, the proposed method can provide the basis for a number of important applications in the medical domain, such as the accurate hyperthermia treatment of large area tumors.

We realize a superconducting nanodevice in which vortex traps in the form of an aluminum square are integrated with a Dayem nanobridge. We perform field cooling of the traps arriving to different vortex configurations, dependent on the applied magnetic field, to demonstrate that the switching current of the bridge is highly sensitive to the presence and location of vortices in the trap. Our measurements exhibit unprecedented precision and ability to detect the first and successive vortex entries into all fabricated traps, from few hundred nm to $2\text{μ}\mathrm{m}$ in size. The experimental results are corroborated by Ginzburg-Landau simulations, which reveal the subtle yet crucial changes in the density of the superconducting condensate in the vicinity of the bridge with every additional vortex entry and relocation inside the trap. An ease of integration and simplicity make our design a convenient platform for studying dynamics of vortices in strongly confining geometries, involving a promise to manipulate vortex states electronically with simultaneous in situ control and monitoring.

Frequency interface, namely, converting the colors of photons while retaining their other features, is indispensable for numerous applications ranging from up-conversion imaging to the multimode quantum network. However, limited by the nonuniform nonlinear frequency-conversion efficiency, constructing the frequency interface for high-dimensional spatial modes is still challenging. Here, to break this fundamental barrier, we construct a high-dimensional (HD) orbital-angular-momentum (OAM) frequency interface via conducting sum-frequency generation between HD OAM states to be converted and a radial structured pump. Specifically, by replacing the conventional Gaussian pump with an optimized coherent superposition of HD Laguerre-Gaussian radial modes (i.e., its azimuthal number is zero), we experimentally achieve the OAM frequency interface in nine dimensions with a record fidelity up to 90.38 %. Additionally, by increasing the number of radial modes, our scheme can be flexibly extended to higher dimension. Such a high-dimensional frequency interface could find potential applications in the high-capacity free-space optical communication and would also pave the way for constructing high-dimensional quantum networks.

We report a combined theoretical and experimental study of the topological semimetal CrFeVGa with an emphasis on the role of atomic disorder on the magnetoelectronic properties. CrFeVGa belongs to the quaternary Heusler alloy family and crystallizes in the cubic structure with B2 disorder. It is found that the disorder plays a crucial role in quenching the magnetization (net moment $\sim 5\times {10}^{-2}{\mu }_B$ per formula unit) and other anomalies. Ac and dc magnetization data reveal the occurrence of Griffith’s-phase-like behavior in the presence of small magnetic clusters with a weak antiferromagnetic or ferrimagnetic ordering. A nonsaturating, linear positive magnetoresistance is observed even at 70 kOe, in a wide temperature range, which is attributed to the quantum linear magnetoresistance arising due to the zero- or small-gap band structure. Hall measurements show some anomalous behavior (including an anomalous Hall conductivity ${\sigma }_{xy0}=270\mathrm{S}{\mathrm{cm}}^{-1}$ and an anomalous Hall angle of 0.07 at 2 K) with a significant contribution from the semimetallic bands. Hall data analysis also reveals the presence of some non-negligible topological Hall contribution, which is significant at low temperatures. Ab initio calculations confirm the topological Weyl behavior of CrFeVGa, which originates from a unique combination of broken time-reversal symmetry and noncentrosymmetry. The nontrivial band topology stems from the $p$ and $d$ states of vanadium, which overlap near the Fermi level. The presence of multi-Weyl points (24 pairs) near the Fermi level causes a large Berry curvature and hence reasonably high anomalous Hall conductivity. The coexistence of so many emerging features in a single material is rather rare and thus opens up new avenues for future topological and spintronics-based research.

A wide variety of practical applications utilize three-dimensional (3D) hollow spots. To improve their performance, it is critical to independently control the transverse and longitudinal size of a 3D hollow spot. Here, we propose a method of creating a superoscillation 3D hollow spot by properly engineering the spatial polarization distribution. A cylindrical vector wave can be generated and the transverse and longitudinal sizes of the 3D hollow spot can be independently controlled by individually optimizing the wave fronts of the radial and azimuthal components in the cylindrical vector wave. A cylindrical vector metalens integrated with the functions of polarization conversion and wave-front manipulation is optimized and fabricated. The generated 3D hollow spot is experimentally demonstrated with a transverse size of (0.336 ± 0.005)λ and a longitudinal size of (1.170 ± 0.005)λ. Our method provides an easy and practical approach to generate a 3D hollow spot with a subwavelength transverse size, which can be intriguing for nanoparticle manipulation and in nanomicroscopy.

We demonstrate the ultimate sensitivity allowed by quantum physics in the estimation of the time delay between two photons by measuring their interference at a beam splitter through frequency-resolving sampling measurements. This sensitivity can be increased quadratically by decreasing the photonic temporal bandwidth even at values smaller than the time delay when standard two-photon interferometers become inoperable and without adapting the path of the reference photon, nor the need of time-resolving detectors with an unfeasible high resolution. Applications can range from the more feasible imaging of nanostructures, including biological samples, and nanomaterial surfaces to quantum enhanced estimation based on frequency-resolved boson sampling in optical networks.

We address the scaling-up problem for superconducting quantum circuits by using lumped-element resonators based on an alternative fabrication method of aluminum-aluminum oxide-aluminum (Al-${\mathrm{AlO}}_x$-Al) parallel-plate capacitors. The size of the resonators is only $0.04{\mathrm{mm}}^2$, which is more than one order smaller than the typical size of coplanar resonators ($1{\mathrm{mm}}^2$). The fabrication method we develop easily fits into the standard superconducting qubit fabrication process. We obtain capacitance per area $14\mathrm{fF}/\text{μ}{\mathrm{m}}^2$ and the internal quality factor $1\times {10}^3$–$8\times {10}^3$ at the single-photon level. Our results show that such devices based on Al-${\mathrm{AlO}}_x$-Al capacitors could be further applied to the qubit readout scheme, including resonators, filters, amplifiers, as well as microwave metamaterials and innovative types of qubits, such as $0-\pi$ qubit.

Restricted by pulse dispersion, dephasing, and bunch deflection, it has been a challenging task to realize high-gain particle acceleration and bunch focusing by using an ultrashort-pulse laser to drive an integrable acceleration structure, which is necessary to develop an on-chip particle accelerator for practical applications. Here we propose a laser-driven traveling-wave linac (linear accelerator), which uses the cascade reflection and refraction of an ultrashort laser pulse on a microscale dielectric structure to achieve long-range laser-particle interaction, avoiding waveguide dispersion, and enhancing sustainable acceleration gradient. It is scalable and extensible, and can realize full-course particle acceleration by using a single laser source via the inverse Cherenkov effect. With this accelerator scheme, we further propose a dynamic synchronization and focusing method, which not only counteracts dephasing but also restrains the bunch spread and deflection caused by space-charge and emittance effects, realizing stable bunch transport and acceleration in a tiny-size bunch channel without resorting to the need for external focusing equipment. This accelerator scheme paves the way toward a high-efficiency laser-driven all-dielectric on-chip particle accelerator for practical applications.

Alternatively to the full reconstruction of an unknown quantum process, the so-called selective and efficient quantum process tomography (SEQPT) allows estimating, individually and up to the required accuracy, a given element of the matrix that describes such an operation with a polynomial amount of resources. The implementation of this protocol has been carried out with success to characterize the evolution of a quantum system that is well described by a trace-preserving quantum map. Here, we deal with a more general type of quantum process that does not preserve the trace of the input quantum state, which naturally arises in the presence of imperfect devices and system-environment interactions, in the context of quantum information science or quantum dynamics control. In that case, we show with the aid of a priori information on the losses structure of the quantum channel that the SEQPT reconstruction can be adapted to reconstruct the non-trace-preserving map. We explicitly describe how to implement the reconstruction in an arbitrary Hilbert space of finite dimension $d$. The method is experimentally verified on a superconducting quantum processor provided by IBM Quantum services, by estimating several non-trace-preserving quantum processes in dimensions up to $d=6$. Our results show that it is possible to efficiently reconstruct non-trace-preserving processes, with high precision, and with significantly higher fidelity than when the process is assumed to be trace preserving.

The rotational Doppler effect (RDE) is of fundamental importance in the detection of rotating systems, ranging from molecules to macroscopic bodies. Metasurfaces, which are potential substitutes for traditional optical devices, have been reported to induce a RDE. However, the mechanism of the interaction between an electromagnetic wave and a spinning artificial meta-atom is not yet fully understood. Here, we report a multiple RDE based on a time-varying generalized Pancharatnam-Berry phase, obtained from a single spinning meta-atom placed in a rectangular waveguide. Twofold and sixfold rotational Doppler shifts with respect to the rotational velocity are obtained from meta-atoms with C2 and C3 rotational symmetry, respectively. In contrast to full-size devices, a single meta-atom has minimal rotational inertia and size, enabling its application in integrated systems. This work represents the interaction of an electromagnetic wave with a single spinning meta-atom, which may have potential applications in rotation-detection systems, frequency-gradient metasurfaces, and frequency modulators.

Spoof-surface-plasmon polaritons (SSPPs) supported by artificial microwave metawaveguides can mimic other properties of optical-surface-plasmon polaritons (SPPs) and have the potential to build the next generation of circuits and systems. However, the traditional model of SSPP metawaveguides take only physical characters of electrical length and characteristic impedance into consideration and thus can hardly guide the design of integrated SSPP systems efficiently. In this work, a modified model of SSPP metawaveguide is proposed to realize multicharacteristic optimization design of integrated SSPP systems. To validate the modified model, a SSPP-based frequency-shifting keying (FSK) modulation and demodulation system is realized. In comparison to microstrips and SSPP metawaveguides based on the traditional model, the SSPP metawaveguides based on the modified model bring lower discontinuity, lower coupling, and lower system complexity to the FSK modulation and demodulation system, which improves the quality of demodulated signals significantly. Hence, exploring physical characteristics of SSPP metawaveguides by introducing modified models is an effective route to realize outstanding integrated SSPP systems.

This paper presents a compact low-temperature atomic vector magnetometer for weak-field measurements, using an atomic cell containing two orthogonal multipass cavities. At the working temperature of $75{}^{\circ }\mathrm{C}$, the magnetic field sensitivities at all three axes are better than $45\mathrm{fT}{\mathrm{Hz}}^{-1/2}$ at 10 Hz limited by photon noise, and $85\mathrm{fT}{\mathrm{Hz}}^{-1/2}$ at 0.1 Hz. This sensor also shows measurement stabilities better than 1.5 pT at three axes for an integration time of ${10}^4\mathrm{s}$, even with the laser frequency unlocked. The sensor response to a rotation is demonstrated, which is also developed to measure the effective gyromagnetic ratio of atoms in this sensor when the bias field is nulled. This magnetometer makes an important step towards long-term stable measurements and calibrations of ultralow fields.