Quantum computation has demonstrated advantages over classical computation for special hard problems, where a set of universal quantum gates is essential. Geometric phases, which have built-in resilience to local noise, have been used to construct quantum gates with excellent performance. However, this advantage has been smeared in previous schemes. Here, we propose a state-independent nonadiabatic geometric quantum-gate scheme that is able to realize a more fully geometric gate than previous approaches, allowing for the cancelation of dynamical phases accumulated by an arbitrary state. Numerical simulations demonstrate that our scheme has significantly stronger gate robustness than the previous geometric and dynamical ones. Meanwhile, we give a detailed physical implementation of our scheme with the Rydberg atom system based on the Rydberg blockade effect, specifically for multiqubit control-phase gates, which exceeds the fault-tolerance threshold of multiqubit quantum gates within the considered error range. Therefore, our scheme provides a promising way for fault-tolerant quantum computation in atomic systems.

The presence of ferroelectric domain walls (DWs) can generate an above-band-gap photovoltage of a ferroelectric photovoltaic device, which is the anomalous photovoltaic (APV) effect, and its mechanism is still under debate. Here, the effective electric field and the local bulk photovoltaic (BPV) component at 71° DWs are reported by quantitatively analyzing the light polarization angle-dependent photovoltaic effect of nonperiodic DWs and periodic stripe DWs in ${\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_3$ films. The photovoltaic measurement under white light illumination directly reveals a significantly enhanced electric field at stripe DWs in comparison with the domains. The BPV effect at stripe DWs is about 25 times as large as that of the domains. Furthermore, the defect states at the DWs may recombine the photogenerated carriers and drastically weaken the electric field of the DWs, whereas they negligibly mitigate the BPV effect. This work offers a deeper insight into the mechanism of the APV effect at ferroelectric DWs.

It has been recently reported that elastic waves induced by nanosecond light pulses can be used to drive nanomotion of micro-objects on frictional solid interfaces, a challenging task for traditional techniques using tiny optical force. In this technique, the main physical quantities and parameters involved are temporal width and energy of light pulses, thermal heating and cooling time, friction force, and elastic waves. Despite a few experimental observations based on microfiber systems, a microscopic theory, which reveals how these quantities collaboratively enable motion of the micro-objects and derives what the underlying manipulation principles emerge, is absent. In this paper, a comprehensive theoretical analysis—centralized around the above listed physical quantities, and illuminated by a single-friction-point model in conjunction with numerical simulations—is established to pedagogically clarify the physics. Our results reveal the two essential factors in this technique: (1) the use of short light pulses for rapid thermal expansion overwhelming friction resistance and (2) the timescale asymmetry in thermal heating and cooling for accumulating a net sliding distance. Moreover, we examine the effects of spatially distributed friction beyond the single-friction-point consideration, and show “tug-of-war”-like friction stretching in the driving process. Given these insights, we positively predict that this elastic-wave-based manipulation principle could be directly translated to micro- and nanoscale optical waveguides on optical chips, and propose a practical design. We wish that these results offer theoretical guidelines for ongoing efforts of optical manipulation on solid interfaces with light-induced elastic waves.

Graphitic carbon nitride ($g$-${\mathrm{C}}_3{\mathrm{N}}_4$) shows favorable performance as a photocatalyst and has attracted widespread attention in recent years. As its wide band gap of 2.70 eV limits light absorption in the visible range, many efforts have been made to optimize the band gap. In this report, pressure is used to engineer the band gap and photoelectric response of nitrogen-deficient $g$-${\mathrm{C}}_3{\mathrm{N}}_4$ nanoflakes. The band gap of the sample is first narrowed to 2.40 eV due to the introduction of nitrogen vacancies and then further narrowed to 1.70 eV by pressure, which is the lowest value reported in the literature for undoped $g$-${\mathrm{C}}_3{\mathrm{N}}_4$. Accordingly, the photoelectric response increases by nearly 50% because of the enhanced light absorption at high pressure. More interestingly, after depressurization to ambient pressure, the optimized band gap survives with a minimum value of 1.87 eV accompanied by enhanced photoelectric responsivity. In situ synchrotron x-ray diffraction and Raman spectra suggest that the tunable band gap originates from irreversible pressure-induced amorphization with the assistance of vacancies for $g$-${\mathrm{C}}_3{\mathrm{N}}_4$. The collaborative approach of introducing deficiency and pressure treatment adopted here shows the ability to engineer the band gap continuously over a prominently wider region than that for the single band-gap-narrowing technique, and thus, enhances the photoelectric performance for broadened semiconductors.

The variational quantum eigensolver (VQE) is a hybrid quantum classical algorithm designed for current and near-term quantum devices. Despite its initial success, there is a lack of understanding involving several of its key aspects. There are problems with VQE that forbid a favorable scaling towards quantum advantage. In order to alleviate the problems, we propose and extensively test a quantum annealing inspired heuristic that supplements VQE. The improved VQE enables an efficient initial state-preparation mechanism, in a recursive manner, for a quasidynamical unitary evolution. We conduct an in-depth scaling analysis of finding the ground-state energies with increasing lattice sizes of the Heisenberg model, employing simulations of up to 40 qubits that manipulate the complete state vector. In addition to systematically finding the ground-state energy, we observe that it avoids barren plateaus, escapes local minima, and works with low-depth circuits. For the current devices, we further propose a benchmarking toolkit using a mean-field model and test it on IBM Q devices. Realistic gate execution times estimate a longer computational time to complete the same computation on a fully functional error-free quantum computer than on a quantum computer emulator implemented on a classical computer. However, our proposal can be expected to help accurate estimations of the ground-state energies beyond 50 qubits when the complete state vector can no longer be stored on a classical computer, thus enabling quantum advantage.

Coherent coupling in magnon-based hybrid systems has many potential applications in quantum information processing. Magnons can propagate in magnetically ordered materials without any motion of electrons, offering a unique method to build low-power-consumption devices and information channels free of heat dissipation. In this paper, we demonstrate the coherent propagation of hybridized modes between spin waves and Love surface acoustic waves in a multiferroic ${\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_3$ and ferromagnetic ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{Mn}\mathrm{O}}_3$-based heterostructure. The magnetoelastic coupling enables a giant enhancement of the strength of the hybridized mode by a factor of 26 compared to that of the pure spin waves. A short wavelength down to 250 nm is demonstrated for the hybridized mode, which is desirable for nanoscale acoustomagnonic applications. Our combined experimental and theoretical analyses represent a step towards the coherent control in hybrid magnonics, which may inspire the study of magnon-phonon hybrid systems for coherent information processing and manipulation.

We present a hybrid quantum system composed of a magnetic vortex and a nanomechanical resonator. We show that the gyrotropic mode of the vortex can coherently couple to the quantized mechanical motion of the resonator through magnetic interaction. Benefiting from the topologically protected properties and the low damping of vortices, as well as the excellent coherent features of nanomechanical resonators, the proposed system can achieve strong coupling and even the ultrastrong-coupling regime by choosing appropriate parameters. In combination with other quantum systems, such as a nitrogen-vacancy (N-V) center, coherent state transfer between the vortex excitation and the spin can be realized. This setup provides a potential platform for quantum information processing and investigations into the ultrastrong-coupling regime and macroscopic quantum physics.

We study the twist-induced control of the near-field radiative heat transfer between two hyperbolic antiferromagnetic insulators under external magnetic fields. We show that the near-field heat flux can be affected by both the twist angle $\theta$ and the magnitude of the applied magnetic field with different broken symmetries. Irrespective of the twist angle, the external magnetic field causes the radiative heat flux to change nonmonotonically, and the minimum heat flux can be found with magnetic fields of approximately 1.5 T. Such nonmonotonic behavior is because the magnetic field can radically change the nature of the magnon polaritons with time-reversal symmetry breaking. The field not only affects the topological structure of surface magnon polaritons but also induces volume magnon polaritons that progressively dominate the heat transfer as the field increases. We further propose a twist-induced thermal switch device with inversion symmetry breaking, which can strongly regulate radiative heat flux through different magnetic fields. Our findings account for a characteristic modulation of radiative heat transfer with implications for applications in efficient thermal management.

We introduce a simple widely applicable formalism for designing “error-divisible” two-qubit gates: a quantum gate set where fractional rotations have proportionally reduced error compared to the full entangling gate. In current noisy intermediate-scale quantum (NISQ) algorithms, performance is largely constrained by error proliferation at high circuit depths, of which two-qubit gate error is generally the dominant contribution. Further, in many hardware implementations, arbitrary two-qubit rotations must be composed from multiple two-qubit stock gates, further increasing error. This work introduces a set of criteria, and example wave forms and protocols to satisfy them, using superconducting qubits with tunable couplers for constructing continuous gate sets with significantly reduced leakage and dynamic $ZZ$ errors for small-angle rotations. If implemented at scale, NISQ-algorithm performance could be significantly improved by our error-divisible gate protocols.

The ability to control and modify infrared excitations in condensed matter is of both fundamental and applied interest. Here we explore a system supporting low-energy excitations, in particular, mid-infrared localized plasmon modes and phonon polaritons that are tuned to be strongly coupled. We study the coupled modes by using far-field infrared spectroscopy, state-of-the-art monochromated electron energy-loss spectroscopy, numerical simulations, and analytical modeling. We demonstrate that the electron probe facilitates a precise characterization of polaritons constituting the coupled system, and enables an active control over the coupling and the resulting sample response both in frequency and space. Although far-field optical spectra can be substantially different from near-field electron energy-loss spectra, we show that a direct comparison is possible via postprocessing and right positioning of the electron beam. The resulting spectra allow us to evaluate the key parameters of the coupled system, such as the coupling strength, which we demonstrate to be probe independent. Our work establishes a rigorous description of the spectral features observed in light- and localized electron-based spectroscopies, which can be extended to the analysis of analogous optical systems with applications in heat management and electromagnetic field concentration or nanofocusing.

We study using three-dimensional kinetic Monte Carlo (KMC) simulations to what extent the formation of Schottky contacts between a metal electrode and a molecularly doped disordered organic semiconductor can be understood from the theory for crystalline inorganic semiconductors, adapted to include the effects of the localized nature of the states in which the charge carriers reside and the hopping transport in between these states. The thickness of the Schottky-contact depletion region is found to be significantly smaller than as expected when the energetical disorder is neglected. The presence of energetic disorder is also found to influence the voltage dependence of the width of the depletion regions near the contacts of single-layer double-Schottky-contact devices. The voltage drop over the two depletion regions and the remaining charge-neutral bulk layer is shown to be described successfully by a semianalytical model, based on an accurately parameterized bulk mobility function of the dopant concentration, energetic disorder, and the electric field. We furthermore find that the mobility in the depletion regions is drastically reduced. As a result, the depletion-region formation process can be ultraslow, with a characteristic time scale ranging from microseconds to beyond milliseconds.

High-precision and wide-band microthrust testing and evaluation on the ground is key to achieving precision, drag-free control, which is extremely demanding for spaceborne gravitational-wave detection missions. However, unlike a stable space environment, complex ground vibrations inevitably affect the evaluation of microthrust. To reduce the interference of ground vibrations, this paper proposes a suppression solution based on a hanging pendulum with an adjustable mass center. The theoretical analysis shows that the response of the pendulum to ground vibration can be effectively reduced with a matched mass center. The dual-frequency modulation experiment verified the linear relationship between vibration noise and mass-center-to-swing-point distance. By setting the mass-center distance from the swing point to 0.2 mm, the noise of the sub-micro-Newton balance is better than $0.1\text{μ}\mathrm{N}{\mathrm{Hz}}^{-1/2}$ from 6 mHz to 20 Hz. This method effectively suppresses the interference of ground vibration, which helps us to obtain an accurate microthrust model for space gravitational-wave missions, while providing a solution for weak-force, ground testing over wide-band frequencies.

We have developed a method of determining the effective mass of charge carriers in a two-dimensional electron system (2DES) based on the phase analysis of the radiation transmitted through the 2DES. This measurement technique is demonstrated in the experiments with a high-quality 2DES in $\mathrm{In}\mathrm{As}$/$\mathrm{Al}\mathrm{Sb}$ and $\mathrm{Ga}\mathrm{As}$/$(\mathrm{Al},\mathrm{Ga})\mathrm{As}$ heterostructures. Furthermore, we find that the proposed approach gives compatible results with the cyclotron resonance spectroscopy method.

Surface acoustic waves at frequencies beyond a few GHz are promising components for quantum technology applications. Applying scanning x-ray diffraction microscopy we directly map with a high lateral spatial resolution the complete strain field generated near the $\mathrm{Ga}\mathrm{As}$ surface by a standing surface acoustic wave with wavelength $\lambda \simeq 500$ nm corresponding to frequencies near 6 GHz. We find that the lattice distortions perpendicular to the surface are phase shifted compared to those in propagation direction. Model calculations based on Rayleigh waves confirm our measurements. Our results represent a break through in providing a full characterization of a radio-frequency surface acoustic wave beyond plain imaging.

Recently synthesized two-dimensional (2D) van der Waals (vdW) ferromagnets, ${\mathrm{Fe}}_x{\mathrm{Ge}\mathrm{Te}}_2$ (x = 4 and 5), have attracted great attention due to their room-temperature Curie temperature. By using ab initio noncollinear-spin quantum transport simulations, we predict a monotonic increasing tendency of the tunneling magnetoresistance (TMR) with increasing θ (the angle between the spins of the two electrodes) in ${\mathrm{Fe}}_x{\mathrm{Ge}\mathrm{Te}}_2$/graphene/${\mathrm{Fe}}_x{\mathrm{Ge}\mathrm{Te}}_2$ vdW magnetic tunnel junctions (MTJs). The calculated maximal TMR of the two MTJs is up to 7000% and 1100% for x = 4 and 5, respectively, and the former is even nearly 6 times larger than that of the commonly used $\mathrm{Mg}\mathrm{O}$-based MTJ (1000% at 5 K) owing to nearly perfect spin polarization. The calculated maximal spin-transfer torque per voltage is 1–2 orders of magnitude larger than that of the $\mathrm{Mg}\mathrm{O}$-based one, resulting in a reduction in the critical current for magnetization reversal by a factor of 4–5. Such high-performance 2D ${\mathrm{Fe}}_x{\mathrm{Ge}\mathrm{Te}}_2$-based (x = 4 and 5) MTJs are promising for next-generation room-temperature nonvolatile memories.

This paper mainly studies the problem of metasurfaces between different mediums. Despite recent advances on metasurfaces, there has been a critical limitation that wave manipulation between two different mediums is theoretically impossible with general approaches since full transmission and desired phase shift cannot be achieved simultaneously. In order to get over this theoretical issue, we propose an asymmetric metasurface that can manipulate waves between two different mediums. By introducing the asymmetry, achieving both full transmission and desired phase shift simultaneously is theoretically enabled. From theoretical approaches, an actual continuum metasurface is designed and applied to various wave manipulations between two different mediums. We expect that the proposed metasurface can be applied to various applications in the area of ultrasonics and vibrations.

True random number generators are of great interest in many computing applications, such as cryptography, neuromorphic systems, and Monte Carlo simulations. Here, we investigate perpendicular magnetic-tunnel-junction nanopillars (pMTJs) activated by short-duration (nanosecond) pulses in the ballistic limit for such applications. In this limit, a pulse can transform the Boltzmann distribution of initial free-layer magnetization states into randomly magnetized down or up states, i.e., a bit that is 0 or 1, easily determined by measurement of the tunnel resistance of the junction. It is demonstrated that bit streams with millions of events: (1) are very well approximated by a normal distribution; (2) pass multiple statistical tests for true randomness, including all the National Institute of Standards and Technology tests for random number generators with only one xor operation; (3) can be used to create a uniform distribution of 8-bit random numbers; and (4) can have no drift in the bit probability with time. The results presented here show that pMTJs operated in the ballistic regime can generate true random numbers at around 50-MHz bit rates, while being more robust to environmental changes, such as their operating temperature, compared to other stochastic nanomagnetic devices.

$L{1}_0$-phase $\mathrm{Fe}\mathrm{Pt}$ is well known for its unusually robust perpendicular magnetic anisotropy (PMA) properties arising from strong conduction-electron spin-orbit coupling (SOC) with the $\mathrm{Fe}$ orbital moment. The strong PMA enables stable magnetic storage and memory devices with ultrahigh capacity. Meanwhile, SOC is also the premise of the recently discovered spin-orbit-torque (SOT) effect, which opens avenues for possible electrical manipulation of magnetization for $L{1}_0$-$\mathrm{Fe}\mathrm{Pt}$. The bulk SOT of the $L{1}_0$-$\mathrm{Fe}\mathrm{Pt}$ single layer was discovered recently; this leads to the magnetization of $L{1}_0$-$\mathrm{Fe}\mathrm{Pt}$ reversibly switching on itself. However, deterministic SOT switching of bulk perpendicularly magnetized $\mathrm{Fe}\mathrm{Pt}$ magnets relies on an external magnetic field to break the symmetry. Here, the symmetry-breaking issue is resolved by interlayer exchange coupling, where the $\mathrm{Fe}\mathrm{Pt}$ layer is coupled with an in-plane magnetized $\mathrm{Ni}\mathrm{Fe}$ layer through a $\mathrm{Ti}\mathrm{N}$ spacer layer. Furthermore, our device also presents memristive or gradual switching behaviors, even without an external field, offering the potential for constructing spin synapses and spin neurons for neuromorphic computing. An artificial neural network with high accuracy (∼91.17%) is realized based on the constructed synapses and neurons. Our work paves the way for field-free SOT switching of single bulk PMA magnets and their potential applications in neuromorphic computing.

We report on the observation of large and tunable perpendicular magnetic anisotropy (PMA) in $\mathrm{Co}$-based ferromagnetic (FM) films induced by an antiferromagnetic (AFM) $\delta \text{−}\mathrm{Mn}$ layer. The perpendicular anisotropic energy of the bilayers can be manipulated by varying the thickness of the $\delta \text{−}\mathrm{Mn}$ layer and the maximum reaches 2.41 × ${10}^7$ erg/cm${}^3$. The coercivity of bilayers is also effectively regulated over a broad range from 0.02 to 7.09 T. We demonstrate that this large PMA originates from strong interfacial exchange coupling and the AFM anisotropic energy. In addition, the antisymmetric longitudinal magnetoresistance occurs in the bilayers in the absence of asymmetric geometry or magnetic field. These results enrich our understanding of AFM-induced large PMA in an AFM/FM bilayer system and provide a promising bilayer structure for exploring high-density magnetic memory devices.