The ability to perform entangling operations in parallel with a low error is essential for a large-scale fault-tolerant quantum computer. However, for trapped-ion systems, it is a challenging task due to the crosstalk resulting from the collective motional modes. Here, we develop a highly paralleled quantum circuit demonstrating a logical qubit based on the Steane code and study the impact of the crosstalk error on the performance of the fault-tolerant protocol. We show that the crosstalk indeed greatly destroys the fault-tolerant property of the quantum error correction. To achieve the break-even point with encoded qubits, we identify the suppression requirement of the crosstalk error to be less than ${10}^{-6}$ for the Steane code. Furthermore, to mitigate the crosstalk below the fault-tolerant threshold, we propose a highly efficient optimization scheme by utilizing the programmable optical tweezer array. Overall, we make an elegant combination of the pulse-control optimization of parallel gate operations with the fault-tolerant protocol on the error-protected universal quantum computer.

In the presence of physical noise of all platforms for quantum computation, quantum error correction (QEC) becomes a critical way to realize quantum algorithms with large quantum volumes. In order to understand the influence of quantum noise on QEC codes and further improve the performance of logical circuits, the noises should be accurately analyzed with proper models. Here we focus on the trapped-ion system. Fundamentally, we start from the laser pulses of the quantum gates in the circuits and extract the noise components from the complete evolution of the quantum states, beyond the standard depolarizing model and other simplified models. Our simulations indicate that the logical performance under real noises is significantly better than that predicted by previous models. Meanwhile, the advantage of QEC is shown in the levels of one, two, and more logical qubits. Moreover, we can increase the logical fidelity by the method of ion mapping, which is based on knowledge of the specific noise distribution of different ions. Some powerful evidence from the numerical results demonstrates the possibility to access fault-tolerant quantum computation with the trapped-ion system.

This paper proposes an optimized quantum block-$ZXZ$ decomposition method that results in more optimal quantum circuits than the quantum Shannon decomposition, which was presented in 2005 by M. Möttönen, and J. J. Vartiainen [in Trends in quantum computing research, edited by S. Shannon (Nova Science Publishers, 2006) Chap. 7, p. 149, arXiv:quant-ph/0504100]. The decomposition is applied recursively to generic quantum gates, and can take advantage of existing and future small-circuit optimizations. Because our method uses only single-qubit gates and uniformly controlled rotation-Z gates, it can easily be adapted to use other types of multi-qubit gates. With the proposed decomposition, a general three-qubit gate can be decomposed using 19 cnot gates (rather than 20). For general $n$-qubit gates, the proposed decomposition generates circuits that have $\frac{22}{48}{4}^n-\frac{3}{2}{2}^n+\frac{5}{3}$ cnot gates, which is less than the best-known exact decomposition algorithm by $(4^{n-2}-1)/3$ cnot gates.

Hot-carrier solar cells offer potential for enhancing the energy-conversion efficiency of photovoltaic devices. Transport properties of such systems remain largely unexplored but could hinder their efficiency. In this work, we develop a suitable framework for describing the thermoelectric ambipolar transport of photogenerated hot carriers and derive analytical expressions for the ambipolar transport coefficients that are valid even in the degenerate case. We demonstrate that these transport coefficients can be measured from hyperspectral photoluminescence imaging. We validate this experimental determination by showing its consistency with the Boltzmann transport equation in the relaxation-time approximation.

Magnetic insulators, such as yttrium iron garnets (YIGs), are important for spin-wave or magnonic devices as their low damping enables low-power dissipation. Magnetic insulator heterostructures can offer larger design space for realizing exotic magnonic quantum states, provided that individual layers have low damping and their exchange coupling is strong and engineerable. Here, we show that, in a high-quality all-insulator thulium iron garnet (TmIG)/YIG bilayer system, TmIG exhibits an ultralow dissipation rate thanks to its low-damping, low-saturation magnetization and strong orbital momentum. The low dissipation rates in both YIG and TmIG, along with their significant coupling strength due to interfacial exchange coupling, enable strong and coherent magnon-magnon coupling. The coupling strength can be tuned by varying the magnetic insulator layer thickness and magnon modes, which is consistent with analytical calculations and micromagnetic simulations. Our results demonstrate TmIG/YIG as a novel platform for investigating hybrid magnonic phenomena and open opportunities for magnon devices comprising all-insulator heterostructures.

Tuning thermal transport in nanostructures is essential for many applications, such as thermal management and thermoelectrics. Nanophononic metamaterials (NPMs) have shown great potential for reducing thermal conductivity. In this work, the thermal conductivity of NPMs with crystalline $\mathrm{Si}$ ($c$-$\mathrm{Si}$) pillar, crystalline $\mathrm{Ge}$ ($c$-$\mathrm{Ge}$) pillar, and amorphous $\mathrm{Si}$ ($a$-$\mathrm{Si}$) pillar are systematically investigated by a molecular dynamics method. An analysis of phonon dispersion and spectral energy density shows that phonon dispersions of a $\mathrm{Si}$ membrane are flattened due to local resonant hybridization induced by both crystalline and amorphous pillars. In addition, an $a$-$\mathrm{Si}$ pillar can cause a larger reduction in thermal conductivity compared with a $c$-$\mathrm{Si}$ pillar. Specifically, when the atomic mass of the atoms in the pillars increases, the thermal conductivity of NPMs with a crystalline pillar increases because of the weakened phonon hybridization. However, the thermal conductivity of NPMs with an amorphous pillar is almost unchanged. The analyses of the reduction of thermal conductivity show that both resonant hybridization and scattering mechanisms are important in NPMs with a crystalline pillar, while the scattering mechanism dominates in NPMs with an amorphous pillar and NPMs with a short crystalline pillar. The results of this work can provide meaningful insights into controlling thermal transport in NPMs by choosing the materials and atomic mass of pillars for specific applications.

We present a target-field approach to analytically design magnetic fields using permanent magnets. We assume that their magnetization is bound to a two-dimensional surface and is composed of a complete basis of surface modes. By posing the Poisson’s equation relating the magnetic scalar potential to the magnetization using Green’s functions, we derive simple integrals that determine the magnetic field generated by each mode. This approach is demonstrated by deriving the governing integrals for optimizing axial magnetization on cylindrical and circular-planar surfaces. We approximate the governing integrals numerically and implement them into a regularized least-squares optimization routine to design permanent magnets that generate uniform axial and transverse target magnetic fields. The resulting uniform axial magnetic field profiles demonstrate more than a tenfold increase in uniformity across equivalent target regions compared to the field generated by an optimally separated axially magnetized pair of rings, as validated using finite element method simulations. We use a simple example to examine how two-dimensional surface magnetization profiles can be emulated using thin three-dimensional volumes and determine how many discrete intervals are required to accurately approximate a continuously varying surface pattern. Magnets designed using our approach may enable higher-quality bias fields for electric machines, nuclear fusion, fundamental physics, magnetic trapping, and beyond.

We derive from first principles a general circuit model for open, frequency dispersive electromagnetic resonators in the full-wave regime. This model extends the concepts of radiation impedance to the polarization current-density modes induced in open resonators by an arbitrary external excitation. Its physics-based elements offer physical insights into the scattering problem and enable efficient modeling of the resonance frequency and associated bandwidth for arbitrary scattering resonances, establishing a powerful platform for the design and optimization of nanophotonic circuits. Our findings offer compelling prospects for electromagnetic scattering and ultrafast nanophotonics, streamlining the analysis and design of nanoresonators with enhanced operational speeds, and outlining a physics-based model of their temporal dynamics.

Exploring two-dimensional (2D) narrow-gap materials with exceptional stability and outstanding photoelectric performance has become a key focus in nano-optoelectronics. However, most existing 2D materials contain relatively large band gaps, and those with narrow band gaps tend to have inadequate stability. This study employed first-principles calculation to predict three alternative narrow-gap 2D binary group (${\mathrm{II}}_3$-${\mathrm{V}}_2$) materials in the $P\overline{3}m1$ space group: ${\mathrm{Ca}}_3{\mathrm{N}}_2$, ${\mathrm{Ba}}_3{\mathrm{P}}_2$, and ${\mathrm{Ba}}_3{\mathrm{As}}_2$. All these materials exhibit excellent energetic, mechanical, dynamic, and thermal stability. Their mechanical properties reveal isotropic characteristics and demonstrate excellent in-plane stiffness and flexibility. Regarding electronic properties, monolayer ${\mathrm{Ca}}_3{\mathrm{N}}_2$, ${\mathrm{Ba}}_3{\mathrm{P}}_2$, and ${\mathrm{Ba}}_3{\mathrm{As}}_2$ possess indirect narrow band gaps of $0.41$, $0.61$, and $0.68$ eV, respectively. Moreover, they exhibit high electron mobilities (about ${10}^3$–${10}^4{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$) and are nearly isotropic. In terms of optical properties, they demonstrate a significantly broad absorption range, spanning from the IR to visible and UV regions, with remarkably high absorption coefficients (approximately ${10}^4$–${10}^5{\mathrm{cm}}^{-1}$). Additionally, their exciton binding energies are higher than those observed in traditional bulk materials while lower than most other 2D materials, facilitating excellent light-driven performance. We propose that these alternative 2D $P\overline{3}m1{\mathrm{Ca}}_3{\mathrm{N}}_2$, ${\mathrm{Ba}}_3{\mathrm{P}}_2$, and ${\mathrm{Ba}}_3{\mathrm{As}}_2$ binary narrow-gap semiconductors will hold promising application prospects in nano-optoelectronic fields such as IR light detection, ambipolar transistors, medical imaging, electrodes, optical communication, and remote sensing.

We investigate evaporative electron cooling in cascading semiconductor double-quantum-well (QW) structures. In this cascading double QW structure (QW1 and QW2, where QW2 is on the anode side), one electron absorbs two longitudinal optical (LO) phonons as it travels from the cathode to the anode, for which efficient thermionic cooling is expected. By analyzing the high-energy tail of the photoluminescence spectra, the electron temperature in each QW is determined. When ${\mathrm{Al}}_{0.35}{\mathrm{Ga}}_{0.65}\mathrm{As}$ barriers are used, anomalous electron heating in QW2 due to hot electron distribution above the barrier is observed. By introducing taller barriers (${\mathrm{Al}}_{0.7}{\mathrm{Ga}}_{0.3}\mathrm{As}$) before QW2 to suppress hot electron distribution above the barrier, electron cooling in both QWs by several tens of kelvins is achieved. Furthermore, oscillatory anticorrelated electron temperature change in the two QWs that results from LO-phonon scattering is observed.

Cycloidal computed tomography, by which a lateral sample translation and rotation are combined, is a fully-fly-scan-compatible acquisition scheme for micro-computed-tomography systems using amplitude-modulated beams. Such systems have gained popularity, as they enable x-ray phase-contrast imaging (XPCI) and aperture-driven spatial resolution. The former provides superior contrast for weakly attenuating samples, while the latter allows the resolution of a micro-computed-tomography system to be increased beyond the conventional limit dictated by the source and detector. Such systems initially required time-inefficient step-and-shoot acquisitions, a limitation that has been removed by the development of cycloidal computed tomography. Here we derive cycloidal sampling conditions that are optimal in the sense of the Nyquist-Shannon theorem. Their availability enables the acquisition of well-sampled (i.e., high-resolution) XPCI images in a time-efficient manner, a long-sought outcome with relevance to laboratory implementations, where scan times have traditionally been long, and to synchrotron implementations, where the next frontier is to achieve high-speed (e.g., dynamic) imaging. We make no assumptions on the type of x-ray source used, but demonstrate the optimal conditions with a rotating-anode x-ray tube.

Mitigation of fluid-borne noise in hydraulic power systems is of paramount importance for both machine reliability and human comfort. One typical approach involves using compliant inline hydraulic silencers to lower the sound speed within devices, e.g., pressurized bladders or syntactic foams. However, the exploration of innovative compliant materials for silencer designs has been limited; this is largely due to the absence of a comprehensive model that can accommodate a large range of anisotropic materials to evaluate the performance of hydraulic silencers. In this work, we develop a general analytical model for silencer design that incorporates anisotropic reflective materials. The model enables us to identify optimized solutions within a broader material spectrum, tailored to meet pressure-resistance requirements. Building upon these insights, we design and fabricate an anisotropic compliant metallic lattice with low impedance and integrate it into a hydraulic silencer as the reflective material. Experimental results demonstrate that this silencer can achieve an average sound-transmission loss of 21 dB across a frequency range of 100 Hz to 2 kHz, in good agreement with predictions from our proposed model. This work paves the way for selecting and designing innovative materials for the mitigation of hydraulic noise.

Hybrid magnonic systems have emerged as a promising direction for information propagation with preserved coherence. Because of the high tunability of magnons, their interactions with microwave photons can be engineered to probe novel phenomena based on strong photon-magnon coupling. Improving the photon-magnon coupling strength can be done by tuning the structure of microwave resonators to better interact with the magnon counterpart. Planar resonators have been explored due to their potential for on-chip integration, but only common modes from stripline-based resonators have been used. Here, we present a microwave spiral resonator supporting spoof localized surface plasmons (LSPs) and implement it in the investigation of photon-magnon coupling for hybrid magnonic applications. We showcase strong magnon-LSP photon coupling using a ferrimagnetic yttrium iron garnet sphere. We discuss the engineering capacity of the photon mode frequency and spatial field distributions of the spiral resonator via both experiment and simulation. As a result of the localized photon mode profiles, the resulting magnetic field concentrates near the surface dielectrics, giving rise to an enhanced magnetic filling factor. The strong coupling and large engineering space render the spoof LSPs an interesting contender in developing novel hybrid magnonic systems and functionalities.

Quantum metrology has been shown to surpass classical limits of correlation, resolution, and sensitivity. It has been introduced to interferometric radar schemes, with intriguing preliminary results. Even quantum-inspired detection of classical signals may be advantageous in specific use cases. Following ideas demonstrated so far only in the optical domain, where practically no thermal background photons exist, we realize room-temperature microwave frequency super-resolved phase measurements with trillions of photons, while saturating the Cramer-Rao bound of sensitivity. We experimentally estimate the interferometric phase using the expectation value of the parity operator by two methods. We achieve superresolution up to 1200 times better than the wavelength with 25-ns integration time and 56-dB SNR.

Engineering high-fidelity two-qubit gates is an indispensable step toward practical quantum computing. For superconducting quantum platforms, one important setback is the stray interaction between qubits, which causes significant coherent errors. For transmon qubits, protocols for mitigating such errors usually involve fine-tuning the hardware parameters or introducing usually noisy flux-tunable couplers. In this work, we propose a simple scheme to cancel these stray interactions. The coupler used for such cancelation is a driven high-coherence resonator, where the amplitude and frequency of the drive serve as control knobs. Through the resonator-induced-phase interaction, the static $ZZ$ coupling can be entirely neutralized. We numerically show that such a scheme can enable short and high-fidelity entangling gates, including cross-resonance controlled-not (cnot) gates within 40 ns and adiabatic controlled-$Z$ gates within 140 ns. Our architecture is not only $ZZ$-free, but also contains no extra noisy components, such that it preserves the coherence times of fixed-frequency transmon qubits. With the state-of-the-art coherence times, the error of our cross-resonance cnot gate can be reduced to below ${10}^{-4}$.

Chromium telluride ${\mathrm{Cr}}_x{\mathrm{Te}}_y$ has great potential applications in spintronics due to its intrinsic ferromagnetism and strong magnetic anisotropy. In this study, we systematically investigate magnetic properties of a ferromagnetic ${\mathrm{Cr}}_2{\mathrm{Te}}_3$ single crystal with strong perpendicular magnetic anisotropy (PMA). Apart from ferromagnetic-to-paramagnetic (FM-PM) transitions at $T_C\sim 181$ K for both $H//c$ and $H//ab$, other exotic magnetic behaviors are revealed, such as a field-modulated first-order transition uncovered by the anisotropic magnetization, a canted FM coupling rather than previously reported spin-glass behavior demonstrated by the ac susceptibility. Furthermore, anisotropic magnetization reveals significant PMA stronger than any other $\mathrm{Cr}$-based transition metal chalcogenide, with a negligible saturation field for $H//c$ but a distinct one up to 155 kOe for $H//ab$. Critical exponents $\beta =0.340(5)$, $\gamma =1.114(1)$, and $\delta =4.504(5)$ are obtained for $H//c$, which fall between the three-dimensional (3D)-$XY$ and 3D-Ising models indicative of anisotropic magnetic coupling. An $H$-$T$ phase diagram of the ${\mathrm{Cr}}_2{\mathrm{Te}}_3$ single crystal is constructed for $H//c$, which distinguishes canted FM1, canted FM2, forced FM (FFM), and PM phases. The phase diagram indicates that the transition to the canted FM2 under lower fields is of a first-order type, which is suppressed into a second-order one by the external magnetic field. The multiple phase transitions and complex magnetic structures is suggested to derive from the competition between the intralayered superexchange (FM couplings) and the interlayered direct interaction (AFM coupling). The various magnetic configurations and strong PMA make ${\mathrm{Cr}}_2{\mathrm{Te}}_3$ highly promising for spintronic device applications.

Low-energy electron microscopy (LEEM) was performed on $p$-$\mathrm{Ga}\mathrm{N}$ samples during in situ cesium deposition. LEEM images of electron reflectivity recorded as a function of the incident electron energy at different $\mathrm{Cs}$ coverages allowed to spatially resolve the evolution of the local work function (WF) during the activation process. While the average WF drops by more than 3 eV, the local WF remains quite uniform across the surface throughout the activation process. Maximum fluctuations of less than 0.2 eV were observed in the WF maps for $\mathrm{Cs}$ coverage of a fraction of a monolayer. These fluctuations are mainly related to the surface topography, in particular, to the atomic steps’ structure, which replicates the substrate miscut. Apart from these weak spatial fluctuations, no $\mathrm{Cs}$ clusters that would induce strong local WF contrast were observed at the scale of the 20-nm resolution of the measurements. These observations agree with the simple model of semiconductor activation to negative electron affinity that describes the formation of a dipole layer as responsible for the lowering of the WF. Additionally, at complete $\mathrm{Cs}$ coverage, the WF becomes fully homogeneous over the surface, smoothing out features originating from defects and topography.

Spin waves in magnetic films are affected by the vicinity to a superconductor. Here we focus on a bilayer stack made of an insulating yttrium iron garnet (YIG) film and a high-$T_c\mathrm{YB}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_7$ (YBCO) superconducting planar resonator and report microwave transmission spectra to monitor the temperature evolution of magnon-photon polaritons. We show that the observed temperature dependence of normal-mode splitting and frequency shift with respect to the unperturbed magnon mode can be ultimately related to the penetration depth of YBCO, as an effect of the interplay between spin waves and Meissner currents.