Using a fluxonium qubit with in situ tunability of its Josephson energy, we characterize its energy relaxation at different flux biases as well as different Josephson energy values. The relaxation rate at qubit energy values, ranging more than 1 order of magnitude around the thermal energy $k_{B}T$, can be quantitatively explained by a combination of dielectric loss and $1/f$ flux noise with a crossover point. The amplitude of the $1/f$ flux noise is consistent with that extracted from the qubit dephasing measurements at the flux sensitive points. In the dielectric loss dominant regime, the loss is consistent with that arising from the electric dipole interaction with two-level-system (TLS) defects. In particular, by increasing the Josephson energy, thus decreasing the qubit frequency at the flux insensitive spot, we find that the qubit exhibits increasingly weaker coupling to TLS defects, which is desirable for high-fidelity quantum operations. Our work establishes a generic noise model for the design of high coherence fluxonium and future generations of noise resilient superconducting qubits.

We investigate the effect of buffer gases on the coherent population trapping resonance induced by a $\sigma$-polarized optical field in ${}^{87}\mathrm{Rb}$ atoms. Our experimental results show that inert gases, which depolarize the excited state of alkali-metal atoms, provide higher contrast than nitrogen that effectively quenches their fluorescence. We also demonstrate that elimination of spontaneous radiation does not significantly decrease the width at moderate temperatures of an atomic medium. Therefore, a mixture of inert gases can be preferable over a mixture with nitrogen for atomic clocks.

Weyl semimetals are bulk solids in which chiral anomalies, i.e., negative magnetoelectric and magnetothermal resistances, exist as a result of the chiral properties of the Weyl fermions. The thermal chiral anomaly has potential in devices that actively control heat fluxes; these would be an early application of topological properties, realized after the materials are optimized. Here, we optimized the band structure of ${\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$ alloys in the topological insulator phase and in their field-induced Weyl semimetal phases to maximize the thermal chiral anomaly by changing the $\mathrm{Sb}$ concentration and by doping ${\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$ alloys either with n-type $\mathrm{Te}$ or with p-type $\mathrm{Sn}$. We show that the chiral anomalies are maximized when the chemical potential is at the Weyl points and that Weyl fermions are protected against scattering on phonons and neutral defects but not necessarily on charged particles like ionized impurities and electrons in trivial pockets. In our optimum material, around 30% of the total heat (carried by phonons, trivial electrons, and the chiral anomaly) is carried by the anomalous heat current (the chiral anomaly). The latter is highly switchable under a magnetic field. The maximum effect we observe is an anomalous thermal conductivity at 7 T that is 700% larger than the zero-field electronic thermal conductivity at T = 40 K in a x = 0.1 sample with p-type doping to 3.90 × ${10}^{15}{\mathrm{cm}}^{-3}$ with a mobility of $2350000{\mathrm{cm}}^2{V}^{-1}{\mathrm{s}}^{-1}$.

Asymmetric heat-transfer systems, often referred to as thermal diodes or thermal rectifiers, have garnered increasing interest due to their wide range of application possibilities. Most of those previous macroscopic asymmetric thermal devices either resort to nonlinear thermal conductivities with strong temperature dependence that may be quite limited by or fixed in natural materials or rely on active modulation that necessitates auxiliary energy payloads. Here, we establish a straightforward strategy of passively realizing asymmetric heat transfer with linear conductive materials. The strategy also introduces an interrogative perspective into the previous design of passive asymmetric heat transfer utilizing nonlinear thermal conductivity, correcting the misconception that thermal rectification is impossible with separable nonlinear thermal conductivity. The nonlinear-perturbation mode can be versatilely engineered to produce an effective and wide-ranging perturbation in heat conduction, which imitates and bypasses intrinsic thermal nonlinearity constraints set by naturally occurring counterparts. Independent experimental characterizations of surface thermal radiation and thermal convection verify that heat exchange between a graded linear thermal metamaterial and the ambient surroundings can be tailored to achieve macroscopic asymmetric heat transfer. Our work is envisaged to inspire conceptual models for heat-transfer control, serving as a robust and convenient platform for advanced thermal management and thermal computation.

Dirac cone formation and a method for dynamically controlling the band gap using double-layer ring dipole arrays (RDAs) are demonstrated and proposed. The design is mainly based on the composite right-handed–left-handed circuit theorem. It is theoretically and analytically confirmed that the Dirac cone appears at the optimum separation in double-layer RDAs, which are known to have surface-wave modes in the case of a single-layer RDA. It is also found that the band gap can be formed and controlled by decreasing the separation between the two layers. The Dirac cone formation and its dynamic control method on the artificial structure will open the possibility of new transistor applications as an artificial electronic material showing the properties of Dirac half-metals.

We demonstrate single-photon emission in strongly confined piezoelectric (211)B $\mathrm{In}\mathrm{As}/\mathrm{Ga}\mathrm{As}$ quantum dots at an elevated temperature of 230 K, exploiting the enhanced exciton-biexciton splittings in the system. This is a high temperature allowing for noncryogenic operation of a single-photon emitter based on III-arsenide quantum dots. A determining factor toward this result is the incorporation of the quantum dot layer in between $\mathrm{Ga}\mathrm{As}/\mathrm{Al}\mathrm{As}$ short-period superlattices, improving drastically the carrier confinement and temperature stability of the dot emission, allowing the observation of distinct exciton and biexciton emission peaks up to 260 K and single-photon emission at a high temperature.

Multifunctional tunnel junction is a kind of electronic device and the emergence of van der Waals (vdW) materials provides a promising opportunity for the development of multifunctional tunnel junctions and the miniaturization of electronic devices beyond Moore’s law. Here, we propose a symmetric vdW antiferroelectric multiferroic tunnel junction (AFMFTJ) based on ${\mathrm{Fe}}_3{\mathrm{Ge}\mathrm{Te}}_2$/$h$-BN/bilayer-${\mathrm{In}}_2{\mathrm{Se}}_3$/$h$-$\mathrm{BN}/{\mathrm{Fe}}_3{\mathrm{Ge}\mathrm{Te}}_2$ vdW heterostructure, and investigate the spin-dependent transport of this vdW AFMFTJ by using nonequilibrium Green’s function combined with density-functional theory. It is found that multiple resistance states are realized in this proposed vdW AFMFTJ and the considerable tunneling electroresistance ratio of about $1.0\times {10}^4\mathrm{\%}$ and the large tunneling magnetoresistance ratio of up to 695% are simultaneously achieved at zero bias. Interestingly, the regulatable negative differential conductance (NDC) by magnetic field and electric field is produced in this vdW AFMFTJ under bias voltages. The NDC effect originates from the changes in the conductive channels of ${\mathrm{Fe}}_3{\mathrm{Ge}\mathrm{Te}}_2$ electrodes and the electronic states of the ${\mathrm{In}}_2{\mathrm{Se}}_3$ barrier under different bias voltages. This work not only benefits exploring of the tunnel junction with NDC effect, but also provides a promising route for the design of multifunctional microelectronic devices based on vdW materials.

Passive metasurfaces are known for their fixed and usually single-wave manipulation functionality, which limits their potential applications for diverse scenarios. To expand the functionality of the passive metasurfaces, frequency-multiplexed technology has been proposed to encode multiple operation frequencies in a single metasurface for function selection and switching. Although this technology has been extensively utilized for electromagnetic waves, there have been few studies on designing frequency-multiplexed metasurfaces for acoustic-wave manipulation. This work applies a topology optimization method based on a multiobjective genetic algorithm (GA) to develop different frequency-encoded multifunctional acoustic metasurfaces to attain acoustic focusing and anomalous wave refraction. The effectiveness of the optimized metasurfaces is validated both numerically and experimentally. Additionally, the underlying physical mechanisms of the designed frequency-multiplexed acoustic metasurfaces are systematically analyzed. This study presents high-performance frequency-multiplexed metasurfaces for acoustic-wave-front modulation and demonstrates the promising potential of the GA-based topology optimization approach in designing integrated, miniaturized multifunctional acoustic devices for real-world applications.

Acoustic vortices (AVs) carrying orbital angular momentum (OAM) have shown great significance in communication. However, crosstalk in acoustic communication based on traditional AVs with single OAM remains an issue. Here, we propose a periodic-phase acoustic vortex (PPAV) with a comblike OAM spectrum. The sample interval of the OAM spectrum of the PPAV can be modulated by the period number of the azimuthal phase. The influence of the period number on the acoustic properties of the PPAV and the evolution of the PPAV are investigated theoretically. Moreover, an acoustic artificial-structure plate engraved with 24 filled circular holes is designed to generate the PPAV in water. By changing the height of the resin layer filling each hole unit, the transmitted phase shift of the ultrasonic wave through them can be flexibly and efficiently manipulated. Both simulations and experiments confirm that the designed artificial plate with filled holes can produce the PPAV with an arbitrary topological charge. Finally, we preliminarily explore the possibility of applying the PPAV in acoustic communication and show that the OAM sample interval of the PPAV can be used as an independent degree of freedom for acoustic encoding-decoding communication. We believe that the PPAV generated by the acoustic artificial-structure plates may find good applications in microparticle manipulation and acoustic communication.

Microwave cavities are commonly used in many experiments, including optomechanics, magnetic field sensing, magnomechanics, and circuit quantum electrodynamics. Noise, such as variations in the magnetic field or mechanical vibrations, can cause fluctuations of the natural frequency of the cavity, creating challenges in operating them in experiments. To overcome these challenges, we demonstrate a dynamic feedback system implemented by the locking of a microwave drive to the noisy cavity. A homodyne-interferometer scheme monitors the cavity resonance fluctuations due to low-frequency noise, which is mitigated by frequency modulating the microwave generator. The feedback has a bandwidth of 400 Hz, with a reduction of cavity fluctuations by $85\mathrm{\%}$ integrating up to a bandwidth of 2 kHz. Moreover, the cavity resonance frequency fluctuations are reduced by $73\mathrm{\%}$. This scheme can be scaled to enable multitone experiments locked to the same feedback signal. As a demonstration, we apply the feedback to an optomechanical experiment and implement a cavity-locked multitone mechanical measurement. As low-frequency cavity frequency noise can be a limiting factor in many experiments, the multitone microwave locking technique presented here is expected to be relevant for a wide range of microwave-cavity experiments.

In dark-matter searches using axion haloscopes, the search sensitivity depends on the quality factors ($Q_0$) of radio-frequency cavities immersed in multitesla magnetic fields. Increasing $Q_0$ would increase the scan rate through the parameter space of interest. Researchers developing superconducting radio-frequency cavities for particle accelerators have developed methods for obtaining extremely high $Q_0$ of approximately ${10}^{11}$ in microteslascale magnetic fields. In this paper, we describe efforts to develop high-$Q$ cavities made from ${\mathrm{Nb}}_3\mathrm{Sn}$ films using a technique developed for particle-accelerator cavities. Geometry optimization for this application is explored, and two cavities are tested: an existing particle-accelerator-style cavity and a geometry developed and fabricated for use in high fields. A quality factor of $(5.3\pm 0.3)\times {10}^5$ is obtained at 3.9 GHz and 6 T at 4.2 K.

Accelerometers have widespread applications and are an essential component in many areas, such as automotive, consumer electronics, and industrial applications. Most commercial accelerometers are based on a microelectromechanical system (MEMS) that is limited in downscaling and power consumption. Spintronics-based accelerometers are proposed as alternatives; however, current proposals suffer from design limitations that result in reliability issues and high cost. Here, we propose spintronic accelerometers with magnetic tunnel junctions (MTJs) as building blocks, which map accelerations into a measurable voltage across the MTJ terminals. The device exploits elastic and dipolar coupling as a sensing mechanism and the spintronic diode effect for the direct readout of acceleration. The proposed technology represents a potentially competitive and scalable solution to current capacitive MEMS-based approaches that could lead to a step forward in many of the commercial applications.

Channel materials with symmetrical performances for n- and p-type transistors and shrinking transistors to the ultrascale limit are essential for CMOS integrated circuits (ICs) in the coming post-$\mathrm{Si}$ era. Monolayer (ML) boron pnictides (i.e., $\mathrm{BP}$ and $\mathrm{B}\mathrm{As}$) possess both high electron and hole mobilities and flat atomic thick configurations, which are beneficial for symmetrical performance and short natural lengths, respectively. Herein, we provide a theoretical study on the device performances of sub-5-nm ML boron pnictide MOSFETs using the ab initio quantum transport method. Symmetrical n- and p-type performances are achieved for the ML boron pnictide MOSFETs. The optimal n- and p-type ML $\mathrm{BP}$ and $\mathrm{B}\mathrm{As}$ MOSFETs can reach the International Roadmap for Devices and Systems goals for the 2028 horizon for high-performance devices at gate lengths ($L_{\mathrm{g}}$) of 3 and 5 nm, respectively. In particular, the optimal n-type (p-type) ML $\mathrm{BP}$ MOSFETs possess superhigh on-state currents ($I_{\mathrm{ON}}$) of 2974 (2937) µA/µm at $L_{\mathrm{g}}$= 5 nm, exceeding most reported ML MOSFETs. Our study suggests that ML boron pnictides are prospective channel materials in the post-$\mathrm{Si}$ era for CMOS ICs.

The stability of lithium-ion batteries is of paramount importance for their commercialization. However, strategies for improving electrode stability are still quite unsatisfactory due to the unclear mechanism of diffusion-induced stress and especially the regulation methods based on it. Herein, based on a columnar lithium-ion diffusion electrode model, a double high-elastic-modulus modification (DHEMM) method is proposed to inhibit deformation and relieve the generated stress during cycling. In this light, ${\mathrm{Ti}\mathrm{O}}_2/{\mathrm{V}}_2{\mathrm{O}}_5/$polypyrrole (PPy) nanofibers are accordingly synthesized with a significantly enhanced rate capacity (198.2 mAh ${\mathrm{g}}^{-1}$ at 1600 mA ${\mathrm{g}}^{-1}$) and electrochemical stability (91.9% capacity retention for 100 cycles at 100 mA ${\mathrm{g}}^{-1}$), offering an alternative way to fabricate stable lithium-ion batteries.