Many precision laser applications require active frequency stabilization. However, such stabilization loops operate by pushing noise to frequencies outside their bandwidth, leading to large “servo bumps” that can have deleterious effects for certain applications. The prevailing approach to filtering this noise is to pass the laser through a high-finesse optical cavity, which places constraints on the system design. Here, we propose and demonstrate a different approach where a frequency error signal is derived from a beat note between the laser and the light that passes through the reference cavity. The phase noise derived from this beat note is fed forward to an electro-optic modulator after the laser, carefully accounting for relative delay, for real-time frequency correction. With a hertz-line-width laser, we show $\gtrsim 20\mathrm{dB}$ noise suppression at the peak of the servo bump (approximately $250\mathrm{kHz}$) and a noise-suppression bandwidth of approximately $5\mathrm{MHz}$—well beyond the servo bump. By simulating the Rabi dynamics of a two-level atom with our measured data, we demonstrate substantial improvements to the pulse fidelity over a wide range of Rabi frequencies. Our approach offers a simple and versatile method for obtaining a clean spectrum of a narrow-line-width laser, as required in many emerging applications of cold atoms, and is readily compatible with commercial systems that may even include wavelength conversion.

Nitrogen-vacancy centers in diamond have recently been established as effective sensors of the magnetization dynamics in vicinal ferromagnetic materials. We demonstrate sub-100-nm placement accuracy of nitrogen-vacancy-containing nanodiamonds and use these as local sensors that probe optically detected ferromagnetic resonance in mesoscopically patterned Permalloy islands. These measurements reveal variations in the ferromagnetic resonance signal at different sites on these structures with distinct behavior in the edge and the bulk of patterned features. These test measurements establish an easily implemented approach for spatially targeted measurements of spin dynamics in mesoscale ferromagnets. In principle, the methodology can also be extended to local studies of nanoscale ferromagnets, such as single magnetic nanowires and nanoparticles.

Low-loss deposited dielectrics will benefit superconducting devices such as integrated superconducting spectrometers, superconducting qubits, and kinetic inductance parametric amplifiers. Compared with planar structures, multilayer structures such as microstrips are more compact and eliminate radiation loss at high frequencies. Multilayer structures are most easily fabricated with deposited dielectrics, which typically exhibit higher dielectric loss than crystalline dielectrics. We measure the subkelvin and low-power microwave and millimeter-submillimeter-wave dielectric loss of hydrogenated amorphous silicon carbide ($a$-SiC:H), using superconducting chips with Nb-Ti-$\mathrm{N}/a$-SiC:H/Nb-Ti-N microstrip resonators. We deposit the $a$-SiC:H by plasma-enhanced chemical vapor deposition at a substrate temperature of $400{}^{\circ }\mathrm{C}$. The $a$-SiC:H has a millimeter-submillimeter loss tangent ranging from $0.9\times {10}^{-4}$ at 270 GHz to $1.5\times {10}^{-4}$ at 385 GHz. The microwave loss tangent is $3.1\times {10}^{-5}$. These are the lowest low-power subkelvin loss tangents that have been reported for microstrip resonators at millimeter-submillimeter and microwave frequencies. The $a$-SiC:H films are free of blisters and have low stress: $-20$ MPa compressive at 200-nm thickness to 60 MPa tensile at 1000-nm thickness.

Hole spin qubits in semiconductor quantum dots (QDs) are promising candidates for quantum information processing due to their weak hyperfine coupling to nuclear spins, and to the strong spin-orbit coupling, which allows for rapid operation time. We propose a coherent control on two heavy-hole spin qubits in a double QD by a fast adiabatic driving protocol, which helps to achieve higher fidelities than other experimentally commonly used protocols as linear ramping, $\pi$ pulses or Landau-Zener passages. Using fast quasiadiabatic driving via spin-orbit coupling, it is possible to reduce charge noise significantly for qubit manipulation and achieve high robustness for the qubit initialization. We also implement one- and two-qubit gates, in particular, not, cnot, and swaplike gates, of hole spins in a double QD achieving fidelities above $99\mathrm{\%}$, exhibiting the capability of hole spins to implement universal gates for quantum computing.

The gate-all-around (GAA) $\mathrm{Si}$ nanowire (NW) field-effect transistor (FET) is considered one of the most promising successors of the current mainstream $\mathrm{Si}$ fin FET (FinFET) owing to its better electrostatic gate control. Experimentally, the diameter of $\mathrm{Si}$ NWs has been scaled down to 1 nm. In this paper, the performance limit of the GAA $\mathrm{Si}$ NWFET with a 1-nm diameter is investigated by utilizing ab initio quantum transport simulations. We prove that the electrical conduction is concentrated in the core of the ultranarrow wire channel. The minimum gate length ($L_g$) at which the n- and p-type GAA $\mathrm{Si}$ NWFET can satisfy the high-performance application requirements (on-state current, gate capacitance, delay time, and power dissipation) of the International Technology Roadmap for Semiconductors is 3 nm. The best-performing 5-nm-$L_g$ n-type GAA $\mathrm{Si}$ NWFET exhibits an energy-delay product comparable with typical monolayer two-dimensional FETs. Compared with the similar-sized trigate $\mathrm{Si}$ NW FinFET, an approximately 200% increase in the on-state current and about 15% decrease in the subthreshold swing are witnessed in GAA $\mathrm{Si}$ NWFET at the same 5-nm $L_g$. Through strain engineering, about an 80% increase of on-state current is observed in the 5-nm-$L_g$ p-type GAA $\mathrm{Si}$ NWFET. Our research demonstrates the vast potential of the GAA $\mathrm{Si}$ NWFET in the sub-3-nm gate-length region.

The topological quantum field-effect transition in buckled two-dimensional-Xenes can potentially enable subthermionic transistor operation coupled with a dissipationless on-state conduction. We investigate realistic device structures that exploit the quantum field-effect transition between the dissipationless topological phase and the band-insulator phase. We find that the previously considered dual-gate structure is disadvantageous, leading to a near doubling of the subthreshold swing. However, we identify a single-gate strategy capable of overcoming the thermionic limit at the cost of sacrificing the dissipationless on-state conduction. By introducing an out-of-plane antiferromagnetic exchange in the material via proximity coupling, we exploit transitions between the quantum spin-valley Hall and the spin quantum anomalous Hall phase, which restore the topological robustness of the on state while simultaneously surpassing the thermionic limit. Our work thus outlines a realistic pathway to topological transistors that can overcome Boltzmann’s tyranny while preserving topological robustness.

In recent years, multifunctional materials have attracted increasing interest for magnetic memories and energy-harvesting applications. Magnetic insulating materials are of special interest for this purpose, since they allow the design of more efficient devices due to the lower Joule heat losses. In this context, ${\text{Ga}}_{0.6}{\text{Fe}}_{1.4}{\text{O}}_3$ (GFO) is a good candidate for spintronics applications, since it can exhibit multiferroicity and presents a spin Hall magnetoresistance similar to the one observed in a yttrium-iron-garnet (YIG)/$\mathrm{Pt}$ bilayer. Here, we explore GFO utilizing thermospin measurements in an on-chip approach. By carefully considering the geometry of our thermospin devices we are able to quantify the spin Seebeck effect and the spin-current generation in a GFO/$\mathrm{Pt}$ bilayer, obtaining a value comparable to that of YIG/$\mathrm{Pt}$. This further confirms the promises of an efficient spin-current generation with the possibility of an electric field manipulation of the magnetic properties of the system in an insulating ferrimagnetic material.

One route to create tunable metamaterials is through integration with “on-demand” dynamic quantum materials, such as vanadium dioxide (${\mathrm{VO}}_2$). This enables modalities to create high-performance devices for historically challenging applications. Indeed, dynamic materials have often been integrated with metamaterials to imbue artificial structures with some degree of tunability. Conversely, metamaterials can be used to enhance and extend the natural tuning range of dynamic materials. Utilizing a complementary split-ring resonator array deposited on a ${\mathrm{VO}}_2$ film, we demonstrate enhanced terahertz transmission modulation upon traversing the insulator-to-metal transition (IMT) at approximately $340$ K. Our complementary metamaterial increases the modulation amplitude of the original ${\mathrm{VO}}_2$ film from 0.42 to 0.68 at 0.47 THz upon crossing the IMT, corresponding to an enhancement of 62%. Moreover, temperature-dependent transmission measurements reveal a significant redshift of the resonant frequency in a narrow temperature range where phase coexistence is known to occur. Neither Maxwell-Garnett nor Bruggeman effective medium theory adequately describes the observed frequency shift and amplitude decrease. However, a Drude model incorporating a significant increase of the effective permittivity does describe the experimentally observed redshift. Our results highlight that symbiotic integration of metamaterial arrays with quantum materials provides a powerful approach to engineer emergent functionality.

The stochastic magnetic tunnel junction (MTJ), the resistance of which fluctuates in time between low and high states under thermal fluctuation, is expected to serve as a key element in probabilistic computers. For reliable operation and versatile application, one needs to address the challenge that the relaxation time in each state should be virtually independent of external magnetic fields in the range of, for example, several mT. In this research, we fabricate in-plane easy-axis elliptical stochastic MTJs with a synthetic antiferromagnetic (SAF) free layer and examine the robustness of their properties against external fields while comparing them with stochastic MTJs with a conventional single ferromagnetic structure. We show that the MTJ with a SAF free layer shows more robust relaxation times against fields applied along the easy- and hard-axis directions. The results are reproduced with a macrospin simulation, from which design guidelines for robust stochastic MTJs targeting probabilistic computers are discussed.

We investigate magnetization-reversal processes in half-metallic epitaxial films of ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{Mn}\mathrm{O}}_3$ on ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ (110) substrates. At 150 K, major-loop magnetization reversal (MLMR) occurs beyond minor-loop switching fields, implying that MLMR is limited by domain nucleation. At 280 K, MLMR overlaps with minor-loop switching fields if there are deliberately introduced precipitates, implying that the precipitates limit MLMR by pinning domain walls. To confirm that the precipitates pin domain walls at 280 K, we use a two-dimensional analogue of the Gaunt pinning model to show that pinning-limited switching occurs at fields consistent with the observed precipitate density of 0.3–2.0 μm${}^{-2}$. Our work demonstrates that comparing major and minor loops at any temperature of interest represents a simple way to check whether spintronic electrode materials show nucleation-limited MLMR, as circumstantially required for single-domain switching in micron-scale elements of ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{Mn}\mathrm{O}}_3$ that represent spintronic electrodes [L. C. Phillips et al., Phys. Rev. Appl. 4, 064004 (2015)].

Strong Coulomb repulsion and spin-orbit coupling are known to give rise to exotic physical phenomena in transition metal oxides. Here, we report magnetic characteristics of a ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ perovskite thin film, having both 3d and 5d elements on the $B$ sites, with a strong perpendicular magnetic anisotropy (PMA), which is rare in perovskite oxide thin films. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ films have been epitaxially deposited on (001)-oriented ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ single-crystal substrates by pulsed-laser deposition, exhibiting a para-to-ferromagnetic transition at about 110 K. The average valence of $\mathrm{Mn}$ and $\mathrm{Ir}$ cations are estimated as +3.61 and +4.17, respectively, by x-ray photoelectron spectroscopy. X-ray absorption spectroscopy reveals that $\mathrm{Mn}$ $e_g$ electrons occupy preferentially the $d_{3z^2-r^2}$ orbital, which produces the observed PMA in the framework of spin-orbital coupling. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ thin film shows a large effective anisotropy constant of about 1.2 × ${10}^6$ erg ${\mathrm{cm}}^{-3}$ at 10 K, which is found to decrease with decreasing tetragonality c/a of the film. First-principles calculations reveal that $\mathrm{Mn}$ and $\mathrm{Ir}$ cations provide opposite magnetizations in ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ and the $\mathrm{Mn}$ $e_g$ orbital polarization comes from both lattice distortion and oxygen octahedron rotation. The ${\mathrm{Sr}\mathrm{Mn}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ thin film with strong PMA may have applications in future low-power-consumption oxide spintronic devices.

Physical parameters, such as decay rates and photoluminescence (PL) quantum efficiencies, associated with thermally activated delayed fluorescence (TADF) emitters play a critical role in determining the performance of organic light-emitting diodes (OLEDs). Herein, we investigate the impact of TADF decay rates and PL quantum efficiencies on external quantum efficiency (EQE) roll-off. Our analysis reveals that a high EQE with suppressed efficiency roll-off in TADF OLEDs can be achieved by shortening the delayed lifetime with an increasing delayed contribution or by shortening the prompt lifetime with increasing prompt contribution simultaneously. We further show that TADF compounds with long delayed and/or prompt lifetimes can give rise to multiple spin cycling and subsequently result in significant exciton quenching and efficiency roll-off in OLEDs. These results provide universal selection criteria for TADF emitters in OLEDs to concurrently achieve a high maximum EQE and low-efficiency roll-off.

We study experimentally the propagation of spin waves in waveguide structures consisting of two submicrometer-width yttrium iron garnet waveguides intersecting at a right angle. We show that, despite the significant spatial variations of the internal static magnet field and the in-plane anisotropy of the dispersion characteristics, the incident spin wave can efficiently pass through the microscopic cross-shaped structure and be transmitted into all its arms. This process depends strongly on the frequency of the wave and the orientation of the static magnetic field. By varying these parameters, one can achieve a controllable uniform or preferential transmission of the wave into different arms of the cross. Our results create the basis for the implementation of nanoscale magnonic networks to be used for the realization of complex non-Boolean data-processing schemes, including neuromorphic computing.

Full-space metasurfaces exhibit considerable capacities in the fields of electromagnetic wave-front tailoring due to their functional and spatial integration, and extensive applications in modern communication systems. However, almost all metasurfaces for wave-front tailoring are implemented by multilayer dielectric cascade structures, which not only present imperfections in the cost and manufacturing process, but are also detrimental to integration. As such, it is highly desirable to actualize a high-performance metasurface that merely relies on elaborated designs and simple manufacturing process. This study combines frequency multiplexing, spatial channel multiplexing, and polarization multiplexing to propose a full-space metahologram with four different information channels based on a thin double-face copper-cladded metasurface. Exploiting the propagation phase, linear-polarized incident waves can be independently manipulated for the reflection semispace. Integrating the Pancharatnam-Berry (PB) phase, circular-polarized incident waves are tailored for the transmission semispace. To validate the concept, a metahologram sample is fabricated and tested. The experimental results are fully consistent with theoretical calculations and numerical simulation results. The metasurface has a useful role in multifunctional metadevices, and paves the way for potential applications in the fields of antennas and communication systems.

We report on a spin-orbit-torque study of the spin-current generation in ${\mathrm{Cr}}_{1-x}{\mathrm{Pt}}_x$ alloy, using the light 3d ferromagnetic Co as the spin-current detector. We find that the dampinglike spin-orbit torque of ${\mathrm{Cr}}_{1-x}{\mathrm{Pt}}_x/\mathrm{Co}$ bilayers can be enhanced by tuning the $\mathrm{Cr}$ concentration in the ${\mathrm{Cr}}_{1-x}{\mathrm{Pt}}_x$ layer, with a maximal value of 0.31 at the optimal composition of ${\mathrm{Cr}}_{0.2}{\mathrm{Pt}}_{0.8}$. The mechanism and the efficiency of spin-current generation in the ${\mathrm{Cr}}_{1-x}{\mathrm{Pt}}_x$ alloy can be fully understood by the characteristic trade-off between the intrinsic spin Hall conductivity of $\mathrm{Pt}$ and the spin carrier lifetime in the dirty limit. This suggests that $\mathrm{Cr}$ is simply as effective as other metals, oxides, and nitrides (e.g., $\mathrm{Hf}$, $\mathrm{Au}$, $\mathrm{Pd}$, $\mathrm{Cu}$, $\mathrm{Ti}$, $\mathrm{Mg}\mathrm{O}$, and ${\mathrm{Si}}_3{\mathrm{N}}_4$) in enhancing the dampinglike spin-orbit torque generated by the spin Hall effect of a $\mathrm{Pt}$ host via strengthening the spin carrier scattering and that alloying $\mathrm{Pt}$ with $\mathrm{Cr}$ does not employ observable spin-current generation via additional spin Hall effect, orbital Hall effect, or interfacial spin-orbit coupling effects. This work also establishes the low-resistivity ${\mathrm{Cr}}_{0.2}{\mathrm{Pt}}_{0.8}$ as an energy-efficient spin-orbit-torque provider for magnetic memory and computing technologies.

Surface-acoustic-wave (SAW) devices have a wide range of applications in microwave signal processing. Microwave SAW components benefit from higher quality factors and much smaller crosstalk when compared to their electromagnetic counterparts. Efficient routing and modulation of SAWs are essential for building large-scale and versatile acoustic wave circuits. Here, we demonstrate integrated thermoacoustic modulators using two SAW platforms: bulk lithium niobate and thin-film lithium niobate on sapphire. In both approaches, the gigahertz-frequency SAWs are routed by integrated acoustic waveguides, while on-chip microheaters are used to locally change the temperature, and thus, control the phase of the SAW. Using this approach, we achieve phase changes of over 720° with the responsibility of 2.6°/mW for bulk lithium niobate and 0.52°/mW for lithium niobate on sapphire. Furthermore, we demonstrate amplitude modulation of SAWs using acoustic Mach-Zehnder interferometers. Our thermoacoustic modulators can enable reconfigurable acoustic signal processing for next-generation wireless communications and microwave systems.