Solid-state qubits have recently advanced to the level that enables them, in principle, to be scaled up into fault-tolerant quantum computers. As these physical qubits continue to advance, meeting the challenge of realizing a quantum machine will also require the development of new supporting devices and control architectures with complexity far beyond the systems used in today’s few-qubit experiments. Here, we report a microarchitecture for controlling and reading out qubits during the execution of a quantum algorithm such as an error-correcting code. We demonstrate the basic principles of this architecture using a cryogenic switch matrix implemented via high-electron-mobility transistors and a new kind of semiconductor device based on gate-switchable capacitance. The switch matrix is used to route microwave waveforms to qubits under the control of a field-programmable gate array, also operating at cryogenic temperatures. Taken together, these results suggest a viable approach for controlling large-scale quantum systems using semiconductor technology.

The formation of conducting channels of ${\mathrm{Ti}}_4{\mathrm{O}}_7$ inside $\mathrm{Ti}{\mathrm{O}}_2$-based memristors is believed to be the origin for the change in electric resistivity of these devices. While the properties of the bulk materials are reasonably well known, the interface between them has not been studied up to now, mostly because of their different crystalline structures. In this work, we present a way to match the interfaces between $\mathrm{Ti}{\mathrm{O}}_2$ and ${\mathrm{Ti}}_4{\mathrm{O}}_7$ and subsequently the band offset between these materials is obtained from density-functional-theory-based calculations. The results show that, while the valence band is located at the ${\mathrm{Ti}}_4{\mathrm{O}}_7$, the conduction band is found at the $\mathrm{Ti}{\mathrm{O}}_2$ structure, resulting in a type-II interface. In this case, the ${\mathrm{Ti}}_4{\mathrm{O}}_7$ acts as a donor to the $\mathrm{Ti}{\mathrm{O}}_2$ matrix.

In this paper, we present a method for a comprehensive analysis of the efficiency roll-off with current density in phosphorescent organic light-emitting diodes (OLEDs). By combining electrical and optical excitation in time-resolved spectroscopic experiments, we are able to measure the excited-state lifetime for different driving conditions. It is, thus, possible to correlate changes of the triplet lifetime with a decrease of the radiative quantum efficiency of the emitting system due to exciton quenching processes. As compared to the conventional analysis of the measured external quantum efficiency (EQE) in dependence of the applied current density, the lifetime analysis is not affected by changes of the charge-carrier balance with current, which can have a significant impact on the interpretation of the results. By performing time-resolved spectroscopy for a series of red phosphorescent OLEDs, triplet-polaron quenching (TPQ) is identified as the dominant mechanism behind the efficiency roll-off up to a current density of $100\mathrm{mA}/{\mathrm{cm}}^2$, while the conventional EQE vs current plot rather suggests triplet-triplet annihilation as the main quenching mechanism. We show that this apparent discrepancy is caused by exciton quenching occurring already at very low current densities, where EQE measurements are not reliable due to significant changes of the charge-carrier balance in this region. In addition, we present evidence that the triplet-polaron quenching rate ${\mathrm{\Gamma }}_{\mathrm{TPQ}}$ is independent of the microcavity so that variations of the triplet lifetimes of a series of devices exhibiting different layer thicknesses can be described with a single parameter set.

By means of experiments in microgravity conditions, we show that granular systems subjected to sinusoidal vibrations respond either by harmonic or gaslike dynamics, depending on the parameters of the vibration, amplitude and frequency, and the container size, while subharmonic response is unstable, except for extreme material properties and particular initial conditions. The absence of subharmonic response in vibrated granular systems implies that granular dampeners cannot reveal higher-order resonances, which makes them even more attractive for technical applications. Extensive molecular dynamics simulations support our findings.

We report on a liquid-nitrogen-cooled compact source for continuous terahertz (THz) emission. The emitter is a ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ intrinsic Josephson-junction stack embedded between two gold layers and sandwiched between two MgO substrates. The radiation is emitted to free space through a hollow metallic tube acting as a waveguide. The maximum emission power is $1.17\mu \mathrm{W}$. The tunable emission frequency bandwidth is up to 100 GHz with a maximum emission power at 0.311 THz. Since the operation voltage is about 1 V and the current is less than 30 mA, we are able to drive this terahertz source at 77 K with only one commercial 1.5-V battery, just like a torch. This convenient and economical setup may find applications in fields like tracer-gas detection or nondestructive evaluation.

We study the thermocapillary deformation, induced by infrared laser irradiation, of thin liquid films on moving substrates. We develop numerical models for the temperature distribution and film thickness evolution. Steady-state film thickness profiles are measured for different values of substrate speed and laser power. The experimental results compare well with the simulations. In the case of partially wettable substrates, the thin liquid films tend to become unstable. We find that, for certain ranges of the laser power and substrate speed, the film ruptures in a single location and subsequently dewets without the occurrence of residual droplets. Such “clean” dewetting is highly desirable in the context of immersion lithography or solution processing of organic electronic devices.

Graphene mechanical resonators have recently attracted considerable attention for use in precision force- and mass-sensing applications. To date, readout of their oscillatory motion typically requires cryogenic conditions to achieve high sensitivity, restricting their range of applications. Here we report the demonstration of an evanescent optical readout of graphene motion, using a scheme which does not require cryogenic conditions and exhibits enhanced sensitivity and bandwidth at room temperature. We utilize a high-$Q$ microsphere to enable the evanescent readout of a $70\text{−}\mu \mathrm{m}$-diameter graphene drum resonator with a signal-to-noise ratio of greater than 25 dB, corresponding to a transduction sensitivity of $S_N^{1/2}=2.6\times {10}^{-13}\mathrm{m}{\mathrm{Hz}}^{-1/2}$. The sensitivity of force measurements using this resonator is limited by the thermal noise driving the resonator, corresponding to a force sensitivity of $F_{\min }=1.5\times 10^{-16}\mathrm{N}{\mathrm{Hz}}^{-1/2}$ with a bandwidth of 35 kHz at room temperature ($T=300\mathrm{K}$). Measurements on a $30\text{−}\mu \mathrm{m}$ graphene drum have sufficient sensitivity to resolve the lowest three thermally driven mechanical resonances. The graphene drums couple both dispersively and dissipatively to the optical field with coupling coefficients of $G/2\pi =0.21\mathrm{MHz}/\mathrm{nm}$ and ${\mathrm{\Gamma }}_{\mathrm{dp}}/2\pi =0.1\mathrm{MHz}/\mathrm{nm}$, respectively.

Vacancy-mediated migration of Al in single-crystal zinc oxide (ZnO) is investigated using secondary-ion mass spectrometry (SIMS) combined with hybrid density-functional theory (DFT) calculations. A thin film of Al-doped ZnO is deposited by sputtering onto the single-crystal bulk material and heat treated at temperatures in the range of $900°\mathrm{C}–1300°\mathrm{C}$. The migration of Al is found to be Zn-vacancy mediated. In order to elucidate the physical processes involved, an alternative model based on reactive diffusion is developed. The model includes the time evolution of the concentration of Al atoms on the Zn site (${\mathrm{Al}}_{\mathrm{Zn}}$), Zn vacancies ($v_{\mathrm{Zn}}$), and a complex between the two, where the influence of the charge state of $v_{\mathrm{Zn}}$ on its formation energy is incorporated through the free carrier concentration. The modeling results exhibit close agreement with the experimental data and the ${\mathrm{Al}}_{\mathrm{Zn}}{v}_{\mathrm{Zn}}$ complex is found to diffuse with an activation energy of 2.6 eV and a preexponential factor of $4\times {10}^{-2}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$. The model is supported by the results from hybrid DFT calculations combined with thermodynamical modeling, which also suggest that a complex between ${\mathrm{Al}}_{\mathrm{Zn}}$ and $v_{\mathrm{Zn}}$ is promoted in $n$-doped material. The charge state of this complex is effectively $-1$, and it thus acts as a compensating acceptor, limiting full utilization of the shallow ${\mathrm{Al}}_{\mathrm{Zn}}$ donor. Furthermore, the DFT calculations also predict a high formation energy for both substitutional Al on the O site (${\mathrm{Al}}_{\mathrm{O}}$) and interstitial Al (${\mathrm{Al}}_i$), and are therefore of minor importance for Al migration in ZnO. The close coupling between the hybrid DFT calculations and the developed diffusion model enable benchmarking of the accuracy of several parameters extracted from the DFT calculations. Furthermore, since the diffusion model hinges strongly on defect concentrations, it couples directly to results from measurements by other experimental techniques than those used in this paper and provides an opportunity for independent verification of the estimated values by future studies.

We present a theoretical proposal for a microwave-driven circuit composed of superconducting resonators and qubits, which shows a bistable behavior, and we present a simple mechanism that allows single- or few-photon microwave pulses to work as set and reset signals that switch the circuit between its stable modes. The resulting system constitutes an ultralow-energy set-reset flip-flop device, and we show that its memory lifetime far exceeds the lifetime of states stored in any of its separate components.

Laser-induced forward transfer (LIFT) is a 3D direct-write method suitable for precision printing of various materials, including pure metals. To understand the ejection mechanism and thereby improve deposition, here we present visualizations of ejection events at high-spatial (submicrometer) and high-temporal resolutions, for picosecond LIFT of copper and gold films with a thickness $50\mathrm{nm}\le d\le 400\mathrm{nm}$. For increasing fluences, these visualizations reveals the fluence threshold below which no ejection is observed, followed by the release of a metal cap (i.e., a hemisphere-shaped droplet), the formation of an elongated jet, and the release of a metal spray. For each ejection regime, the driving mechanisms are analyzed, aided by a two-temperature model. Cap ejection is driven by relaxation of thermal stresses induced by laser-induced heating, whereas jet and spray ejections are vapor driven (as the metal film is partly vaporized). We introduce energy balances that provide the ejection velocity in qualitative agreement with our velocity measurements. The threshold fluences separating the ejection regimes are determined. In addition, the fluence threshold below which no ejection is observed is quantitatively described using a balance between the surface energy and the inertia of the (locally melted) film. In conclusion, the ejection type can now be controlled, which allows for improved deposition of pure metal droplets and sprays.

We examine the mechanical properties of graphene devices stretched on flexible elastomer substrates. Using atomic force microscopy, electrical transport measurements, and mechanics simulations, we show that microrips form in the graphene during the initial application of tensile strain; however, subsequent applications of the same tensile strain elastically open and close the existing rips. Correspondingly, while the initial tensile strain degrades the devices’ transport properties, subsequent strain-relaxation cycles affect transport only moderately, and in a largely reversible fashion. Graphene’s electrical and mechanical robustness even after partial mechanical failure is unique among conducting thin films. This understanding of the creation and dynamics of rips in graphene is relevant to the design of flexible graphene-based devices which are required to function under strain.

The spontaneous flapping of a flag in a steady flow can be used to power an output circuit using piezoelectric elements positioned at its surface. Here, we study numerically the effect of inductive circuits on the dynamics of this fluid-solid-electric system and on its energy-harvesting efficiency. In particular, a destabilization of the system is identified, leading to energy harvesting at lower flow velocities. Also, a frequency lock-in between the flag and the circuit is shown to significantly enhance the system’s harvesting efficiency. These results suggest promising efficiency enhancements of such flow-energy harvesters through the output circuit optimization.

We present an approach for realizing confined quantum-well cavity polaritons that enables in situ tuning of the cavity length and thereby of the polariton energy and lifetime. Our setup is based on a versatile semi-integrated low-temperature fiber-cavity platform, which allows us to demonstrate the formation of strongly confined polaritons with unprecedented quality factors. At high pump powers, we observe signatures of polariton lasing.

We demonstrate radio-frequency thermometry on a micrometer-sized metallic island below 100 mK. Our device is based on a normal-metal–insulator–superconductor tunnel junction coupled to a resonator with transmission readout. In the first generation of the device, we achieve $90\mu \mathrm{K}/\sqrt{\mathrm{Hz}}$ noise-equivalent temperature with 10 MHz bandwidth. We measure the thermal relaxation time of the electron gas in the island, which we find to be of the order of $100\mu \mathrm{s}$. Such a calorimetric detector, upon optimization, can be seamlessly integrated into superconducting circuits, with immediate applications in quantum-thermodynamics experiments down to single quanta of energy.

We investigate the use of guided modes bound to defects in photonic crystals for achieving double resonances. Photoluminescence enhancement by more than 3 orders of magnitude is observed when the excitation and emission wavelengths are simultaneously in resonance with the localized guided mode and cavity mode, respectively. We find that the localized guided modes are relatively insensitive to the size of the defect for one of the polarizations, allowing for flexible control over the wavelength combinations. This double-resonance technique is expected to enable the enhancement of photoluminescence and nonlinear wavelength-conversion efficiencies in a wide variety of systems.

Inline holography, like other lensless imaging methods, circumvents limitations of x-ray optics through an a posteriori phase-retrieval step. However, phase retrieval for optically thick, i.e., strongly absorbing and phase shifting, specimens remains challenging. In this paper, we demonstrate that near-field ptychography can be used to efficiently perform phase retrieval on a uranium sphere with a diameter of about $46\mu \mathrm{m}$, which acts as an optically thick sample. This particular sample was not accessible by inline holography previously. The reconstruction is based on a statistical model and incorporates partial coherence by decomposing the illumination into coherent modes. Furthermore, we observe that phase vortices, which can occur as artifacts during the reconstruction, pose a greater challenge than in far-field methods. We expect that the methods described in this paper will allow production of reliable phase maps of samples which cannot be accessed by inline holography.

Thermoelectric performance is of interest for numerous applications such as waste-heat recovery and solid-state energy conversion and will be seen to be closely connected to topological-insulator behavior. In this context, we here report first-principles transport and defect calculations for ${\mathrm{Bi}}_2{\mathrm{Te}}_2\mathrm{Se}$ in relation to ${\mathrm{Bi}}_2{\mathrm{Te}}_3$. The two compounds are found to contain remarkably different electronic structures in spite of being isostructural and isoelectronic. We discuss these results in terms of the topological-insulator characteristics of these compounds.

We report the kinetics of screening charge removal and rescreening on periodically poled lithium niobate using charge-gradient microscopy and electrostatic force microscopy (EFM). A minimum pressure needs to be applied to initiate mechanical screening charge removal, and increasing the pressure leads to further removal of charge until a threshold is reached when all screening charges are removed. We fit all rescreening EFM contrast curves under various pressures into a universal exponential decay. The findings imply that we can control the screening degree of ferroelectric surfaces by mechanical means without affecting the polarization underneath.

In this paper, we propose a model to investigate the electron thermionic emission from single-layer graphene (ignoring the effects of the substrate) and to explore its application as the emitter of a thermionic energy converter (TIC). An analytical formula is derived, which is a function of the temperature, work function, and Fermi energy level. The formula is significantly different from the traditional Richardson-Dushman (RD) law for which it is independent of mass to account for the supply function of the electrons in the graphene behaving like massless fermion quasiparticles. By comparing with a recent experiment [K. Jiang et al., Nano Res. 7, 553 (2014)] measuring electron thermionic emission from suspended single-layer graphene, our model predicts that the intrinsic work function of single-layer graphene is about 4.514 eV with a Fermi energy level of 0.083 eV. For a given work function, a scaling of $T^3$ is predicted, which is different from the traditional RD scaling of $T^2$. If the work function of the graphene is lowered to 2.5–3 eV and the Fermi energy level is increased to 0.8–0.9 eV, it is possible to design a graphene-cathode-based TIC operating at around 900 K or lower, as compared with the metal-based cathode TIC (operating at about 1500 K). With a graphene-based cathode ($\text{work}\text{function}=4.514\mathrm{eV}$) at 900 K and a metallic-based anode ($\text{work}\text{function}=2.5\mathrm{eV}$) like ${\mathrm{LaB}}_6$ at 425 K, the efficiency of our proposed TIC is about 45%.

Thermally activated delayed-fluorescence (TADF) is a promising approach for realizing highly efficient organic light-emitting diodes (OLEDs). By controlling the spatial overlap between the frontier orbitals to suppress nonradiative decay, we develop a highly efficient TADF emitter, $N^1$-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-$N^1$-[4-(diphenylamino)-phenyl]-$N^4$, $N^4$-diphenylbenzene-1,4-diamine (DPA-TRZ). DPA-TRZ exhibits a photoluminescence quantum efficiency of 100% when doped into a host material, suggesting that nonradiative decay from its excited states is completely suppressed. Transient photoluminescence measurements confirm that DPA-TRZ emits TADF in a doped film. An OLED containing DPA-TRZ as a green emitter shows a maximum external quantum efficiency of 13.8%, which exceeds the theoretical limit for conventional fluorescent OLEDs. This high efficiency results from the effective generation of TADF and suppressed nonradiative decay in DPA-TRZ. Our molecular design strategy based on quantum chemistry provides a rational approach to control radiative and nonradiative decays for optimizing TADF materials.