In this paper, we show that the Gouy phase shift plays a key role in the far-field waveform evolution of the reflected harmonic radiations from plasma surfaces driven by a relativistic Gaussian laser. With a proper adjustment of laser focal position away from the plasma surface, the inherent separations between the peaks of different harmonic carrier waves as well as the fundamental wave due to different wavelengths can be cleared away when they propagate from near to far field, since they experience the same Gouy phase shift of $\pi /2$. Using this method, intense attosecond pulses can be obtained in the far field with no need of any spectral filters. Three-dimensional particle-in-cell simulations show that far-field attosecond pulses with intensity of $4\times {10}^{15}\mathrm{W}/{\mathrm{cm}}^2$ ($2.56\times {10}^{17}\mathrm{W/sr}$; 65 times increase) and duration of $76\mathrm{as}$ (50% decrease) can be obtained by lasers at intensities of ${10}^{21}\mathrm{W}/{\mathrm{cm}}^2$. Such brilliant pulses with fully reserved spectra significantly benefit applications in attosecond science.

The mapping of the potential landscape with high spatial resolution is crucial for quantum technologies based on ultracold atoms. However, the imaging of optical dipole traps is challenging because purely optical methods, commonly used to profile laser beams in free space, are not applicable in a vacuum. In this work, we demonstrate precise in situ imaging of optical dipole traps by probing a hyperfine transition with Ramsey interferometry. Thereby, we obtain an absolute map of the potential landscape with micrometer resolution and shot-noise-limited spectral precision. The idea of the technique is to control the polarization ellipticity of the trap laser beam to induce a differential light shift proportional to the trap potential. By studying the response to polarization ellipticity, we uncover a small but significant nonlinearity in addition to a dominant linear behavior, which is explained by the geometric distribution of the atomic ensemble. Our technique for imaging of optical traps can find wide application in quantum technologies based on ultracold atoms, as it applies to multiple atomic species and is not limited to a particular wavelength or trap geometry.

We demonstrate that the effects of spin-orbit coupling and inversion asymmetry exist in a single $\mathrm{Gd}\text{−}\mathrm{Fe}\text{−}\mathrm{Co}$ ferrimagnetic layer, even without a heavy-metal interface. We use electric transport measurements to quantify the spin-orbit torques. We measure the Dzyaloshinskii-Moriya interaction using the Brillouin light-scattering measurement technique, and we observe the resulting chiral magnetic textures using x-ray photoemission electron microscopy. We attribute these effects to a composition variation along the thickness that we observe by scanning transmission electron microscopy. We show that these effects can be optimized by varying the $\mathrm{Gd}\text{−}\mathrm{Fe}\text{−}\mathrm{Co}$ thickness or in combination with interfacial effects.

Two-qubit gates in trapped-ion quantum computers are generated by applying spin-dependent forces that temporarily entangle the internal state of the ion with its motion. Laser pulses are carefully designed to generate a maximally entangling gate between the ions while minimizing any residual entanglement between the motion and the ion. The quality of the gates suffers when the actual experimental parameters differ from the ideal case. Here, we improve the robustness of frequency-modulated Mølmer-Sørensen gates to motional mode-frequency offsets by optimizing the average performance over a range of systematic errors using batch optimization. We then compare this method with frequency-modulated gates optimized for ideal parameters that include an analytic robustness condition. Numerical simulations show good performance up to 12 ions, and the method is experimentally demonstrated on a two-ion chain.

Nanoribbons of topological insulators (TIs) have been suggested for a variety of applications exploiting the properties of the topologically protected surface Dirac states. In these proposals it is crucial to achieve a high tunability of the Fermi energy, through the Dirac point while preserving a high mobility of the involved carriers. Tunable transport in TI nanoribbons has been achieved by chemical doping of the materials so to reduce the bulk carriers’ concentration, however at the expense of the mobility of the surface Dirac electrons, which is substantially reduced. Here we study bare ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ nanoribbons transferred on a variety of oxide substrates and demonstrate that the use of a large relative permittivity ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ substrate enables the Fermi energy to be tuned through the Dirac point and an ambipolar field effect to be obtained. Through magnetotransport and Hall conductance measurements, performed on single ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ nanoribbons, we demonstrate that electron and hole carriers are exclusively high-mobility Dirac electrons, without any bulk contribution. The use of ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ allows therefore an easy field effect gating in TI nanostructures providing an ideal platform to take advantage of the properties of topological surface states.

The superconducting transmon qubit is currently a leading qubit modality for quantum computing, but the gate performance in a quantum processor with transmons is often insufficient to support the running of complex algorithms for practical applications. It is thus highly desirable to further improve gate performance. Due to the weak anharmonicity of a transmon, a static $ZZ$ interaction between coupled transmons commonly exists, undermining the gate performance and, in the long term, it can become performance limiting. Here, we theoretically explore a promising parameter region in an all-transmon system to address this issue. We show that a feasible parameter region, where the $ZZ$ interaction is heavily suppressed, while leaving the $XY$ interaction with an adequate strength to implement two-qubit gates, can be found for all-transmon systems. Thus, two-qubit gates, such as a cross-resonance gate or an iswap gate, can be realized without a detrimental effect from the static $ZZ$ interaction. To illustrate this, we demonstrate that an iswap gate with a fast gate speed and dramatically lower conditional phase error can be achieved. By scaling up to a large-scale transmon quantum processor, especially for cases with fixed coupling, addressing errors, idling errors, and crosstalk that arise from the static $ZZ$ interaction can also be strongly suppressed.

Thin films are gaining ground in photonics and optoelectronics because of promising improvements in their efficiency and functionality, as well as decreased material usage compared with bulk technologies. However, the proliferation of thin films would benefit not only from continuous improvements in their fabrication, but also from a unified and accurate theoretical framework of the interplay of photons and charge carriers. In particular, such a framework would need to account quantitatively and self-consistently for photon recycling and interference effects. To this end, here, we combine the drift-diffusion formalism of charge-carrier dynamics and the fluctuational electrodynamics of photon transport self-consistently using the recently introduced interference-extended radiative-transfer equations. The resulting equation system can be solved numerically using standard simulation tools and, as an example, here, we apply it to study well-known $\mathrm{Ga}\mathrm{As}$ thin-film solar cells. In addition to obtaining the expected device characteristics, we analyze the underlying complex photon-transport and recombination-generation processes, demonstrating the physical insight provided for unevenly excited structures through the direct and self-consistent description of photons and charge carriers. The methodology proposed here is general and can be used to obtain an accurate physical insight into a wide range of planar optoelectronic devices, of which the thin-film single-junction solar cells studied here are only one example.

Using a multilayer containing a cobalt detector layer, a copper spacer, and a Permalloy source layer, we show experimentally how the nonreorientable spin-orbit torque generated by the Permalloy source layer—the component of spin-orbit torque that does not change when the Permalloy magnetization is rotated—can be measured using spin-torque ferromagnetic resonance (ST FMR) with line-shape analysis. We find that dynamic spin pumping between the magnetic layers exerts torques on the magnetic layers as large as, or larger than, the spin-orbit torques, so that if dynamic spin pumping is neglected, the result will be a large overestimate of the spin-orbit torque. Nevertheless, the two effects can be separated by performing ST FMR as a function of the frequency. We measure a nonreorientable spin torque ratio ${\xi }_{\mathrm{DL}}=0.04\pm 0.01$ for the spin-current flow from Permalloy through an 8-nm $\mathrm{Cu}$ spacer to the $\mathrm{Co}$ and a strength of dynamic spin pumping that is consistent with previous measurements by conventional ferromagnetic resonance.

Holographic acoustical tweezers based on Archimedes-Fermat spiraling interdigitated transducers (SIDTs) are a versatile tool for the selective manipulation of microparticles [Baudoin et al., Sci. Adv. 5, eaav1967 (2019)] and cells [Baudoin et al., Nat. Commun., 11, 4244 (2020)] in a standard microfluidic environment. These binary active holograms produce some focused helical wave, with the ability to trap particles at the vortex core. Yet, all the studies conducted with SIDTs have so far been restricted to two-dimensional (2D) manipulation only. Here we show through a theoretical study that (i) a 3D radiation trap for microparticles and cells can be obtained with spiraling tweezers with sufficiently large aperture and that (ii) the particles can be displaced axially by simply tuning the driving frequency, without any motion of the transducer. This work opens perspectives for 3D cells and microparticles manipulation with single-beam acoustical tweezers.

Metamaterials with near-zero permittivity exhibit extraordinary total transmission of waves within the length-independent conduit. However, such an ε-near-zero (ENZ) transmission mode demonstrates an intrinsic narrow-band property using low-loss metastructures, e.g., extremely narrow waveguide transition at the cutoff frequency. As the counterpart to the ENZ mode, the Fabry-Perot (FP) mode also has near-zero reflection but depends on the channel length. For application considerations, the phenomenon of superpositioning ENZ and FP modes is analyzed theoretically and numerically to enhance the bandwidth of near-zero reflection within extreme mismatching waveguide transitions. The achieved bandwidth of the ENZ and FP mode cooperation is larger than the sum of two single modes, exhibiting feasible applications in the integrated waveguide structures, such as integrated transmission lines, circuits, and antennas. As an application example of this physical property, a waveguide crossover is proposed and experimentally verified to achieve wideband dual-narrow-channel total transmission within only one dielectric layer with an extremely low profile.

Recently discovered photonic higher-order topological insulators enable unprecedented flexibility in the robust localization of light in structures of different dimensionality. While the potential of the two-dimensional systems is currently under active investigation, only a few studies explore the physics of the three-dimensional higher-order topological insulators. Here we propose a three-dimensional structure with cubic symmetry exhibiting vanishing bulk polarization but nonzero corner charge and hosting a zero-dimensional corner state mediated by the long-range interactions. We trace the evolution of the corner state with the next-nearest-neighbor coupling strength and prove the topological origin of the corner mode, calculating the associated topological invariants. Our results thus reveal the potential of long-range couplings for the formation of three-dimensional higher-order topological phases.

Two-dimensional (2D) materials with intrinsic metal properties are promising for battery applications. Herein, we theoretically design a series of $X_2\mathrm{BC}$ ($X=$ $\mathrm{Mg}$, $\mathrm{Ca}$, $\mathrm{Sr}$, $\mathrm{Ti}$, $\mathrm{V}$, $\mathrm{Mo}$) sheets as anode materials for $\mathrm{Li}$-ion and $\mathrm{Na}$-ion batteries (LIBs and NIBs) using first-principles calculations based on density functional theory. The $X_2\mathrm{BC}$ sheets are found to be intrinsically metallic with good stability. Besides, $X_2\mathrm{BC}$ ($X=$ $\mathrm{Mg}$, $\mathrm{Ca}$, $\mathrm{Sr}$) sheets are auxetic 2D materials. More interestingly, the highest predicted specific capacities are calculated to be 1502, 1042, and $905{\mathrm{mAh\; g}}^{-1}$ for ${\mathrm{Mg}}_2\mathrm{BC}$, ${\mathrm{Ca}}_2\mathrm{BC}$, and ${\mathrm{Ti}}_2\mathrm{BC}$, respectively. The activation energy barrier of $\mathrm{Na}$ on ${\mathrm{Ti}}_2\mathrm{BC}$ (0.105 eV) is the lowest among all the considered $\mathrm{Li}$ and $\mathrm{Na}$ $X_2\mathrm{BC}$ structures. The calculated open-circuit voltage values of 0.040 V (0.153 V) and 0.353 V (0.200 V) for $\mathrm{Li}$ ($\mathrm{Na}$) of ${\mathrm{Ca}}_2\mathrm{BC}$ and ${\mathrm{Ti}}_2\mathrm{BC}$, respectively, fall within the acceptable range of 0.1–1.0 V for anode materials. They are found to be smaller than or comparable with those of commercial graphite anode. The results show that $X_2\mathrm{BC}$ sheets are promising candidates for both LIBs and NIBs.

We theoretically propose a switching device that operates at room temperature. The device is an in-plane heterostructure based on a periodically boron-doped (nitrogen-doped) armchair graphene nanoribbon, which has been experimentally fabricated recently. The calculated $I$-$V$ curve shows that for a realistic device with interface width longer than $20$ nm, nonzero electric current occurs only in the region of bias voltage between $-0.22$ and $0.28$ V, which is beneficial to low-voltage operation. Furthermore, in this case, the electric current is robust against the change of the potential profile in the interface since the metallic impurity-induced sub-bands with delocalized wave functions contribute to the transmission exclusively. This also suggests the high response speed of the proposed device. We also discuss the temperature dependence, the output impedance, the effect of phonons, and the possible regimes to extend our work, which suggest that our model may have potential room-temperature nanoelectronics applications.

We study experimentally the propagation of nanosecond spin-wave pulses in microscopic waveguides made of nanometer-thick yttrium iron garnet films. For these studies, we use microfocus Brillouin light-scattering spectroscopy, which provides the possibility to observe propagation of the pulses with high spatial and temporal resolution. We show that, for most spin-wave frequencies, dispersion leads to broadening of the pulse by several times at propagation distances of 10 µm. However, for certain frequency interval, the dispersion broadening is suppressed almost completely resulting in a dispersionless pulse propagation. We show that the formation of the dispersion-free region is caused by the competing effects of the dipolar and the exchange interaction, which can be controlled by the variation of the waveguide geometry. These conclusions are supported by micromagnetic simulations and analytical calculations. Our findings provide a simple solution for the implementation of high-speed magnonic systems that require undisturbed propagation of short information-carrying spin-wave pulses.

Great challenges are encountered when solving problems based on continuously generated data streams due to the online data input fashion and limited memory space. Quantum properties are helpful in dealing with stream data. In this work, we design and experimentally implement a quantum streaming algorithm (QSA) with various lengths of input data in a single-defect spin system in silicon carbide at room temperature. We explore the schemes with trusted advice on the output results during the algorithm execution. Quite contrary to the classical case, outdated advice is still useful in the quantum case, as revealed by a proper performance function. Our work demonstrates the advantage of the QSA, which would be useful for investigating complex online problems. The room-temperature solid-state spin platform based on such a technological material opens the door for scalable quantum-information processing.

We explore the deformation of tin microdroplets of various diameters induced by two consecutive laser pulses having pulse durations of 0.4 ns. Impact of laser pulses with this duration mainly leads to shock-wave-induced cavitation and spallation. The main result obtained in this work is the observation of a strong reduction of the spall velocity that depends on the time delay between the two pulses. This reduction reveals a complex interplay between plasma recoil pressure and shock-wave-driven deformation, and enables an estimation of the moment of spall formation and the average shock-wave propagation velocity. We find that the shock wave traverses the droplet with an average velocity ranging from 1.2 to 1.6 times the speed of sound. We study the effects of the energy of the second pulse on the deformation and qualitatively discuss the formation of microjets. Crucially, we demonstrate the ability to manipulate the microdroplet expansion and spallation with double-pulse sequences, thereby increasing the portfolio of obtainable target shapes for droplet-based extreme ultraviolet light sources.

We propose a method to assist fault mitigation in quantum computation through the use of sensors co-located near physical qubits. Specifically, we consider using transition edge sensors co-located on silicon substrates hosting superconducting qubits to monitor for energy injection from ionizing radiation, which has been demonstrated to increase decoherence in transmon qubits. We generalize from these two physical device concepts and explore the potential advantages of co-located sensors to assist fault mitigation in quantum computation. In the simplest scheme, co-located sensors beneficially assist rejection of calculations potentially affected by environmental disturbances. Investigating the potential computational advantage further required development of an extension to the standard formulation of quantum error correction. In a specific case of the standard three-qubit, bit-flip quantum error-correction code, we show that given a 20% overall error probability per qubit, approximately 90% of repeated calculation attempts are correctable. However, when sensor-detectable errors account for 45% of overall error probability, the use of co-located sensors uniquely associated with independent qubits boosts the fraction of correct final-state calculations to 96%, at the cost of rejecting 7% of repeated calculation attempts.

We demonstrate a superconducting transmon qubit in which a Josephson junction has been engineered to act as its own parallel shunt capacitor. This merged-element transmon potentially offers a smaller footprint than conventional transmons. Because it concentrates the electromagnetic energy inside the junction, it reduces the relative electric field participation from other interfaces. By combining micrometer-scale $\mathrm{Al}$/$\mathrm{Al}\mathrm{O}$${}_x$/$\mathrm{Al}$ junctions with long oxidations, we produce functional devices with $E_J/E_C$ in the low-transmon regime ($E_J/E_C\lesssim 30$). Cryogenic $I$-$V$ measurements show a sharp $dI/dV$ structure with low subgap conduction. Qubit spectroscopy of tunable versions shows a small number of avoided level crossings, suggesting the presence of two-level systems. We observe mean $T_1$ times typically in the range of $10–90\mu \mathrm{s}$, with some annealed devices exhibiting $T_1>100\mu \mathrm{s}$ over several hours. The results suggest that energy relaxation in conventional small-junction transmons is not limited by junction loss.