We propose a theoretical protocol to implement multiqubit geometric gates (i.e., the Mølmer-Sørensen gate) using photonic cat-state qubits. These cat-state qubits stored in high-$Q$ resonators are promising for hardware-efficient universal quantum computing. Specifically, in the limit of strong two-photon drivings, phase-flip errors of the cat-state qubits are effectively suppressed, leaving only a bit-flip error to be corrected. Because this dominant error commutes with the evolution operator, our protocol preserves the error bias, and, thus, can lower the code-capacity threshold for error correction. A geometric evolution guarantees the robustness of the protocol against stochastic noise along the evolution path. Moreover, by changing detunings of the cavity-cavity couplings at a proper time, the protocol can be robust against parameter imperfections (e.g., the total evolution time) without introducing extra noises into the system. As a result, the gate can produce multimode entangled cat states in a short time with high fidelities.

Spin torque is a promising tool for driving magnetization dynamics for computing technologies. These torques can be easily produced by spin-orbit effects, but for most conventional spin source materials, a high degree of crystal symmetry limits the geometry of the spin torques produced. Magnetic ordering is one way to reduce the symmetry of a material and allow exotic torques, and antiferromagnets are particularly promising because they are robust against external fields. We present spin torque ferromagnetic resonance (ST-FMR) measurements and second harmonic Hall measurements characterizing the spin torques in antiferromagnetic iron rhodium alloy. We report extremely large, strongly temperature-dependent exotic spin torques with a geometry apparently defined by the magnetic ordering direction. We find the spin torque efficiency of iron rhodium to be (207 ± 94)% at 170 K and (88 ± 32)% at room temperature. We support our conclusions with theoretical calculations showing how the antiferromagnetic ordering in iron rhodium gives rise to such exotic torques.

We report the detection of a gate-tunable kinetic inductance in a hybrid $\mathrm{In}\mathrm{As}$/$\mathrm{Al}$ nanowire. For this purpose, we embed the nanowire into a quarter-wave coplanar waveguide resonator and measure the resonance frequency of the circuit. We find that the resonance frequency can be changed via the gate voltage that controls the electron density of the proximitized semiconductor and thus the nanowire inductance. Applying Mattis-Bardeen theory, we extract the gate dependence of the normal-state conductivity of the nanowire, as well as its superconducting gap. Our measurements complement existing characterization methods for hybrid nanowires and provide a useful tool for gate-controlled superconducting electronics.

Spontaneous symmetry breaking is a source of the phase transition in a variety of physical systems including such as non-Hermitian. It has recently been demonstrated that so-called exceptional points, which are singularities in non-Hermitian systems, separate the areas with symmetrical and asymmetrical eigenstates. Such separation is evidence of phase transitions in non-Hermitian systems taking place at exceptional points. In this paper, we experimentally demonstrate that exceptional-point phase transition in a system of two coupled magnonic waveguides coupled by dipole-dipole interaction occurs. Using infrared laser irradiation to control the spin-wave losses in one of the waveguides covered by a semiconductor $\mathrm{GaAs}$ layer, we observe a change in the wave numbers of the propagating spin waves and a change in the distribution of spin-wave intensity between the waveguides. Retrieving the experimental data, we find the spin-wave propagation parameters and, based on these and the use of coupled mode theory, we argue that in the system of magnonic waveguides the exceptional-point phase transition is observed.

Fragmentation of liquid-metal droplets irradiated by linearly and circularly polarized femtosecond laser pulses is observed in our experiment. The obtained shadowgraph snapshots demonstrate that a circularly polarized pulse may produce several randomly oriented jets effused from the expanding droplets, while a linearly polarized laser pulse generates strictly the cruciform jets. The latter orientation is tied with polarization plane, rotation of which causes rotation of the cruciform jets by the same angle. To shed light on the experimental data we perform molecular dynamics simulation of droplet expansion induced by angle-dependent heating. Our simulation shows that the jet directions are determined by an oriented angle-dependent energy distribution within a frontal hemisphere layer of droplet after absorption of linearly polarized light. As a result, the produced flow velocity field guided by surface tension forms two high-speed opposite jets oriented across the electric field vector as in our experiment. A shock-wave pulse generated in the frontal layer has angle-dependent amplitude inherited from the oriented energy deposition. The release part of shock pulse produces a cavitation zone nearby the droplet center, and thus an expanding spherical shell is formed from the droplet. The flow velocities within a rearside hemisphere of the shell, produced after reflection of the shock wave from the rear side of droplet, generate two low-speed opposite jets oriented along the electric field vector. Thus we find that the cruciform jets are originated independently from the frontal and rear sides of droplet, and a pair of frontal jets is faster than a pair of rearside jets.

We present an antiferromagnetically exchange-coupled composite (soft and hard layers) spin torque oscillator (AF-ECC STO) and demonstrate its operation via both analytical and micromagnetic modeling. The operation exploits the exchange field due to the antiferromagnetic coupling between soft and hard sublayers of the free layer as well as on the easy-plane anisotropy of the soft sublayer. Optimized AF-ECC STO structures can generate large-amplitude magnetization oscillations, which can be tuned over a broad frequency range with precessions mostly generated by the soft layer. We demonstrate that the AF-ECC STO structure offers flexibility in current control of the oscillation frequency and magnetization angle for realistic material parameters.

Airy beams are peculiar beams that are nondiffracting, self-accelerating, and self-healing, and they have offered great opportunities for ultrasound-beam manipulation. However, one critical barrier that limits the broad applications of Airy beams in ultrasound is the lack of simply built devices to generate Airy beams in water. This work presents a family of Airy-beam-enabled binary acoustic metasurfaces (AB BAMs) to generate Airy beams for underwater ultrasound-beam manipulation. AB BAMs are designed and fabricated by three-dimensional (3D) printing with two coding bits: a polylactic acid (which is the commonly used 3D printing material) unit acting as a bit “1” and a water unit acting as a bit “0.” The distribution of the binary units on the metasurface is determined by the pattern of Airy beam. To showcase the wave-front engineering capability of the AB BAMs, several examples of AB BAMs are designed, 3D printed, and coupled with a planar single-element ultrasound transducer for experimental validation. We demonstrate the capability of AB BAMs in flexibly tuning the focal region size and beam focusing in 3D space by changing the design of the AB BAMs. The focal depth of AB BAMs can be continuous and electronical tuned by adjusting the operating frequency of the planar transducer without replacing the AB BAMs. The superimposing method is leveraged to enable the generation of complex acoustic fields, e.g., multifoci and letter patterns (e.g., “W” and “U”). The more complex focal patterns are shown to be also continuously steerable by simply adjusting the operating frequency. Furthermore, the proposed 3D-printed AB BAMs are simple to design, easy to fabricate, and low cost to produce with the capabilities to achieve tunable focal size, flexible 3D beam focusing, arbitrary multipoint focusing, and continuous steerability, which creates unprecedented potential for ultrasound-beam manipulation.

Transition-edge-sensor (TES) microcalorimeters and bolometers are used for a variety of applications. The sensors are based on the steep temperature-dependent resistance of the normal-to-superconducting transition, and are thus intrinsically sensitive to magnetic fields. Conventionally the detectors are shielded from stray magnetic fields using external magnetic shields. However, in particular for applications with strict limits on the available space and mass of an instrument, external magnetic shields might not be enough to obtain the required shielding factors or field homogeneity. Additionally, these shields are only effective for magnetic fields generated external to the TES array, and are ineffective to mitigate the impact of internally generated magnetic fields. Here we present an alternative shielding method based on a superconducting groundplane deposited directly on the backside of the silicon nitride membrane on which the TESs are located. We demonstrate that this local shielding for external magnetic fields has a shielding factor of at the least approximately $80$, and is also effective at reducing internal self-induced magnetic fields, as demonstrated by measurements and simulation of the eddy current losses in our ac-biased detectors. Measurements of 5.9-keV x-ray photons show that our shielded detectors have a high resilience to external magnetic fields, showing no degradation of the energy resolution or shifts of the energy-scale calibration for fields of several microtesla, values higher than expected in typical real-world applications.

Very recently, strongly non-Gaussian states have been observed via a direct three-mode spontaneous parametric down-conversion in a superconducting cavity [Phys. Rev. X 10, 011011 (2020)]. The created multiphoton non-Gaussian correlations are attractive and useful for various quantum information tasks. However, how to detect and classify multipartite non-Gaussian entanglement has not yet been completely understood. Here, we present an experimentally practical method to characterize continuous-variable multipartite non-Gaussian entanglement, by introducing a class of nonlinear squeezing parameters involving accessible higher-order moments of phase-space quadratures. As these parameters can depend on arbitrary operators, we consider their analytical optimization over a set of practical measurements, in order to detect different classes of multipartite non-Gaussian entanglement ranging from fully separable to fully inseparable. We demonstrate that the nonlinear squeezing parameters act as an excellent approximation to the quantum Fisher information within accessible third-order moments. The level of the nonlinear squeezing quantifies the metrological advantage provided by those entangled states. Moreover, by analyzing the above-mentioned experiment, we show that our method can be readily used to confirm fully inseparable tripartite non-Gaussian entangled states by performing a limited number of measurements without requiring full knowledge of the quantum state.

The static and dynamic properties of skyrmions have recently received increased attention due to the potential application of skyrmions as information carriers and for unconventional computing. While the current-driven dynamics has been explored deeply, both theoretically and experimentally, the theory of temperature gradient-induced dynamics—skyrmion caloritronics—is still at its early stages of development. Here, we move the topic forward by identifying the role of entropic torques due to the temperature dependence of magnetic parameters. Our results show that skyrmions move towards higher temperatures in single-layer ferromagnets with interfacial Dzyaloshinski-Moriya interactions, whereas, in multilayers, they move to lower temperatures. We analytically and numerically demonstrate that the opposite behaviors are due to different scaling relations of the material parameters as well as a non-negligible magnetostatic field gradient in multilayers. We also find a spatially dependent skyrmion Hall angle in multilayers hosting hybrid skyrmions due to variations of the thickness-dependent chirality as the skyrmion moves along the temperature gradient.

The conversion between spin and orbital angular momentum plays a crucial role in modern science and has a wide range of applications in optical multistate magnetization, optical micromanipulation, classical and quantum optical communications. However, it becomes difficult in many complex environments due to the inherent scattering effect. Here, we experimentally demonstrate the active control of spin and orbital angular-momentum conversion of light by a scattering system. We obtain significant optimization results and prove that the angular-momentum conversion process in scattering medium is tunable and flexible. Our work opens the door for high-dimensional optical information exchange in complex circumstance and paves the way for applications of optical angular momentum in optical communication.

Herein, we demonstrate the ability to optically tune the mobility of electrically powered Janus particles (JPs) that are half-coated with various zinc oxide ($\mathrm{Zn}\mathrm{O}$) semiconducting layers, i.e., polycrystalline, amorphous, and amorphous with a ${\mathrm{Si}\mathrm{O}}_2$ passivation layer. The $\mathrm{Zn}\mathrm{O}$ semiconductor photoresponse causes an increase in its electrical conductivity with light having wavelengths of sufficient photon energy with respect to the semiconductor band gap. This effect, which we name optically modulated electrokinetic propulsion (OMEP), can be harnessed to increase the contrast in polarizability between the dielectric and semiconducting hemispheres, which, in turn, results in an increased electrokinetic mobility. Optical control of electrical field propulsion enables an additional degree of control of JP mobility. We also demonstrate optical modulation of collective behavior and particle-particle interactions for dense semiconducting Janus particle populations.

Type-II superlattices (T2SLs) exemplified by $\mathrm{In}\mathrm{As}/\mathrm{Ga}\mathrm{Sb}$ are promising for infrared detection as the cutoff wavelength can simply be tuned by the layer thickness. Computational material design is thus highly desirable, but traditional methods such as tight binding and k·p depend on the choice of parameters. Ab initio density-functional-theory (DFT) calculations, on the other hand, suffer from a dilemma because band-gap accuracy and computational efficiency cannot be reached simultaneously due to band-gap underestimation. Here we show the great potential of the shell DFT-1/2 method in the material design of T2SLs. With a single parameter input, the lattice constant, or even without parameter, the method yields satisfactory electronic structures for a series of $\mathrm{In}\mathrm{As}/\mathrm{Ga}\mathrm{Sb}$ T2SLs considering spin-orbit coupling, with the band-gap mismatch limited to 5% compared with our industry-class samples. Detailed miniband analysis is presented based on the ab initio results. For covalent semiconductors without strong correlation, shell DFT-1/2 proves to be an excellent candidate for accurate band-structure calculation with local-density-approximation-level efficiency. It enables the material design of III-V superlattice materials at the engineering level without introducing empirical parameters.