Quantum control techniques applied at macroscopic scales provide us with opportunities in fundamental physics and practical applications. Among them, measurement-based feedback allows efficient control of optomechanical systems and quantum-enhanced sensing. In this paper, we propose a near-resonant narrow-band force sensor with extremely low optically added noise in a membrane in the middle optomechanical system subject to a feedback-controlled in-loop light. The membrane’s intrinsic motion consisting of zero-point motion and thermal motion is affected by the added noise of measurement due to the backaction noise and imprecision noise. We show that, in the optimal low-noise regime, the system is analogous to an optomechanical system containing a near quantum-limited optical parametric amplifier coupled to an engineered reservoir interacting with the cavity. Therefore, the feedback loop enhances the mechanical response of the system to the input while keeping the optically added noise of measurement below the standard quantum limit. Moreover, the system based on feedback offers a much larger amplification bandwidth than the same system with no feedback. Without the need to hybridize it with other quantum systems or introduce nonlinearities, our force sensor may have broad applications ranging from biology and medicine to gravitational wave detection and tests of fundamental physics.

Due to their limited number of units but outstanding ability to control rather complex wave-propagation phenomena, acoustic coding metasurfaces (ACMs) as two-dimensional metamaterials show a stronger competitiveness in metamaterial applications. However, hindered by their narrow-band modulation capability, the previously reported ACMs do not exhibit a broadband applicability. To address the frequency-based coding capability, in this paper we report broadband acoustic coding metasurfaces (BACMs) whose units are designed by the bottom-up topology optimization method. Subsequently, by utilizing our optimization strategy, we design the 1-bit coding units “0” and “1” with out-of-phase responses and the 2-bit coding units “00”, “01”, “10,” and “11” with four different phase shifts of 0°, 90°, 180°, and 270°. The topological features show constant phase differences, and in the following analysis, we attempt to explain this phenomenon by the related mechanisms of the internal resonances and the bianisotropy effect. The optimized BACMs are beneficial to improve the functions of a fixed coding metasurface in the frequency range. This idea provides an inspiration for fabricating fast-sector-scanning sound antenna. In combination with the convolution method, we also present the design strategy for the broadband fast-scanning multiple-beam antenna. The design of the acoustic antenna is a fixed coding sequence, and its scanning and echolocation mode does not depend on the reconfiguration of the coding units. Furthermore, we also demonstrate a pair of opposite functions, namely the broadband sound focusing and diffusion-scattering characteristics, which have potential applications in ultrasonic therapy, low-scattering target design and noise control, and so on.

As an alternative degree of freedom for wireless communications, orbital angular momentum (OAM) multiplexing and demultiplexing can be applied to achieve higher communication capacity. Metasurface has advanced ability to manipulate electromagnetic (EM) waves, and has gradually become an enabling EM technology for future wireless communications. It is meaningful and useful to combine the advantages of OAM and metasurfaces. Here we propose a multi-OAM-mode vortex wave multiplexing and demultiplexing scheme based on shared-aperture reflective metasurface. The specifically designed reflective metasurface can realize the corresponding OAM-mode modulations and demodulations of different incident carrier waves in the corresponding data channels. By modulating multiple data channels on multiple OAM modes, the multiplication of the communication capacity could be achieved. A prototype operating at microwave frequencies is designed, simulated, and fabricated for proof-of-concept illustration. To validate the OAM multiplexing and demultiplexing scheme, we conduct dual-channel OAM-mode transmission experiments, in which two shared-aperture reflective metasurfaces are adopted as the transmitter and receiver, respectively. This work paves the way for the metasurface-based OAM communication applications in future wireless communication technologies.

We present an eigenvalue-based approach for studying the magnetization dynamics in magnetic nanostructures driven by spintronic excitations, such as spin-transfer torque and spin-orbit torque. The approach represents the system dynamics in terms of normal oscillation modes (eigenstates) with corresponding complex eigenfrequencies. The dynamics is driven by a small number of active eigenstates and often considering just a single eigenstate is sufficient. We develop a perturbation theory that provides semianalytical dynamic solutions by using eigenstates for the case in the absence of damping and spintronic excitations as a basis. The approach provides useful insights into dynamics in such systems and allows solving several difficulties in their modeling, such as extracting the switching current in magnetic random-access memories and understanding switching mechanisms. We show that the presented approach directly predicts the critical switching current, i.e., switching current for an infinite time. The approach also provides solutions for the switching dynamics allowing the switching current to be obtained for a finite switching time, provided that the system symmetry is broken, e.g., by tilting the polarizer, so that switching by a finite pulse is possible.

Nonadiabatic holonomic quantum computation (NHQC) has attracted significant attention due to its fast evolution and the geometric nature-induced resilience to local noises. However, its long operation time and complex physical implementation make it hard to surpass the dynamical scheme, and thus hindering its wide application. Here, we present to implement NHQC with the shortest path under some conditions, through the inverse Hamiltonian engineering technique, which posseses higher fidelity and stronger robustness than previous NHQC schemes. Meanwhile, the gate performance in our scheme can be further improved by using the proposed composite dynamical decoupling pulses, which can efficiently improve both the gate fidelity and robustness, making our scheme outperform the optimal dynamical scheme in a certain parameter range. Remarkably, our scheme can be readily implemented with Rydberg atoms, and a simplified implementation of the controlled-not gate in the Rydberg blockade regime can be achieved. Therefore, our scheme represents a promising progress towards future fault-tolerant quantum computation in atomic systems.

The clinical utility of microfluidic techniques is often hampered by an unsatisfying sample throughput. Here, the effect of inertial forces on acoustofluidic particle sorting at high sample throughputs is investigated experimentally and theoretically. Polystyrene particles are acoustically prefocused to obtain precise trajectories. At increased flow rates it is observed that the particle stream is displaced towards the channel center, and above specific flow settings the particles spill over into the center outlet. This effect, coined the spillover effect, illustrates the complex interplay of viscous and inertial forces inside the microchannel. The effect is due to increased bending of the separatrices at the inlet and outlets and not due to the wall-lift force. The impact of the spillover effect on the separation of two different-sized particles is subsequently studied. Efficient sorting is done for subcritical splitting ratios and flow rates, but for close to critical settings or beyond, there is a breakdown of the acoustofluidic separation.

In two-dimensional van der Waals (vdW) materials, the relative twist angle between adjacent layers not only controls their electronic properties but also determines their stacking energy. This effect makes it difficult to stabilize the vdW materials with twist angles. Here, we demonstrate that we can controllably stabilize the system with custom-designed twist angles, for example, magic angle, which is realized by tailoring the adhesive-energy landscape of graphene nanostructures on graphene by using a one-dimensional tilt grain boundary (GB). Our result demonstrates that the flat band of the custom-built nanoscale magic-angle-twisted bilayer graphene is still robust, even when its size is comparable to a single moiré spot. Moreover, in our experiments, the area ratio with different stacking orders separated by the tilt GB can be continuously tuned by using the scanning-tunneling-microscope tip, and we can repeatedly fold and unfold the graphene nanostructure along the one-dimensional GB, demonstrating the ability to manipulate the graphene nanostructure at the atomic scale.

We show a concept of optical frequency tweezers for tweezing light in the optical frequency domain with a high resolution, which is the frequency version of optical tweezers for the spatial manipulation of microscopic objects. We report a proof-of-principle experiment via frequency conversion inside a cavity only for the converted light. Owing to the atypical configuration, the experiment successfully achieves the tweezing operation in the frequency domain, which picks light at a target frequency from the frequency-multiplexed input light and converts it to a different frequency, without touching any other light sitting in different frequency positions and shaking the frequency by the pump light.

Quantum entanglement represents an ideal resource to guarantee the security of random numbers employed in many scientific and cryptographic applications. However, entanglement-based certified random number generators are particularly challenging to implement. Here, we demonstrate a certified quantum random number generator based on momentum-polarization entangled single-photon states. The use of single-photon entanglement allows an attenuated laser source to be employed and a simple setup where only linear optical components are utilized. For the latter, a semi-device-independent modeling of the photonic quantum random number generator is developed, which certifies a minimum entropy of $(2.5\pm 0.5)\mathrm{\%}$, corresponding to a generation rate of 4.4 kHz. At the expenses of a higher level of trust in the system, the certified minimum entropy can be increased to $(30.1\pm 0.5)\mathrm{\%}$, implying a generation rate of 52.7 kHz. Our results show that a simple optical implementation combined with an accurate modeling provide an entanglement-based high-security quantum random number generator using imperfect devices.

We use phase-resolved imaging to directly study the nonlinear modification of the wavelength of spin waves propagating in 100-nm-thick in-plane magnetized yttrium iron garnet waveguides. We show that, by using moderate microwave power, one can realize spin waves with large amplitudes corresponding to precession angles in excess of 10° and nonlinear wavelength variation of up to 18% in this system. We also find that, at large precession angles, the propagation of spin waves is strongly affected by the onset of nonlinear damping, which results in a strong spatial dependence of the wavelength. This effect leads to spatially dependent controllability of the wavelength by the microwave power. Furthermore, it leads to the saturation of nonlinear spectral shift effects several micrometers away from the excitation point. These findings are important for the development of nonlinear integrated spin-wave signal-processing devices and can be used to optimize their characteristics.

The faithful distribution of entanglement over noisy channels is a vital prerequisite for many quantum technological applications. Quantum information can be encoded in different degrees of freedom (DOF) of photons, where each encoding comes with its own advantages and disadvantages with respect to noise resilience and practicality in manipulation. In this work, we experimentally implement a deterministic entanglement purification protocol that allows us to faithfully distribute entanglement in one DOF over a noisy channel and then remotely transfer it to another DOF for manipulation. In particular, we distribute robust energy-time entanglement and transfer it to polarization entanglement at the communicating parties. The remotely obtained polarization state is independent of the polarization noise during distribution and reaches fidelities to a Bell state of up to $97.6\mathrm{\%}$. Our scheme enables robust and efficient polarization entanglement distribution in the presence of arbitrary polarization noise, which is relevant for future large-scale quantum networks.

The moiré effect provides an interpretation for the steering of antennas that form beams through internal spatial interferences. We make an explicit connection between such antennas and the moiré effect, and use it to model six planar antennas that steer by scaling, rotating, or translating operations. Three of the antennas illustrate how to use moiré patterns to generate antenna designs.

Resistive random-access memory has attracted tremendous attention and numerous investigations as a promising next-generation nonvolatile memory device to address the physical limits of flash memory. Particularly, physically transient resistive switching memory is intensively researched for its degradable and environmentally friendly characteristics. Zinc oxide ($\mathrm{Zn}\mathrm{O}$), as a low-cost biocompatible and biodegradable material, has been widely used in the dielectric layer, yet many previous studies on $\mathrm{Zn}\mathrm{O}$-based memory devices show unsatisfactory switching properties. In this work, ${\mathrm{Mo}\mathrm{S}}_2$ quantum dots (QDs) are added between the $\mathrm{W}$ bottom electrode and $\mathrm{Zn}\mathrm{O}$ insulator by spin coating ($\mathrm{W}/{\mathrm{Mo}\mathrm{S}}_2$ QD$/\mathrm{Zn}\mathrm{O}/\mathrm{Ag}$) to improve its resistive switching behavior. The modified device exhibits distinctly better properties, including more-uniform switching parameters (low- and high-resistance states, $V_{\mathrm{set}}$, $V_{\mathrm{reset}}$), ultralow threshold voltages, and steady retention. Moreover, we transfer the device onto polyvinyl alcohol substrate, making it fully degradable, and it is completely dissolved in phosphate-buffered solution after 40 min. These results indicate that the ${\mathrm{Mo}\mathrm{S}}_2$ QD–optimized transient resistive switching memory shows great potential in green electronics, implantable biomedical devices, and secure information-storage applications.

An ultrahigh electric field induced by ionic liquid gating (ILG) can be employed to manipulate ferromagnetism with low Joule heating dissipation, showing great potential for spintronics applications. In ferromagnetic/heavy metal thin films, however, typical materials used in both layers are electron-carrier dominant, which significantly suppresses the ILG effect due to the short electrostatic screening length in metal. Here, we employ ${\mathrm{Mn}}_2\mathrm{Co}\mathrm{Al}$, a spin gapless semiconductor with hole carriers, as the ferromagnetic layer and investigate the ILG effect in $\mathrm{Mg}\mathrm{O}/{\mathrm{Mn}}_2\mathrm{CoAl/Pd}$ ultrathin films with perpendicular magnetic anisotropy. Reversible change of the magnetic anisotropy from the out-of-plane to the in-plane direction is achieved, induced by electrostatic charge accumulation. Moreover, ambipolar transport behavior has been observed and explained by a two-carrier model. Finally, we find that skew scattering is the mechanism of the anomalous Hall effect and can be enhanced at a positive gate voltage in our system. Our results strongly demonstrate that a significant ILG effect on magnetism can be easily achieved in two-carrier dominant ultrathin films.

The interaction of radiation with chiral molecular films is not macroscopically invariant under mirror reflections and, accordingly, chiro-optical effects exist which affect the spatial symmetry of the radiation profile and which almost exclusively show up in the near field due to the large mismatch between molecule size and wavelength size. Here we prove that the scattering of a mirror-symmetric pair of plane waves by a nanowire lying on a chiral nanofilm is not mirror-symmetric with an angular dissymmetry factor that can be as large as a few tenths. Due to evanescent coupling, the nanowire efficiently experiences molecular chirality which produces a spatially asymmetric near field so that the self-consistent unbalanced excitation of nanowire photonic modes with opposite angular momenta yields asymmetric far-field interference. In addition to enriching the physical understanding of mirror symmetry breaking in chiral nanophotonics, our results could suggest ultra-efficient schemes for enantiomeric discrimination which is essential in biological chemistry and pharmacology.

Voltage-controlled magnetic anisotropy (VCMA) is a low-energy alternative to manipulate the ferromagnetic state, which has been recently also considered in antiferromagnets (AFMs). Here, we theoretically demonstrate that VCMA can be used to excite linear and parametric resonant modes in easy-axis AFMs with perpendicular anisotropy, thus opening the way for an efficient electrical control of the Néel vector and for the detection of high-frequency dynamics. Our work leads to two key results: (i) VCMA parametric pumping experiences the so-called “exchange enhancement” of the coupling efficiency and, thus, is 1–2 orders of magnitude more efficient than microwave magnetic fields or spin-orbit torques, and (ii) it also allows for zero-field parametric resonance, which cannot be achieved by other parametric pumping mechanisms in AFMs with an out-of-plane easy axis. Therefore, we demonstrate that VCMA parametric pumping is the most promising method for coherent excitation and manipulation of AFM order in perpendicular easy-axis AFMs.

We explore the implementation of hybridly protected quantum operations combining the merits of geometry and holonomy, dynamical decoupling approach, and dephasing-free feature based on a simple and experimentally achievable spin model. The implementation of the quantum operations can be achieved in different physical systems with controllable parameters. The protected quantum operations are hence controllable and well suited for resolving various quantum-computation tasks, such as executing quantum error-correction codes or quantum error mitigation. Our scheme is based on an experimentally achievable Hamiltonian with reduced requirement of computational resources and thus, it brings us closer towards realizing protected quantum operations for resolving quantum-computation tasks in near-term quantum devices.

Scanning superconducting quantum interference device (SQUID) microscopy is a magnetic imaging technique combining high field sensitivity with nanometer-scale spatial resolution. Here, we demonstrate a scanning probe that combines the magnetic and thermal imaging provided by an on-tip SQUID with the tip-sample distance control and topographic contrast of a noncontact atomic force microscope (AFM). We pattern the nanometer-scale SQUID, including its weak-link Josephson junctions, via focused-ion-beam milling at the apex of a cantilever coated with Nb, yielding a sensor with an effective diameter of 365 nm, field sensitivity of $9.5\mathrm{nT}/\sqrt{\mathrm{Hz}}$, and thermal sensitivity of $620\mathrm{nK}/\sqrt{\mathrm{Hz}}$, operating in magnetic fields up to 1.0 T. The resulting SQUID-on-lever probe is a robust AFM-like scanning probe that expands the reach of sensitive nanometer-scale magnetic and thermal imaging beyond what is currently possible.

The modulation of millimeter-wave transmission through a silicon wafer upon photoexcitation is typically very inefficient for off-the-shelf low effective charge carrier lifetime wafers, typically requiring tens of kilowatts of photoexciting intensity to generate significant modulation. Here we demonstrate that increasing the light-matter interaction for the millimeter waves using diffractively coupled waveguide modes leads to an increase in photomodulation efficiency of greater than two orders of magnitude, while maintaining the switching speed, of the order of $10\mu \mathrm{s}$, of the bare wafer.