Cavity optomechanics enables photon-phonon interaction and correlations by harnessing the radiation-pressure force. Here, we realize a “cavity-in-a-membrane” optomechanical architecture, which allows detection of the motion of lithographically defined, ultrathin membranes via an integrated optical cavity. Using a dissipative filtering method, we are able to eliminate the probe light in situ and observe photon-phonon correlations associated with the low-frequency membrane mechanical mode. The developed method is generally applicable for study of low-frequency light-scattering processes where conventional frequency-selective filtering is unfeasible.

We present a gate-voltage-tunable transmon qubit (gatemon) based on planar $\mathrm{In}\mathrm{As}$ nanowires that are selectively grown on a high-resistivity silicon substrate using III-V buffer layers. We show that low-loss superconducting resonators with an internal quality of $2\times {10}^5$ can readily be realized using these substrates after the removal of buffer layers. We demonstrate coherent control and readout of a gatemon device with a relaxation time, $T_1\approx 700\mathrm{ns}$, and dephasing times, $T_2^{\ast }\approx 20\mathrm{ns}$ and $T_{2,\mathrm{echo}}\approx 1.3\mu \mathrm{s}$. Further, we infer a high junction transparency of $0.4$–$0.9$ from an analysis of the qubit anharmonicity.

A spin ensemble in thermal equilibrium continuously undergoes random fluctuations analogous to those observed in Brownian motion, a process known as spin noise. Here, we investigate the dynamics of a system comprising a spin-1 paramagnetic center and a hyperfine-coupled spin-1/2 nucleus in the vicinity of a level crossing. We theoretically show that nuclear spins polarize efficiently under the combined action of thermal fluctuations and a closed-loop feedback protocol. The latter articulates periodic observations of the electronic magnetization and radio-frequency pulses connecting hybrid states with opposite nuclear spin alignment. Since nuclear polarization emerges from electronic spin fluctuations, not spin order, this microwave-free technique generically benefits from warmer, not colder, operation temperatures. Furthermore, because the spin dynamics at play near a level crossing is rather insensitive to the absolute value of the magnetic field, our work promises opportunities for high-field dynamic nuclear polarization, which is difficult to attain through present methods.

Optical vector beams with a higher-order polarization state, represented by a point on a higher-order Poincaré sphere, have recently found advantages in various applications. However, the considered beams are usually spatially fully coherent (monochromatic), which makes them susceptible to complex environments. In this work, we introduce a coherence-engineering protocol to generate partially coherent vectorial secondary light sources in which a higher-order polarization state is encoded into the structure of electromagnetic spatial coherence. The encoded complex polarization state is well reconstructed in the far field whose global degree of polarization can be controlled with the transverse coherence length of the source. In particular, the produced partially coherent beams are highly robust against obstructions, which is demonstrated theoretically and experimentally by inserting a static obstacle against the source or introducing strong atmospheric turbulence into the transmission link. The results of this work can find useful applications in the transfer of complicated polarization-encoded information in harsh environments.

Owing to their dual-resonance enhanced sensitivity, cavity optomechanical systems provide an ideal platform for ultrasound sensing. In this work, we realize high-sensitivity air-coupled ultrasound sensing from kilohertz to megahertz frequency range based on whispering gallery mode microcavities. Using a $57$-$\mu \mathrm{m}$-diameter microtoroid with high optical Q factor (approximately ${10}^7$) and mechanical Q factor (approximately $700$), we achieve sensitivities of $46\mu \mathrm{Pa}$ ${\mathrm{Hz}}^{-1/2}$–10 mPa ${\mathrm{Hz}}^{-1/2}$ in a frequency range of 0.25–3.2 MHz. Thermal-noise-limited sensitivity is realized around a mechanical resonance at 2.56 MHz, in a frequency range of 0.6 MHz. We also observe the second- and third-order mechanical sidebands, and quantitatively study the intensities of each mechanical sideband as a function of the mechanical displacement. Measuring the combination of signal-to-noise ratios at all sidebands has the potential to extend the dynamic range of ultrasound sensing.

Micromagnetic simulation results on dynamic hysteresis loops of clusters of iron oxide nanoparticles (NPs) with internal structure composed of nanorods are compared with the widely used macrospin approximation. Such calculations allowing for nanorod-composed NPs is facilitated by a previously developed coarse-graining method based on the renormalization group approach. With a focus on applications to magnetic hyperthermia, we show that magnetostatic interactions improve the heating performance of NPs in chains and triangles, and reduce heating performance in fcc arrangements. Hysteresis loops of triangular and fcc systems of complex NPs are not recovered within the macrospin approximation, especially at smaller interparticle distances. For triangular arrangements, the macrospin approximation predicts that magnetostatic interactions reduce loop area, in contrast to the complex NP case. An investigation of the local hysteresis loops of individual NPs and macrospins in clusters reveals the impact of the geometry of their neighbors on individual versus collective magnetic response, inhomogeneous heating within clusters, and further differences between simulating NPs with internal structure and the use of the macrospin approximation. Capturing the internal physical and magnetic structure of NPs is thus important for some applications.

A family of $M{A}_2{Z}_4$ materials has recently inspired great interest due to its exotic geometry and intriguing electronic properties. Here we investigate the electronic transport and photoelectric properties of ${\mathrm{Mo}\mathrm{Si}}_2{\mathrm{P}}_4$ monolayer (MSP ML) that has a small direct gap using first-principles calculations. We design several model nanodevices based on MSP ML, including p-n junction diodes, p-i-n junction field-effect transistors, and photoelectric transistors. We demonstrate that these MSP-ML-based nanodevices yield superb transport properties, including significant rectifying effect, high electrical anisotropy, pronounced field-effect behavior, strong photoelectric response, and large photovoltaic power. These findings reveal the multifunctional nature of ${\mathrm{Mo}\mathrm{Si}}_2{\mathrm{P}}_4$ monolayer, promising its application as a designer material in next-generation ultrathin flexible semiconductor nanodevices.

Metallic antiferromagnets are demonstrated to show an unconventional spin Hall effect (SHE) and the inverse spin Hall effect (ISHE), which are very promising for Néel-vector detection. However, the ISHE is absent in insulating antiferromagnets, as it does not conduct charge current. Here, we report our observation of the anomalous ISHE at the interface of the easy-plane insulator antiferromagnetic nickel oxide and the heavy metal platinum. We find that, at the interface of $\mathrm{Ni}\mathrm{O}/\mathrm{Pt}$, the ISHE generates an anomalous hysteretic transverse voltage in both Hall and planar Hall measurements, depending on spin-current propagation and the polarization direction. The observation of a nonzero transverse voltage in $\mathrm{Pt}$ indicates the appearance of a spin current with longitudinal polarization reflected from $\mathrm{Ni}\mathrm{O}$, implying Néel-vector reorientation from the transverse to longitudinal direction. Our simulation indicates that the Néel vector can be reoriented by a spin current injected from the heavy metal and an applied magnetic field. The observed anomalous ISHE permits the manipulation and detection of the Néel order in insulating antiferromagnets.

Rydberg atoms show significant promise as the basis for highly sensitive detectors of continuous radio-frequency (rf) electric fields (E fields). Here, we study their time-dependent response to pulse-modulated rf E fields at 19.4 GHz using a cesium vapor cell at room temperature. We use density-matrix simulations to explain the timescales that shape the transient atomic response under different laser conditions, finding them to be limited by dephasing mechanisms, including transit-time broadening, Rydberg-Rydberg collisions, and ionization. Using a matched filter, we demonstrate the detection of individual pulses with durations from 10 µs down to 50 ns and amplitudes from 15 000 µV ${\mathrm{cm}}^{-1}$ down to about 170 µV ${\mathrm{cm}}^{-1}$, corresponding to a sensitivity of about 240 nV ${\mathrm{cm}}^{-1}$ ${\mathrm{Hz}}^{-1/2}$. Finally, we highlight the potential of a Rydberg vapor cell as a receiver by detecting pulse trains from a rotating emitter on a simulated passing aircraft.

Viscous fingering (VF) is a well-known interfacial instability occurring when a viscous fluid in a porous medium is displaced by a lower viscosity fluid. In this work, we show that electrokinetic control of the instability is possible, even in the case of a perfect dielectric viscous defending fluid. Using Hele-Shaw cell experiments in which a nonconducting viscous mineral oil is displaced by a conducting less viscous brine solution, we observe that we are able to effectively control the stability of the interface. We evaluate the interfacial stability at different field strengths, both positive and negative with respect to the pressure-driven flow and find that an electric field in the same direction as the pressure-driven flow significantly stabilizes the interface. In contrast, an electric field opposing the pressure-driven flow further destabilizes the displacement. We attribute this to the interplay between the different $\zeta$ potentials (fluid-fluid and fluid-wall) and preferential oil wettability of the system, resulting in the formation of an oil-film layer throughout the displacement. The nonconducting mineral oil in our system acts then as a dead-end pore for the brine, which under the influence of an electric field develops an electro-omostic flow velocity. We qualitatively and quantitatively show that for all positive electric field strengths VF is reduced, while for negative electric fields VF is increased and that the electric field strength has limited influence on the degree of (de)stabilization. The results from this work are of particular relevance in applications where VF occurs in a system containing one nonconducting fluid, which are common in many applications such as enhanced oil recovery.

Dispersion-suppressed mode depletion in a resonant cavity is usually challenging due to the entanglement of amplitude and phase response dictated by the Kramers-Kronig relationship. In this study, we examine the dispersion-suppressed mode depletion induced by parity–time- (PT-) symmetric dual resonators by taking advantage of the exotic property at the exceptional point (EP). We show that this technique can modify the linear spectrum of an optical resonator for relaxed phase-matching conditions in nonlinear optics, thus profoundly altering the nonlinear behavior of integrated Kerr combs. Indeed, dissipation-induced modulation instability (MI) is predicted and numerically verified in normal group-velocity dispersion (GVD) microresonators, and the single-soliton-generation probability is greatly enhanced in the anomalous GVD regime. The merging of two vibrant disciplines, i.e., non-Hermitian optics and nonlinear optics, especially Kerr microcombs, can deepen our understanding of non-Hermitian optical frequency combs and opens broad applications ranging from fiber-optic communications, microwave photonics, and ultrafast optics to quantum state manipulations.

We analyze a high-fidelity two-qubit gate using fast flux pulses on superconducting fluxonium qubits. The gate is realized by temporarily detuning the magnetic flux through the fluxonium loop away from the half flux quantum sweet spot. We simulate dynamics of two capacitively coupled fluxoniums during the flux pulses and optimize the pulse parameters to obtain a highly accurate $\sqrt{i\mathrm{SWAP}}$-like entangling gate. We also evaluate the effect of the flux noise and qubit relaxation on the gate fidelity. Our results demonstrate that the gate error remains below ${10}^{-4}$ for a currently achievable magnitude of the flux noise and qubit relaxation time.

It is well known that a particle put into an ultrasonic standing wave tends to move towards an equilibrium position, where the acoustic pressure-induced force on its surface compensates the particle weight. We demonstrate, by means of a full three-dimensional numerical analysis and a thorough experimental study, that the acoustic force, and thus the particle’s behavior, critically depends on its size. While particles within certain size ranges, including those smaller than half the wavelength, are trapped on axis around the pressure nodes, particles in other size ranges are trapped off axis nearby the pressure antinodes. This behavior, related with sign inversions of the radiation force, implies that the magnitude of the force, and thus the trapping stiffness, can be maximum or null for some specific sizes. As a case of study, we analyze expanded polystyrene particles levitated in air with an ultrasonic frequency of 40 kHz, a relevant system due to recent applications for the development of volumetric displays. Yet, our results illustrate a general behavior of radiation-based traps with structured wave fields.

Effective low-energy theories represent powerful theoretical tools to reduce the complexity in modeling interacting quantum many-particle systems. However, common theoretical methods rely on perturbation theory, which limits their applicability to weak interactions. Here we introduce the Variational Adiabatic Gauge Transformation (VAGT), a nonperturbative hybrid quantum algorithm that can use nowadays quantum computers to learn the variational parameters of the unitary circuit that brings the Hamiltonian to either its block-diagonal or full-diagonal form. If a Hamiltonian can be diagonalized via a shallow quantum circuit, then VAGT can learn the optimal parameters using a polynomial number of runs. The accuracy of VAGT is tested through numerical simulations, as well as simulations on Rigetti and IonQ quantum computers.