Owing to the excitation of nonreciprocal surface plasmon polaritons, Weyl semimetals have attracted much attention in the study of near-field radiative heat transfer. Here, we find a large twisted switch ratio at a high (low) heat flux intensity range with an aligned (parallel) axion-field configuration. The heat flux can be modulated over a wide range, spanning several orders of magnitude, and the switching effect is attributed to the strong nonreciprocity of the surface plasmon polaritons in Weyl semimetal layers. In addition, the thickness variation of the Weyl semimetal layers results in diverse change behaviors of the total heat flux, owing to the band overlap of the surface mode. Our research provides a critical understanding of heat transfer for different twisting types and thickness adjustment.

Photonic integrated Brillouin lasers have emerged as a key tool to realize a wide range of precision applications, including atomic time keeping, low-noise microwave-signal generation, fiber and quantum sensing, and ultrahigh capacity coherent communications. While Brillouin lasers routinely achieve sub-Hz instantaneous linewidths, many of these applications also require exceptional frequency stability and high-power single-mode emission. A recent demonstration showed that extending the resonator length increases the laser power while simultaneously improving the frequency stability through suppression of low-frequency thermorefractive noise. However, as the resonator length scales to larger size, multiple optical resonances can be found within the Brillouin gain bandwidth, greatly complicating the laser dynamics and extending beyond the validity of existing coupled-mode Brillouin laser models. Given the potential to scale lasers of this type to watt-level output powers at sub-mHz linewidths, a theoretical model describing this physics is needed to provide key insights into their performance. Here, we develop a coupled-mode theory of integrated large mode volume Brillouin lasers, accounting for multiple cavity modes with the potential to lase within the gain bandwidth. We obtain expressions for the steady-state dynamics, spontaneous spectrum, relative intensity noise, and frequency noise. Our analysis reveals that the broad gain bandwidth results in atypical Brillouin dynamics, giving rise to distinct features in the noise spectra, and consequently modifications of the standard, single-mode fundamental linewidth of Brillouin lasers. Additionally, these features may be used for a variety of tangential applications, such as phonon spectroscopy or quality-factor enhancement. Furthermore, we find that the linewidth can be significantly impacted by transferred RIN from the external pump in Brillouin lasers that lack ideal phase matching.

Germanium ($\mathrm{Ge}$) has the potential to be incorporated into the next generation of electronic and optoelectronic devices due to its quasidirect band gap and high carrier mobility. With $\mathrm{Ge}$ as the primary semiconductor, it is essential to engineer the energy-band structure and optical properties. To understand alterations in the band structure and variations in optical response, three distinct conditions were investigated via spectroscopic ellipsometry: defect density, buffer-layer thickness, and substrate orientation and offcut angles. As the threading-dislocation density in $\mathrm{Ge}$ is increased from $5\times {10}^3{\mathrm{cm}}^{-2}$ to ${10}^{10}{\mathrm{cm}}^{-2}$, a characteristic redshift in the indirect and direct band gaps and optical critical points (CPs; $E_0$, $E_0+{\mathrm{\Delta }}_0$, $E_1$, and $E_1+{\mathrm{\Delta }}_1$) was observed, along with a significant increase in the absorption onset. In the case of lattice-matched epitaxial $\mathrm{Ge}$ on an $\mathrm{Al}\mathrm{As}$ buffer, the band gaps are redshifted with increasing $\mathrm{Al}\mathrm{As}$ thickness, which is attributed to surface local fields. A similar trend is observed in the direct-band-gap CPs ($E_0$ and $E_0+{\mathrm{\Delta }}_0$), while the high-energy CPs ($E_1$ and $E_1+{\mathrm{\Delta }}_1$) remain unchanged. Deviating from this trend, the $\mathrm{Ge}$ sample grown on a $\mathrm{Ga}\mathrm{As}$ ($100/6^{\circ }$ offcut) substrate exhibits a redshift in its $E_0$ and $E_0+{\mathrm{\Delta }}_0$ CPs, which is attributed to superior growth quality due to the $6^{\circ }$ offcut substrate. In this case, it is observed that the $\mathrm{Ge}$ on $\mathrm{Ga}\mathrm{As}$ ($100/6^{\circ }$ offcut) has the highest direct-band-gap CPs ($E_0$ and $E_0+{\mathrm{\Delta }}_0$) and $\mathrm{Ge}$ on $\mathrm{Ga}\mathrm{As}$ ($100/2^{\circ }$ offcut) has the lowest. In contrast, the $\mathrm{Ge}$ on $\mathrm{Ga}\mathrm{As}$ (110), with the highest unintentional doping of approximately ${10}^{19}$, exhibits a high absorption onset, potentially compensating for the Burstein-Moss (BM) effect due to band-gap narrowing (BGN); however, the $\mathrm{Ge}$ sample grown on a $\mathrm{Ga}\mathrm{As}$ ($100/2^{\circ }$ offcut) substrate exhibits a blueshift in its indirect band gap, which can be attributed to the BM effect overpowering the BGN effect. A significant redshift in the $E_0$ and $E_0+{\mathrm{\Delta }}_0$ CPs is observed with changes in substrate orientation, while the $E_1$ and $E_1+{\mathrm{\Delta }}_1$ CPs remain the same. Thus, our findings indicate that the optical response in the epitaxial $\mathrm{Ge}$ layer is sensitive to defects, the $\mathrm{Al}\mathrm{As}$ buffer-layer thickness, and substrate orientation.

We present a theoretical proposal for, and simulation study of, a digital closed-loop thermal atomic beam interferometer for inertial navigation applications. The scheme synchronizes phase biasing with momentum-kick reversal through the atomic transit time, extracting four interferometric phases to suppress Raman beam path-length errors, while two-photon detuning feedback maintains a pseudoinertial frame and eliminates cross-coupling. The interferometer enables simultaneous measurements of acceleration and rotation based on an absolute, atom-interferometric reference, with high bandwidth and a wide dynamic range. Numerical simulations verify that acceleration and angular velocity can be measured simultaneously and independently in real time without cross-coupling, demonstrating the absolute, decoupled nature of the proposed measurement scheme. We further evaluate the noise-limited performance of the sensor and obtain sensitivities of $3(\text{μ}\mathrm{m}/{\mathrm{s}}^2)/\sqrt{\mathrm{Hz}}$ (velocity random walk) and $15\text{μ}\mathrm{deg}/\sqrt{\mathrm{h}}$ (angular random walk) for a $170{}^{\circ }\mathrm{C}{}^{85}\mathrm{Rb}$ beam and an interferometer arm length of 100 mm, surpassing the performance of sensors currently used in state-of-the-art inertial navigation systems.

We present two methods to achieve real-time inertial phase compensation in atom interferometers. Both methods, based on jumping of the position of the retroreflection mirror or frequencies of Raman lasers, demonstrate similar state-of-the-art performance on our cold-atom gyroscope, comparable to that of the reference method, based on optical phase jumping. These alternative approaches broaden the scope of applications for real-time inertial phase compensation methods in atomic interferometers, particularly for space applications.

Topological interface states exhibit exceptional potential for robust sound transmission, owing to their distinctive topological characteristics. However, current studies are primarily concentrated on the sound transmission along well-defined passages, disregarding the potential significance of multichannel energy transfer between coupled topological interface states. In this work, by introducing coupled interface states in $C_4$-rotationally symmetric composite sonic crystals, we experimentally observe the topological energy transfer between adjacent channels for both symmetric and antisymmetric interface states. Leveraging the varied coupling wavelengths of interface states, we implement a functional acoustic frequency splitter that spatially splits acoustic signals of different wavelengths into different waveguide channels. Interestingly, the mirrored topological channels support the propagating eigenmodes with recognizable symmetries, creating the opportunity for selective acoustic transmission and communication. Our work offers unique strategies to precisely control the topological interface state transport in sonic crystals, enabling advanced acoustic devices, such as directional couplers, wavelength demultiplexers, and acoustic signal processors.

Quantum sensors based upon atom interferometry typically rely on radio-frequency or optical pulses to coherently manipulate atomic states and make precise measurements of inertial and gravitational effects. An advantage of these sensors over their classical counterparts is often said to be that their measurement scale factor is precisely known and highly stable; however, in practice the finite pulse duration makes the sensor scale factor dependent upon the pulse shape and sensitive to variations in control-field intensity, frequency, and atomic velocity. Here, we explore the concept of a temporal pulse origin in atom interferometry, where the inertial phase response of any pulse can be parameterized using a single point in time. We show that the temporal origin permits a simple determination of the measurement scale factor and its stability against environmental perturbations. Moreover, the temporal origin can be treated as a tunable parameter in the design of tailored sequences of shaped pulses to enhance scale-factor stability and minimize systematic errors. We demonstrate through simulations that this approach to pulse design can reduce overall sequence durations while increasing robustness to realistic fluctuations in control-field amplitude. Our results show that the temporal pulse origin explains a broad class of systematic errors in existing devices and enables the design of short, robust pulses, which we expect will improve the performance of current and next-generation interferometric quantum sensors.

Currently, quantum-key-distribution (QKD) systems are evolving toward high-speed implementations to meet the demands of large-scale data encryption. High-performance, high-speed gated single-photon detectors (SPDs) are essential for enabling such systems. However, the practical security of these detectors remains a critical concern. Recently, an attack targeting high-speed sine-gated SPDs was reported, in which the detector was blinded by deceiving the width discrimination mechanism. Inspired by this work, we further optimize the attack strategy by customizing the blinding pulse and modifying the temporal offset between the blinding pulse and the gate signal, thereby achieving a more effective attack. Experimental and simulation results show that in short-distance communication scenarios, the additional quantum bit error rate (QBER) introduced by our proposed attack strategy is less than 0.5%. Of note, we propose and evaluate three practical countermeasures to defend against such attacks, which include auxiliary conventional discrimination monitoring, avalanche current monitoring, and temporal distribution analysis of detection events. These defense strategies enhance the robustness of high-speed SPDs and contribute to the development of more secure and reliable QKD systems.

We present a class of mechanical lattices based on elliptical gears with quasiperiodic modulation and geometric nonlinearity that are capable of exhibiting topologically protected modes and amplitude-driven transitions. Starting from a one-dimensional chain of modulated elliptical gears, we demonstrate the emergence of localized edge states arising from quasiperiodic variation in the gears’ moments of inertia, analogous to the topological edge modes of the Aubry-André-Harper model. Under increasing excitation amplitude, the system undergoes a nonlinear transition, where edge localization breaks down and energy delocalizes into the bulk. By coupling multiple such chains with varying modulation phase, we construct a two-dimensional lattice in which the phase acts as a synthetic dimension. This structure supports topological wave propagation along the synthetic dimension. Nonlinearity again induces a breakdown of topological states, leading to complex, amplitude-dependent wave propagation. We further propose a numerical-continuation approach to analyzing the periodic orbits and their linear stability, effectively discovering the boundary of the basin of bounded motion and detecting the occurrence of delocalization under certain excitation amplitudes. Our results reveal that elliptical geared systems offer a passive, amplitude-dependent platform for exploring topological phenomena and synthetic dimensionality in mechanical metamaterials.

Stochasticity in spintronic systems is crucial for neuromorphic and probabilistic computing applications. Systems such as low-barrier nanomagnets and magnetic tunnel junctions have shown stochastic behavior primarily driven by thermal noise; this limits their effectiveness at low temperatures. In this study, we demonstrate that spin Hall nano-oscillators (SHNOs) can efficiently exhibit inherent stochastic behavior independent of thermal noise, making them suitable for probabilistic computing and Ising machines. This stochasticity stems from energy dissipation through magnon propagation. We demonstrate that field-free SHNOs can display transient chaotic behavior. Further, we show that the observed stochasticity emerges from the transient chaos that has specific dependence on the excitation current values during oscillation mode transitions due to the induced spin wave instabilities. We present an application of such stochastic SHNOs for true random number generators in nanosecond time scale (∼20 ns) (in a simple configuration) and evaluate it with a statistical test suite (nist-sts). Our findings imply that SHNOs can be utilized for the development of efficient spintronic-based stochastic devices and novel computing paradigms, such as probabilistic computing.

The relative instability of high-efficiency blue phosphorescent organic light-emitting devices (OLEDs) is an important and longstanding challenge. Conventional models of degradation emphasize the dynamics of emissive triplet excitons on phosphorescent molecules, neglecting the potential role of nonemissive, “dark,” triplet excitons on host and charge blocking molecules. Bright and dark triplet dynamics are probed in situ using surface plasmon polariton-coupled modulation and magnetic exciton annihilation modulation, respectively. It is observed that dark triplet excitons dominate both the instability and efficiency roll-off of a high-performance blue phosphorescent OLED. Dissociating dark triplets both improves device stability and reduces efficiency losses at high brightness by a factor of 2. The combined benefit to stability of Purcell engineering and dark triplet management is a factor of 3.5. The results demonstrate that dark triplet excitons reduce the potential benefit of Purcell engineering, emphasizing the importance of in-situ characterization and control of dark triplets to realize the goal of stable blue phosphorescent OLEDs.

Epsilon-near-zero (ENZ) thin films facilitate strong light-matter interactions with a widespread impact in nonlinear, quantum and thermal photonics. Here, we extend the scope of thin-film ENZ modes by elucidating the generalized polaritonic modes emerging from anisotropy and near-zero permittivity. Through a theoretical investigation of generalized ENZ polaritons on silicon carbide metasurfaces, we reveal a complex polaritonic landscape, consisting of an eight-region phase diagram. We show that the complex interplay between material properties and geometry changes the nature of the modes, and we clarify when ENZ modes with closed and open isofrequency curves can be observed, and how they coexist with surface phonon polaritons and hyperbolic modes. The associated photonic topological transitions are accompanied by phase velocity sign reversals and induce dramatic modifications of near-field profiles and Purcell enhancement factors. Our work merges insights from anisotropic and ENZ effects, enabling enhanced control over polariton behavior with broad implications for subwavelength optics, material design, nonlinear effects, thermal emission, and quantum technologies.

Leaky-wave metasurfaces (LWMs) are artificial structures that can convert space-confined waves into free-space-propagating waves. They have recently attracted much attention in the field of electromagnetics. Similar structures for acoustic waves have been proposed as beam generators, acoustic prisms, direction-finding devices, and vortex-beam generators. We observe that, although various structures have been proposed, existing design methods are difficult to extend to inversely map a customized leaky-wave solution to a specific structure. In this paper, we propose an inverse design method for the acoustic LWM (ALWM) design. With this method, structures can be designed to support leaky-wave solutions with customized wave fronts. To demonstrate the utility of the proposed method, two ALWMs have been designed as examples. The first structure is designed as a frequency-scanning antenna that can continuously steer the direction of the radiation beam from backfire to endfire by changing the working frequency. The second structure is designed to emit a Bessel-like beam with a customized nondiffractive range. The performances of both structures are verified using finite-element simulations. The second structure is further fabricated via three-dimensional printing technology, and the shape of the Bessel-like beam and its self-healing behavior are measured. The agreement between the numerical and experimental results demonstrates the effectiveness of the proposed structure and design method. This work not only provides an efficient method for ALWM design, by which two simple structures usable in sensing and communication are created, but also offers a general understanding of leaky-wave solutions necessary for the design of other artificial leaky-wave structures.

Optical Schrödinger cat states are non-Gaussian states with applications in quantum technologies, such as for building error-correcting states in quantum computing. Nevertheless, the efficient generation of high-fidelity optical Schrödinger cat states is an outstanding problem in quantum optics. Here we propose using squeezed superpositions of zero and two photons, $|\theta ⟩=\cos (\theta /2)|0⟩+\sin (\theta /2)|2⟩$, as ingredients for protocols to efficiently generate high-fidelity cat states. We present a protocol using linear optics with success probability $P\gtrsim 50\mathrm{\%}$ that can generate cat states of size $|\alpha {|}^2=5$ with fidelity $F>0.99$. The protocol relies only on detecting single photons and is remarkably tolerant of loss, with 2% detection loss still achieving $F>0.98$ for cat states with $|\alpha {|}^2=5$. We also show that squeezed $\theta$ states are ideal candidates for nonlinear photon subtraction using a two-level system with near-deterministic success probability and fidelity $F>0.98$ for cat states of size $|\alpha {|}^2=5$. Schemes for generating $\theta$ states using quantum emitters are also presented. Our protocols can be implemented with current state-of-the-art quantum optics experiments.

To encode quantum information in semiconductor spin qubits, voltage pulses are necessary for initialization, gate operation, and readout. However, these pulses dissipate heat, shifting spin-qubit frequencies and reducing gate fidelities. The cause of this pulse heating in quantum dot devices is unknown. Here, we measure pulse heating using charged two-level fluctuators (TLFs) in $\mathrm{Si}$/($\mathrm{Si}$-$\mathrm{Ge}$) quantum dots. Specifically, we observe that voltage pulses on nearby gates tend to increase TLF switching rates and occupation biases. The amount of heating depends on the pulse amplitude and frequency, but not on the distance between the pulsed gates and the TLFs. The amount of heating also generally depends on the idling voltage of the pulsed gates, suggesting that electrons accumulated under or near the gates contribute to the heating. We hypothesize that reducing the area of the gates with electrons nearby could mitigate the heating.