Communications Physics最新文献

Photonic ultrasound sensors promise unparalleled spatial and temporal resolution in ultrasound imaging due to their size-independent noise figure, high sensitivity, and broad bandwidth. Optical materials can further improve performance and stability, but achieving small size, high sensitivity, and wide bandwidth remains challenging. This work introduces amorphous silicon carbide (a-SiC) for ultrasound sensing, offering strong optical confinement, low propagation loss, and high stability for miniaturized microring sensors. We demonstrate a compact detection system with a 20-transducers linear array coupled to a single bus waveguide. The sensors achieve an optical finesse of 1320 and intrinsic sensitivity of 78 fm kPa^-1, leading to a noise-equivalent pressure below 55 $\mathrm{mPa}/\sqrt{\mathrm{Hz}}$ , calibrated from 3.36 MHz to 30 MHz. High-resolution imaging of fine structures validates real-world applicability. a-SiC is also easily integrated on most substrates due to its low deposition temperature. Our results position a-SiC as a promising solution for optical ultrasound sensing, combining miniaturization, low-loss, and high-sensitivity.

Two-dimensional non-Hermitian photonic lattices with asymmetric couplings offer rich possibilities for controlling wave localization, through the emergence of the non-Hermitian skin effect at lattice corners or sides. Yet, how optical nonlinearity modifies these boundary-localization characteristics remains largely unexplored. Here we show that in a two-dimensional Hatano-Nelson lattice with Kerr nonlinearity, the interplay between self-trapping and directional propagation leads to position-dependent amplitude thresholds. Single-site excitations having above a critical amplitude become confined to their initial position, with lower thresholds near the position where the linear eigenmodes are localized and higher thresholds within the lattice's bulk. Additionally, we study the differences of this dynamical interplay, for wider initial excitations, between the focusing and defocusing Kerr-nonlinearity regimes. Lastly, we identify skin soliton solutions in a variety of two-dimensional lattice geometries featuring coupling asymmetry. This work paves the way for future investigations regarding transport and soliton formation in higher-dimensional nonlinear non-Hermitian lattices.

The carbon oxygen ratio (C/O) at the end of stellar helium burning is a crucial nuclear input to stellar evolution theory. Knowledge of the C/O ratio with sufficient accuracy has eluded measurement over the past five decades. It is determined by the rate of oxygen formation in the fusion of helium with ¹²C, denoted as ¹²C(α, γ)¹⁶O. Even though recent methods employing a time projection chamber can measure the time-reverse photo-dissociation reaction, the results still do not show unambiguous agreement with the predictions of quantum scattering theory. Here, we improve this method using a N₂O gas target. This improvement allows us to eliminate the background caused by ¹²C photo-dissociation events, obtain complete angular distributions (0^∘-180^∘), and measure the cross sections over the 1^- resonance in ¹⁶O at E _cm ~ 2.4 MeV. These measurements resolve the discrepancy that was previously observed between the measured E1-E2 mixing phase angle (ϕ ₁₂) of ¹²C(α, γ)¹⁶O and the predictions of quantum scattering theory. This newfound agreement demonstrates the viability of our method for conducting measurements at lower energies.

Many electrically active devices rely on nonlinear signal mixing (heterodyning) between two electrical signals. Heterodyning between electric and acoustic signals can allow for active control of typically passive components such as transmission lines, acoustic resonators, and electrical resonators built from piezoelectric materials. However, there are few techniques to characterize the nonlinear properties of materials that lead to heterodyning between electric and acoustic signals within the material. Here we demonstrate a proof-of-concept microwave interferometer that uses electromagnetic and acoustic waves to measure second-order mixing from electrical and acoustic signals in a piezoelectric material. The sum and difference frequencies of signal mixing can be detected in the electromagnetic spectrum in our measurement. We show the effect of frequency and power of the fundamental signals on the mixing products. We additionally characterize the heterodyne signal to show that it is electric-acoustic in nature, versus purely electric. Characterizing nonlinear electric-acoustic properties is important to the development of next generation piezoelectric materials models and devices.

Controlling crystal growth is a challenge across numerous industries, as the functional properties of crystalline materials are determined during formation and often depend on particle shape. Current approaches rely on expensive, time-consuming experimental studies complemented by exhaustive parameter space simulations, creating significant computational and analytical burdens. Despite machine learning advances in crystal growth for structure-property relationships, applications targeting morphological control remain underdeveloped. Here, we demonstrate how disentangling autoencoders combined with particle aspect ratio and spherical harmonics descriptors can enhance simulation workflows for crystal growth. This approach reveals continuous transformation pathways between different crystal morphologies whilst preserving underlying crystallographic principles. Our method significantly reduces data analytics burdens, shortens design study timelines, and deepens understanding of crystal shape control. This framework enables more efficient exploration of possible crystal morphologies, facilitating the targeted design of crystalline materials with specific functional properties.

Multi-Penning traps are an excellent tool for high-precision tests of fundamental physics in a variety of applications, ranging from atomic mass measurements to symmetry tests. In such experiments, single ions are transferred between distinct trap regions as part of the experimental sequence, resulting in measurement dead time and heating of the ion motions. Here, we report a procedure to reduce the duration of adiabatic single-ion transport in macroscopic multi-Penning-trap stacks by using ion-transport waveforms and electronic filter predistortion. For this purpose, transport adiabaticity of a single laser-cooled ⁹Be⁺is analyzed via Doppler-broadened sideband spectra obtained by stimulated Raman spectroscopy, yielding an average heating per transport of 2.6 ± 4.0 quanta for transport times between 7 and 15 ms. Applying these techniques to current multi-Penning trap experiments could reduce ion transport times by up to three orders of magnitude. Furthermore, these results are a key requisite for implementing quantum logic spectroscopy in Penning trap experiments.

Electro-optic (EO) modulation is a key functionality to have on-chip. However, achieving a notable linear EO effect in stoichiometric silicon nitride has been a persistent challenge due to the material's intrinsic properties. Recent advancements revealed that the displacement of thermally excited charge carriers under a high electric field induces a second-order nonlinearity in silicon nitride, thus enabling the linear EO effect in this platform regardless of the material's inversion symmetry. In this work, we introduce optically-assisted poling of a silicon nitride microring resonator, removing the need for high-temperature processing of the device. The optical stimulation of charges avoids the technical constraints due to elevated temperature. By optimizing the poling process, we experimentally obtain a long-term effective second-order nonlinearity ${\chi }_{\mathrm{eff}}^{\left(2\right)}$ of 1.218 pm/V. Additionally, we measure the high-speed EO response of the modulator, showing a bandwidth of 4 GHz, only limited by the quality factor of the microring resonator. This work goes towards the implementation of monolithic, compact silicon nitride EO modulators, a necessary component for high-density integrated optical signal processing.

Due to the ortho-positronium formed prior to the annihilation, the lifetime of a positron is sensitive to the tissue microenvironment and can potentially provide valuable information for monitoring disease progression and treatment response. However, the lifetime of positrons before annihilation has long been overlooked in current positron emission tomography (PET). Here we develop a positron lifetime image reconstruction method called SIMPLE (Statistical IMage reconstruction of Positron Lifetime via time-wEighting) and demonstrate its performance using a real scan on a time-of-flight PET scanner. The SIMPLE method achieves high-resolution positron lifetime imaging of extended heterogeneous tissue illuminated by a ²²Na point source, successfully resolving the boundary between muscle and fat. It delivers spatial resolution comparable to that of conventional PET activity images while maintaining a computational cost equivalent to reconstructing two PET images. This work paves the way for clinical translation of high-resolution positron lifetime imaging.

Collective phenomena involving motorcycles in mixed traffic, and more generally bicycles and other new micromobilities in cities, are of great interest, as the behavior of these vulnerable road users raises major safety concerns. This is especially true when the limited urban infrastructure is shared with conventional vehicles, such as cars. However, this topic is severely understudied from a physics point of view and a solid theoretical foundation of multispecies traffic does not exist. By studying the pNEUMA dataset, we first establish a nonlinear relationship between maneuverability and speed, which maps to the nonequilibrium concept of a sample space reducing process (SSR). Coupling SSR with Newell's nonlinear traffic model, we identify a power-law relationship between the average maneuverability (interpreted as temperature) and the mean speed difference between motorcycle and car populations. Simulation results allow us to recover a nonequilibrium phase transition from an ordered state of lane formation to a disordered state of cluster formation governed by a universal scaling exponent that is robust to traffic conditions and model variants. Our contribution creates a link between microscopic behaviors and the macroscopic theory of percolation.

The Kondo effect is a prototypical strongly correlated phenomenon, and it is usually discussed in the context of unitary dynamics. Here, we demonstrate that the Kondo effect can be induced through non-linear dissipative channels, without requiring any coherent interaction on the impurity site. Specifically, we consider a reservoir of noninteracting fermions that can hop on a few impurity sites that are subjected to strong two-body losses. In the simplest case of a single lossy site, we recover the Anderson impurity model in the regime of infinite repulsion, with a small residual dissipation as a perturbation. While the Anderson model gives rise to the Kondo effect, this residual dissipation competes with it, offering an instance of a nonlinear dissipative impurity where the interplay between coherent and incoherent dynamics emerges from the same underlying physical process. We further outline how this dissipative engineering scheme can be extended to two or more lossy sites, realizing generalizations of the Kondo model with spin 1 or higher. Our results suggest alternative implementations of Kondo models using ultracold atoms in transport experiments, where localized dissipation can be naturally introduced, and the Kondo effect observed through conductance measurements.