Communications Physics最新文献

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.

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.

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.

With recent progress in quantum simulations of lattice-gauge theories, it is becoming a pressing question how to reliably protect the gauge symmetry that defines such models. Recently, an experimentally feasible gauge-protection scheme has been proposed that is based on the concept of a local pseudogenerator, which is required to act identically to the full gauge-symmetry generator in the target gauge sector, but not necessarily outside of it. The scheme has been analytically and numerically shown to reliably stabilize lattice gauge theories in the presence of perturbative errors on finite-size analog quantum-simulation devices. In this work, through uniform matrix product state calculations, we demonstrate the efficacy of this scheme for nonperturbative errors in analog quantum simulators up to all accessible evolution times in the thermodynamic limit, where it is a priori neither established nor expected that this scheme will succeed. Our results indicate the presence of an emergent gauge symmetry in an adjusted gauge theory even in the thermodynamic limit, which is beyond our analytic predictions. Additionally, we show through quantum circuit model calculations that gauge protection with local pseudogenerators also successfully suppresses gauge violations on finite quantum computers that discretize time through Trotterization. Our results firm up the robustness and feasibility of the local pseudogenerator as a viable tool for enforcing gauge invariance in modern quantum simulators and noisy intermediate-scale quantum devices.

The study of ultrafine particle aerosols, those with particle diameters of 100 nm or less, is important due to their impact on our health and environment. However, given their small sizes, such particles can be difficult to measure and trace. Most common optical methods are unable to reach this size range. Other methods exist but incur other limitations, such as the need for electrically charged particles. Here we show how light scattering can be used to detect and measure the size and location of single viruses and protein complexes forming an aerosol beam, as well as trace their path. We were able to detect individual particles down to 16 nm in diameter. The primary purpose of our instrument is to monitor the delivery of single bioparticles to the focus of an X-ray laser to image those particles, but it has the potential to study any other aerosols such as those resulting from ultrafine sea spray, with important consequences for cloud formation and climate modeling, or from combustion, responsible for most air pollution and resulting health impacts.

Thermalization in quantum many-body systems typically unfolds over timescales governed by intrinsic relaxation mechanisms. Yet, its spatial aspect is less understood. We investigate this phenomenon in the nonequilibrium steady state (NESS) of a Bose-Hubbard chain subject to coherent driving and dissipation at its boundaries, a setup inspired by current designs in circuit quantum electrodynamics. The dynamical fingerprints of chaos in this NESS are probed using semiclassical out-of-time-order correlators within the truncated Wigner approximation. At intermediate drive strengths, we uncover a two-stage thermalization along the spatial dimension: phase coherence is rapidly lost near the drive, while amplitude relaxation occurs over much longer distances. This separation of scales gives rise to an extended hydrodynamic regime exhibiting anomalous temperature profiles, which we designate as a "prethermal" domain. At stronger drives, the system enters a nonthermal, non-chaotic finite-momentum condensate characterized by sub-Poissonian photon statistics and a spatially modulated phase profile, whose stability is undermined by quantum fluctuations. We explore the conditions underlying this protracted thermalization in space and argue that similar mechanisms are likely to emerge in a broad class of extended driven-dissipative systems.

Non-line-of-sight (NLOS) imaging typically relies on the use of ultrashort laser pulses and time-resolved detection to then reconstruct 3D environments that are hidden from the direct line-of-sight. However, the same scattering mechanism and wall-reflections that allow light to propagate into the hidden environment and back again ultimately limit both resolution and imaging distances even at high laser powers. Non-optical, such as acoustic and radio-wave approaches promise to solve some of these issues but have yet to achieve results comparable to optical systems. We present an ultrasound-based NLOS imaging system based on a scanning ultrasound emitter and receiver operating in a frequency range similar to common bats that demonstrates high-resolution 3D reconstruction of hidden scenes. We successfully image multiple targets and complex scenes with  ~ cm depth resolution at distances up to 2 m away from the scattering surface. Measurements of the NLOS modulation transfer function quantify the spatial resolution to also be  ~ 1 cm, which is comparable to traditional optical NLOS techniques.

A compact platform to integrate emitters in a cavity-like support is to embed quantum dots (QDs) in a photonic crystal (PhC) structure, making them promising candidates for integrated quantum photonic circuits. The emission properties of QDs can be modified by tailored photonic structures, relying on the Purcell effect or strong light-matter interactions. However, the effects of photonic states on spatial features of exciton emissions in these systems are rarely explored. Such effect is difficult to access due to random positions of self-assembled QDs in PhC structures, and the fact that quantum well excitons' wavefunctions resemble photonic states in a conventional distributed Bragg reflector cavity system. In this work, we instead observe a spatial signature of exciton emission using site-controlled QDs embedded in PhC cavities. In particular, we observe the detuning-dependent spatial repulsion of the QD exciton emissions by polarized imaging of the micro-photoluminescence, dependent on the controlled QD's position in a spatially extended photonic pattern. The observed effect arises due to the quantum interference between QD decay channel in a spatially-extended cavity mode. Our findings suggest that integration of site-controlled QDs in tailored photonic structures can enable spatially distributed single-photon sources and photon switches.

The electric field is known as an effective approach to improving pool boiling. However, there has been limited research on electric field-enhanced boiling of leaky dielectric fluids and the associated bubble dynamics. In this work, we employ a mesoscopic multiphase lattice Boltzmann method to perform large-scale three-dimensional simulations of electric field-enhanced pool boiling in leaky dielectric fluids. Our findings confirm that, compared to conventional pool boiling, electric field-enhanced pool boiling significantly increases heat transfer efficiency in the transition boiling regime. Furthermore, we propose a theoretical model based on the hydrodynamic theory that accurately predicts the heat flux across a wide range of operating parameters. Finally, we reveal size effects of the electric force on nucleation sites and rising bubbles, explaining the contrasting phenomena of bubble suppression and enhanced bubble detachment observed in electric field-enhanced boiling. The results of this study provide theoretical insight for optimizing phase‑change heat transfer efficiency.