Communications Physics最新文献

Synchronization is a universal phenomenon underpinning various natural processes and finds direct application in control engineering and photonics. Among several synchronization mechanisms, subharmonic entrainment (SHE) is a nonlinear synchronization phenomenon where an oscillator locks to an external drive with a fraction of the oscillator's frequency. While its mechanism is well understood for scalar couplings and finds application in the stabilization of ultrafast laser pulses, the potential of SHE with vectorial coupling is still unexplored. In this work, we demonstrate vector SHE (VSHE) using a passively mode-locked fiber laser as a testbed. We unveil the mechanism of vector SHE, in which weak external signals can entrain internal laser dynamics through vector coupling. Vector SHE presents in the form of synchronization between the subharmonic of mode-locking-driven oscillations and continuous wave (CW) signal with an evolving state of polarization. This CW signal, driven by the internal dynamics of the injected signal, causes VSHE with the frequencies' ratios of multiples of ten, resulting in a partially mode locking regime operation. Our findings offer new control techniques over mode-locking and additional dimension such as polarization states.

Terahertz-frequency (THz) carrier waves in free-space optical (FSO) communications offer the potential for  > 1 Tbit/s data rates and stable latency. They offer wider bandwidths than available in the microwave region, together with reduced scattering and relaxed pointing requirements compared with visible and near-infrared regions. However, 1-10 THz FSO communications systems have thus far been limited to data rates several orders of magnitude lower than those of infrared systems. This work describes an experimental demonstration of multi-gigabit-per-second FSO communication using a THz quantum cascade laser (QCL), opening a new frontier for next-generation wireless communications. The FSO communication system consists of a 2.4 THz QCL source as the transmitter and a room-temperature Schottky barrier diode detector as the receiver. By directly modulating the terahertz QCL, we achieved non-return-to-zero on-off keying (NRZ-OOK) with a transmission rate of up to 4 Gbit/s. We evaluated the performance of the communication link by analyzing the bit error rate (BER) of the demodulated signal at the receiver while examining its relation to received optical power, QCL modulation power, and various bias points. Our work establishes the foundation for high-speed optical wireless communication based on terahertz QCL technology systems.

Ultra-high power lasers are becoming important tools for advancing high-field physics and fusion research. However, their development is constrained by the damage thresholds of conventional optical components; it is challenging to design optical elements capable of withstanding high powers without them becoming impractically large. Here we show that transient plasma photonic structures, formed by the interaction of intercepting laser pulses in gas, can act as compact and robust reflective elements. Because these structures evolve in space and time, and rely on many interdependent parameters, designing optical components using traditional trial-and-error design methods is challenging. We show that machine learning can efficiently explore this complex parameter space to rapidly design robust, high reflectivity plasma mirrors. Moreover, this design process unexpectedly discovers a regime where unchirped laser pulses are compressed. This work demonstrates machine learning as a powerful tool for design, discovery and development of ultra-compact optical components for next-generation lasers.

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.

Hydrides are considered to be one of the most promising families of compounds for achieving high temperature superconductivity. However, there are very few experimental reports of ambient-pressure hydride superconductivity, and the superconducting critical temperatures (T _c) are typically less than 10 K. At the same time several hydrides have been predicted to exhibit superconductivity around 100 K at ambient pressure but in thermodynamically unfavorable phases. In this work we aim at assessing the superconducting properties of thermodynamically stable hydride superconductors at room pressure by investigating the GNoME material database, which has been recently released and includes thousands of hydrides thermodynamically stable at 0K. To scan this large material space we have adopted a multi stage approach which combines machine learning for a fast initial evaluation and cutting edge ab initio methods to obtain a reliable estimation of T _c. Ultimately we have identified 25 cubic hydrides with T _c above 4.2 K and reach a maximum T _c of 17 K. While these critical temperatures are modest in comparison to some recent predictions, the systems where they are found, being stable, are likely to be experimentally accessible and of potential technological relevance.

Competition between short- and long-range interactions underpins many emergent phenomena in nature. Despite rapid progress in their experimental control, computational methods capable of accurately simulating open quantum many-body systems with complex long-ranged interactions at scale remain scarce. Here, we address this limitation by introducing an efficient and scalable approach to dissipative quantum lattices in one and two dimensions, combining matrix product operators and time-dependent variational Monte Carlo. We showcase the versatility, effectiveness, and unique methodological advantages of our algorithm by simulating the non-equilibrium dynamics and steady states of spin- $\frac{1}{2}$ lattices with competing algebraically-decaying interactions for as many as N = 200 sites, revealing the emergence of spatially-modulated magnetic order far from equilibrium. This approach offers promising prospects for advancing our understanding of the complex non-equilibrium properties of a diverse variety of experimentally-realizable quantum systems with long-ranged interactions, including Rydberg atoms, ultracold dipolar molecules, and trapped ions.

The electron diffusion region is central to NASA's Magnetospheric Multiscale (MMS) mission to understand collisionless magnetic reconnection, the plasma physics phenomenon crucial to triggering the explosive energy release of solar flares, powering auroras generated in planetary magnetospheres, and driving sawtooth crashes in laboratory fusion devices. Inside the diffusion region, electron velocity distributions exhibit highly-structured velocity-space signatures critical for elucidating the kinetic mechanisms fueling reconnection. Recent multi-spacecraft analysis techniques enabled observational study of the spatial gradient in the electron velocity distribution, which has been reported in electron-scale current layers to explain the kinetic origins of electron pressure gradients. However, electron gradient distributions have not yet been investigated inside the reconnection diffusion region. In this work, we discover that electron gradient distributions exhibit a smile-shaped velocity-space structure in the electron diffusion region of asymmetric magnetic reconnection at Earth's magnetopause. Characterizing the nature and prevalence of these smile-shaped electron gradient distributions offers a kinetic perspective into how electrons spatially evolve to provide the net electron pressure divergence that self-consistently supports non-ideal electric fields in the electron diffusion region of magnetopause reconnection. These results are relevant to space, astrophysical, and laboratory plasma communities working to understand the long-standing mystery of collisionless magnetic reconnection.

Swimming is ubiquitous in nature and crucial for the survival of a wide range of organisms. The physics of swimming at the viscosity-dominated microscale and inertia-dominated macroscale is well studied. However, in between lies a complicated mesoscale with swimmers affected by non-linear and time-dependent fluid mechanics. The intricate motility strategies, combined with complex and periodically changing body shapes add extra challenges for accurate meso-swimming modelling. Here, we have further developed the micropipette force sensor to directly probe the swimming forces of the meso-organism Artemia. Through deep neural network-based image analysis, we show how Artemia achieves an increased propulsive force by increasing its level of time-reversal symmetry breaking. We present a universal force-based scaling law for a wide range of micro- to meso-organisms with different body shapes, swimming strategies, and level of inertia at the mesoscale. These results capture fundamental aspects of biological meso-swimming dynamics and provide guidance for future biomimicking meso-robot designs.

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.