Free-space optical communication is emerging as a cornerstone technology for next-generation wireless networks, driven by the escalating demand for fiber-optic-level data rates in applications ranging from data center interconnects to satellite and deep-space communications. Despite its substantial theoretical capacity advantage, reliable long-distance optical links remain challenging because of atmospheric turbulence, pointing and tracking inaccuracies, and stringent power budgets. These impairments are becoming increasingly intertwined with advanced modulation formats and various multiplexing techniques aimed at boosting throughput. In this Review, we examine the interplay between increasing capacity and maintaining reliability under turbulence in long-distance, high-capacity optical systems. We trace the evolution of the field from carrying more information on a single optical carrier to fully integrated, multi-dimensional multiplexing architectures. Key strategies for mitigating atmospheric impairments are analyzed, and we conclude by highlighting the major challenges and future opportunities. Free-space optical communication promises fiber-like data rates for next-generation wireless networks. This Review examines the interplay between capacity and reliability, covering advanced modulation, multidimensional multiplexing and strategies for robust long-distance transmission, and highlights challenges and future opportunities.
The phase space (velocity and real space) dynamics of bulk ions is a critical issue for the heating scenario in magnetically confined plasma. Bulk ions accelerate parallel to the magnetic field, and the velocity distribution function can depart from a Maxwellian due to wave-particle interactions such as Landau and transit-time damping. Here we show flattening in velocity space (a decrease in the velocity gradient) and a rapid increase in ion energy parallel to the magnetic field within 0.1 ms of the onset of the MHD burst, by 30% at the location of the MHD burst in the Large Helical Device. In velocity space, the anisotropy of ion-velocity distribution due to the acceleration of ions parallel to the magnetic field disappears within the ion-ion collision time scale (2 ~ 3 ms). The transient increase in ion energy decays within 6 ms at the plasma periphery but persists much longer in the plasma core, contributing to the rise in core-ion energy. The authors study the phase-space (velocity and real-space) dynamics of bulk ions during an energetic-particle-driven MHD burst in LHD. They find a rapid increase in ion energy parallel to the magnetic field within 0.1 ms of the MHD burst onset, rising by 30% at the MHD burst location and contributing to the rise in core-ion energy.
The quantum vacuum is not really empty; it is a reservoir of operationally accessible non-classical resources. Understanding how to extract these resources, especially in curved spacetime, to fuel information processing is one of the core objectives in quantum technologies and lies at the heart of relativistic quantum information (RQI). We investigate the harvesting of non-stabilizerness by a qutrit Unruh-DeWitt detector interacting with a scalar field in anti-de Sitter spacetime, which is intractable by using traditional numerical integral method. To this end, we develop an analytic series method to deal with divergence of the coherence, which has remained largely overlooked in RQI and even in quantum field theory. We show that stronger spacetime curvature and higher dimensionality significantly suppress the amount of extractable magic resource from the vacuum. Our series method can have broad application in quantum theories and field theories.
Nanoconstriction spin Hall nano-oscillators (SHNOs) are cutting-edge spintronic devices for gigahertz signal generation and neuromorphic computing, offering a CMOS-compatible nanoscale footprint, ultra-wide frequency tunability, and robust synchronization in large networks. Most previous studies have focused on constrictions narrower than 200 nm, where a single dominant spin-wave mode typically emerges. The auto-oscillation dynamics of wide constrictions remain largely unexplored. Here, using micromagnetic simulations, we demonstrate the coexistence of two independently tunable auto-oscillation modes in constrictions wider than 200 nm: a low-frequency in-phase mode and a high-frequency out-of-phase mode, both localized at opposite constriction edges. The out-of-phase mode arises from the interplay of exchange, magnetodipolar coupling, and the antisymmetric Oersted field component, producing strongly edge-localized oscillations with a nearly 180∘ phase difference. We develop an analytical two-mode framework that captures their hybridization and nonlinear competition. Their distinct subharmonic injection-locking responses enable phase-binarized states within a single wide SHNO, opening opportunities for multimode synchronization, unconventional computing, and complex phase locking in SHNO networks.
Controlling how particles diffuse through low-dimensional materials, where long-range repulsion couples every particle to every other, is central to ionic conductors, intercalation compounds, and many confined transport systems. Yet how such repulsion shapes diffusion at realistic temperatures has remained poorly understood, because the ordered states it stabilizes and the rare hops that govern motion are difficult to treat analytically or to sample numerically. Here we show, by combining large-scale simulations with a theoretical framework, that diffusion is sharply suppressed at a hierarchy of commensurate densities forming a devil’s staircase, most prominently at one-half, one-third, and two-thirds filling, and that random defects destabilize these ordered states and restore transport. To explain this, we represent particle configurations as evenly spaced building blocks whose rearrangements map the complex interacting system onto a simple symmetric exclusion process. Our results provide a unified, quantitative account of diffusion suppression in long-range interacting materials.
