We measured the energy efficiency of information erasure using silicon DRAM cells capable of counting charges on capacitors at the single-electron level. Our measurements revealed that the efficiency decreased as the erasure error probability decreased, and notably, the Landauer limit was not achieved even under effectively infinite-time bit erasure. By comparing the measured efficiency with the Landauer limit, we identified a thermodynamic constraint that prevents DRAM from reaching this limit: the inability to prepare the initial state in thermal equilibrium, which in turn prohibits quasistatic operations. This finding has broad implications for DRAM cells and for many electronic circuits sharing similar structures. Furthermore, it validates our experimental approach to discovering thermodynamic constraints that impose tighter, practically relevant limits, opening a new direction in information thermodynamics research.
The explosive growth of global data traffic demands scalable and energy-efficient optical communication systems. Spatial division multiplexing (SDM) using multicore or multimode fibres is a promising solution to overcome the capacity limit of single-mode fibres. However, long-haul SDM transmission faces substantial challenges due to modal dispersion, which imposes heavy computational loads on digital signal processing for signal equalization. Here we propose parameterized SDM transmission, where programmable photonic unitary processors are installed at intermediate nodes. Instead of relying on conventional digital equalization on only the receiver side, our approach enables direct optimization of the SDM transmission channel itself by the programmable unitary processor, which reduces digital post-processing loads. We introduce a gradient-based optimization algorithm using a differentiable SDM transmission model to determine the optimal unitary transformation. Using this approach, we implement a telecom-grade programmable photonic unitary processor for low-loss, wideband (full C band), polarization-independent and high-fidelity (R2 > 96% across the C band) operation and experimentally report 1,300-km transmission using a three-mode fibre. The optimized photonic processor substantially reduces modal dispersion and post-processing complexity. Our results establish a scalable framework for integrating photonic computation into optical layers, enabling more efficient, high-capacity optical networks. A programmable photonic unitary processor for compensating modal dispersion allows long-haul (1,300 km) high-quality data transmission over a three-mode fibre.
Diffusive conductors share a universal shot noise reduction of 1/3. This result can be obtained from quantum scattering, Boltzmann-Langevin kinetics, or by symmetric simple exclusion process, but experiments have been limited to cryogenic conditions and the understanding of this universality remains incomplete. Here we show that ferrocene redox cycling in a microfluidic gap is room temperature realization of this universality. An analytical model of the current and its noise is derived and confirmed experimentally. The universal 1/3 shot noise suppression is recovered in the diffusion-limited regime, providing a bridge between mesoscopic physics and electrochemistry, opening a new route for probing molecular dynamics through room-temperature noise measurements.
Alloy engineering of group III–VI van der Waals (vdWs) semiconductors requires precise control of composition during bottom-up growth. We synthesized GaS _x Se _1− _x nanobelts by self-catalyzed vapor–liquid–solid (VLS) growth. The alloy composition depends nonlinearly on the source-gas fraction. This behavior is quantitatively reproduced by a kinetic model based on VLS growth considering adsorption, desorption, and crystallization of chalcogen at the Ga catalyst droplet. Analysis reveals that the nonlinear dependence is attributed to a much larger desorption-to-crystallization ratio for S than for Se. Our findings provide essential guidelines for precise composition control in mixed-chalcogen van der Waals semiconductors.
Abstract Scanning tunneling microscopy and spectroscopy were performed on a cleaved n -InAs(110) surface at 78 K in an ultra-high vacuum. An effective-Fermi-level-dependent charge state transition of defects was driven by Fröhlich-scattering-induced tunnel electron doping, manifesting as a donor state transition from D + to D 0 . An approximation formula of the effective Fermi level is proposed to estimate the chemical potential for defect formation. We detected the formation of metastable DX − centers, stimulated by the elevated quasi-Fermi level of secondary electrons, in the near-surface region at energies exceeding the threshold for tunnel electron impact-ionization. Furthermore, a shift in the Fermi level pinning position from the DX center energy level (near the charge neutrality level of InAs) to the mid-gap position was observed near zero bias, originating from the self-compensation effect governed by the amphoteric nature of extrinsic dopants at the near-surface region of the bulk crystal.
