Direct coupling

Abstract: Natural photosynthesis, which achieves efficient solar energy conversion through the combined actions of many types of molecules ingeniously arranged in a nanospace, highlights the importance of a technique for site-selective coupling of different materials to realize artificial high-efficiency devices1. In view of increasingly serious energy and environmental problems, semiconductor-based artificial photosynthetic systems consisting of isolated photochemical system 1 (PS1), PS2 and the electron-transfer system have recently been developed2,3. However, the direct coupling of the components is crucial for retarding back reactions to increase the reaction efficiency. Here, we report a simple technique for forming an anisotropic CdS–Au–TiO2 nanojunction, in which PS1(CdS), PS2(TiO2) and the electron-transfer system (Au) are spatially fixed. This three-component system exhibits a high photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of vectorial electron transfer driven by the two-step excitation of TiO2 and CdS.

Abstract: We present an area-efficient neural signal-acquisition system that uses a digitally intensive architecture to reduce system area and enable operation from a 0.5 V supply. The architecture replaces ac coupling capacitors and analog filters with a dual mixed-signal servo loop, which allows simultaneous digitization of the action and local field potentials. A noise-efficient DAC topology and an compact, boxcar sampling ADC are used to cancel input offset and prevent noise folding while enabling “per-pixel” digitization, alleviating system-level complexity. Implemented in a 65 nm CMOS process, the prototype occupies 0.013 mm2 while consuming 5 μW and achieving 4.9 μVrms of input-referred noise in a 10 kHz bandwidth.

Abstract: The harmonic oscillator is a simple and ubiquitous physical system, and various oscillators functioning at the quantum mechanical level are known. Previously, linkage between two quantum mechanical oscillators has been achieved only indirectly, but two groups now demonstrate direct coupling at the quantum level between two harmonic oscillators in separate locations. Such systems could be used as the building blocks for quantum information processors and simulators. Brown et al. achieve direct controllable coupling between 9Be+ ions held 40 micrometres apart in trapping potentials. In a similar experiment, Harlander et al. couple single 40Ca+ ions trapped 54 μm apart. In their system, additional ions act as antennae to amplify the coupling. The harmonic oscillator is a simple and ubiquitous physical system. This paper reports a new realization in the quantum regime, achieving direct controllable coupling between quantized mechanical oscillators. The oscillators are ions held in trapping potentials (separated by 40 micrometres) and coupled through their mutual Coulomb interaction. The system could be used as a building block for quantum computers and simulators. The harmonic oscillator is one of the simplest physical systems but also one of the most fundamental. It is ubiquitous in nature, often serving as an approximation for a more complicated system or as a building block in larger models. Realizations of harmonic oscillators in the quantum regime include electromagnetic fields in a cavity1,2,3 and the mechanical modes of a trapped atom4 or macroscopic solid5. Quantized interaction between two motional modes of an individual trapped ion has been achieved by coupling through optical fields6, and entangled motion of two ions in separate locations has been accomplished indirectly through their internal states7. However, direct controllable coupling between quantized mechanical oscillators held in separate locations has not been realized previously. Here we implement such coupling through the mutual Coulomb interaction of two ions held in trapping potentials separated by 40 μm (similar work is reported in a related paper8). By tuning the confining wells into resonance, energy is exchanged between the ions at the quantum level, establishing that direct coherent motional coupling is possible for separately trapped ions. The system demonstrates a building block for quantum information processing and quantum simulation. More broadly, this work is a natural precursor to experiments in hybrid quantum systems, such as coupling a trapped ion to a quantized macroscopic mechanical or electrical oscillator9,10,11,12,13.

Abstract: A non-radiative energy transformer, commonly referred as Witricity and based on `strong coupling' between two coils which are separated physically by medium-range distances, is proposed to realize efficient wireless energy transfer. The distance between the resonators can be larger than the characteristic sizes of each resonator. Non-radiative energy transfer between the first resonator and the second resonator is facilitated through the coupling of their resonant-field evanescent tails. The proposed system operates as traditional inductive magnetic coupling devices when the operating frequencies are not the resonant frequency. Corresponding finite element analysis (FEA) and experiments have been carried out to facilitate quantitative comparison. Compared with typical magnetic inductive coupling energy transmission devices, the efficiency of the proposed system is much higher. This investigation indicates that it is feasible to use wireless energy transfer technology to recharge batteries, particularly in implant devices.