The progress of charge manipulation in semiconductor-based nanoscale devices opened up a novel route to realise a flying qubit with a single electron. In the present review, we introduce the concept of these electron flying qubits, discuss their most promising realisations and show how numerical simulations are applicable to accelerate experimental development cycles. Addressing the technological challenges of flying qubits that are currently faced by academia and quantum enterprises, we underline the relevance of interdisciplinary cooperation to move emerging quantum industry forward. The review consists of two main sections:Pathways towards the electron flying qubit: We address three routes of single-electron transport in GaAs-based devices focusing on surface acoustic waves, hot-electron emission from quantum dot pumps and Levitons. For each approach, we discuss latest experimental results and point out how numerical simulations facilitate engineering the electron flying qubit.Numerical modelling of quantum devices: We review the full stack of numerical simulations needed for fabrication of the flying qubits. Choosing appropriate models, examples of basic quantum mechanical simulations are explained in detail. We discuss applications of open-source (KWANT) and the commercial (nextnano) platforms for modelling the flying qubits. The discussion points out the large relevance of software tools to design quantum devices tailored for efficient operation.
The efficiency of photoconductive switches, which continue to be used for the generation and detection of THz waves, has been overlooked for a long time. The so far “optics-dominated” devices are making their way through to new and emerging fields of research that require ultrafast picosecond voltage pulses, as well as to new applications where power efficiency is of uttermost importance. To address the efficiency problems, in this Article we present a novel photoconductive switch that is based on a three-dimensional design. In contrast to conventional planar designs, our photoconductive switch drastically enhances the overall efficiency by maximizing the laser absorption within the device, while at the same time optimizing the carrier collection efficiency at the electrodes. To maximize the optical absorption, we take advantage of photonic and plasmonic modes that are excited in our device due to a periodic array of nanopillars, whereas the collection efficiency is optimized by converting each nanopillar into a single nano-photoconductive switch. Our numerical calculations show a 50-fold increase in the overall generated current and a 5-fold bandwidth increase compared to traditional interdigitated planar photoconductive switches. This opens up a wealth of new possibilities in quantum science and technology where efficient low power devices are indispensable.
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