Nature-inspired Single-electron Computers

A single-electron circuit is one that creates electronic functions by controlling movements of individual electrons [11]. The circuit uses tunneling junctions, each of which generally consists of two conducting materials facing each other very closely (statically, they are normal capacitors). Under a low-temperature environment, electron tunneling is governed by the physical phenomenon called the Coulomb blockade, where an electron does not tunnel through a junction if the tunneling increases the circuit's electrostatic energy (E _c ). To comply with the Coulomb blockade, the capacitance of a tunneling junction must be sufficiently small; for example, if we use 1 pF of capacitance, E _c corresponds approximately to 1 mK in temperature (T). Generally, observing the Coulomb blockade in practical experimental environment (e.g., T ~ 0.1 K) is difficult because the blockade effect is disturbed by thermal fluctuations. Therefore, elemental devices of single-electron circuits, that is, tunneling junctions and capacitors, must be constructed in nanoscale (lower than a few tens of nanometers).

These intrinsic quantum behaviors may give us an insight in developing modern computing paradigms, including nature-inspired computing and quantum computing. However, if we employ conventional (deterministic) computing architectures, we need a fully worked-out plan for both computing and circuit architectures, for example, see [5, 10, 27, 29, 30]. Thermal noise tolerance is an important characteristic of single-electron computers, because the rate of random electron tunneling increases exponentially as the temperature increases. Several practical circuits have been developed by improving the process for fabricating ultra-low capacitance of tunneling junctions [29] and by using an error-compensation algorithm in the architecture [27].