Naoto Shibata

Annealing method for operating quantum-cellular-automaton systems

We propose an annealing method as an effective way of operating quantum-cellular-automaton (QCA) systems, which are devices for computation that utilize the minimum energy state of electrons in a quantum cell system. A QCA system has an energy function with many local minima and therefore cannot be operated as desired if placed under the conditions of a thermodynamically open system. Accordingly, for successful operation of a QCA system (i.e., making the QCA system converge successfully to its minimum-energy state), we propose a method of operation based on the concept of thermodynamic annealing. We simulate the dynamics of various QCA logic-gate systems operated by this annealing method, and show that data processing in QCA systems can be carried out accurately by means of this annealing method. The applicability of QCA systems to non-Neumann parallel-processing computation is also described.

Boltzmann machine neuron device using quantum-coupled single electrons

A quantum Boltzmann machine (QBM) neuron device is proposed. It consists of a two-dimensional (2D) arrangement of quantum dots that is occupied by quantum-coupled single electrons. The two possible polarizations, “down” and “up,” of the electron spin are used to encode the binary states 0 and 1. The QBM neuron device produces stochastic operations naturally because the electron spin takes the polarization down or up with a certain probability. Calculations for the operation of the QBM neuron device are presented and it is demonstrated that the device can perform the stochastic operations of the BM neuron.

QUANTUM CELLULAR AUTOMATON DEVICE USING THE IMAGE CHARGE EFFECT

A quantum cellular automaton (QCA) device that uses the image charge effect is proposed. This image-charge QCA device is constructed from many unit cells on a metal substrate covered with an insulator layer. Each unit cell consists of four quantum dots and two excess electrons. Two positive image charges in the metal substrate maintain the charge neutrality of each cell. The distance between two neighboring cells is designed to allow intercellular electron tunneling. The image-charge QCA cell can overcome two basic problems: establishing charge neutrality in each cell and loading electrons easily and precisely. We designed signal-transmission and elemental logic gate circuits using these image-charge QCA cells, and simulated operation of the circuits by computer simulation. It is demonstrated that the image-charge QCA circuits can perform signal transmission and elemental logic operations and that electrons (two per cell) can be easily loaded into the image-charge QCA circuits.