We examine the possible implementation of logic devices using coupled quantum dot cells. Each quantum cell contains two electrons which interact Coulombically with neighboring cells. The charge distribution in each cell tends to align along one of two perpendicular axes, which allows the encoding of binary information using the state of the cell. The state of each cell is affected in a very nonlinear way by the states of its neighbors. A line of these cells can be used to transmit binary information. We use these cells to design inverters, programmable logic gates, dedicated AND and OR gates, and non-interfering wire crossings. Complex arrays are simulated which implement the exclusive-OR function and a single-bit full adder.

This paper presents an experimental demonstration of a basic cell of the quantum-dot cellular automata, a transistorless approach to computation that addresses the issues of device density, interconnection, and power dissipation. The device under study was composed of four metal dots, connected with tunnel junctions and capacitors, and operated at <50 mK. Operation was evidenced by switching of a single electron between output dots controlled by a single electron switching in input dots, demonstrating a nonlinear, bistable response.

A functioning logic gate based on quantum-dot cellular automata is presented, where digital data are encoded in the positions of only two electrons. The logic gate consists of a cell, composed of four dots connected in a ring by tunnel junctions, and two single-dot electrometers. The device is operated by applying inputs to the gates of the cell. The logic AND and OR operations are verified using the electrometer outputs. Theoretical simulations of the logic gate output characteristics are in excellent agreement with experiment.

A numerical algorithm for the solution of the two-dimensional effective mass Schrödinger equation for current-carrying states is developed. Boundary conditions appropriate for such states are developed and a solution algorithm constructed that is based on the finite element method. The utility of the technique is illustrated by solving problems relevant to submicron semiconductor quantum device structures.