Ratchet Cellular Automata

In this work we propose a ratchet effect which provides a general means of performing clocked logic operations on discrete particles, such as single electrons or vortices. The states are propagated through the device by the use of an applied ac drive. We numerically demonstrate that a complete logic architecture is realizable using this ratchet. We consider specific nanostructured superconducting geometries using superconducting materials under an applied magnetic field, with the positions of the individual vortices in samples acting as the logic states. These devices can be used as the building blocks for an alternative microelectronic architecture.

Figure 1

(a) Pipeline without ratchet. (b) Schematic of ratchet for pipeline. $U(x)$ indicates potential as a function of $x$. Positions and motion of vortices are indicated at $\mathbf{J}=0$. (c) Schematic of second stage of ratchet, for $\mathbf{J}=-J\widehat{y}$.

Figure 2

Simulated signal propagation through a pipeline. The time at which the vortex in each well changes states is indicated. (a) Thermally activated ratchet operating at $T=0.5$. Inset: Detail of the occasional backward and nonpropagating motion of the signal. (b) Deterministic, perfectly clocked ratchet at $T=0.$ Inset: Detail showing the slight asymmetry in switching times of the three wells.

Figure 3

(a) Schematic of fanout. The spacing between wells is slightly increased where marked by the double arrow. (b) Schematic of NAND gate. Spacing between wells is slightly increased where marked by the double arrow, to force both pipelines into the same state.