Emerging Technologies of Computation

1. Emerging Technologies of Computation Montek Singh COMP790-084 Aug 25, 2011

2. Today: Quantum Dot Cellular Automata • Cellular automata • Quantum dot cellular automata (QCA) • Wires and gates using QCA • Implementation

3. Cellular Automata • Discrete model studied in computability • grid made up of “cells” • each cell can be in one of finite number of states • each cell has a defined “neighborhood” • at each new time step, the state of a cell is determined by the state of its neighborhood in prior time step • Conway’s Game of Life

4. Cellular Automata: Elementary examples • e.g., “Rule 110” • e.g., “Rule 30”

5. Cellular Automata: Biology ex Conus textile • Seashell patterns • each cell’s pigment controlled by activating and inhibiting activity of neighbors

6. Quantum Dot Cellular Automata • QCA • proposed models of quantum computation • analogous to conventional CAs • but based on quantum mechanical phenomenon of “tunneling” • Quantum dots • 4-dot cell • basic unit of storage and computation • two states: -1 and +1 • electrostatic repulsion

7. QCA: wires • Wires formed by juxtaposition of cells • if leftmost is controlled externally, all others align same direction • like “dominoes” falling

8. QCA: inverter • Key idea is to place cells at 45 degrees w.r.t. each other • Two branches used here, one can work too

9. QCA: basic gate • Majority gate • 2 out of 3 inputs determine output • Can you make? • AND gate • OR gate

10. QCA: wire crossing • Single-plane crossover without “touching”! • values along two wires propagate independently

11. QCA: controlling state transitions • QCA clocking • “freeze” cell when clock low • equivalent to latching • free it up when clock high • equivalent to computing • Often use 4 or more clock phases

12. QCA: Fabrication • Metal-island • aluminum dots • 1 micron, so very low temperatures • Semiconductor • 20 nm, so ordinary temperatures • most common • Molecular • single molecules, so very fast • future, not yet • Magnetic • magnetic exchange interactions instead of electron tunneling • room temperature