Limits of adiabatic clocking in quantum-dot cellular automata

Abstract

Ultimate bounds on the maximum operating frequency of networks of quantum dot cellular automata devices have yet to be established. We consider the adiabaticity of such networks in the two-state approximation where clocking is achieved via modulation of the inter-dot tunneling barriers. Estimates of the maximum operating frequency that would allow a 99% probability of observing the correct logical output are presented for a subset of the basic components used in QCA network design. Simulations are performed both in the coherent limit and for a simple dissipative model. We approach the problem of tunnel-based clocking from the perspective of quantum annealing, and present an improved clocking schedule allowing for faster operation. Using an analytical solution for driven QCA wires, we show that the maximum operating frequency in the coherent limit falls off with the square of the wire length, potentially limiting the size of clocked regions.

A Design Methodology of Line Feedback Shift Registers With Quantum Cellular Automata

“…Thermal fluctuations can excite the QCA array above its ground state, which may produce incorrect outputs. A QCA wire in every clock zone has an upper bound, which is subjected to the thermodynamic effects of cells [18], [22] and clock frequency [23]. It is reckoned that a QCA wire cannot exceed more than 47 molecular cells in a clock zone at room temperature [18].…”

Zwitterionic Mixed-Valence Species for the Design of Neutral Clocked Molecular Quantum-Dot Cellular Automata

“…A three-dot QCA half-cell allows an additional level of control that has important implications for the way in which QCA cells can be used in large circuits where encoded information may be lost due to slow energy dissipation. ,− Clocking enables also true power gain in QCA devices. ,− A clocking signala local electric field for instancecan vary the potential of the middle “null” (inactive) dot and the active end dots and, therefore, controls the activity of the cell (Figure d). When the potential is large and attractive, the mobile charge is drawn into the middle null dot, and when the potential becomes large and repulsive, the charge is forced out into the active end dots.…”