Crosstalk effects in QCA wires: Insights from tunnel and Coulomb couplings

Abstract

Quantum cellular automata (QCA) circuits offer promising prospects for ultra-low power and high-speed computing by leveraging the nanoscale dimensions of molecules and inherent parallelism. However, the pervasive challenge of crosstalk effects complicates their design and implementation. This study explores the intricate interplay between tunnel and Coulomb couplings, analyzing their combined influence on crosstalk and metastability in QCA wires, where the operation of each cell is governed by classical dynamics on a single-well Born–Oppenheimer potential energy surface. In this work, vibronic coupling is neglected, and tunnel coupling refers exclusively to electronic coupling, representing tunneling rates in purely electronic states. Through full-basis quantum mechanical analysis and large-scale numerical simulations, we examine how structural and layout parameters, including interwire Coulomb coupling and tunnel coupling, impact circuit performance. Our results highlight the critical role of these couplings in modulating metastability and threshold voltage levels, providing insights into the trade-offs between power dissipation and circuit stability. Additionally, the study investigates the thermal robustness of QCA wires, linking excited-state dynamics to the persistence of crosstalk effects. These findings offer actionable guidance for optimizing QCA circuit designs.