First-Principles Study of Spin-Selective Transport Properties and Quantum Bit Operation in Transition-Metal-Capped Nanowires

Abstract

Realizing spin-operated quantum logic circuits at the nanoscopic level has been one of the major challenges of designing modern computing architectures by encoding quantum information in the spin states of electrons. The ability to manipulate these spin orientations through various physicochemical mechanisms offers a promising route towards energy-efficient, non-volatile, and high-speed alternatives to conventional electronics. In this work, we report a reconfigurable spin molecular logic device (SMLD) based on a transition-metal-terminated carbon nanowire bridged between two zigzag-edged graphene electrodes. Using DFT combined with the non-equilibrium Green's function formalism, we explore spin-polarized quantum transport under various biases. The developed constructed nano-model device exhibits strong spin polarization and voltage-dependent switching behavior, enabling the realization of multiple quantum logic gate operations-including NAND, OR, NOR, YES, and NOT-within a single architecture. I-V characteristics, transmission spectra, and transmission pathways reveal the physical origin of logic functionality. Additionally, spin-resolved entropy analysis indicates logic-dependent information loss of ∆S = ¬0.09 qubits for irreversible quantum logic gates (NAND, NOR & OR), in contrast to zero-entropy transitions for reversible gates (NOT & YES). These findings trigger an expected versatile spintronics platform for low-powered, spin-based molecular logic applications such as a quantum nanochip for quantum computation.