Two-Qubit Logic Gates Based on the Ultrafast Spin Transfer in π-Conjugated Graphene Nanoflakes

Ultrafast optical spin control allows gate operations to be performed within a picosecond timescale, orders of magnitude faster than microwave or electrical control. Here, using high-level quantum chemical computations, we suggest a two-qubit logic gate based on the optically induced ultrafast spin-flip and spin-transfer processes over rhombic graphene nanoflakes (Co4-GNF). It is demonstrated that the π-conjugated Co atoms can significantly influence the spin properties of the system. The spin density is distributed on different Co atoms in different energy levels, in this way opening a channel for successful spin-transfer processes between the Co atoms. Thus, the reversible local spin-flip processes on each Co atom and global spin-transfer processes between the Co atoms are realized. Importantly, based on various spin-dynamics processes achieved in Co4-GNF structures, both classical (OR, AND, NAND) and quantum (CNOT, SWAP) two-qubit logic gates are constructed, and the spin manipulation process can be completed in subpicosecond timescale with fidelity above 96%. This theoretical design based on the laser-induced ultrafast spin dynamics provides a new implementation of qubit manipulation, which could pave the way towards the construction of nano magnetic logic circuits and spintronic devices.