Ultrafast spin-transfer dynamics and single-qubit logic gate design in monocyclic carbon rings with transition metal atoms adsorbed.

We present a first-principles study of ultrafast spin-transfer dynamics and single-qubit logic gate design in transition metal (TM) atom-adsorbed monocyclic carbon ring systems. The structure- and size-dependent features of geometries, electronic structures, and spin localizations are analyzed. Notably, the TM2-C4n+2 systems generally prefer out-of-plane configurations and exhibit localized states with spin localized singly on one TM atom or doubly on two TM atoms, rather than the carbon ring-related localized states found in the mostly coplanar TM-C4n+2 systems. Driven by well-tailored nonchirped ultrafast laser pulses, sub-picosecond, high-fidelity spin transfer is achieved in most structures (except for the ones with only one type of spin localized states). The laser detuning and chirp effects on these scenarios are further explored. The tolerance and sensitivity characteristics of them can provide valuable guidance for both experimental implementation and sensor applications. In addition, based on the achieved ultrafast dynamics for the representative structures FeC14 and Fe2C18, four basic single-qubit quantum logic gates Pauli X, Pauli Y, Pauli Z, and S are all constructed, with an additional non-Clifford T gate achieved in the latter one. All these results demonstrate the great potential of the TM atom adsorbed carbon ring structures and provide significant guidance for experimental realization of the ultrafast spin dynamics and design of carbon-based molecular spintronic devices toward quantum computing.