Coherently manipulating triplet-exciton qubit by circularly polarized laser

We theoretically propose a scheme for the coherent manipulation of a single qubit, which is constructed using the self-trapped triplet exciton (STTE) in FM/polymer/FM sandwich. The STTE serves as a quantum dot, comprising two degenerate triplet states with opposite magnetizations, thereby forming the qubit’s subspace. We demonstrate that the spin state of this qubit can be coherently manipulated by applying an external circularly polarized laser (CPL) to form the Floquet state. The manipulation exhibits significant helicity dependence: when the CPL’s angular momentum is antiparallel to the STTE’s spin orientation, the STTE undergoes Rabi oscillations between the |↑↑〉 and |↓↓〉 state, corresponding to a π-rotation around the x-axis on the Bloch sphere. Conversely, when the CPL’s angular momentum is parallel to the STTE’s spin orientation, the STTE remains unresponsive to the CPL. Two-axis coherent control of the STTE qubit can be potentially realized by additionally applying a static magnetic field B_z. Our work provides a theoretical perspective for realizing the coherent manipulation of a qubit in organic devices.