Full tunability and quantum coherent dynamics of a driven multilevel system

The tunability of a quantum system is crucial to its capacity in quantum computing, though it always poses significant demand on the design and fabrication of a device. Here, we demonstrate that Floquet engineering based on a longitudinal drive provides possibilities for enhancing the tunability of a quantum system without additional resources. In particular, we study a driven singlet-triplet (ST) system in a gate-defined quantum dot system and derive the effective Hamiltonian which captures the dynamics well. Notably, the engineered Hamiltonian reveals a full tunability controlled by the microwave field. Such tunability yields several featured phenomena as we would like to discuss, such as the odd-even effect, engineered coherent population trapping (CPT), and adiabatic state transfer based on amplitude modulation. We demonstrate the odd-even effect and engineered CPT based on an ST system in a double-quantum-dot system. With no surprise, the experimental phenomena agree well with the effective Hamiltonian, which indicates the nontrivial tunability enabled by the driving field.