Realizing coherently convertible dual-type qubits with the same ion species

Trapped ions constitute one of the most promising systems for implementing quantum computing and networking^1,2. For large-scale ion-trap-based quantum computers and networks, it is critical to have two types of qubit: one for computation and storage, and another for auxiliary operations such as qubit detection³, sympathetic cooling^4–7 and entanglement generation through photon links^8,9. Although the two qubit types can be implemented using two different ion species^3,10–13, this approach introduces substantial complexity into creating and controlling each qubit type^14,15. Here we resolve these challenges by implementing two coherently convertible qubit types using one ion species. We encode the qubits into two pairs of clock states of the ¹⁷¹Yb⁺ ions, and achieve microsecond-level conversion rates between the two types with one-way fidelities of 99.5%. We further demonstrate that operations on one qubit type, including sympathetic laser cooling, single-qubit gates and qubit detection, have crosstalk errors less than 0.06% on the other type, which is below the best-known error threshold of ~1% for fault-tolerant quantum computing using the surface code^1,16. Our work establishes the feasibility and advantages of using coherently convertible dual-type qubits with the same ion species for large-scale quantum computing and networking.