Progress towards dual-type scheme implemention in ¹³⁷Ba⁺ ion chains

In trapped ion platforms, two species of ions are utilized: one for quantum information storage and the other for cooling and measurement. This architecture takes advantage of sympathetic cooling but introduces complications. Recently, the dual-type scheme[1] and the OMG architecture [2] have been proposed as alternatives. These schemes use single ion species and encode different qubits based on electronic levels. The ¹³⁷Ba⁺ ions are well suited for implementing the schemes due to long metastable level lifetime.

We demonstrate Electromagnetically Induced Transparency (EIT) cooling of ¹³⁷Ba⁺ ions despite the lack of a Lambda system. Using this technique, we cool the radial modes of a five-ion chain to near the motional ground state.[3] Furthermore, the laser used in the EIT cooling scheme has little influence on the qubit in the metastable state, which suits the scheme. We also show the MS interaction between different types of qubits using a 532nm laser. Along with acousto-optic deflectors and objective lens, we can steer the laser beam onto individual ions for state preparation and gate operations. The gate fidelity between a ground state qubit and a metastable qubit is comparable to that between a pair of ground state qubits or a pair of metastable state qubits.[4]