High-fidelity population transfer in a Josephson three-level atom with optimized level anharmonicity

We propose a theoretical scheme to enhance the fidelity of population transfer in a Josephson three-level atom by optimizing the level anharmonicity. Without the leakage effect, the ideal population transfer can be performed via Raman adiabatic passage. In the general case, we consider the dependence of transfer fidelity on the leakage error, and then present an effective way to implement the high-fidelity population transfer using the optimized level structure. The scheme could offer a potential route towards the robust population transfer with artificial Josephson atoms experimentally.