Trade off-free entanglement stabilization in a superconducting qutrit-qubit system

The approach to stabilizing a quantum state by coupling to engineered reservoirs is limited by a trade-off between state fidelity and stabilization rate. Here the authors implement a protocol based on parametric system-bath coupling to achieve fast and high-fidelity Bell state stabilization in a qutrit-qubit system. Quantum reservoir engineering is a powerful framework for autonomous quantum state preparation and error correction. However, traditional approaches to reservoir engineering are hindered by unavoidable coherent leakage out of the target state, which imposes an inherent trade off between achievable steady-state state fidelity and stabilization rate. In this work we demonstrate a protocol that achieves trade off-free Bell state stabilization in a qutrit-qubit system realized on a circuit-QED platform. We accomplish this by creating a purely dissipative channel for population transfer into the target state, mediated by strong parametric interactions coupling the second-excited state of a superconducting transmon and the engineered bath resonator. Our scheme achieves a state preparation fidelity of 84% with a stabilization time constant of 339 ns, leading to a 54 ns error-time product in a solid-state quantum information platform.