Deterministic quantum state transfer of atoms in a random magnetic field

We propose a method for transferring atoms to a target quantum state for a multilevel quantum system with sequentially increasing, but otherwise unknown, energy splitting. This is achieved with a feedback algorithm that processes off-resonant optical measurements of state populations during adiabatic rapid passage in real time. As a demonstration, we reliably perform the state transfer |F  = 2,m F  = 2〉 → |1,1〉 → |2,1〉 for a sample of ultracold 87 Rb in the presence of a random external magnetic field.