Adiabatic theorem revisited: The unexpectedly good performance of adiabatic passage

Adiabatic passage employs a slowly varying time-dependent Hamiltonian to control the evolution of quantum system along eigenstates. For processes finite duration, exact time evolving state may deviate from adiabatic eigenstate at intermediate times, but in numerous applications it is observed that this deviation reaches maximum and then decreases significantly towards end process. We provide straightforward theoretical explanation for welcome often unappreciated fact. Our analysis emphasizes separate adiabaticity criterion high fidelity state-to-state transfer points new effective shortcut strategies near dynamics.