  We put forward nonadiabatic charge pumping as a method for accessing the
different charge relaxation rates as well as the relaxation rates of excited
orbital states in double-quantum-dot setups, based on extremely size-limited
quantum dots and dopant systems. The rates are obtained in a well-separated
manner from plateaus, occurring when comparing the steady-state current for
reversed driving cycles. This yields a reliable readout independent of any
fitting parameters. Importantly, the nonadiabatic pumping spectroscopy
essentially exploits the same driving scheme as the operation of these devices
generally employs. We provide a detailed analysis of the working principle of
the readout scheme as well as of possible errors, thereby demonstrating its
broad applicability. The precise knowledge of relaxation rates is highly
relevant for the implementation of time-dependently operated devices, such as
electron pumps for metrology or qubits in quantum information.
