  We study the loading of electrons into a quantum dot with dynamically
controlled tunnel barriers. We introduce a method to measure tunneling rates
for individual discrete states and to identify their relaxation paths.
Exponential selectivity of the tunnel coupling enables loading into specific
quantum dot states by tuning independently energy and rates. While for the
single-electron case orbital relaxation leads to fast transition into the
ground state, for electron pairs triplet-to-singlet relaxation is suppressed by
long spin-flip times. This enables the fast gate-controlled initialization of
either a singlet or a triplet electron pair state in a quantum dot with broad
potential applications in quantum technologies.
