  Two-terminal electronic transport systems with a rectangular transmission can
violate standard thermodynamic uncertainty relations. This is possible beyond
the linear response regime and for parameters that are not accessible with rate
equations obeying detailed-balance. Looser bounds originating from fluctuation
theorem symmetries alone remain respected. We demonstrate that optimal
finite-sized quantum dot chains can implement rectangular transmission
functions with high accuracy and discuss the resulting violations of standard
thermodynamic uncertainty relations as well as heat engine performance.
