Origin of the even-odd noise-sensitivity effect

Identify the precise origin of the enhanced even-odd dependence of noise sensitivity in classically optimized parametrized circuits on Quantinuum hardware, including the reason for its stronger amplitude on hardware than in depolarizing-noise simulations.

Background

The paper reports that the heating per gate of classically optimized parametrized circuits varies sharply with whether the number of circuit steps is even or odd. Although the effect also appears in noisy numerical simulations, its magnitude is substantially larger on the hardware, and incorporating gate-angle-dependent noise does not explain the discrepancy. The authors explicitly state that the precise origin of this effect remains unresolved.