SEUs are more of a problem in space. CPUs used for space missions mitigate the errors in a few different ways. In the past, the feature size on the CPU substrate was large enough to absorb most cosmic radiation without incident. As the feature sizes have shrunk and the old foundries are no longer producing the old chips, many missions have adopted "multiple voting" architectures. Satellites often use "triple voted" processors. The Space Shuttle had a system with five votes.

I'm not a quantum computing expert, but I wonder if a SEU would even matter in some parts of a quantum system. The bits are in an undefined state during operation anyway.