"Quantum probability" in this case should really be called "noncommutative probability": that emphasizes that there's no direct connection to quantum mechanics as a physical theory. The basic mathematical feature is that random variables don't commute.
It's well-established that 0 decibans means 1:1 odds or 50% confidence; that 10 decibans means 10:1 odds; that -10 decibans means 1:10 odds; and that fractional numbers of decibans have similar meaning.
Does it make sense to talk about "i decibans", or "10 + 20i decibans"? If so, what does that actually mean?
I'm currently roughing out what may eventually become a formal specification for a protocol. It includes a numerical field for a level of confidence, measured in decibans. I'd like to know if I should simply define the spec as only allowing real numbers, or if there could be some purpose in allowing for complex numbers, as well.