The most common and most likely answer to this crossword clue is the 6 plus 4 letter word LIVING DEAD
I've seen this crossword clue in The Guardian
L
I
V
I
N
G
D
E
A
D
More clues leading to the result LIVING DEAD
Buddy explains!
The straight part
We know that "Schrödinger’s cat, perhaps/reduced to a zombie?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case schrödinger’s cat, perhaps/reduced to a zombie? = living dead.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.