This question is about a puzzle from the book of Raymond Smullyan: The Lady or the Tiger? The description of the puzzle starts in Chapter 8, p. 103, and here is the important part (copy-pasted from Bruce Ediger's webpage):

Property Q: For any combination x, the combination QxQ is specially related to x.

Property L: If x is specially related to y, then Lx is specially related to Qy.

Property V (the reversal property: If x is specially related to y, then Vx is specially related to the reverse of y.

Property R (the repetition property: If x is specially related to y, then Rx is specially related to yy.

Property Sp: If x is specially related to y, then if x jams the lock, y is neutral, and if x is neutral, then y jams the lock.

Smullyan provides a key of length 10 on p. 163, however, this is not the shortest, I know a key of length 8. Is this the shortest? Spoiler alert: You can find this key in my comment to the accepted answer.)