Backslash escape characters in zsh string for use as a path argument

Question

In zsh, what is the most efficient and/or most concise way to backslash escape characters in a string for use as a path argument?

I do not want to enclose the whole path in any type of quotes.

e.g., if I have a zsh string a & b, I want to get a\ \&\ b.

I do not want: 'a & b', "a & b", $'a & b', etc. (those can be obtained via various q parameter expansion flags; none of the q flags that I found backslash escape spaces or ampersands, so they won't work for me)

I haven't been able to find a way to do this concisely, either via parameter expansion or via any other simple command, other than to use a regex replace parameter expansion (of the form ${name//pattern/repl}), but that would require me to learn all the characters that must be escaped, and would require me to update the expansion if there are any changes.