I have successfully used back-quotes in order to protect the literal superscript from being interpreted. Thus

x^$&# is input as x^`$&#`. More realistically: x⁽¹⁾ is input as x^`(1)`. When using both superscripts and subscripts the order seems to matter. For example T_a^b is input as T__a^`b`. But T^a_b  does not work by this method, i.e. T^`a`__b is not accepted.