We would like to define the output of a QTM which halts as the superposition of the tape contents of the configurations in the machine’s final superposition. However, we must be careful to note the position of the tape head and the alignment relative to the start cell in each configuration since these details determine whether later paths interfere. Recall that the output string of a final configuration of a TM is its tape contents from the leftmost nonblank symbol to the rightmost nonblank symbol. This means that giving an output string leaves unspecified the alignment of this string on the tape and the location of the tape head to be identified.