Earlier quoted context omitted.
> You go online with your private receipt number and it can validate your vote. What precisely do you mean by "validate" here? Would this scheme make the ballot non-secret?
If each ballot has a unique ID and there is no association between the person voting and the ID, then the voter can retain that number, possibly by tearing off a section of the ballot as is done in CA, and check that number online to verify their vote was tallied as expected.
This seems somewhat contradictory. The voter retaining possession of the ID creates a link between the ballot and the voter, doesn't it?
Then again, it does open the door to plausible deniability, though correctly pulling that off could introduce new complications and/or avenues of attack.
> and check that number online to verify their vote was tallied as expected.
"as expected" is the key phrase here. If it includes seeing what candidate(s) the voter voted for (i.e., trying to verify that the ballot was read correctly), then that seems like it would break the secret ballot. If it means just checking that the ballot was included in the count without revealing precisely what candidate(s)/issue(s) the vote was for, then that might work.