Hirashin,
Please remember this rule: when a word is out of order, that word is emphasized.
(1A) Mike has already gone back to Britain.
This is the normal, correct word order.
(1B) Mike already has gone back to Britain.
The word "already" is out of order and is emphasized. (And this example sounds a little strange.)
(2A) I have never been to China.
This is the normal, correct word order.
(2B) I never have been to China.
This is a mistake.
(3A) He is no longer a professional player.
This is the normal, correct word order.
(3B) He no longer is a professional player.
The phrase "no longer" is out of order and is emphasized. (And this example sounds a little strange.)
Consider this example:
"No longer is he a professional player." The phrase "no longer" is out of order and is emphasized. (This example sounds like poetry.)