Perhaps you should try some spelling variations:
"quantum mechanical" » "quantum mechanics"
"quantum chemical" » "quantum chemistry"
"quantum optical" » "quantum optics"
"quantum physics" » "quantum physical"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("quantum physics") OR ((("quantum optical") OR ((("quantum chemical") OR ("quantum mechanical")))))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"quantum physics\") or (((\"quantum optical\") or (((\"quantum chemical\") OR (\"quantum mechanical\"))))))".
• Removing quotes may allow a broader search: (( quantum physics ) or ((( quantum optical ) or ((( quantum chemical ) OR ( quantum mechanical )))))).
• Adding a wildcard symbol may retrieve word variants: (("quantum physics") or ((("quantum optical") or ((("quantum chemical") OR ("quantum mechanical"))))))*.