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

Try widening your search to All Fields.

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 physical") OR ("quantum classical"))) OR ((("quantum chemical") OR ("quantum mechanical")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"quantum physical\") or (\"quantum classical\"))) or (((\"quantum chemical\") OR (\"quantum mechanical\"))))".
• Removing quotes may allow a broader search: (((( quantum physical ) or ( quantum classical ))) or ((( quantum chemical ) OR ( quantum mechanical )))).
• Adding a wildcard symbol may retrieve word variants: (((("quantum physical") or ("quantum classical"))) or ((("quantum chemical") OR ("quantum mechanical"))))*.