Perhaps you should try some spelling variations:
"quantum classical" » "quantum chemical"
"quantum physical" » "quantum physics", "quantum chemical", "quantum critical"
"quantum optical" » "quantum optics", "quantum chemical"

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