Quantum is singular, not singular possessive. The singular possessive form is quantum's.
The singular noun form is glass.There are two accepted forms for possessive singular nouns that end with an s:Add an apostrophe (') after the existing s at the end of the word:glass'Add an apostrophe s ('s) after the existing s at the end of the word:glass'sExamples:The glass' monogram is that of my grandfather.The glass's monogram is that of my grandfather.
The singular possessive form for the noun clock is clock's.
The possessive form for the singular noun speed is speed's.Example: This device will measure your speed's velocity.
The noun quantum is a singularnoun. The plural form is quanta.A possessive noun requires the use of an apostrophe.The singular possessive form is quantum's. The plural possessive form is quanta's.
The possessive form for the singular noun glass is glass's (just as you have it in your question).The plural form is glasses. The plural possessive form is glasses'.Example: I like these glasses' pattern the best.
The possessive form is Amos's.
The singular form is goose; the singular possessive form is goose's.The plural form is geese; the plural possessive form is geese's.
Quantum is singular, not singular possessive. The singular possessive form is quantum's.
The singular possessive form is week's.
The singular possessive form is frontiersman's.
The singular possessive form is aircraft's.
The singular possessive form is contralto's.
The singular possessive form is speculum's.
The singular possessive form is herd's.
The singular possessive form is heart's; the plural possessive form is hearts'.
The singular form for the noun families is family. The singular possessive form is family's.