Yes, QUANTA is a Scrabble word!

Letter values in Scrabble US: Q 10, U 1, A 1, N 1, T 1, A 1.

Is it a valid word?

QUANTA is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a discrete amount of something that is analogous to the quantities in quantum theory
(physics) the smallest discrete quantity of some physical property that a system can possess (according to quantum theory)