The phrase "quantum leap" has been generalised in common speech to mean a big step forward. It sounds like impressive scientific jargon, but it is technically incorrect. A quantum in Quantum mechanics is the smallest possible discrete unit. A quantum leap is a change that emits a quantum. It is the smallest possible step forward. It may be discontinuous and sudden; but it is not big, radical change. It is a sub-microscopic increment.

Don't use this phrase to mean "a big change"1. If you feel the need to get pretentious and use big words, say "paradigm shift"2 to mean a fundamental change. At least you'll be making sense.

Or you could just say "a big step forward".

1) It makes you sound ignorant, and makes me wince. It's a pet hate of mine, like very unique, though not as bad.

2) For instance the change of mindset in the advance from Newtonian physics to Quantum mechanics.