Question

what is quantum physics?

Answer 1

it is the branch of physics concerned with quantum theory .where the Quantum mechanic also included.
Quantum mechanics, including quantum field theory, is a fundamental theory in physics which describes nature at the smallest scales of energy levels of atoms and subatomic particles

Answer 2

it's the physics that explains how everything works: the best description we have of the nature of the particles that make up matter and the forces with which they interact. Quantum physics underlies how atoms work, and so why chemistry and biology work as they do.