Question

what is quantum physics?

Answer 1

the branch of physics concerned with quantum theory.

"quantum physics allows for particles to be in two states at the same time"

Answer 2

Quantum physics is necessary to understand the properties of solids, atoms, nuclei, subnuclear particles and light. In order to understand these natural phenomena, quantum principles have required fundamental changes in how humans view nature. To many philosophers (Einstein included), the conflict between the fundamental probabilistic features of quantum mechanics and older assumptions about determinism provided a cognitive shock that was even more unsettling that the revised views of space and time brought by special relativity.