Yes, a fundamental property of quantum information undergoing unitary evolution (meaning, no measurements, no discarding stuff into the environment, etc.) is th

Yes, a fundamental property of quantum information undergoing unitary evolution (meaning, no measurements, no discarding stuff into the environment, etc.) is that it can be neither created nor destroyed. This fact enters into my work, or the work of anyone else in quantum information, sort of like how the number '2' enters into our work---i.e., so thoroughly that it would be hard to pick it out as a separate ingredient!