Quantum mechanics is almost always described in terms of single particle states. An experiment measures something about one particle, and then the particle is known to be in the quantum state associated with that measurement.
It is allowed to measure something about an aggregate of many particles. In fact that is the rule, rather than the exception. When we hear about quantum physics, we seldom hear about many-particle states (there are exceptions, e.g., lasers). The reason is not that they are rare but that the equations are too complicated to solve, even for a few particles, let alone for the huge number of particles in a macroscopic object.
It has been a favorite idea of mine that life functions as a quantum system with an observer on the inside. My consciousness plays the role of the experimenter, constantly monitoring the state of the system as a whole, thereby keeping it alive. “Alive” is a quantum state.
Alex Wendt is a step ahead of me. He says that not just single brains but whole social systems can be in a quantum state.