  Quantum information, a field in which great advances have been made in the
past decades, now presents opportunities for chemistry. One roadblock to
progress, especially for experimental chemical science, is that new concepts
and technical definitions need to be learned. In this paper, we review some
basic, but sometimes misunderstood, concepts of quantum information based on
the mathematical formulation of quantum mechanics that will be useful for
chemists interested in discovering ways that chemistry can contribute to the
quantum information field. We cover topics including qubits and their density
matrix formalism, quantum measurement as a quantum operation, information
theory, and entanglement. We focus on the difference between the concepts in
the quantum context and the classic context. We also discuss the relation and
distinction among entanglement, correlation, and coherence. We aim to clarify
the rigorous definition of these concepts, and then indicate some examples in
physical chemistry.
