thumb|upright=1|Optical lattices use lasers to separate [[rubidium atoms (red) for use as information bits in neutral-atom quantum processors—prototype devices which designers are trying to develop into full-fledged quantum computers.]]
Quantum information is the information of the state of a quantum system. It is the basic entity of study in quantum information science, Since any two non-commuting observables are not simultaneously well-defined, a quantum state can never contain definitive information about both non-commuting observables. These studies emphasized the philosophical aspects of measurement rather than a quantitative approach to extracting information via measurements.
See: Dynamical Pictures
Development from communication
In the 1960s, Ruslan Stratonovich, Carl Helstrom and Gordon and the conditional quantum entropy.
Unlike classical digital states (which are discrete), a qubit is continuous-valued, describable by a direction on the Bloch sphere. Despite being continuously valued in this way, a qubit is the smallest possible unit of quantum information, and despite the qubit state being continuous-valued, it is impossible to measure the value precisely. Five famous theorems describe the limits on manipulation of quantum information.