Quantum information is a field that merges principles from quantum mechanics with information theory. It explores how quantum systems can be used to encode, manipulate, and transmit information. Here are some of the key aspects of quantum information: 1. **Quantum Bits (Qubits)**: In classical computing, the basic unit of information is the bit, which can be either 0 or 1. In quantum computing, the analogous unit is the quantum bit or qubit.
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Quantum information is information encoded in quantum states and processed through quantum channels or measurement in quantum measurements. A qubit supplies a two-dimensional state space; quantum phase and entanglement affect which operations and outcome statistics are possible. The Born rule connects the state description with the probabilities of classical measurement records.
The continuously varying probability amplitudes of a qubit do not supply a readable list of arbitrarily many classical bits. A measurement produces a classical record with state-dependent probabilities. Quantum state tomography estimates the state from many identically prepared systems. For a classical label encoded into one transmitted qubit, with no additional shared resource, Holevo's theorem bounds the mutual information available from a measurement by one bit. This bound concerns information about the label, rather than the number of possible outcome labels a measuring device can print. [ref]
https://jhwatrous.github.io/TQI-notes.pdf#page=116. Watrous's lecture notes, Lecture 12, on accessible information and the Holevo bound
