**Definition:**

*Quantum information theory*is the study of how to integrate information theory with quantum mechanics, by studying how information can be stored with (and retrieved from) a quantum mechanical system. The primary piece of information in quantum information theory is the qubit, an analog to the bit (1 or 0) in classical information theory.

Some specific areas of research into quantum information theory include:

- quantum computers and quantum computing
- quantum communication
- quantum cryptography
- quantum entanglement
- quantum teleportation

*quantum information science*.

A key feature of quantum information theory is that the information contained in one system cannot be completely from one system to another - the information within the historical quantum states cannot entirely be retained once the system has collapsed from a superposition of states into a specific state. That lost information can never be retained, as opposed to classical theory where information transformations can be reversed to obtain a history of the previous states of the system.

**Also Known As:**quantum information science