Quantum information theory is a branch of science that combines principles from quantum mechanics and information theory. It studies how information is stored, processed, and transmitted using quantum systems, such as quantum bits or qubits. Unlike classical bits, which can be either 0 or 1, qubits can exist in multiple states simultaneously, allowing for more complex information processing. This field has significant implications for various technologies, including quantum computing and quantum cryptography. Quantum computing leverages the unique properties of qubits to perform calculations much faster than classical computers, while quantum cryptography offers enhanced security for data transmission by utilizing the principles of quantum mechanics.