Quantum computers

This article provides a concise overview of the physical concepts, experimental implementations, and algorithmic potential of quantum computers and quantum cryptography. After distinguishing them from classical, irreversible information processing, the article introduces the quantum mechanical fundamentals of qubits. Regarding physical implementation, established architectures such as ion traps and NMR systems are analyzed, and semiconductor-based solid-state concepts (donors in silicon, quantum dots) are discussed as scalable alternatives. The theoretical superiority of quantum computers is quantified using key algorithms, including Shor’s polynomial factoring algorithm and Grover’s search algorithm. Finally, secure communication via quantum key distribution (QKD) is discussed using the B92 protocol as an example, highlighting the technological challenges of optical implementation through single-photon detection.