Kvantbiten

Kvantbiten is the basic unit of quantum information, analogous to the classical bit. It is represented by a two-level quantum system that can exist in a superposition of the basis states 0 and 1, written as a|0> + b|1>, where a and b are complex amplitudes with |a|^2 + |b|^2 = 1.

When measured in an appropriate basis, a kvantbiten yields 0 or 1 with probabilities |a|^2 and |b|^2, and the measurement collapses the state to the corresponding basis state. In the general case, its state can be described by a point on the Bloch sphere. The kvantbiten therefore embodies both probabilistic outcomes and coherent evolution, which is not possible for a classical bit.

Kvantbitens are realized in various physical platforms, including superconducting circuits, trapped ions, quantum dots, and photonic systems. Real devices implement quantum gates that manipulate the state and allow entanglement between multiple kvantbiten, forming the basis of quantum computation. The ability to create and preserve superposition and entanglement enables computational tasks that are difficult for classical systems, such as certain search and factorization problems when scaled to many quanta.

Important principles include superposition, interference, and entanglement, as well as the no-cloning theorem, which states that an unknown kvantbiten state cannot be copied perfectly. These features underpin the potential advantages of quantum information processing, while also presenting challenges related to decoherence and error correction.

The concept emerged from efforts to combine quantum mechanics with information theory in the late 20th century and has since become central to quantum information science. The term qubit is widely used in English-language literature, while kvantbiten appears in Swedish-language sources.