Kubits

Kubits are a theoretical unit of quantum information used in a generalized model of quantum computing that extends the concept of a qubit to a k-dimensional system. A kubit, sometimes called a k-ary quantum unit, has a state in a k-dimensional Hilbert space and can be described by a superposition sum_{i=0}^{k-1} a_i |i>. The amplitudes a_i satisfy sum|a_i|^2 = 1. When measured in the computational basis, the kubit's outcome is one of the k basis states with probability |a_i|^2.

Two or more kubits can be entangled, producing high-dimensional entangled states such as generalized Bell states. Computation on kubits is carried out with unitary operations acting on the k-dimensional state space, known as kubit gates. Like qubits, kubits are sensitive to decoherence and noise, and quantum error correction in kubit systems uses codes adapted to the higher-dimensional structure.

Information content: a single kubit carries log2(k) bits of classical information in ideal conditions, though no measurement reveals this content completely. When k = 2, a kubit reduces to a conventional qubit. For k > 2, kubits are more information-dense but require more complex control.

In theory, kubits have potential advantages for certain tasks, such as more compact representations of data and error-correcting codes with higher efficiency. They have attracted interest in theoretical studies of high-dimensional quantum information, but they remain a conceptual extension with limited experimental realization.

See also qubit, qudit, quantum computing.