Nichtunitary

Nichtunitary refers to a type of quantum operation that does not preserve the total probability of a quantum system. In standard quantum mechanics, unitary operations are used to describe the evolution of closed quantum systems, where the total probability of all possible outcomes remains constant. However, in open quantum systems, which interact with their environment, the total probability can change due to processes such as decoherence and dissipation.

A non-unitary operation is typically represented by a completely positive trace-preserving (CPTP) map, which describes how the state of a quantum system evolves over time when it is not isolated. These maps can be used to model various physical processes, including measurement, decoherence, and dissipation.

The study of non-unitary operations is crucial in quantum information theory and quantum computing, as it helps to understand and mitigate the effects of noise and decoherence in quantum systems. By using non-unitary operations, researchers can develop more robust quantum algorithms and error-correction techniques, which are essential for building practical quantum computers.

In summary, non-unitary operations are a fundamental concept in quantum mechanics that describe the evolution of open quantum systems. They are represented by CPTP maps and play a crucial role in the development of quantum information theory and quantum computing.