Nichtunitarität

Nichtunitarität refers to a property in quantum mechanics where the time evolution of a quantum system is not described by a unitary operator. Unitary operators preserve the norm of quantum states, meaning the total probability of finding the system in some state remains constant over time. This is a fundamental requirement for the conservation of probability in standard quantum mechanics.

A system is considered nichtunitary if its evolution operator U does not satisfy U†U = I, where U† is the adjoint of U and I is the identity operator. This can arise in various contexts, such as open quantum systems that interact with their environment, leading to dissipation or decoherence. In such cases, the system can lose or gain probability to its surroundings, violating the strict conservation of norm within the system itself.

Another scenario where nichtunitarity might appear is in theoretical frameworks that go beyond standard quantum mechanics, such as certain approaches to quantum gravity or theories involving non-Hermitian Hamiltonians. These non-unitary evolutions can lead to phenomena like spontaneous symmetry breaking or the decay of unstable states. However, in experimental physics, observed deviations from unitarity are often interpreted as evidence of underlying non-unitary processes or experimental limitations rather than a fundamental breakdown of quantum mechanics. The interpretation and implications of nichtunitarity are active areas of research.