Hamed Mohammady (ULdB): Measurement disturbance and conservation laws in quantum mechanics

Quantum Information and Quantum Computing Seminars CTP PAS 2021-11-03

Measurement disturbance and conservation laws in quantum mechanics. The disturbance caused by measurements in quantum mechanics depends on the interaction between system and apparatus. If this interaction obeys a conservation law, the observables that may be non-disturbed will be restricted. We obtain general bounds that indicate the necessary conditions for non-disturbance in the presence of a conservation law and show that an observable not commuting with the conserved quantity admits a repeatable measurement – a special instance of a non-disturbing measurement – only if it is unsharp, and the apparatus is prepared in a state with a large uncertainty in the conserved quantity. This generalises the well-known Wigner-Araki-Yanase theorem.