2026.03.23. Gakuhen-B "Quantum Energy Innovation" Seminar Series (M. Hamed Mohammady)

As part of our area’s seminar series, a seminar by M. Hamed Mohammady will be held on Monday, March 23, 2026, at Kyushu University’s Ito Campus.

Details are as follows:

Speaker: M. Hamed Mohammady (Research Centre for Quantum Information, Institute of Physics, Slovak Academy of Sciences)
Date: Monday, March 23, 2026, 14:40–
Place: Room 826, West Building 2, Ito Campus, Kyushu University

Title:Wigner-Araki-Yanase theorems for general quantum measurements
Abstract:
According to the unitary interaction based model of quantum measurement dating back to von Neumann, a sharp (projective) observable is measured in a quantum system by a unitary premeasurement interaction between the system being measured and a quantum measuring apparatus, followed by objectification of the apparatus with respect to a pointer observable. In many physically relevant scenarios, however, the premeasurement interaction is constrained by an additive conservation law. That is, the interaction conserves some total quantity of the system and apparatus such as energy, charge, or angular momentum. The Wigner-Araki-Yanase (WAY) theorem states that in such a case, if either (i) the measurement is “repeatable”, i.e., repeated measurements are guaranteed to produce the same outcome, or (ii) the pointer observable commutes with the apparatus part of the conserved quantity, referred to as the “Yanase condition”, then the observable measured in the system must commute with the system part of the conserved quantity. However, provided that the apparatus is prepared in a state with sufficiently large coherence or asymmetry with respect to the conserved quantity, then approximately accurate and repeatable measurements of observables not commuting with the conserved quantity are not ruled out. In this talk, I will present several extensions of the WAY theorem for general quantum observables, represented as positive operator valued measures (POVMs), and general premeasurement interactions, represented as completely positive trace preserving maps. In particular, I will show that the strict impossibility part of the WAY theorem is more properly understood as not pertaining to sharpness of the measured observable, but rather as its “definitiveness”, i.e., the property that for some states it is possible to predict with certainty that a given outcome of measurement obtains, or does not obtain.