» IQS Seminar Series

Weak Measurements Reconcile Incompatible Observables by Jonathan Monroe

Monday, 18 October, 2021 @ 12PM in 370 Keck Center

or on Zoom

AbstractTraditional uncertainty relations dictate a minimal amount of noise in incompatible projective quantum measurements. The noise is often thought to come from the measurements' failure to commute. However, not all measurements are projective. In particular, weak measurements are minimally invasive tools for obtaining partial state information without projection. 

In this talk, I'll describe an experiment in which such measurements can reconcile two incompatible (non-commuting) strong measurements. The weak measurements' slight back action on the state accounts for a majority of the reconciliation. The measurements obey an entropic uncertainty relation based on generalized measurement operators. In this relation a weak value appears, lowering the uncertainty bound.

Energy measurements with quantum clocks and non-inertial clock frames by Ismael De Paiva

Monday, 11 October, 2021 @ 12PM in 370 Keck Center

or on Zoom

Abstract: Uncertainty relations play a crucial role in quantum mechanics. Well-defined methods exist for the derivation of such uncertainties for pairs of observables. Specific methods also lead to time-energy uncertainty relations. However, in these cases, different approaches are associated with different meanings and interpretations. In this talk, the time-energy uncertainty relation of interest revolves around the idea of whether quantum mechanics inherently imposes a fundamental minimum duration for energy measurements with a certain precision. Within the Page and Wootters timeless framework, it will be discussed how energy measurements modify the relative ``flow of time'' between internal and external clocks. This provides a unified framework for discussing the subject, allowing the recovery of previous results and derivation of new ones. In particular, it will be shown that the duration of an energy measurement carried out by an external system cannot be performed arbitrarily fast from the perspective of the internal clock. Moreover, it will be demonstrated that the evolution given by the internal clock during any energy measurement is non-unitary. Finally, if time allows, new developments associating non-unitarity to non-inertial clocks will be presented.