Wigner Friend scenarios with non-invasive weak measurements

Abstract

Wigner Friend scenarios -in which an external agent describes quantum mechanically a laboratory in which a Friend is making a measurement -give rise to possible inconsistencies due to the ambiguous character of quantum measurements. In this work, we investigate Wigner Friend scenarios in which the external agents can probe in a non-invasive manner the dynamics inside the laboratories. We examine probes that can be very weakly coupled to the systems measured by the Friends, or to the pointers or environments inside the laboratories. These couplings, known as Weak Measurements, are asymptotically small and do not change the outcomes obtained by the Friends nor their probabilities. Within our scheme, we show that the weakly coupled probes indicate to the external agents how to obtain consistent predictions, irrespective of the possible inconsistencies of quantum measurement theory. These non-invasive couplings could be implemented with present-day technologies.

Quantum measurements with, and yet without an Observer

“…In the context of the previous Section, it is only natural to wonder how an act of perceiving an outcome could succeed in replacing a unitary evolution ( 7) by a non-unitary one in Eq. (11). With Observer's consciousness now drawn into the discussion, there are at least two possibilities.…”

“…Recently there was a renewed interest in in whether quantum theory is internally consistent in its present form, or if new assumptions need to be added to its already well established principles. The discussion initiated by the authors of [1] was quickly joined, and various opinions were expressed [2]- [11]. An analysis often centres on two issues, the "collapse" of the quantum state, and the role and place of a conscious Observer.…”

“…( 7), Eqs. ( 9)- (11) may present a conceptual problem. A wave function seen as a substance in continuous flow (7), decimated each time a conscious Observer makes an enquiry and perceives an outcome, presents a rather bizarre picture.…”

“…( 9) -Eqs. (11) as their consequences [19], which can be derived and used, e.g., for computational convenience.…”