If Quantum Measurements Are Secretly Continuous Nonunitary Processes, Weak Measurements Can Detect It

TL;DR

This paper explores whether quantum measurements are actually continuous nonunitary processes and proposes that weak measurements can distinguish this from traditional instantaneous collapse, with an experimental protocol demonstrated on a hydrogen atom.

Contribution

It introduces a method using weak postselected measurements to differentiate between instantaneous collapse and continuous nonunitary evolution in quantum measurements.

Findings

Weak measurements can detect the difference between collapse types.

An experimental protocol for identifying measurement nature is proposed.

Analysis of a hydrogen atom illustrates the method's application.

Abstract

The standard approach to quantum measurements is to assume that they lead to effectively instantaneous collapse of the quantum state. However, if we assume that we are unable to enforce at what exact moment of time the measurement occurs due to a finite resolution of any time measurement device, at the level of the ensemble, the measurement would lead to an effectively nonunitary evolution involving a mixed state. Each individual ensemble member would face an instantaneous collapse at different moments of time. This process is completely indistinguishable from fundamental nonunitary evolution at the level of each individual ensemble member, within the framework of strong projective measurements. In this paper, we show that weak postselected measurements can distinguish these two types of evolution. An experimental protocol for determining the nature of quantum collapse is described, and the example of a hydrogen atom is analyzed in detail.