A Flea on Schroedinger's Cat

TL;DR

This paper presents a mathematical reformulation of the quantum measurement problem, showing that tiny perturbations in a double-well system can cause wave function collapse, potentially resolving measurement issues within standard quantum theory.

Contribution

It introduces a new perspective on the measurement problem by linking ground state instability in double-well Hamiltonians to wave function collapse, avoiding modifications to quantum mechanics.

Findings

Tiny perturbations can cause wave function collapse in the classical limit.

Numerical simulations demonstrate adiabatic perturbations lead to collapse.

The approach combines virtues of decoherence and dynamical collapse models without their drawbacks.

Abstract

We propose a technical reformulation of the measurement problem of quantum mechanics, which is based on the postulate that the final state of a measurement is classical. Unlike the usual formulation (in which the post-measurement state is a unit vector in Hilbert space), our version actually opens the possibility of admitting a purely technical solution within the confines of conventional quantum theory (as opposed to solutions that either modify this theory, or introduce unusual and controversial interpretative rules and/or ontologies). To that effect, we recall a remarkable phenomenon in the theory of Schroedinger operators (discovered in 1981 by Jona-Lasinio et al), according to which the ground state of a symmetric double-well Hamiltonian becomes exponentially sensitive to tiny perturbations of the potential as h -> 0. We show that this instability emerges also from the textbook WKB approximation, extend it to time-dependent perturbations, and study the dynamical transition from the ground state of the double well to the perturbed ground state (in which the cat is typically either dead or alive, depending on the details of the perturbation). Numerical simulations show that adiabatically arising perturbations may (quite literally) cause the collapse of the wave-function in the classical limit. Thus, at least in the context of a simple mathematical model, we combine the technical and conceptual virtues of decoherence (which fails to solve the measurement problem but launches the key idea that perturbations may come from the environment) with those of dynamical collapse models a la GRW (which do solve the measurement problem but are ad hoc), without sharing their drawbacks: single measurement outcomes are obtained (instead of merely diagonal reduced density matrices), and no modification of quantum mechanics is needed.