Violation of smooth observable macroscopic realism in a harmonic oscillator

TL;DR

This paper investigates how macrorealism can be violated in a harmonic oscillator through consecutive measurements, especially under extreme squeezing, and proposes an experimental test using entangled photons.

Contribution

It demonstrates the violation of macrorealism in a harmonic oscillator with smooth observables and proposes an experimental test involving entangled photons.

Findings

Macrorealism is violated in a wide parameter range, maximized at extreme squeezing.

Violations occur even with measurements of classically smooth observables.

An experimental test with entangled photons is proposed to demonstrate the violation.

Abstract

We study the emergence of macrorealism in a harmonic oscillator subject to consecutive measurements of a squeezed action. Since the harmonic oscillator dynamics admits a hidden trajectory formulation, the assumptions of macrorealism are violated only by the measurement process. We demonstrate a breakdown of macrorealism in a wide parameter range that is maximized in a scaling limit of extreme squeezing. A semiclassical analysis shows that macrorealism is violated even with measurements of classically smooth observables that do not resolve quantum levels. We propose an experimental test of macrorealism with entangled photons by demonstrating that local realism in a composite system implies macrorealism in a subsystem.