# Quantifying continuous-variable realism

## TL;DR

This paper introduces a quantitative measure for the degree of reality of continuous variables like position and momentum in quantum mechanics, revealing how quantum effects prevent classical realism for conjugate pairs.

## Contribution

It develops an operational criterion and a quantifier for the irreality of discretized continuous variables, linking it to an uncertainty relation and applying it to dissipative quantum dynamics.

## Key findings

- The irreality measure obeys an uncertainty relation for conjugate variables.
- Quantum mechanics prevents classical realism for position and momentum.
- Application to dissipative dynamics shows emergence of elements of reality at equilibrium.

## Abstract

The debate instigated by the seminal works of Einstein, Podolsky, Rosen, and Bell, put the notions of realism and nonlocality at the core of almost all philosophical and physical discussions underlying the foundations of quantum mechanics. However, while experimental criteria and quantifiers are by now well established for nonlocality, there is no clear quantitative measure for the degree of reality associated with continuous variables such as position and momentum. This work aims at filling this gap. Considering position and momentum as effectively discrete observables, we implement an operational notion of projective measurement and, from that, a criterion of reality for theses quantities. Then, we introduce a quantifier for the degree of irreality of a discretized continuous variable which, when applied to the conjugated pair position-momentum, is shown to obey an uncertainty relation, this meaning that quantum mechanics prevents classical realism for conjugated quantities. As an application of our formalism, we study the emergence of elements of reality in an instance where a Gaussian state is submitted to the dissipative dynamics implied by the Caldirola-Kanai Hamiltonian. In particular, at the equilibrium, we make some links with the measurement problem and identify aspects that can be taken as the quantum counterpart for the notion of rest.