A measure of physical reality

Abstract

From the premise that an observable is real after it is measured, we envisage a tomography-based protocol that allows us to propose a quantifier for the degree of indefiniteness of an observable given a quantum state. Then, we find that the reality of an observable can be inferred locally only if this observable is not quantumly correlated with an informer. In other words, quantum discord precludes Einstein's notion of separable realities. Also, by monitoring changes in the local reality upon measurements on a remote system, we are led to define a measure of nonlocality. Proved upper bounded by discordlike correlations and requiring indefiniteness as a basic ingredient, our measure signals nonlocality even for separable states, thus revealing nonlocal aspects that are not captured by Bell inequality violations.

Quantifying continuous-variable realism

“…This shows that the irreality increases with the width of the superposition, in this case also being a direct measure of quantum coherence [45]. For our second example, we return to the Gaussian state, (20).…”

“…In fact, as shown in Ref. [45], irreality can be written in the form I(A|ρ) = I(A|ρ A ) + D A (ρ). The first parcel,…”

“…Recently, Bilobran and Angelo put forward a proposal for quantifying elements of reality of discrete-spectrum observables [45]. Here we present a brief review of the BA approach since it is the main platform for the present work.…”

“…With that, different shades of reality were attached to physical realism. A few years ago, Bilobran and Angelo (BA) introduced a measurementbased criterion of reality which allowed for the quantification of the degree of reality of a discrete-spectrum observable for a given multipartite quantum state [45]. This approach led to further foundational developments, as, for instance, the definition of the realism-based nonlocality [46,47], which captures nonlocal aspects that are dramatically different from Bell nonlocality, and the derivation of an information-reality complementarity relation [48], which is shown to apply even to scenarios of weak disturbances.…”

Hardy’s Paradox as a Demonstration of Quantum Irrealism

“…Even though only local interactions are assumed throughout the experiment-which explains the check-marks for local causality in Table (1)(b)realism-based non-locality does manifest itself at stages 3 and 4. Within the operational scheme devised by Bilobran and Angelo [37], this means that changes in the positron path-irreality due to unrevealed measurements performed on the electron can be experimentally detected. For the Hardy experiment, the conceptual picture can be as follows.…”