State updates and useful qubits in relativistic quantum information

TL;DR

This paper introduces a covariant formalism for updating quantum states in relativistic settings, resolving causality issues and preserving correlations during measurements.

Contribution

It presents the 'polyperspective' formalism, a minimal extension of multipartite states that ensures causally consistent and covariant state updates in relativistic quantum information.

Findings

Ensures causally consistent state updates in relativistic quantum scenarios

Preserves multipartite correlations during state updates

Respects conservation laws in relativistic quantum information

Abstract

We address the longstanding challenge of consistently updating quantum states after selective measurements in a relativistic spacetime. Standard updates along the future lightcones preserve causality but break correlations between causally disconnected parties, whereas updates along the past lightcone either imply retrocausality or do not respect the causal propagation of information. We introduce a minimal extension of multipartite states to encode subsystem-specific contextual information. This "polyperspective" formalism ensures causally consistent covariant state updates, preserves multipartite correlations, and respects conservation laws.