Timelike correlations and quantum tensor product structure

TL;DR

This paper explores alternative quantum state space structures and demonstrates that they can produce correlations beyond standard quantum limits in timelike scenarios, impacting quantum communication and foundational principles.

Contribution

It introduces and analyzes non-standard composite quantum models, showing they can generate beyond quantum correlations in timelike scenarios and affect communication capacities.

Findings

Beyond quantum correlations can arise in timelike scenarios.

Classical information capacity is bounded by quantum limits.

Different composite models lead to distinct communication utilities.

Abstract

The state space structure for a composite quantum system is postulated among several mathematically consistent possibilities that are compatible with local quantum description. For instance, unentangled Gleason's theorem allows a state space that includes density operators as a proper subset among all possible composite states. However, bipartite correlations obtained in Bell type experiments from this broader state space are in-fact quantum simulable, and hence such spacelike correlations are no good to make distinction among different compositions. In this work we analyze communication utilities of these different composite models and show that they can lead to distinct utilities in a simple communication game involving two players. Our analysis, thus, establishes that beyond quantum composite structure can lead to beyond quantum correlations in timelike scenario and hence welcomes new principles to isolate the quantum correlations from the beyond quantum ones. We also prove a no-go that the classical information carrying capacity of different such compositions cannot be more than the corresponding quantum composite systems.