CANA Seminar - 04_06_2024.mp4 [4 juin 2024]

 Description

Presentation of Ravi Kunjwal (LIS) during the CANA seminar.

Title : Nonclassicality in correlations without causal order

Abstract :
A Bell scenario can be conceptualized as a "communication" scenario
with zero rounds of communication between parties, i.e., although
each party can receive a system from its environment on which it can
implement a measurement, it cannot send out any system to another
party. Under this constraint, there is a strict hierarchy of
correlation sets, namely, classical, quantum, and non-signalling.
However, without any constraints on the number of  communication
rounds between the parties, they can realize arbitrary correlations
by exchanging only classical systems. We consider a multipartite
scenario where the parties can engage in at most a single round of
communication, i.e., each party is allowed to receive a system once,
implement any local intervention on it, and  send out the resulting
system once. Taking our cue from Bell nonlocality in the "zero
rounds" scenario, we propose a notion of nonclassicality---termed
antinomicity---for correlations in scenarios with a single round of
communication. Similar to the zero rounds case, we establish a
strict hierarchy of correlation sets classified by their
antinomicity in single-round communication scenarios. Since we do
not assume a global causal order between the parties, antinomicity
serves as a notion of nonclassicality in the presence of indefinite
causal order (as witnessed by causal inequality violations). A key
contribution of this work is an explicit antinomicity witness that
goes beyond causal inequalities, inspired by a modification of the
Guess Your Neighbour's Input (GYNI) game that we term the Guess Your
Neighbour's Input or NOT (GYNIN) game. Time permitting, I will
speculate on why antinomicity is a strong notion of nonclassicality
by interpreting it as an example of fine-tuning in classical models
of indefinite causality.

This is based on joint work with Ognyan Oreshkov, arXiv:2307.02565.