Nonclassicality in correlations without causal order


Kunjwal, R. (2024). Nonclassicality in correlations without causal order. Perimeter Institute. https://pirsa.org/24050066


Kunjwal, Ravi. Nonclassicality in correlations without causal order. Perimeter Institute, May. 07, 2024, https://pirsa.org/24050066


          @misc{ pirsa_PIRSA:24050066,
            doi = {10.48660/24050066},
            url = {https://pirsa.org/24050066},
            author = {Kunjwal, Ravi},
            keywords = {Quantum Foundations},
            language = {en},
            title = {Nonclassicality in correlations without causal order},
            publisher = {Perimeter Institute},
            year = {2024},
            month = {may},
            note = {PIRSA:24050066 see, \url{https://pirsa.org}}

Ravi Kunjwal Aix-Marseille University


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.


Zoom link