Dr. Ravi Kunjwal, Universit´e libre de Bruxelles, QuIC, Brussels, Belgium and Aix-Marseille University, CNRS, LIS, Marseille, France gave an online talk on What’s nonclassical about indefinite causal order? on 14 April. Here is the summary for the talk as explained by Dr. Ravi Kunjwal:
Causal inequalities are device-independent constraints on correlations realizable via local operations under the assumption of definite causal order between these operations. While causal inequalities in the bipartite scenario require nonclassical resources within the process-matrix framework for their violation, there exist tripartite causal inequalities that admit violations with classical resources. The tripartite case puts into question the status of a causal inequality violation as a witness of non-classicality, i.e., there is no a priori reason to believe that quantum effects are in general necessary for a causal inequality violation. Here we propose antinomicity as a notion of non-classicality for correlations in the presence of indefinite causality and prove strict inclusions between correlation sets classified by their antinomicity. This article provides a causal perspective on antinomicity, complementing the device-independent perspective adopted in arXiv:2411.11397. Besides providing important background to the results reported in arXiv:2411.11397, including proofs of key technical results, we also define a weight-based measure for the antinomicity of correlations that we term the antinomy weight of a correlation. We then investigate antinomic correlations in bipartite and tripartite scenarios with binary settings and outcomes. In doing so, we discover antinomic correlations that are impossible in the process-matrix framework.
Dr. Ravi Kunjwal is a tenure-track lecturer-researcher at Aix-Marseille Université (AMU), Marseille, France. He was an FNRS postdoctoral researcher at the Centre for Quantum Information and Communication (QuIC) of the Université libre de Bruxelles (ULB), Brussels, Belgium. Prior to this, he was a postdoctoral researcher at the Perimeter Institute for Theoretical Physics, Waterloo, Canada. He did his PhD in theoretical physics at the Institute of Mathematical Sciences, Chennai, India.
April 2025