Frustrated photon emission: From path identity to Bell nonclassicality
Marcin Markiewicz

Date, Time
22.10, 15:30 - 16:00

Location
hybrid meetnig (room 16), link (MSTeams) >>>

Affiliation
International Centre for Theory of Quantum Technologies , Uniwersytet Gdański, Gdańsk, Poland
Institute of Theoretical and Applied Informatics, PAS, Gdańsk, Poland

Abstract
Frustrated parametric down-conversion provides a striking example of quantum interference between indistinguishable photon-generation processes: depending on their relative phases, pair-production amplitudes may interfere constructively or even cancel completely. Recent experiments have extended this idea to interwoven path-identity configurations and have reported Bell-type violations based on phase-controlled multiphoton interference.

In this talk, I will revisit the relation between such interference effects and Bell nonclassicality. I will show that the underlying photonic state is mode-entangled, while the correlations obtained when only the optical phases are treated as local settings admit an explicit local hidden-variable description. Thus, high-visibility multiphoton interference, by itself, does not constitute a Bell test.

I will then show how the same experimental architecture can be turned into a genuine Bell experiment by promoting the local parametric down-conversion pumps to binary on/off measurement settings. The resulting probabilities violate a Clauser–Horne inequality, with a threshold visibility, which is below the visibility already achieved experimentally. The construction naturally extends to interwoven multipartite configurations, providing a route from frustrated photon emission to multipartite Bell nonclassicality.

References:
[1]. P. Cieśliński, J.-A. Larsson, M. Markiewicz, K. Schlichtholz, M. Żukowski, Unquestionable Bell Theorem for Interwoven Frustrated Downconversion Processes, Phys. Rev. Lett. 136, 090206 (2026).
[2]. M. Żukowski, P. Cieśliński, M. Markiewicz, K. Schlichtholz,  Multipartite Bell-GHZ nonclassicality from interwoven frustrated down-conversion, arXiv:2602.18381 (2026)