Two-time quantities as elements of physical reality

• Published in: Physics letters. A 2024-11, Vol.525, p.129943, Article 129943
• Main Authors: Maquedano, Lucas, Ribeiro, Alexandre D., Costa, Ana C.S., Angelo, Renato M.
• Format: Article
• Language: English
• Subjects: Elements of reality; Realism; Time correlators
• ISSN: 0375-9601
• DOI: 10.1016/j.physleta.2024.129943

In recent years, time correlators have received renewed attention, especially under the guise of identifiers of nonclassical correlations. However, the physical interpretation of these objects, and more generally of multi-times variables, remains ambiguous, which may be one of the reasons why they are so difficult to measure. In this work, we introduce and advance the perspective that a two-time correlator should actually be regarded as an average involving a novel single physical observable, one that cannot be rephrased in terms of the primitive ones, according to quantum principles. In particular, we provide examples showing that the presumed constituents of a two-time correlator and the proposed two-time operator itself cannot be simultaneous elements of the physical reality. •The manuscript discusses the debated physical interpretation of time correlators and sequential measurements.•We analyze the two-point measurement protocol used in out-of-time-order correlators.•A quantum formulation for two-time operators is introduced as a single physical observable.•Two-time operators are discussed as prepared quantities, not emerging from their constituents.•Our work may advance research on testing time correlators and two-time operators.