Latent Nonclassicality: Implicit Information from Conditionally Prepared States

Abstract

Optical nonclassicality is not only compelling evidence of the quantum nature of the electromagnetic field but also a crucial resource for various quantum technologies. A quantum state of an optical mode is considered nonclassical if it cannot be expressed as a statistical mixture of coherent states. However, in many scenarios involving informationally incomplete measurements—such as realistic photodetection—the resulting measurement statistics can be reproduced using classical electromagnetic radiation even for nonclassical states, making nonclassicality seemingly inaccessible from measurement data [1, 2]. This suggests that, in such cases, information about nonclassicality appears to be entirely lost. In our talk, we will challenge this intuitive statement by demonstrating cases where nonclassicality remains detectable even in the mentioned scenarios [3]. Specifically, when states are conditionally prepared in one mode of light through measurements on another mode, nonclassicality can still be revealed—even when the observed measurement statistics can be reproduced by classical mixtures of coherent states. This phenomenon is captured by the concept of steering of latent nonclassicality (SLN)—a type of correlations that extends beyond quantum entanglement and quantum discord. We will discuss the relationship between SLN and other quantum correlations, such as standard quantum steering [4] and nonclassical steering [5]. Additionally, we will explore whether SLN constitutes a distinct class of genuine quantum correlations and propose potential generalizations of this approach to other quantum resources.