  Correlation has been widely used to facilitate various information retrieval
methods such as query expansion, relevance feedback, document clustering, and
multi-modal fusion. Especially, correlation and independence are important
issues when fusing different modalities that influence a multi-modal
information retrieval process. The basic idea of correlation is that an
observable can help predict or enhance another observable. In quantum
mechanics, quantum correlation, called entanglement, is a sort of correlation
between the observables measured in atomic-size particles when these particles
are not necessarily collected in ensembles. In this paper, we examine a
multimodal fusion scenario that might be similar to that encountered in physics
by firstly measuring two observables (i.e., text-based relevance and
image-based relevance) of a multi-modal document without counting on an
ensemble of multi-modal documents already labeled in terms of these two
variables. Then, we investigate the existence of non-classical correlations
between pairs of multi-modal documents. Despite there are some basic
differences between entanglement and classical correlation encountered in the
macroscopic world, we investigate the existence of this kind of non-classical
correlation through the Bell inequality violation. Here, we experimentally test
several novel association methods in a small-scale experiment. However, in the
current experiment we did not find any violation of the Bell inequality.
Finally, we present a series of interesting discussions, which may provide
theoretical and empirical insights and inspirations for future development of
this direction.
