  Generic mesoscopic quantum systems that interact with their environment tend
to display appreciable correlations with environment that often play an
important role in the physical properties of the system. However, the
experimental methods needed to characterize such systems either ignore the role
of initial correlations or scale unfavourably with system dimensions. Here, we
present a technique that is agnostic to system-environment correlations and can
be potentially implemented experimentally. Under a specific set of constraints,
we demonstrate the ability to detect and measure specific correlations. We
apply the technique on a hybrid quantum system of Nitrogen Vacancy Centers (NV)
coupled to an optical cavity with initial correlations. We extract the
interaction strength and effective number of interacting NVs from the initial
correlations using our technique.
