  From an operational perspective, quantumness characterizes the exotic
behavior in a physical process which cannot be explained with Newtonian
physics. There are several widely used measures of quantumness, including
coherence, discord, and entanglement, each proven to be essential resources in
particular situations. There exists evidence of fundamental connections amongst
the three measures. However, those quantumnesses are still regarded differently
and such connections are yet to be elucidated. Here, we introduce a general
framework of defining a unified quantumness with an operational motivation
founded on the capability of interferometry. The quantumness appears
differently as coherence, discord, and entanglement in different scenarios with
local measurement, weak reference frame free measurement, and strong reference
frame free measurement, respectively. Our results also elaborate how these
three measures are related and how they can be transformed from each other.
This framework can be further extended to other scenarios and serves as a
universal quantumness measure.

Quantum Physics