  We introduce a family of entanglement witnesses for continuous variable
systems, which rely on the sole assumption that their dynamics is that of
coupled harmonic oscillators at the time of the test. Entanglement is inferred
from the Tsirelson nonclassicality test on one of the normal modes, without any
knowledge about the state of the other mode. In each round, the protocol
requires measuring only the sign of one coordinate (e.g., position) at one
among several times. This dynamic-based entanglement witness is more akin to a
Bell inequality than to an uncertainty relation: in particular, it does not
admit false positives from classical theory. Our criterion detects non-Gaussian
states, some of which are missed by other criteria.
