  The rotational motion of solar jets is believed to be a signature of the
untwisting process resulting from magnetic reconnection, which takes place
between twisted closed magnetic loops (i.e., magnetic flux ropes) and open
magnetic field lines. The identification of the pre-existing flux rope, and the
relationship between the twist contained in the rope and the number of turns
the jet experiences, are then vital in understanding the jet-triggering
mechanism. In this paper, we will perform a detailed analysis of imaging,
spectral and magnetic field observations of four homologous jets, among which
the fourth one releases a twist angle of 2.6$\pi$. Non-linear force free field
extrapolation of the photospheric vector magnetic field before the jet eruption
presents a magnetic configuration with a null point between twisted and open
fields - a configuration highly in favor of the eruption of solar jets. The
fact that the jet rotates in the opposite sense of handness to the twist
contained in the pre-eruption photospheric magnetic field, confirms the
unwinding of the twist by the jet's rotational motion. Temporal relationship
between jets' occurrence and the total negative flux at their source region,
together with the enhanced magnetic submergence term of the photospheric
Poynting flux, shows that these jets are highly associated with local magnetic
flux cancellation.
