  The colour fields created by the static tetraquark system are computed in
quenched SU(3) lattice QCD, in a 24^3 x 48 lattice at beta=6.2 corresponding to
a lattice spacing a=0.07261(85) fm. We find that the tetraquark colour fields
are well described by a double-Y, or butterfly, shaped flux tube. The two flux
tube junction points are compatible with Fermat points minimizing the total
flux tube length. We also compare the diquark-diantiquark central flux tube
profile in the tetraquark with the quark-antiquark fundamental flux tube
profile in the meson, and they match, thus showing that the tetraquark flux
tubes are composed of fundamental flux tubes.
