  The Weyl semimetals [1-6] are three-dimensional (3D) gapless topological
phases with Weyl cones in the bulk band, and host massless quasiparticles known
as Weyl fermions which were theorized by Hermann Weyl in the last twenties [7].
The lattice theory constrains that Weyl cones must come in pairs, with the
minimal number of cones being two. The semimetal with only two Weyl cones is an
ideal Weyl semimetal (IWSM) which is the optimal platform to explore broad Weyl
physics but hard to engineer in solids. Here, we report the experimental
realization of the IWSM band by synthesising for the first time a 3D spin-orbit
(SO) coupling for ultracold atoms. Engineering a 3D configuration-tunable
optical Raman lattice [8], we realize the Weyl type SO coupling for ultracold
quantum gas, with which the IWSM band is achieved with controllability. The
topological Weyl points are clearly measured via the virtual slicing imaging
technique [8, 9] in equilibrium, and further resolved in the quench dynamics,
revealing the key information of the realized IWSM bands. The realization of
the IWSM band opens an avenue to investigate various exotic phenomena based on
the optimal Weyl semimetal platforms.
