Fig. 2: Formation of second-band condensates.

a, The experimental sequence used to populate the second band. Initially, atoms are loaded into the s orbitals of the deep B wells (left). Subsequently, the relative potential offset of A and B wells is rapidly tuned until the local s orbitals in shallow B wells are centred between the s and the p orbitals in the deep A wells (right). For this setting, the s orbitals in the shallow B wells are predominantly populated and form the second band. b, Exact band calculation of the momentum distribution for the Bloch function \({\Phi }_{{{\rm{K}}}_{\Delta }}\). h, Planck’s constant. c, Momentum spectra at various holding times. The top and bottom rows correspond to second-band condensates with dominant condensate fractions at K_Δ and K_∇, respectively. The middle row shows condensates with nearly equal condensate fractions at K_Δ and K_∇.