“…The large variety of atomic BECs that have been produced experimentally and the ability to engineer tailored potentials [2,3] as well as to control interactions [4] offer a plethora of research directions. A fascinating possibility is the creation of binary mixtures using different hyperfine levels ( 87 Rb [5][6][7]), different isotopes (e.g., 87 Rb -85 Rb [8], 168 Yb -174 Yb [9]), different elements (e.g., 87 Rb -41 K [10], 87 Rb -133 Cs [11,12], 87 Rb -84 Sr and 87 Rb -88 Sr [13], 87 Rb -39 K [14,15], and 87 Rb - 23 Na [16]) or even atoms with different statistics (e.g., 6 Li - 7 Li [17]). Experimentally, these mixtures have been used to explore such diverse issues as collective modes [7,17], pattern formation [18,19], phase separation [8,11,14,16], nonlinear dynamical excitations [20,21], the Kibble-Zurek mechanism [22], and the production of dipolar molecules [23].…”