Sodium Bose-Einstein Condensates in theF=2State in a Large-Volume Optical Trap

We have investigated the properties of Bose-Einstein condensates of sodium atoms in the upper hyperfine ground state. Condensates in the high-field seeking $|F=2,m_F=-2⟩$ state were created in a large volume optical trap from initially prepared $|F=1,m_F=-1⟩$ condensates using a microwave transition at 1.77 GHz. We found condensates in the stretched state $|F=2,m_F=-2⟩$ to be stable for several seconds at densities in the range of ${10}^{14}\mathrm{\text{atoms}}/{\mathrm{c}\mathrm{m}}^3$. In addition, we studied the clock transition $|F=1,m_F=0⟩\to |F=2,m_F=0⟩$ in a sodium Bose-Einstein condensate and determined a density-dependent frequency shift of $(2.44\pm 0.25\pm 0.5)\times {10}^{-12}\mathrm{H}\mathrm{z}{\mathrm{c}\mathrm{m}}^3$.