Bose-Einstein Condensation of Lithium: Observation of Limited Condensate Number

Bose-Einstein condensation of ${}^7\mathrm{Li}$ has been studied in a magnetically trapped gas. Because of the effectively attractive interactions between ${}^7\mathrm{Li}$ atoms, many-body quantum theory predicts that the occupation number of the condensate is limited to about 1400 atoms. We observe the condensate number to be limited to a maximum value between 650 and 1300 atoms. The measurements were made using a versatile phase-contrast imaging technique.