Probing Long-Time Spin Dynamics in a Rb Bose-Einstein Condensate


In this thesis we study long-time spin dynamics in the F = 1 hyperfine manifold of a 87Rb Bose-Einstein condensate (BEC). The magnetic sub-levels constitute a spin-1 system with ferromagnetic interactions. We initialize the system out of equilibrium and monitor the subsequent evolution employing a new readout scheme. Thereby we simultaneously measure two orthogonal spin directions and extract the transverse magnetization, which captures coherences between the individual sub-levels. The energy scale of the spin dependent interactions introduces a timescale around 500 ms. At comparable evolution times, we observe coherent oscillations compatible with the corresponding mean field predictions. Furthermore, we investigate the dynamics for long evolution times up to 15 s. In particular, we examine the impact of controlled heating of the condensate density. For settings with minimal heating, a significant transverse spin survives and the associated fluctuations are captured by Truncated Wigner simulations. In this case, the system retains long-term coherence and is mainly affected by dephasing of the internal dynamics. In contrast, for larger heating the transverse spin significantly decays and the late-time fluctuations are smaller. This indicates a distinct longterm evolution influenced by decoherence and a dissipative relaxation due to finite temperature effects.