  We develop a relativistic Langevin dynamics under the background of strongly
interacting quark-gluon fluid described by the (3+1)-dimensional hydrodynamics.
The drag force acting on charm and bottom quarks is parametrized according to
the formula obtained from the anti-de-Sitter space/conformal field theory
(AdS/CFT) correspondence. In this setup, we calculate the nuclear modification
factor $R_{\rm{AA}}$ for the single-electrons from the charm and bottom quarks
to extract the magnitude of the drag force from the PHENIX and STAR data. The
$R_{\rm{AA}}$ for single-electrons with $p_{T}\geq 3$ GeV indicates that the
drag force is close to the AdS/CFT prediction. Effects of the drag force on the
elliptic flow of single-electrons are also discussed. Moreover, we predict the
electron-muon correlation which is closely related to the heavy-quark pair
correlation in hot matter.
