Measurements of the spin relaxation rate at low magnetic fields in a quantum dot

We measure the relaxation rate $W\equiv T_1^{-1}$ of a single electron spin in a quantum dot at magnetic fields from 7 T down to 1.75 T, much lower than previously measured. At 1.75 T we find that $T_1$ is 170 ms. We find good agreement between our measurements and theoretical predictions of the relaxation rate caused by the spin-orbit interaction, demonstrating that spin-orbit coupling can account for spin relaxation in quantum dots.