  The spin-flip tunneling rates are measured in GaAs-based double quantum dots
by time-resolved charge detection. Such processes occur in the Pauli spin
blockade regime with two electrons occupying the double quantum dot. Ways are
presented for tuning the spin-flip tunneling rate, which on the one hand gives
access to measuring the Rashba and Dresselhaus spin--orbit coefficents. On the
other hand they make it possible to turn on and off the effect of SOI with a
high on/off-ratio. The tuning is accomplished by choosing the alignment of the
tunneling direction with respect to the crystallographic axes, as well as by
choosing the orientation of the external magnetic field with respect to the
spin--orbit magnetic field. Spin-lifetimes of 10 s are achieved at a tunnel
rate close to 1 kHz.
