  The transport of quantum information between different nodes of a quantum
device is among the challenging functionalities of a quantum processor. In the
context of spin qubits, this requirement can be met by coherent electron spin
shuttling between semiconductor quantum dots. Here we theoretically study a
minimal version of spin shuttling between two quantum dots. To this end, we
analyze the dynamics of an electron during a detuning sweep in a silicon double
quantum dot (DQD) occupied by one electron. Possibilities and limitations of
spin transport are investigated. Spin-orbit interaction and the Zeeman effect
in an inhomogeneous magnetic field play an important role for spin shuttling
and are included in our model. Interactions that couple the position, spin and
valley degrees of freedom open a number of avoided crossings in the spectrum
allowing for diabatic transitions and interfering paths. The outcomes of single
and repeated spin shuttling protocols are explored by means of numerical
simulations and an approximate analytical model based on the solution of the
Landau--Zener problem. We find that a spin infidelity as low as $1-F_s\lesssim
0.002$ with a relatively fast level velocity of $\alpha = 600\, {\mu}$eV/ns is
feasible for optimal choices of parameters or by making use of constructive
interference.
