  Semiconductor spin qubits have gained increasing attention as a possible
platform to host a fault-tolerant quantum computer. First demonstrations of
spin qubit arrays have been shown in a wide variety of semiconductor materials.
The highest performance for spin qubit logic has been realized in silicon, but
scaling silicon quantum dot arrays in two dimensions has proven to be
challenging. By taking advantage of high-quality heterostructures and carefully
designed gate patterns, we are able to form a tunnel coupled 2 $\times$ 2
quantum dot array in a $^{28}$Si/SiGe heterostructure. We are able to load a
single electron in all four quantum dots, thus reaching the (1,1,1,1) charge
state. Furthermore we characterise and control the tunnel coupling between all
pairs of dots by measuring polarisation lines over a wide range of barrier gate
voltages. Tunnel couplings can be tuned from about $30~\rm \mu eV$ up to
approximately $400~\rm \mu eV$. These experiments provide a first step toward
the operation of spin qubits in $^{28}$Si/SiGe quantum dots in two dimensions.
