\begin{array}{c} \Qcircuit@C=1em @R=.7em{
& \gate{D_{1, 1}~\mbox{on}~U_{1, 1}} \qwx[1] & \gate{D_{2, 1}~\mbox{on}~U_{2, 1}} \qwx[1] & \gate{\cdots} \qwx[1] & \gate{D_{n, 1}~\mbox{on}~U_{n, 1}} \qwx[1] & \qw \\
& \gate{D_{1, 2}~\mbox{on}~U_{1, 2}} \qwx[1] & \gate{D_{2, 2}~\mbox{on}~U_{2, 2}} \qwx[1] & \gate{\cdots} \qwx[1] & \gate{D_{n, 2}~\mbox{on}~U_{n, 2}} \qwx[1] & \qw \\
& \gate{\vdots} \qwx[1] & \gate{\vdots} \qwx[1] & \gate{\ddots} \qwx[1] & \gate{\vdots} \qwx[1] & \qw \\
& \gate{D_{1, k}~\mbox{on}~U_{1, k}} & \gate{D_{2, k}~\mbox{on}~U_{2, k}} & \gate{\cdots} & \gate{D_{n, k}~\mbox{on}~U_{n, k}} & \qw
} \end{array}