  Fast operations, an easily tunable Hamiltonian, and a straightforward
two-qubit interaction make charge qubits a useful tool for benchmarking device
performance and exploring two-qubit dynamics. Here, we tune a linear chain of
four Si/SiGe quantum dots to host two double dot charge qubits. Using the
capacitance between the double dots to mediate a strong two-qubit interaction,
we simultaneously drive coherent transitions to generate correlations between
the qubits. We then sequentially pulse the qubits to drive one qubit
conditionally on the state of the other. We find that a conditional
$\pi$-rotation can be driven in just 74 ps with a modest fidelity demonstrating
the possibility of two-qubit operations with a 13.5 GHz clockspeed.
