  Multi-electron semiconductor quantum dots have found wide application in
qubits, where they enable readout and enhance polarizability. However, coherent
control in such dots has typically been restricted to only the lowest two
levels, and such control in the strongly interacting regime has not been
realized. Here we report quantum control of eight different resonances in a
silicon-based quantum dot. We use qubit readout to perform spectroscopy,
revealing a dense set of energy levels with characteristic spacing far smaller
than the single-particle energy. By comparing with full configuration
interaction calculations, we argue that the dense set of levels arises from
Wigner-molecule physics.
