  A practical quantum computer requires quantum bit (qubit) operations with low
error rates in extensible architectures. We study a packaging method that makes
it possible to address hundreds of superconducting qubits by means of
three-dimensional wires: The large-scale quantum socket. A qubit chip is housed
in a superconducting box, where both box and chip dimensions lead to unwanted
modes that can interfere with qubit operations. We theoretically analyze these
interference effects in the context of qubit coherent leakage. We propose two
methods to mitigate the resulting errors by detuning the resonance frequency of
the modes from the qubit frequency. We perform detailed electromagnetic field
simulations indicating that the resonance frequency of the modes increases with
the number of installed three-dimensional wires and can be engineered to be
significantly higher than the highest qubit frequency. Finally, we show
preliminary experimental results towards the implementation of a large-scale
quantum socket.
