Microwave integrated quantum circuits with cap wafer and methods for making the same

A method of fabricating a quantum processor cell in a quantum processing unit, the quantum processor cell comprising a plurality of stacked circuit wafers, the method comprising:

• forming first quantum circuitry on a surface of a first circuit wafer, the first quantum circuitry comprising a plurality of qubit devices;
• forming second quantum circuitry on a surface of a second circuit wafer, the second quantum circuitry comprising a plurality of filters;
• forming a plurality of recesses, a plurality of standoff bumps, and an electrically conducting layer that conforms to the plurality of recesses and the plurality of standoff bumps on a third circuit wafer;
• and
• forming a stack of circuit wafers comprising the first circuit wafer, the second circuit wafer, the third circuit wafer, and routing circuitry, wherein the routing circuitry couples the first quantum circuitry on the first circuit wafer with the second quantum circuitry on the second circuit wafer.