Tri-layer Merged-element Transmon Qubit

A method of manufacturing a quantum circuit, comprising:

• providing a multilayer material stack comprising a first superconducting material, a dielectric layer, and second superconducting material on a substrate;
• forming a bottom electrode in the first superconducting material, wherein the bottom electrode comprises a contact portion and a coupling portion;
• forming a top electrode in the second superconducting material;
• forming a transmon qubit, wherein the transmon qubit comprises a vertical Josephson junction and a shunt capacitor, wherein the vertical Josephson junction comprises the contact portion of the bottom electrode, a tunnel barrier formed in the dielectric layer, and the top electrode, and wherein the shunt capacitor is formed by the top electrode and the contact portion of the bottom electrode as shunt capacitor plates;
• and
• capacitively coupling a readout circuit to the bottom electrode, wherein the coupling comprises fitting the coupling portion of the bottom electrode into a recess formed in a coupling head of the readout circuit, wherein the top electrode of the vertical Josephson junction is configured as a floating electrode.