Fabrication of Radio-Frequency Quantum Upconverters with Double-Angle Aluminum Junctions

Many Circuit Quantum Electrodynamics techniques exist for manipulating and engineering quantum states of microwave photons above 1 GHz. The development of these techniques have led to increasingly sensitive probes of fundamental physics. Unlike microwave frequencies, quantum electromagnetic measurements below 300 MHz have not been well developed.

We describe the fabrication of the radio-frequency quantum upconverter (RQU), a superconducting device that uses the flux-sensitive inductance of a three-junction interferometer to couple low-frequency electromagnetic signals (5 kHz - 30 MHz) into sidebands on high frequency carrier waves (4-6 GHz). RQUs can utilize a variety of quantum protocols to reduce noise below the Standard Quantum Limit in the 5 kHz-30 MHz range and achieve quantum-enhanced sensitivity. This talk will cover the physics and design of RQUs, and focus on the fabrication of RQUs using a double-angle aluminum deposition method, with nominal junction overlap regions of 0.5-5 μm² and critical currents of 0.5-5 μA.