QDev Seminar: Maja Cassidy

On-chip Microwave Generation with a Josephson Laser

Coherent microwave radiation has applications in technologies ranging from quantum sensing to quantum information processing and astronomical observation. For example, microwave signals are employed for measuring and controlling superconducting and semiconducting qubits, as well as to detect the motion of nanomechanical resonators and to read out the spin information in nitrogen-vacancy centers in diamonds. Scaling up from single devices to commercially viable technologies will require a massive increase in the number of individual circuit elements. However routing a large number of microwave signals from room temperature places an unacceptable thermal burden on the cryogenic environment. Microwave generation at cryogenic temperatures is therefore essential for this scale-up to occur.

Here we demonstrate strong microwave lasing from a DC biased Josephson junction strongly coupled to a superconducting microwave cavity. The emission is powered by application of a small DC voltage across the Josephson junction, with the emission frequency tunable by the cavity frequency. Unlike emitters based on single charge tunneling events in semiconductors, such as the quantum cascade laser or quantum dot-cavity coupled systems, emission is stabilized by the coherence of the Cooper-pairs in the superconducting condensate, and so the device is unaffected by environmental charge noise. The device can be injection locked over a range of exceeding 100 MHz at 5.6 GHz, with an injection locked linewidth df/f ~ 10-9. The simple fabrication allows for easy integration into a spin based or superconducting quantum computing architecture, allowing for efficient generation of coherent microwave photons at mK temperatures.