Distributed Processor for FPGA-based Superconducting Qubit Control Using QubiC

Implementing quantum circuits utilizing mid-circuit measurement and fast feedback requires flexible, low-latency classical control. To this end, we have developed a custom FPGA-based processor for QubiC, an open source platform for superconducting qubit control. The processor is distributed in nature, with one core per arbitrary waveform generator (AWG); simplifying the design and allowing for straightforward scaling. Each processor core implements an instruction set consisting of timed pulse commands as well as simple arithmetic and branching instructions. Our design also includes interfaces for synchronizing different cores and requesting/receiving (optionally processed) measurement results. Together, these features allow a user to program arbitrary control flow within a quantum circuit based on previous measurement results. In this presentation, we will detail our design, describe its integration with the QubiC control stack, and demonstrate the processor's capabilities with a simple mid-circuit measurement and feedback experiment using transmon qubits at the LBL AQT (advanced quantum testbed).