Using Software Defined Radios for Qubit Control and Readout

Software Defined Radios (SDR) generating VHF, UHF, and microwave signals can be used to calibrate and operate superconducting qubits with some caveats. The premise of SDR is that a high-power computer, such as an Intel-based server, computes signals to be transmitted by the SDR and processes signals received from the SDR. This usage model treats the SDR as a non-intelligent peripheral that is only capable of forwarding raw signals from a host PC to a signal generator and from a downmixer/digitizer to a host PC. This usage model requires high-bandwidth Ethernet activity, particularly when operating multiple qubits, and limits the repetition rate of qubit operations and measurements. Incorporating custom HDL into the SDR, making it more like a piece of custom measurement equipment, increases the achievable repetition rate and substantially increases communications and system reliability. This paper describes practical details of using SDRs to operate a quantum computer. This paper describes Rigetti Computing's approach and experiences using National Instruments Universal Software Radio Peripherals (USRP) to reduce the cost of implementing multi-qubit control systems.