Measurement and Control of Superconducting Qubits Using Single Flux Quantum Digital Logic

While remarkable progress has been made in the realization of small scale superconducting quantum circuits comprised of order 10 qubits, it is unclear how to scale existing control and readout methods to the millions of qubits required for full implementation of a surface code that can outperform the best available classical computers. In this talk, I describe the development of high-fidelity qubit control and measurement based on the superconducting Single Flux Quantum (SFQ) digital logic family. I present data on SFQ-driven Rabi oscillations of a superconducting qubit and discuss limits to SFQ-based gate fidelity. Additionally, I present a qubit measurement approach based on microwave photon counting. Qubit states are mapped to bright and dark pointer states of a linear resonator followed by subsequent photodetection. Combined, these approaches allow for qubit measurement and control at the millikelvin stage of the cryostat, without the need for microwave pulse shaping, heterodyning, or thresholding at room temperature. These experiments represent a first step toward the integration of a large-scale superconducting quantum processor with proximal logic and control, with the potential for significant reductions in latency, wiring heat load and system footprint.