Cryogenic on-chip digital readout of a superconducting qubit
ORAL
Abstract
Current experimental approaches to superconducting qubit readout rely on microwave components distributed between room and cryogenic temperatures, imposing significant technological and economic challenges to scalability. In this work, we demonstrate high-fidelity on-chip digital readout of superconducting qubits using the Josephson Digital Phase Detector (JDPD) [1]. The JDPD’s potential energy landscape exhibits a distinctive transition from a single-well to a double-well configuration when the system is properly flux-excited. This property enables direct digitization, at the millikelvin stage, of the phase sign of a coherent GHz-frequency input tone that encodes the qubit state information. This innovative technology promises a key step toward scalable quantum computing architectures, where qubit readout and control [2] can be fully integrated within the cryogenic environment.
The JDPD readout architecture can be implemented in both flip-chip [2] and split-chip configurations, where the JDPD chip and the Quantum Processing Unit (QPU) are placed in close proximity and interconnected via PCB wires. This approach enables seamless integration of the JDPD with any QPU without design modifications. Moreover, the same implementation supports on-chip multiplexed qubit readout, allowing multiple qubits to be measured in parallel with minimal additional hardware overhead. The split-chip configuration has been experimentally tested with a commercial QPU, achieving single-qubit readout fidelities exceeding 99% with a fast detection speed, primarily limited by the ring-up time of the qubit resonators.
[1] Di Palma L., et al. "Discriminating the Phase of a Coherent Tone with a Flux-Switchable Superconducting Circuit." Phys. Rev. Appl., vol. 19, no. 6, 7 June 2023, p. 064025, doi:10.1103/PhysRevApplied.19.064025.
[2] Bernhardt J., et al. "Quantum Computer Controlled by Superconducting Digital Electronics at Millikelvin Temperature", doi:10.48550/arXiv.2503.09879.
The JDPD readout architecture can be implemented in both flip-chip [2] and split-chip configurations, where the JDPD chip and the Quantum Processing Unit (QPU) are placed in close proximity and interconnected via PCB wires. This approach enables seamless integration of the JDPD with any QPU without design modifications. Moreover, the same implementation supports on-chip multiplexed qubit readout, allowing multiple qubits to be measured in parallel with minimal additional hardware overhead. The split-chip configuration has been experimentally tested with a commercial QPU, achieving single-qubit readout fidelities exceeding 99% with a fast detection speed, primarily limited by the ring-up time of the qubit resonators.
[1] Di Palma L., et al. "Discriminating the Phase of a Coherent Tone with a Flux-Switchable Superconducting Circuit." Phys. Rev. Appl., vol. 19, no. 6, 7 June 2023, p. 064025, doi:10.1103/PhysRevApplied.19.064025.
[2] Bernhardt J., et al. "Quantum Computer Controlled by Superconducting Digital Electronics at Millikelvin Temperature", doi:10.48550/arXiv.2503.09879.
–
Presenters
-
Luigi Di Palma
- Seeqc, Inc.