Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multichip Module

C. H. Liu, A. Ballard, D. Olaya, D. R. Schmidt, J. Biesecker, T. Lucas, J. Ullom, S. Patel, O. Rafferty, A. Opremcak, K. Dodge, V. Iaia, T. McBroom, J. L. Dubois, P. F. Hopkins, S. P. Benz, B. L.T. Plourde, R. McDermott

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Single flux quantum (SFQ) digital logic has been proposed for the scalable control of next-generation superconducting-qubit arrays. In the initial implementation, SFQ-based gate fidelity was limited by quasiparticle (QP) poisoning induced by the dissipative on-chip SFQ driver circuit. In this work, we introduce a multichip-module architecture to suppress phonon-mediated QP poisoning. Here, the SFQ elements and qubits are fabricated on separate chips that are joined with In-bump bonds. We use interleaved randomized benchmarking to characterize the fidelity of SFQ-based gates and we demonstrate an error per Clifford gate of 1.2(1)%, an order-of-magnitude reduction over the gate error achieved in the initial realization of SFQ-based qubit control. We use purity benchmarking to quantify the contribution of incoherent error at 0.96(2)%; we attribute this error to photon-mediated QP poisoning mediated by the resonant millimeter-wave antenna modes of the qubit and SFQ-qubit coupler. We anticipate that a straightforward redesign of the SFQ driver circuit to limit the bandwidth of the SFQ pulses will eliminate this source of infidelity, allowing SFQ-based gates with error approaching approximate known theoretical limits, of order 0.1% for resonant sequences and 0.01% for more complex pulse sequences involving variable pulse-to-pulse separation.

Original languageEnglish (US)
Article number030310
JournalPRX Quantum
Issue number3
StatePublished - Jul 2023

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • General Computer Science
  • Mathematical Physics
  • General Physics and Astronomy
  • Applied Mathematics
  • Electrical and Electronic Engineering


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