Superconducting Qubit Signal Delivery
Integrated Qubit X/Y Controllers using Single Flux Quantum Digital Logic
1:30 pm – 1:42 pmCurrent superconducting quantum computers rely on a brute-force scaling approach where quantum chips operating at the millikelvin stage inside dilution refrigerators are connected to room-temperature electronics via an ever-increasing number of refrigerated signal wires. This scheme is quickly limited by the cryostat's heat load capacity. In order to drastically scale up such systems without facing refrigeration challenges, qubit control electronics need to be co-located with quantum circuit elements at the mK stage. Superconducting Energy-efficient Rapid Single Flux Quantum logic (ERSFQ) [1] is a promising technology for the implementation of such a cryogenic control electronics. We present X/Y control of a transmon qubit from an ERSFQ circuit which sends a SFQ pulse train through a transmission line (TL) that is capacitively coupled to the qubit. This circuit produces single qubit gates with an average Clifford fidelity of 99.6%, the highest number reported to date using this approach. Previous demonstrations of qubit control by SFQ pulse trains show gate fidelity coherence limit reductions due to quasiparticle (QP) generation from the SFQ circuitry [2, 3]. We discuss the sources of the remaining gate error in our implementation, including results from QP poisoning experiments which show that our fidelities are not limited by QP poisoning.
[1] D. E. Kirichenko et al., Zero Static Power Dissipation Biasing of RSFQ Circuits, IEEE Transactions on Applied Superconductivity 21, 776 (2011).
[2] C. H. Liu et al., Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multichip Module, PRX Quantum 4, 030310 (2023).
[3] E. Leonard et al, Digital Coherent Control of a Superconducting Qubit, Phys. Rev. Appl. 11, 1 (2019).