Single-flux-quantum-based qubit control with tunable driving strength

Abstract

Single-flux-quantum (SFQ) circuits have great potential in building cryogenic quantum-classical interfaces for scaling up superconducting quantum processors. SFQ-based quantum gates have been designed and realized. However, current control schemes are difficult to tune the driving strength to qubits, which restricts the gate length and usually induces leakage to unwanted levels. In this study, we design the scheme and corresponding pulse generator circuit to continuously adjust the driving strength by coupling SFQ pulses with variable intervals. This scheme not only provides a way to adjust the SFQ-based gate length, but also proposes the possibility to tune the driving strength envelope. Simulations show that our scheme can suppress leakage to unwanted levels and reduce the error of SFQ-based Clifford gates by more than an order of magnitude.

Simulations of superconducting quantum gates by digital flux tuner for qubits

“…[6] To overcome the bottleneck, rapid single flux quantum (RSFQ) logic circuits [7] integrated with qubits for qubit control and readout are desirable. [8,9] This kind of RSFQ circuits can be called quantum-classical interface (QCI), which was proposed by McDermott et al [10] The theory of RSFQ digital coherent XY control was studied [11][12][13] and the fidelities of single-qubit gate for transmons performed by SFQ pulses were measured to be about 95% [14] and improved to over 98.8% with multichipmodule (MCM) architecture. [9] Two-qubit gates based on SFQ including cross-resonance (CR) gates and controlled-phase (CZ) gates were also studied.…”