# Scalable Hardware-Efficient Qubit Control with Single Flux Quantum Pulse Sequences

## TL;DR

This paper presents a scalable, hardware-efficient method for qubit control in superconducting quantum computers using Single Flux Quantum pulse sequences, achieving high fidelity and frequency selectivity.

## Contribution

It introduces compact SFQ pulse sequences with variable timing, enabling high-fidelity qubit control at multiple frequencies with minimal hardware overhead.

## Key findings

- Achieves >99.99% control fidelity for over 20 qubit frequencies
- Demonstrates suppression of leakage out of the computational manifold
- Enables local storage and delivery of SFQ pulses via classical Josephson circuits

## Abstract

The hardware overhead associated with microwave control is a major obstacle to scale-up of superconducting quantum computing. An alternative approach involves irradiation of the qubits with trains of Single Flux Quantum (SFQ) pulses, pulses of voltage whose time integral is precisely equal to the superconducting flux quantum. Here we describe the derivation and validation of compact SFQ pulse sequences in which classical bits are clocked to the qubit at a frequency that is roughly a factor 5 higher than the qubit oscillation frequency, allowing for variable pulse-to-pulse timing. The control sequences are constructed by repeated streaming of short subsequence registers that are designed to suppress leakage out of the computational manifold. With a single global clock, high-fidelity (> 99.99%) control of qubits resonating at over 20 distinct frequencies is possible. SFQ pulses can be stored locally and delivered to the qubits via a proximal classical Josephson digital circuit, offering the possibility of a streamlined, low-footprint classical coprocessor for monitoring errors and feeding back to the qubit array.