Fluxon readout of a superconducting qubit

TL;DR

This paper demonstrates a novel method for reading out a superconducting flux qubit using single-flux quantum (SFQ) electronics, potentially enabling scalable integration of quantum and classical superconducting circuits.

Contribution

It introduces a direct link between SFQ electronics and a superconducting qubit, enabling qubit state readout via fluxon frequency shifts, advancing quantum-classical integration.

Findings

Qubit state readout achieved through fluxon frequency shift

Measured the energy spectrum of a flux qubit using SFQ-based technique

Demonstrated potential for integrating quantum processors with SFQ digital electronics

Abstract

Quantum computing using superconducting circuits underwent rapid development in the last decade. This field has propelled from quantum manipulation of single two-level systems to complex designs employing multiple coupled qubits allowing one to execute simple quantum algorithms. On the way to a practical quantum computer, a need for scalable interfaces between classical circuits and the quantum counterparts has arisen. Low-temperature superconducting single-flux quantum (SFQ) logic employs magnetic fluxons in Josephson transmission lines (JTLs) as basic bits for classical computation. Here, we report on an experiment implementing a direct link between SFQ electronics and a superconducting qubit. We demonstrate a readout of the state of a flux qubit through a frequency shift of a single fluxon oscillating in a JTL. The energy spectrum of the flux qubit is measured using this technique. The demonstrated approach may open ways to future full-scale integration of solid-state quantum computers with digital SFQ electronics.