# Flux Qubit Readout in the Persistent Current Basis at arbitrary Bias Points

## TL;DR

This paper introduces an indirect, detector-dominated flux qubit readout method that enables projective, quantum nondemolition measurements in the persistent current basis across all bias points with near-perfect fidelity.

## Contribution

It presents a novel measurement protocol allowing basis change in flux qubit readout, enabling high-fidelity QND measurements in the persistent current basis at arbitrary bias points.

## Key findings

- Achieved near 100% fidelity in QND measurements
- Enabled basis change from energy eigenbasis to persistent current basis
- Demonstrated measurement at all flux bias points

## Abstract

Common flux qubit readout schemes are qubit dominated, meaning they measure in the energy eigenbasis of the qubit. For various applications meausrements in a basis different from the energy eigenbasis are required. Here we present an indirect measurement protocol, which is detector dominated instead of qubit dominated, yielding a projective measurements in the persistent current basis for arbitrary bias points. We show that with our setup it is possible to perform a quantum nondemolition measurement (QND) in the persistent current basis at all flux bias points with fidelities reaching almost 100%.