Improved readout of qubit-coupled Gottesman-Kitaev-Preskill states

TL;DR

This paper introduces a new readout method for Gottesman-Kitaev-Preskill (GKP) qubits in harmonic oscillators that significantly enhances fidelity, especially in systems lacking Gaussian operations like homodyne detection.

Contribution

The authors propose an alternative readout strategy for GKP qubits in qubit-coupled systems, improving fidelity and outperforming traditional homodyne detection in certain regimes.

Findings

Readout fidelity improved by several orders of magnitude.

Method surpasses homodyne detection fidelity in low squeezing regimes.

Applicable to trapped-ion and superconducting systems.

Abstract

The Gottesman-Kitaev-Preskill encoding of a qubit in a harmonic oscillator is a promising building block towards fault-tolerant quantum computation. Recently, this encoding was experimentally demonstrated for the first time in trapped-ion and superconducting circuit systems. However, these systems lack some of the Gaussian operations which are critical to efficiently manipulate the encoded qubits. In particular, homodyne detection, which is the preferred method for readout of the encoded qubit, is not readily available, heavily limiting the readout fidelity. Here, we present an alternative read-out strategy designed for qubit-coupled systems. Our method can improve the readout fidelity with several orders of magnitude for such systems and, surprisingly, even surpass the fidelity of homodyne detection in the low squeezing regime.