Improving Transmon Qudit Measurement on IBM Quantum Hardware

TL;DR

This paper presents two optimized measurement strategies for distinguishing states in transmon qudits on IBM Quantum hardware, enhancing readout fidelity for higher-dimensional quantum states.

Contribution

It introduces and analyzes two new measurement methods tailored for transmon qudits, optimizing state discrimination in practical quantum computing hardware.

Findings

Identifies optimal regimes for each measurement strategy based on hardware parameters.

Demonstrates improved distinguishability of ququart states on IBM Quantum hardware.

Provides a model for transmon qudit readout that guides practical implementation.

Abstract

The Hilbert space of a physical qubit typically features more than two energy levels. Using states outside the qubit subspace can provide advantages in quantum computation. To benefit from these advantages, individual states of the $d$-dimensional qudit Hilbert space have to be discriminated during readout. We propose and analyze two measurement strategies that improve the distinguishability of transmon qudit states. Based on a model describing the readout of a transmon qudit coupled to a resonator, we identify the regime in hardware parameter space where each strategy is optimal. We discuss these strategies in the context of a practical implementation of the default measurement of a ququart on IBM Quantum hardware whose states are prepared by employing higher-order $X$ gates that make use of two-photon transitions.