Improving transmon qudit measurement on IBM Quantum hardware
Tobias Kehrer, Tobias Nadolny, Christoph Bruder
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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>d</a:mi></a:math>-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 <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>X</b:mi></b:math> gates that make use of two-photon transitions. Published by the American Physical Society 2024