Charge noise and overdrive errors in reflectometry-based charge, spin and Majorana qubit readout

TL;DR

This paper analyzes physical mechanisms causing errors in reflectometry-based readout of various solid-state qubits, highlighting charge noise, overdriving effects, and optimal probe conditions for improved fidelity.

Contribution

It provides a theoretical model explaining how charge noise and overdriving impact readout fidelity across different qubit types, including Majorana qubits.

Findings

Readout fidelity saturates at high probe strengths for charge and spin qubits.

Majorana qubits have an optimal probe strength for maximum fidelity.

Resonance-like errors occur at high pulse strengths due to multi-photon transitions.

Abstract

Solid-state qubits incorporating quantum dots can be read out by gate reflectometry. Here, we theoretically describe physical mechanisms that render such reflectometry-based readout schemes imperfect. We discuss charge qubits, singlet-triplet spin qubits, and Majorana qubits. In our model, we account for readout errors due to slow charge noise, and due to overdriving, when a too strong probe is causing errors. A key result is that for charge and spin qubits, the readout fidelity saturates at large probe strengths, whereas for Majorana qubits, there is an optimal probe strength which provides a maximized readout fidelity. We also point out the existence of severe readout errors appearing in a resonance-like fashion as the pulse strength is increased, and show that these errors are related to probe-induced multi-photon transitions. Besides providing practical guidelines toward optimized readout, our study might also inspire ways to use gate reflectometry for device characterization.