Charge Noise and Overdrive Errors in Dispersive Readout of Charge, Spin, and Majorana Qubits

Solid-state qubits incorporating quantum dots can be read out dispersively. 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 the large amplitude of the probe field generates 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 resonancelike fashion as the pulse strength is increased, and show that these errors are related to probe-induced multiphoton transitions. Besides providing practical guidelines toward optimized readout, our study might also inspire ways to use gate reflectometry for device characterization.