Readout error mitigated quantum state tomography tested on superconducting qubits

Quantum technologies rely heavily on accurate control and reliable readout of quantum systems.
Current experiments are limited by numerous sources of noise that can only be partially captured by
simple analytical models and additional characterization of the noise sources is required. We test the
ability of readout error mitigation to correct noise found in systems composed of quantum two-level
objects (qubits). To probe the limit of such methods, we designed a beyond-classical readout error
mitigation protocol based on quantum state tomography (QST), which estimates the density matrix of
a quantum system, and quantum detector tomography (QDT), which characterizes the measurement
procedure. By treating readout error mitigation in the context of state tomography the method
becomes largely readout mode-, architecture-, noise source-, and quantum state-independent. We
implement this method on a superconducting qubit and evaluate the increase in reconstruction fidelity
for QST. We characterize the performance of the method by varying important noise sources, such as
suboptimal readout signal amplification, insufficient resonator photon population, off-resonant qubit
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drive, and effectively shortened T1 and T2 coherence. As a result, we identified noise sources for which
readout error mitigation worked well, and observed decreases in readout infidelity by a factor of
up to 30.