Spectral quantum tomography
Jonas Helsen (TU Delft - Quantum Information and Software, TU Delft - QuTech Advanced Research Centre)
Francesco Battistel (TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/Terhal Group)
Barbara M. Terhal (Forschungszentrum Jülich, TU Delft - Quantum Computing, TU Delft - QCD/Terhal Group, TU Delft - QuTech Advanced Research Centre)
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Abstract
We introduce spectral quantum tomography, a simple method to extract the eigenvalues of a noisy few-qubit gate, represented by a trace-preserving superoperator, in a SPAM-resistant fashion, using low resources in terms of gate sequence length. The eigenvalues provide detailed gate information, supplementary to known gate-quality measures such as the gate fidelity, and can be used as a gate diagnostic tool. We apply our method to one- and two-qubit gates on two different superconducting systems available in the cloud, namely the QuTech Quantum Infinity and the IBM Quantum Experience. We discuss how cross-talk, leakage and non-Markovian errors affect the eigenvalue data.