Experimental Multi-Time Process Tomography on Superconducting Qubits

The maturation of quantum technologies in the past decade has been enabled, in no small part, by the ongoing advancement of noise characterisation techniques. For Markovian noise sources, quantum process tomography or QPT (a natural extension of quantum state tomography) is one such technique which has become ubiquitous in the experimental toolbox. However, techniques like QPT have no capacity to characterise sources of non-Markovian noise (e.g. memory effects, system drifts and crosstalk), which we know exist nontrivially in the vast majority of experimental hardware. In this talk, we introduce a methodology to perform multi-time quantum process tomography, which uses a process matrix formalism to allow for full characterisation of non-Markovian dynamics. We discuss the experimental procedure required to perform multi-time process tomography on a superconducting quantum device, and present results where we successfully detect quantum memory effects on an in-house superconducting device and a publicly available IBM processor.