Geometric Characterization of Quantum Memory in Superconducting Qubits

Quantum memories capable of preserving entanglement constitute a fundamental resource for distributed quantum information networks. Verifying this ability reduces to testing whether the memory operates as a non-entanglement-breaking (non-EB) channel. Conventional approaches, such as quantum process tomography (QPT), are device-dependent and highly sensitive to state-preparation-and-measurement (SPAM) errors. Here we employ the channel ellipsoid framework to characterize non-EB channels in a semi-device-independent paradigm that only requires trusted measurement apparatus. We first demonstrate the preparation-error-free advantage of our method by comparing it with QPT; subsequently, we reveal its ability to capture non-Markovian effects via controlled qubit–qubit interaction. Furthermore, by tuning dephasing rates via flux control, we experimentally show that the ellipsoid shrinks with increasing dephasing. Entanglement preservation is guaranteed when the ellipsoid remains sufficiently large. Such robustness against dephasing and SPAM errors not only eclipses conventional QPT but accelerates the deployment of scalable semi-device-independent protocols in distributed quantum networks.