Quantum Process Tomography of a Quantum Memory

In order to realize a quantum memory, a memory protocol for a superconducting qubit coupled to a 3D cavity resonator is realized with a Z fidelity of 85%. By exploiting the multimode structure of the 3D cavity, we combine readout and storage capability in a single device, thereby significantly enhancing scalability. With the goal of accurately characterizing the information loss during the protocol, the overall process fidelity has to be measured. To this end, we perform quantum process tomography on our quantum memory system. The protocol consists of four pulses with a total length of 240 ns. The qubit density matrix is reconstructed with standard quantum state tomography for a suitable set of qubit states. The comparison of the measured outcome with the theoretical value gives us knowledge about the process matrix $\chi$. We present tomography data and compare the quantum process fidelity to the Z fidelity.