Dynamic quantum process tomography on the Washington DC metropolitan quantum network (DC-QNet)

In a large-scale quantum network, quantum process tomography is a powerful tool for quantifying and verifying the quality of quantum channels. Within this framework, ancilla-assisted process tomography (AAPT) provides a significant advantage for in situ network metrology, as the same states used for entanglement distribution can also be used for tomography. Here, we perform AAPT within a reconfigurable three-node topology on the Washington DC metropolitan quantum network (DC-QNet), consisting of deployed fiber links up to 11.5 km in length. Using a source of polarization-entangled photon pairs at one node, single photons are routed to either of the two receiver nodes via optical switch, and correlations to the local (ancilla) qubits are leveraged to characterize all relevant links in the network. Additionally, AAPT performance is characterized in the presence of noise from coexistent classical synchronization signals, and the advantages of dynamic routing are shown theoretically for larger network topologies.