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Toward Ancilla-Assisted Process Tomography for Dynamic In-Situ Metrology of Metropolitan Quantum Network Links

Cory M. Nunn, W. McKenzie, Evan Dowling, J. Su, Stav Haldar, Daniel E. Jones, Ivan A. Burenkov, Sergey V. Polyakov, Joseph M. Lukens, Brian T. Kirby

Published Jan 1, 2026• 0 citations
Publisher

Abstract

We characterize a subset of the Washington DC metropolitan quantum network (DC-QNet) using Bayesian ancilla-assisted process tomography with polarization qubits, demonstrating quantum-classical coexistence with White Rabbit synchronization over deployed fiber in a reconfigurable network topology.
DOI
10.1364/cleo_at.2026.jtu.103

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Quantum networking protocols relying on interference and precise time-of-flight measurements require high-precision clock synchronization. This study describes the design, implementation, and characterization of two optical time transfer methods in a metropolitan-scale quantum networking research testbed. With active electronic stabilization, sub-picosecond time deviation (TDEV) was achieved at integration times between 1 and 105 s over 53 km of deployed fiber. Over the same integration periods, 10-ps level TDEV was observed using the White Rabbit–Precision Time Protocol over 128 km. Measurement methods are described to understand the sources of environmental fluctuations on clock synchronization toward the development of in situ compensation methods. Path delay gradients, chromatic dispersion, polarization drift, and optical power variations all contributed to clock synchronization errors. The results from this study will inform future work in the development of compensation methods essential for enabling experimental research in developing practical quantum networking protocols.