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arXiv · 2304.09517

Calibration-Independent Certification of a Quantum Frequency Converter

Matthias Bock·Pavel Sekatski·Jean-Daniel Bancal·Stephan Kucera·Tobias Bauer·Nicolas Sangouard·Christoph Becher·Jürgen Eschner
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Abstract

We report on a method to certify a unitary operation with the help of source and measurement apparatuses whose calibration throughout the certification process needs not be trusted. As in the device-independent paradigm our certification method relies on a Bell test, but it removes the need for high detection efficiencies by including the single additional assumption that non-detected events are independent of the measurement settings. The relevance of the proposed method is demonstrated experimentally with the certification of a quantum frequency converter. The experiment starts with the heralded creation of a maximally entangled two-qubit state between a single $^{40}$Ca$^+$ ion and a 854$\,$nm photon. Entanglement preserving frequency conversion to the telecom band is then realized with a non-linear waveguide embedded in a Sagnac interferometer. The resulting ion-telecom photon entangled state is characterized by means of a Bell-CHSH test from which the quality of the frequency conversion is quantified. We demonstrate the successful frequency conversion with an average certified fidelity of $\geq 84\,\%$ and an efficiency $\geq 3.1\times 10^{-6}$ at a confidence level of $99\,\%$. This ensures the suitability of the converter for integration in quantum networks from a trustful characterization procedure.

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Matthias Bock, Pavel Sekatski, Jean-Daniel Bancal, Stephan Kucera, Tobias Bauer, Nicolas Sangouard, Christoph Becher, Jürgen Eschner. 2023-04-19. Calibration-Independent Certification of a Quantum Frequency Converter. https://doi.org/10.1038/s41534-024-00859-0

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