As a measure of the 'closeness' of two quantum states, fidelity plays a fundamental role in quantum information theory. Fidelity estimation protocols try to strike a balance between information gleaned from an experiment, and the efficiency of its implementation, in terms of the number of states consumed by the protocol. Here we adapt a previously reported optimal state verification protocol (Phys. Rev. Lett. 120, 170502, 2018) for fidelity estimation of two-qubit states. We demonstrate the protocol experimentally using a fully-programmable silicon photonic two-qubit chip. Our protocol outputs significantly smaller error bars of its point estimate in comparison with another widely-used estimation protocol, showing a clear step forward in the ability to estimate the fidelity of quantum states produced by a practical device.
@article{arxiv.2306.01068,
title = {Fidelity estimation of quantum states on a silicon photonic chip},
author = {Sabine Wollmann and Xiaogang Qiang and Sam Pallister and Ashley Montanaro and Noah Linden and Jonathan C. F. Matthews},
journal= {arXiv preprint arXiv:2306.01068},
year = {2023}
}