Quantum Coherence Witness with Untrusted Measurement Devices
You-Qi Nie, Hongyi Zhou, Jian-Yu Guan, Qiang Zhang, Xiongfeng Ma, Jun Zhang, Jian-Wei Pan · Physical Review Letters · 2019
Coherence is a fundamental resource in quantum information processing, which can be certified by a coherence witness. Due to the imperfection of measurement devices, a conventional coherence witness may lead to fallacious results. We show that the conventional witness could mistake an incoherent state as a state with coherence due to the inaccurate settings of measurement bases. In order to make the witness result reliable, we propose a measurement-device-independent coherence witness scheme without any assumptions on the measurement settings. We introduce the decoy-state method to significantly increase the capability of recognizing states with coherence. Furthermore, we experimentally demonstrate the scheme in a time-bin encoding optical system.