Figure 1. Experimental schematic diagram of quantifying detector coherence.
The structure and application scenarios of quantum detectors are more complicated than those of classical detectors, so the parameters used to quantify the performance of classical detectors, such as detection efficiency and noise intensity, cannot fully describe the performance of quantum detectors. Instead, a new method to quantify the performance of quantum detectors should be proposed from the perspective of quantum resources. Quantum coherence is the basic resource for quantum technology to surpass the performance of traditional equipment, and the premise of realizing this advantage is that the measuring equipment can effectively extract the quantum state and the coherence in quantum operation. Based on the recently published resource theory of quantum operation coherence, the research team extended it and used it to quantitatively study the ability of quantum detectors to extract coherence, and studied the ability of an important kind of quantum detectors-tunable weak-field homodyne detectors to detect quantum coherence, and reconstructed the measurement operators of the detectors through quantum detector tomography experiments, and then calculated the coherence of the detectors. Through the experimental calibration of the coherence of tunable weak-field homodyne detectors with different configurations, the research team obtained the factors that led to the change of the detection coherence ability of quantum detectors, which provided a powerful theoretical guidance for the further use of this kind of detectors in the future. At the same time, this work studies quantum measurement from the perspective of resource theory for the first time, which provides a new idea for accurately evaluating the performance of quantum measurement equipment.
Figure 2. Variation trend of coherent value of adjustable weak-field homodyne detector under different local oscillator and interference contrast.
Quantum coherence plays an indispensable role in quantum computing, quantum communication, quantum metrology and quantum biology. Therefore, quantum coherence has aroused extensive interest as a quantitative evaluation of resources, and people have done a lot of work to study the generation and regulation of coherence. However, in order to apply quantum coherence to a wider range of fields, it is not enough to only generate and regulate coherence, but also to be able to detect coherence, and this work just fills this gap, thus perfecting the research framework of quantum coherence and further popularizing its application.
Xu Huichao and Xu Feixiang, Ph.D. students from School of Modern Engineering and Applied Science of Nanjing University, and Thomas theuer, Ph.D. students from university of ulm, are the first authors of this paper. Dario Egloff of Dresden University of Technology strongly supported and participated in this research. Professor Zhang and Professor Martin B. Plenio are the co-authors of this paper, and Nanjing University is the first unit of this paper. This research is supported by the National Key R&D Program (20 18YFA0306202, 20 17YFA0303703), the National Natural Science Foundation, the Collaborative Innovation Center of Artificial Microstructure Science and Technology and the State Key Laboratory of Solid Microstructure Physics.
Paper link: https://journals.aps.org/PRL/abstract/10.1103/physravelette.125.6665366