Wang Yi-Tao, Tang Jian-Shun, Wei Zhi-Yuan, Yu Shang, Ke Zhi-Jin, Xu Xiao-Ye, Li Chuan-Feng, Guo Guang-Can
CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, People's Republic of China.
Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China.
Phys Rev Lett. 2017 Jan 13;118(2):020403. doi: 10.1103/PhysRevLett.118.020403. Epub 2017 Jan 12.
Quantum coherence is the most distinguished feature of quantum mechanics. It lies at the heart of the quantum-information technologies as the fundamental resource and is also related to other quantum resources, including entanglement. It plays a critical role in various fields, even in biology. Nevertheless, the rigorous and systematic resource-theoretic framework of coherence has just been developed recently, and several coherence measures are proposed. Experimentally, the usual method to measure coherence is to perform state tomography and use mathematical expressions. Here, we alternatively develop a method to measure coherence directly using its most essential behavior-the interference fringes. The ancilla states are mixed into the target state with various ratios, and the minimal ratio that makes the interference fringes of the "mixed state" vanish is taken as the quantity of coherence. We also use the witness observable to witness coherence, and the optimal witness constitutes another direct method to measure coherence. For comparison, we perform tomography and calculate l_{1} norm of coherence, which coincides with the results of the other two methods in our situation. Our methods are explicit and robust, providing a nice alternative to the tomographic technique.
量子相干是量子力学最显著的特征。它作为基本资源处于量子信息技术的核心，并且还与包括纠缠在内的其他量子资源相关。它在各个领域甚至生物学中都起着关键作用。然而，相干性严格且系统的资源理论框架直到最近才得以发展，并且提出了几种相干性度量。在实验上，测量相干性的常用方法是进行态层析成像并使用数学表达式。在此，我们转而开发一种直接利用其最本质行为——干涉条纹来测量相干性的方法。辅助态以各种比例混入目标态，并且将使“混合态”的干涉条纹消失的最小比例作为相干量。我们还使用见证可观测量来见证相干性，并且最优见证构成了另一种测量相干性的直接方法。为作比较，我们进行层析成像并计算相干性的(l_1)范数，在我们的情形中它与其他两种方法的结果一致。我们的方法明确且稳健，为层析成像技术提供了很好的替代方案。
