Anwer Hammad, Muhammad Sadiq, Cherifi Walid, Miklin Nikolai, Tavakoli Armin, Bourennane Mohamed
Department of Physics, Stockholm University, S-10691 Stockholm, Sweden.
Institute of Theoretical Physics and Astrophysics, National Quantum Information Center, Faculty of Mathematics, Physics and Informatics, University of Gdansk, 80-952 Gdánsk, Poland.
Phys Rev Lett. 2020 Aug 21;125(8):080403. doi: 10.1103/PhysRevLett.125.080403.
Unsharp measurements are increasingly important for foundational insights in quantum theory and quantum information applications. Here, we report an experimental implementation of unsharp qubit measurements in a sequential communication protocol, based on a quantum random access code. The protocol involves three parties; the first party prepares a qubit system, the second party performs operations that return both a classical and quantum outcome, and the latter is measured by the third party. We demonstrate a nearly optimal sequential quantum random access code that outperforms both the best possible classical protocol and any quantum protocol that utilizes only projective measurements. Furthermore, while only assuming that the involved devices operate on qubits and that detected events constitute a fair sample, we demonstrate the noise-robust characterization of unsharp measurements based on the sequential quantum random access code. We apply this characterization towards quantifying the degree of incompatibility of two sequential pairs of quantum measurements.
非锐测量对于量子理论的基础见解和量子信息应用越来越重要。在此，我们报告了基于量子随机访问码在顺序通信协议中进行非锐量子比特测量的实验实现。该协议涉及三方；第一方制备一个量子比特系统，第二方执行操作以返回经典和量子结果，后者由第三方测量。我们展示了一种近乎最优的顺序量子随机访问码，它优于最佳可能的经典协议以及任何仅使用投影测量的量子协议。此外，仅假设所涉及的设备在量子比特上运行且检测到的事件构成一个公平样本，我们展示了基于顺序量子随机访问码的非锐测量的抗噪声特性。我们将此特性应用于量化两对顺序量子测量的不相容程度。
