School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
Jun Gao
School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
Lu-Feng Qiao
School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
Ruo-Jing Ren
School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
Zhu Cao
Center for Quantum Information, Institute for Interdisciplinary Information Sciences, Tsinghua University, Beijing, China
Zeng-Quan Yan
School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
Zhi-Qiang Jiao
School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
Hao Tang
School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
Zhi-Hao Ma
School of Mathematical Sciences, MOE-LSC, Shanghai Jiao Tong University, Shanghai 200240, China
Xian-Min Jin
School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
In quantum theory, the retrodiction problem is not as clear as its classical counterpart because of the uncertainty principle of quantum mechanics. In classical physics, the measurement outcomes of the present state can be used directly for predicting the future events and inferring the past events which is known as retrodiction. However, as a probabilistic theory, quantum-mechanical retrodiction is a nontrivial problem that has been investigated for a long time, of which the Mean King Problem is one of the most extensively studied issues. Here, we present the first experimental test of a variant of the Mean King Problem, which has a more stringent regulation and is termed “Tracking the King.” We demonstrate that Alice, by harnessing the shared entanglement and controlled-not gate, can successfully retrodict the choice of King’s measurement without knowing any measurement outcome. Our results also provide a counterintuitive quantum communication to deliver information hidden in the choice of measurement.
