Electrical Engineering Department, University of Southern California, Los Angeles, California 90089, USA.
Nature. 2013 Apr 25;496(7446):456-60. doi: 10.1038/nature12035.
Quantum computation and cryptography both involve scenarios in which a user interacts with an imperfectly modelled or 'untrusted' system. It is therefore of fundamental and practical interest to devise tests that reveal whether the system is behaving as instructed. In 1969, Clauser, Horne, Shimony and Holt proposed an experimental test that can be passed by a quantum-mechanical system but not by a system restricted to classical physics. Here we extend this test to enable the characterization of a large quantum system. We describe a scheme that can be used to determine the initial state and to classically command the system to evolve according to desired dynamics. The bipartite system is treated as two black boxes, with no assumptions about their inner workings except that they obey quantum physics. The scheme works even if the system is explicitly designed to undermine it; any misbehaviour is detected. Among its applications, our scheme makes it possible to test whether a claimed quantum computer is truly quantum. It also advances towards a goal of quantum cryptography: namely, the use of 'untrusted' devices to establish a shared random key, with security based on the validity of quantum physics.
量子计算和密码学都涉及用户与不完善建模或“不可信”系统交互的场景。因此，设计能够揭示系统是否按指令运行的测试具有基础和实际意义。1969 年，克劳泽、霍恩、希莫尼和霍尔特提出了一个实验测试，量子力学系统可以通过，但受限于经典物理的系统不能通过。在这里，我们扩展了这个测试，以实现对大型量子系统的特性描述。我们描述了一种方案，可以用于确定初始状态，并按照所需的动力学经典地命令系统演化。双体系统被视为两个黑盒，除了它们遵守量子物理之外，对其内部工作原理没有任何假设。即使系统被明确设计来破坏该方案，该方案也能检测到任何错误行为。在其应用中，我们的方案使得测试声称的量子计算机是否真正是量子的成为可能。它还朝着量子密码学的目标迈进：即使用“不可信”的设备来建立共享的随机密钥，其安全性基于量子物理的有效性。
