Dipartimento di Ingegneria dell'Informazione, Università di Padova, via Gradenigo 6B, 35131 Padova, Italy.
Centro di Ateneo di Studi e Attività Spaziali "G. Colombo", Università di Padova, via Venezia 15, 35131 Padova, Italy.
Phys Rev Lett. 2018 Nov 9;121(19):190401. doi: 10.1103/PhysRevLett.121.190401.
Entanglement is an invaluable resource for fundamental tests of physics and the implementation of quantum information protocols such as device-independent secure communications. In particular, time-bin entanglement is widely exploited to reach these purposes both in free space and optical fiber propagation, due to the robustness and simplicity of its implementation. However, all existing realizations of time-bin entanglement suffer from an intrinsic postselection loophole, which undermines their usefulness. Here, we report the first experimental violation of Bell's inequality with "genuine" time-bin entanglement, free of the postselection loophole. We introduced a novel function of the interferometers at the two measurement stations, that operate as fast synchronized optical switches. This scheme allowed us to obtain a postselection-loophole-free Bell violation of more than 9 standard deviations. Since our scheme is fully implementable using standard fiber-based components and is compatible with modern integrated photonics, our results pave the way for the distribution of genuine time-bin entanglement over long distances.
纠缠是进行物理基础检验和实现量子信息协议（如设备无关的安全通信）的宝贵资源。特别是，由于其实现的鲁棒性和简单性，时间-bin 纠缠在自由空间和光纤传播中都被广泛用于实现这些目的。然而，所有现有的时间-bin 纠缠的实现都存在固有后选择漏洞，这削弱了它们的有用性。在这里，我们报告了首次使用“真正的”时间-bin 纠缠实验违反贝尔不等式，且没有后选择漏洞。我们在两个测量站的干涉仪中引入了一种新的功能，该功能可作为快速同步光学开关运行。该方案使我们能够获得超过 9 个标准差的无后选择漏洞的贝尔不等式违反。由于我们的方案可以完全使用标准的基于光纤的组件来实现，并且与现代集成光子学兼容，因此我们的结果为在长距离上分配真正的时间-bin 纠缠铺平了道路。
