[论文解读] Loophole-free quantum steering

Bernhard Wittmann, Sven Ramelow+6 more|arXiv (Cornell University)|Nov 3, 2011

Quantum Information and Cryptography被引用 6

一句话总结

该论文首次在无漏洞条件下通过偏振纠缠光子实验演示了爱因斯坦-波多利-罗森（EPR）导引，同时关闭了局域性、自由选择和公平采样漏洞。通过利用高检测效率和快速随机数生成，违反了三设置二次导引不等式，排除了局部实在论理论的主要类别，并实现了从不可信源安全分发纠缠态。

ABSTRACT

Tests of the predictions of quantum mechanics for entangled systems have provided increasing evidence against local realistic theories. However, there still remains the crucial challenge of simultaneously closing all major loopholes - the locality, freedom-of-choice, and detection loopholes - in a single experiment. An important sub-class of local realistic theories can be tested with the concept of steering. The term steering was introduced by Schrodinger in 1935 for the fact that entanglement would seem to allow an experimenter to remotely steer the state of a distant system as in the Einstein-Podolsky-Rosen (EPR) argument. Einstein called this spooky action at a distance. EPR-Steering has recently been rigorously formulated as a quantum information task opening it up to new experimental tests. Here, we present the first loophole-free demonstration of EPR-steering by violating three-setting quadratic steering inequality, tested with polarization entangled photons shared between two distant laboratories. Our experiment demonstrates this effect while simultaneously closing all loopholes: both the locality loophole and a specific form of the freedom-of-choice loophole are closed by having a large separation of the parties and using fast quantum random number generators, and the fair-sampling loophole is closed by having high overall detection efficiency. Thereby, we exclude - for the first time loophole-free - an important class of local realistic theories considered by EPR. As well as its foundational importance, loop-hole-free steering also allows the distribution of quantum entanglement secure from an untrusted party.

研究动机与目标

• 在一次实验中同时关闭局域性、自由选择和公平采样等主要漏洞，以测试量子导引。
• 在严格条件下实验演示EPR导引作为一种量子信息任务。
• 排除爱因斯坦-波多利-罗森佯谬中提出的可通过隐变量解释纠缠的局部实在论理论。
• 即使源不可信，也能实现量子纠缠的可靠分发。
• 提供一个无已知漏洞的基础性实验，以检验量子非定域性。

提出的方法

• 使用在两个远距离实验室之间分发的偏振纠缠光子对来测试EPR导引。
• 实施三设置二次导引不等式以检测非定域关联。
• 采用快速量子随机数生成器，通过确保测量设置不可预测来关闭自由选择漏洞。
• 通过保持双方之间的大空间距离来关闭局域性漏洞。
• 通过实现测量装置中高总体检测效率来关闭公平采样漏洞。
• 采用适配于导引的贝尔型测试框架，其中一方（被导引方）被视为不可信。

实验结果

研究问题

• RQ1 是否能在单次实验中无漏洞地实现EPR导引？
• RQ2 无漏洞导引测试在多大程度上能排除局部实在论理论？
• RQ3 高检测效率与随机测量设置是否能确保量子非定域性测试的安全与可靠？
• RQ4 无漏洞导引是否能实现与不可信源的安全量子通信？
• RQ5 在关闭所有主要实验漏洞的条件下，能否验证EPR导引效应？

主要发现

• 实验实现了三设置二次导引不等式的无漏洞违反，无任何已知漏洞地证实了EPR导引。
• 通过保持两个远距离实验室之间的大距离，关闭了局域性漏洞。
• 通过使用快速量子随机数生成器选择测量设置，关闭了自由选择漏洞。
• 通过在测量装置中实现高总体检测效率，关闭了公平采样漏洞。
• 结果排除了爱因斯坦、波多利和罗森提出的局部实在论理论的主要类别。
• 该演示即使在源不可信的情况下也能实现纠缠的可靠分发，为量子密码学开辟了新应用。