Optical Quantum Information Theory Group, Max Planck Institute for the Science of Light, Günther-Scharowsky-Strasse 1/Bau 24, 91058 Erlangen, Germany.
Phys Rev Lett. 2013 Jun 28;110(26):260501. doi: 10.1103/PhysRevLett.110.260501. Epub 2013 Jun 24.
We show that optically encoded two-qubit Bell states can be unambiguously discriminated with a success probability of more than 50% in both single-rail and dual-rail encodings by using active linear-optical resources that include Gaussian squeezing operations. These results are in contrast to the well-known upper bound of 50% for unambiguous discrimination of dual-rail Bell states using passive, static linear optics and arbitrarily many vacuum modes. We present experimentally feasible schemes that improve the success probability to 64.3% in dual-rail and to 62.5% in single-rail for a uniform random distribution of Bell states. Conceptually, this demonstrates that neither interactions that induce nonlinear mode transformations (such as Kerr interactions) nor auxiliary entangled photons are required to go beyond the one-half limit. We discuss the optimality of our single-rail scheme and talk about an application of our dual-rail scheme in quantum communication.
我们表明，通过使用包括高斯压缩操作在内的主动线性光学资源，可以在单轨和双轨编码中以超过 50%的成功率明确区分光学编码的两量子比特贝尔态。这些结果与使用无源、静态线性光学和任意多个真空模式明确区分双轨贝尔态的著名 50%上限形成对比。我们提出了实验上可行的方案，可将双轨的成功率提高到 64.3%，单轨的成功率提高到 62.5%，适用于贝尔态的均匀随机分布。从概念上讲，这表明超越一半的限制既不需要诱导非线性模式变换的相互作用（如克尔相互作用），也不需要辅助纠缠光子。我们讨论了我们的单轨方案的最优性，并讨论了我们的双轨方案在量子通信中的应用。
