标题： 双粒子量子干涉在非线性光学介质中：类时不可区分性的见证 显示英文标题

标题： Two-particle quantum interference in a nonlinear optical medium: a witness of timelike indistinguishability

摘要： Hong-Ou-Mandel效应是一个典型的量子现象，展示了两个不可区分的光子在50:50分束器上线性耦合时的干涉。 在这里，我们将这种两粒子量子干涉效应转移到非线性区域，当两个单光子照射到参量下转换晶体上时。 形式上，这种转移相当于交换空间和时间变量，从而产生一种未知的时间类量子干涉形式。 输出态的两光子部分是入射光子被传输或重生（即由于与非线性晶体相互作用而被不可区分的替代品所取代）的叠加态。 我们实验上展示了当放大增益调节为2时，检测到恰好一对光子的概率被抑制，这是由传输光子对和重生光子对之间的破坏性干涉引起的。 这种迄今为止未观察到的时间不可区分性的量子表现将非线性量子干涉推向了一个包含多个光子的新领域。 因此，将这种效应与更大的线性光学电路结合，应该能提供一种生成多模量子非高斯态的工具，这对于光子量子计算机来说是关键资源。 显示英文摘要

摘要： The Hong-Ou-Mandel effect is a paradigmatic quantum phenomenon demonstrating the interference of two indistinguishable photons that are linearly coupled at a 50:50 beam splitter. Here, we transpose such a two-particle quantum interference effect to the nonlinear regime, when two single photons are impinging on a parametric down-conversion crystal. Formally, this transposition amounts to exchanging space and time variables, giving rise to an unknown form of timelike quantum interference. The two-photon component of the output state is a superposition of the incident photons being either transmitted or reborn, that is, replaced by indistinguishable substitutes due to their interaction with the nonlinear crystal. We experimentally demonstrate the suppression of the probability of detecting precisely one photon pair when the amplification gain is tuned to 2, which arises from the destructive interference between the transmitted and reborn photon pairs. This heretofore unobserved quantum manifestation of indistinguishability in time pushes nonlinear quantum interference towards a new regime with multiple photons. Hence, composing this effect with larger linear optical circuits should provide a tool to generate multimode quantum non-Gaussian states, which are essential resources for photonic quantum computers.