A strong limitation of linear optical quantum computing is the probabilistic operation of two-quantum-bit gates based on the coalescence of indistinguishable photons. A route to deterministic operation is to exploit the single-photon nonlinearity of an atomic transition. Through engineering of the atom–photon interaction, phase shifters, photon filters and photon–photon gates have been demonstrated with natural atoms. Proofs of concept have been reported with semiconductor quantum dots, yet limited by inefficient atom–photon interfaces and dephasing. Here, we report a highly efficient single-photon filter based on a large optical nonlinearity at the single-photon level, in a near-optimal quantum-dot cavity interface. When probed with coherent light wavepackets, the device shows a record nonlinearity threshold around 0.3 ± 0.1 incident photons. We demonstrate that 80% of the directly reflected light intensity consists of a single-photon Fock state and that the two- and three-photon components are strongly suppressed compared with the single-photon one.

中文翻译：

---

固态单光子滤波器

线性光学量子计算的一个强大限制是基于不可区分的光子的合并，两个量子位门的概率运算。确定性操作的一种途径是利用原子跃迁的单光子非线性。通过对原子-光子相互作用的工程设计，已经证明了利用自然原子的移相器，光子滤光片和光子-光子门。已有关于半导体量子点的概念证明，但受到无效的原子-光子界面和相移的限制。在这里，我们报告了一个高效的单光子滤波器，该滤波器基于单光子级的光学非线性，在接近最佳的量子点腔界面中具有很大的光学非线性。当用相干光波包探测时，该器件显示出记录的非线性阈值，入射阈值约为0.3±0.1。