Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria.
Nature. 2011 Oct 12;478(7369):360-3. doi: 10.1038/nature10463.
Single photons are excellent quantum information carriers: they were used in the earliest demonstrations of entanglement and in the production of the highest-quality entanglement reported so far. However, current schemes for preparing, processing and measuring them are inefficient. For example, down-conversion provides heralded, but randomly timed, single photons, and linear optics gates are inherently probabilistic. Here we introduce a deterministic process--coherent photon conversion (CPC)--that provides a new way to generate and process complex, multiquanta states for photonic quantum information applications. The technique uses classically pumped nonlinearities to induce coherent oscillations between orthogonal states of multiple quantum excitations. One example of CPC, based on a pumped four-wave-mixing interaction, is shown to yield a single, versatile process that provides a full set of photonic quantum processing tools. This set satisfies the DiVincenzo criteria for a scalable quantum computing architecture, including deterministic multiqubit entanglement gates (based on a novel form of photon-photon interaction), high-quality heralded single- and multiphoton states free from higher-order imperfections, and robust, high-efficiency detection. It can also be used to produce heralded multiphoton entanglement, create optically switchable quantum circuits and implement an improved form of down-conversion with reduced higher-order effects. Such tools are valuable building blocks for many quantum-enabled technologies. Finally, using photonic crystal fibres we experimentally demonstrate quantum correlations arising from a four-colour nonlinear process suitable for CPC and use these measurements to study the feasibility of reaching the deterministic regime with current technology. Our scheme, which is based on interacting bosonic fields, is not restricted to optical systems but could also be implemented in optomechanical, electromechanical and superconducting systems with extremely strong intrinsic nonlinearities. Furthermore, exploiting higher-order nonlinearities with multiple pump fields yields a mechanism for multiparty mediation of the complex, coherent dynamics.
它们被用于最早的纠缠演示以及迄今为止产生的最高质量纠缠的产生。然而，目前用于制备、处理和测量它们的方案效率低下。例如，下转换提供了被标记的，但随机定时的单光子，而线性光学门是固有概率性的。在这里，我们引入了一种确定性过程——相干光子转换（CPC）——它为光子量子信息应用提供了一种新的生成和处理复杂多量子态的方法。该技术使用经典泵浦的非线性来诱导多个量子激发的正交态之间的相干振荡。基于泵浦四波混频相互作用的 CPC 的一个示例被证明可以提供一种单一的、通用的过程，该过程提供了一套完整的光子量子处理工具。该工具集满足可扩展量子计算架构的 DiVincenzo 标准，包括基于新型光子-光子相互作用的确定性多量子比特纠缠门（based on a novel form of photon-photon interaction）、高质量的无高阶缺陷的单光子和多光子标记态以及稳健、高效率的检测。它还可用于产生标记的多光子纠缠，创建光学可切换量子电路，并实现具有降低的高阶效应的改进形式的下转换。这些工具是许多量子技术的有价值的构建块。最后，我们使用光子晶体光纤实验证明了源于适用于 CPC 的四色非线性过程的量子相关性，并使用这些测量来研究利用当前技术达到确定性状态的可行性。我们的方案基于相互作用的玻色子场，不仅限于光学系统，而且还可以在具有极强固有非线性的光机械、机电和超导系统中实现。此外，利用具有多个泵浦场的高阶非线性产生了一种用于多方介导复杂相干动力学的机制。
