High-dimensional Frequency Gates in Integrated Photonics for Scalable Quantum Interconnects

在量子科学和技术的整体格局中，量子网络的发展对于分布式量子计算、连接量子传感器和盲量子计算等应用至关重要。虽然在使用基于卫星的自由空间链路促进端节点之间的纠缠和通信方面已经取得了进展，但是对于密集和短距离网络，考虑到对视线接入的需要，这些通信模式是不现实的。相比之下，光纤在长达约100公里的长度上提供了巨大的带宽和低损耗，使其成为局域和城域量子网络的合理选择。然而，量子网络之前的大部分工作都利用了光子自由度，如偏振，这在标准单模光纤中无法轻易保持。另一方面，频率编码在光纤中提供了自然的稳定性，使用高效滤波器和检测器进行直接测量，并与波分复用兼容。我们建议利用光谱域中的量子干涉来实现高维模式变换，从而为直接量子通信协议提供更多的每光子信息。 为了实现这些方案所需的功能，我们将利用硅光子学和有机电光材料的最新进展，在集成光子平台中开发量子频率处理器。拟议工作的一个关键成果将是演示与光谱可区分光子的纠缠交换-这是一个里程碑，对于转向基于光谱复用和/或频率编码量子信息的网络范式非常重要。此外，一个本科生团队将通过工程学院支持的体验式学习计划下的长期项目融入这项研究。该团队将从开发实验室自动化技能和重复基础量子光学实验到光子器件设计和系统级测试，直至项目结束。该项目将解决量子互连领域的三个关键挑战-（i）对损耗更鲁棒的信息传输的高维编码，（ii）用于纳秒级调度和路由的高速，低损耗和宽带光开关，以及（iii）用于纠缠异构节点/源的光子-光子互连。为此，我们将开发一种基于硅光子学的量子频率处理器（QFP），它可以实现高维模式变换和逻辑门。我们将克服硅/氮化硅中二阶非线性的缺乏，通过建立在有机电光材料的进展上，这已经被利用来实现低功率和高带宽调制器。硅光子学代工厂的工艺进步将被利用来实现具有窄光谱通道的脉冲整形器，从而使得在有限的模拟带宽上驱动具有许多RF谐波的QFP成为可能。反过来，这将有助于实现高维量子频率门（d 6）。在并行轨道上，我们将进行概念验证实验，以验证QFP协议向更高维度的推广。这两条轨道将朝着实现频率量子比特的双态贝尔状态分析器的方向收敛，该分析器将用于一个预示着的纠缠生成协议，其中参与联合测量的光子在光谱上是可区分的。该协议可推广到更高的维度，并可能促进量子纠缠交换。在网络层面，这有可能放松对光谱不可逆性的限制，并且在量子存储器中的量子比特被有意移动的情况下将是有用的（经由量子频率转换）到电信频带中的不同光谱仓以用于光谱复用光纤传输，或者当试图在不同类型的物质之间产生纠缠时，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Within the overall landscape of quantum science and technology, the development of quantum networks is critical for applications such as distributed quantum computing, connected quantum sensors, and blind quantum computing. While there has been progress in facilitating entanglement and communication between end nodes using satellite-based free space links, for dense and short reach networks these modes of communication are unrealistic given the need for line-of-sight access. In contrast, optical fiber offers tremendous bandwidth and low loss over lengths up to about 100 km, making it the logical choice for local area and metropolitan area quantum networks. However, much of the previous work in quantum networking has utilized photonic degrees of freedom, like polarization, which cannot be easily preserved in standard single-mode fiber. On the other hand, frequency encoding provides natural stability in optical fiber, straightforward measurement with high-efficiency filters and detectors, and compatibility with wavelength-division multiplexing. We propose to harness quantum interference in the spectral domain to implement high-dimensional mode transformations that support increased information per photon for direct quantum communication protocols. To realize the functionality required for these schemes, we will leverage recent advances in silicon photonics and organic electro-optic materials to develop a quantum frequency processor in an integrated photonic platform. A key outcome of the proposed work will be a demonstration of entanglement swapping with spectrally distinguishable photons – a milestone important for moving to a networking paradigm based on spectrally multiplexed and/or frequency-encoded quantum information. In addition, a team of undergraduates will be integrated into this research through long term projects under an experiential learning initiative supported by the College of Engineering. The team will progress from developing lab automation skills and repeating foundational quantum optics experiments to photonic device design and system-level testing toward the end of the project. TechnicalThis project will tackle three critical challenges in the field of quantum interconnects – (i) high-dimensional encoding for information transport more robust to loss, (ii) high-speed, low-loss, and broadband optical switches for nanosecond scale scheduling and routing, and (iii) photon-photon interconnects for entangling heterogeneous nodes/sources. To do so, we will develop a silicon photonics-based quantum frequency processor (QFP) that can implement high-dimensional mode transformations and logic gates. We will overcome the lack of a second order nonlinearity in silicon/silicon nitride by building on progress in organic electro-optic materials, which have been harnessed to realize low-power and high bandwidth modulators. Process advances at silicon photonics foundries will be leveraged to realize pulse shapers with narrow spectral channels, thereby making it possible to then drive a QFP with many RF harmonics over a limited analog bandwidth. This, in turn, will facilitate implementation of high-dimensional quantum frequency gates (d 6). On a parallel track, we will carry out proof-of-concept experiments to validate the generalization of the QFP protocol to higher dimensions. Both tracks will converge toward the realization of a two-state Bell state analyzer for frequency qubits, which will be used in a heralded entanglement generation protocol where photons participating in the joint measurement are spectrally distinguishable. This protocol is generalizable to higher dimensions and may facilitate entanglement swapping of qudits. At the network level, this has the potential to relax constraints on spectral indistinguishability and will be useful in situations where qubits from quantum memories are intentionally shifted (via quantum frequency conversion) to different spectral bins in the telecom band for spectrally multiplexed fiber transmission or when trying to generate entanglement between different types of matter-based qubits or between qubits in different local environments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.