Collaborative Research: Toward universal quantum computing with heterogeneously integrated quantum optical frequency combs

量子计算是一种颠覆性技术，能够解决经典的棘手问题，如整数分解和破解加密代码，并对主要社会影响进行量子模拟，如用于化肥生产的固氮、用于固碳的二氧化碳固定，以及解锁室温超导。迈向全面量子计算的道路面临着艰巨的挑战。与占主导地位的量子门方法不同的一种方法是基于测量的量子计算，特别是使用簇态的单向量子计算。这种方法避免了对可伸缩性的低去相干和记忆的要求。我们的方法纯粹基于使用光子，在室温下工作，并使用与目前的光通信网络兼容的波长。利用量子光学频率梳将产生大的二维团簇态。这些团簇状态是确定的、无条件地产生的，并且按指数方式扩展。团簇态基于连续变量量子光学系统，并在量子场上进行编码。该方案的关键目标是演示芯片上连续变量簇态的产生，以及资源状态的制备，称为Gottesman-Kitaev-Preskill(GKP)网格状态，这是纠错和普适量子计算的关键。为了实现芯片规模的量子态发生器，将使用不同平台技术在硅板上的异质集成。具体地说，将在SiN/SiO_2平台上实现使用光栅的高品质因数(Q)纳米腔，并将产生光学频率梳。基于耦合到高Q腔的III-V增益芯片的窄线宽半导体激光器将安装在硅平台上。最后，在硅平台上异质集成用于高速调制的薄膜LiNbO_3调制器。将建立一项广泛的影响计划，以教育高中生量子物理，培训量子工程中未被充分代表的群体，并教育研究生在工程研究中取得成功。实现量子计算的现实途径需要实施独立的芯片级系统来创建和操纵光的量子态。理想情况下，这些系统应该在室温下工作，并且波长与经典光通信系统兼容。在本项目中，将展示一种新型的集成平台，以实现一些高效率和保真度的基本量子协议。该方案旨在首次在光子芯片上实现团簇态、CAT态和GKP(Gottesman-Kitaev-Preskill，GKP)态，总体目标是实现容错光子量子计算机所需的所有构件。基于测量的量子计算原语，即通过场零差和光子数分辨(PNR)检测通知的团簇状态的前馈将被实现。该实验平台基于一个集成在硅上的光学参量振荡器和一个电光相位调制器。设想中的量子系统的核心是一个集成的毫米级光栅法布里-珀罗谐振器，其自由光谱范围为几十GHz，在1550 nm处的Q因子优于100万。Si3N4微谐振器由共集成窄线宽单模激光器泵浦，由于介质的内置克尔非线性，输出分布在光频梳光谱模式中的量子关联光子。芯片到光纤的高效光耦合将被用于与光检测的接口。第一个实验目标是演示大规模集群状态在芯片上的生成。第二个实验目标是使用PNR检测测量，在芯片上演示非高斯(如CAT和GKP)状态的产生。这种量子光子芯片的全部可能性也将在运行在阈值以上的微谐振器光学参量振荡器中进行研究。该奖项反映了NSF的法定使命，并已通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Quantum computing is a disruptive technology capable of solving classically intractable problems, such as factoring integers and breaking encryption codes, and performing quantum simulations of major societal impact such as nitrogen fixation for fertilizer production, carbon dioxide fixation for carbon sequestration, and unlocking room-temperature superconductivity. The route toward full scale quantum computing faces daunting challenges. One approach away from the dominant quantum gate approach is measurement-based quantum computing, and, in particular, one-way quantum computing using cluster states. This approach circumvents the requirement of low decoherence and memories for scalability. Our approach is purely based on using photons, operates at room-temperature, and uses a wavelength compatible to present optical communication networks. Large two-dimensional cluster states will be produced using quantum optical frequency combs. These cluster states are deterministically and unconditionally generated and scale exponentially. The cluster states are based on continuous-variable quantum optical systems and are encoded over quantum fields. The key objective of this proposal is to demonstrate the generation of continuous variable cluster states on chip and to demonstrate the preparation of resource states called Gottesman-Kitaev-Preskill (GKP) grid states, which are key to error correction and to universal quantum computing. To realize the chip-scale quantum state generator, hetero-integration of different platform technology on a silicon board will be used. In particular, a high quality factor (Q) nanocavity using gratings will be realized on the SiN/SiO2 platform and will produce an optical frequency comb. A narrow linewidth semiconductor laser based on a III-V gain chip coupled to a high Q cavity will be mounted on the Si platform. Finally, a thin-film LiNbO3 modulator for high speed modulation will be heterogeneously integrated on the Si platform. A broad impact plan will be set-up to educate high school students in quantum physics, train under-represented groups in quantum engineering, and educate graduate students for success in engineering research.A realistic path to quantum computation requires the implementation of standalone chipscale systems to create and manipulate quantum states of light. These systems should ideally operate at room temperature and at wavelengths compatible with those of classical optical communication systems. In this project, a novel integrated platform to realize some basic quantum protocols with high efficiency and fidelity will be demonstrated. The proposal aims at the first realization of cluster states, cat states, and Gottesman-Kitaev-Preskill (GKP) states on a photonic chip, with the overarching goal of realizing all the required building blocks for a fault-tolerant photonic quantum computer. Measurement based quantum computation primitives, namely, feedforward on cluster states informed by field-homodyne and photon-number-resolving (PNR) detection will be realized. The experimental platform is based on one optical parametric oscillator and one electro-optic phase modulator integrated on Si. The core of the envisioned quantum system is an integrated millimeter-size grating Fabry-Perot resonator, featuring a free-spectral range of a few tens of GHz and a Q-factor better than a million at 1550 nm. The Si3N4 microresonator is pumped by a co-integrated narrow-linewidth single mode laser, and owing to the built-in Kerr nonlinearity of the medium, outputs quantum-correlated photons distributed in the spectral modes of an optical frequency comb. High-efficiency optical coupling from chip to optical fibers will be used to interface with photodetection. The first experimental objective is to demonstrate large-scale cluster state generation on chip. The second experimental objective is to demonstrate non-Gaussian (e.g. cat and GKP) state generation on chip, using PNR detection measurements. The full spectrum of possibilities of this quantum photonic chip will also be studied in microresonator optical parametric oscillators operated above threshold.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.