Advanced Photonic Quantum Information Processing

新兴的量子信息领域承诺了惊人和重要的功能，如超安全加密、超快速计算和超精确计量。光子是量子信息的优秀载体，已被用于许多开创性的量子信息处理实验。然而，尽管人们正在寻求实现可靠的单光子周期性源（量子应用的关键资源）的许多方法，但迄今为止，还没有一种方法能够达到足以实现可扩展光量子信息处理的水平。迄今为止，几乎所有的实验都受到低效光子对源和探测器的限制。因此，例如，需要五个光子的协议将相当于滚动五个骰子并在每个骰子上获得“6”，其可能性仅为（1/6）（1/6）（1/6）（1/6）（1/6）（1/6）(1/6)= 0.00013。通过结合光子源的时间复用——多次尝试（~20次），直到我们得到一个成功的输出，从原理上讲，产生5个光子的成功率增加到88%。大规模的量子信息处理也需要高效的探测器和高保真的光子电路。该项目将结合周期单/多光子源、集成光子波导电路和高效单光子探测器的先进技术，解决这些需求。最终结果将是光量子信息处理的新能力，大大超过迄今为止的可能性。实现不可区分光子的有效周期源是许多量子信息协议的使能技术，包括单向量子计算、改进量子密码学和量子计量学。它将立即增强几乎所有现有的量子通信协议，同时提高可能的速率，同时减少多光子事件的有害影响。自发参数下转换是众所周知的预示单光子的来源-探测到其中一个子光子表明另一个的存在。然而，下转换过程本身是概率性的，因此产生的单光子不是按需的；此外，使用更亮的泵浦脉冲来增加产生一对的可能性会自动增加产生多于一对的不必要的概率。通过使用时间复用，允许在任意一个（例如，50个时隙）中创建的光子被映射到单个最终时间窗口，可以大大提高单光子创建的净效率，同时最小化不必要的多光子事件的可能性。当有意尝试用许多光子创建状态时，好处就更大了：这里开发的方法可以使速率提高5个数量级以上（一个实验高达12个数量级！）。光学电路的类似改进（关于尺寸和稳定性）是通过将定制的波导写入低损耗玻璃来实现的。这项工作的一个关键特点是与以色列研究员Yaron Silberberg的合作，他将开发所需的光子波导电路，并与该小组合作开发最终的应用程序。将大量波导和光学器件（如分束器和移相器）“集成”到一个微小的玻璃基板上（大约跨越5厘米的面积）的技术将提供增强的稳定性和多个光子之间的干扰。因此，该提案中独特的两国联系使复杂的量子光子系统的开发和实施远远超出了迄今为止可能的范围，到目前为止仅限于几个光子。将新光源与优化的光子波导电路相结合，该项目将研究几种有趣的基于光子的量子效应，包括潜在的可扩展光学量子逻辑和量子行走。

The nascent field of quantum information promises amazing and important capabilities, such as ultra-secure encryption, ultra-fast computation, and ultra-precise metrology. Photons are excellent carriers of quantum information, having been employed in numerous groundbreaking quantum information processing experiments. However, although many approaches to realizing a reliable periodic source of single photons - a critical resource for quantum applications - are being pursued, to date none operates at a level sufficient for realizing scalable optical quantum information processing. To date, nearly all experiments have been limited by inefficient photon-pair sources and detectors. Consequently, for example, a protocol needing five photons would be the equivalent of rolling five die and getting a "6" on each one, with the likelihood of only (1/6)(1/6)(1/6)(1/6)(1/6)= 0.00013. By incorporating time multiplexing of the photon source - making multiple attempts (~20) until we get a successful output, the success probability to create five photons is increased in principle to 88%. Large-scale quantum information processing also requires highly efficient detectors and high-fidelity photonic circuits. This project will solve these needs, combining advanced technologies for periodic single-/multi-photon sources, integrated photonic waveguide circuits, and highly efficient single-photon detectors. The net result will be a new capability for optical quantum information processing, greatly exceeding what has been possible until now.The realization of an efficient periodic source of indistinguishable photons is an enabling technology for many quantum information protocols, including one-way quantum computing, improved quantum cryptography, and quantum metrology. It would immediately enhance almost all existing quantum communication protocols, simultaneously increasing the possible rate while reducing the deleterious effects of multi-photon events. Spontaneous parametric downconversion is well known as a source of heralded single photons - detecting one of the daughter photons indicates the presence of the other one. However, the downconversion process itself is probabilistic, and therefore the resulting single photons are not on-demand; furthermore, using a brighter pump pulse to increase the likelihood of producing a pair automatically increases the unwanted probability of producing more than one pair. By employing temporal multiplexing, allowing photons created in any one of, e.g., 50 time slots to be mapped onto a single final time window, the net efficiency for single-photon creation can be greatly enhanced, while minimizing the likelihood of unwanted multi-photon events. The benefit becomes even greater when intentionally trying to create states with many photons: the methods developed here could enable rate enhancements over five orders of magnitude (and for one experiment up to 12 orders!). A similar improvement in optical circuitry (with regard to size and stability) is realized using custom-fabricated waveguides written into low-loss glass. One key feature of this work is the collaboration with Israeli researcher Yaron Silberberg, who will develop the required photonic waveguide circuitry, and work with the group on the final set of applications. The technology of 'integrating' a large number of waveguides and optics such as beamsplitters and phase shifters into a tiny glass substrate (approximately cross 5 centimeter area) will provide enhanced stability and interference between multiple photons. Thus, the unique bi-national connection in this proposal enables the development and implementation of sophisticated quantum photonic systems well beyond those that have been possible to date, until now limited to only a few photons. Combining the new source with optimized photonic waveguide circuitry, the project will then investigate several interesting photon-based quantum effects, including potentially scalable optical quantum logic and quantum walks.