Photon Temporal Modes as a Quantum Information Resource

量子信息科学(QIS)承诺以传统(基于经典物理的)信息技术无法实现的方式来存储、传输和处理信息。QIS的成功可以通过新的计算和通信能力给技术和科学带来革命性的变化。在这些成为现实之前，仍需取得重大突破。人们普遍认为，最强大的量子计算将使用材料系统(原子或电子)进行。相比之下，通过网络(“量子互联网”)进行的量子通信将使用光(光子)进行。此外，专门的量子信息处理将使用光或光和相互作用原子的组合进行，例如，根据需要构建信号中继器，以扩大更长距离的量子通信范围。该项目将开发一种激进而实用的新方法来使用光子来编码量子信息。光束中的光子具有四种不同的特性，其中任何一种都可以用于编码量子信息：偏振(例如，垂直或水平)、光束轮廓的二维(空间形状)和时间形状(光脉冲期间亮度的时间变化)。为了充分利用光在量子网络中传输信息，必须能够根据与这些属性中的每一个相关联的状态来操纵和分类光束。虽然以前已经开发出偏振和空间光束轮廓作为对光子上的量子信息进行编码的手段，但光子的时间形状在很大程度上没有被认为是一种重要的潜在技术。该项目致力于通过开发使用光子时间形状对信息进行编码的方法来完成基于光子的QIS的“工具包”。这种方法的预期好处在于：1)它允许在单个光子上编码超过1比特的信息，2)编码方法对在长光纤中传输时发生的光变化具有健壮性，3)该方法与基于原子的量子光存储器很好地接口，该存储器将用于未来的量子互联网建设。控制量子系统在科学和信息技术、计量学、量子化学和纳米力学中有着广泛的兴趣。光学技术和基于量子光学的信息科学提供了将研究与科学教育相结合的绝佳机会。为了提高非理科专业普通科学教育的质量，P.I.于2010年在俄勒冈大学共同创立了科学素养计划(SLP)，并担任该计划的联席主任。SLP为许多担任科学素养课程联合导师的研究生和本科生提供了指导机会。他开发并教授了一门SLP课程，即面向所有人的量子物理，向非理科专业的学生介绍量子信息科学，使用主动学习技术来吸引学生。他将继续担任SLP联席董事。从更技术的角度来看，该项目将发展这样的想法，即在QIS中，光子的时间模式(TM)，以及更广泛的光场，应该与偏振模式和横向模式同等看待。TM是波包模式，具有相同的载波频率、极化和横向空间模式，并且占据相同的时间区间，但仍是时间正交的。为了能够开发用于量子比特和量子比特的TMS，需要的核心技术是量子脉冲门(QPG)，它将实现近乎100%的场正交TMS的空间分选。基于他们最近提出的时间模式干涉测量(TMI)方法，研究人员将展示利用单光子时间模式的场正交性的完整量子信息框架的元素。这三个要求--资源状态的生成、TMS的目标和有效操作、以及它们的检测和表征--可以用现有技术来实现。特别是，研究人员将从实验和理论上研究使用量子脉冲门器件作为基本构建块来实现单量子比特量子逻辑运算(Pauli-X、-Y和-Z门；以及移相门)的方法。他们还将证明，通过改变设备内部的相移，QPG可以充当一个实时可控的开关，具有时间模式选择性。此外，他们将使用一种新形式的量子状态层析成像来演示验证这种门操作的保真度的方法，这种方法可以直接以TM为基础确定量子态。

Quantum information science (QIS) promises means for storing, transmitting, and processing information in ways not achievable using conventional (classical-physics-based) information technology. Success in QIS could revolutionize both technology and science through new computation and communication capabilities. Major breakthroughs are still needed before these can become reality. It is generally recognized that the most powerful quantum computation will take place using material systems (atoms or electrons). In contrast, quantum communication across a network (a "Quantum Internet") will take place using light (photons). In addition, specialized quantum-information processing will take place using light or a combination of light and interacting atoms, as needed, for example, to construct signal repeaters for extending the range of quantum communication over longer distances. This project will develop a radical, yet practical, new approach to using photons to encode quantum information.Photons in a light beam have four distinct properties, any of which could be used to encode quantum-information: polarization (e.g., vertical or horizontal), two-dimensions of beam profile (spatial shape), and temporal shape (variation in time of brightness during a light pulse). In order to fully utilize light for transmitting information in a quantum network, it is necessary to be able to manipulate and sort a beam of light according to the states associated with each of these properties. While polarization and spatial beam profiles have been previously developed as means for encoding quantum information on photons, the temporal shape of photons has gone largely unrecognized as an important potential technique. The project endeavors to complete the "tool kit" for photon-based QIS by developing means to use photon temporal shape to encode information. This approach has predicted benefits in that 1) it allows more than one bit of information to be encoded on a single photon, 2) the encoding method is robust against the alterations of light that occur while traveling in a long optical fiber, and 3) the method nicely interfaces with atom-based quantum-light memories, which will be used in the future construction of a Quantum Internet. Controlling quantum systems is of broad interest in science and information technology, metrology, quantum chemistry, and nano-mechanics. Optical technology and quantum-optics-based information science offer excellent opportunities to integrate research with science education. To improve the quality of general science education for non-science majors, the P.I. cofounded in 2010 the Science Literacy Program (SLP) at the University of Oregon, and serves as its Co-Director. The SLP has provided mentored instructional opportunities to many graduate students and undergraduate science majors serving as co-instructors in science literacy courses. He developed and taught an SLP course, Quantum Physics for Everyone, which presented quantum information science to non-science majors, using active learning techniques to engage the students. He will continue serving as SLP Co-Director.From a more technical perspective, the project will develop the idea that in QIS, temporal modes (TMs) of photons, and more generally light fields, should be viewed on an equal footing with polarization and transverse modes. TMs are wave-packet modes that have the same carrier frequency, polarization, and transverse spatial mode, and occupy the same time bin, but yet are temporal orthogonal. To enable the development of TMs for use as qubits and qudits, the central needed technology is the quantum pulse gate (QPG), which will implement a near-100% efficient spatial sorting of field-orthogonal TMs. Based on their recently proposed method of temporal-mode interferometry (TMI), the researchers will demonstrate the elements of a complete quantum information framework that employs field orthogonality of single-photon temporal modes. The three requirements - generation of resource states, the targeted and efficient manipulation of TMs, and their detection and characterization - can be fulfilled with current technology. In particular, the researchers will study, experimentally and theoretically, means for implementing single-qubit quantum-logic operations (Pauli-X, -Y, and -Z gates; and phase-shift gate) using the quantum pulse gate device as the basic building block. They will also demonstrate that the QPG can act as a real-time controllable switch that is temporal-mode selective, by varying a phase shift internal to the device. In addition, they will demonstrate means for verifying the fidelity of such gate operations, using a new form of quantum-state tomography, which can determine the quantum state directly in a TM basis.