Collaborative Research: Optically Driven Quantum Dot Spins for Quantum Information: 2- and 3-Qubit Behavior with Nuclear Spin Narrowing

合作研究：光驱动量子点自旋获取量子信息：具有核自旋窄化的 2 和 3 量子位行为

• 批准号: 1413956
• 负责人: Lu Sham
• 金额: $ 21万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-15 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1413956&HistoricalAwards=false
• 关键词: Collaborative; Research; Optically; Driven; Quantum

Gordon Moore, the founder of Intel, was the first to note that the number of transistors per chip roughly doubled every two years (this is called Moore's Law). The corresponding volume per transistor had to decrease exponentially with time. Miniaturization would eventually lead to such a small number of electrons per transistor that the discriminable charging effect of the electrons in a transistor fails. The point where miniaturization destroys the transistor function is known as Moore's limit. This limit is imminent within the next generation of scientists and engineers. New avenues of progress beyond current technology must be sought. This research follows the approach of quantum technology to continue the evolution of information processing beyond Moore's limit. It works to develop the necessary foundational knowledge for an approach to devices, where the behavior of these devices is governed not by the usual rules that govern the aggregate properties of a large number of particles, but by the laws of quantum mechanics, which governs electrons in the atomic limit. Specifically, this project focuses on the study of optically controlled semiconductor quantum dots. A dot effectively traps one electron, which is manipulated by ultrafast pulses of light that enable terahertz control speeds without the complexities of metal contacts. The studies emphasize the isolation of the electron from the influence of the other electrons (known as the valence electrons) and the nuclei, in particular, which constitute the dot, and the networking of the target electrons in separate dots. Light is used to excite the valence electrons to control a single target electron and to entangle two target electrons, while shielding them from the effects of nuclear fluctuations. The primary intellectual merit is based on the scientific objectives of this three-year research program; produce quantum entangled states between two electron spins separated by a large distance, demonstrate a multi-quantum-bit high-speed logic gate, and explore the feasibility of using optical control of nuclear states to store and or process information. The broader impact includes developing the basic knowledge to advance the technology of information processing beyond Moore's limit via a highly interdisciplinary and collaborative research program, training and preparing the next generation of scientists and engineers for new challenges they will be facing, and facilitating efforts by both our universities to inform and educate the public and students about the importance of this quantum research to society's well-being, including how this research is training students in STEM areas in order to maintain a competitive work force. This research focuses on quantum information processing by ultrafast optical control of electron spins trapped individually in structurally defined semiconductor quantum dots (QDs). Numerous advances made possible by previous NSF support, have helped meet many of the milestones of quantum operations required by the Di Vincenzo criteria. Recent advances such as demonstration of the flying qubit and nuclear spin fluctuation freezing to extend the electron-spin coherence time and creation of high optical quality laterally positioned dots are fundamental to the quantum network approach to scaling up the system. The critical discovery of nuclear spin fluctuation freezing enables lengthening the coherence time of the qubit by over 2-3 orders of magnitude for time scales lasting longer than 1 second. This allows the time for a complete sequence of computational steps with the ultrafast control including error correction. The method consists in freezing out the fluctuations of the nuclear spins unavoidably present in QDs and temporally separates the decoherence abatement from the control operations, in contrast to the common but more limited and complex method of dynamic decoupling of the qubits being processed at the same time. Building on these achievements five experimental objectives to advance the frontier of scalable quantum information processing based on optical control of the spins will be accomplished: demonstrate a two-bit controlled not-gate and of a simple algorithm using a quantum dot molecule; demonstrate teleportation of information in a single photon qubit to a QD using spontaneous parametric (singe-photon) down conversion (SPDC) to produce the single photon source; produce an entangled state between a quantum dot spin and a spontaneously emitted photon (at 960nm) and convert it to the telecom wavelength around 1.55 microns; demonstrate heralded entanglement of two QD spins using photons.; and extend the work on nuclear spin fluctuation freezing to using optically detected NMR to more completely understand the underlying physics state of nuclei in the dot. The work is an interdisciplinary research effort in the physics of semiconductor nano-structures, high-precision coherent optical control, and spectroscopy of QDs. These studies are paralleled by the coherent transient time domain studies consistent with device applications and scalable architectures. The amelioration of the environmental problem (decoherence) lies in the coordinated theoretical and experimental treatment of the quantum correlated dynamics of the optically controlled electron spin and the nuclear spins in the QD through the hyperfine interaction without additional stochastic assumptions.The intellectual merit arises from the increasingly sophisticated understanding of the interaction effects between a microscopic system (the electron spins as the qubits) and a macroscopic system (the dot environment, control or measurement) within quantum theory. The broad bandwidth control of the quantum physics makes the QD system the high speed processing unit partner to the quantum memory device of trapped ions. The operating temperature of 4-10 K is above the milli-K required by gated dots and superconducting circuits and optical control avoids some of the connection problems.The broader impact is first in the development of highly trained people critical to the infrastructure of quantum technology, at all levels of higher education: postdocs, graduate and undergraduate students. The second broader impact is that the optical approach positions our research to play a key role in the transition from the electronic devices that currently drive the Moore?s law to the new paradigm of post CMOS era. The further miniaturization of the current devices that process classical information will reach the quantum barrier where devices operating on quantum information will take over. The future lies in a hybrid structure of classical devices for interface with human and quantum devices for information processing. The optical approach to quantum devices, based on the established III-V material with a large industrial infrastructure and optical sources and gating based on telecom technology, may provide a smooth transition to the hybrid structure.

英特尔的创始人戈登·摩尔（Gordon Moore）是第一个注意到每个芯片的晶体管数量大约每两年翻一番的人（这被称为摩尔定律）。每个晶体管的相应体积必须随时间呈指数级下降。小型化最终将导致每个晶体管的电子数量如此之少，以至于晶体管中电子的可辨别的充电效应失效。小型化破坏晶体管功能的临界点被称为摩尔极限。在下一代科学家和工程师中，这个极限即将到来。必须寻求超越现有技术的新进步途径。本研究遵循量子技术的方法，继续发展超越摩尔极限的信息处理。它致力于开发一种设备方法所需的基础知识，在这种方法中，这些设备的行为不是由控制大量粒子聚集特性的通常规则控制，而是由量子力学定律控制，量子力学定律控制原子极限下的电子。具体而言，本项目重点研究光控半导体量子点。一个点有效地捕获一个电子，这个电子被超快的光脉冲操纵，使太赫兹控制速度，而不需要金属接触的复杂性。这些研究强调了电子不受其他电子（称为价电子）和原子核的影响的隔离，特别是原子核，它们构成了点，以及目标电子在单独的点上的网络。光被用来激发价电子来控制一个目标电子，并使两个目标电子纠缠在一起，同时保护它们不受核波动的影响。主要的智力价值是基于这个为期三年的研究计划的科学目标；在距离较远的两个电子自旋之间产生量子纠缠态，演示多量子比特高速逻辑门，探索利用光控制核态存储和/或处理信息的可行性。更广泛的影响包括发展基础知识，通过高度跨学科和合作的研究计划，推动信息处理技术超越摩尔极限，培训和准备下一代科学家和工程师迎接他们将面临的新挑战，并促进我们两所大学的努力，告知和教育公众和学生关于量子研究对社会福祉的重要性。包括这项研究如何培养STEM领域的学生，以保持劳动力的竞争力。本研究的重点是通过超快光学控制在结构定义的半导体量子点（QDs）中单独捕获的电子自旋来处理量子信息。在以前NSF的支持下，许多进展成为可能，已经帮助满足了迪文森佐标准所要求的量子运算的许多里程碑。最近的进展，如飞行量子比特和核自旋涨落冻结的演示，以延长电子自旋相干时间，创造高光学质量的横向定位点，是量子网络方法扩大系统规模的基础。核自旋涨落冻结的关键发现使量子位的相干时间在持续时间超过1秒的时间尺度上延长了2-3个数量级。这允许时间为一个完整的序列计算步骤与超快控制，包括纠错。该方法包括冻结不可避免地存在于量子点中的核自旋的波动，并暂时将退相干衰减从控制操作中分离出来，与同时处理的量子比特的常见但更有限和复杂的动态解耦方法形成对比。在这些成果的基础上，将完成五个实验目标，以推进基于自旋光学控制的可扩展量子信息处理的前沿：展示一个两位控制的非门和一个使用量子点分子的简单算法；演示了利用自发参数（单光子）下转换（SPDC）将单光子量子比特中的信息隐形传态到量子点以产生单光子源；在量子点自旋和自发发射的光子（960nm）之间产生纠缠态，并将其转换为1.55微米左右的电信波长；用光子证明预示着两个量子点自旋的纠缠。并将核自旋涨落冻结的工作扩展到利用光学探测核磁共振更全面地了解点内原子核的潜在物理状态。这项工作是在半导体纳米结构物理学、高精度相干光学控制和量子点光谱学方面的跨学科研究工作。这些研究与与器件应用和可扩展架构相一致的相干瞬态时域研究并行。环境问题（退相干）的改善在于通过不附加随机假设的超精细相互作用对量子点中光学控制的电子自旋和核自旋的量子相关动力学进行协调的理论和实验处理。智力上的优点来自于对量子理论中微观系统（作为量子比特的电子自旋）和宏观系统（点环境、控制或测量）之间相互作用的日益复杂的理解。量子物理的宽频带控制使量子点位系统成为囚禁离子量子存储器件的高速处理单元伙伴。4-10 K的工作温度高于门控点和超导电路所需的毫K，光学控制避免了一些连接问题。更广泛的影响首先是培养对量子技术基础设施至关重要的训练有素的人才，包括各级高等教育的博士后、研究生和本科生。第二个更广泛的影响是，光学方法使我们的研究在从目前驱动摩尔？在后CMOS时代的新范式。当前处理经典信息的设备的进一步小型化将达到量子屏障，在量子信息上操作的设备将接管。未来是一种混合结构，经典设备用于人机界面，量子设备用于信息处理。量子器件的光学方法基于已建立的III-V材料，具有大型工业基础设施和基于电信技术的光源和门控，可以提供向混合结构的平稳过渡。