Optimal control for robust ion trap quantum logic

稳健离子阱量子逻辑的优化控制

• 批准号: EP/P024890/1
• 负责人: Richard Thompson
• 金额: $ 141.52万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FP024890%2F1
• 关键词: Optimal; control; robust; ion; trap

Minuscule objects that follow the laws of quantum mechanics have the promise of carrying out delicate tasks fundamentally better than macroscopic objects that are bound by the laws of Newtonian classical mechanics. The superposition principle permits individual quantum mechanical objects to follow multiple trajectories in parallel, and pairs (or larger collections) of such objects can be entangled with each other, such that a measurement on one object affects the properties of the other objects even if they are far apart. The superposition principle and entanglement provide the basis for applications like precision metrology or quantum computation that are expected to revolutionise our technology, just like the steam engine or the advent of electricity has done in the past.The explicit utilisation of these quantum mechanical effects for useful applications, however, requires extremely accurate control over quantum objects and their interaction with their surroundings. Trapped ions are one of the leading systems in this context. Selected energy levels of an ion define a qubit, which is the elementary unit of a quantum computer, just like a classical computer is comprised of many bits. Confined by electric and magnetic trapping fields, ions can be manipulated with laser beams, and the collective motion of strings of ions enables the exchange of information between several qubits. For this to work with high accuracy it is typically required to cool the ions to a temperature close to absolute zero. Once such a temperature has been reached, one makes use of the fact that any manipulation of the ions changes their motional state in order to implement logical operations that define the elementary building blocks of a quantum algorithm.Since the ions' motion is easily heated by its room-temperature environment, the intentionally induced changes in the motional state can be accompanied by uncontrolled heating processes, and any deviation from the desired change in motional state results in reduced accuracy of the operations being implemented. The goal of the present project is the development and experimental implementation of laser control of trapped ions that achieves desired operations with high accuracy and robustness in the presence of undesired heating and other experimental imperfections.In a strong collaboration between theory and experiment, control sequences will be developed and tested in a novel ion trap whose parameters can be varied over a wide range. The ability to tune the strength of the interaction between qubits and motion (the Lamb-Dicke parameter) and the strength of thermal effects will allow us to identify the control strategies that deal with each type of imperfection in an ideal fashion. Most current experiments are conducted with a rather weak interaction between qubits and motion, but we aim at the realisation of logical operations between qubits that interact strongly with the motion. The increased manipulation speed that comes with the strong interaction increases the number of logical operations that can be implemented within the limits imposed by finite decoherence time, and as such will help us to move from proof-of-principle experiments to a practical application.The immediate goal of our work is the improvement in the control of trapped ions for quantum computing, but the advanced control techniques we will develop directly apply to any type of coherent manipulation of trapped ions. Since strong interactions between qubits are beneficial for fast information transfer but challenging for the implementation of accurate manipulations in essentially any quantum system, the control techniques to be developed are expected to find application in a broad range of other systems in quantum optics and quantum electronics.

遵循量子力学定律的微小物体有望比受牛顿经典力学定律约束的宏观物体更好地执行微妙的任务。叠加原理允许单个量子力学物体并行遵循多个轨迹，并且此类物体对（或更大的集合）可以彼此纠缠，使得对一个物体的测量会影响其他物体的属性，即使它们是相隔很远。叠加原理和纠缠为精密计量或量子计算等应用提供了基础，这些应用有望彻底改变我们的技术，就像过去的蒸汽机或电力的出现一样。这些量子力学效应的明确利用然而，应用需要对量子物体及其与周围环境的相互作用进行极其精确的控制。捕获离子是这方面的主要系统之一。离子的选定能级定义了一个量子位，它是量子计算机的基本单位，就像经典计算机由许多位组成一样。在电场和磁场捕获场的限制下，可以用激光束操纵离子，并且离子串的集体运动使得多个量子位之间能够交换信息。为了使其高精度工作，通常需要将离子冷却到接近绝对零的温度。一旦达到这样的温度，人们就会利用离子的任何操纵都会改变其运动状态这一事实来实现定义量子算法的基本构建块的逻辑运算。因为离子的运动很容易被加热在室温环境下，故意引起的运动状态变化可能伴随着不受控制的加热过程，并且与所需的运动状态变化的任何偏差都会导致所实施的操作的准确性降低。本项目的目标是开发和实验实施捕获离子的激光控制，在存在不需要的加热和其他实验缺陷的情况下，以高精度和鲁棒性实现所需的操作。在理论和实验之间的紧密合作中，控制序列将在新型离子阱中进行开发和测试，其参数可以在很宽的范围内变化。调整量子位和运动之间相互作用的强度（兰姆-迪克参数）以及热效应强度的能力将使我们能够确定以理想方式处理每种类型缺陷的控制策略。目前大多数实验都是在量子位和运动之间的相互作用相当弱的情况下进行的，但我们的目标是实现与运动强烈相互作用的量子位之间的逻辑运算。强交互带来的操作速度的提高增加了在有限退相干时间所施加的限制内可以实现的逻辑运算的数量，因此将帮助我们从原理验证实验转向实际应用。我们工作的直接目标是改进量子计算中捕获离子的控制，但我们将开发的先进控制技术直接适用于捕获离子的任何类型的相干操纵。由于量子位之间的强相互作用有利于快速信息传输，但对于在任何量子系统中实现精确操作都具有挑战性，因此待开发的控制技术预计将在量子光学和量子电子学的其他系统中得到广泛应用。

项目成果

Characterisation and control of trapped-ion qubit

俘获离子量子位的表征和控制

• 发表时间: 2022
• 作者: Lee Chungsun

Population dynamics in sideband cooling of trapped ions outside the Lamb-Dicke regime

• DOI: 10.1103/physreva.99.013423
• 发表时间: 2018-09
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: M. Joshi;P. Hrmo;V. Jarlaud;F. Oehl;R. Thompson

Quantum coherence in trapped ions

被捕获离子的量子相干性

• 发表时间: 2022
• 作者: Corfield Oliver

Measurement-based ground state cooling of a trapped ion oscillator

基于测量的俘获离子振荡器基态冷却

• DOI: 10.48550/arxiv.2208.05332
• 发表时间: 2022
• 作者: Lee C

Coherent fluctuation relations: from the abstract to the concrete

• DOI: 10.22331/q-2019-02-25-124
• 发表时间: 2019-02-25
• 期刊: QUANTUM
• 影响因子: 6.4
• 作者: Holmes, Zoe;Weidt, Sebastian;Mintert, Florian
• 通讯作者: Mintert, Florian