Optimal Control for Robust Ion Trap Quantum Logic

鲁棒离子阱量子逻辑的优化控制

• 批准号: 1801494
• 金额: --
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1801494
• 关键词: Optimal; Control; Robust; Ion; Trap

The use of trapped ions as an experimental medium for the realisation of quantum information protocol was established in 19951{3. The M lmer S rensen scheme 4;5 enabled the entanglement of 66 and then 147 qubits, and two qubit gate delities well above the threshold for fault tolerant computation8{10. Trapped ions are currently used in quantum simulations11;12, however in order to increase the scalability, and thus utility of these systems, both the scale of traps must be reduced and the speed of operations increased. The increased proximity of ions to their trap electrodes however increases heating rates in the system, whilst faster gate operation requires higher intensity laser elds, increasing o -resonant excitation and thus reducing gate delity. The aim of this project is to design and build a linear `blade' radio-frequency trap, and use it to investigate quantum gate protocol, robust under these conditions, through the use of optimal control techniques. The reduction of o -resonant transitions is usually achieved by operating within the Lamb-Dicke regime, where only carrier and rst order sideband transitions are considered to be signi cant. All multi-qubit gate operations involve entanglement between the internal state of an ion and a collective motional mode. Any motional heating therefore acts to decohere the nal state of the qubit. Reduced occupation of the motional state, by the increased detuning of Raman beams in the M lmer S renesen scheme, acts to minimise this source of in delity. Increased detuning however requires increased Rabi frequencies, which reduce the coupling strength to sideband transitions. Consequently, either higher intensity radiation, or longer interaction time, is required to implement the gate - both of which are undesirable. Operation outside the Lamb-Dicke regime enables stronger coupling to sidebands for a given laser intensity, which can thus reduce gate time, but increases coupling strength to unwanted transitions. By considering these transitions, optimal control designed pulse sequences, which suppress or negate the e ects of o -resonant driving, will be designed and realised experimentally. We plan to implement conventional entangling gates, and subsequently investigate the e ects of increasing Lamb-Dicke parameter. Experimental ndings will be fed back to improve the design of pulse sequences, and their resilience to the e ects of noise and heating will be optimised.

利用囚禁离子作为实现量子信息协议的实验介质是在19951{3]中建立的。M lmer S的Rensen方案4；5实现了66个量子比特的纠缠，然后是147个量子比特的纠缠，以及远高于容错计算阈值的两个量子比特门8{10。囚禁离子目前用于量子模拟11；12然而，为了增加可伸缩性，从而提高这些系统的实用性，必须减小陷阱的规模并提高操作速度。然而，离子与其陷阱电极的接近程度增加了系统中的加热速度，而更快的栅极操作需要更高强度的激光场，从而增加了O-共振激发，从而降低了栅极的灵敏度。这个项目的目的是设计和建造一个线性的‘刀片’射频陷阱，并利用它通过使用最优控制技术来研究在这些条件下具有健壮性的量子门协议。O共振跃迁的减少通常是通过在Lamb-Dicke区域内操作来实现的，其中只有载流子和一阶边带跃迁被认为是显著的。所有的多量子比特门操作都涉及到离子的内态和集体运动模式之间的纠缠。因此，任何运动加热都会在这里解码量子比特的NAL状态。在M-M-S方案中，通过增加拉曼光束的失谐，减少了对运动态的占据，从而最小化了这种不灵敏的来源。然而，失谐增加需要增加拉比频率，这降低了边带跃迁的耦合强度。因此，要么需要更高强度的辐射，要么需要更长的相互作用时间来实现门--这两种情况都是不可取的。在Lamb-Dicke区域之外运行，可以在给定的激光强度下实现对边带的更强耦合，从而可以减少选通时间，但增加对不需要的跃迁的耦合强度。通过考虑这些转变，最优控制设计的脉冲序列将被设计并实验实现，这些脉冲序列抑制或否定O谐振驱动的影响。我们计划实现传统的纠缠门，并随后研究增加Lamb-Dicke参数的影响。实验终端将被反馈以改进脉冲序列的设计，并且它们对噪声和加热的恢复能力将被优化。