Measurement-based entanglement of single-dopant As spin qubits

基于测量的单掺杂剂 As 自旋量子位的纠缠

• 批准号: 2723776
• 金额: --
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2723776
• 关键词: Measurement; based; entanglement; single; dopant

The elementary unit of quantum information is the quantum bit or qubit. Like the classical bit, the qubit is a two-level system but with the intriguing ability to exist in a superposition of states. This means it can be in the on and off state at the same time which has profound implications if we consider quantum systems of more than one qubit. Instead of each qubit carrying any well-defined information of its own, the information is encoded in their joint properties. In quantum mechanics, the qubits are described as being entangled. The challenge is to find ways to harness quantum phenomena such as superposition and entanglement to construct a quantum computer that is able to perform computational tasks that are unattainable in a classical context.A very natural qubit is the electron spin. The energy difference between spin states of an electron can be precisely controlled by magnetic fields and, using the electron's charge, it is also possible to isolate and manipulate individual spins electrically. One route to achieve entanglement between spin qubits is to use the interaction of their electron wavefunction overlap by placing them in close proximity. While such an approach is feasible for a small number of qubits, a large-scale quantum processor which relies on direct nearest neighbour coupling becomes rapidly impractical. Here we therefore propose an alternative strategy which makes use of an intriguing quantum mechanical effect by which two spatially separated quantum bits become entangled if a measurement cannot tell them apart.As has been shown theoretically, measurement-based entanglement can be used to couple large numbers of physically separated qubits, building up so-called graph states. Computation is then achieved by a sequence of measurements on individual qubits that consumes the entanglement - known as one-way quantum computation - which is entirely different from the standard circuit-based approach. In practise this also requires the presence of a quantum memory where quantum information is stored to allow graph-state growth without the risk of losing existing entanglement. Here we propose to use a solid-state implementation which is ideally suited to this task: single As-dopants in isotopically pure Si-28.To fabricate the devices, we will use the most precise silicon dopant incorporation technique available: scanning tunnelling microscopy (STM) hydrogen resist lithography. The atomically precise incorporation of individual As-dopants is essential in satisfying a key requirement of the measurement-based entanglement protocol: qubit indistinguishability.Having fabricated the devices, we will be able to manipulate the electron spins of the As-dopants and create entanglement between remote qubits using projective measurements. For this we will be using radio-frequency reflectometry techniques which allows us to perform these tasks on a timescale significantly faster than electron spin lifetimes. Once entanglement generation has been achieved, hyperfine coupling will be used to transfer the quantum information from the electron to the As nuclear spin states. This approach takes advantage of record nuclear spin coherence, in the 10-100 second range, of dopants in Si and allows us to grow the entangled graph state. Moreover, since the As nucleus has a non-zero electric quadrupole moment and a four dimensional Hilbert space we will be able to control the nuclear spins electrically and store and control the equivalent of two qubits in each dopant.For a proof-of-principle demonstrator we will entangle four spatially separated devices, each consisting of two As-dopant atom qubits with all-to-all qubit connectivity, equivalent to a 16-qubit processor. The experimental efforts will be supported by theoretical studies to further develop the most efficient strategies for growing a resilient remote network taking into account realistic experimental parameters such as spin dephasing and signal loss.

量子信息的基本单位是量子位或量子位。与经典比特一样，量子比特是一个两能级系统，但具有以状态叠加存在的有趣能力。这意味着它可以同时处于开启和关闭状态，如果我们考虑多个量子位的量子系统，这将产生深远的影响。每个量子位不是携带其自己的任何明确定义的信息，而是将信息编码在它们的联合属性中。在量子力学中，量子位被描述为纠缠的。我们面临的挑战是找到利用叠加和纠缠等量子现象来构建量子计算机的方法，该计算机能够执行在经典背景下无法实现的计算任务。一个非常自然的量子位是电子自旋。电子自旋态之间的能量差可以通过磁场精确控制，并且利用电子的电荷，还可以以电方式隔离和操纵单个自旋。实现自旋量子位之间纠缠的一种途径是将它们紧密放置，利用电子波函数重叠的相互作用。虽然这种方法对于少量量子位是可行的，但依赖于直接最近邻耦合的大规模量子处理器很快就变得不切实际。因此，在这里，我们提出了一种替代策略，利用一种有趣的量子力学效应，如果测量无法区分两个空间分离的量子比特，它们就会纠缠在一起。正如理论上所表明的，基于测量的纠缠可以用于耦合大数物理上分离的量子位，建立所谓的图状态。然后通过对消耗纠缠的各个量子位进行一系列测量来实现计算 - 称为单向量子计算 - 这与基于标准电路的方法完全不同。在实践中，这还需要存在量子存储器，其中存储量子信息以允许图状态增长，而不会有丢失现有纠缠的风险。在这里，我们建议使用非常适合此任务的固态实现：同位素纯 Si-28 中的单一 As 掺杂剂。为了制造这些器件，我们将使用可用的最精确的硅掺杂剂掺入技术：扫描隧道显微镜（ STM）氢抗蚀光刻。单个砷掺杂剂的原子精确掺入对于满足基于测量的纠缠协议的关键要求：量子位不可区分性至关重要。制造完这些器件后，我们将能够操纵砷掺杂剂的电子自旋并在它们之间产生纠缠。使用投影测量的远程量子位。为此，我们将使用射频反射测量技术，该技术使我们能够在比电子自旋寿命快得多的时间尺度上执行这些任务。一旦实现了纠缠生成，超精细耦合将用于将量子信息从电子转移到 As 核自旋态。这种方法利用了硅中掺杂剂在 10-100 秒范围内创纪录的核自旋相干性，使我们能够生长纠缠图态。此外，由于 As 核具有非零电四极矩和四维希尔伯特空间，我们将能够以电方式控制核自旋，并存储和控制每个掺杂剂中两个量子位的等效值。对于原理验证在演示器中，我们将纠缠四个空间上分离的设备，每个设备由两个具有全量子位连接的 As 掺杂原子量子位组成，相当于一个 16 量子位处理器。实验工作将得到理论研究的支持，以进一步开发最有效的策略来发展弹性远程网络，同时考虑到自旋相移和信号丢失等现实实验参数。