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。像经典位一样，量子位是一个两级系统，但具有在状态叠加中存在的有趣能力。这意味着它可以同时处于开局和关闭状态，如果我们考虑多个量子的量子系统，则具有深远的影响。该信息并非每个量子携带任何定义明确的信息，而是在其联合属性中编码。在量子力学中，量子位被描述为纠缠。挑战是找到利用量子现象的方法，例如叠加和纠缠，以构建能够执行在经典环境中无法实现的计算任务的量子计算机。一种非常自然的值是电子旋转。电子的自旋状态之间的能量差可以由磁场精确控制，并且使用电子电荷，也有可能隔离和操纵单个旋转。旋转Qubits之间纠缠的一种途径是通过将它们的电子波函数重叠的相互作用放置在近距离上。尽管这种方法对于少数Qubits是可行的，但依赖于直接邻居耦合的大规模量子处理器迅速不切实际。因此，在这里，我们提出了一种替代策略，该策略利用了有趣的量子机械效应，如果测量无法分解，则两个空间分离的量子位会纠缠。根据理论上表明，基于测量的纠缠可用于几个物理分离的Qubits，以建立所谓的图形状态。然后，通过对纠缠纠缠（称为单向量子计算）的单个量子位的测量序列来实现计算，该量子与基于标准电路的方法完全不同。在实践中，这也需要存在量子记忆的存在，其中存储量子信息以允许图形状态增长而不会失去现有纠缠的风险。在这里，我们建议使用固态实现，该实现非常适合此任务：同位素纯Si-28中的单一倍增剂。要制造设备，我们将使用最精确的硅掺杂剂技术：扫描隧道显微镜（STM）氢气抗性石器。在满足基于测量的纠缠协议的关键要求时，原子上精确的融合至关重要：固定性无法可区分性。制造的设备，我们将能够使用投影测量来操纵远程量的电子旋转并在远程量子之间进行纠缠。为此，我们将使用射频反射仪技术，使我们能够在时间尺度上执行这些任务的速度明显快于电子旋转寿命。一旦实现了纠缠产生，将使用超精细耦合将量子信息从电子转移到核自旋状态。该方法利用了SI中掺杂剂的10-100范围内的记录核自旋连贯性，并使我们能够生长纠缠的图状态。 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个Qubit处理器。理论研究将支持实验性工作，以进一步开发有效的远程网络的最有效策略，以考虑现实的实验参数，例如旋转倾向和信号丢失。