Quantum spintronics using donors in isotopically engineered silicon

对材料制造和自旋控制技术的精细控制已经达到成熟，自旋电子学可以超越纯粹的经典效应，并开始充分利用叠加和纠缠的独特量子特性。量子自旋电子学的潜在应用包括量子信息处理器，包括通过巡回电子自旋传输量子信息，自旋系综内的单微波光子存储，以及利用纠缠产生根本性增强精度的新一代传感器。量子自旋电子学的关键要素包括自旋相干性的保持和高纯度纠缠的产生。通过这个合作研究项目，我们建议使用同位素工程硅中供体的电子和核自旋来解决这两个挑战。我们的初步实验表明，这种材料提供了最大的潜力，高纯度的纠缠和长的相干时间，和他们的潜在集成在传统的电子学是一个进一步的优势。通过我们的初步合作，我们已经证明了电子和核自旋之间的“伪纠缠”与硅中的P-施主在X波段（0.3 T）和6 K。我们已经使用我们在这些实验中获得的纠缠度来计算通过这种技术产生纯纠缠的阈值：例如移动到更高的磁场（>3.5T）和更低的温度（<4K）。我们拥有满足这些要求的主要仪器，并将作为该项目的一部分演示硅内纯自旋纠缠的受控产生。然后我们将开发保持纠缠的方法并了解自旋输运的影响。将硅同位素纯化为28 Si会使施主电子的自旋相干性显著提高到数十毫秒。然而，核自旋是一个强大的资源，相干电子自旋状态可以暂时存储和检索。我们已经证明了以这种方式使用核自旋作为量子存储器，产生的相干时间长达几秒钟。我们将了解自旋退相干的机制，并使用材料改进和动态解耦和纠错等主动技术，我们将推动固态中最长自旋相干时间的极限。我们将要研究的自旋系综能够以分布式状态存储多比特信息，类似于全息信息存储。我们将在我们最初的工作基础上，在一个系综中存储和检索100个相干弱微波激发，建立多模量子存储器，i）在低应用磁场下工作ii）低至单光子水平iii）能够存储相干量子态几秒钟。在整个项目中，我们将进行仪器和材料的迭代开发：由同位素工程材料实现的更长的相干时间将把我们推向仪器的极限，通过改进仪器，我们可以提取和理解材料的固有特性，以便进一步增强它们。在项目结束时，我们将在同位素工程硅中建立施主自旋，作为量子自旋电子学，并展示了量子自旋电子学器件的基本组成部分。

The exquisite control over materials fabrication and spin control techniques has reached a maturity where spintronics can go beyond purely classical effects and begin to fully exploit the unique quantum properties of superposition and entanglement. Potential applications arising from quantum spintronics range from quantum information processors, including the transmission of quantum information via itinerant electron spins, single microwave photon storage within spin ensembles, and new generation of sensors exploiting entanglement to yield fundamentally enhanced precision. Key ingredients for quantum spintronics include the preservation of spin coherence and the generation of high-purity entanglement. Through this collaborative research project, we propose to address both of these challenges using both the electron and nuclear spin of donors in isotopically engineered silicon. Our preliminary experiments show that such materials offer the greatest potential for high-purity entanglement and long coherence times, and their potential integration within conventional electronics is a further advantage.Through our initial collaboration, we have already demonstrated 'psuedo-entanglement' between the electron and nuclear spin associated with a P-donor in silicon at X-band (0.3 T) and 6K. We have used the fidelities which we achieved in those experiments to calculate thresholds for generating pure entanglement by this technique: for example moving to higher magnetic fields (>3.5T) and lower temperatures (<4K). We possess the major instrumentation to meet these requirements, and will demonstrate the controlled generation of pure spin entanglement within silicon as part of this project. We will then develop methods for preserving entanglement and understand the effect of spin transport.The isotopic purification of silicon to 28Si yields dramatic improvements in the donor electron spin coherence to tens of milliseconds. However, the nuclear spin is a powerful resource into which the coherent electron spin state may be temporarily stored and retrieved. We have demonstrated the use of the nuclear spin as a quantum memory in this way, yielding coherence times up to several seconds. We will understand the mechanisms for spin decoherence and, using materials refinement and active techniques such as dynamic decoupling and error-correction, we will push the limits of the longest spin coherences times in the solid state. The spin ensembles which we will be studying are capable of storing multiple bits of information in distributed states, analogous to holographic information storage. We shall build on our initial work, in which we stored and retrieved 100 coherent weak microwave excitations within an ensemble, to establish multimode quantum memories working i) at low applied magnetic fields ii) down to the single photon level iii) capable of storing coherent quantum states for several seconds.Throughout this project we will be performing an iterative development of instrumentation and materials: longer coherence times enabled by the isotopically engineered materials will push us to the limits of our instrumentation, and by improving the instrumentation we can then extract and understand intrinsic properties of the materials so that they may be further enhanced.At the end of the project we shall have established donor spins in isotopically engineered silicon as the forerunner material for quantum spintronics and demonstrated the essential components for a quantum spintronics device.