Electron spin state manipulation in quantum dot circuits with engineered g-factor for quantum memory and communication applications

目前，人们对利用量子物体的性质进行量子计算和通信产生了广泛的兴趣。预计量子计算机在某些任务上比经典计算机更强大，例如，用于建模复杂的化学品，如药物，用于解决优化问题（例如航班时刻表），以及破解加密代码。量子通信保证了使用纠缠光子作为资源的各方之间绝对安全的信息传输，第三方的检查或操纵不会损害发送消息的安全性。量子物理学中的“不可克隆”定理从根本上禁止对这种连接进行克隆。光子是传输量子信息的理想量子实体，例如，在其偏振态中编码。另一方面，由于光子不容易相互作用，因此很难操纵和存储它们。这些都是构建长距离量子网络的必要功能。这些限制可以通过在光子和量子点（QD）中捕获的单电子自旋之间使用量子接口来缓解，因为电子自旋状态更容易使用NRC开发的最先进技术来存储，操纵和测量。从光子到电子的量子状态转移过程需要特别设计的量子状态参与该过程。特别地，价带空穴状态应该被平面内磁场分裂，而导带电子自旋向上和自旋向下状态应该保持简并，即具有相同的能量。在科学术语中，电子g因子（自旋分裂能量和磁场之间的比例系数）应该接近于零。在这种情况下，除了通过直接测量自旋之外，不可能知道哪一个电子自旋被创建。因此，自旋态的量子叠加可以由具有明确能量的光子产生。在这个过程中产生的电子态映射出光子的量子态。实现这种自旋-光子界面的第一步是实现g*~0的特殊量子点。这是拟议研究的主要目标。我们将开发由工程g因子材料制成的双量子点器件，并探索它们在光子和电子自旋之间进行量子信息传输的可行性。电子g因子将使用单自旋共振技术通过监测通过被调谐到所谓的自旋阻断机制的双量子点设备的电流来测量。在这种情况下，由于泡利不相容原理，电流被抑制，泡利不相容原理防止移动的电子从一个点隧穿到另一个点，如果它已经包含相同自旋的电子。自旋态的操纵将通过将短微波爆发和脉冲序列应用于量子点门来实现。在这个项目中，我们解决了一个更大的全球性活动的一个小而关键的组成部分，该活动旨在发展安全的量子网络。必要的和缺乏的组件是一个有效的自旋光子接口，这将有助于建立有效的量子存储器和中继器所需的量子网络中的纠缠分布。这项工作的结果将很容易被越来越多对量子技术感兴趣的初创公司和中心采用。

Currently, there is broad interest in harnessing properties of quantum objects for quantum computation and communication. Quantum computers are predicted to be exponentially more powerful than the classical counterparts for certain tasks, for example, for modeling complex chemicals like drugs, for solving optimization problems (e.g. flight schedules), and breaking encryption codes. Quantum communication promises absolutely secure information transfer between parties using entangled photons as a resource, whose inspection or manipulation by a third party cannot compromise the security of the message being sent. Eavesdropping on such a connection is fundamentally disallowed by the quantum physics law called “no-cloning” theorem.Photons are the ideal quantum entities for transferring quantum information encoded, for example, in their polarization states. On the other hand, because photons do not interact easily, it is hard to manipulate and store them. These are necessary functionalities for building long distance quantum networks. These restrictions can be eased by using a quantum interface between photons and single electron spins trapped in quantum dots (QD), because electron spin states are much easier to store, manipulate, and measure using demonstrated state of the art techniques developed at NRC.The process of quantum state transfer from a photon to an electron requires specially engineered quantum states to participate in the process. In particular, the valance band hole state should be split by an in-plane magnetic field, while conduction band electron spin up and spin down states should remain degenerate, i.e. have the same energy. In scientific terms, the electron g-factor (the proportionality coefficient between spin splitting energy and the magnetic field) should be close to zero. In this condition it is impossible to tell which of the electron spins is created, except through direct measurement of the spin. Therefore, a quantum superposition of spin states can be created by a photon of well-defined energy. The electron state created in this process maps out the photon quantum state. In other words, one bit of quantum information is transferred.The first step in achieving this spin-to-photon interface is to realize special quantum dots with g*~0. This constitutes the main goal of the proposed research. We will develop double quantum dot devices made from the engineered g-factor materials and explore their feasibility for quantum information transfer between photons and electron spins. The electron g-factor will be measured using single spin resonance techniques by monitoring current through a double quantum dot device tuned to the so-called spin-blockade regime. In this regime current is suppressed due to the Pauli exclusion principle, which prevents a mobile electron from tunneling from one dot to the other dot if it already contains an electron of the same spin. Manipulation of spin states will be achieved by applying short microwave bursts and pulse sequences to the QD gates.In this project we tackle a small but critical component of a greater worldwide activity directed onto the development of secure quantum networks. The necessary and lacking component is an effective spin to photon interface that would ease building efficient quantum memories and repeaters required for the distribution of entanglement in quantum networks. The results of this work will be easily adopted by a growing number of start-up companies and centers interested in quantum technologies.