Hybrid Architectures for Quantum Repeaters

为了实现基于量子通信或量子互联网的全球互联网的目标，量子中继器将实现任意长距离的量子通信。量子中继器通过放大或纠缠交换在远端节点之间分配纠缠，只使用短程量子信道来扩展通信范围。混合量子中继器的工作原理是：首先，将存储在偏振编码光子量子比特（理想的长距离传输）中的量子信息传输到固态自旋量子比特（理想的存储和处理信息），其次，在自旋量子比特之间产生纠缠以建立通信信道。采用混合量子中继器代替全光方法具有许多优点，包括(i)通过电子电路中的电荷检测对入射光子进行稳健的预警，（ii）用于存储和处理量子信息的更长的量子比特相干时间，以及（iii）建立量子信道的纠缠协议理论上高达100%的效率。基于光学活性材料的量子点电路，如砷化镓、双层石墨烯和二维过渡金属二硫属化合物（TMDs），由于其直接带隙特性，是混合量子中继器实现相干光子到自旋转换的必要组成部分。该项目将在三个主要方面并行进行。首先，它将专注于设计砷化镓量子点电路，以有效地产生和限制光产生的电子-空穴对的自旋。其次，我们将开发和实现量子点中自旋量子比特的贝尔状态测量协议，这将允许两个不同的自旋通过将它们投射到四个贝尔状态之一来纠缠。与光子量子比特相比，这个想法的主要优点是，原则上，贝尔态测量失败不会使波函数崩溃，并且可以尝试另一次测量，直到它成功为止。最后，我们还将研究用于实现量子点电路的新型二维材料。材料的选择包括双层石墨烯、二硫化钼（MoS2）和二硒化钨（WSe2）。这些光学活性材料直到最近才开始被研究用于实现静电定义的量子点。NSERC对该项目的支持将通过在量子技术中增加一种新的信息传输方法以及更好地理解实现它的材料和设备要求，从而使科学界受益。此外，随着量子通信的进步，加拿大电信业和整个社会将在寻求远程量子通信方面拥有世界领先的优势。

Towards the goal of achieving a global internet network based on quantum communications, or quantum internet, quantum repeaters will enable quantum communications over arbitrarily long distances. Quantum repeaters extend the communication range by using only short-range quantum channels through amplification or entanglement swapping to distribute entanglement between distant end nodes. The principle of operation of a hybrid quantum repeater is based on, first, the transfer of quantum information stored in polarization encoded photonic qubits (ideal for travelling long distances) to solid state spin qubits (ideal for storing and processing information) and second, creating entanglement between spin qubits to establish the communication channel. Employing hybrid quantum repeaters instead of all-optical approaches offers numerous advantages including (i) robust heralding of the incoming photons by charge detection in the electronic circuit, (ii) longer qubit coherence times for storing and processing quantum information and (iii) theoretical up to 100% efficiency of the entanglement protocol to establish the quantum channel. Quantum dot circuits based on optically active materials, such as GaAs, bilayer graphene, and 2D transition metal dichalcogenides (TMDs), are a necessary component of the hybrid quantum repeater to achieve coherent photon-to-spin conversion due to their direct band gap character. The project will run on three main fronts in parallel. First, it will focus on the design of GaAs quantum dot circuits to efficiently create and confine spins from photo-generated electron-hole pairs. Second we will develop and implement Bell state measurement protocols for spin qubits in quantum dots, which will allow the entanglement of two different spins by projecting them onto one of the four Bell states. The main advantage of this idea compared to photonic qubits, is that in principle a failed Bell state measurement doesn't collapse the wave function and another measurement can be attempted until it succeeds. Finally, we will also investigate novel 2D materials for the realization of quantum dot circuits. The choice of materials include bilayer graphene, molybdenum disulfide (MoS2) and tungsten diselenide (WSe2). These optically active materials have only very recently started to be investigated for the implementation of electrostatically defined quantum dots. NSERC support to this project will benefit the scientific community by adding a novel information transfer approach in quantum technologies as well as by better understanding the material and device requirements to implement it. Additionally, with the advancement of quantum communications the Canadian telecommunication industry, and society in general, will have a world leading advantage in the quest for long range quantum communication.