Spin Based Quantum Computation Using Photon Mediated Interactions

在量子网络中，信息是使用称为量子比特的量子力学对象来传输和处理的。这一革命性的计算模式实现了前所未有的信息处理能力，如牢不可破的加密代码和计算任务的指数加速。要实现这些非凡的能力，需要同时存储量子比特和创建长距离量子比特-量子比特相互作用的能力。被困在固体中的自旋为存储量子信息提供了一个非凡的系统，但这些自旋除非非常接近，否则不容易相互作用。光子为这个问题提供了一个有希望的解决方案，因为它们可以长距离传输，在相隔很长距离的自旋之间产生有效的相互作用。然而，长距离通信需要光学频率的光子，而自旋通常在微波频率范围内有共振。由于这种大的频率失配，光子通常不会与自旋相互作用。在这个项目中，该小组将使用与量子点中的单个自旋强耦合的光学腔来解决这个问题。空穴可以通过增强光与物质的相互作用来创建一个强大的有效的自旋-光子界面。这些增强的相互作用为光频光子在量子网络中耦合相隔很长距离的自旋开辟了可能性。该小组将使用耦合到光学腔的量子点来演示光子介导的自旋相互作用。量子点是一种纳米级的结构，其行为类似于人造原子。量子点可以捕获额外的电荷，表现为捕获的自旋量子比特。通过将量子点与空腔强烈耦合，该团队将开发一种名为量子晶体管的设备，它构成了复杂量子网络的基本构件。将探索利用该设备实现远距离量子逻辑操作的方法。这些结果最终可能使芯片集成固态量子设备成为远程量子网络的基石。一种新的基于自旋的量子信息处理方法将被开发出来，其中光子介导有效的自旋-自旋相互作用。这种方法的基本构件是自旋光子量子晶体管，它使单个自旋量子比特(量子比特)能够对光子应用量子逻辑操作。这种自旋光子晶体管将使用光子晶体腔中带电的砷化铟(InAs)量子点来实现。带电的点包含一个额外的电子或空穴，它提供了长相干时间的自旋自由度。通过将量子点耦合到光子晶体腔，有可能获得一个强大的光-物质界面，其中自旋的状态调制腔光谱。这项工作将对系统和潜在的退相干机制有更好的科学理解，并解决创建可扩展量子体系结构的实际器件设计和制造挑战。这将为基于自旋的量子信息处理提供一种独特的方法，这种方法具有许多重要优势，包括能够耦合任意自旋，在超快时间尺度上实现门操作，以及为量子网络创建长距离有效的相互作用。将研究能够在紧凑和可扩展的芯片集成设备中进行量子信息处理的新型设备。将解决对可扩展实施至关重要的主要器件设计和制造挑战，包括优化光子晶体中的光-物质相互作用，以及在空间和光谱上将量子点与谐振器模式对准。这为在半导体芯片上开发高度紧凑和可扩展的量子信息处理提供了一条直接的途径。这一能力将对信息技术产生革命性的影响，使计算速度成倍提高，无条件安全地通信，并使高精度传感器的运行远远低于经典的噪声限制。所开发的设备可能会在其他领域产生重大影响，如光电子学、非线性光学和自旋电子学。除了拟议的研究努力外，该研究计划还将支持对研究生和本科生的培训，并开发一个外展计划，为当地高中生创造跨学科的研究机会。

In a quantum network, information is transmitted and processed using quantum mechanical objects called qubits. This revolutionary computational paradigm enables unprecedented information processing capabilities such as unbreakable cryptographic codes and exponential speedup of computational tasks. To achieve these remarkable capabilities requires the ability to both store qubits and create qubit-qubit interactions over long distances. Trapped spins in solids offer a remarkable system for storing quantum information, but these spins cannot easily interact with each other unless they are in close proximity. Photons provide a promising solution to this problem because they can be transmitted over long distances to create effective interactions between spins that are separated by long distances. However, long distance communication requires photons at optical frequencies while spins usually have resonances in the microwave frequency ranges. Because of this large frequency mismatch, photons typically don't interact with spins. In this project, the group will use optical cavities strongly coupled to a single spin trapped in a quantum dot to solve this problem. Cavities can create a strong effective spin-photon interface by enhancing light-matter interactions. These enhanced interactions open up the possibility for optical frequency photons to couple spins separated by long distances for quantum networks. The group will demonstrate photon mediated spin interactions using quantum dots coupled to optical cavities. Quantum dots are nanoscale structures that behave as artificial atoms. A quantum dot can capture an additional charge that behaves as a trapped spin qubit. By strongly coupling the quantum dot to a cavity, the group will develop a device called a quantum transistor, which forms the basic building block for complex quantum networks. Methods to utilize this device to implement quantum logic operations over long distances will be explored. These results could ultimately enable chip-integrated solid-state quantum devices that form the building blocks for long distance quantum networks. A novel approach to spin-based quantum information processing where photons mediate effective spin-spin interactions will be developed. The fundamental building block for this approach is the spin-photon quantum transistor, which enables a single spin quantum bit (qubit) to apply quantum logic operations on a photon. This spin-photon transistor will be realized using a charged indium arsenide (InAs) quantum dot in a photonic crystal cavity. The charged dot contains an additional electron or hole that provides a spin degree of freedom with long coherence times. By coupling the quantum dot to a photonic crystal cavity, it is possible to attain a strong light-matter interface where the state of the spin modulates the cavity spectrum. This work will attain a better scientific understanding of the system and underlying decoherence mechanisms, and address practical device design and fabrication challenges for creating a scalable quantum architecture. This will provide a unique approach to spin-based quantum information processing that have many important advantages including the ability to couple arbitrary spins, implement gate operations on ultra-fast timescales, and create effective interactions over long distances for quantum networking. Novel devices that could enable quantum information processing in a chip-integrated device that is compact and scalable will be investigated. Major device design and fabrication challenges will be addressed that are crucial for scalable implementation including optimizing light-matter interactions in photonic crystals and aligning quantum dots spatially and spectrally with resonator modes. This could provide a direct pathway for developing highly compact and scalable quantum information processing on a semiconductor chip. This capability would have a revolutionary impact on information technology, enabling exponential faster computation, unconditionally secure communication, and high precision sensors that operate far below the classical noise limit. The devices developed could have major impact in other fields such as opto-electronics, nonlinear optics, and spintronics. In addition to the proposed research effort, the research program will support training of graduate and undergraduate students, and develop an outreach program to create interdisciplinary research opportunities for local high school students.