NIRT: Quantum-State Transfer Between Photons and Nanostructures

光子已被证明是对特殊量子态进行编码并通过自由空间或光纤传输它们的最有用的方法。对于局域量子态操作，光子不太有利，而良好局域的量子系统是可取的。在这方面，通常被称为人造原子的量子点特别有吸引力。这项研究旨在将光子的优点与人造原子的优点结合起来。主要目的是将单光子的偏振量子态转移到量子点中的激子上，反之亦然。预期的结果是：一种新的光波导中量子点定位技术，演示了具有本征透镜的微柱内单个量子点的单光子吸收和再发射，演示了单光子和单量子点之间的偏振量子态转移，以及在量子点和光子之间以及两个量子点之间产生纠缠。实现这些目标的第一个要求是光子和量子点之间的耦合必须是共振的，以便保持量子相位相干性。为此，将使用与入射光子和腔内量子点同时共振的光学腔。我们将探索两种新的方法来实现与量子点的强光学模式重叠。第一种是在含有光学透镜的微柱内使用量子点，通过使用锥形氧化层。第二个是开发一种技术，将单个量子点定位在光学微腔的中心。第二个要求是量子点必须是有效对称的，才能获得激子自旋简并。为此，将探讨磁场和/或应变对微柱的影响。第三个要求是，从量子点重新发射的光子应该能够与从样品表面反射的光子区分开来。为此，将使用迈克尔逊干涉仪，其中两个端镜被一个包含共振量子点的微腔和一个不包含共振量子点的微柱所取代。实现这些目标将是在量子态控制以及利用和理解纳米结构中的量子退相干方面向前迈出的重要一步。这项研究是基于加州大学圣巴巴拉分校材料、工程和物理系之间的密切合作。这一合作为年轻研究人员提供了一个极好的机会，让他们在量子(和经典)通信和信息处理以及纳米结构制造等重要课题上进行跨学科研究。实现这些目标将启动未来在量子信息存储和实施量子中继器方案(实现远程量子密码术)、量子纠错和量子网络方面的研究。

Photons have proven to be most useful for encoding special quantum states and for transmitting them through free space or optical fibers. For local quantum-state operations photons are less favorable and well-localized quantum systems are desirable. In this respect quantum dots, often referred to as artificial atoms, are particularly attractive. This research aims at combining the advantages of photons with those of artificial atoms. The main objective is to transfer the polarization quantum state of a single photon onto excitons in quantum dots and visa versa. The anticipated results are: a novel positioning technique for a quantum dot in the center of an optical waveguide, the demonstration of a single-photon absorption and reemission by a single quantum dot inside a micro-pillar with intrinsic lensing, the demonstration of the polarization quantum-state transfer between single photons and single quantum dots, and creating entanglement between a quantum dot and a photon and between two quantum dots. The first requirement to achieve the objectives is that the coupling between photons and quantum dots has to be resonant in order to preserve the quantum-phase coherences. For this optical-cavities resonant both with the incoming photon and the quantum dot inside the cavity will be used. Two novel ways of achieving a strong optical mode overlap with the quantum dots will be explored. The first is to use quantum dots inside micro pillars that containing optical lensing through the use of tapered oxidation layer. The second is to develop a technique to position a single quantum dot in the center of an optical micro cavity. The second requirement is that the quantum dots have to be effectively symmetric in order to obtain exciton spin degeneracy. For this magnetic fields and/or strain-induced effects on the micro-pillars will be explored. The third requirement is that the reemitted photon from the quantum dot should be distinguishable from photons reflected from the sample surface. For this a Michelson interferometer will be used where the two end mirrors are replaced by one micro-cavity containing a quantum dot on resonance and one micro-pillar containing no quantum dots on resonance. Reaching the objectives will be a major step forwards in quantum-state control and harnessing and understanding quantum decoherence in nano-structures. The research is based on a close collaboration between the Materials, Engineering and Physics Departments at the University of California Santa Barbara. This collaboration provides an excellent opportunity for young researchers to perform interdisciplinary research on important topics in quantum (and classical) communication and information processing and in nano-structure fabrication. Reaching the objectives will initiate future research in storage of quantum information and in implementing the quantum repeater scheme (enabling long-distance quantum cryptography), quantum error correction and quantum networks.