Hybrid semiconductor-superconductor photonic quantum circuits

该项目的目的是实现一个量子光学器件的集成平台，用于演示半导体芯片上的CNOT功能。这意味着在所提出的情况下，实现单光子源，低损耗的单模波导结构和片上腔体与超导纳米线单光子探测器(SNSPD)相结合。这种结构的实现到目前为止还没有得到证实，它将是迈向光子量子技术微型化应用的重要一步。只有对集成环境中光子探测和产生过程的物理原理有了详细的了解，才能实现这一点。该平台由GaAs光波导和NbN纳米线组成，其中InAs量子点(QD)作为光发射体嵌入其中，NbN纳米线与这些光波导相耦合。除了实现波导、分束器、发射器和探测器的结构外，我们还必须详细地研究发射到波导中的耦合。对于目标功能，在不同的波导臂中产生的光子必须是不可区分的。因此，不同的共振激发过程必须与通过斯塔克位移将不同的量子点跃迁能量电调整为一个预先选择的能量相结合。具有不同分束比的波导耦合器的组合决定了光子集成电路。调整为单光子波长的波导型分束器是电路的核心，也将被用来通过双光子干涉测量来证明两个不同的InAs量子点的光子的不可区分性。在检查发射器的同时，还将研究探测器的实施。超导纳米线必须经过优化，才能在920 nm的量子点发射波长下，在GaAs片上实现接近100%的单光子探测效率。因此，必须根据不同的探测器结构来确定和分析纳米线的所有关键参数，如耦合效率、吸收、本征检测效率以及定时抖动，以便对其进行优化。此外，还必须开发SNSPD和读出电子器件，以便在集成系统中进行光子数分辨检测。最后，所有组件必须在一个芯片中实现，其中包括用于抑制共振QD激发的滤波元件，并将演示量子光学功能。这些具有挑战性的目标只有在这些高质量的单光子探测器、半导体材料和单光子源的制造和表征方面的领导小组目前的合作下才能实现。

The aim of this project is the realization of an integrated platform of quantum optical devices for the demonstration of a CNOT functionality on a semiconductor chip. This implies in the proposed case, the realization of single-photon sources, of low-loss single-mode waveguide structures and on-chip cavities combined with superconductor nanowire single-photon detectors (SNSPD). The realization of this architecture was not demonstrated so far and would be a major step towards a miniaturized application in the photonic quantum technologies. It can only be achieved in a detailed understand-ing of the physical principles of the photon detection and generation process in the integrated envi-ronment. The platform consists of GaAs waveguides where InAs quantum dots (QD) were embed-ded as light emitters and NbN nanowires are evanescent coupled to these waveguides.To realize this goal, different intermediate steps have to be performed. Next to the realization of the waveguide, splitter, emitter and detector structures, we have to study the emission coupling into the waveguide in detail. For the targeted functionality, the created photons in different waveguide arms have to be indistinguishable. Therefore, different resonant excitation processes have to be applied in combination with the electrical adjustment of the different QD transition energies to one pre-selected energy via the Stark shift. Combinations of waveguide couplers with different splitting rati-os determine the photonic integrated circuit. Waveguide beam splitters adjusted to the single photon wavelength are the core of the circuit and will as well be used to prove the indistinguishability of the photons of the two different InAs QDs by two-photon interference measurements. Parallel to the examination of the emitter, the detector implementation will be studied. The super-conducting nanowires have to be optimized to allow a close to 100% detection efficiency of the sin-gle photons at 920 nm wavelength of QD emission on GaAs wafers. Thus, all the key parameters of nanowire such as coupling efficiency, absorption, intrinsic detection efficiency, as well as timing jitter have to be determined and analyzed in detail in dependence of different detector configura-tions for their optimization. Additionally, the SNSPDs and the readout electronics have to be devel-oped to allow photon number resolving detection in integrated systems. Finally, all components have to be implemented in one chip including filter elements for suppression of the resonant QD excitation and the quantum optical functionality will be demonstrated. These challenging goals can only be realized by the present cooperation of the leading groups in the fabri-cation and characterization of these kinds of high quality single-photon detectors, semiconductor material and single-photon sources.