Semiconductor Integrated Quantum Optical Circuits

应用量子规则而不是经典物理规则，对我们如何处理信息产生了很大的不同。一个经典的“位”数据可以有两个值中的一个：“0”或“1”。它的量子对应物，量子比特，可以处于一种状态，这是两个值的叠加，从同时拥有两个值的意义上说。这一点，再加上纠缠(爱因斯坦在远处的“诡异”行为)，可能会使量子计算机的性能远远超过目前的计算机。然而，制造这样一台机器非常困难；在控制大型量子系统的同时，将它们与环境隔离得足够好，以便能够进行有用的计算，这是一项具有挑战性的任务。目前，使用许多不同种类的硬件(囚禁离子、纳米开尔文温度下的原子、超导电路、硅波导中的单光子)，可以在几个量子比特的阵列上执行一些简单的量子算法。然而，对于所有这些系统来说，将这些演示器放大到有用的设备上存在着非常巨大的挑战。我们建议使用一种不同的技术来开发量子电路，即使用III-V半导体材料(GaAs、AlGaAs、InGaAs等)。我们的电路将使用光子和电子自旋作为量子比特，利用III-V材料的光学性质来执行量子操作。III-V半导体的一大优势是已经存在具有先进制造能力的成熟光电子技术，这将使我们能够将电路的所有元件放在一个微芯片上。有了这种级别的集成，我们的方法本质上是可扩展的。我们的五年目标是构建包含实现量子信息处理所需的所有基本构件的电路：用于产生光子量子比特的单光子源、量子比特之间的通信通道、量子逻辑门、由自旋量子比特组成的存储器和芯片上的单光子探测器。这种类型的电路可以构成未来量子计算机的基础，但它们也可以在大规模量子计算领域之外执行有用的量子功能。有了这种复杂程度，就有可能建造能够实现大规模安全量子通信网络的量子中继器。在量子计量学中也有应用，量子力学的性质可以用来获得超出经典物理强加的基本限制的精度。这里可能受益的潜在领域是磁性传感器和显微镜。为了实现这一集成量子技术的愿景，我们将不得不推动半导体物理和器件制造的最先进水平。在物理方面，我们预期的亮点包括展示对设备中核自旋的完全控制，在芯片上获得远程量子比特的纠缠，创建光子阻挡结构，其中单个光子的存在阻止更多的光子进入，以及在单量子尺度上发展对光-物质相互作用的控制。技术方面的目标同样具有挑战性，将包括调整量子点的属性以实现严格控制的发射属性，在指定位置生长点以并入光腔，以及高度可重复性的光刻以实现高效的电路性能。所有这些主题都将是我们目标的核心，并将在提案中得到解决；此外，它们可能对范围广泛的相关纳米级光子技术具有重要意义。

Applying the rules of quantum rather than classical physics makes big differences to how we can manipulate information. A classical 'bit' of data can have one of two values, '0' or '1'. Its quantum counterpart, the qubit, can be in a state which is a superposition of the two values, in the sense of having both values at the same time. This, along with entanglement (Einstein's 'spooky' action at a distance) could enable quantum computers to out-perform current computers by huge margins. However making such a machine is very difficult; it is challenging to control large quantum systems while simultaneously isolating them from their environment sufficiently well to be able to carry out a useful calculation. Currently, using a number of different sorts of hardware (trapped ions, atoms at nano-Kelvin temperatures, superconducting circuits, single photons in silicon waveguides), it is possible to perform some simple quantum algorithms on arrays of a few qubits. However, for all these systems, there are very significant challenges to scaling such demonstrators up into useful devices.We propose to develop quantum circuits using a different technology, III-V semiconductor materials (GaAs, AlGaAs, InGaAs etc). Our circuits will employ photons and electron spins as qubits, making use of the optical properties of the III-V materials to carry out the quantum operations. A big advantage of the III-V semiconductors is that a mature photonics technology with advanced fabrication capabilities already exists, which will enable us to put all the elements of a circuit on a single microchip. With this level of integration, our approach is intrinsically scalable. Our five year vision is to construct circuits containing all the basic building blocks required to achieve quantum information processing: single photon sources to generate photon qubits, communication channels between qubits, quantum logic gates, memories consisting of spin qubits, and on-chip single photon detectors.Circuits of this type could form the building blocks of future quantum computers, but they can also perform useful quantum functions outside the realm of large scale quantum computation. With this level of complexity, it is possible to build quantum repeaters that enable wide-scale secure quantum communication networking. There are also applications in quantum metrology, where the properties of quantum mechanics can be used to obtain precision beyond the fundamental limits imposed by classical physics. Potential areas that may benefit here are magnetic sensors and microscopy.To pursue this vision of an integrated quantum technology, we will have to push forward the state of the art in semiconductor physics and device fabrication. On the physics side, our expected highlights include demonstrating full control of the nuclear spins in a device, obtaining entanglement of remote qubits on a chip, creating photon blockade structures, where the presence of a single photon prevents any more from entering, and developing control of light-matter interactions on the scale of single quanta. The targets on the technology side are equally challenging and will include tuning of quantum dot properties to achieve tightly controlled emission properties, the growth of dots in defined positions for incorporation in optical cavities, and highly reproducible lithography to achieve efficient circuit performance. All these topics will be central to our goals and will be addressed within the proposal; in addition they have potential to be of significance for a wide range of related nanoscale photonic technologies.