Microwave devices based on inelastic Cooper pair tunneling

量子微波（即在电子电路中具有微波光子的量子光学）解决了光量子光学中的几个极其困难的问题，并探索了新的物理学。然而，到目前为止，只有一种量子微波机制得到了充分的探索：腔（或电路）量子电动力学机制，光子驻留在电谐振器中。 我的研究计划的目标是发展电路量子光学的另一个领域，宽带领域，其中光子是巡回的，即紧凑的波包沿沿着传输线传播。为此，我将重点介绍一类基于非弹性库珀对隧穿约瑟夫森结的新型约瑟夫森结器件。这些器件的关键思想是，隧穿库珀对的势能2 eV被转移到一个或多个光子。 正如我所发现的，这种光-电荷相互作用过程是非常通用的，可以通过设计嵌入约瑟夫森结的线性电路来定制各种各样的设备，例如单光子或纠缠光子的源，量子力学施加的最小噪声放大器，或者单光子探测器，微波领域仍然非常缺乏的设备。 类似于其他约瑟夫森量子器件，其中约瑟夫森结用于产生非线性自由度，非弹性库珀对隧穿中的约瑟夫森结用作从简单DC电压产生宽带纠缠微波辐射的强非线性驱动。这允许仅受超导体的差距限制的更宽的带宽和更高的操作频率。 我的目标是揭示非弹性库珀对隧穿器件的全部潜力，并使它们实际上有用。更准确地说，我想： - 开发宽带量子微波器件工具箱，用于产生和检测巡回量子态， - 将这些器件的频率范围从GHz扩展到低THz范围，以便与广泛的量子系统兼容， - 使这些设备易于使用，使它们中的许多可以很容易地部署在量子系统中，从而简化规模扩大。 一旦优化，这些设备将是一个有价值的工具，用于加速在1 GHz和1 THz之间的辐射活动的进展，在单光子水平。它们将成为量子信息处理的关键成分，作为经典控制电子和高度相干量子比特之间的界面层。

With quantum microwaves (i.e. quantum optics with microwave photons in electronic circuits) several extremely hard problems in quantum optics with light have been tackled and new physics been explored. However, so far only one regime of quantum microwaves has been fully explored: The cavity (or circuit) quantum electrodynamics regime, where photons reside in electrical resonators. The goal of my research program is to develop the other regime of circuit quantum optics, the wideband regime, where photons are itinerant, i.e. compact wave packets propagating along transmission lines. To do so I will focus on a new class of Josephson junction devices based on inelastic Cooper pair tunneling through Josephson junctions, which I have pioneered. The key idea of these devices is that the potential energy 2eV of a tunneling Cooper pair is transferred to one or more photons. As I have discovered, this light-charge interaction process is extremely versatile and can be tailored into a large variety of devices by engineering the linear circuit into which the Josephson junction is embedded, e.g. sources of single photons or entangled photons, amplifiers with minimal noise as imposed by quantum mechanics, or a single photon detector, a device still dearly missing in the microwave regime. Contrarily to other Josephson quantum devices, where the Josephson junction is used to produce nonlinear degrees of freedom, the Josephson junction in inelastic Cooper pair tunneling is used as a strongly nonlinear drive generating broadband entangled microwave radiation from a simple DC voltage. This allows for much wider bandwidths and higher operation frequencies only limited by the gap of the superconductor. My goal is to reveal the full potential of inelastic Cooper pair tunneling devices and making them practically useful. More precisely, I want to: - develop a toolbox of wideband quantum microwave devices generating and detecting itinerant quantum states, - extend the frequency range of these devices from the GHz to low THz range, in order to be compatible with a broad range of quantum systems, - make these devices simple to use, so that many of them can easily be deployed in quantum systems, thereby simplifying scale-up. Once optimized, these devices will be a valuable tool for accelerating progress in activities involving radiation between 1 GHz and 1 THz, at the single photon level. They will be an key ingredient for quantum information processing as an interface layer between classical control electronics and highly coherent qubits.