Microwave devices based on inelastic Cooper pair tunneling

利用量子微波(即在电子电路中含有微波光子的量子光学)，已经解决了带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，人们只充分探索了量子微波的一种区域：腔(或电路)量子电动力学区域，即光子驻留在电谐振器中。我的研究计划的目标是开发另一种电路量子光学区域，即宽带区域，其中光子是巡回的，即紧凑的波包沿传输线传播。为此，我将把重点放在一种新的约瑟夫森结器件上，这种器件基于我开创的非弹性库珀对通过约瑟夫森结的隧道效应。这些器件的关键思想是将隧道库珀对的势能2 eV转移到一个或多个光子。正如我所发现的那样，这种光电荷相互作用过程非常多样，并且可以通过设计嵌入约瑟夫森结的线性电路来定制成多种器件，例如单光子或纠缠光子源、具有量子力学施加的最小噪声的放大器，或者单光子探测器，这是微波系统中仍然严重缺失的器件。与其他约瑟夫森量子器件相反，在其他约瑟夫森量子器件中，约瑟夫森结被用来产生非线性自由度，利用非弹性库珀对隧道效应中的约瑟夫森结作为强非线性驱动，利用简单的直流电压产生宽带纠缠微波辐射。这允许更宽的带宽和更高的工作频率，只受超导体的间隙限制。我的目标是揭示非弹性库珀对隧道器件的全部潜力，并使其实用。更确切地说，我想：-开发一个产生和检测巡回量子态的宽带量子微波设备工具箱，-将这些设备的频率范围从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，以便其中许多设备可以轻松部署在量子系统中，从而简化放大。一旦进行优化，这些设备将成为在单光子水平上加快涉及1 GHz到1 THz辐射的活动进展的宝贵工具。它们将作为经典控制电子学和高度相干量子比特之间的接口层，成为量子信息处理的关键组成部分。

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.