Grant: Discovery Grants Program - Individual

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.