Nonequilibrium dynamics in nanoscale resonators driven by mesoscopic conductors

Abstract

In hybrid quantum circuits, different mesoscopic systems can be combined to harness advantages and properties of each constituent, facilitating the unraveling of new phenomena which surmount the usual paradigm of light-matter interaction. Specifically, they can exhibit complex behavior as they operate far from equilibrium, and strong nonlinear interactions can emerge. Furthermore, their open dynamics due to the unavoidable coupling to the environment can be tailored using engineered reservoirs. In this Thesis, I have addressed these fundamental aspects in three specific systems formed by mesoscopic conductors and quantum dots coupled to localized resonators.<br /><br />First, I have considered a solid-state implementation of a single-atom laser in a quantum-dot spin valve, where electronic spin is coupled to a harmonic oscillator. A spin-polarized current injected in the dot induces lasing, whereby energy is pumped with high efficiency into the resonator. This pumping mechanism rapidly leads to a breakdown of the widely employed rotating-wave approximation (RWA) without any requirement of ultrastrong light-matter coupling. Such RWA breakdown is associated with multistability of the resonator, characterized by multiple peaks in its Fock distribution and detectable with simple current measurements displaying telegraph dynamics.<br /><br />In a second work, I have examined a Cooper-pair splitter consisting of two quantum dots, each coupled capacitively to a local resonator and a common superconductor. I derived an effective Hamiltonian validated by numerical simulations, and I demonstrated that the process of cross-Andreev reflection can be used to pump nonlocally single photons between the two resonators or to simultaneously cool them into their ground state. The system has possible applications such as coherent heat-control, cooling with single-photon precision, and microwave photon buses.<br /><br />The third system that I studied consists of a Josephson junction in series with an electromagnetic resonator. When a voltage is applied to the junction, such that each Cooper pair can provide half the energy to generate a cavity photon, charge transport and photon emission can be dominated by effective inelastic tunneling of two Cooper pairs. The system displays a crossover from incoherent to coherent double Cooper-pair tunneling and can be further used as a single-photon source due to a form of photon-blockade effect.