Quantum transport and electron-phonon/electron-photon interaction
Nanoscale conductors coupled to localized resonators, such as microwave photon cavities or mechanical resonator, have become commonly studied systems. They combines electronic with photonic/phononic degrees of freedom on-chip. Compared to other mesoscopic systems, the innovative aspect here is the single-electron transport with its related phenomena (Coulomb blockade, quantum interference effects, shot noise, etc.). These systems turn out to be an ideal platform to study fundamental and theoretical problems of solids state physics - the electron-photon and the electron-phonon interaction - at the most elementary level including quantum coherence aspects. Such nanoelectronic devices with tailored functionalities are also promising for quantum technologies since they prospect the electric control of non-electronic excitations (photons or phonons).
Nonlinearity and fluctuations in mechanical resonators
Nanomechanical and micromechanical vibrational systems have been attracting much attention in recent years. They fill in the gap between the microscopic world of molecular vibrations and the world of macroscopic vibrational systems. They are archetypical systems for studying fundamental aspects of resonance including energy transfer, dissipation, and optimization of driving schemes. In the past, they have been studied mostly in the linear response regime. Only recently the nonlinear regime of mechanical resonators came into the focus of systematic research. Beyond being model systems for nonlinear dynamics, they bear the means for exploring, quantitatively, generic features of fluctuations (noise) in a driven system far away from thermal equilibrium.
Quantum dissipation and decoherence in many-body systems
Understanding the influence of the environment on the dynamics of physical quantum systems is important for the development of quantum-based technologies.
In the past, dissipation and decoherence dynamics for individual systems - as for instance a single spin coupled to a bath (spin-boson model) - have been extensively studied theoretically, whereas this issue has been relatively unexplored in many-body systems. Owing to recent experimental progress, the study of artificial quantum many-body systems (or synthetic quantum matter), has attracted great interest. Superconducting circuits made by Josephson junctions or qubits are one of the most remarkable experimental platforms. Such engineered systems have the important property that distinguishes them from correlated systems in solid state materials: their interaction with the environment cannot be neglected. A clear theoretical understanding of the effects of an environment on correlated quantum many-body systems is presently lacking. Although dissipation produces in general decoherence - with the net result of destroying quantum states on which the power of quantum computation is based - it can also have remarkably the opposite effect: it acts as a resource to obtain a purely coherent quantum dynamics. This is the basic idea underlying the study of engineered dissipation.
Topological superconducting systems
Topological superconducting systems have become of paramount interest because they have the potential to host exotic quasi-particles, as Majorana states, which can be used for quantum computation. At the same time, the continuous search for new types of topological quantum matter has recently led to the discovery of topologically nontrivial quantum states in conventional multiterminal Josephson junctions. These systems have turned out to be an ideal platform where synthetic topological materials can be engineered almost at will. In particular, multiterminal contacts embedding quantum dots host discrete so-called Andreev quantum states which can be coherently manipulated for quantum information processing.