Nano-Electro-Mechanical Systems and Quantum Transport

Nano-electro-mechanics (NEMS) pave the way to the formidable task of observing quantum effects in large mechanical systems formed by millions of atoms. Reaching the quantum ground state of a nanomechanical oscillator consisting of millions of atoms would allow to study the weirdness of quantum mechanics in a new regime. Coupling a nanoresonator to a mesoscopic conductor is a promising strategy to manipulate the mechanical motion in quantum regime using single-electron transport.

In this topic, our main goal is to study the nonequilibrium and eventually quantum states of the nanoresonators coupled to quantum dots. For instance, we have shown that coupling a spin current to the bending of a suspended carbon nanotube can be used to control the vibrational state and cool the flexural mode close to the ground state.

Superconducting Josephson circuits and quantum circuits

Josephson tunneling junction is one of the most versatile element and with widespread use in quantum mesoscopic systems.

It is a nonlinear and almost ideal non-dissipative element, two crucial features that make it the optimal building block to engineer quantum coherent systems, as superconducting circuits, qubits and circuit Quantum-Electro-Dynamics. It is also integrated in other hybrid systems, as electromechanical resonators, optomechanical systems or Josephson photonics systems with voltage-biased Josephson junctions coupled to superconducting microwave cavities. Such systems are fascinating because of their complexity: they typically operate far from equilibrium and can be very strongly nonlinear, allowing us to explore a wide range of novel quantum dynamics. When the unavoidable interaction with the environment is taken into account, Josephson junctions with small capacitance have become the paradigmatic system for studying decoherence and dissipation of a quantum particle.

Our main objectives concern the theoretical study of the dissipative, non-equilibrium dynamics of tailored superconducting (and hybrid) circuits based on Josephson junctions.

Quantum dissipation and decoherence in 1D many-body systems: Josephson chains and qubit lattices

Superconducting circuits formed by many Josephson junctions or lattice of qubits pave the way for exploring the interplay between interaction and macroscopic quantum coherent effects. These elements can be compared to individual atoms forming crystal lattices but with the remarkable possibility of wiring up the elemental units in way to design the many-body interaction. For instance, they are the prototypical examples to study quantum phase transitions.

Furthermore, contrary to conventional classical atoms, these systems can preserve macroscopic quantum coherence on a certain time scale whose limit is dictated by the decoherence and dissipation due to the electromagnetic environment. In this topic, our main research issues are: (i) to study the phase-diagram of the quantum dissipative phase transition in Josephson chains with unconventional interaction with the environment and (ii) to study the decoherence dynamics of interacting qubits in special configurations with some topological constraints or geometrical frustrations.