Heat flux exchanged between two hot bodies at subwavelength separation distances can exceed the limit predicted by the blackbody theory. However, this super-Planckian transfer is restricted to these separation distances. Here we demonstrate the possible existence of a super-Planckian transfer at arbitrary large separation distances if the interacting bodies are connected in the near field with weakly dissipating hyperbolic waveguides. This result opens the way to long-distance transport of near-field thermal energy.

I will present our studies of the Casimir-Lifshitz interaction in a system consisting of two different one-dimensional dielectric lamellar gratings at two different temperatures, immersed in an environment having a third temperature [1]. The calculations are based on the knowledge of the scattering operators, obtained through the Fourier modal method. It will be shown that the interplay between non-equilibrium effects and geometrical periodicity offers a rich scenario for the manipulation of the force. Finally I will present our latest results on a sphere-grating system at equilibrium [2]. 

Heat transfer or between bodies and Casimir-Lifshitz (CL) interactions between them share in common the fact that they can be characterized by the electromagnetic response of these bodies. It has been shown, in the framework of a general theory [1], that the knowledge of the so-called scattering matrix of an object is sufficient to perform its thermal of Casimir interaction with another body. Among the different configurations studied experimentally, those involving gratings and spheres are of special interest. From the theoretical point of view, when one is equipped with the scattering matrix based theory [1], it is “in principle” straightforward to compute the heat transfer or the CL force. In reality, it turns out that computing the S-matrices is not that easy, especially when it has to be determined for a huge number of modes. It is thus of fundamental importance to use extremely efficient methods. We will discuss the different families of existing approaches for diffraction gratings and examine in more details one of the most efficient ones: the Fourier Modal Method that we used recently to compute CL interactions between gratings out of thermal equilibrium [2] and between a sphere and a grating [3].

We show that the electromagnetic forces generated by the excitations of a mode in graphene-based optomechanical systems are highly tunable by varying the graphene chemical potential, and orders of magnitude stronger than usual non-graphene-based devices, in both attractive and repulsive regimes. We analyze coupled waveguides made of two parallel graphene sheets, either suspended or supported by dielectric slabs, and study the interplay between the light-induced force and the Casimir-Lifshitz interaction. These findings pave the way to advanced possibilities of control and fast modulation for optomechanical devices and sensors at the nano- and microscales.

We study the functioning of a three-level thermal machine when acting on a many-qubit system, the entire system being placed in an electromagnetic field in a stationary out-of-thermal-equilibrium configuration. This realistic setup stands between the two so-far-explored cases of single-qubit and macroscopic object targets, providing information on the scaling with system size of purely quantum properties in thermodynamic contexts. We show that, thanks to the presence of robust correlations among the qubits induced by the field, thermodynamic tasks can be delivered by the machine both locally to each qubit and collectively to the many-qubit system: This allows a task to be delivered also on systems much bigger than the machine size.

We propose a quantum Otto cycle based on the properties of a two-level system in a realistic out-of-thermal-equilibrium electromagnetic field acting as its sole reservoir. This steady configuration is produced without the need of active control over the state of the environment, which is a noncoherent thermal radiation, sustained only by external heat supplied to macroscopic objects. Remarkably, even for nonideal finite-time transformations, it largely over-performs the standard ideal Otto cycle and asymptotically achieves unit efficiency at finite power.

We will discuss the behavior of one or more elementary quantum systems (atoms, molecules, quantum dots,etc) interacting with a stationary, simple and rich electromagnetic environment out of thermal equilibrium. Particularattention will be devoted to the new features that this system offers toward the possibility to manipulatecollective atomic states and leading to improved performances in: creation and protection of entanglement,quantum thermal machines, transport of excitations.