Controlling Local Thermal States in Classical Many-Body Systems.

The process of thermalization in many-body systems is driven by complex interactions among subsystems and a surrounding environment. Here we lay the theoretical foundations for the active control of local thermal states in arbitrary nonreciprocal systems close to their equilibrium state. In particular we describe how to (i) force some part of the system to evolve according to a prescribed law during the relaxation process (i.e., thermal targeting probem), (ii) insulate some elements from the rest of the system, or (iii) synchronize their evolution during the relaxation process. We also derive the general conditions a system must fulfill in order that some parts relax toward a minimal temperature with a minimum energetic cost or relax toward a prescribed temperature with a minimum time. Finally, we consider several representative examples in the context of systems exchanging heat radiatively.

Conduction-Radiation Coupling between Two Closely Separated Solids.

In the theory of radiative heat exchanges between two closely spaced bodies introduced by Polder and van Hove, no interplay between the heat carriers inside the materials and the photons crossing the separation gap is assumed. Here we release this constraint by developing a general theory to describe the conduction-radiation coupling between two solids of arbitrary size separated by a subwavelength separation gap. We show that, as a result of the temperature profile induced by the coupling with conduction, the radiative heat flux exchanged between two parallel slabs at nanometric distances can be orders of magnitude smaller than the one predicted by the conventional theory. These results could have important implications in the fields of nanoscale thermal management, near-field solid-state cooling, and nanoscale energy conversion.

Photon Thermal Hall Effect.

A near-field thermal Hall effect (i.e., Righi-Leduc effect) in networks of magneto-optical particles placed in a constant magnetic field is predicted. This many-body effect is related to a symmetry breaking in the system induced by the magnetic field, which gives rise to preferential channels for the heat transport by near-field interaction thanks to the particle's anisotropy tuning.

Hyperbolic metamaterials as an analog of a blackbody in the near field.

We study the near-field heat exchange between hyperbolic materials and demonstrate that these media are able to support broadband frustrated modes which transport heat by photon tunneling with a high efficiency close to the theoretical limit. We predict that hyperbolic materials can be designed to be perfect thermal emitters at nanoscale and derive an upper limit for the heat flux due to hyperbolic modes.

Nanoscale heat flux between nanoporous materials.

By combining stochastic electrodynamics and the Maxwell-Garnett description for effective media we study the radiative heat transfer between two nanoporous materials. We show that the heat flux can be significantly enhanced by air inclusions, which we explain by: (a) the presence of additional surface waves that give rise to supplementary channels for heat transfer throughout the gap, (b) an increase in the contribution given by the ordinary surface waves at resonance, (c) and the appearance of frustrated modes over a broad spectral range. We generalize the known expression for the nanoscale heat flux for anisotropic metamaterials.

Energetic and optical consequences in isotropic curved space and time.

In numerous media (nonlinear material, moving dielectrics, superfluids, Bose-Einstein condensates, and others) and different in vacuo states (nontrivial quantum electrodynamics in vacuo) matter or vacuum fluctuations modify light propagation in the same way that an effective gravitational field does. This nonlinear optical behavior affects not only the energy paths but also the form of the energetic invariant. However, such a function plays a key role when we try to develop a phenomenological kinetic theory for participating media. I analyze how modification of light propagation transforms the energetic invariant and modifies its transport inside a participating medium. A semianalytical method is presented to solve the radiative transfer equation for any spherically symmetric problems.

Optical remote sensing inside an inhomogeneous axisymmetric medium: the absorption field measurement.

It is shown that the absorption field inside an inhomogeneous, rotationally symmetric medium with a spatially variable refractive index can be reconstructed by means of a tomographic technique. The classic Abel transform is extended to non-Euclidean optical media. The optical behavior of such a medium is described and, provided that the product of the refractive index with the radial distance is a monotonic function, an exact inverse formula is found. Both a numerical and an analytical test on a phantom function is carried out to prove the exactness of this formula. In contrast, when the assumption of a monotonic function is not true, it is shown that the reconstruction problem becomes subdeterminate because of the presence of annular regions, known as blind areas, inside of which no curved path reaches an extremum. The spatial localization and the size of these regions are related to the extrema of the index of refraction times the radial distance.