Adiabatic Thermal Radiation Pumps for Thermal Photonics

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an instantaneous scattering matrix approach to unveil the critical role of wave interference in radiative heat transfer. We find that appropriately designed adiabatic pumping cycling near diabolic singularities can dramatically enhance the efficiency of the directional energy transfer. We confirm our results using a realistic electronic circuit setup.

Figure 1

Proposed implementations of our thermal radiation pumping scheme. (a) A nanophotonic structure consisting of three single-mode resonators. The resonant frequencies of the first and third resonators (purple colors) are periodically modulated via a weak adiabatic modulation of the permittivities of the resonators. The system is in contact with two independent baths at the same temperature $T$. (b) A circuit consisting of three $LC$ resonators. Two of these resonators are modulated via their (purple) capacitances. The circuit is coupled capacitively to two artificial reservoirs at the same temperature $T$. The reservoirs are implemented by synthesized noise sources generating random voltages $V_{1,2}^s$ with a prescribed spectral distribution. The positive direction for the pumped flow is chosen to match the green arrows.

Figure 2

Eigenvalue surfaces of the effective Hamiltonian $H_{\mathrm{eff}}^t$ around ${\omega }_{\mathrm{DP}}={\omega }_0-1$, when (a) the coupling strength $ϵ=0$, and (b) $ϵ=-0.2$. When the system is coupled to leads, the DP [indicated by the green dot in (a)] evolves into two EPs; see the red dots in (b). Another common parameter is ${\omega }_0=3$.

Figure 3

Numerical evaluation (dashed lines) of rescaled radiative (time-averaged) thermal energy flux $\overline{\mathcal{I}}\times (2\pi /\mathrm{\Omega })$ versus the control parameter $d$ for driving angles (a) $\theta =45°$ and (b) $\theta =135°$. The coupling $\epsilon$ between the leads and the system is indicated in the insets. In (a), we also report the theoretical result (symbols) of Eq. (11). Other parameters are $k_{B}T/\hslash =1.25$ and ${\omega }_0=3$ (in units of coupling strength).

Figure 4

(a) Total pumped energy density $Q(\omega )$ versus frequency for a typical value of the rescaled mutual inductance coupling at the DP, $\mu ={\mu }_{\mathrm{DP}}$. (b) Total (averaged) pumped radiative energy current $\widehat{\mathcal{I}}$ versus the mutual inductance $\mu$. The highest values of $\widehat{\mathcal{I}}$ are reached at the proximity of the DP (red dashed line). (a),(b) The lines are obtained from the numerical evaluation of $Q(\omega )$ using Eq. (6). The symbols are results from a direct time-domain simulation of net power at the left terminal [50].