Quantum nonlinear mixing of thermal photons to surpass the blackbody limit

TL;DR

This paper demonstrates that nonlinear quantum effects in thermal radiation can surpass blackbody limits, enabling frequency-selective emission and non-trivial photon statistics without external signals.

Contribution

It introduces a quantum formalism for thermal radiation in nonlinear systems, revealing new ways to shape emission beyond classical limits.

Findings

Frequency-selective enhancement of thermal emission via upconversion

Thermal light exhibits non-trivial photon statistics and biphoton correlations

Surpassing blackbody limits with nonlinear quantum effects

Abstract

Nearly all thermal radiation phenomena involving materials with linear response can be accurately described via semi-classical theories of light. Here, we go beyond these traditional paradigms to study a nonlinear system which, as we show, necessarily requires quantum theory of damping. Specifically, we analyze thermal radiation from a resonant system containing a $\chi^{(2)}$ nonlinear medium and supporting resonances at frequencies $\omega_1$ and $\omega_2\approx 2\omega_1$, where both resonators are driven only by intrinsic thermal fluctuations. Within our quantum formalism, we reveal new possibilities for shaping the thermal radiation. We show that the resonantly enhanced nonlinear interaction allows frequency-selective enhancement of thermal emission through upconversion, surpassing the well-known blackbody limits associated with linear media. Surprisingly, we also find that the emitted thermal light exhibits non-trivial statistics ($g^{(2)}(0) \neq 2$) and biphoton intensity correlations (at two distinct frequencies). We highlight that these features can be observed in the near future by heating a properly designed nonlinear system, without the need for any external signal. Our work motivates new interdisciplinary inquiries combining the fields of nonlinear photonics, quantum optics and thermal science.