  Circularly polarized light can be obtained by using either polarization
conversion or structural chirality. Here we reveal a fundamentally unrelated
mechanism of generating circularly polarized light using coupled nonequilibrium
sources. We show that thermal emission from a compact dimer of subwavelength,
anisotropic antennas can be highly circularly polarized when the antennas are
at unequal temperatures. Furthermore, the handedness of emitted light is
flipped upon interchanging the temperatures of the antennas, thereby enabling
reconfigurability of the polarization state lacked by most circularly polarized
light sources. We describe the fundamental origin of this mechanism using
rigorous fluctuational electrodynamic analysis and further provide practical
examples for its experimental implementation. Apart from the technology
applications in reconfigurable devices, communication, and sensing, this work
motivates new inquiries of angular-momentum-related thermal-radiation phenomena
using thermal nonequilibrium, without applying magnetic field.
