The exotic physics emerging in non-Hermitian systems with balanced distributions of gain and loss has recently drawn a great deal of attention. These systems exhibit phase transitions and exceptional point singularities in their spectra, at which eigen-values and eigen-modes coalesce and the overall dimensionality is reduced. So far, these principles have been implemented at the expense of precise fabrication and tuning requirements, involving tailored nano-structured devices with controlled optical gain and loss. In this work, anti-parity-time symmetric phase transitions and exceptional point singularities are demonstrated in a single strand of single-mode telecommunication fibre, using a setup consisting of off-the-shelf components. Two propagating signals are amplified and coupled through stimulated Brillouin scattering, enabling exquisite control over the interaction-governing non-Hermitian parameters. Singular response to small-scale variations and topological features arising around the exceptional point are experimentally demonstrated with large precision, enabling robustly enhanced response to changes in Brillouin frequency shift.

Thermal emission manipulation is of key importance in numerous applications, yet a number of challenges have prevented its full technical maturation. Efficient mid-and far-infrared sources are valuable for sensing and thermal engineering, yet they are far from matching the sophistication of sources at lower or higher frequencies. Spectrally or spatially narrowband thermal emission has been proposed, partially overcoming the inherent incoherence of thermal processes. However, designing an ideal thermal source with spectral and spatial tailoring of the emission, and enhancing its line width within a small footprint, remains significantly challenging. Here we show how embedded eigenstates in the radiation continuum can be employed to realize compact thermal sources with narrow frequency and spatial spectra of emission, broadening the opportunities for thermal emission manipulation. The proposed concept can be extended to a wide class of thermal emitters, as well as more broadly within the context of thermal management.