A '''transition edge sensor''' or '''TES''' is a type of [[bolometer|bolometric detector]] consistingconsists of a [[superconductivity|superconducting material]],such as [[aluminum]] or [[titanium]],material held on its [[Superconductor#Superconducting phase transition|superconducting transition]]. When biased on the superconducting transition, the device has a finite electrical resistance that is less than the resistance in the fully non-superconducting state. Energy coupled to the detector increases the temperature of the superconducting material, pushing it further into the non-superconducting state and thereby increasing its electrical resistance. This increase in resistance can be used to detect very small changes in temperature, and hence in energy. TESs are often operated with low noise [[SQUID]] readouts. The low input impedance of the SQUID provides negative electrothermal feedback that can significantly speed up the device response and improve the energy resolution.<ref>K. D. Irwin and G. C. Hilton, "Transition-Edge Sensors," ''Cryogenic Particle Detection'', ed. C. Enss, Springer, 2005.</ref>
TES arrays are becoming increasingly common in physics and astronomy experiments such as the [[Atacama Cosmology Telescope]], the [[BICEP2/Keck Array]] CMB polarization experiment, [[the E and B Experiment]], the [[SCUBA-2 All Sky Survey]], the [[South Pole Telescope]], and the [[Spider (polarimeter)|Spider polarimeter]].
