Abstract

We report the first calorimetric detection of individual hbox {He}_2^* excimers within a bath of superfluid ^4hbox {He}. The detector used in this work is a single superconducting titanium transition edge sensor (TES) with an energy resolution of {sim }1~hbox {eV}, immersed directly in the helium bath. hbox {He}_2^* excimers are produced in the surrounding bath using an external gamma-ray source. These excimers exist either as short-lived singlet or long-lived triplet states. We demonstrate detection (and discrimination) of both states: In the singlet case the calorimeter records the absorption of a prompt {approx }15~hbox {eV} photon, and in the triplet case the calorimeter records a direct interaction of the molecule with the TES surface, which deposits a distinct fraction of the {approx }15~hbox {eV}, released upon decay, into the surface. We also briefly discuss the detector fabrication and characterization.

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