  Spectroscopy and imaging in the mid-infrared (2.5 $\mu$m $\sim$ $\lambda$
$\sim$ 25 $\mu$m) is bedevilled by the presence of a strong 300 K thermal
background at room temperature that makes IR detectors decades noisier than can
be readily achieved in the visible. The technique of "imaging with undetected
photons" (IUP) exploits the quantum correlations between entangled photon pairs
to transfer image information from one spectral region to another, and here we
show that it does so in a way that is immune to the thermal background. This
means that IUP can be used to perform high speed photon counting measurements
across the mid-IR, using uncooled visible detectors that are many times
cheaper, faster, and more sensitive than their IR counterparts.

Quantum Physics;Optics