  Quantum imaging with undetected photons spatially transfers amplitude and
phase information from one spectral region of physical interest to another
spectral region that is easy to detect. The photon energy of the two spectral
regions can, in principle, be separated by several orders of magnitude.
However, quantum imaging with undetected photons has so far only been
demonstrated in spectral regions of similar order of magnitude in frequency
(and for which cameras are commercially available). Here, we demonstrate
amplitude- and phase-sensitive imaging in the terahertz spectral region (1.5
THz center frequency) by detecting only visible photons (center wavelength
662.2 nm, 452.7 THz center frequency) more than two orders of magnitude apart.
As a result, terahertz spectral information can be reliably detected with a
standard CMOS camera without cooling, achieving a spatial resolution close to
the wavelength. By taking advantage of quantum distillation in a nonlinear
interferometer, the influence of ubiquitous thermal terahertz photons can be
neglected. Our results are in good agreement with numerical simulations of the
imaging process and demonstrate the huge potential of this method to address
otherwise challenging spectral regions where cameras do not exist.
