Quantum Rangefindng

If the illumination source of a rangefinder [1] is replaced with a spontaneous parametric down-conversion (SPDC) source [2], producing broadband photon-pairs, the light sent towards the target will emulate thermal background light. This can be achieved by carefully engineering the phase-matching condition inside a periodically poled Potassium titanyl phosphate (ppKTP) crystal to generate photon pairs on many spectral modes (see figure 1). One half of the two-mode squeezed state produced in each of these spectral modes is then presented to the target as a maximally mixed state and is consequently camouflaged against background light. This is especially true since the photon statistics of such a state are identical to those of thermal light.