  Long-baseline interferometry (LBI) is used to reconstruct the image of faint
thermal objects. The image quality, for a given exposure time, is in general
limited by a low signal-to-noise ratio (SNR). We show theoretically that a
significant increase of the SNR, in a LBI, is possible by adding or subtracting
photons to the thermal beam. At low photon counts, photon addition-subtraction
technology strongly enhances the image quality. We have experimentally realized
a nondeterministic physical protocol for photon subtraction. Our theoretical
predictions are supported by experimental results.
