Iqueye is a high speed astronomical photon counting device, tested at the ESO 3.5 m New Technology Telescope in La
Silla (Chile). The optics splits the telescope pupil into four portions each feeding a Single Photon Avalanche Diode. A
time-to-digital converter board time tags the pulses from the 4 channels, and the times sent to a storage device. The
instrument is capable of running continuously up to a rate of 8 MHz, with an absolute rms accuracy better that 0.5 ns.
The time is obtained by means of a rubidium clock referenced to UTC through the GPS signal. The paper describes the
analysis performed on data taken on bright stars in order to perform 'quantum-like' measurements in the photon stream,
namely the calculation of the second-order correlation functions g(2)(x,0) and g(2)(0,t). To this end, an ad hoc software
correlator has been developed. Taking advantage of the pupil-splitting concept, the calculation of g(2)(x,0) has been made
between the sub-apertures of the telescope, as a first step to verify the zero-baseline correlation coefficient in an
Hanbury-Brown Twiss intensity interferometer . Our experiment demonstrates the value of an Iqueye-like instrument
applied to larger telescopes, like the four 8 m VLTs or the two 10m Keck telescopes, and even more the sub-pupils of the
future 42 m E-ELT for a novel exploitation of the photon stream from celestial objects.