  The two MAGIC 17-m diameter Imaging Atmospheric Cherenkov Telescopes have
been equipped to work also as an intensity interferometer with a deadtime-free,
4-channel, GPU-based, real-time correlator. Operating with baselines between
approx. 40 and 90 m the MAGIC interferometer is able to measure stellar
diameters of 0.5-1 mas in the 400-440 nm wavelength range with a sensitivity
roughly 10 times better than that achieved in the 1970s by the Narrabri Stellar
Intensity Interferometer. Besides, active mirror control allows to split the
primary mirrors into sub-mirrors. This allows to make simultaneous calibration
measurements of the zero-baseline correlation or to simultaneously collect six
baselines below 17 m with almost arbitrary orientation, corresponding to
angular scales of approx. 1-50 mas. We plan to perform test observations adding
the nearby Cherenkov Telescope Array (CTA) LST-1 23 m diameter telescope by
next year. All three telescope pairs will be correlated simultaneously. Adding
LST-1 is expected to increase the sensitivity by at least 1 mag and
significantly improve the u-v plane coverage. If successful, the proposed
correlator setup is scalable enough to be implemented to the full CTA arrays.
