Dual frequency extension for ALMA

Atacama Large Millimeter Array (ALMA) is an interferometer in Atacama desert in Chile at altitude of 5 km, which is now in a final stage of construction. This array consists of 12-m and 7-m diameter antennas with base line up to 16 km. Each antenna will be equipped with a state of art heterodyne receivers covering atmospheric windows in the range of 30 to 950 GHz. The design of current generation of detectors is finished, nevertheless ALMA is the best platform for new receivers and observing techniques and there are already significant efforts aimed on future improvement and upgrade. Towards this direction we would like propose and consider in detail to operate ALMA array at two different observation frequencies at the same time and from the same point on the sky. This regime will give an advantage by increasing of the available observing time twice, will improve algorithm correcting the atmospheric transparency fluctuations and will give opportunity for cross correlation of different frequency bands. In parallel we consider to use ALMA in a new way, by employing “dual photon” interferometry, which is working in the same way as Hanbury Brown and Twiss effect. In particular we discuss possible implementations of dual ALMA Band 9 (602-720 GHz)/Band X receiver.