OHANA NUI: Using quantum optics to measure astrophysical quantum degeneracy in Sirius B

Between 1999 and 2012, a collaboration of Observatories strived to connect telescopes at the summit of Maunakea with single mode optical fibres into a kilometric baseline interferometer to operate at near infrared wavelengths; it was the OHANA project, (Optical Hawaiian Array for Nanoradian Astronomy, with all the telescopes operating as a family). We achieved some success, first injecting starlight into single mode fibres (at CFHT, Keck and Gemini in 2001, 2002 and 2003 respectively) and then succeeding in coherently transporting light from the two Kecks through fibres and measuring stellar fringes in 2005. Unfortunately, luck was not with us and adverse weather conditions prevented us from performing astronomical observations of YSOs and AGNs at Keck until 2009. The ‘OHANA iki experiment was developed around the same time in preparation for a CFHT-Gemini baseline, to demonstrate the interferometric chain using 8” telescopes, from acquisition and fringe capture to reduced data for outdoor fiber links. At that time, the lengths of the fibers were not servoed and this was clearly identified as an issue that would need to be addressed for effective fibered  links between telescopes for coherent detection in the future. The project came to an end in 2012, leaving some of us feeling that we had been young and foolish to embark on such an ambitious project.

Now that we are older and presumably wiser, we propose to revive the idea of interferometric connection of the Maunakea telescopes, but this time in the visible and using quantum optics. The technique of intensity interferometry, developed by Hanbury-Brown and Twiss in the 1950s and used with great success in the 1960s at the Narrabri Interferometer, fell into neglect with the advent of amplitude interferometry, pioneered by Antoine Labeyrie in the 1970s. But technological progress driven by quantum optics and telecommunications has led to the development of new components (SPADs, SNSPDS) which have allowed to extend the sensitivity of the technique by orders of magnitude. We have developed a collaboration between quantum optics physicist and astronomers at Université Côte d'Azur since 2016 and have demonstrated the promise of the technique using our 1m telescopes to achieve original and meaningful astrophysical measurements. One of the main advantages of the technique, besides being insensitive to atmospheric turbulence, is that it requires no physical link between the telescopes, making it ideally suited for implementation on a site such as Maunakea, with no impact on the mountain whatsoever. 

The longest baselines on Maunakea would allow to obtain a visibility measurement in one night of integration on Sirius B, the closest known white dwarf. These exotic objects are supported by Fermi electron degeneracy, and their diameter is estimated from their luminosity; such a measurement would uniquely constrain the diameter and demonstrate quantum mechanics at work on an astrophysical size object!