ANR project: Intensity Interferometry at Calern (I2C)

This collaborative project gathers physicists, astrophysicists, and specialists of time metrology in the Nice area in order to revive intensity interferometry with modern photonic technologies. This technique, initially pionneered by  Hanbury Brown and Twiss (HBT) in the 1950s-1970s, was abandonned because of its poor sensitivity. Today, the progress in photon detectors and digital electronics, and the prospects of using this technique with arrays of large collectors, motivates a revival.

Our approach in Nice is to work with standard optical telescopes (as opposed to Cherenkov telescopes) and photon-counting detectors. This allowed us to be the first group since HBT to succeed in observing temporal and spatial photon bunching with star light (2017).

In 2020 we obtained a research grant from the French national research agency (ANR) to support our effort (Grant ANR-20-CE31-0003, 409 k€ for 4 years: 2021-2024).

News & events

Sept. 2024: A workshop at Porquerolles

We're organizing a workshop on stellar intensity interferometry at Porquerolles in Septembre 2024. Check out the webpage of the event to know more!

April 2024: An ERC grant for Robin Kaiser !


Robin's ERC proposal, called IC4Stars (Intensity Correlations for Stars) has been accepted! This is a follow-up of the ANR I2C project. This new grant will allow us to move forward much faster. Congratulation Robin and to all of us!

May 2023: Successful interferometric observation with 3 telescopes at Paranal!

The team at Paranal
The team at Paranal
Three members of our team, Nolan Matthews, Robin Kaiser and Jean-Pierre Rivet, had the chance to go the the VLT site at Cerro Paranal (Chile) for an observing mission over 5 nights. We have used three Auxiliary Telescopes (1.7 m) set in a triangular arrangement (stations B1-B3-C1) with baselines in the range 10 - 20 m.
With the help of two VLT scientitists, Nicolas Schuhler (first left) and Pierre Bourget (first right), we succeeded in observing the intensity correlations on 2 different stars. As last time, the "stellar interferometer" has been transported in only three suitcases!

April 2022: Nolan Matthews won a PhD thesis prize!

Nolan has been awarded the Cecilia Payne-Gaposchkin Doctoral Dissertation Award in Astrophysics from the American Physical Society for his PhD work on intensity interferometry at the VERITAS observatory. He was invited to present his work at the APS April meeting in New York. Congratulations!


March 2022: Successful interferometric observation at Paranal (VLT)!

The Dream Team
The Dream Team
Three members of our team, Mathilde Hugbart, William  Guerin and Jean-Pierre Rivet, had the chance to go the the VLT site at Cerro Paranal (Chile) for an observing mission over 6 nights. We have used two Auxiliary Telescopes (1.7 m) on their maintenance station (separation 49 m).
With the help of two VLT scientitists, Pierre Bourget (first left) and Nicolas Schuhler (fourth left), we succeeded in adapting our instrument to the telescopes and in observing the intensity correlations on 3 different stars.

Jan. 2022: Successful interferometric observations between MéO and David Vernet's mobile telescope

Nice telescopes
Nice telescopes
So far our inteferometric measurement were all performed using the two telescopes of C2PU with a separation of 15 m. Now we have performed intensity interferometry between the laser-ranging telescope MéO and David Vernet's 1 m mobile telescope. This allows us to use different interferometric baselines at Calern. This has been made possible thanks to the tip-tilt active correction implemented by Nolan for David's telescope, without which the light injection into the optical fiber would not have been stable enough. Congratulation to Nolan, David, the MéO team and everyone that made that possible.

Oct. 2021: The I2C webpage is back!

After several months of interruption and the complete loss of data (due to the fire of the data center), the I2C webpage is finally back. But this is still a work in progress...

April 2021: Welcome to Nolan Matthews!

Nolan joined our team as a post-doc, funded by the ANR grant. He did his PhD on intensity interferometry on the VERITAS array and is already a recognized expert in the subject. Welcome in Nice!


Institut de Physique de Nice, team "cold atoms" (UCA, CNRS)
  • William Guerin (PI of the ANR project)
  • Mathilde Hugbart
  • Guillaume Labeyrie
  • Robin Kaiser
      Alumni : Nolan Matthews (Post-doc, 2021-2023), Antonin Siciak (PhD, 2018-2021), Antoine Dussaux (Post-doc, 2015-2016)
Lagrange Laboratory (Observatoire de la Côte d'Azur, UCA, CNRS)
  • Olivier Lai (co-PI of the ANR project)
  • Jean-Pierre Rivet
  • Armando Domiciano
  • Farrokh Vakili
  • Pierre-Marie Gori (PhD student)
Géoazur Laboratory, team MéO (Observatoire de la Côte d'Azur, UCA, CNRS)
  • Julien Chabé (co-PI of the ANR project)
  • Clément Courde


  • May 2023: Observing mission (5 nights) at Paranal observatory in Chile: successful interferometry with 3 telescopes.
  • Mar. 2022: Observing mission (6 nights) at Paranal observatory in Chile. Publication of the data (among other things) in a SPIE proceedings in 2022.
  • Jan. 2022: First interferometric measurements between the laser-ranging MéO telescope and David Vernet's mobile 1 m telescope. Publication in Astron. J. in 2023.
  • May 2021: Publication in MNRAS of the I3T concept (Intensity Interferometry Imaging Telescope).
  • Jan. 2021: Start of the ANR project I2C. Arrival of Nolan Matthews as a post-doc in April.
  • Fev. and Aug. 2020: Observing campaigns on C2PU in Hα, of Rigel in February and P Cygni in August. Publication in MNRAS in 2022.
  • Apr. 2019: One-night observing mission to the 4 m SOAR telescope in Chile. Publication of those data in the SF2A 2021 proceedings.
  • Oct. 2018: OCA joins the CTA consortium through its working group on intensity interferometry.
  • Aug. 2018: Interferometric measurement campaign on P Cygni using its bright Hα emission line. Publication in MNRAS in 2020.
  • Oct. 2017: Observation of spatial photon bunching using the two telescopes of C2PU separated by 15 m. Publication in MNRAS in 2018.
  • Feb. 2017: Observation of photon bunching with stellar light using a single telescope, in the photon-counting regime. Publication in MNRAS in 2017.
  • Jan. 2015: Start of the project with Antoine Dussaux's arrival as a post-doc (grant from UNS).