Massive black hole binaries (MBHBs) are the most extreme, fascinating yet elusive astrophysical objects in the Universe. Establishing observationally their existence will be a milestone for contemporary astronomy, providing a fundamental missing piece in the puzzle of galaxy formation, piercing through the… Read more (hydro)dynamical physical processes shaping dense galactic nuclei from parsec scales down to the event horizon, and probing gravity in extreme conditions. We can both see and listen to MBHBs. Remarkably, besides arguably being among the brightest variable objects shining in the Cosmos, MBHBs are also the loudest gravitational wave (GW) sources in the Universe. As such, we shall take advantage of both the type of messengers – photons and gravitons – they are sending to us, which can now be probed by all-sky time-domain surveys and radio pulsar timing arrays (PTAs) respectively. B MASSIVE leverages on a unique comprehensive approach combining theoretical astrophysics, radio and gravitationalwave astronomy and time-domain surveys, with state of the art data analysis techniques to: i) observationally prove the existence of MBHBs, ii) understand and constrain their astrophysics and dynamics, iii) enable and bring closer in time the direct detection of GWs with PTA. As European PTA (EPTA) executive committee member and former I International PTA (IPTA) chair, I am a driving force in the development of pulsar timing science world-wide, and the project will build on the profound knowledge, broad vision and wide collaboration network that established me as a world leader in the field of MBHB and GW astrophysics. B MASSIVE is extremely timely; a pulsar timing data set of unprecedented quality is being assembled by EPTA/IPTA, and Time-Domain astronomy surveys are at their dawn. In the long term, B MASSIVE will be a fundamental milestone establishing European leadership in the cutting-edge field of MBHB astrophysics in the era of LSST, SKA and LISA.

We propose to forge a partnership between the leading European groups working on the next generation of solid state quantum emitters based on novel growth methods such as Droplet Epitaxy. Future, practical Nano-photonics and Quantum Circuits applications demand semiconductor quantum… Read more dots that can be grown on substrates with different lattice parameters (Si, Ge, GaAs), different substrate orientations (such as (001) and (111)) and tuneable optical, electrical and spin properties. All these requirements are met by high quality quantum dots grown with Droplet based Epitaxy techniques, circumventing the limitations of currently available systems based on strain-driven dot self-assembly. This vast novel research area at the crossroads of photonics, material science, quantum physics and nano-scale device fabrication will allow delivering top level multidisciplinary training to 15 early stage researcher (ESRs). The successful training of the ESRs by leading academic and 3 full industrial partners will be crucial for achieving the headline goals of this first ever consortium on droplet dot devices: (1) Entangled light emitting diodes with droplet dots grown on (111) substrates (2) Electrically triggered, droplet dot based single photon sources on Si/Ge substrates (3) Strain tuning in droplet dots without wetting layer: photon polarization and single spin control (4) Droplet Dot based single photon sources for non- classical light storage devices based on hybrid quantum systems (dots & laser-cooled atoms). The training and research progress will be discussed and monitored during the 4 project meetings, 3 summer schools and the final international conference on Droplet Dot Devices, all of which are open to the whole scientific community. We expect this network, based on the solid collaboration between growth groups, microscopists, quantum optics experimentalists and theorists to explore the full potential of this emerging technology.