Final Report Summary - TWISTS (Twists & more: the complex shape of light) Light is usually considered in terms of its intensity. Nowhere is this more true than in imaging where the intensity of the light is measured for each and every pixel in the image. However, in addition to having an intensity, the wave nature of light means it has a phase too. Normal laser beams have both a uniform intensity and phase, but this need not always be the case. Structuring the intensity over the beam cross section is how we project images at the cinema, but structuring the phase allows us to change the way that the light beam propagate through space. One example of this structuring is the focussing of a light beam after a lens. Another example is the introduction of a twist to the light that can send small objects into rotation. In this project we have used both intensity and phase structuring, both in classical and quantum regimes, to pioneering new forms of imaging. Perhaps the most exciting of these is the detection of entangled photons to build imaging systems that surpass the performance limits of classical physics. During the course of this work we have shown that entangled photons can • Probe the object at one wavelength whilst imaging at another (Aspden et al. Optica 2015) • Distinguish real images from the thermal background (Gregory et al., In press Science Advances 2019)• Improve the imaging resolution beyond the diffraction limit (Toninelli et al., Optica 2019).All of these achievements has been made possible by our use of software enhanced conventional camera technology for the measurement of single photons and their position within the field of view. As such our work is not only relevant to imaging but to all multidimensional measurements within quantum communication and information processing systems.More conventionally we have used the measurement of spatially structured single-photons to create new forms of 3D imaging systems without need of scanning mechanisms or complicated cameras (Sun et al. Nature Comms. 2016).One the benefits of ERC funding lies in the support of research groups of critical mass within which creativity can flourish. Areas where this creativity led to new discoveries were• A realisation and demonstration of the fact that shaping the phase of the light beam reduces the group velocity to be slower than the free-space speed of light (light slower than light) – (Giovannini et al., Science, 2015).• The demonstration that extreme Doppler shifts can create negative frequencies and a reversal of light’s twist, potentially switching loss into gain (Gibson et al., PNAS, 2018).• An examination of how a rotating reference frame impacts upon the indistinguishability of photon pairs potentially linking the quantum science with general relativity (Restuccia et al. Phys. Rev. Letts. 2019).Beyond the research itself, an important aspect of any programme are the careers that it developed. Researchers from this programme have transitioned both to academic careers of their own and careers in industry, in many cases pursuing the exploitation of the research they developed during the programme.
