The study of the interaction between light and matter has revolutionised our understanding of the modern world, with applications as far-reaching as the development of semiconductors to quantum technology for communication and cryptography. In this thesis, we theoretically analyse light-matter interaction using quantum emitter systems that span a range of scales, from individual quantum dots to ensembles of millions of atoms. By combining our theoretical modelling with experimental expertise at the Niels Bohr Institute, we further deepen our understanding of the effects of experimental losses in these diverse light-matter systems.
At an emitter number N = 1, we study the nonlinear scattering of individual photons off a quantum dot embedded in a photonic crystal waveguide. We use this single-photon nonlinearity to generate time-energy entanglement, which is of practical importance in opening opportunities for quantum computing and cryptography, as well as quantum optical information processing, communication and measurement protocols.
We add another quantum dot to reach N = 2, investigating the entirely new
physics arising from the ability to absorb, re-emit and then re-absorb the re-emitted light field. We show how super- and subradiance arises from this coupled system and find our theoretical model can describe the first experimental demonstration of emitter-emitter coupling in waveguide coupled quantum dots.
We then study N = 10 − 100 quantum emitters, arranged periodically in an
atomic lattice. We propose a novel quantum sensing protocol that exploits the cooperative enhancement arising from the coherent interaction of the lattice atoms with impurities embedded at some lattice sites. Our protocol is several orders of magnitude more sensitive in the lattice than in free space and is robust to noise introduced by lattice disorder.
Finally, we use an atomic ensemble with N ∼ 1 million to investigate the production of frequency dependent squeezing. This is of interest for gravitational wave interferometers, as it can improve sensitivity beyond the so-called standard quantum limit. By exploiting electromagnetically induced transparency (EIT) and motional averaging, we can produce a broadband suppression of the quantum noise in a gravitational wave interferometer, even when accounting for experimental losses. Lower noise opens the door to more sensitive gravitational wave astronomy, allowing us to see further than ever before.