As photon sources get smaller, their shape and the nature of their
surroundings increasingly affect the quantum fields that live inside
them. I will bridge the gap in our theoretical understanding at these
scales, leading not only to the study of fascinating new physics, but
also to the formulation of the blueprints required to achieve small,
nano-optic, photon sources.
Both quantum communication and quantum sensing depend directly on our
ability to generate and manipulate information carriers, with photons
(the quantum constituents of light) being the sole viable candidate
carrier. To be a useful quantum technology, this must in practice be
done on-chip in integrated devices. Photonic devices must thus
inevitably come on an ever-decreasing scale, reaching the scale where
quantum vacuum effects are known to be important.
Interestingly, the quantum vacuum of light is not a true vacuum, and
photons continuously pop in and out of existence. This is quantified by
what is known as the local mode structure of the vacuum state. We can
modify this local vacuum state by building spatial structures with
boundaries between materials possessing different optical properties. It
is known that vacuum forces arise between closely spaced metal sheets,
and levitation of nanoscopic objects has been achieved through this.
Importantly, spontaneous photon generation processes, including those
table-top set-ups that are a staple of current quantum optics
experiments, are seeded by the local vacuum state which in turn depends
crucially on its surroundings. Whilst bulk and boundaries are
well-separated for table-top optical crystals, at the nano-optic scale
they are not. Knowledge about the local vacuum state will therefore
become paramount for nano-scale photon sources. I will here provide a
unified method that can account for such spatio-temporal modifications
of the vacuum state. Through this, I will present the theoretical
understanding needed to bring our current photon generation technology
to the nanoscopic scale.
